bplant.org Blog
Range Map & Taxonomic Update Progress
January 31st, 2024 by Alex Zorach
Back in September of 2022 we announced that we had completely retired our first-generation range maps, replacing them with new and improved maps. However, many aspects of our maps remained incomplete. Many species still lacked maps, and most maps were strictly limited to the lower 48 US states, not extending into Canada, Alaska, or Mexico.We have since made great strides in map completion:
- 16838 plants now have range maps. This is over 81.5% of the plants listed on our site.
- 5061 maps have been completed for all of North America, including Canada, Alaska, and Mexico for species that occur there. This is now over 30% of our published maps.
- 5653 plants (over 27% of plants) have been interlinked with Plants of the World Online (POWO) and had their taxonomy updated to reflect the information from POWO.
- We began marking plants that we wanted to list on our site, but that do not occur in the wild in North America and thus have no map or an empty map. We currently list 27 such plants and this number will probably increase quickly now that we have this category.
Why has the rate of map completion slowed down?
If you have been following us since the beginning, you will notice that our rate of completion of range maps has slowed down considerably. We have been putting more time and effort into range maps recently though. The slowdown is both because we completed the easier maps first, and because we are developing higher standards as we further refine existing maps.In many cases, constructing maps was straightforward because there was complete, accurate data available from the various sources we consult, and the different authorities agreed on plant ranges and establishment means (i.e. native vs. introduced.)
In other cases, things get messy. Sometimes data is missing or incomplete. Often, different sources disagree, and we need to research and make tough judgment calls about which material to accept as correct. Common issues include misidentifications, and different standards in different sources about when to consider a record a cultivated plant, vs. a waif (a transient introduction into the wild that does not persist), vs. solidly established in the wild. Many plants also have taxonomic complexities, such as splits, merges, and other reclassifications. Taxonomy can also interact with identification issues, such as when a record was identified as a particular variety or subspecies, but that taxon then later up getting moved into another species.
We have been building our range maps by conducting multiple sweeps through the data. On each sweep, we construct maps using the tools and processes we have available, and put a certain portion of the remaining map in a "messy" bin, to do later. At the same time, we also work to improve and streamline our map building process. Over time, the plants left in the "messy" bin become progressively more difficult to deal with, so even with better tools to facilitate our work, our maps become slower to build with each pass.
Legend | Color |
Native | |
Introduced | |
Extirpated | |
Expanded | |
Not Present | |
Native or Not Present | |
Native or Expanded | |
Expanded or Not Present |
The map for slender snakecotton (Froelichia gracilis) illustrates multiple challenges and complexities. Its native range extends into Mexico, in ecoregions that do not intersect the United States. Although native to North America, it is now found in areas beyond its native range, but it has also been extirpated from part of its native range. Some of the new parts of its range are adjacent to the native range (and thus we mark them Expanded) whereas the California populations are separated by long distances and major geographic divides (and thus we mark it Introduced.) Different sources also disagree as to exactly where it is native; in this case we took BONAP's report over POWO's. And all of this has happened without any taxonomic complexity; this map, believe it or not, was relatively easier to build than many of the ones we have completed recently.
Our standards are also higher with our second-generation range maps; early on we just wanted to get something out, whereas now we have more different categories on the map legend and are taking care to notate uncertainty in the map itself. Related to these high standards, if you see something that you think is inaccurate or could be improved, please contact us. You do not need to be an expert to help us refine our maps. Seeing a species in the wild outside its reported range, or just seeing something on a map that you think doesn't make sense, are both signs that you may have something to contribute.
Interlinking with Plants of The World Online (POWO)
POWO is a taxonomic backbone run by the Kew Botanical Garden in London. In contrast to our routine, mostly-automated interlinking with other databases, our interlinking with POWO involves examining POWO's treatment of each taxon and comparing it to the schemes used by other authorities. Records integrated with POWO have mostly been brought up-to-date with modern taxonomic changes. In the overwhelming majority of cases, we adopt POWO's treatment. In the few cases where we adopt a different treatment (this usually happens in the rare cases where POWO is not up-to-date on newer work and another source we consult is), we still carefully examine POWO's listing. In a few cases we have enacted splits that POWO has not, in line with Flora of the Southeastern U.S. (FSUS) by Alan Weakley.Differences in classification are a primary reason for discrepancies in plant range maps between different sources. There is often not a 1-to-1 relationship between records. You can read about how we resolved these discrepancies in the notes fields on each plant page. Taxonomy notes are located above the table-of-contents, right under the plant's names. This placement ensures people will have a clearer idea of what taxon the page refers to before reading the article or seeing the map, in the case that there have been confusing reclassifications or inconsistencies in naming. The range map notes are found directly under the map, and explain any judgment calls we made in constructing the map as well as any clarifying info beyond that conveyed by the legend.
Although the notes are brief on most articles, and many articles lack notes entirely, the total extent of notes is massive. We have already published over 16,000 words in the taxonomy notes, and over 58,000 words in the range map notes. This amounts to about 250 full pages of text. These counts do not include automatically-generated legends nd other verbal notes listed under many maps. The volume of these notes explains why our progress on the more difficult plants is progressing more slowly. We want to make sure we both document and explain our choices, especially in the cases where different sources disagree on taxonomy or ranges.
No Maps: Plants Not Occurring in The Wild in North America
Although we focus on plants occuring in the wild in North America, we list a number of plants with empty range maps, meaning that these species are not and have never been found in the wild here. These plants broadly fit into one of two categories: plants that are widely cultivated, but have never established or been recorded in the wild, or plants that were reported somewhere in the wild but where those records were later deemed to be invalid. We retain both of these types of records for several reasons.For garden and landscaping plants not recorded establishing in the wild, it is always possible that these plants will establish in the wild at some point in the future. Being aware of these plants and knowing how to identify them can ensure they are more quickly detected if they ever do escape and naturalize.
