Resilience of soil nutrient availability and organic matter decomposition to hurricane impact in a tropical dry forest ecosystem

Abstract

Hurricanes Jova and Patricia were the first hurricanes in recent history to make landfall on the tropical dry forest ecosystem of the Pacific coast of Mexico. We examined the resilience of soil N and P availability and organic matter decomposition to the effects of both hurricanes in pastures, successional fields and old-growth forests of this region. We evaluated resistance by comparing measurements made before and after each hurricane. We also examined temporal trends to test if variables non-resistant to Jova recovered during the four-year period between both hurricanes. We considered resilient those variables that either showed resistance or were not resistant but showed recovery. We hypothesized that decomposition and soil nutrient availability would increase shortly due to the massive incorporation of high-quality decomposing materials after both hurricanes, especially under land covers with more woody vegetation, and return to pre-hurricane values within a couple of years. Our tests showed that most variables measured were not resistant to either hurricane and that the direction or magnitude of change sometimes differed between hurricanes. There was a fourfold increase in soil available N after hurricane Jova and a twofold increase after hurricane Patricia. Soil available P changed little over the entire period. Total litter stocks resisted hurricane passage and differed only among land covers whereas litter C, N and P stocks changed with the hurricane and became more similar in all land covers over the following three years. The soil N peak caused a decrease in the C:N and N:P ratios in the litter produced from the leaf flush some months after Hurricane Jova. This decrease was measured, however, only two years after hurricane Jova in total accumulated litter. Decomposition rates of local recent litter decreased after hurricane Jova and increased after hurricane Patricia but recovered within two years after hurricane Jova. Decomposition of a standard material in all sites, used as a control, showed a decreasing trend suggesting a continuous reduction in decomposer activity after hurricane Jova. Overall there were smaller differences among land covers than we had expected and their inter-annual fluctuations in most variables were surprisingly similar. We conclude that nutrient availability and decomposition were in general not resistant but returned to pre-hurricane levels within the four years between hurricane Jova and hurricane Patricia. Therefore, these ecosystem functions seemed resilient, at least to hurricane Jova.