Abstract
Research Highlights: Sentinel-2 Normalized Difference Vegetation Index (NDVI) products show greater potential to detect indications of disturbance by bark beetles in the southeastern US than Moderate Resolution Imaging Spectroradiometer (MODIS), as the high spatiotemporal heterogeneity of the southeastern forest land prevents its deployment at the current resolution. Background and Objectives: Remote sensing technologies have been an essential tool to detect forest disturbances caused by insect pests through spectral trait variation. In the US, coordinated efforts such as ForWarn, led by the US Forest Service and based on MODIS satellite data, are used to monitor biotic and abiotic disturbances. Because of the particular characteristics of the southeastern US landscape, including forest fragmentation and rapid forest turnover due to management, detection and visualization of small bark beetle spots using remote sensing technology developed for more homogeneous landscapes has been challenging. Here, we assess the ability of MODIS and Sentinel-2 time-series vegetation index data products to detect bark beetle spots in the Florida Panhandle. Materials and Methods: We compared ForWarn’s detection ability (lower resolution images) with that of Sentinel-2 (higher resolution images) using bark beetle spots confirmed by aerial surveys and ground checks by the Florida Forest Service. Results: MODIS and Sentinel-2 can detect damage produced by bark beetles in the southeastern US, but MODIS detection via NDVI change exhibits a high degree of false negatives (30%). Sentinel-2 NDVI products show greater potential for identifying indications of disturbance by bark beetles than MODIS change maps, with Sentinel-2 capturing negative changes in NDVI for all spots. Conclusions: Our research shows that for practical bark beetle detection via remote sensing, higher spatial and temporal resolution will be needed.
Highlights
Tree mortality has significant effects on the ecology and value of both natural and commercial forests
343 ha. (847 ac) actively attacked by bark beetles was detected by Sentinel-2, whereas ha. (808 ac) attacked by bark beetles was detected by Moderate Resolution Imaging Spectroradiometer (MODIS)
Sentinel-2 detected negative departures in Normalized Difference Vegetation Index (NDVI) for all of our study stands with known bark beetle infestations, while MODIS failed to detect negative changes in NDVI for 30% of the stands
Summary
Tree mortality has significant effects on the ecology and value of both natural and commercial forests. In the Southeast, bark beetles such as southern pine beetle (Dendroctonus frontalis) and Ips engraver beetles (Ips avulsus, I. grandicollis, and I. calligraphus) cause extensive damage to pine forests, shaping the forest structure and composition [4,5,6]. Because of their potential to grow rapidly, spots of infestation require effective and economically efficient interventions. During early stages of the attack, the generation of adult beetles has not yet emerged. Later stages of beetle colonization include discoloration of the foliage, with crowns turning red-brown as the attack continues (red-stages)
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