Some plants were widely planted for years or even decades without naturalizing, only to eventually escape into the wild, sometimes even becoming invasive. For example, kudzu (Pueraria montana) was brought to the US in 1876, but the first herbarium specimen we could find, collected from the wild in North America, was from 1901, and kudzu was not recognized as invasive until decades after that.
It is also possible that plants are already present in the wild in North America, but that people have not reported them because they are hard to identify and/or they do not know that they need to check against them. For eaxmple, we have found Japanese honewort (Cryptotaenia japonica) in the wild in two ecoregions, in Delaware and Pennsylvania, and that species is not reported occurring in the wild by BONAP or POWO. Excepting the purple-leaf cultivar, that species may be underreported because it is visually similar to the native honewort (Cryptotaenia canadensis).
A completely different scenario is when older sources report a particular plant somewhere in North America, but the record has been deemed invalid. In these cases, we retain a record specifically because there is other information out there that needs to be corrected. Even when the original source has been updated to correct the record, it is common, especially with sites like USDA PLANTS, that numerous other websites and print sources repeated the inaccurate information before it was corrected, and these other sources are often not corrected. Sometimes misinformation can propagate in secondary sources for decades after the original source corrected it because no one goes back to check the primary source. In the plant world, this phenomenon is especially prevalent in sources relating to horticulture, gardening, and the commercial nursery industry, where the standards of scholarship are much lower than in the sort of scientific sources we rely on.
Examples of such plants include mountain soursop (Annona montana), Syrian cephalaria (Cephalaria syriaca), braceletwood (Jacquinia armillaris), and willowleaf frostweed (Helianthemum salicifolium). We have noticed such errors are especially common in south Florida where there is a huge volume of introduced tropcial species that cannot survive in most of the rest of the continental US.
The First Range Maps and Lists for Canada and Mexico Finer-Tuned Than Provinces/States
One thing that has frustrated me for years is the lack of fine-tuned range maps and plant lists for regions outside the US, particularly, for Canada and Mexico. Apart from specific sources such as the Silvics of North America, which only covers about 200 tree species, and some print field guides, which similarly do not exhaustively cover the plants of North America, there are no sources with range data as fine-tuned as that presented by BONAP and USDA Plants.Although Canada and Mexico both have administrative divisions finer than States and Provinces, there is no equivalent of USDA PLANTS and BONAP for these countries. Canadensys, the closest to a Canadian analogue of these sources, only has data at the level of individual provinces, and the existence of finer-tuned regional data, when it is available at all, is spotty and not accessible in a single place. In Mexico, there is no such website at all.
Although the lack of data has made it much harder for us to build range maps in Canada and Mexico, it also makes our maps much more valuable and groundbreaking in the cases in which we have been able to build them. In these cases, our maps offer a finer level of detail than anything else out there.
Clematis tangutica is one of many species whose range in North America is restricted to Canada and Alaska; in the two ecoregions that cross the border, it is only known to occur north of the border.
The process of constructing these maps is slow and also error-prone. In many cases, it involves examining individual herbarium records. Although there are good tools (the most important of which is GBIF, the Global Biodiversity Information Facility), there are numerous limitations of the data available. Some herbarium specimens have yet to be digitized, thus making it hard to assess the completeness of some range maps (i.e. it being harder to conclude that a species does not occur somewhere, relative to knowing that it does occur somewhere.) Where records exist, many records have geolocation errors, and in many cases there is insufficient verbal description of the location to catch such errors. Even when the locations are accurate, other aspects of the records can be erroneous, such as plants reported as wild that were actually cultivated, or specimens that were misidentified. And on top of this, we have all the same reclassification issues discussed above, but they are uglier because different herbaria (and even different individuals) may follow different schemes, and reclassifications can thus play out differently from one record to the next.
The process of building these maps thus involves delving into individual herbarium records in a way that rarely is necessary when constructing maps for the lower 48 US. As such, it is much slower. However the results can be rewarding.
As we complete these maps, we move towards plant lists for ecoregions outside the continental US. Back when we launced ecoregion-based plant lists in March of 2022, a major deficiency of our lists was that we had no lists for Canada, Alaska, and Mexico. Although we have not completed them, we are seeing the beginnings of these lists for all three of these regions, and it's just a matter of time before they are complete enough that we can publish tentative lists. Our work is also improving the accuracy and completeness of the plant lists for ecoregions that are split between the lower 48 US and either Canada or Mexico, and there are many such regions. Canada and Alaska will likely be completed long before Mexico, both because there is much less plant biodiversity in the Arctic and more in the Tropics, and also because there are more sources available for Canada and Alaska, and lastly because there is less of a language barrier.
Moving Forward: Things To Come
You can expect a continued focus on range map completion over the next few months. We are still in a phase where we are getting a lot done and we hope to keep improving our tools and techniques so that we don't end up getting completely stuck on the difficult maps. So far, so good!I also want to thank everyone too for ongoing financial support that has allowed me to keep working on this project. Although we still have not met our next financial goal of $20,000, we are getting a lot closer to it. The vision of expanding into a larger organization with staff may remain far off, but for now we are able to keep the site going and keep it ad-free for the forseeable future. I have not yet published the year-end finances but this is another thing to expect in the next several weeks.
Giving Thanks To Everyone We Rely On
November 22nd, 2023 by Alex Zorach
The Thanksgiving holiday is approaching in the US, and we want to take this opportunity to thank everyone who has contributed to our site, whether financially or otherwise, over the past year and since the founding of our site.These contributors include financial donors, people who have helped share our material so it reaches a broader audience, and also those who have provided corrections, bug reports, feature and article requests, and other valuable feedback. Lastly, we want to thank the numerous other organizations, websites, publications, and groups whose work we rely on, and the people who created and maintain these works.
