Investigating the spatial heterogeneity of a subtropical montane cloud forest plantation with a QuickBird image

摘要

Forest plantations, consisting of a single, even-age species, have long been recognized as homogeneous landscapes. However, the heterogeneity of the system may be amplified by bioclimate, which in turn can be modified by physical environments. This study attempted to assess the ramifications of two major factors, topography and the edge effect, on a subtropical montane cloud forest (MCF) yellow cypress (Chamaecyparis obtusa var. formosana, CHFO) plantation in Taiwan by integrating field observations, a high spatial resolution QuickBird satellite image and spatial layers of topography. Our regional analysis indicated that there was a negative relationship between slope and the size of CHFO. Surprisingly, we also observed a significant amount of natural broadleaf plant patches within the site, and large-size patches were frequently encountered at low elevation. For the edge-effect analysis, the area (0-30 m) along the road and natural edges yielded low canopy area and carbon (kgC stem~(-1)) for each individual CHFO plant, as well as low CHFO population (stems ha~(-1)) and carbon (MgC ha~(-1)) densities. Contrarily, large broadleaf plant patches were found along the road edges. Our findings suggest that topography and the edge effect may alter the spatial patterns of nutrients and bioclimate that vary the structure of the vegetation; the heterogeneity of forest plantation may be underestimated. This study also demonstrates the feasibility of integrating field, remote-sensing and geographical information system (GIS) techniques to quantify forest structure at the landscape scale. The derived structure parameters can be further utilized to model ecosystem carbon dynamics over a vast region.