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The Bias Against Tall Plants

November 11th, 2025 by Alex Zorach

In our October 2024 post we noted that gardening and landscaping practices have ecological consequences, especially as an increasing portion of our land consists of managed landscapes. Gardening and landscaping practices are subject to cultural norms, which can include long-standing beliefs as well as fads and trends. These norms also influence the management of wild lands, especially at edges and other interfaces between wild and managed lands such as are common in parks.

Currently, the concept of native plants is trending, in part due to the popularity of the books by Doug Tallamy. But even though the concept of native plants has broken into the mainstream, numerous ecological concepts are going under-appreciated, and numerous biases, many of which have negative ecological consequences, are persisting.

This post tackles a particular bias: the bias against "tall" plants, and its counterpart, the bias in favor of "short" plants. This bias goes hand-in-hand with lawn culture, and has consequences diverse areas, including:

• proliferation of invasive plants
• weakening of native plants by breeding cultivars to be shorter
• failure of ecological restoration projects because of selecting shorter plants on sites suited to taller plants
• degradation of edge habitats by selective removal of herbaceous plants that are "too tall"

This post outlines each of these forms of potential harm, but it starts with the groundwork of explaining why some herbaceous plants grow so tall in the first place.

The Ecology of Plant Height

Plants' physical attributes, including height, are a function of their ecology, reflecting adaptation to their habitats. Habitat includes both the environmental conditions (such as moisture and light availability, and soil texture and chemistry) and other organisms present in the ecosystem, including both animals and competing plants.

In order to grow taller, herbaceous plants need resources, including water, nutrients, and light. However, growing taller is still costly, so it is only advantageous if it offers something that a short habit does not. The main advantage of height is pushing up through competing vegetation to reach more light. Competition not only increases the reward of height, but also facilitates it, since plants can lean on each other for structure. Many tall plants cannot support their own weight alone, staying upright and pushing up through other vegetation only by leaning against each other. As such, most tall plants occur in communities of other tall plants.

Besides the increased light capture, there are secondary benefits of height, including visibility of flowers to pollinators, and in wind-pollinated plants, increased reach of pollen and ability to capture pollen from distant plants. Wind-dispersed seeds can also spread over longer distances. These wind-facilitated benefits though come with a price: the higher wind speeds at greater heights worsens drought stress, thus increasing water demands more than would be expected by light exposure and leaf surface area alone.

For these reasons, most tall herbaceous plants occur in habitats where there is abundant water, light, and nutrients, and heavy ground-level competition. These habitats include tallgrass prairie, wet meadows and openings in floodplain forests, rich, moist forest edge habitats (including streambanks and shores of lakes, ponds, and open wetlands, as well as anthropogenic forest edges), swamps, and locally-disturbed sites in bottomland forests or rich mesic upland forests. In drier habitats and on sites with poorer soil, the drought stress, lack of competition, and scarcity of nutrients combine to favor shorter plants. On shadier sites such as a closed-canopy forest, low-light conditions favor either woody plants like trees or shrubs, or low-growing herbaceous plants.

Much of North America's population is found in areas favoring tall herbaceous plants.

The human population in North America concentrates along the humid coasts where forests were dominant, and into the eastern portion of the Great Plains, where tallgrass prairies were dominant. Furthermore, in forested regions, humans tend to settle near sources of water and in areas with richer soil, as these areas support agriculture capable of feeding larger populations.

Humans often increase the habitat for tall herbaceous plants.

Without the influence of humans, much of the Eastern Temperate Forests would support closed-canopy forests in which there are fewer tall herbaceous plants. In many of these regions, historically, Native Americans practiced controlled burns which favored savannas, which supported more tall herbaceous plants, including both grasses and broadleaf plants. European colonization brought the clearing of forests and conversion of land to agriculture, and tall plants proliferated on cropland margins, fallow fields, and in the early-successional growth on sites where agriculture was abandoned and forest was allowed to grow up again. In the present day, an abundance of roads and paths and the fragmenting of forests has created more edge habitat, where higher levels of light reach the ground underneath trees, and tall herbaceous plants thrive.

Resisting a natural equilibrium has a cost.

I hope I've convinced you that, at least some of the time and on some sites, the conditions favor tall plants. Attempting to resist such a natural equilibrium comes with its costs, which the rest of this post will explore.

Leaving The Tall Plant Niches Vulnerable to Invasion

If you remove a certain species from an ecosystem, its niche will usually be colonized by some other plant. Removing a tall native plant will usually lead its niche to be colonized by a plant of similar height. However, if over time, tall native plants are repeatedly and systematically removed from ecosystems, their niches will be colonized either by shorter native plants, or by non-native plants. Because tall plants tend to be more competitive than short plants on sites rich enough to support tall plants, systematic removal of tall native plants can lead a site to be more vulnerable to invasive plants.

Many of the invasive plants that fill these niches are themselves tall. But the bias against tall plants acts on them as well. People are more likely to notice tall invasives and target them for removal, and much of the management of land is not done with respect to a plant's native status, so the bias against tall plants acts equally on tall invasives. When all tall plants are excluded, they become replaced by shorter vegetation. And as I explain below, there are some systemic reasons why this shorter vegetation is more likely to be dominated by introduced plants.

Proliferation of Invasive Plants Selected for Shortness

One pattern I have noticed about invasive plants in North America is that a surprisingly large portion of the worst invasive species have a low-growing habit. This pattern is the opposite of what one would expect based on competition, as tall plants often out-compete shorter plants. Although there are more examples of such low-growing invasive plants in the humid east, this problem is not restricted to that region. The southwest has crystalline ice plant (Mesembryanthemum crystallinum) and slenderleaf iceplant (Mesembryanthemum nodiflorum), and fire-prone areas of the interior west and western great plains have cheatgrass (Bromus tectorum), both of which are lower-growing than many of the plants in the ecosystems they tend to invade.

The low height of these invasive plants tends to create other ecological problems, beyond the typical collapse of the food web caused by non-native species being eaten by fewer insect specialists. The food web problem is not directly related to height. However, another serious problem, erosion, is directly related. Although there are some exceptions, on average, shorter or smaller plants tend to have shallower and less-extensive root systems than tall plants. And, as-such, the proliferation of short or low-growing invasive plants tends to worsen erosion and increase the risk of larger-scale mass wasting such as slumping of soil.

Shorter plants also tend to have less biomass and thus, when they dominate ecosystems and out-compete taller plants, they reduce the total extent of the ecosystem, which reduces not only food available to animals, but also other ecosystem services plants provide, including cover for animals, solar capture, reduction of wind speed, and evapotranspiration, which in turn provides both temperature regulation and runoff reduction. The replacement of tall native vegetation by short invasives causes a cascade of harm extending beyond the ecosystem itself, leading to a reduction in climate regulation in the surroundings, harm to wildlife that spends only a portion of time in the ecosystem, and harm to waterways downstream.

The reason there are so many low-growing invasive plants is that humans have imported these plants to the continent disproportionately. One of the main ways short plants get introduced is through lawns, so our first examples of invasive plants will be forms of turfgrass.

Turfgrass

A large portion of the introduced grasses in North America were brought here as turfgrass. Although states and other governments are reluctant to label these plants as invasive, the reasons for doing so are more economic and cultural than ecological. One of the most widely-planted turfgrasses in the US is tall fescue (Lolium arundinaceum), which also happens to be one of the most aggressive in the wild. The USDA's FEIS acknowledges "Tall fescue can be invasive in native vegetation," giving the example of the Clymer Meadow Preserve in Texas, where it is encroaching on native vegetation, and notes "Tall fescue has devastated many other prairie remnants in Texas and to the north."