Thank You For Financial Contributions!
As the year is not yet over, we don't have full financial results to report, and we still have quite a way to go towards our next goal, but we still have several things to give thanks for on the fundraising front. 2023 is the first year in which an appreciable number of donors returned to give a second time. Furthermore, many of these donors not only increased their contribution amount, but switched from a one-time donation to annual and/or quarterly subscriptions. These subscriptions are particularly helpful as they help us to develop a sustainable budget while minimizing the amount of effort we need to put into fundraising.We also hosted our first in-person event, a plant walk in Newark, DE, and attendees of this event generously donated $160 towards the site. These sorts of donations are especially helpful because they allow us to raise funds in the context of educational programming, again reducing our need to put resources into fundraising. We plan to host more such events in the near future.
Thank You For Sharing and Engagement!
The main purpose of bplant.org is educational: we want to provide information that will ultimately drive real-world conservation, such as protection and restoration of wild habitats and the species that depend on them, and the use of locally-native plants in landscaping and gardening. The goal is to shift human society from having a negative to having a positive effect on our environment.To achieve these goals, our material needs to reach as broad an audience as possible. And people are already helping us to do that, by engaging with and resharing our posts. As with donations, when people share our material it reduces the energy we need to put into publicizing our articles, and frees up more resources for us to work on the website itself.
In 2023 we achieved some new records; our post on yellow nutsedge (Cyperus esculentus) reached over 73,650 people and was shared a total of 188 times. These shares have real-world implications: in the case of yellow nutsedge, that species is native (by most definitions) to much of the U.S., but people expend great resources trying to eradicate it, mostly in monoculture lawns, and often without much regard to its lifecycle or habitat requirements. Yellow nutsedge can be a problematic weed in certain types of cropland but not others; it also has value to wildlife, including to turkeys.
We hope to take the energy people spend trying to control "weeds" like yellow nutsedge in lawns, and redirect it towards controlling invasives and/or protecting native plants. Related to this goal, we are also pleased that our most popular two pages on our site, both with over 11,000 people viewing them annually, are the comparison guides for Norway Maple vs. Sugar Maple, and Red Mulberry vs. White Mulberry; each of these compares a native species to an easily-confused invasive relative.
Thank You For Corrections, Bug Reports, and Requests!
Yet another way people contribute to our site is through feedback. Such contributions can take the form of corrections, bug reports, feature requests, or requests for us to prioritize certain articles or ID guides.Although we always do our best to keep our site as accurate as possible, there are still a lot of errors. The errors include typos, misinformation, omissions, and errors in plant ranges and/or native status. Over time, as people catch and report these mistakes, it helps us to improve the quality of our site as a reference for everyone. We want to thank each and every person who has sent us a correction, whether for something as small as a typo, or something as big as inaccurate information about whether or not a plant is native to a certain area.
Bug reports are also crucial. Over the past year, we fixed bugs reported by users in diverse components of the site, including glitches in the donation system, problems with the search function, broken or incorrect links, and erroneous information displayed in tables.
We also welcome requests for completing or expanding articles or ID guides. With a site of this magnitude and scope, there are literally thousands of choices of where to focus our efforts, and it can be challenging to know which tasks to prioritize. Requests from readers are one of our best guides!
Thank You To All Other Organizations, Publications, and People We Rely On!
Lastly, we want to give thanks for the many other organizations that we rely on. Our site would not be possible without the countless other resources we consult as references, and we have used so many that it is not possible to list them exhaustively.Some key resources we rely on for building and maintaining our range maps include BONAP and USDA PLANTS. We also make heavy use of regional resources including Go Botany, Maryland Biodiversity Project, Calflora, Digital Atlas of the Virginia Flora, Illinois Wildflowers, Minnesota Wildflowers, and Missouri Plants, E-Flora BC, and the Flora of the Southeastern US, among others. Many of these sites also have information on habitat, faunal relationships, and identification.
A key resource we use for plant taxonomy and global range maps is POWO. For referencing garden and landscaping use we consult resources including the MOBOT's Plant Finder and the North Carolina Extension Gardener Plant Toolbox. For information about ecology and habitat, we also rely heavily on the US Forest Service's Fire Effects Information System, and for trees, the Silvics of North America. We consult Lady Bird Johnson Wildflower Center for its searchable field-based data on just about all aspects of plants, Flora of North America for detailed botanical descriptions, and NatureServe Explorer for information on the conservation status of plants. On top of this we rely on many print sources not available online, one of the most useful of which is Plants of Pennsylvania by Rhoads and Block.
A key resource we use for many different purposes is iNaturalist; we use iNaturalist for investigating user-reported data about plant distribution around the edges of their range, for connecting with people knowledgeable about plant ID and habitat, and as a massive repository of open-licensed images for use in our articles and ID guides. Two of the images in this blog post came from iNaturalist! Another resource we are grateful for for its open-licensed images, particularly for ecoregions, is Flickr, and yet another is Wikimedia Commons. Without iNaturalist, our ID guides would progress much slower, and without Flickr, our process of finding ecoregion images would also be much slower.
Over time we have also been interlinking our plant articles with more of these resources.
In addition we participate in countless Facebook groups focused on local and regional native plants, invasive plant control, plant identification and education, and ecological restoration and habitat management. These groups are key not only for helping share our material, but for gathering information and getting valuable feedback. And, like all the above resources, these groups are maintained through the hard work of numerous individuals, especially those acting as moderators and administrators.
We both want to give thanks to these organizations, publications, and informal groups, and the people who run them, and the authors and maintainers of the many books and websites we use. We also want to draw attention to these resources so that the readers of our site can discover and consult them for additional information beyond what they may find here. And we encourage those with the means to do so to also contribute to some of these other resources, as they are all immensely important, serving related purposes than synergize with our mission. For entities funded through the government and/or receiving a component of government funding, you can also write to your relevant representatives to let them know that you appreciate the resources and want to ensure that they stay well-funded and well-staffed.
