DENDROGEOMORPHOLOGICAL ANALYSIS OF SLOPE PROCESSES, TYLER STATE PARK, PENNSYLVANIA

Slope processes along stream banks exert a major influence on channel morphology, flow regime, sediment input, and overall stream health. Because the shifting center of gravity induces observable “reaction wood” growth, preferentially on the upslope side of a deciduous tree, the asymmetry of ring width in riparian trees was used to reconstruct the history of stream bank slope development over several decades, punctuated by adjustments to rapid changes. Field research conducted at two sites along the tributaries of the Neshaminy Creek: 1) serves as a case study in utilizing reaction wood history to establish the chronology of slope processes, and 2) corroborates previous findings that rings of a curved/tilted deciduous tree tend to be thicker on the upslope side. Birches (Betula sp.) that exhibited an “elbow” bend or variable tilt yielded a trend of preferential ring growth on the upslope side, with an average upslope/downslope ring width ratio (U/D) of 1.24. Several periods of anomalously high U/D (>1.50) are interpreted as responses to event-scale changes in land surface gradient. An example of an acute preferential growth on the upslope side dating to 2000-2001 may represent dendrological reaction to Hurricanes Dennis and Floyd (1999), with likely additional stresses from storm events. Our findings show that whereas a number of large deciduous and coniferous trees at Tyler State Park were toppled by the 2012 Hurricane Sandy, many younger trees (<30 years) have adjusted to slope processes along small streams and withstood storm damage.