Long-Term Changes in Populations of Endangered and Threatened Plants at Clarke & Pine, Hoosier Prairie, Indiana Dunes State Park, and Tolleston Ridges/Gibson Woods Nature Preserves
DescriptionReport to the Indiana Department of Natural Resources.
AbstractGoals and methods - To assess their current status and long-term changes, we re-sampled 65
populations of 60 Indiana endangered or threatened plant species at the Clarke & Pine, Hoosier
Prairie, Indiana Dunes, and Tolleston Ridges/Gibson Woods Nature Preserves. These
populations were initially sampled between 1986 and 1989, which allowed assessment of their
long-term changes. To help understand factors that might be contributing to these changes, we
also re-surveyed and analyzed structural changes in associated plant community vegetation at
Clarke & Pine and Tolleston Ridges.
Status and change- We were able to assess the status of about 78 % of the original
populations. Another 8 % were present in low numbers and were not quantified, and the status
of 14 % was unknown. Among all plant populations studied, 35 % appeared to be stable over
time, while 37 % declined and 6 % increased either in numbers or other critical measures, such
as % flowering or genet size. These results suggest that most populations either have been
stable or have declined, and that populations are more likely to decline that to increase in
numbers over time. At Clarke & Pine, 4 of 18 species underwent significant declines, while 7
other species were not present or too rare to quantify. Among these species, Hypericum
kalmianum had the greatest decline. Paper birch, as well as the alien buckthorn Rhamnus
frangula also increased significantly. At Hoosier Prairie, 4 species, including Eriophorum
angustifolium, could not be relocated and their status is unknown. Several other species were
either too rare to quantify or their populations have shifted. The orchid Malaxis unifolia
increased significantly. At Indiana Dunes State Park, dynamic changes appear to be occurring
in many shoreline populations, while others are either recovering from deer browsing, or may
have been extirpated. Polygala paucifolia appears to be extremely vulnerable to human
impacts. At Tolleston Ridges/Gibson Woods, the orchids Cypripedium reginae and C.
parviflorum declined, while the sedges Carex aurea and C. richardsonii could not be relocated.
Causes of change - Lack of experimental treatments limits understanding causes of change in
many populations, and multiple factors may have contributed to changes at different sites. Low
frequency of fire appears to be a critical factor in change among some species at Clarke & Pine,
including an increase in woody vegetation. Ongoing fire management at Hoosier Prairie also
may be driving successional changes in vegetation and shifting spatial patterns among species,
including both perennials and short lived species that respond rapidly to fire. At Indiana Dunes,
population sizes of shoreline-adapted species may fluctuate in response to lake level cycles that
drive sand erosion and deposition, as well as vegetation succession, while human impacts and
over browsing from deer appear to have impacted other species. Lack of prescribed burning
has lead to decline of species and structural shifts of vegetation at Tolleston Ridges and Gibson
Woods. Periodic natural fluctuations in population sizes, as well as natural long-term changes
in vegetation structure may also be important causes of changes that were detected in this
Recommendations - More frequent monitoring and greater replication of plots (when possible)
are needed to better understand how rare plant populations are changing at these study sites.
Sampling frequency should be based upon the longevity and life history strategy of different
plants, with more frequent monitoring for short-lived species. To better understand population
trajectories, annual demographic monitoring would be required, which is being used for Cirsium
pitcheri. Monitoring within an experimental framework, such comparing between burned and
unburned treatments, also may be needed to better understand how to maintain some
populations. Increased use of fire appears to be a critical need for recovery of species at
Tolleston Ridges and Gibson Woods, and it may be important in long term maintenance of
vegetation at Clarke & Pine.