If a tree falls in the forest: Examining canopy changes in the wake of Sudden Oak Death using object-based image analysis

Sudden oak death (SOD) is a disease of epidemic proportions, sweeping through many coastal hardwood forests in California. Since 1999, P. ramorum has produced overstory mortality in China Camp State Park (CCSP) and the surrounding open space, creating a number of gaps which effectively alter the structure of the forest. In the following four years, ADAR high-resolution (1 m) multispectral imagery for CCSP was acquired. We segmented and classified this existing imagery using object-based methods to identify gaps within the forest mosaic. We also tested a variety of object-based segmentation parameters on one image to determine potential error resulting from segmentation. Once the gaps were identified, they were measured for area, perimeter, and Euclidean nearest neighbor. We then compared these spatial measures of variation to temporal ones, creating a time-sequence of gap formation and the resulting gaps' closure or persistence. Between 2000 and 2001, 910 gaps within China Camp contained one or more trees dead from P. ramorum. Preliminary results indicate that the majority decreased in both size and perimeter while the distance between them grew. Those that increased in size, however, were smaller on average than those that decreased, a potential consequence of the spatial distribution of SOD. This research provides insight into changes in the canopy structure at China Camp following P. ramorum mortality. Furthermore, it also illustrates the necessity of object-based methods in tracking changes in forest gaps over time.