Some other turfgrasses that can become invasive include bermudagrass (Cynodon dactylon), Kentucky bluegrass (Poa pratensis) (which, contrary to its name, is not from Kentucky), rough bluegrass (Poa trivialis), perennial ryegrass (Lolium perenne), italian rye-grass (Lolium multiflorum), hard fescue (Festuca trachyphylla), creeping bentgrass (Agrostis stolonifera), bahiagrass (Paspalum notatum), centipede grass (Eremochloa ophiuroides), and Korean lawngrass (Zoysia japonica). This list is hardly exhaustive.

So many turfgrasses are invasive because they been bred over many generations both to be vigorous in North America's climates and soils, to be competitive against "weeds" (i.e. any other plant that might compete with them), and to resist any insect "pests" that might eat them. All three factors increase the likelihood of a species becoming invasive.

Groundcovers

Groundcovers are low-growing plants, typically either vines or herbaceous plants that reproduce by rhizomes or stolons, and that stay relatively low to the ground without needing to be mowed. Some grow taller than a typical lawn, but most are shorter than about 18 inches (1.5 feet) and some are much shorter. Many of them are evergreen. Some are succulents. Some have showy flowers. It is important to understand that groundcover is a horticultural term, not an ecological one: it refers to a plant's use in the garden, not its natural growth habit in the wild.

Some of the worst invasive plants in North America were introduced by being widely planted as groundcovers. Such examples include English ivy (Hedera helix), lesser celandine (Ranunculus ficaria), common iceplant (Mesembryanthemum crystallinum), winter creeper (Euonymus fortunei), Japanese pachysandra (Pachysandra terminalis), creeping jenny (Lysimachia nummularia), common periwinkle (Vinca minor), bigleaf periwinkle (Vinca major), stringy stonecrop (Sedum sarmentosum), and goldmoss stonecrop (Sedum acre).

Other groundcovers that have established in the wild but are not quite as aggressive include spotted henbit (Lamium maculatum), green hellebore (Helleborus viridis), bugleweed (Ajuga reptans), common houseleek (Sempervivum tectorum), evergreen candytuft (Iberis sempervirens), and several more stonecrops including orpin aizoon (Phedimus aizoon), white stonecrop (Sedum album), spanish stonecrop (Sedum hispanicum), European stonecrop (Sedum ochroleucum), and tasteless stonecrop (Sedum sexangulare). These plants can still be aggressive in some contexts, and any of them has the potential risk of becoming invasive at some point in the future.

There are likely many other plants with potential to become invasive if widely planted as groundcovers, but that have not yet become so simply because they have not been widely planted and/or bred. An example of a plant that is currently in the process of becoming more invasive is creeping liriope (Liriope spicata), which was widely planted as a replacement for English ivy, a decision that was both short-sighted and lacking in ecological awareness.

As with turfgrasses, groundcovers are also bred for traits that increase their likelihood of becoming invasive: tolerance of North America's climate and soil conditions, resistance to invasion by "weeds", and insect resistance.

Weedy low-growing plants that survive in lawns

Not all the introduced low-growing plants ended up here intentionally. A large portion of them propagate and spread as lawn weeds. Lawns provide an ideal habitat for the spread of such plants, not only because the mowing removes any taller competition, but also because the lawn equipment itself spreads plant seeds around, both locally and to new sites when the seeds ride on the equipment.

Introduced weedy plants that grow in lawns include unwanted grasses, such as annual bluegrass (Poa annua), hairy crabgrass (Digitaria sanguinalis), smooth crabgrass (Digitaria ischaemum), quackgrass (Elymus repens), awnless brome (Bromus inermis), plantain signalgrass (Brachiaria plantaginea), and indian goosegrass (Eleusine indica). Some of the turfgrasses discussed above, which may be intentionally planted on some sites, can also be unwanted weeds in other lawns. Such sometimes-unwanted grasses include tall fescue, creeping bentgrass, and rough bluegrass.

The list of introduced broadleaf weedy plants that thrive in lawns is even longer. Some of the most common ones include lesser celandine, mock strawberry (Duchesnea indica), European cinquefoil (Potentilla reptans), birdeye speedwell (Veronica persica), common plantain (Plantago major), narrowleaf plantain (Plantago lanceolata), common dandelion (Taraxacum officinale), scarlet pimpernel (Lysimachia arvensis), white clover (Trifolium repens), japanese clover (Kummerowia striata), korean clover (Kummerowia stipulacea), suckling clover (Trifolium dubium), black medick (Medicago lupulina), bird's-foot trefoil (Lotus corniculatus), ground ivy (Glechoma hederacea), common chickweed (Stellaria media), henbit deadnettle (Lamium amplexicaule), purple deadnettle (Lamium purpureum), and low smartweed (Persicaria longiseta). Again, this list is far from comprehensive; a full list for North America would be pages long.

Although people are not actively breeding these weeds to be more invasive, lawn culture unintentionally has this effect. In nature, many of the habitats that these plants would colonize are ephemeral, persisting only temporarily in response to a disturbance. But the regular mowing of lawns creates a new, artificial habitat in which these plants can produce generation after generation, persisting in this habitat consistently and long-term, often in large numbers.

So, instead of having a small number of plants producing seed and then dying out after a year or two, only to have suitable habitat crop up, potentially farther away, potentially years later, we now have a scenario in which the plants are breeding in large numbers every year. The massive amount of lawn further increases the population of these plants, and the fact that lawn equipment can move seeds from site to site, increases the speed with which genetic material spreads over large regions. All of these factors make the populations more vigorous and allow them to adapt to the conditions on this continent, increasing the likelihood that these plants become invasive.

Weakening of native plants by breeding short cultivars

Modern horticulture, landscaping, and gardening practices don't just introduce new, potentially invasive plants, but also alter our native plants. The horticulture industry breeds cultivars to have "desirable" traits in gardens. Modified traits may include flower color and structure, foliage color, and growth habit. One of the most common modifications made with such breeding is to decrease the height of plants.

Above we explained how a plant's height is a key aspect of its fitness and adaptation to its habitat. Modifying a plant's height by selective breeding makes it less fit in the habitats to which it is otherwise adapted. Shortened plants tend to be less competitive with other vegetation, and are usually less shade tolerant as the upper leaves tend to capture the most light. Shortened plants may also be less able to quickly and successfully cross-pollinate, whether the plant is wind- or insect-pollinated, and less able to distribute its seed larger distances particularly if its seed is wind-distributed. Although there are also potential benefits of shorter height (such as greater tolerance of drought and low-nutrient conditions), altering a plant from its equilibrium under natural selection tends to decrease its fitness. If it were beneficial to be shorter, it would have already become shorter through natural selection.

Plants also have some morphological plasticity, meaning that, even plants of identical genetics adjust their characteristics (including height) dynamically based on conditions. Cultivars are not just bred for specific traits, they are also typically bred to have less variation in those traits on different sites, so they are more "predictable" in the garden. In other words, their morphological plasticity is reduced, which also reduces their fitness in the wild.

One such cultivar is 'Little Joe' cultivar of coastal plain joe pye weed (Eutrochium dubium). Although E. dubium is naturally the shortest of the five Eutrochium species, this cultivar has been bred to make its maximum height even shorter: it grows only to about 4 feet, contrasting with the wild forms of the plant, which commonly grow to about 5 feet. This cultivar is also a classic example of the decrease in variability: both the cultivar and wild forms range in height, and can be as short as 3 feet at maturity. But the cultivar ranges from 3-4 feet in height, whereas the wild form ranges from 3-5 feet. The difference of that missing last foot of height tends to occur on plants grown in the conditions with greater moisture and nutrients, conditions where the plant is most likely to face competition from other plants.

