Fragmentation increases wind disturbance impacts on forest structure and carbon stocks in a western Amazonian landscape

Abstract

Tropical second-growth forests could help mitigate climate change, but the degree to which their carbon potential is achieved will depend on exposure to disturbance. Wind disturbance is common in tropical forests, shaping structure, composition, and function, and influencing successional trajectories. However, little is known about the impacts of extreme winds on second-growth forests in fragmented landscapes, though these ecosystems are often located in mosaics of forest, pasture, cropland, and other land cover types. Indirect evidence suggests that fragmentation increases risk of wind damage in tropical forests, but no studies have found such impacts following severe storms. In this study, we ask whether fragmentation and forest type (old vs. second growth) were associated with variation in wind damage after a severe convective storm in a fragmented production landscape in western Amazonia. We applied linear spectral unmixing to Landsat 8 imagery from before and after the storm, and combined it with field observations of damage to map wind effects on forest structure and biomass. We also used Landsat 8 imagery to map land cover with the goals of identifying old- and second-growth forest and characterizing fragmentation. We used these data to assess variation in wind disturbance across 95,596 ha of forest, distributed over 6,110 patches. We find that fragmentation is significantly associated with wind damage, with damage severity higher at forest edges and in edgier, more isolated patches. Damage was also more severe in old-growth than in second-growth forests, but this effect was weaker than that of fragmentation. These results illustrate the importance of considering landscape context in planning tropical forest restoration and natural regeneration projects. Assessments of long-term carbon sequestration potential need to consider spatial variation in disturbance exposure. Where risk of extreme winds is high, minimizing fragmentation and isolation could increase carbon sequestration potential.

Fire, fragmentation, and windstorms: A recipe for tropical forest degradation

“…Forest fragmentation, fires, and windstorms each cause some level of forest disturbance in Amazonia (Brando et al, ; Broadbent et al, ; Chambers et al, ; Haddad et al, ; Negrón‐Juárez et al, ), but if they act synergistically, the impacts on forest structure, dynamics, and carbon stocks could be amplified. Most of the current understanding on the effects of wind disturbances on Amazonia forests derives from studies that quantified the spatial extent of blowdown events using remote sensing imagery (Chambers et al, ; Espírito‐Santo et al, ; Negrón‐Juárez et al, ) or from postdisturbance field inventories, which often lag the windstorm event by many months or years (Marra et al, ; Schwartz et al, ). While these studies have shown that wind disturbance exerts strong influences on the structure and diversity of tropical forests, they often lack mechanistic approaches to understand how forests respond to synergistic interactions between windstorms and other forest disturbances.…”

“…Amazonia, biomass loss, fire scar, forest degradation, forest dynamics, tree mortality, windstorms spatial extent of blowdown events using remote sensing imagery (Chambers et al, 2013;Espírito-Santo et al, 2014;Negrón-Juárez et al, 2010) or from postdisturbance field inventories, which often lag the windstorm event by many months or years (Marra et al, 2014;Schwartz et al, 2017). While these studies have shown that wind disturbance exerts strong influences on the structure and diversity of tropical forests, they often lack mechanistic approaches to understand how forests respond to synergistic interactions between windstorms and other forest disturbances.…”

Fragmentation, forest structure, and topography modulate impacts of drought in a tropical forest landscape

“…, Schwartz et al. ). Differences in species composition between old‐ and second‐growth forests suggest that second‐growth forests are likely to suffer stronger drought impacts.…”

“…Over 70% of all remaining tropical forests in the world are second-growth forests growing on former agricultural or logged lands (Food and Agriculture Organization of the United Nations [FAO] 2010). These regenerating forests differ from old growth in composition, size structure, and spatial configuration in the landscape and thus are expected to respond differently to climate extremes (FAO 2010, Anderson-Teixeira et al 2013, Uriarte et al 2016a, Schwartz et al 2017. Differences in species composition between old-and second-growth forests suggest that second-growth forests are likely to suffer stronger drought impacts.…”

Rapid remote sensing assessment of impacts from Hurricane Maria on forests of Puerto Rico

“…Previous work has also demonstrated significant correlations between wind speed estimates using models (e.g. H*wind, Powell et al 1998), and forest damage determined by spectral shifts before and after the storm (Chambers et al 2007, Zeng et al 2009, Negron-Juarez et al 2014, Rifai et al 2016, Schwartz et al 2017). …”