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Bowles, Marlin L.
Jones, Michael D.
McBride, Jenny

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

Date created
Report to the Indiana Department of Natural Resources.
Goals 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. 2 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 study. 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.