The genetics encoding for height of these cultivars get passed on to future generations. Although the plants do tend to revert back to a more wild-type plant eventually, the shortened height does tends to persist, somewhat unpredictably, through at least one or two generations. I have done a lot of ecological restoration work in New Castle County, Delaware, a region where E. dubium is both common in the wild, and where the 'Little Joe' cultivar is widely planted in gardens. E. dubium is a particularly good example of the effect of these cultivars on wild plants, because the species self-seeds prolifically both in wild ecosystems and in suburban gardens and weedy marginal areas in suburbs. And I have noticed a clear pattern of volunteer E. dubium near source populations of these short cultivars, themselves being shorter at maturity than volunteer plants of the same species found in more intact wild areas, such as along the lower Christina river where it is separated from a large chunk of forest in Lewden Greene Park, or adjacent to larger wetlands in Phillips Park, Newark.

Locally-sourced wild plants grown in gardens can protect the populations of those plants in nearby wild ecosystems, by seeding out into wild areas. The offspring of these garden plants compete more favorably against invasive plants in the wild because the wild populations have genetics that were the product of generations of natural selection for fitness in the wild. Such garden plants also serve as a reservoir for the genetics of the local wild populations, and can help preserve these genetics if a local wild population is temporarily extirpated. The importance of these reservoirs cannot be over-emphasized in a world where we have reduced wild land to a tiny proportion of its original extent, wild habitats are highly fragmented, and the local genetics of wild plant populations are at risk of being lost entirely.

When gardeners instead plant horticultural cultivars, it is not clear what the long-term effects on the local populations of these species will be. I have seen a lot of evidence to suggest that concern is warranted, and that these cultivars often produce seedlings that are less fit for survival in the wild. And excepting in the rare cases where cultivars are planted in the region from which their ancestors were sourced, they do not preserve the local genetics. There is also the possibility that a "worst case scenario" is also happening, in which the weakened cultivars are interbreeding with wild populations in ways that reduces their fitness, leading to decline of the populations of certain species, at least in some areas.

I have not yet seen any specific evidence that this is happening, but I also have not seen conclusive evidence that it is not. Concerningly, the horticulture industry is not studying any of these potential effects; they continue to breed and market and distribute plants primarily for their performance in gardens. What little consideration of ecology is being done has focused on the value of plants to insect populations (such as is studied at Mt. Cuba Center's trial garden.) But I have yet to see any research at all on the effect of cultivars on the genetics or fitness of local wild populations of plants.

Removal of Native Plants that Are "Too Tall"

The bias against tall plants affects property management both in home gardens and semi-wild spaces in managed parkland.

A lot of people grow "native plant gardens" but manage them intensely, not allowing plants to reproduce freely. People who want to grow only shorter plants end up only growing a subset of plants adapted to drier, more nutrient-poor conditions. People sometimes remove even showy, visually-appealing plants such as cutleaf coneflower (Rudbeckia laciniata), tall goldenrod (Solidago altissima), and late boneset (Eupatorium serotinum), specifically because of their height.

The absence of tall native plants in suburban gardens is directly related to the ways in which rich, moist habitats, the ones where tall plants tend to naturally be dominant, are so overrun with invasives. An example of such habitats are wet meadows in floodplains, which are often common in suburban areas in land too low and flood-prone to build on. Many of these meadows are overrun with invasive plants, some of which colonize from seeds washed downstream from the suburban yards themselves. If people were less averse to planting tall plants, these meadows might have more intact ecosystems, populated by plants like cutleaf coneflower, wingstem (Verbesina alternifolia), and giant goldenrod (Solidago gigantea). The reduced height of vegetation from removing tall plants can create additional problems, increasing water speed during floods, which can increase flood severity downstream, and also increase erosion which causes soil loss upstream, and nutrient pollution, resulting in eutrophication, downstream.

Bias against tall plants in managed parkland can lead park staff to expend resources removing or killing native plants, driven either by complaints from the public, or just the discretion of the staff themselves. For example, in Newark, Delaware, I have seen park workers spray and kill American pokeweed (Phytolacca americana), Canada lettuce (Lactuca canadensis), and tall blue lettuce (Lactuca biennis), but leaving in place many shorter plants which were non-native such as prickly lettuce (Lactuca serriola) and the various sow thistles (Sonchus sp.) So the management was unintentionally favoring introduced vegetation. Changing these practices, however, is relatively easy and can have benefits.

During one year I went out with park staff along the James Hall Trail in Newark, DE and showed them how to distinguish the native lettuces from the invasive prickly lettuce. That year, the staff sprayed only the prickly lettuce, and a few of the native lettuces growing too close to the path, but left native lettuces that were not posing any risk of flopping into the path. In the next year, I saw a dramatic shift in the relative abundances of lettuce species along the trail, with the two native species becoming dominant, whereas in all prior years, the invasive prickly lettuce had been dominant. This change then produced other benefits. The native lettuces supported more aphids, which in turn supported other animals higher up on the food chain such as mantises and migrating warblers.

Failure of Ecological Restoration Projects

Projects can fail due to selection of short plants on sites better-suited to tall plants.

When I first started working in the area of ecological restoration, I was not prepared for just how much plant selection would be influenced by horticultural thinking and aesthetics. Pure ecological projects are rare. A large portion of ecological restoration projects are not conducted on truly wild land, they are only semi-wild landscapes in parks, historic preserves of old estates, or on grounds owned by schools, universities, cemeteries, or other organizations. They don't necessarily want a truly wild meadow, they want something that looks a certain way, and this "look" is plagued by the bias against tall plants.

Many times I have consulted with organizations looking to restore a site, come up with a plant list, and have some of the plants I or others recommended as "ecological powerhouses" be removed in the final list, often replaced by plants that are shorter and less vigorous. A common substitution is that people want the lower-growing butterfly milkweed (Asclepias tuberosa) in place of the taller, more aggressive common milkweed (Asclepias syriaca). Similarly, people often want to substitute shorter goldenrods such as gray goldenrod (Solidago nemoralis) or early goldenrod (Solidago juncea) for tall goldenrod (Solidago altissima), canada goldenrod (Solidago canadensis), or giant goldenrod (Solidago gigantea). Although these choices might work in a managed garden, they do not work in even a semi-wild landscape where plants freely seed in from the wind or bird droppings, and "duke it out", with the winners chosen by survival of the fittest.

Shorter plants only win the battle on sites with adverse conditions, like drought-prone coarse sandy soils, thin soil over a rock outcropping, or exposed mineral soil that is devoid of organic matter. But as I observed above, humans tend to live mostly on or near rich sites where the ecology favors tall plants, so restoration projects where the short plants are favored by conditions are the exception rather than the norm.

Predictably, the restored site becomes invaded by unwanted tall plants, often rhizomatous invasives such as common mugwort (Artemisia vulgaris), creeping thistle (Cirsium arvense), johnsongrass (Sorghum halepense), Japanese knotweed (Reynoutria japonica), or in the south, giant reed (Arundo donax). Sometimes unwanted native plants move in, such as common ragweed (Ambrosia artemisiifolia) or giant ragweed (Ambrosia trifida), both major allergens.

Degradation of Edge Habitats

The management of edge habitats poses an even more widespread problem than the half-hearted ecological restoration projects discussed above. Edge habitats include forests adjacent to parks or lawns on residential, commercial, industrial, or other institutional properties, as well as edges of roads and bike/pedestrian pathways that cut through forests. Many edge habitats are managed without any consideration of ecology whatsoever, and when it is considered at all, it is usually little more than an afterthought. Once again, the bias against tall plants rears its ugly head.

