Detecting Ecological Patterns Along Environmental Gradients: Alpine Treeline Ecotones

Everyone is familiar with that age-old adage: "a picture is worth a thousand words". Among ecologists, the word "picture" easily could be replaced with the word "pattern", although the significance remains the same: the pattern we observe in a single snapshot more than sums up what could be expressed if we tried to describe all the original events that led to the pattern. One particular class of patterns, spatial patterns, are the backbone of much contemporary ecological research. [...

Increased stem density and competition may diminish the positive effects of warming at alpine treeline

The most widespread response to global warming among alpine treeline ecotones is not an upward shift, but an increase in tree density. However, the impact of increasing density on interactions among trees at treeline is not well understood. Here, we test if treeline densification induced by climatic warming leads to increasing intraspecific competition. We mapped and measured the size and age of Smith fir trees growing in two treelines located in the southeastern Tibetan Plateau. We used spatial point-pattern and codispersion analyses to describe the spatial association and covariation among seedlings, juveniles, and adults grouped in 30-year age classes from the 1860s to the present. Effects of competition on tree height and regeneration were inferred from bivariate mark-correlations. Since the 1950s, a rapid densification occurred at both sites in response to climatic warming. Competition between adults and juveniles or seedlings at small scales intensified as density increased. Encroachment negatively affected height growth and further reduced recruitment around mature trees. We infer that tree recruitment at the study treelines was more cold-limited prior to 1950 and shifted to a less temperature-constrained regime in response to climatic warming. Therefore, the ongoing densification and encroachment of alpine treelines could alter the way climate drives their transitions towards subalpine forests.Organismic and Evolutionary Biolog

Impact de la canicule et de la sécheresse de l'année 2003 sur les principales espèces forestières en France Méditerranéenne

The drought and scorching heat of 2003 had a deep impact on the Mediterranean vegetation: important dry back of forest undergrowth, loss of needles for the conifers, early loss of leaves for broad-leaved trees. Conifers annual ring latewood for 2003 is particularly narrow and light and sometimes absent. The bad health status of trees and their lack of reserves induced in 2004 also a very narrow ring. The negative impact of 2003 seems more severe than that of any other drought of the previous century.La canicule et la sécheresse de 2003 ont eu un impact important sur la végétation méditerranéenne: désèchements importants du sous bois, perte d'aiguille des résineux, pertes précoce des feuilles chez les feuillus. Les cernes de croissance des résineux montrent un bois final particulièrement mince et léger et parfois absent. Le mauvais état sanitaire des arbres et leur manque de réserves après 2003 fait que le cerne 2004 est également très étroit. L'effet de 2003 semble plus important que celui de toute autre sécheresse au cours du siècle précédent

Detecting Ecological Patterns Along Environmental Gradients: Alpine Treeline Ecotones.

Everyone is familiar with that age-old adage: "a picture is worth a thousand words". Among ecologists, the word "picture" easily could be replaced with the word "pattern", although the significance remains the same: the pattern we observe in a single snapshot more than sums up what could be expressed if we tried to describe all the original events that led to the pattern. One particular class of patterns, spatial patterns, are the backbone of much contemporary ecological research. [...