Abstract
Investigating the timing of key phenological events across environments with variable seasonality is crucial to understand the drivers of ecosystem dynamics. Leaf production in the tropics is mainly constrained by water and light availability. Identifying the factors regulating leaf phenology patterns allows efficiently forecasting of climate change impacts. We conducted a novel phenological monitoring study across four Neotropical vegetation sites using leaf phenology time series obtained from digital repeated photographs (phenocameras). Seasonality differed among sites, from very seasonally dry climate in the caatinga dry scrubland with an eight-month long dry season to the less restrictive Cerrado vegetation with a six-month dry season. To unravel the main drivers of leaf phenology and understand how they influence seasonal dynamics (represented by the green color channel (Gcc) vegetation index), we applied Generalized Additive Mixed Models (GAMMs) to estimate the growing seasons, using water deficit and day length as covariates. Our results indicated that plant-water relationships are more important in the caatinga, while light (measured as day-length) was more relevant in explaining leafing patterns in Cerrado communities. Leafing behaviors and predictor-response relationships (distinct smooth functions) were more variable at the less seasonal Cerrado sites, suggesting that different life-forms (grasses, herbs, shrubs, and trees) are capable of overcoming drought through specific phenological strategies and associated functional traits, such as deep root systems in trees.
Highlights
Temporal patterns of leaf replacement, or leaf exchange phenology, are of major importance in understanding ecosystem processes such as carbon, water, and energy exchanges, controlling seasonal cycles of photosynthetic activity [1,2,3]
We found that water and light are the most important predictors for leaf phenological patterns across seasonally dry environments
Degree of seasonality, which is related to the length and intensity of the dry season, reflected on community leafing patterns and on what drives the deciduous component of these communities
Summary
Temporal patterns of leaf replacement, or leaf exchange phenology, are of major importance in understanding ecosystem processes such as carbon, water, and energy exchanges, controlling seasonal cycles of photosynthetic activity [1,2,3]. We conducted a novel phenological multi-site near-surface monitoring study using digital cameras to describe community leafing patterns in four Neotropical seasonally dry environments that differ in their degree of seasonality and vegetation structure: a seasonally dry tropical forest (SDTF), locally known as caatinga, and three different Cerrado (Neotropical savanna) vegetation types—two woody savannas (cerrado and dense cerrado) and a grassy shrubland savanna (cerrado shrubland). We investigated: (i) whether the timing and length of the growing season differs across the four seasonally dry tropical communities and what are the drivers of phenological transitions in each environment; and (ii) whether the growing season varies according to the vegetation structure (woody versus grassy) and degree of seasonality, determined by the water deficit observed during the dry season. [36], while the leafing pattern for the caatinga community should be restricted to the onset of the rtahientyemsepasoornal. niche separation hypothesis [36], while the leafing pattern for the caatinga community 2s.hMoualtderbiealreasntdricMteedthtoodthse onset of the rainy season
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