Landscape Representation by a Permanent Forest Plot and Alternative Plot Designs in a Typhoon Hotspot, Fushan, Taiwan

Abstract

Permanent forest dynamics plots have provided valuable insights into many aspects of forest ecology. The evaluation of their representativeness within the landscape is necessary to understanding the limitations of findings from permanent plots at larger spatial scales. Studies on the representativeness of forest plots with respect to landscape heterogeneity and disturbance effect have already been carried out, but knowledge of how multiple disturbances affect plot representativeness is lacking—particularly in sites where several disturbances can occur between forest plot censuses. This study explores the effects of five typhoon disturbances on the Fushan Forest Dynamics Plot (FFDP) and its surrounding landscape, the Fushan Experimental Forest (FEF), in Taiwan where typhoons occur annually. The representativeness of the FFDP for the FEF was studied using four topographical variables derived from a digital elevation model and two vegetation indices (VIs), Normalized Difference Vegetation Index (NDVI) and Normalized Difference Infrared Index (NDII), calculated from Landsat-5 TM, Landsat-7 ETM+, and Landsat-8 OLI data. Representativeness of four alternative plot designs were tested by dividing the FFDP into subplots over wider elevational ranges. Results showed that the FFDP neither represents landscape elevational range (<10%) nor vegetation cover (<7% of the interquartile range, IQR). Although disturbance effects (i.e., ΔVIs) were also different between the FFDP and the FEF, comparisons showed no under- or over-exposure to typhoon damage frequency or intensity within the FFDP. In addition, the ΔVIs were of the same magnitudes in the plots and the reserve, and the plot covered 30% to 75.9% of IQRs of the reserve ΔVIs. Unexpectedly, the alternative plot designs did not lead to increased representation of damage for 3 out of the 4 tested typhoons and they did not suggest higher representativeness of rectangular vs. square plots. Based on the comparison of mean Euclidian distances, two rectangular plots had smaller distances than four square or four rectangular plots of the same area. Therefore, this study suggests that the current FFDP provides a better representation of its landscape disturbances than alternatives, which contained wider topographical variation and would be more difficult to conduct ground surveys. However, upscaling needs to be done with caution as, in the case of the FEF, plot representativeness varied among typhoons.

Assessing Typhoon-Induced Canopy Damage Using Vegetation Indices in the Fushan Experimental Forest, Taiwan

“…Second, some of our results may have been affected by cloud obstruction in analyzed images, which is substantial for all images used in this study (17.5-48.8%). A previous study showed that cloud contamination does not distribute across the FEF, with more cloud cover at higher elevations [66]. Because typhoon-induced vegetation change varied with elevation (Table 6), the observed topographical patterns of vegetation change are likely affected to some degree by the non-random cloud contamination.…”

“…2020, 12, x FOR PEER REVIEW 3 of 23 [42,64,65]. The frequent typhoon occurrence in this site has permitted the study of disturbance representativeness of large forest plots over a wider landscape [66], but understanding of damage variation and the comparability of different VIs across typhoons is lacking. Here, taking advantage of the FEF location, we use remotely sensed data to examine: 1) the consistency of patterns of typhoon damages among different typhoons; 2) the spatial patterns of typhoon damage in relation to cyclone properties (i.e., wind direction) and site topographical features (e.g., elevation, slope, and aspect); 3) the relationships between typhoon frequency and severity of typhoon damage; and 4) whether patterns of typhoon damage are consistent among different vegetation indices.…”

Wind Speed Controls Forest Structure in a Subtropical Forest Exposed to Cyclones: A Case Study Using an Individual-Based Model

“…Finally, although the current study focuses on the impacts of wind on a cyclone-prone forest, the model we developed could also be applied to explore wind vulnerability of forests that are less accustomed to wind disturbances, as well as the effects of localized wind blowdown events, which are thought to shape the structure and dynamics of Amazonian forest (Magnabosco Negrón-Juárez et al, 2018;Peterson et al, 2019). The exploration of more forest settings and wind regimes could help us go beyond single forest plots and take into account landscape-and regional-level heterogeneity in the model (Seidl et al, 2014;Peereman et al, 2020), in order to explore the consequences of wind disturbance at a landscape or even regional level.…”

Research Trends and Methodological Approaches of the Impacts of Windstorms on Forests in Tropical, Subtropical, and Temperate Zones: Where Are We Now and How Should Research Move Forward?

“…The profound effects of windstorms on forests had long been studied, but most of these, if not limited to a particular area, had been focused primarily on short-term impacts on individual trees, such as defoliation, branch loss, and canopy disturbance [9][10][11]. Later on, much progress has been reported in explaining visible windstorms' impacts on forest physical environment, tree regeneration dynamics, and forest recovery in temperate and tropical regions [12][13][14], resulting in the evolution of a contemporary view of windstorms as a multi-scale forest ecological disturbance [15][16][17]. Recently, a study of Lin [18] has shown a scale-link perspective of tropical cyclone ecology, in which the effects of cyclones at the community and ecosystem levels are linked to effects at the individual and species levels.…”