Secondary succession of spring flora associated with windthrow pits as influenced by microtopography and light in an old-growth beech-maple forest in east-central Indiana
This research focused on the secondary succession of spring flora occurring within pits of windthrows located in the area described as Ginn/ Nixon Woods, an old growth beech-maple forest community that transitions to a mixed mesophytic forest community, approximately 12 miles north of Muncie, IN. More specifically, this research sought to identify the vegetative production capacities of pits as well as determine the extent to which pit microtopography and light influx affect the production of spring flora.In all sixty plots were established--30 test plots within the confines of windthrow pits, and 30 control plots, each one just six feet away from a test plot on undisturbed forest soil. One sampling period occurred in 1993 (just prior to leafing); four sampling periods occurred in 1994 (two prior to leafing and two after leafing). Species presence, density and cover data were used to produce two-dimensional ordinations for examination. Species presence, plot depth, slope, and light data were subjected to the Spearman Rank Order Correlation Test to determine the extent of influence pit microtopography and light influx have on spring flora.Examination of the data clearly showed that disturbed areas known as windthrow pits experience a significant decline in vegetative production--at least for a few years but likely for many years, after the initial disturbance or windthrow occurs. The data also clearly showed that over time windthrow pits eventually recover vegetative production.The recovery of vegetative production in pits was shown to have a positive correlation with plot depth; that is to say, as pit depth decreases, vegetative diversity increases. Standing water in pits, though not recorded statistically, was observed in the field as having a strong negative impact on vegetative recovery. Consequently, the environmental factors that work together to affect the topographical recovery of the pit to an elevation equal to or greater than the surrounding forest floor were found to be critical in the vegetative recovery of pits. This researcher has appropriately termed this recovery process as "elevation equilibrium," since the end result is a pit whose topographical relief has given way to a relatively static elevation equal to adjacent undisturbed areas of the forest floor.Unlike plot depth, the amount of slope in pits did not seem to play a significant role in reducing or encouraging vegetative recovery. Likewise the amount of shade cast on pits prior to leafing, and the size and/or presence of gaps in the canopy after leafing, appeared to have little influence on the recovery of spring flora. When plant diversity data for each test plot was correlated with its slope, pre-leafing light influx and post-leafinglight influx data using the Spearman Rank Order Correlation test, it found no significant relationships between any of the sets of variables.