Variation in forest and landslide carbon pools along complex environmental gradients in the Sierra de Las Minas of eastern Guatemala

Background/Question/Methods

Mountains may play a significant albeit little understood role in biogeochemical cycles.  Large-scale topographic controls on climate in combination with geomorphic processes create a complex matrix of environmental conditions that influence the production, storage, and transfer of nutrients from local to regional scales.  Here we focus on Carbon and take advantage of the unique setting provided by the Sierra de Las Minas (SLM) of eastern Guatemala to investigate how carbon pools in forest and 10-year old landslides vary with elevation and aspect.  Constraining the magnitude of these pools is a first step for understanding the role of landslides in regional C budgets.  The vegetation and soil were sampled in plots distributed in the southern mesic (16 in forest, 8 in landslides, 3 in second-growth) and northern wet (2 in forest, 3 in landslides) slopes of the SLM between 1000 – 2600 m.  Estimates of above-ground biomass C pools were based on field measurements (tree height and diameter at breast height) and allometric equations.  Estimates of below-ground biomass and soil C pools were based on soil samples collected at three depths (0-10, 10-20, and 20-30 cm depths), separation of fine roots, and analysis of soil for total carbon and nitrogen.

Results/Conclusions

The size of the C pools was highly variable ranging between 0.3 - 16.0 MgC ha^-1 in the litter, 0.1 - 10.0 MgC ha^-1 in the below-ground biomass, and 0.1 - 22.2 MgC ha^-1 in the soil.  In the southern mesic forests the size of these pools vary non-linearly with elevation.  Once the data from the northern wet slope of the SLM is included some interesting patterns emerge.  First, C content in litter is greater in mesic than in wet forest sites; surprisingly, the litter C content in the northern wet slope landslides is similar or greater than that of all forests.  Second, the C content in the below-ground biomass is lesser in the mesic than in the wet sites irrespective of habitat (forest versus landslides); landslides in the mesic slopes have the lowest values.  Third, the C content in soils is greatest in mesic than wet forests; in turn forests had greatest soil C contents than landslide sites.  Lastly, C in litter and below-ground biomass but not in the soil is similar between landslide and forest sites.  These findings suggest that ecosystem functions are diverse along the complex mosaic of environmental conditions that exist in mountainous environments.