Edge habitats are often managed by workers whose instructions or intentions are little more than to keep an edge "maintained" or "neat". As such, they have a great deal of discretion. They may also respond to complaints from the general public (especially in municipal parks) or the whims of management.

Tall plants also pose a practical management concern, in that they tend to flop into paths or roads. Forward-looking trail managers might want to act proactively, removing tall plants early, before they flop into a path. This removal can happen by mowing or bushwhacking farther back from the path than the standard mow line, by spot-treating plants behind the mow line with herbicide, or by weed-whacking or cutting isolated plants. Plants I have seen targeted in this way include lettuces, especially the native canada lettuce (Lactuca canadensis) and tall blue lettuce (Lactuca biennis) (which tend to grow taller than the invasive prickly lettuce (Lactuca serriola)), American pokeweed (Phytolacca americana), the taller species of goldenrod, common milkweed, and American burnweed (Erechtites hieraciifolius) (which is often mistaken for a thistle). Non-target plants are often killed in these control efforts, creating localized dead zones.

When tall plants are selected against in management of edge habitats, it can cause cascading problems in the interior of the habitat. Relative to open habitats, forest interiors have lower light levels, greater leaf litter, and a more moderate microclimate, with lower wind speeds and more regular temperatures. A natural forest edge produces a buffer of vegetation blocking both light and wind. This buffer consists both of vegetation from woody plants, such as trees and shrubs on the edge, and ground-level herbaceous plants. Edges tend to favor taller vegetation than forest interiors because of the higher light availability, and there is a bit of a positive feedback loop because taller ground-level vegetation captures more leaf litter around the base of plants, leading to high nutrient availability.

Removing the tall herbaceous plants right at the edge causes changes to the interior, farther back than the actively managed zone. Wind speeds increase, light increases, and temperature swings become more extreme. The removal of vegetation and increase in wind speed can cause leaf litter near the edge to blow away, exposing soil to erosion. These changes degrade the habitat for native plants and animals alike. Invasive shrubs and woody vines can colonize the zone set back from the edge in response to the higher light levels and disturbed soil. In the mid-Atlantic, such shrubs include Amur honeysuckle (Lonicera maackii) and burning bush (Euonymus alatus), and vines include Japanese honeysuckle (Lonicera japonica) and oriental bittersweet (Celastrus orbiculatus). The vines, and shrubs like Amur honeysuckle with a wide-arching habit, can root in a pocket of fertile soil and then extend their photosynthetic branches over areas with degraded soil. Once they establish in place of the native vegetation, they then begin the process of capturing leaf litter and nutrients, but creating a new structure that remains stable in the face of management practices, because they are rooted farther back, outside the zone of active management.

Without management that removes tall plants, there would still be invasive plants but they would find it more difficult to penetrate as far into the forest interior. Tall herbaceous plants tend to outcompete vines like Japanese honeysuckle, because the plant cannot reach a high permanent height without climbing woody vegetation, and herbaceous plants grow rapidly and shade out the honeysuckle's leaves. Removing the tall plants tends to make the honeysuckle more vigorous, as more light reaches the carpet of honeysuckle leaves growing on the ground.

Another problem with such removal is the creation of temporary dead zones, small patches which disturbance-loving plants can colonize. Depending on the timing of the control, there are a number of opportunistic invasive plants that can take advantage of these patches. Japanese stiltgrass (Microstegium vimineum) tends to colonize areas disturbed in spring to early summer, and short-lived plants like common groundsel (Senecio vulgaris) can colonize at just about any time of year. Edge habitats, which in our society are so prevalent that they form an interconnected network extending throughout whole regions, become corridors along which these invasive plants can spread.

The degradation of managed edge habitats, because it is such a widespread phenomenon, can spread to unmanaged edge habitats, such as shores of lakes and ponds, or borders between forests and open wetlands or forests and natural clearings or barrens such as rock outcroppings. Although management pressures change the nature of edge habitats, there is some overlap in the species that can occur in both. The widespread dominance of degraded anthropogenic edge habitats dominated by invasive species creates a reservoir of invasive plants such that there are more seed sources for these plants, relative to the native species that would colonize natural edge habitats.

How you can help: tips and tricks

The most important thing you can do to combat the bias against tall plants is to become aware of it, reflect on it, and move beyond it on your own. There are also some tricks to add to your toolbox that can lead to a "best of both worlds" for preserving populations of tall plants on sites where their height poses practical problems.

Utilize topography

One of the best ways to utilize tall plants is in small depressions on an otherwise dry, upland site or site with poorer soils. These depressions accumulate both moisture and litter, forming islands of richer, moister soil in drier, nutrient-poor surroundings. Their natural equilibrium is thus to support taller plants. You can utilize this gradient of conditions in a flower bed, planting tall plants that will stay put in the central dip, and shorter, more drought-tolerant plants around the outside of the bed. The lower height in the dip will also level out the plant heights somewhat.

Use stakes, trellises or other support

Although these practices are more labor-intensive and not practical on a large scale, gardeners who wish to grow tall plants in a small space can use their own structures such as a trellis or stakes to support tall plants. These supports mimic the natural support these plants would have from other vegetation, and they can keep the plants out of paths or roads.

Growing tall plants but keeping them short: the "Chelsea chop"

If you want to grow species of plants that naturally would grow tall, on a site rich enough to support such height, but you want to keep them shorter for practical reasons, a useful trick is the "Chelsea chop". The Chelsea chop refers to the practice of cutting perennials or biennials fullly or partway to the ground mid-growing-season, typically in late spring. It is named for the Chelsea Flower Show in London, which is typically held in late May; the name originated in reminding people who were aware of the dates of the show, when to cut back their plants, but it has persisted in usage even in North America where few people are aware of the dates of the actual show. Some people remember the timing as being between mother's and father's day, although this timing allows for it to be a few weeks later.

Most perennials and biennials are resilient to top-kill, and this is especially true of plants that naturally grow taller, as the lush environments where these plants thrive tend to attract heavy herbivore browsing, such as White-tailed deer in the gaps and edges in the Eastern Temperate Forests, and, historically, bison in the Great Plains. If you cut off these plants, they will simply regrow. Their maximum height will be reduced, but they will usually still flower.

The timing of the chop is important: it must be late enough to remove growth from a significant portion of the time plants were extending their height, but early enough not to affect flowering. Early bloomers, such as foxglove beardtongue (Penstemon digitalis) in the east and many other Penstemon species, will have their flowering negatively affected by the chop if too much is removed. But most taller plants bloom later, either in mid-summer at the earliest, or in late summer to fall. A full top-kill in late May will give these plants ample time to regrow, flower profusely, and produce seeds.

You can use the Chelsea chop to grow otherwise tall plants in areas such as next to paths and roads where flopping plants are a liability. You can also use it selectively on only a few isolated tall plants if you want to allow other, shorter plants to remain competitive with them, to keep a balance that can increase biodiversity. And you can use it for purely aesthetic reasons.

Park and land managers and road crews can also use the same general principle, mowing or bushwhacking a narrow strip next to paths and roads once a season, around the same time, so as to reduce vegetation flopping into the pavement, while allowing some taller plants to still grow up during the peak of the growing season. In much of North America, where sudden downpours from thunderstorms are more common in summer, this mow timing also protects soil by keeping vegetation lush during the the time when erosion risk is highest.

The optimal timing and cut length vary by vegetation type, site, and region. But the optimal timing usually falls somewhere in late spring, and plants can be cut back either to the ground, only a small distance, or anywhere in between.