Thank you to all and enjoy your holiday to those who celebrate it!
Thinking More Deeply About Habitat
April 5th, 2023 by Alex Zorach
When I created bplant, a lot of people asked me "Why are you creating yet another plant website, when there are already so many good ones out there?" My broad answer to this question is a greater focus on ecology. There are many specific answers as well, such as my original post about using ecoregions over political boundaries, and today I want to explore a different one: habitat.In ecology, habitat is a broad term that refers to the environmental factors that allow a species to survive, thrive, and reproduce in a particular area. For plants, habitat encompasses climate, including both macroclimate (the climate of the broader region) and microclimate (details of temperature, moisture availability, and weather patterns particular to a local site), soil conditions (including both chemistry and texture), and the presence or absence of other organisms on the site. Plant habitat is directly influenced by factors such as topography or slope aspect, and hydrology, which includes the presence or absence of bodies of water, the depth of the water table, and the way water moves through the area.
This post can serve both as an introduction to the different aspects of habitat and preparation for what you will find in the habitat section of completed plant articles on our site, and as a reference on the different aspects of habitat.
Why is it important to understand plant habitat needs?
Matching a plant to the right habitat is critically important if you want plants to thrive. A plant growing in unsuitable conditions may struggle or die. Often, death occurs gradually, with a plant first becoming stressed and later succumbing to disease or insect infestation. Often, multiple factors interact, such as cold, flooding, or drought damaging a plant, followed by greater decline. A lot of gardeners wrongly blame disease, insects, or inclement weather for the death of their plants, however these causes are often secondary. Opportunistic infection or infestation can take advantage of stress caused by a plant growing in conditions it is poorly adapted to.Knowledge of habit preferences is also critical for protecting endangered species, because it can guide which habitats are most in need of conservation. It can also help locate new habitat when trying to increase the population of rare or endangered plants. This knowledge is especially important in today's world, especially in major metro areas where wild habitats are small and highly fragmented, and plants often need extra help from humans in transporting them into suitable habitats.
Limits of a Superficial View of Habitat
Prior to creating bplant.org, when researching plants for gardening or ecological restoration work, I found I was continually frustrated when looking up information plants and their growing conditions.Most gardening books and websites broke down plants' growing requirements into only two variables: moisture and light. Typically there were only three categories for each: moist, average, and dry, and full shade, part shade/sun, and full sun. Soil texture, nutrient levels, and other factors were mentioned only in passing, if at all. And more often than not, the sources repeated the same nearly-useless information on nearly all plants: "Best grown in moist, well-drained soil." Most plants can survive in moist, well-drained soil. But just because a plant survives there does not mean that it prefers or is most competetive in those conditions.
Many plants that gardening sources will advice you to plant in "moist, well-drained" conditions, actually are more competitive (and only found in the wild in) other, more adverse conditions. For example, although the red maple (Acer rubrum) will grow just about anywhere in landscaping, in the wild it is mostly found either in swamps or on dry, rocky ridges, rarely in mesic, i.e. "moist, well-drained" conditions.
I found myself frequently confronted with a list of 20 or more different plants which were all described as liking the same sun and moisture conditions. Yet when I looked in the wild, I would see some of these plants thriving on a particular site, and not others. Sometimes I would even try to grow a plant, only to find it fared poorly, whereas on other sites it would be vigorous, even aggressive. I found myself continually asking: "Why?" and this question led me to examine the less obvious aspects of habitat. And as I did, I became better at growing plants, both in my garden and in ecological restoration projects.
And if you want to do ecological restoration work, whether in the wild, or using your own garden or yard as a semi-wild habitat, you need to look more deeply too. You need to treat plants not as an aesthetic decoration, but as part of an ecosystem, with unique adaptations, needs, and strengths and weaknesses.
Important (and Often-Neglected) Aspects of Plant Habitat
As gardening sources suggest, moisture and light availability are often (not always) two of the most important factors in determining whether not a particular plant will grow on a particular site. However, there are many others, and part of the purpose of bplant is to draw attention to these other factors:- Soil texture
- Soil nutrients
- Soil pH / acidity
- Drainage
- Microclimate
- Disturbance regime
- Presence or absence of other organisms
Soil Texture
Soil texture is one of the most important aspects of soil because it influences drainage, moisture availability, and the possible root structures a plant can develop. A simple way of looking at soil texture is as a continuum of particle sizes:rock > gravel > sand > silt > clay
Most soils are not uniform, but contain a mix of particles of different sizes. Because the smaller particles determine water percolation and drainage, usually when considering soil texture, people pay most attention to the ratios of sand, silt, and clay in a soil. A common term you will encounter is loam. Loam is not a particle size so much as a range of mixtures of particles that describes a "middle" or "ideal" soil texture that balances drainage, water retention, air circulation, and nutrient availability. Usually, loamy soils are well-developed soils that have been created by biological processes, balancing organic matter with mineral content and air pockets.
Soils very high in organic matter and low in mineral content have different texture-related terms. Muck refers to a fine-textured, waterlogged organic soil in which the original organic matter is so broken down that it is unrecognizable. Muck is common in wetlands with poor drainage and low mineral content. Peat, on the other hand, is similarly predominately-organic soil that is a bit less broken down, coarser and more spongy in texture. A related term is humus, which refers to the fine-textured dark organic matter in any soil.
