MONITORING CONTINUOUS COVER FORESTS; DESCRIBING SPATIAL STRUCTURAL HETEROGENEITY FROM HIGH RESOLUTION OPTICAL IMAGERY.

摘要

The conversion of British even-aged conifer plantations to Continuous Cover Forestry (CCF), a form of forest management that creates more heterogeneous stands, requires new ways of monitoring spatial aspects of forest structure. This study aims to quantify horizontal aspects of forest structure to allow comparison of different forest stands and the detection of changes over time. The study aims to describe structure, from high resolution optical imagery, based on the distribution of canopy openings within a stand. This approach has the advantage that canopy openings also influence understorey light levels, and in turn, natural regeneration, an important feature of CCF. The study focuses on established experimental plots of Sitka spruce (Picea sitchensis) in which canopy gaps have been artificially created by management. The two main study sites are Clocaenog Forest in North Wales, which contains experimental CCF plots managed and surveyed by the Tyfiant Coed project (The University of Wales, Bangor), and Glasfynydd Forest in the Brecon Beacons, the site of a thinning experiment by Forest Research. Both sites were surveyed by NERC ARSF during summer 2006 and CASI, ATM, AISA Eagle and Hawk hyperspectral and Lidar data collected. Extensive field work was carried out to supplement and update existing field data in two 1ha plots at each site. A novel technique was used to map all canopy openings within smaller sub-plots and canopy density was measured to assess spatial heterogeneity. Preliminary results of the identification and delineation of canopy openings from ATM and CASI data for the Glasfynydd site are presented. The potential of spectral indices and band ratios for the identification of gaps is assessed, with particular focus on the use of ratios of the near infrared and short-wave infrared ATM bands.