Dynamical trajectories of secondary forest succession in the tropics often exhibit high levels of stochasticity. Effects of inter-annual climate variability on successional dynamics may account for part of such stochasticity, but this issue is still poorly understood. Here, we employ a long-term study (2000-2018) to explore the role of inter-annual rainfall variation on the dynamics of secondary forest succession in a tropical rainforest region in Southern Mexico. The aim is to assess the relative influence of climate temporal variability respect to other factors driving secondary forest dynamics.
In October 2000, we established a chronosequence of abandoned cornfields with fallow ages ranged from 1 to 17 years. At each site, all trees with 1.5 m height or taller were tagged and monitored for survival, growth, and recruitment (new trees reaching 1.5 m height) over 18 continuous year intervals. Annual rates of recruitment, mortality, and the net community rate of change (calculated as community density at year t+1 divided by community density at year t) were calculated per year. Over the study period the mean annual precipitation was 2,700 mm and varied between 1,741 to 3,482 mm/yr. This inter-annual variation was more than 10-fold when considered rainfall in the dry season (range January to May: 58-689 mm).
Results/Conclusions
Overall, the rates of recruitment and mortality, as well as net community rate of change, decreased as successional time advances. Within these trajectories, mortality increased as rainfall in the dry season decreased. A strong ENSO-related drought event occurred in 2001-2001, producing the highest mortality rate over the study period. Also recruitment rate, and consequently the net community rate of change, reduced as rainfall in the dry season decreased. However, the percentage of variation in community rates across sites and years explained by rainfall variation was no more than 20%. Also, there was a high heterogeneity among secondary forests of similar age in their dynamics and response to rainfall variation. We discuss how other variables affecting successional dynamics (e.g. land-use history, matrix structure, and biotic interactions) and rainfall temporal variation may interact in complex ways, producing important levels of apparent stochasticity in the dynamics of second-growth tropical rainforests.