Soil texture is often different at different layers, too. Typically, the surface layers of soil are more weathered than deeper layers, and the depth to reach bedrock through soil can range from essentially zero in a rock outcropping, to hundreds of feet deep, completely outside the reach of plant roots. Sometimes a fragipan, an impermeable or slowly-permeable layer of clay, underlies coarser-textured soil. All of these factors affect plant growth, and many plants specialize in soil with one texture at the surface and another deeper down.
Soil Nutrients
Plants require a variety of nutrients in a particular balance, and typically, different nutrients will be limiting in different ecosystems. However, different plants have different nutrient needs, and some are thus better-adapted than others to survive on a particular site.Nitrogen is a key nutrient for plants, and a key component of proteins, which are the building-blocks of all living organisms. The atmosphere provides an essentially endless supply of nitrogen, but in a form unavailable to most plants. Certain plants, called nitrogen-fixers, have a symbiotic relationship to bacteria, typically in root nodules, which convert atmospheric nitrogen to a form plants can use. Nitrogen-fixing plants have a major advantage in nitrogen-poor soils, and will not only grow faster than other plants in these environments, but in the long-run they will also boost the growth of surrounding plants as they shed nitrogen-rich litter and release nitrogen through their roots. Nitrogen tends not to be limiting in the long-term in undisturbed ecosystems, but it can be limited on eroded or exposed mineral soils, or following a fire or the clearing of land by humans.
Phosphorus is another key nutrient for plants. Phosphorus in ecosystems originates in rocks and minerals and tends to be released as rocks are weathered, but the phosphorus content of different rocks, and thus different soils, varies widely. As such, plants have widely different adaptations to high or low levels of phosphorus. Plants in low phosphorus environments tend to have more surface roots and more total roots relative to shoots. Because the processes that release phosphorus into bioavailable forms are slow, phosphorus tends to be a limiting factor in the growth of most ecosystems in the long-run. High-phosphorus ecosystems tend to develop denser, richer canopies and contain more shade-tolerant species, relative to phosphorus-poor systems, when other factors are not limiting.
Calcium is a key nutrient for plants not only because it is directly used by plants, but because it is an important buffer that affects soil pH. Soils or rocks rich in calcium are called calcareous; the most common calcareous soils are those derived from limestone, dolomite, or marble (which is metamorphosed limestone.) Poorly-developed rocky soils on calcareous rocks tend to have a high pH that limits plant growth, whereas well-developed calcareous soils tend to have a neutral pH. Calcium tends to form slightly-soluble compounds, and thus leaches from soil faster than metals like iron or aluminum, but slower than magnesium, sodium, or potassium. Thus, arid and semiarid regions tend to have more calcium in the soil and higher pH regions, whereas regions with high rainfall tend to have low calcium and more acidic soils. The presence of calcium in soil often allows plants to move into slightly drier conditions than they would prefer in lower-calcium soils, which relates to plants utilizing calcium as a way of protecting themselves from drought stress.
Magnesium is another essential nutrient with a similar buffering effect to calcium, tending to raise the pH. It is also an essential ingredient in chlorophyll, the chemical plants use to capture energy from sunlight. Magnesium tends to leach more readily than calcium, and like with calcium, it tends to be leached more in areas of high rainfall. Soils derived from dolomite tend to be highest in magnesium, whereas any acidic soils tend to be deficient in it.
Together, soils high in the total of calcium and magnesium are called base-rich soils.
Other ingredients can, under less common circumstances, be limiting in plant growth as well. Potassium is probably the most important essential nutrient not mentioned above; it is abundant in most plant growth and litter, including ash from burned plants, but it can occasionally be deficient in some soils. Iron is essential for plant growth but is usually abundant in soils. Under certain rare circumstances, soils can be deficient in manganese, copper, zinc, or molybdenum.
Unlike animals, sodium is not essential for most plant growth. However, some plants can utilize it to a degree, and it is an important factor inhibiting plant growth in some ecosystems. Because sodium and its salts are highly soluble, the salinity of water and/or soil is only an issue for plants either along coasts, including along coastal estuaries, and in endorheic basins, basins in the center of the continent that do not drain to the ocean. Saline soils are thus a major factor limiting plant growth in arid regions of the West.
Soils can also contain other toxic elements that inhibit plant growth, such as chromium, cobalt, and nickel. This phenomenon occurs naturally in soils derived from serpentine minerals, creating an environment called serpentine barrens. However, it can also occur on polluted sites, such as former industrial sites, mine spoils, and other brownfields.
Soil pH or Acidity
Acidity is one of the most important aspects of soil chemistry, as it interacts with all the nutrients above and it tends to be a single dimension that captures and relates to the presence and availability of many different nutrients. pH is the most widely-used measure of acidity.Neutral pH is 7, the pH of water. Higher pH is basic, whereas lower pH is acidic. Although there are exceptions to both trends, organic matter tends to be more acidic, whereas mineral-nutrients often tend to contribute to higher pH. Soils tend to range between about 3.3 at the most acidic, to 10 at the most basic.
Plants tend to grow most vigorously in neutral to slightly acidic soil, ranging from 6.0 to 7.0. Soils derived from calcareous rocks tend to stay above 5.5, but soils poor in calcium and magnesium often become much more acidic. The most acidic soils tend to be found in bogs, which tend to range from 3.3-5.5. In humid climates, acidic soils are also found under boreal forests, in coarse sandy barrens, and on rocky soils derived from calcium-poor rocks such as sandstone, quartzite, or granite.
Soil pH is directly related to climate, with rainfall being the biggest factor and temperature also being important. Because rainfall tends to leach calcium and magnesium from soil, minerals which contribute to higher soil pH, higher rainfall tends to create more acidic conditions and lower soil pH, whereas drier regions tend to have higher soil pH. Because warmer climates speed plant growth and the accumulation of organic matter, warmer temperatures also tend to further decrease soil pH in areas already sufficiently moist or humid. However, this effect is insignificant in arid areas because there is little plant growth, so hot arid regions tend to still have high pH soils.