In Summary

The bias against tall plants has a myriad of negative effects on North America's ecosystems. Its effects include the introduction, breeding, and spread of invasive plants originating as turfgrass, groundcovers, and lawn weeds. The breeding of shortened cultivars of native plants may weaken populations of those species, and at a bare minimum, the direct offspring of these plants are less competitive in the wild, reducing the benefit of growing them in gardens. The exclusion of tall plants from ecological restoration projects can lead to the failure of those projects and their becoming overrun by invasives. And lastly, the targeting of tall plants in the management of edge habitats can degrade these habitats and lead to the establishment of invasive plants both in the interiors behind the managed spaces, and in the disturbed areas along the edge itself. These edges then become networks through which the invasive plants spread throughout whole regions.

You can help address these issues first by becoming aware of them, and then by talking about them with others. If you are in a decisionmaking position in any organization or project where these issues are relevant, use your knowledge to make more informed choices. There are also numerous techniques that can help you to use tall plants even on sites where their height may pose problems. Utilizing topography and planting taller plants in dips, using support, and cutting plants back to the ground in late spring, a.k.a. the "Chelsea chop", are three techniques to incorporate tall plants into managed landscapers where flopping plants are a liability.

A Focus on Goldenrods (Solidago sp.)

July 23rd, 2025 by Alex Zorach

When we launched our site and began prioritizing which plant articles and ID guides to complete, the initial focus was on trees, which made sense because trees are the largest plants in an ecosystem, there are relatively fewer tree species, and there were more sources writing about them.

However, herbaceous plants (plants that do not grow woody parts) are also important to ecosystems, and there are some regions, such as the Great Plains, where they are more dominant than woody plants. And arguably one of the most important genera of herbaceous plants in north America is the goldenrods (Solidago sp.)

Including hybrids, BONAP recognizes a whopping 100 species of goldenrod in North America, all of which are native. We currently list 77, as we have not yet listed all hybrids. There are even some species that have been split from BONAP's 2014 listing, so the final count may number higher than 100.

Lately we have begun the difficult task of building ID guides for the goldenrods of North America. There are several reasons we have chosen to prioritize these plants, and I hope this post can highlight both the goldenrods and our reasons for prioritizing them.

Goldenrods as Keystone Species

Goldenrods are often hailed as keystone species, meaning that they have disproportionately large effects on their environment relative to their abundance. The importance of goldenrods in their environment is not limited to any one factor, so we will explore several.

High Biodiversity in North America

Although goldenrods are found on several continents, including Europe, Asia, South America, and a small region in northwest Africa, North America is the global center for goldenrod diversity; only 4 are found in South America and 6-10 in Europe, depending on how you classify them.

The diversity among goldenrod species enables them to thrive in surprisingly different habitats. People mostly think of goldenrods occurring in disturbed, open, sunny habitats, but there are numerous species that are found in shade, and they have partitioned the niches even in these habitats. For example, in the east, zigzag goldenrod (Solidago flexicaulis) is found in moist, rich forests, often on north- or east-facing slopes. Blue-stemmed goldenrod (Solidago caesia) also occurs on woods and in slopes, but usually on drier sites, often with some clay and/or rock in the soil. Another woodland goldenrod, elmleaf goldenrod (Solidago ulmifolia), is usually found on dry uplands with calcareous soils.

Seaside goldenrod (Solidago sempervirens) has adapted itself to coastal sand dunes with their coarse sandy soils and salt spray. In the north, Bog goldenrod (Solidago uliginosa), as its name suggest, grows in bogs. In the southwest, Wright's goldenrod (Solidago wrightii) grows on dry hillsides and Juniper-Pinyon woods. And these are all what one might think of as "atypical" goldenrods. There is even a goldenrod that isn't yellow: white goldenrod (Solidago bicolor).

The species richness in goldenrods is directly related to their abundance and wide distribution in different habitats, which is in turn related to their support of insects, as insects tend to evolve to eat plants that are abundant.

Support for Insects

It is hard to write a section about how many insects goldenrods support, as there is so much to say. Goldenrods are best known for their showy flowers and support for pollinators. Their inflorescences are large, with long bloom periods in which new flowers open as others are pollinated. The nectar tubes tend to be short and accessible, with spots for larger insects to perch. So the flowers tend to attract small and large pollinators alike, both short-tongued and long-tonged bees, as well as wasps, flies, and lepidoptera (butterflies, skippers, and moths), as well as less-well-known pollinators such as beetles, ants, and even the occasional true bug. Each of these groupings of insects has numerous different species which visit goldenrod flowers, and in the cases of the bees, wasps, and flies, the list is quite long.

But pollinators are only a small portion of the insects supported by goldenrods. Numerous insects feed destructively on the various parts of the plants, including the leaves, stems, roots, and even other portions of the flowerheads. These herbivorous insects include both generalists, and a large number of specialists that use goldenrods as their preferred food source, and in a few cases, their only food source. Numerous lepidoptera eat goldenrods in their larval form; a lot of sources cite figures saying 100 or more species, but data from the UK Hosts Database, which is no longer publicly available but which we have archived and used for our internal analyses, shows an even higher count of 143 Lepidoptera species recorded eating goldenrods in North America.

So each goldenrod plant is teeming with insect life. The abundance of insects attracts predators and parasites. Both insect predators and other invertebrate predators such as spiders thrive on goldenrods. There are even specialist insects that prefer host or prey insects that themselves specialize on goldenrods. A whole miniature ecosystem is found within a single plant. And all these organisms then become food for larger animals such as birds.

High Biomass

Number of species alone is not the only measure of the importance of a particular genus; it is also relevant how common and dominant in their ecosystems particular plants are. In the case of goldenrods, many of them are both abundant and dominant in many ecosystems. One of the most dominant species, tall goldenrod (Solidago altissima), ranges across most of North America, and frequently forms clonal colonies with 40 or more stems each. Other aggressive species include canada goldenrod (Solidago canadensis) in the northeast, giant goldenrod (Solidago gigantea) in floodplains, wrinkleleaf goldenrod (Solidago rugosa) in the east, western goldenrod (Solidago lepida) in the west and north, and Missouri goldenrod (Solidago missouriensis) which is more dominant in the great plains. This list is hardly exhaustive.

Even "smaller" goldenrods are often robust relative to the ecosystems they occur in. For example, sweet goldenrod (Solidago odora) is often one of the larger perennials in the acidic, nutrient-poor soils it grows in.

The large biomass of these species amplifies their benefit to the food web, such that they support not only diversity, but also large numbers of insects. The volume of insects then supports larger animals such as nesting birds. But the contributions to the food web are only one among many ecosystem services provided by goldenrods.

The physical robustness of goldenrods, especially the taller species, makes them valuable as cover for animals, and structure that other plants can use for support, not just including small vines but also other, floppier herbaceous plants that cannot support their own weight. The dense structure also reduces wind speeds and moderates temperature and humidity at lower levels in a thicket of plants.

The below-ground biomass, including the aggressive and extensive root systems of large colonies of goldenrods, also plays a key role in soil health. The aggressive roots help to stabilize soil and prevent erosion. The feeding of insects on roots creates burrowing action that aerates soil and cycles nutrients down to lower layers of soil. This process plays a key role in improving the soil structure and ultimately paving the way for succession to larger trees on some sites, such as when Solidago altissima colonizes sites with rich but compacted soil.

