Leonardo Paolini

RAINFALL-CONTROLLED TREE GROWTH IN HIGH-ELEVATION SUBTROPICAL TREELINES

It is generally assumed that tree growth in the upper limit of a forest is mainly controlled by summer temperature. This general statement is mostly based on studies from extra-tropical mountains and has been rarely evaluated in subtropical latitudes frequently characterized by drier climates. In the subtropical mountains from Northwestern Argentina (∼23° S), annual precipitation decreases with elevation from >1500 mm at 1200– 1500 m, to <200 mm above 4000 m. In consequence, tree growth at high elevations in the region may be seriously limited by water supply. In order to assess the influence of precipitation on tree growth, we evaluated the relationships between climatic variations and radial growth in four species growing at different altitudinal zones: Juglans australis from the montane cloud forest at 1800 m; Alnus acuminata from the montane savanna-like woodland at 2700 m; Prosopis ferox from the subalpine dryland at 3500 m; and Polylepis tarapacana from the high-elevation alpine dryland at 4750 m. D...

Subtropical dendroecology—dating disturbances and forest dynamics in northwestern Argentina montane ecosystems

The use of dendroecological techniques to describe temporal patterns of disturbances and forest dynamics has been largely restricted to high-latitude ecosystems. In this review, we present the results of recent developments in subtropical northwestern Argentina (22–28°S). The area is characterized by a subtropical monsoonal climate (wet summers, dry winters) which implies that some species respond to climatic seasonality by producing annual tree rings. Alnus acuminata, a deciduous species that dominates the upper montane forests (1700–2700 m), has been successfully used to describe patterns of forest regeneration, fire, landslides, and floods by dating scars, establishment events and changes in growth patterns and to relate these patterns with climate and land use during the twentieth century. Establishment dates, growth releases, and resprout dates of species with annual tree rings (e.g. Cedrela lilloi, Solanum riparium, Cinammomum porphyria) have been used in lower montane forests to describe regeneration dynamics in relation to treefall gaps. These results indicate that dendroecology is a feasible and promising research line that needs further exploration in this geographical area. Among the research priorities we identified are: (1) exploration of the use of these species in forests of lower latitudes (e.g. southern Peru and Bolivia), (2) increase of sample sizes and target species, in order to extend the temporal and spatial domains of these studies, (3) explore the use of other species in the same area to study other ecological processes or the same ones in different environments.

Tree-growth responses across environmental gradients in subtropical Argentinean forests

Subtropical forests in montane ecosystems grow under a wide range of environmental conditions. However, little is known about the growth responses of subtropical trees to climate along ecological gradients. To assess how, and to what extent climate controls tree growth, we analyzed tree responses to climate for 15 chronologies from 4 different species (Schinopsis lorentzii, Juglans australis, Cedrela lilloi, Alnus acuminata) across a variety of environments in subtropical forests from northwestern Argentina (22–28°S, 64–66°W). Using correlation and principal component analysis, site and species differences in tree-growth responses to precipitation and temperature were determined along the elevation gradient from the dry-warm Chaco lowlands to the wet-cool montane Yungas. Our results show that species responses differ according to the severity in climate conditions along the elevation gradient. At sites with unfavorable conditions, mainly located at the extremes of the environmental gradient, responses of different species to climate variations are similar; in contrast, at sites with relatively mild conditions, tree growth displays a large variety of responses reflecting differences in both local environmental conditions and species physiology. Our research suggests that individualistic responses to environmental variability would determine differences in the type and timing of the responses of dominant trees to climate, which ultimately may shift species’ assemblages in montane subtropical regions of South America under future climate changes.

Efectos de la invasión del ligustro, Ligustrum lucidum, en la dinámica hídrica de las Yungas del noroeste Argentino

Las Yungas argentinas (bosques de montana) tienen alta biodiversidad y un rol clave en la regulacion hidrica. El ligustro (Ligustrum lucidum) es una de las especies exoticas que dominan sus bosques secundarios. Debido a sus altas tasas de crecimiento y follaje verde todo el ano, se planteo la hipotesis de que la disponibilidad de agua en el suelo se reduciria en bosques de ligustro en comparacion con bosques nativos, principalmente durante la epoca seca (invierno-primavera). Se trabajo en seis pares de parcelas de bosques nativos y bosques secundarios monodominantes de ligustro en la Sierra San Javier, Tucuman, Argentina. Se registro la humedad edafica mediante mediciones de contenido volumetrico y potencial hidrico y se estimo la productividad de los distintos tipos de bosque mediante el indice de vegetacion de diferencia normalizada (NDVI). Durante la epoca seca de 2011 y 2012, los suelos en ligustrales presentaron un contenido volumetrico de agua 32,5 % y 24 % y un potencial hidrico en el suelo ocho y cuatro veces menor. Se observaron mayores valores de NDVI (8,5 %) en bosques de ligustro que en bosques nativos, principalmente en las selvas localizadas a menor altura y con mayor deficit hidrico inverno-primaveral. Los resultados sugieren que el bosque de ligustro estaria consumiendo mayor cantidad de agua, sobre todo en la epoca seca, debido a una actividad fenologica mas prolongada respecto al bosque nativo y que su invasion en las Yungas podria alterar el funcionamiento hidrico de este ecosistema.

Rainfall Up, Mountain Down?

Climate and natural disturbances are strongly related. Several studies have shown the strong relationships between precipitation, soil-water content, and landslide occurrence (e.g. Keefer and Johnson 1983; Schwab 1983; Iverson and Major 1987; Bovis and Jones 1992; Schwab 2002).