Also, in climates that get cold enough to be dominated by evergreen conifers, such as the Northern (Boreal) Forests, Marine West Coast Forest, and the higher elevations of the Western Cordillera, the cold temperatures lead to slower breakdown of organic matter and slower weathering of rocks, which also contributes to acidic soils.
In arid regions with varied topography, three factors lead higher elevations to have more acidic soil and low elevations higher soil pH: higher elevations tend to have higher rainfall, mountains often have conifer-dominated forests that drop acidic litter, and water tends to transport the water-soluble calcium and magnesium downhill.
Preferences for soil pH explains the distributions of many plant species. For example, many plants that prefer higher ph soils, such as bur oak (Quercus macrocarpa), are absent from the southeast, but have ranges that extend quite far south in the great plains, into central Texas, where the semiarid climate leads calcium to be more conserved in the soil, and also range farther east into humid climates in the northeast and upper midwest, where cold temperatures also conserve calcium. At the other end of the soil pH preference spectrum, chestnut oak (Quercus montana) prefers acidic soils, and as such its range stops at the part of Ohio that consistently has calcium-rich soils, whereas on the east coast, it ventures well into coastal habitats such as the Pine Barrens of Long Island and New Jersey.
Drainage
Soil and site drainage is one of the most important aspects of a plant's habitat, as it influences both water availability and soil aeration. Some people do not realize that plants actually need air as well as water, and receive air through their roots. Although some aquatic or partially aquatic plants have special adaptations that help them capture air in their above-water parts and use it to supply underwater parts, most plants rely on their root system for capturing air. As such, soil aeration is essential for most plants.Soil drainage can be divided into classes with self-explanatory names: "excessively drained", "somewhat excessively drained", "well drained", "moderately well drained", "somewhat poorly drained", "poorly drained", and "very poorly drained". Although going deep into the definitions and implications of these different categories is beyond the scope of this post, it can be helpful to understand some of the basic ideas of the different levels of drainage.
Excessively drained soils are such that water is drained so rapidly that there is almost no retention in the soil. Typically this occurs when soils consist mostly of coarse sands, but it can also occur on thin soils over impermeable bedrock that causes water to run off. Excessively drained soils create drought- and fire-prone habitats even in areas with high rainfall. Examples of such habitats include the New Jersey Pine Barrens or the Newaygo Barrens in the western portion of Michigan's Lower Peninsula. Regions with excessively drained sands have some unusual phenomena, like deep water tables with levels remaining nearly constant year-round, and rivers and streams that never freeze, even in surprisingly cold climates, like portions of the Muskegon River in Michigan. All of these factors create unique habitats for distinctive plant communities. Excessively-drained sands typically are found on a site with a history of water depositing them at some point in the past, such as sand dunes of past ocean or lake shorelines, or glacial outwash fields.
Well-drained soils tend to strike a balanced between availability of moisture and aeration and tend not to produce any stress from lack of soil aeration, while they retain enough moisture to provide plants with adequate moisture except during periods of prolonged drought. Discussed above in the soil texture section, loam is usually well-drained or close to it.
Poorly-drained soil drains so slowly that the soil tends to stay wet at shallow depths after it rains. However, is important to note that wet is not the same as moist. Wet, which can also be termed "waterlogged", means that the soil is so saturated with water that there are few or no air bubbles left in the soil. Moist soil, on the other hand, has ample water availability but still has air pockets in it. Wet soil creates stress on most plants whereas moist soil typically does not. In most regions, poor drainage is defined as soils in which water percolates more slowly than 1 inch per hour.
It is also important to understand that, while wetlands and other sites with a high water table are often poorly-drained, poorly-drained soils or habitats are not necessarily moist. A small depression in an upland habitat, with clay soil, exposed to full sun, will likely be poorly drained and may remain waterlogged for hours or days, yet may also become completely dry after just a few days without rain, and plants there may experience significant drought stress. Small depressions in impermeable bedrock, such as a depression in a granite rock outcropping, are an even more extreme example of a habitat which is poorly drained but prone to being extremely dry most of the time. An ecoregion rich in habitats that are both dry and poorly-drained is the Blackland Prairie of Mississippi and Alabama, but many other regions have at least some isolated sites with these properties.
Microclimate
Microclimate represents the ways in which climate or weather varies on a particular site, relative to the average or typical climate of the broader region. Terrain is one of the biggest influences on microclimate. Ridgetops and peaks often have higher winds, greater temperature extremes, and receive more total sunlight relative to valleys. The steeper the slope, the bigger its influence on microclimate.Slope aspect refers to the direction a slope faces. In the northern hemisphere, south-facing slopes receive more sunlight and thus tend to be warmer and drier whereas north-facing slopes receive less sun and tend to be cooler and moister. Because the sun rises in the east and sets in the west, and the air tends to heat up and clouds tend to burn off throughout the day, west-facing slopes are similarly sunnier, warmer, and drier than east-facing slopes. So, ecologically, the main microclimate division in hilly terrain tends to be between warmer south- and west-facing slopes and cooler north and east-facing slopes.
Bodies of water, especially larger ones, tend to modify microclimate. One obvious effect is increasing the humidity of nearby air, but water also has a moderating effect on temperature. Because of its high specific heat relative to air or rock, water stores a great deal of heat and tends to warm or cool slowly. This effect becomes diminished somewhat in winter in areas where the bodies of water completely freeze over. At the same time, a large, open body of water creates space for high winds. Larger bodies of water, such as oceans or the Great Lakes, can also create lake effect precipitation downwind from them, especially when hills or other elevation gains are downwind from the water.