By investing so much energy in below-ground growth, goldenrods help make ecosystems resilient in the face of disturbances. When above-ground vegetation is cleared, such as by fire, flooding, deposition of sediment, heavy browsing by large mammalian herbivores, or anthropogenic disturbances such as mowing or weedwhacking, goldenrods just resprout, often after sending their rhizomes and/or stems into new locations to reconfigure in response to shifting ground. Goldenrods are critical for quickly revegetating disturbed sites, covering the ground with new foliage, and thus both reducing erosion, and moderating the ground-level temperature swings that often follow any disturbance that exposes the ground to sunlight. In the regions in which they are native, goldenrods can be seen as part of nature's healing mechanisms following a disturbance.

Maintenance of Open Habitats

Especially in the more humid parts of North America, such as the east and northwest, goldenrods play a key role in keeping open habitats open. Most of eastern North America has rich enough soil and high enough rainfall to support closed-canopy forests in the absence of disturbance that kills or removes trees. Following European colonization of North America, fire suppression, both intentional and unintentional (such as through building roads, which act as firebreaks) has led to the reduction of open habitats in areas of the east where land is left wild. A disproportionate number of open habitats are now managed, such as mowed lawn or cropland, not open habitat such as meadows, prairies, or savannas.

Most goldenrods tend to grow on open sites such as meadows and prairies. But the relationship between goldenrods and open habitats is not merely one-directional: some goldenrods, including tall and Canada goldenrod, are allelopathic, meaning that they produce chemicals that inhibit the growth of other plants. This process delays, but cannot fully prevent, the colonization of open sites by trees. In slowing the growth of woody plants, these goldenrods protect open habitats, causing them to persist longer even in the absence of fire.

Resistance to Invasive Species

The combination of allelopathy and general robustness makes goldenrods a good buffer against a newer threat to ecosystems: invasive plants, plants that have been introduced across a major geographic divide, and threaten to disrupt ecosystems, often because native herbivores are not adapted to eat them. An invasive plant is generally going to have a much tougher time invading a habitat with goldenrods than one without.

I have also seen goldenrods competing, sometimes successfully, against some of the worst invasives, such as giant goldenrod pushing up through a patch of the Eurasian common reed (Phragmites australis), or tall goldenrod holding its own against common mugwort (Artemisia vulgaris). Sometimes goldenrods can even compete against invasives in unexpected, novel anthropogenic habitats, such as seaside goldenrod (Solidago sempervirens) seeding into patches of giant foxtail (Setaria faberi) in sandy and gravely soil along a railroad track.

The insects supported by goldenrods can also indirectly protect against invasion by other invasive insects. The insect community supported by goldenrods includes numerous generalist predators, such as praying mantises, spiders, and all manners of predatory bugs and beetles. Goldenrods also directly support larger animals, especially birds, which not only feed on the insect food but also directly on goldenrod seeds. Many of these predators will happily devour a random new insect that comes their way, thus making a habitat with goldenrods a lot more hostile towards a potential invasive insect.

Wrongly Blamed As Allergens

In the past, goldenrod was blamed for allergies, particularly seasonal "hay fever" which tends to strike in late summer into early fall, around when most goldenrods bloom. However, goldenrods are insect-pollinated and thus have heavy, sticky pollen that tends not to become airborne and people tend not to breathe in. Even people who react to goldenrod on a histamine allergy test will typically not experience many allergy symptoms caused by these flowers.

The true culprit in "goldenrod" allergies are a close relative: ragweeds (Ambrosia sp.), which often grow together with goldenrods. Common ragweed (Ambrosia artemisiifolia) often grows together with tall goldenrod (Solidago altissima) in sunny, slightly dry habitats, and giant ragweed (Ambrosia trifida) often grows with giant goldenrod (Solidago gigantea) in moist bottomlands. Ragweeds have light, wind-borne pollen, and allergies to them are common and often quite unpleasant. But because ragweed's flowers are wind-pollinated, they are not showy, and as such, when people walk through an area full of ragweed, they often notice the showy goldenrod flowers and not the ragweed, and wrongly associate their allergy symptoms with the goldenrod.
A side note is that this pattern plays out in general: pollen allergies tend to be caused by tall, wind-pollinated plants, which tend to have less-showy flowers. Such plants include trees such as oak or mulberry, and various conifers, but not showy flowering trees such as cherry or magnolia. Similarly, they include plants such as grasses and nettle-family plants. Some genera of wind-pollinated plants, such as pellitory (Parietaria sp.) are important allergens globally, but the locally-native species, such as Pennsylvania pellitory (Parietaria pensylvanica), are so small that they rarely cause much trouble for people.

Utilizing Goldenrods

Goldenrods can be used both in gardening and landscaping, and in ecological restoration projects. The common complaint I hear about goldenrods is that they are "too aggressive" and "will take over your garden". While there is some truth in these remarks, at least for certain species, there are so many different goldenrods that there is almost always at least one or two species you can choose for a garden that will grow well, but without taking over or creating a problem.

Some of the goldenrods that prefer drier habitats with poorer soils make a better choice for gardens. One such example would be early goldenrod (Solidago juncea), and an example favoring even drier sites would be gray goldenrod (Solidago nemoralis). These species tend to grow slower and reach a smaller maximum size, and their greater drought tolerance can make them look good even in a dry year without watering. Their lower nutrient needs can eliminate the need for fertilizing. They make excellent choices for a bed where you add sand or gravel instead of mulch. They also can be a great choice for urban areas where the conditions are difficult due to reflected heat from pavement and buildings.

Even the more aggressive goldenrods can sometimes be utilized effectively in gardens. Tall and Canada goldenrods are showy, mindlessly easy to grow, and tend to shut out most competition, reducing the need for weeding. Giant goldenrod can also be used effectively in gardens when there is a bed that slopes down into a low, wet area in the back; in this scenario the giant goldenrod will thrive in the low area, pushing up through other plants, but will usually not move up into the drier part of the bed.

Where goldenrods usually shine the most, however, is in mass plantings in ecological restoration work. Giant goldenrod is ideal for riparian restorations, plantings to control erosion along streambanks and in floodplains. Tall goldenrod can be planted along roadsides and sunny edge habitats where soil is nutrient-rich but may be compacted or disturbed. Seaside goldenrod can even be useful for reclamation of former industrial sites, where it tolerates thin soils as well as the presence of salt and some minerals that would kill other plants. It also can thrive in roadside plantings due to its tolerance of drought and road salt.

Identification as Key to Understanding

The best way to understand plants and their habitat needs and ecological relationships is to observe them yourself, in the wild, in areas around you. To this end, it is helpful to know what you are looking at. As such we have prioritized completing ID guides, in many cases before we even complete the articles on each plant.

We invite you to check out our currently completed ID guides on the Solidago genus, and to stay tuned for the completion of more guides.

