Tropical montane forest canopy recovery and biomass accumulation after landslide disturbances across a Peruvian Andean elevational gradient

Cathryn A. Freund and Miles R. Silman, Biology, Wake Forest University, Winston-Salem, NC, Cathryn A. Freund and Gregory P. Asner, Center for Global Discovery and Conservation Science, Arizona State University, Tempe, AZ, Kasey E. Clark, Smithsonian Tropical Research Institute, Jim F. Curran, Biology, Wake Forest University, Winston Salem, NC

Background/Question/Methods
Tropical Andean montane forests are high biodiversity and carbon storage landscapes comprised of a shifting mosaic of forest patches of different sizes, ages, and species compositions. Landslides are the most common natural disturbance creating these patches. While the geomorphic drivers of landslides in the Andes have been studied, the factors controlling post-landslide forest recovery across the steep climatic and topographic gradients characteristic of tropical mountains are poorly understood. This is partly due to the small sample sizes of landslides (<30) that most landslide studies are based on. Here we use a LiDAR-derived canopy height map coupled with a 25-year landslide time series map comprising 608 landslides to examine how landslide, topographic, and biophysical factors, along with intact vegetation left behind after landslides (residual vegetation), affect canopy height and heterogeneity in regenerating landslides. We also calculate aboveground biomass accumulation rates and estimate the time for landslides to recover to mature forest biomass levels.
Results/Conclusions
We find that residual vegetation is present on 42.6% (n = 259) of landslides, and it occurs on larger landslides and at lower elevations. It has substantial effects on forest regeneration: after 25 years, the tree canopy on the average landslide with residual vegetation was 11.9 m tall, compared to 7.5 m on landslides without residual vegetation. The two types of landslides reach approximately equal levels of canopy structural variability after approximately 18 years. We also find that age and insolation are the biggest determinants of forest recovery, with age alone explaining 65-66% of modeled variation, despite high heterogeneity among landslides and the environmental contexts in which they are regenerating. Finally, we estimate that landslides recover aboveground biomass at an average rate of 2.34 Mg/ha/yr. Accumulation rates decline with elevation. Our estimates of time to biomass recovery (29-36 years) are much faster than in previous studies of post-landslide TMF recovery, and as a result we caution against using allometric equations applied to LiDAR data to estimate forest aboveground biomass in frequently disturbed landscapes. Identifying the factors determining TMF canopy regeneration across large landscapes and numbers of disturbances contributes to our growing understanding of tropical montane landscapes as complex environmental mosaics.