Abstract
BackgroundSpatially explicit forest carbon (C) monitoring aids conservation and climate change mitigation efforts, yet few approaches have been developed specifically for the highly heterogeneous landscapes of oceanic island chains that continue to undergo rapid and extensive forest C change. We developed an approach for rapid mapping of aboveground C density (ACD; units = Mg or metric tons C ha−1) on islands at a spatial resolution of 30 m (0.09 ha) using a combination of cost-effective airborne LiDAR data and full-coverage satellite data. We used the approach to map forest ACD across the main Hawaiian Islands, comparing C stocks within and among islands, in protected and unprotected areas, and among forests dominated by native and invasive species.ResultsTotal forest aboveground C stock of the Hawaiian Islands was 36 Tg, and ACD distributions were extremely heterogeneous both within and across islands. Remotely sensed ACD was validated against U.S. Forest Service FIA plot inventory data (R2 = 0.67; RMSE = 30.4 Mg C ha−1). Geospatial analyses indicated the critical importance of forest type and canopy cover as predictors of mapped ACD patterns. Protection status was a strong determinant of forest C stock and density, but we found complex environmentally mediated responses of forest ACD to alien plant invasion.ConclusionsA combination of one-time airborne LiDAR data acquisition and satellite monitoring provides effective forest C mapping in the highly heterogeneous landscapes of the Hawaiian Islands. Our statistical approach yielded key insights into the drivers of ACD variation, and also makes possible future assessments of C storage change, derived on a repeat basis from free satellite data, without the need for additional LiDAR data. Changes in C stocks and densities of oceanic islands can thus be continually assessed in the face of rapid environmental changes such as biological invasions, drought, fire and land use. Such forest monitoring information can be used to promote sustainable forest use and conservation on islands in the future.Electronic supplementary materialThe online version of this article (doi:10.1186/s13021-015-0043-4) contains supplementary material, which is available to authorized users.
Highlights
Explicit forest carbon (C) monitoring aids conservation and climate change mitigation efforts, yet few approaches have been developed for the highly heterogeneous landscapes of oceanic island chains that continue to undergo rapid and extensive forest C change
We developed an approach for monitoring forest aboveground carbon density (ACD; units = Mg or metric tons C ha−1) across island archipelagos at a spatial resolution of 30 m (0.09 ha) using a combination of airborne Light Detection and Ranging (LiDAR) and freely available satellite data (Fig. 1)
Island carbon stocks and distributions Total forest cover and aboveground carbon stock for seven main Hawaiian Islands was estimated at 550,065 ha and 36.0 Tg, respectively (Fig. 2; Table 1)
Summary
Explicit forest carbon (C) monitoring aids conservation and climate change mitigation efforts, yet few approaches have been developed for the highly heterogeneous landscapes of oceanic island chains that continue to undergo rapid and extensive forest C change. The importance of such assessments has grown in the climate change mitigation arena [2] In step with these efforts, there has been increasing focus on developing. Have islands been heavily deforested in some regions of the world, they have undergone enormous change via introduced disturbance regimes, such as fire, and alien invasive species [15, 16] The effects of these and other changes on forest C stocks remain poorly understood, despite numerous local- to landscape-scale assessments [17]. Without continuous and spatially extensive forest monitoring, patterns of change and/or opportunities for recovery of island forests will remain a challenge to incorporate into conservation, management and resource policy initiatives
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