Completed Solidago ID Guides

Guide	Date Started↓	Date Updated
Blue-Stemmed Goldenrod (Solidago caesia) vs. Mountain Decumbent Goldenrod (Solidago curtisii)	Mar 06, 2025	Jul 20, 2025
Tall Goldenrod (Solidago altissima) vs. Sweet Goldenrod (Solidago odora)	Mar 06, 2025	Jul 20, 2025
Early Goldenrod (Solidago juncea) vs. Sweet Goldenrod (Solidago odora)	Mar 05, 2025	Jul 20, 2025
Canada Goldenrod (Solidago canadensis) vs. Giant Goldenrod (Solidago gigantea)	Jan 16, 2025	Jan 17, 2025
Giant Goldenrod (Solidago gigantea) vs. Early Goldenrod (Solidago juncea)	Jan 12, 2025	Feb 07, 2025
Tall Goldenrod (Solidago altissima) vs. Giant Goldenrod (Solidago gigantea)	Dec 04, 2024	Feb 08, 2025
Tall Goldenrod (Solidago altissima) vs. Canada Goldenrod (Solidago canadensis)	Jul 20, 2023	Feb 15, 2025

Under Construction Solidago ID Guides

Guide	Date Started↓	Date Updated
Early Goldenrod (Solidago juncea) vs. Gray Goldenrod (Solidago nemoralis)	Feb 27, 2025	Feb 27, 2025
Canada Goldenrod (Solidago canadensis) vs. Wrinkleleaf Goldenrod (Solidago rugosa)	Feb 05, 2025	Feb 05, 2025
Tall Goldenrod (Solidago altissima) vs. Wrinkleleaf Goldenrod (Solidago rugosa)	Jan 23, 2025	Jan 28, 2025
Blue-Stemmed Goldenrod (Solidago caesia) vs. Elmleaf Goldenrod (Solidago ulmifolia)	Jan 12, 2025	Jan 12, 2025
Wrinkleleaf Goldenrod (Solidago rugosa) vs. Elmleaf Goldenrod (Solidago ulmifolia)	Jan 12, 2025	Jan 31, 2025

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Disturbance and its Role in Plant Habitat Preferences

May 29th, 2025 by Alex Zorach

A critical and often neglected aspect of plants' habitat preferences is disturbance. Broadly speaking, a disturbance in an ecosystem is an event that changes the environment, usually harming and/or killing some plants in the process. Some examples of disturbances include flooding, drought, fire, landslide, logging, or a wind storm.

Disturbances can be natural or anthropogenic (human-induced), and some, such as those related to climate change, result from an interplay between natural and anthropogenic factors. Disturbances can cover all spacial scales, from micro-disturbances such as a small animal digging a hole or a large animal treading on soil with its hooves, through slightly larger ones like a tree or a few trees being thrown by a windstorm, to massive scales like a broad region experiencing drought or a major volcanic eruption.

Disturbance is not inherently good or bad, but it does shape what plants can grow and thrive in a particular environment. And, in the long-run, disturbance plays a key role in creating and maintaining biodiversity.

Understanding disturbance is key for working with plants in any setting, whether in gardening, landscaping, ecological restoration, or conservation work.

Specific Plants have Specific Adaptations to Specific Disturbances

When looking at the variety of plants in our natural environment, a question that arises is: "Why are there so many species? What makes each one different?" One of the key answers is adaptation to different disturbance regimes. For example, among the white oak group, post oak (Quercus stellata) is adapted to withstand both severe drought and fire, and as such, it resists both.

At the other end of the spectrum, bottomland oaks such as overcup oak (Quercus lyrata) are adapted to withstand flooding. Interestingly though, there are many different white oaks that grow in bottomlands. Swamp white oak (Quercus bicolor) and swamp chestnut oak (Quercus michauxii) both are adapted to sites that flood less deeply than overcup oak. Overcup oak tends to grow on the lowest sites next to rivers, but it tends to grow on sites that flood primarily in late winter or spring. It leafs out significantly later than swamp white oak or swamp chestnut oak, allowing it to remain dormant during the period of most severe flooding. This adaptation allows it to inhabit lower, more flood-prone sites where those other two oaks could not survive. However, because it leafs out late, it has a disadvantage on slightly higher, drier sites, and these sites tend to be colonized by other oaks.

There are even white oaks adapted to both flooding and fire, such as bur oak (Quercus macrocarpa). Bur oak tends to be more common farther west, being dominant primarily in the Great Plains, from Texas north through KS, NE, MO, IO, MN, and surrounding states. This region is drier than regions to the east, so fewer trees at all are able to survive on uplands, with these sites instead supporting open prairie. And bottomland sites are such that they can be subjected to both flooding, and drought and wildfire.

These examples explore only a single limited taxon of plants (the white oaks) and their handling of a single type of disturbances: those related to the presence or absence of moisture, i.e. the spectrum of flooding vs. drought and fire. There are countless other taxa and countless other types of disturbances. Thinking from this perspective, it becomes easier to understand how and why there are thousands of plant species native to North America, and sometimes dozens even within a single genus.

Adaptation to Disturbances Has a Cost

Every adaptation to a challenge has a cost. The overcup oak gives up a few weeks of photosynthesis as a trade-off to better withstand deep spring flooding. The post oak grows slowly so that its foliage is not overextended in a drought, and mature trees grow thick bark to insulate against fire.

Plants that forgo these adaptations will have an advantage in a habitat free from these stressors. For example, each of the sugar maple (Acer saccharum) and American beech (Fagus grandifolia) are poorly-adapted to both drought or flooding, requiring mesic (consistently moist but well-drained) conditions to thrive. But by avoiding the costly adaptations to drought or flooding, these trees achieve greater photosynthetic efficiency, and are among the most shade-tolerant of all trees in Eastern North America. In the absence of disturbance, they eventually replace most competing trees. Even their associate, the yellow birch (Betula alleghaniensis), relies on sunnier gaps created by a small disturbance such as a single tree dying, in order to establish.

Another example of such tradeoffs is seen in milkweeds. Whorled milkweed (Asclepias verticillata) is a pioneer species that is among the first colonizers of sunny, dry sites with poor soil, where a disturbance has cleared all vegetation. Its narrow leaves with little surface area make it able to withstand drought stress even before it has had time to establish much of a root system. But these leaves cannot capture much sunlight, which not only limits it to sunny sites, but makes it less competitive against other vegetation. At the other end of the spectrum, poke milkweed (Asclepias exaltata) has broad, thin leaves that are both outstanding at capturing light and inexpensive to manufacture, allowing it to persist in shade. But the thin leaves leave the plant so susceptible to drought stress that it typically can only survive on sites sheltered from wind. A disturbance that removed too many trees would probably eliminate it from a site.

The more one studies these matters, the more one realizes that the disturbances are inseparable from the plants. The adaptations to the various disturbances are reflected in the plant's morphology and behaviors (such as timing and growth responses) which in turn are encoded in the plant's genetics. To understand plants, you need to understand disturbances.

Learning the disturbances a plant is adapted to is as important as learning how to identify it by leaf or flower shape, and indeed, often goes hand-in-hand with learning its morphology because the morphology is an adaptation to its environment. And this is why, in our plant comparison and ID guides, you will find extensive discussion of disturbance and how the plant is adapted to it. Often, disturbance can be a key factor that can help you to identify a plant, as certain plants either will or won't be found on sites subjected to a particular type of disturbance. Understanding the relationship between adaptation and morphology can also help you remember how to identify a plant.

Periodic vs. One-time Disturbance & Succession

Disturbances can be periodic, and the degree of regularity of periodic disturbance can also vary. It is common for some rivers and streams to flood periodically, often in spring. At the same time, the severity of flooding may vary greatly from one year to the next. Drought and fire can also be periodic, but also vary both in intensity and frequency. When disturbance is frequent and regular, it creates a plant community adapted to the disturbance. These communities may include long-lived perennials or woody plants able to survive through the disturbance many times, and also annuals, biennials, or short-lived perennials that quickly germinate following the disturbance.

One-time or rare disturbances create a different sort of environment. A rare disturbance will often kill most or all of the plants in an ecosystem, resetting the ecosystem back to a more barren state in which plants need to recolonize gradually. In some cases, such as when soil was washed away by a flood or landslide, severely burned by fire, or covered in a lava flow, the soil itself may need to accumulate or develop. Plants adapted to rare disturbances may exhibit traits such as long-term seed banking (common in legumes) or off-site dispersal (such as wind-, animal-, or flood-dispersed seeds) so they can establish on a site where all the vegetation has been removed.

