Interactions between deer and vegetation in southern Ontario, Canada: Monitoring and restoration of overgrazed plant communities in Pinery and Rondeau Provincial Parks.

Executive Summary: One of the main goals of this report was to lodge a single record of our numerous research activities on deer-plant interactions in southern Ontario. Table 1 summarizes the project's components and illustrates its wide scope. Not all of the results from these studies are presented in this report; some results are in other reports, while some data, specifically that on stand composition, soil seed bank composition, and woody browse availability, still await analysis. With the large database that we have amassed, we are now well placed to accurately monitor and assess changes in plant communities as vegetation recovers following the deer herd reduction in Rondeau and to place the ongoing degradation of grazed vegetation at Pinery into both a spatial and historical context. In spring 1994 it was clear that there was more herbaceous vegetation at Rondeau than at any time since 1991. This rapid recovery in deer grazed areas was expected based on the results of exclosure studies. Preliminary results from our studies of plant community composition showed that the plant community at Rondeau changed following protection from deer grazing in 1991 and 1978 exclosures. In 1994, both the grazed and ungrazed sites at Rondeau were distinguished from the Pinery sites in having a higher percent cover and a greater abundance of herbaceous species, typical of a mature, undisturbed Carolinian forest (e.g. Viola spp.). However, in 1992 these same Rondeau sites were distinguishable from other less heavily grazed location in southern Ontario because they had a higher percent cover of grazing tolerant species (e.g. Aster spp.). We do not yet know whether the plant community will return to its condition before disturbance by deer grazing or whether the "recovered" community will be fundamentally different - only time will tell. In 1995 we will be analyzing data sets from Rondeau for 1991, 1992, 1994 and 1995 to determine how the plant community has changed with time. We had success with the use of plant species as indicators of overall vegetation recovery following grazing, although only two of the five species which we assessed were suitable. In addition to Trillium grandiflorum (Koh et al., 1995), Circaea quadrisulcata and Polygonatum biflorum were good indicators of grazing pressure and habitat protection at Rondeau. Plant sizes observed throughout the park were determined more by deer grazing, which imposes homogeneity across grazed sites, than by habitat variation (e.g. soil type). The three other candidates for indicator species did not respond to release from deer grazing pressure as well, and their heights appeared to be related more to other factors than deer grazing. In 1995 appropriate indicator species will be determined for Pinery. While some rare plants such as Showy Orchis flowered for the first time in years in Rondeau, in general we found that effective monitoring of the recovery of rare species within the park required greater effort than was possible from two or three individuals doing sporadic searches. Due to the many negative results (failure to find species) we must develop a stringent protocol for quantifying search effort. As a consequence, S. Koh, D. Bazely, and A. Woodliffe (OMNR) will be designing a protocol which accounts for search effort and will make use of the potential volunteer base from Rondeau's visitors. Exotic and invasive plant species are of concern in any habitat which has been released from strong grazing pressure. It appears unlikely that the lower grazing pressure at Rondeau will result in as wide a distribution of weedy, invasive species as at Point Pelee National Park (e.g. Alliaria officinalis) because of the robust seedbank which contains many native species (Koh & Bazely, 1994). The greater crown cover at Rondeau (Koh, pers. comm.), in contrast to Point Pelee which is more open, will not provide as suitable a habitat for these weedy species with respect to light availability. However, in disturbed areas within Rondeau (e.g. along roadsides) some weedy species appear to be spreading. Treatment and monitoring programs initiated in 1994 will continue for A. officinalis in 1995. Berberis thunbergii (woody exotic) may have spread throughout Rondeau due to their thorns which defend them against grazing. This species may be less competitive against native shrubs now that grazing pressure has been reduced. We recommend that treatment programs be continued, and monitoring programs be established for this species. Since a herd reduction has not taken place at Pinery and has only recently occurred at Rondeau, it is vital to have a comprehensive baseline dataset against which to compare continuing habitat degradation or recovery. Such a database is in the process of being created for the woody stand structure and woody-browse, and herbaceous plant communities in both Pinery and Rondeau. Each year, data collected from the parks over the duration of the project can be compared against this baseline to monitor changes over time and grazing pressure. A report after the 1995 field season will provide the first indication of what changes can be expected in the long-term recovery process.