Plant MonitoringReport on successional changes to specified flora at a Goat Hill siteBy Mike Bertram, Kay Davies, Ruth Galantino, and Pat McElhenny | ||||||||||||||||||
AbstractHerbaceous and woody vegetation monitoring results are reported for a reconstructed serpentine grassland in Chester County, Pennsylvania. This grassland is part of the Goat Hill State line Serpentine Barrens on the Pennsylvania – Maryland border. This grassland was reconstructed by removing all the trees and scraping away the organic soil layer. Seeds of Sorghastrum nutans, Schizachyrium scoparium, Andropogon gerardii, Sporobolus heterolepis, and Aristida purpurascens were collected from other parts of the barrens. A majority of the seeds were successfully germinated and the seedlings and remaining seeds were planted in the grassland in 2000 to 2002. Randomly selected plots in the grassland were monitored over the period from 2002 to 2008. During the measurement period the average number of plants of Sorghastrum nutans, Schizachyrium scoparium and Rubus sp. increased while Cirsium sp. declined. IntroductionGoat Hill is part of the State Line Serpentine Barrens that are located on the Maryland – Pennsylvania border. These Barrens occur where serpentine bedrock is either exposed or near enough the surface to influence soil properties. The community has diminished substantially in the last 60 years due to the suppression of fire, the elimination of grazing, and other impacts that sustained the ecosystem. Without intervention serpentine grasslands at Goat Hill are invaded by species such as Eastern Red Cedar (Juniperus virginiana), Pitch Pine (Pinus rigida), and Catbrier (Smilax sp.). Over time a deeper soil layer develops and the serpentine specific plants are eliminated. In 1998 in an attempt to recreate a serpentine environment, and as part of an overall conservation strategy the trees were removed in a plot of around half an acre in The Nature Conservancy Goat Hill Preserve. The soil in the plot was then removed by scraping using a bulldozer. Seeds were collected from other parts of Goat Hill and seedlings raised from these seeds. In 2000, 2001, and 2002 grass seeds and seedlings were planted. The species planted were: Indiangrass (Sorghastrum nutans), Little Bluestem (Schizachyrium scoparium), Big Bluestem (Andropogon gerardii), Prairie Dropseed (Sporobolus heterolepis), and Longleaf threeawn (Aristida purpurascens).
Methods
The overall objective of the study is to improve the understanding of the successional dynamics of serpentine grasslands by monitoring vegetation changes in the cleared plot at Goat Hill. The focus of this study is on the 5 planted grass species and the monitoring was designed to identify a 20% change in population of any species over the time of the experiment. Other species of interest were noted at the time of the measurements. Sampling Design16 permanent 1m2 plots were randomly selected, half being in a center area. This center area was found by first locating and marking the center point with a pin flag. The pin flag established the center and was approximately half way from the edge in all four cardinal points. From the center point the area was divided into to equal areas, an interior central area, and an exterior edge area. Pin flag markers were placed along bearings (N-S, 172 degrees; S-N, 352 degrees; E-W, 256 degrees; and W-E, 76 degrees) that approximated the outside perimeter bearings of the plot, and established the center vegetation monitoring area. The area around the outside of this pin flag marked area was established as the edge area. Field Measurements
Timing of monitoringThe field measurements were taken in October each year for an initial period of 5 years from 2002 to 2006 and then extended for 2 additional years. AnalysesThe variability of the parameters being measured was unknown at the initiation of the study. This variability turned out to be large so that the intended analysis did not give any results of significance. The distribution of the number of plants in the plot was non-normal. Consequently the trends shown in the graphs are statistically non-significant but are considered to be real as they were also observed in the scraped area as a whole over the monitoring period. ResultsThe monitoring data are shown in graphs in the Appendix. The average number of plants and coverage per plot of Indiangrass and Little Bluestem increased during monitoring period. The number of Big Bluestem plants and coverage did not noticeably increase. No plants of Prairie Dropseed or Longleaf threeawn were observed in the monitoring plots. Overall the coverage by grasses increased and the amount of bare ground decreased. The number of thistle plants per plot decreased during the measurement period. Briars (Rubus sp.) increased in the plots. Although Catbrier thickets are common around the scraped area there has been little re-establishment in the scraped area. The number of Black Locust plants did not increase but their size did visibly increase although no measurements were made. As well as the Black Locusts becoming more prominent a similar trend was also observed among the Eastern Red Cedar and Pitch Pine seedlings. There was no noticeable increase in the amount of Catbrier. Exotic Honeysuckles (Lonicera sp.) noticeably invaded the plots near the edges of the grassland. SummaryThe process of clearing trees, scraping the soil, and planting serpentine grass seedlings has proved to be a successful mechanism for reconstructing a serpentine grassland. In order to sustain the grassland tree seedlings and briars need to be controlled. AcknowledgementsJim Subach and Lynn Carroll while working for The Nature Conservancy initiated this project. Prasad Ramnath helped with the seedling production and planting.
AppendixTotal number of plants and average coverage across all plots |
Note: most plots have zero values throughout the measurement period and are not visible on the graphs.
Note: most plots have zero values throughout the measurement period and are not visible on the graphs. Due to elimination work black locust, briars, and thistles were not measured after
year 5.
