Ecosystem function associated with soil organic carbon declines with
tropical dry forest degradation
Abstract
Forest degradation is increasingly recognized as a major threat to
global biodiversity and ecosystems’ capacity to provide ecosystem
services. This study examined the impacts of forest degradation on soil
quality and function in a seasonally dry tropical forest (SDTF) of
Ecuador. We compared soil physical-chemical properties, enzymatic
activity, particulate organic carbon (POC) and mineral-associated
organic carbon (MAOC) along a gradient of SDTF degradation in the dry
and rainy season. Our findings showed a consistent and steady reduction
in soil quality (total C and N) and function (dehydrogenase and
β-glucosidase activity) that paralleled the loss of vegetative structure
and diversity along the degradation gradient. Soil physical-chemical
properties were less variable and enzymatic activity was generally
higher in the dry season compared to the rainy season. We also showed
for the first time a significant and uniform decrease in POC and MAOC
with ecosystem degradation in a SDTF. The relative proportion of these
two components was constant along the gradient except for the most
degraded state (arid land), where POC was higher in proportion to MAOC,
suggesting that a functional tipping point may be crossed with extreme
forest degradation. These findings address an important knowledge gap
for SDTFs by showing a consistent loss of soil quality and functionality
with degradation and suggest that extreme degradation can result in an
alternate state with compromised resilience.