Human modifications to the environment also influence microclimate. Buildings create environments mimicking the effects of slope aspect but often being more severe due to the 90-degree angle buildings make with flat ground, creating very hot, dry south faces and cool, shady north faces. The heat from buildings also leaches into the environment, warming the surroundings at all times of year. On a larger scale, this effect, combined with the clearing of vegetation, produces the urban heat island effect which not only raises temperatures but also increases rainfall downwind from cities. Construction can also alter drainage and create both wet and dry microclimates, as well as both wind tunnels and sites sheltered from wind.
Microclimate is a major factor driving plant ranges as well as plant habitat around the edges of their ranges. For example, the eastern white pine (Pinus strobus) is mostly restricted to cooler north-facing slopes in the south of its range. And most oaks, in the north of their range, are restricted to warmer south-facing slopes. The absence of varied topography also explains why many tree species that are common in eastern and southeastern Ohio, as well as Michigan, but near the borders of their range in both of these regions, become uncommon or are even absent entirely, from northwest Ohio and bordering parts of Indiana: these areas are so flat that there is a lack of warmer or cooler microclimates, so the only trees that thrive are ones solidly within their climate tolerances. Hilly topography thus supports plants with a broader range of climate tolerances.
Microclimate is also a major factor in plants that can survive in urban areas but not in adjacent wild areas. In cities, urban heat island effect, along with huge variations in temperature and moisture availability create a variety of ecological niches that do not exist in the broader region. Because cities tend to have more hotter, drier, and more open habitats, many western species adapted to deserts or the drier portions of the Great Plains have expanded eastward but only or primarily occur in cities in these regions. Many plant also thrive along roadsides and railroads for similar reasons of higher sunlight and drier conditions created by the well-drained roadbeds or railroad beds.
Disturbance Regime
Habitats are not static; they change both due to natural and human-induced disturbances. A disturbance can be seen as any event that kills or removes some part of an ecosystem, opening up space or exposing a particular area to greater sunlight. Disturbances can also have wildly different scales. Small-scale natural disturbances can include individual plants dying, a tree losing a large limb, animals digging holes or eating a particular plant, or a small area of soil slumping down a hill or eroding from a streambank. Medium-scale disturbances can include windthrow of a large tree or a few trees, frost heaving in cold climates, larger rockslides, a brief flood of a small stream, or a permanent flood caused by beavers building a dam. Large-scale disturbances can include wildfires, drought, hurricanes, large tornado outbreaks, large-scale flooding, or a volcanic eruption. Insect outbreaks can also cause disturbances of virtually any scale.Humans induce disturbances of all scales too, from a person uprooting or cutting down a small plant, trampling an area, to regular mowing or weedwhacking of an area, controlled burning, spraying of herbicides, or something large-scale such as logging, strip mining, or clearing of land or alteration of the hydrology by channelizing or damming rivers and flooding large areas.
Disturbance isn't inherently good or bad, and different plants are adapted to different levels or types of disturbance. Many plants rely on specific types of disturbance in order to establish: for instance, yellow birch (Betula alleghaniensis) colonizes gaps in forests of sugar maple (Acer saccharum) and American beech (Fagus grandifolia). The presence of gaps caused by dead trees allows the yellow birch to persist in forests dominated by two more shade-tolerant species that it would not otherwise be able to compete with. In this example, the sugar maple and beech are better-adapted in the scenario of no disturbance, able to reproduce under the shade of a closed forest canopy. However these species also differ in their ability to colonize sites subjected to a large-scale disturbance: the sugar maple is also an early colonizer of completely cleared sites, whereas American beech is not, and only moves into a forest once other mature trees are already present.
A more extreme example is longleaf pine (Pinus palustris), which relies on frequent severe fire to reproduce and survive, and will be eliminated not only on sites that do not burn, but on sites that experience too mild or too infrequent fire.
Many small plants with short lifecycles also rely on disturbance. Most garden weeds, such as purple deadnettle (Lamium purpureum), are disturbance-loving plants, and they thrive in gardens specifically because humans expend so much energy cutting and clearing away vegetation. Understanding disturbance regimes that various plants prefer is critically important for gardening efficiently and sustainably, and can also be critical in ecological restoration work, especially when it comes to control of invasive plants. A lot of attempts to control invasive plants fail or even backfire because the plants actively benefit from the sort of disturbance, such as mowing or herbicide, that people use to try to control them.
Presence or Absence of Other Organisms
The presence of any organism alters a habitat in ways that can either increase or reduce the suitability of the site for a particular plant. This is true of all organism types, including animals, fungi, microorganisms, and other plants.A common example of this sort of effect is browsing by herbivores, which in the eastern U.S. is most likely to be white-tailed deer. Very different plants will thrive on plants where deer are present vs. absent, and the degree of browsing is also a factor, with different plants thriving in areas with deer overpopulation and severe browsing pressure, vs. only light browsing pressure. Besides wild animals, livestock also exerts browsing pressure on plants. This pressure is severe in pastures where the livestock is kept for long periods, and significantly less in open rangeland where livestock might only be brought through for a brief period of time.
Plants directly improve or reduce the suitability of habitat for other plants. One of the most important ways plants influence a habitat is shading, which creates selection pressure for shade-tolerant plants. Plants also compete with each other for water and nutrients, which can create pressure for efficient, nutrient-conserving plants as an ecosystem matures. In some cases, plants can be parasitic or hemiparasitic. The most well-known parasitic plant here is the native indianpipe (Monotropa uniflora). There are also obligate hemiparasites, which photosynthesize but also steal resources from their host, such as mistletoes (Phoradendron sp. being our native species) which attach to trees, or false foxgloves (Agalinis sp.) which are facultative hemiparasites, attaching to the root systems of their hosts. Obligate parasites or hemiparasites require the presence of certain hosts in their environment, whereas facultative ones merely prefer or benefit from their presence but can survive without them.