The schedule or pattern of disturbance is not a function of the type of disturbance alone; the same type of disturbance can be regular in one environment and rare in another. For example, Florida scrub communities would naturally experience fire almost every year, triggered by lightning strikes at the end of the dry season. Because the fire is frequent, fuel accumulation, and thus fire severity, was limited. These communities support trees such as sand pine (Pinus clausa) and longleaf pine (Pinus palustris) that can survive such fire. On the other hand, Chaparral in the California Coastal Sage, Chaparral, and Oak Woodlands tends to experience infrequent, severe fire after years or even decades of fuel accumulation. Here fire kills almost everything, leading to a process where the plants gradually recolonize.

The process through which an ecosystem regrows following a major disturbance is called succession. The term succession is not used for regular disturbances, only rare, catastrophic ones. Early in succession, pioneer species colonize the site. Part of a plant's habitat preferences include which successional stages of the habitat it occurs in. For example, the red mulberry (Morus rubra), which grows in floodplain forests, typically shows up around 80-90 years after a major disturbance. These forests may experience flooding nearly every year, but these disturbances are not severe and generally leave most of the forest intact.

Disturbance in Gardens and Managed Landscapes

Gardens and managed landscapes are subjected to regular, often heavy anthropogenic disturbance, which we can think of as managed disturbance. Mowing, weed-whacking, mulching, weeding, and herbicide use are some of the most common examples of disturbances that humans carry out on managed ecosystems.

If you want plants to thrive in a managed landscape, you need to choose plants adapted to whatever disturbance regime you are carrying out on that landscape. For example, if you want plants to grow in a regularly-mowed lawn, they need to be adapted to mowing. Some native grasses, such as poverty oatgrass (Danthonia spicata), nimblewill (Muhlenbergia schreberi), and buffalo grass (Bouteloua dactyloides), can survive and thrive in lawns, as can some broadleaf plants, like the introduced white clover (Trifolium repens), or the native common blue violet (Viola sororia) or marsh blue violet (Viola cucullata). These broadleaf plants, however, will not survive in lawns treated with selective herbicides like triclopyr or 2,4-D.

Tilling or cultivation of soil is another type of disturbance, in which all of the surface soil on a site is agitated and mixed. Tilling tends to kill certain types of plants, while favoring others. Tilling usually promotes annuals by giving their seeds a space to germinate, whereas refraining from tilling favors perennials. However, shallow tilling can favor perennials with deep rhizomes, such as the persistent invasive japanese knotweed (Reynoutria japonica), creeping thistle (Cirsium arvense), or common mugwort (Artemisia vulgaris), as well as some native plants with similar growth habits such as tall goldenrod (Solidago altissima) or common milkweed (Asclepias syriaca).

A lot of gardeners shoot themselves in the foot by continually weeding their beds, effectively creating conditions where annual weedy plants thrive. Some plants, such as common groundsel (Senecio vulgaris) or hairy crabweed (Fatoua villosa) have such a short lifecycle, able to complete as many as 5 generations per growing season, that they are actively encouraged by frequent weeding. It is nearly impossible to keep up with these plants, because they are specifically adapted to frequent weeding and tilling, and they have often already produced seed by the time people notice them. Instead, they can be kept out by allowing perennial groundcovers to cover all exposed soil.

Natural disturbances can interact with the management of gardens and other landscapes. A typical yard will have its wet and dry spots. If you plant a flood-intolerant plant in a depression that perodically floods, it will die. Similarly, if you plant a drought-intolerant plant on a dry site, it will die unless you go out of your way to water it during droughts, and such watering can be costly and wasteful. Similarly, browsing pressure from mammals such as rabbits, deer, or groundhogs, can kill certain plants, especially those most palatable to these herbivores, whereas others, the more toxic and bitter-tasting ones, or ones with other defenses such as thorns or stinging hairs, will be more resistant. Intelligent, sustainable gardening demands knowing both the natural and managed disturbances your yard will be subjected to, and selecting the right plants to withstand those challenges.

Disturbance in Ecological Restoration Work

Understanding disturbance is key to doing ecological restoration work for multiple reasons. Every site has its particular unique set of disturbances that it experiences. A floodplain may experience regular deep, fast-moving flooding, but may rarely experience drought or fire. An upland site, however may experience more frequent drought, and some may experience occasional wildfire. An exposed hilltop may be more exposed to high winds, whereas coastal dunes are prone to salt spray, storm surge, and shifting sands.

Semi-wild habitats can bring additional anthropogenic disturbances. A meadow under a power-line right of way may be subjected to periodic mowing and/or herbicide application. Sites adjacent to an area (such as cropland or railroad tracks) with heavy herbicide use may be subjected to occasional, irregular herbicide drift from the neighboring site. Highways and urban roadsides may have runoff from road salt in winter. A creek running through cropland may have nutrient pollution from agricultural fertilizers and resulting algal blooms, and a creek running through a formerly mined area may have acid mine drainage. And in general, waterways downstream from areas where land has been cleared and/or paved, and wetlands drained, will tend to experience more severe oscillations of water levels (including both flooding and drought) than natural watersheds with the vegetation cover intact.

When re-vegetating a site, or seeding or transplanting plants in to re-establish the native flora or increase biodiversity, in order for the plants to persist long-term, plants must be chosen that are adapted to the site's disturbance patterns. In order to match a plant to the site, one must understand both the plants and the site.

Keep in mind that the disturbance regime is likely to have changed, so just because certain plants thrived on a site historically does not mean that it will always be possible to reestablish them. Some examples of why it may not be possible to restore the historic flora on a site include:

• Areas upstream in the watershed may have been cleared, leading to more severe flooding and/or water table oscillation.
• Topsoil may have been lost, degraded, or compacted, leading to lower water percolation into the soil and thus worsening of drought.
• Clearing of forests or trees on adjacent sites may expose the site to higher winds and more extreme temperatures.
• Anthropogenic disturbances, such as controlled burns, practiced by indigenous people may have been halted, and may not be legal and/or practical to bring back to the site.
• The site may face greater herbivory pressure, such as from deer overpopulation in suburban areas, or less herbivory, such as in areas of the Great Plains where bison have been extirpated.
• The climate may have changed in such a way that the habitat is now suited for different species than what originally grew there.
• The site may be subjected to new anthropogenic disturbances, such as herbicide, mowing, weedwhacking, or foot traffic or other use.

Often, modification of the anthropogenic disturbances (such as by changing the timing of mowing) can be the most effective way to achieve certain restoration goals, such as the removal of certain invasive plants or the favoring of certain native species. In some cases, such changes do not even require more resources, they simply redirect resources already being used to manage the site such that they achieve better ecological results.

The disturbances in our world will continue to change, both for natural reasons and through the actions of humans. We will achieve better results when we learn to work with these disturbances, picking plants able not only to withstand them, but to exploit or benefit from them.

Although greater knowledge can lead to better matching of plants to the site, there is no substitute for trial-and-error, which can be seen as the human side of the process of natural selection, a process that is always at work in wild ecosystems and is a large part of how plants evolve and adapt to their environment. We emphasize that, even with the articles on our site that are more-or-less "complete", research is best used only as a starting point. The vision of our site is that it will lead to real-world restoration efforts, and those efforts will inevitably involve experimentation and ongoing observation to figure out which methods work best.

Thank you!

Thank you to everyone who has read to the end of this lengthy post, for caring enough about these issues to do so. Thank you to everyone who takes the information in this post out into the world to do ecological restoration work. Thank you to everyone who pays attention to plants and observes their behavior in the real world enough to notice their different responses to disturbance. And thank you also to all the donors who continue supporting our work on this site!