Abstract
Cyclonic windstorms profoundly affect forest structure and function throughout the tropics and subtropics. Remote sensing techniques and vegetation indices (VIs) have improved our ability to characterize cyclone impacts over broad spatial scales. Although VIs are useful for understanding changes in forest cover, their consistency on detecting changes in vegetation cover is not well understood. A better understanding of the similarities and differences in commonly used VIs across disturbance events and forest types is needed to reconcile the results from different studies. Using Landsat imagery, we analyzed the change between pre- and post-typhoon VI values (ΔVIs) of four VIs for five typhoons (local name of cyclones in the North Pacific) that affected the Fushan Experimental Forest of Taiwan. We found that typhoons varied in their effect on forest canopy cover even when they had comparable trajectories, wind speeds, and rainfall. Most VIs measured a decrease in forest cover following typhoons, ranging from −1.18% to −19.87%; however, the direction of ΔVI–topography relationships varied among events. All typhoons significantly increased vegetation heterogeneity, and ΔVI was negatively related to pre-typhoon VI across all typhoons. Four of the five typhoons showed that more frequently affected sites had greater VI decreases. VIs ranged in their sensitivity to detect typhoon-induced changes in canopy coverage, and no single VI was most sensitive across all typhoons. Therefore, we recommend using VIs in combination—for example Normalized Difference Infrared Index (NDII) and Enhanced Vegetation Index (EVI), when comparing cyclone-disturbance-induced changes in vegetation cover among disturbances and across forests.
Highlights
Tropical forests harbor a large portion of global biodiversity [1] and play a key role in global carbon cycling [2,3,4]
The four vegetation indices (VIs) all significantly decreased after the five typhoons except for the significant increase of Normalized Difference Infrared Index (NDII), Enhanced Vegetation Index (EVI), and Soil-Adjusted Vegetation Index (SAVI) associated with Typhoon Herb
While typhoons all led to decreases in vegetation index (VI) values, the magnitude of change (∆VIs) differed among events
Summary
Tropical forests harbor a large portion of global biodiversity [1] and play a key role in global carbon cycling [2,3,4]. Changes in the geographic extent and quality (i.e., structure) of tropical forests have major effects on biodiversity conservation efforts [6,7] and important ecological processes such as carbon sequestration [8,9] Disturbances such as fires, pathogens, and tropical cyclones are important agents affecting the dynamics of many tropical and subtropical forests [10,11,12]. Used in combination with other data, remote sensing can effectively identify broad spatial patterns of cyclone damage in relation to vegetation types and topographical properties [20,32,43,47] that could be otherwise difficult to assess with ground surveys. Landsat images were used to analyze vegetation cover change and recovery within the FEF in relation to typhoon disturbances. Images used to study vegetation recovery were taken during the growth season before typhoon passage, and one year later during at a comparable time with minimal cloud cover
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