The influence or alterations of plants on a habitat can be much more involved than the above examples. Many plants are allelopathic, meaning that they secrete chemicals that inhibit the growth of other plants, and the allelopathy is usually selective, with certain plants being better-adapted to the presence of certain chemicals than others. Allelopathy is a major factor in both the success of certain invasive plants and the damage they cause to ecosystems. Garlic mustard (Alliaria petiolata) is one of the best-known invasive plants that alters habitats through its allelopathy. Garlic mustard has both direct effects on other plants, and indirect effects through inhibiting the growth of soil fungi. However, native plants can also be allelopathic; for example some goldenrods (Solidago sp.) are allelopathic and tend to slow the establishment of trees that would shade them out.
The introduction of pests and pathogens interacts with other habitat factors, often narrowing the range of conditions in which a plant can survive, and in some cases making whole parts of a plant's range unsuitable for it. For example, the hemlock wooly adelgid was introduced to Eastern North America, and threatens the native hemlocks here. However, it tends to hit hemlocks hardest when they are already more stressed by sun or drought. As such, this pest has eliminated eastern hemlock (Tsuga canadensis) from much of the southernmost reaches of its range, even in areas where the plant is able to survive if the adelgid is kept away (such as by chemical treatments.) In more extreme cases, species can be nearly-completely eliminated by a pathogen or insect, such as the American chestnut (Castanea dentata) being almost completely removed from eastern forests by the chestnut blight. Currently, ashes (Fraxinus sp.) are facing severe die-back due to the emerald ash borer, an introduced insect.
Mycorrhizal fungi are also an important factor in the survival of many plants. The fungal network often drives the availability of nutrients and even energy in an ecosystem, and is poorly understood and often ignored, in part because it is hard to directly observe.
The Habitat Section in Plant Articles
If all of these factors seem like a lot, there is no need to feel overwhelmed. This post is intended primarily to expose people to the diversity of habitat factors; the hope is that people will better understand and remember to consider these factors if they've been exposed to them at least once.For a particular plant, however, there are usually a more manageable number of factors that you need to consider when studying or learning about its habitat preferences and needs, and most factors can be ignored. For example, in much of its range, Canada wildrye (Elymus canadensis) will grow in virtually any soil type or texture, and merely needs sun and recent disturbance to establish. Or the common hackberry (Celtis occidentalis) will grow in a wide range of soil textures and moisture and lighting conditions, but requires soil with a high calcium content and not too low pH.
The Habitat section of each plant article, which you can access in one click from the purple table-of-contents at the top of each article, when completed, collects the most important aspects of a particular plant's habitat preferences in one place.
In some cases, there are also a lot of unknowns or open questions. Even for our completed articles, the habitat section is often an ongoing project. If you notice anything interesting about a plant's occurence or absence in particular habitats and have something to contribute, please get in touch with us.
You can also learn a lot by observing plants in nature. There is often a disconnect between what is written in official sources, and what you directly observe in the wild. Part of this is the inherent limitations of human knowledge, but part of it is that plants and ecosystems themselves are dynamic. As climate changes, and as plant populations evolve and adapt to new conditions, and as the other organisms present in ecosystems change, the habitat preferences of various plants will also change. There is thus a continuous need for observation, and questioning and updating of accepted knowledge. When in doubt, treat any information about plant habitat as a working hypothesis, not as established fact, and this goes not only for the material you read on our site, but for any source. Go out into nature and observe plants in the wild: this is ultimately the only way to get an accurate picture of what plants' habitat preferences actually are. In doing so, you may end up contributing to an increased understanding of these plants!
I also hope that, as people come to understand the richness of the factors that go into plants' unique adaptations to diverse habitats, people will ultimately see the value of and need to restore and protect wild habitats, as well as the ways in which we can make the land actively used by humans be better habitat for plants and the other organisms that depend on them.
Archive of All Blogs
Range Map & Taxonomic Update Progress, January 31st, 2024
Giving Thanks To Everyone We Rely On, November 22nd, 2023
Thinking More Deeply About Habitat, April 5th, 2023
2022 Year-End Summary: Successes & New Goals, February 15th, 2023
New Databases Linked: Flora of North America & NatureServe Explorer, November 11th, 2022
All Range Maps 2nd Generation, Taxonomic Updates, & Fundraising Goal Met!, September 29th, 2022
More Range Map Improvements, POWO Interlinking, And Notes Fields, June 7th, 2022
Ecoregion-Based Plant Lists and Search, March 30th, 2022
Progress Updates on Range Maps and More, February 10th, 2022
The Vision for bplant.org, December 9th, 2021
New Server: Software & Hardware, August 30th, 2021
More & Improved Plant Range Maps, July 19th, 2021
A Control Section for Invasive Plants, April 15th, 2021
Progress Bars & State Ecoregion Legends, March 11th, 2021
Our 2020 Achievements, February 9th, 2021
Interlinking Databases for Plant Research, November 11th, 2020
A New Homepage, Highlighting Our Articles, July 29th, 2020
A False Recovery, But North Carolina's Ecoregions are Complete!, June 9th, 2020
We're Back After COVID-19 Setbacks, April 3rd, 2020
Help Us Find Ecoregion Photos, February 27th, 2020
What We Achieved in 2019, December 30th, 2019
Plant Comparison and ID Guides, October 30th, 2019
We Are Now Accepting Donations, October 14th, 2019
US State Ecoregion Maps, New Footer, Ecoregion Article Progress, and References, September 19th, 2019
Tentative Range Maps of Native Plants, August 12th, 2019
Ecoregion Locator and Interactive Maps, July 10th, 2019
Using Ecoregions Over Political Boundaries, May 13th, 2019
How We Handle Wild vs Cultivated Plants, April 16th, 2019
A Blog To Keep People Updated On Our Progress, April 8th, 2019
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