Tree Rings And Climate

Biological invasions in changing ecosystems: vectors, ecological impacts, management and predictions

Spatial and temporal patterns of propagation from meteorological to hydrological droughts in Brazil

Climate response and drought resilience of Nothofagus obliqua secondary forests across a latitudinal gradient in south-central Chile

Interannual variability in the global land carbon sink is strongly related to variations in tropical temperature and rainfall. This association suggests an important role for moisture-driven fluctuations in tropical vegetation productivity, but empirical evidence to quantify the responsible ecological processes is missing. Such evidence can be obtained from tree-ring data that quantify variability in a major vegetation productivity component: woody biomass growth. Here we compile a pantropical tree-ring network to show that annual woody biomass growth increases primarily with dry-season precipitation and decreases with dry-season maximum temperature. The strength of these dry-season climate responses varies among sites, as reflected in four robust and distinct climate response groups of tropical tree growth derived from clustering. Using cluster and regression analyses, we find that dry-season climate responses are amplified in regions that are drier, hotter and more climatically variable. These amplification patterns suggest that projected global warming will probably aggravate drought-induced declines in annual tropical vegetation productivity. Our study reveals a previously underappreciated role of dry-season climate variability in driving the dynamics of tropical vegetation productivity and consequently in influencing the land carbon sink. Dry-season climate variability is a primary driver of tropical tree growth, according to observations from a pantropical tree-ring network. 

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Tropical tree growth driven by dry-season climate variability

South American (SA) societies are highly vulnerable to droughts and pluvials, but lack of long-term climate observations severely limits our understanding of the global processes driving climatic variability in the region. The number and quality of SA climate-sensitive tree ring chronologies have significantly increased in recent decades, now providing a robust network of 286 records for characterizing hydroclimate variability since 1400 CE. We combine this network with a self-calibrated Palmer Drought Severity Index (scPDSI) dataset to derive the South American Drought Atlas (SADA) over the continent south of 12°S. The gridded annual reconstruction of austral summer scPDSI is the most spatially complete estimate of SA hydroclimate to date, and well matches past historical dry/wet events. Relating the SADA to the Australia-New Zealand Drought Atlas, sea surface temperatures and atmospheric pressure fields, we determine that the El Nino-Southern Oscillation (ENSO) and the Southern Annular Mode (SAM) are strongly associated with spatially extended droughts and pluvials over the SADA domain during the past several centuries. SADA also exhibits more extended severe droughts and extreme pluvials since the mid-20th century. Extensive droughts are consistent with the observed 20th-century trend toward positive SAM anomalies concomitant with the weakening of midlatitude Westerlies, while low-level moisture transport intensified by global warming has favored extreme rainfall across the subtropics. The SADA thus provides a long-term context for observed hydroclimatic changes and for 21st-century Intergovernmental Panel on Climate Change (IPCC) projections that suggest SA will experience more frequent/severe droughts and rainfall events as a consequence of increasing greenhouse gas emissions.

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Six hundred years of South American tree rings reveal an increase in severe hydroclimatic events since mid-20th century.

Pine tree invasions threaten many natural ecosystems of the Southern Hemisphere, modifying their structure and functioning through shifts in fire regimes, water balance, and biodiversity The magnitude of such impacts depends on how much of the landscape has been invaded, thus a better understanding of the dispersal ability of pines and predictions of their future invasions are needed Here we depict the spatio-temporal patterns of Pinus elliottii and Pinus taeda invading a new environment away from planted plots (ie, invasion front), and discuss the underlying mechanisms that lead to a very concerning, yet poorly documented, pine invasion in central Argentina Combining high-resolution imagery, allometric field data, and dendrochronology, we reconstructed the pine invasion into mountain grasslands from its onset in 1990 We found that even though the maximum density of invading pines (80 trees ha−1) was very low compared to adjacent plantation (1000 trees ha−1), density decreases exponentially with distance from the plantation edge Remarkably, invading pines were found throughout the sampling plots showing high dispersal capacity, with no differences in age with increasing distance The observed low density and spatially widespread exotic pine establishment, create a stealth type of invasion that is difficult to perceive in its early stages and challenging to manage once large areas are compromised As invasion continues, long-distance dispersal will possibly become a major agent of landscape transformation and may lead to large pine-dominated neo-ecosystems, such as the savanna-like formation described here that replaced native grasslands in only three decades

M. Eugenia Ferrero

Papers

Six hundred years of South American tree rings reveal an increase in severe hydroclimatic events since mid-20th century.

Stealth invasions on the rise: rapid long-distance establishment of exotic pines in mountain grasslands of Argentina