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Significance The state of California has a globally important economy and a population exceeding 38 million. The state relies on its forested watersheds to support numerous services, such as water provisioning, carbon storage, timber products, ecotourism, and recreation. However, secular changes in air temperature, combined with periodic and prolonged drought, pose a compounding challenge to forest health. Here we use new remote-sensing and modeling techniques to assess changes in the canopy water content of California’s forests from 2011 to 2015. Our resulting maps of progressive canopy water stress identify at-risk forest landscapes and watersheds at fine resolution, and offer geographically explicit information to support innovative forest management and policies in preparation for climate change.

Significance The state of California has a globally important economy and a population exceeding 38 million. The state relies on its forested watersheds to support numerous services, such as water provisioning, carbon storage, timber products, ecotourism, and recreation. However, secular changes in air temperature, combined with periodic and prolonged drought, pose a compounding challenge to forest health. Here we use new remote-sensing and modeling techniques to assess changes in the canopy water content of California’s forests from 2011 to 2015. Our resulting maps of progressive canopy water stress identify at-risk forest landscapes and watersheds at fine resolution, and offer geographically explicit information to support innovative forest management and policies in preparation for climate change.

AbstractThe past 40 years in Southeast Asia have seen about 50% of lowland rainforests converted to oil palm and other plantations, and much of the remaining forest heavily logged. Little is known about how fragmentation influences recovery and whether climate change will hamper restoration. Here, we use repeat airborne LiDAR surveys spanning the hot and dry 2015-16 El Niño Southern Oscillation event to measure canopy height growth across 3,300 ha of regenerating tropical forests spanning a logging intensity gradient in Malaysian Borneo. We show that the drought led to increased leaf shedding and branch fall. Short forest, regenerating after heavy logging, continued to grow despite higher evaporative demand, except when it was located close to oil palm plantations. Edge effects from the plantations extended over 300 metres into the forests. Forest growth on hilltops and slopes was particularly impacted by the combination of fragmentation and drought, but even riparian forests located within 40 m of oil palm plantations lost canopy height during the drought. Our results suggest that small patches of logged forest within plantation landscapes will be slow to recover, particularly as ENSO events are becoming more frequent.

AbstractThe past 40 years in Southeast Asia have seen about 50% of lowland rainforests converted to oil palm and other plantations, and much of the remaining forest heavily logged. Little is known about how fragmentation influences recovery and whether climate change will hamper restoration. Here, we use repeat airborne LiDAR surveys spanning the hot and dry 2015-16 El Niño Southern Oscillation event to measure canopy height growth across 3,300 ha of regenerating tropical forests spanning a logging intensity gradient in Malaysian Borneo. We show that the drought led to increased leaf shedding and branch fall. Short forest, regenerating after heavy logging, continued to grow despite higher evaporative demand, except when it was located close to oil palm plantations. Edge effects from the plantations extended over 300 metres into the forests. Forest growth on hilltops and slopes was particularly impacted by the combination of fragmentation and drought, but even riparian forests located within 40 m of oil palm plantations lost canopy height during the drought. Our results suggest that small patches of logged forest within plantation landscapes will be slow to recover, particularly as ENSO events are becoming more frequent.

Fragmentation poses one of the greatest threats to tropical forests with short‐term changes to the structure of forest canopies affecting microclimate, tree mortality, and growth. Yet the long‐term effects of fragmentation are poorly understood because (1) most effects require many decades to materialize, but long‐term studies are very rare, (2) the effects of edges on forest canopy structure as a function of fragment size are unknown, and (3) edge effects are often confounded by fragment shape. We quantified the long‐term (centennial) effects of fragmentation on forest canopy structure using airborne light detection and ranging (LiDAR) of 1060 Hawaiian rain forest fragments ranging in size from 0.02 to 1000 ha, created more than 130 years ago by flowing lava. Along with distance from edge, we developed a metric, minimum span, to gain additional insight into edge effects on three measures of canopy structure: canopy height, height variation, and gap fraction.Fragment size was a strong determinant of the three structural variables. Larger fragments had greater average height, larger variation in height, and smaller gap fraction. Minimum span had a large effect on the depth and magnitude of edge effects for the three structural variables. Locations associated with high span values (those surrounded by more forest habitat) showed little effect of distance to fragment edge. In contrast, locations with low span values (those more exposed to edges) were severely limited in canopy height, showed lower height variation, and were associated with greater gap fraction values. The minimum span attribute allows for a more accurate characterization of edge as well as fragment‐level effects, and when combined with high resolution imagery, can improve planning of protected areas for long‐term ecological sustainability and biodiversity protection.

Fragmentation poses one of the greatest threats to tropical forests with short‐term changes to the structure of forest canopies affecting microclimate, tree mortality, and growth. Yet the long‐term effects of fragmentation are poorly understood because (1) most effects require many decades to materialize, but long‐term studies are very rare, (2) the effects of edges on forest canopy structure as a function of fragment size are unknown, and (3) edge effects are often confounded by fragment shape. We quantified the long‐term (centennial) effects of fragmentation on forest canopy structure using airborne light detection and ranging (LiDAR) of 1060 Hawaiian rain forest fragments ranging in size from 0.02 to 1000 ha, created more than 130 years ago by flowing lava. Along with distance from edge, we developed a metric, minimum span, to gain additional insight into edge effects on three measures of canopy structure: canopy height, height variation, and gap fraction.Fragment size was a strong determinant of the three structural variables. Larger fragments had greater average height, larger variation in height, and smaller gap fraction. Minimum span had a large effect on the depth and magnitude of edge effects for the three structural variables. Locations associated with high span values (those surrounded by more forest habitat) showed little effect of distance to fragment edge. In contrast, locations with low span values (those more exposed to edges) were severely limited in canopy height, showed lower height variation, and were associated with greater gap fraction values. The minimum span attribute allows for a more accurate characterization of edge as well as fragment‐level effects, and when combined with high resolution imagery, can improve planning of protected areas for long‐term ecological sustainability and biodiversity protection.