Abstract
The effects of temporal variation of rainfall on secondary succession of tropical dry ecosystems are poorly understood. We studied effects of inter-seasonal and inter-year rainfall variation on the dynamics of regenerative successional communities of a tropical dry forest in Mexico. We emphasized the effects caused by the severe El Niño Southern Oscillation (ENSO) occurred in 2005. We established permanent plots in sites representing a chronosequence of Pasture (abandoned pastures, 0–1 years fallow age), Early (3–5), Intermediate (8–12), and Old-Growth Forest categories (n = 3 per category). In total, 8210 shrubs and trees 10 to 100-cm height were identified, measured, and monitored over four years. Rates of plant recruitment, growth and mortality, and gain and loss of species were quantified per season (dry vs. rainy), year, and successional category, considering whole communities and separating seedlings from sprouts and shrubs from trees. Community rates changed with rainfall variation without almost any effect of successional stage. Mortality and species loss rates peaked during the ENSO year and the following year; however, after two rainy years mortality peaked in the rainy season. Such changes could result from the severe drought in the ENSO year, and of the outbreak of biotic agents during the following rainy years. Growth, recruitment and species gain rates were higher in the rainy season but they were significantly reduced after the ENSO year. Seedlings exhibited higher recruitment and mortality rate than sprouts, and shrubs showed higher recruitment than trees. ENSO strongly impacted both the dynamics and trajectory of succession, creating transient fluctuations in the abundance and species richness of the communities. Overall, there was a net decline in plant and species density in most successional stages along the years. Therefore, strong drought events have critical consequences for regeneration dynamics, delaying the successional process and modifying the resilience of these systems.
Highlights
Most theoretical and empirical studies on forest succession have focused on the role of light availability on the dynamics of tree communities [1,2,3]
Few studies have addressed the role of water availability in forest succession [4], especially in ecosystems that are severely limited by water, such as seasonal tropical dry forest (TDF), where mean annual rainfall is less than 1000 mm and the dry season spans several months with little or no rain at all
In the two previous years (2003 and 2004) annual rainfall was close to the long-term mean, and in the two years following to the El Nino Southern Oscillation (ENSO) year (2006 and 2007) annual rainfall was substantially above the long-term precipitation mean
Summary
Most theoretical and empirical studies on forest succession have focused on the role of light availability on the dynamics of tree communities [1,2,3]. Current scenarios of global climate change predict that severe drought events, such as those caused by the El Nino Southern Oscillation (ENSO), will increase both in intensity and frequency in tropical regions [11,12]. Under such climatic scenarios it is critical to understand to what extent temporal rainfall variability affects the natural regeneration and succession of TDF ecosystems in abandoned agricultural fields, which have become nowadays dominant components of tropical and non-tropical landscapes [13,14]
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