Dry-season climate drives interannual variability in tropical tree growth

<p>Tropical and subtropical ecosystems are primarily responsible for the large inter-annual variability (IAV) in the global carbon land sink. The response of tropical vegetation productivity to climatic variation likely drives this IAV, but the climate sensitivity of key productivity components are poorly understood. Tree-ring analysis can help fill this knowledge gap by estimating IAV in woody biomass growth, the major carbon accumulation process in tropical vegetation.</p><p> </p><p>Here, we evaluate the climate responses of woody biomass growth throughout the global tropics. Using an unprecedented compilation of tropical tree-ring data, we test hypotheses that (1) precipitation (P) and maximum temperature (T<sub>max</sub>) have opposite and additive effects on annual tree growth, (2) these climate responses amplify with increasing aridity and (3) wet-season climate is a more important driver of growth than dry-season climate.</p><p> </p><p>We established a network of 347 tree-ring width chronologies compiled from (sub-)tropical latitudes, representing 99 tree species on five continents and obtained from contributors (n=112) and the International Tree-Ring Data Bank (ITRDB; n=235). Our network is climatologically representative for 66% of the pantropical land area with woody vegetation.</p><p> </p><p>To test hypotheses we re-developed standardized ring-width index (RWI) chronologies and assessed climate responses using SOM cluster analysis (monthly P and T<sub>max</sub>) and multiple regression analysis (seasonal P and T<sub>max</sub>). Our results were consistent with hypothesis 1: effects of monthly or seasonal P and T<sub>max</sub> on tree growth were indeed additive and opposite, suggesting water availability to be the primary driver of tropical tree growth. In accordance with hypothesis 2, these climate responses were stronger at sites with lower mean annual precipitation or a larger annual water deficit. However, our results contrast those expected under hypothesis 3. Three of the four clusters show a dominant role of dry-season climate on annual tree growth and regression analyses confirmed this strong dry-season role.</p><p> </p><p>The strong dry-season effect on tropical tree growth seemingly contrasts the general notion that tropical vegetation productivity peaks during the wet season but is consistent with studies showing that climatologically benign dry seasons increase reserve storage and xylem growth. We posit that dry-season climate constrains the magnitude of woody biomass growth that takes place during the following wet season, and thus contributes to IAV in tree growth.</p><p> </p><p>By providing field-based insights on climate sensitivity of tropical vegetation productivity, our study contributes to the major task in Earth system science of quantifying, understanding, and predicting the IAV of the carbon land sink.</p>

Fixed or mixed? Variation in tree functional types and vegetation structure in a forest-savanna ecotone in West Africa

We analysed thirty-five 400-m2 plots encompassing forest, savanna and intermediate vegetation types in an ecotonal area in Ghana, West Africa. Across all plots, fire frequency was over a period of 15 years relatively uniform (once in 2–4 years). Although woodlands were dominated by species typically associated with savanna-type formations, and with forest formations dominated by species usually associated with closed canopies, these associations were non-obligatory and with a discrete non-specialized species grouping also identified. Across all plots, crown area index, stem basal area and above-ground biomass were positively associated with higher soil exchangeable potassium and silt contents: this supporting recent suggestions of interplays between potassium and soil water storage potential as a significant influence on tropical vegetation structure. We also found an average NDVI cover increase of ~0.15% year−1 (1984–2011) with plots dominated by non-specialized species increasing more than those dominated by either forest- or savanna-affiliated species. Our results challenge the traditional view of a simple forest vs. savanna dichotomy controlled by fire, and with our newly identified third non-specialized species grouping also potentially important in understanding ecotonal responses to climate change.

Tygarrup javanicus (Chilopoda, Geophilomorpha) – an exotic species that has reached Poland

For the first time in Poland, centipedes of a tropical species Tygarrup javanicus (Attems, 1907) (Geophilomorpha) were found in the hothouses with the tropical vegetation of the Botanical Garden in Wrocław. This Asian species has increasingly been reported from European greenhouses. Its spread is facilitated, among other factors, by small body size and parthenogenesis. In Poland one should also expect other exotic species which have already been found in neighbouring countries.

Modelling the responses of extreme events hydrometeorological events in the landslides and floods of the Combeima river basin.

<p>The village of Juntas has a periodic sequence of hydrometeorological extreme events. The region present a tropical vegetation with a highly dynamic weather. Currently modelling of hydrological events have been limited to the use of conventional rainfall runoff models, that fail to represent accurately the moment when landslides start to occur, as well as to not be able to provide a clear spatial sensitivity of the relationship between landslide event and precipitation. This research presents a contribution in the linking of various modelling concepts to understand more the influence of the spatial variability of rain in the generation of the events. The data avaialable was daily precipitation during 15 years from de satelital imagine and the discharge of geotechnical characterizations, hydraulic analysis, ecological structures, cartography, vulnerability, flood and torrential risk maps.</p><p>The analysis is done by combining the information available in remote sensing rasters and the overall temporal relation of events is mapped with a spatiotemporal analysis of the extremes. The current methodology is expected to contribute to the understanding of the sensitivity of landslides due to the spatiotemporal variation of rain in the region.</p>

Fire susceptibility and transitional climate regime in Amazon tropics

<p>Amazon wildfire surge in 2019 once again raised the alarm about the fate of the Earth’s most biodiverse forest. Climate change and deforestation lead to greater vegetation water stress and susceptibility to fires. We use multiple satellite and climate reanalysis data to explore fire susceptibility in response to shifted climate regime due to global climate change and forest loss in Amazon regions. We found that climate in Amazon has been shifting to increased frequency of extreme conditions with increased drought extent and severity. The tropical vegetation that has adapted to its surrounding climate are less resilient under stress of climate change and highly susceptible to fire.  The fire susceptibility has been expanding through the transition season and northward to the tropical rain and seasonal forests. These results highlighted the links between fire risk, climate change and human activities in Amazon regions.</p>