DENDROGEOMORPHOLOGICAL ASSESSMENT OF SHORT-TERM CHANGES IN PIT-AND-MOUND SYSTEMS: SUPERSTORM SANDY (2012) TREETHROW FIELD, SE PENNSYLVANIA

A post-storm geomorphic development of treethrow pit-and-mound (PM) features was studied along a hilltop site at Tyler State Park (Bucks County, Pennsylvania). This research builds on a contemporary assessment of treefall caused by Superstorm Sandy (October 2012) and was focused on trees exhibiting the WNW-NW fall azimuth and average breast-height diameter of 0.52 m. Unmanaged portions of the forest ensured that PM features have undergone natural decay over a 6-year period. The average dimensions of the pits were 3.00 x 1.81 x 0.381 m, and the mounds measured on average 2.47 x 1.64 x 0.72 m. All mounds displayed well-developed tree saplings, consistent with several years of growth. Some of the organic material and clastic sediment (matrix-supported gravel of Late Triassic Stockton Fm) that was imbedded in the rootplate have partially infilled the pits. This partial infilling of the pit is largely due to the fact that the treethrow was not generated by slope processes, which would have resulted in accumulation and transport of eroded rootplate sediment downslope of the pit. Such co-occurrence of soft sediment within the pits is conducive to mammal burrowing activity, which was observed at several sites. A nearby treethrow resulting from a more recent storm event (Winter 2018) allows direct comparison of relative geomorphic “decay” and re-vegetation of PM microtopography at sites with minimal slope control on post-event sediment redistribution.