Abstract
Fine-scale biomass maps offer forest managers the prospect of more detailed and locally accurate information for measuring, reporting and verification activities in contexts, such as sustainable forest management, carbon stock assessments and ecological studies of forest growth and change. In this study, we apply a locally validated method for estimating aboveground woody biomass (AGWB) from Advanced Land Observing Satellite (ALOS) Phased Array-type L-band Synthetic Aperture Radar (PALSAR) data to produce an AGWB map for the lowland pine savannas of Belize at a spatial resolution of 100 m. Over 90% of these woodlands are predicted to have an AGWB below 60 tha−1, with the average woody biomass of these savannas estimated at 23.5 tha−1. By overlaying these spatial estimates upon previous thematic mapping of national land cover, we derive representative average biomass values of ~32 tha−1 and ~18 tha−1 for the previously qualitative classes of “denser” and “less dense” tree savannas. The predicted average biomass, from the mapping for savannas woodlands occurring within two of Belize’s larger protected areas, agree closely with previous biomass estimates for these areas based on ground surveys and forest inventories (error ≤20%). However, biomass estimates derived for these protected areas from two biomass maps produced at coarser resolutions (500 m and 1000 m) from global datasets overestimated biomass (errors ≥275% in each dataset). The finer scale biomass mapping of both protected and unprotected areas provides evidence to suggest that protection has a positive effect upon woody biomass, with the mean AGWB higher in areas protected and managed for biodiversity (protected and passively managed (PRPM), 29.5 tha−1) compared to unprotected areas (UPR, 23.29 tha−1). These findings suggest that where sufficient ground data exists to build a reliable local relationship to radar backscatter, the more detailed biomass mapping that can be produced from ALOS and similar satellite data at resolutions of ~100 m provides more accurate and spatially detailed information that is more appropriate for supporting the management of forested areas of ~10,000 ha than biomass maps that can be produced from lower resolution, but freely available global data sets.
Highlights
These findings suggest that where sufficient ground data exists to build a reliable local relationship to radar backscatter, the more detailed biomass mapping that can be produced from Advanced Land Observing Satellite (ALOS) and similar satellite data at resolutions of ~100 m provides more accurate and spatially detailed information that is more appropriate for supporting the management of forested areas of ~10,000 ha than biomass maps that can be produced from lower resolution, but freely available global data sets
For the half of the total savanna area of the RBCMA that is covered by the ALOS Phased Array-type L-band Synthetic Aperture Radar (PALSAR) scene, we estimate mean aboveground woody biomass (AGWB) based on 3,632 pixels from MBE100 to be 29.55 ± 0.84 tha−1, where the 95% confidence interval is reported with (±), and for the denser woodland areas sensed in the Deep River (DR) forest reserve (Figure 1D), 38.03 ± 0.92 tha−1 based on 3105 pixels
This study has shown that ALOS PALSAR radar data can be used with semi-empirical modelling to produce estimates of AGWB ha−1 for the woody component of tropical savannas at a spatial resolution of 100 m
Summary
Savannas are an important component of global vegetation, covering approximately 18% of the. In the Neotropics, key threats are the continuing expansion of agriculture and pasture [9,10], as well as overly frequent logging and burning [11,12], which have resulted in the reduced extent and health of this ecosystem [13,14] With these pressures degrading both the biodiversity and economic value of savanna woodlands, techniques are urgently needed to measure, map and monitor the woody component reliably and to produce this information at appropriate scales to support conservation and management actions. Analysing the resulting AGWB map to quantify for the first time the variation in AGWB across the different woodland savannas within the country and exploring how this might provide forest managers with enhanced information about the nature and locality of different woodland components, compared to previous qualitative thematic mapping using the UNESCO land cover classification system. For two specific protected areas of Belize, assessing if this finer scale mapping produces biomass estimates that accord more closely with ground measurements of biomass than estimates based on biomass values extracted from pantropical biomass data sets at 500-m and 1000-m resolution produced by [17,18]
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