Landslide age, elevation and residual vegetation determine tropical montane forest canopy recovery and biomass accumulation after landslide disturbances in the Peruvian Andes

Abstract

Landslides are common natural disturbances in tropical montane forests. While the geomorphic drivers of landslides in the Andes have been studied, factors controlling post‐landslide forest recovery across the steep climatic and topographic gradients characteristic of tropical mountains are poorly understood. Here we use a LiDAR‐derived canopy height map coupled with a 25‐year landslide time‐series map to examine how landslide, topographic and biophysical factors, along with residual vegetation, affect canopy height and heterogeneity in regenerating landslides. We also calculate above‐ground biomass accumulation rates and estimate the time for landslides to recover to mature forest biomass levels. We find that age and elevation are the biggest determinants of forest recovery, and that the jump‐start in regeneration that residual vegetation provides lasts for at least 18 years. Our estimates of time to biomass recovery (31.6–37.1 years) are surprisingly rapid, and as a result we recommend that future research pair LiDAR with hyperspectral imagery to estimate forest above‐ground biomass in frequently disturbed landscapes. Synthesis. Using a high‐resolution LiDAR dataset and a time‐series inventory of 608 landslides distributed across a wide elevational gradient in Andean montane forest, we show that age and elevation are the most influential predictors of forest canopy height and canopy variability. Other features of landslides, in particular the presence of residual vegetation, shape post‐landslide regeneration trajectories. LiDAR allows for a detailed analysis of forest structural recovery across large landscapes and numbers of disturbances, and provides a reasonable upper bound on above‐ground biomass accumulation rates. However, because this method does not capture the effect of compositional change through succession on above‐ground biomass, wherein high‐wood density species gradually replace light‐wooded pioneer species, it overestimates above‐ground biomass. Given previously estimated stem turnover rates along this elevational gradient, we posit that above‐ground biomass recovery takes at least three times as long as our recovery time estimates based on LiDAR‐derived structure alone.

Leveraging time series of satellite and aerial images to promote the long‐term monitoring of restored plant communities

“…Lastly, some studies opt to derive recovery indices from spectral vegetation indices. Recovery indices can be computed from both active and passive sensors and measure the time needed for a pixel to reach its pre‐disturbance greenness (João et al, 2018) or biomass (Freund et al, 2021; Nicolau et al, 2021), or the greenness or biomass of reference sites (Storey et al, 2016) following a disturbance. Because they integrate a baseline value (e.g., 5‐year median, average during normal years), recovery indices can account for spatio‐temporal variability in abiotic characteristics, plant composition, and their spectral properties.…”

“…Lastly, some studies opt to derive recovery indices from spectral vegetation indices. Recovery indices can be computed from both active and passive sensors and measure the time needed for a pixel to reach its pre-disturbance greenness (João et al, 2018) or biomass (Freund et al, 2021;Nicolau et al, 2021), or the greenness or biomass of reference sites (Storey et al, 2016)…”

Network structure of avian mixed-species flocks decays with elevation and latitude across the Andes

“…30 m), and on steep slopes the canopy and understory are only a few metres apart and vertical stratification is greatly reduced in comparison to the well-segregated forest strata in the contiguous lowlands [ 36 ]. Furthermore, frequent landslide disturbances on steep slopes help maintain patches of early- and mid-successional vegetation on the landscape and increase the horizontal heterogeneity of habitat structure [ 36 , 84 ]. By contrast, lowland forest strata are more discrete, resulting in segregated foraging microhabitats for canopy and understory flocks that greatly increase the costs of activity matching [ 9 ] and could decrease the benefits of social information [ 85 ].…”

Long-term recoveries of forest ecosystem components after shallow landslides were asynchronized among slope positions

“…At disturbance legacy-rich sites, live trees can regenerate by advanced seedlings on undisturbed vegetation patches, buried seeds, or sprouts (Guariguata 1990). Freund and others (2021) also suggested that canopy heights are higher for 25 years after landslides at sites that include residual vegetation. Therefore, the accumulation rates of live tree AGB were highest (Figure 2a) in the deposition zone, followed by the transport zone and then the initiation zone.…”