Diversity and distribution of plant communities related to forest fragment size, shape, age, and structure
In the Midwest region of the United States, forested areas have been removed to make way for agriculture and development. In the southern Midwestern states, including Indiana, cultivated and pasture agriculture lands account for 80-90% of rural landscapes. The remaining forests have been fragmented into small, often privately owned, woodlots. Due to their size, these forests typically have a high edge to interior ratio, which creates a greater influence of the surrounding agricultural land matrix upon the forest itself. Fragmentation influences the species in these forests through the distance between, size, age since disturbance, and shape of the forest in addition to management. By quantifying the intensity of these factors on plant species, management strategies could be modified to improve the ecological function of the fragments. The objectives of this study were: 1) to identify the relationships between forest fragment and environment factors; 2) to test that fragmentation theory is applicable to forest patches surrounded by agricultural matrix; and 3) to compare forest fragmentation results in Northeast Indiana to previous studies. I surveyed thirty forest fragments in Adams, Wells, and Allen Counties, Indiana, identifying plants to species in stratified 25 m2 understory and midstory plots. Richness, Shannon Entropy Index, and coefficients of conservatism were used to quantify understory diversity of each forest. Factors tested included ecological (Floristic Quality Index (FQI), basal area, overstory richness and diversity, and selective harvest) and environmental (area, perimeter, perimeter: area ratio, canopy cover, soil moisture, forest age, distance to nearest neighbor). Regression analysis and nonmetric multidimensional scaling (NMDS) was used to quantify interactions of diversity and factors. Forest fragment area positively influenced understory richness and FQI as well as midstory richness. Distance to nearest neighbor had a negative effect with midstory species space and neighbor count within 1 km radius showed negative relation. Low valued species (<7) count doubled with a decrease in forest neighbor count in 1 km while high value species (>7) had a 13% increase with more neighbors. A negative relationship with perimeter: area ratio was noted in the understory species space and midstory diversity and FQI. Intermediate disturbance had a direct positive relationship with midstory richness and FQI values. Intermediate disturbance altered forest age, overstory diversity, and canopy cover, each of which had direct influence on under and midstory richness and diversity. Large forest fragments that are selectively harvested with some perimeter effect show the greatest amount of plant diversity. These results are comparable to other research done on forest fragments and island biogeography with regard to size and disturbance, but not distance, thus fragmentation principles are applicable to forest patches surrounded by an agriculture matrix in northeast Indiana.
Marshall, Purdue University.
Off-Campus Purdue Users:
To access this dissertation, please log in to our