Some Recent Changes in the Illinois Flora

Our favorite records are always the ones of newly discovered native plant species within Illinois. Twenty-three additional native species have been found in the state during the past 20 years. An examination of the list of 23 plants allows very few generalizations that could be viewed as trends reflecting floristic changes. Eleven of the newly found species are at or near their continental northern or northwestern limits of range in Illinois, nine species found are at or near their southern limits of range, and the remaining four are well within their expected range in the state. Therefore, we cannot say that the new discoveries show any significant movement or change in the flora relating to climate or environmental disturbance.

Our least favorite information concerns the native plants that we conclude have been extirpated from the state. There may be some apparent trends reflected in the listing of the 64 species of plants that appear to have been extirpated from Illinois during the same time period. Certainly, the first observation is that this is a very large number of plants to disappear completely in a state in a relatively short time, and we are very concerned about it.

Trends of mass extinction are being seen around the entire planet. Among the 64 native plants that have not been seen in Illinois for many years, despite searches, and which may no longer exist in the state, 31 were at their continental northern range limits, 18 were near their continental southern range limits, 9 were at their central-western range limits, 1 was at its eastern range limit, and 5 were well within their expected ranges in Illinois.

Despite our fears of global warming, the data reveal that more species (48% of the total extirpated) with southern affinities have disappeared from our flora in the past 20 years than species with northern affinities (28% of the total extirpated). We might have expected that the plants vulnerable to heat would have decreased at a greater rate than those that thrive in warmer climates, if global warming was the primary reason. However, the reason for the greater perceived loss of southern species in Illinois may have been for reasons completely unrelated to changes in temperature. One normally finds very specific local causes of local extinction when looking for reasons for the loss of individual species, and this is certainly true in Illinois; each loss has a unique local cause. However, using our often forgotten but useful principle derived from Occam's razor that a simple explanation may be closer to the truth than a complex one, it may be that because there have been more field botanists searching for plants in the Chicago area than in extreme southern Illinois (an easily documented fact based partly on population densities and financial support), more northern species have been sought after and monitored than have southern species. Therefore, assumptions have been made that more southern species have disappeared when, in fact, we simply lack data on them.

Back on the brighter side, some native plants that were formerly thought to have been eliminated from the flora have been rediscovered during the past 20 years. This includes 14 species that have been found after extensive searches by field botanists during this period. The predominant group of plants that has been rediscovered is a group of nine species at their southern range limits (in effect, plants in northern Illinois). Three of the other rediscoveries were at their northern range limits, one was at its western range limit, and one was at its eastern range limit in Illinois. Again, it is hard to explain why cool-climate species have been (or persist) at a higher frequency than species with southern affinities in a time of global warming, unless one were to propose that there are more people hunting for these plants in the Chicago area than in the southern counties of the state (an explanation that I tend to support!).

One of the important results of our field surveys throughout the state during this period has been increased data on rare native plants that are more common than we previously realized, and this has allowed for the removal of 18 plants formerly listed as threatened or endangered within the state from that list. The plants that have been found to be more common than previously thought and that have been removed from the official Illinois list of protected species are seven plants near their northern limit of range, five plants near their southern limit of range, one at its western range limit, and five that were well within their range in Illinois but just were not known very well until recently.

How has the flora of Illinois changed in the past 20 years? We have been shocked to discover that 64 kinds of native Illinois plants known to our forefathers may have been lost from the state forever. We have been pleased to find that 23 kinds of native Illinois plants that we did not know were here, are actually here. We have found that 18 native plants, which we thought we were about to lose, are actually relatively secure here. We have found that 32 non-native plants from outside of Illinois have begun to find a home here, and that at least 4 of these have found it to be an especially good home and have begun to spread. Finally, it appears that because of the relatively small number of field botanists in the state and because of the realities of population centers and financial resources, we are also losing ground in our ability to actually record the numerous changes occurring on a regular basis in our botanical landscape, particularly in southern Illinois.

Steve Hill, Center for Biodiversity

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