Paula Ines Campanello

Tree plantations can facilitate the establishment of native trees, thus providing opportunities for the ecological restoration or rehabilitation of degraded forest lands. Stand variables can influence the establishment of native tree species, but few studies have been carried out to determine how sapling growth response to stand variables varies among functionally different species. We evaluated the effect of stand age, stand basal area, tree density, and time since last logging on stem diameter growth rates, as well as the dependence of such effect on whole plant, stem, and leaf functional traits. We measured the stem diameter increment on 280 individuals of 22 species in permanent plots for a period of 2 years in araucaria (Araucaria angustifolia (Bertol.) Kuntze) plantations in the Atlantic Forest, NE Argentina. Increasing all-species basal area and plantation age negatively affected the growth rates, and such effect tended to be higher in species with low wood density. Two functional axes independently explained growth rate differences between species in growth rate. Growth rates increase with decreasing wood density, increasing leaf phosphorus and potassium content, and decreasing specific leaf area. Among species that are similar in the traits associated with the first functional axis, plant growth increases with increasing leaf nitrogen content.

Stem capacitance and water storage are known to play an important role in the water economy of trees by acting as an intermediate water source for transpiring leaves. The bark, in addition to be involved in protection and mechanical support of the trees, can also serve as a water reservoir. We examined the relationship between inner bark and sapwood biophysical properties in tree species occurring in forests at the opposite ends of a moisture gradient in subtropical South America. We also assessed the relationships between wood density, growth rate and the magnitude of the water reservoir. The inner bark thickness varied between 1.89 and 0.50 cm across species and sites and there were not significant differences between forests. Inner bark capacitance of species from the dry forest was higher than sapwood capacitance, and the opposite was found in the moist forest. Sapwood capacitance (262 ± 80.8 Kg m⁻³ MPa⁻¹) was significantly higher in the moist forest compared to the dry forest (41.9 ± 4.5 Kg m⁻³ MPa⁻¹), while the opposite was found for inner bark (50.7 ± 8.4 and 83.1 ± 11.4 Kg m⁻³ MPa⁻1, respectively). Inner bark capacitance and density were linear and positively correlated across species, while for sapwood the relationship was well-described by a negative exponential function. In species with higher percentage of inner bark, the time lags in the daily contractions of bark and sapwood tissues were lower. Relative growth rate was negatively correlated with inner bark and sapwood density and positively with daily stored water used and percentage of inner bark across species and sites. Our results suggest that sapwood is a relevant water storage tissue in the trees of the moist forest while inner bark is important for tree functioning in the dry forest. High stem capacitance and water storage are needed to cope with short dry spells or seasonal periods of water deficit, and for maintaining growth rates. These stem properties will be more relevant under climatic scenarios with more frequent extreme drought events or seasonal reduction in precipitation in these forest ecosystems.

Deforestation is a global process that has strongly affected the Atlantic Forest in South America, which has been recognised as a threatened biodiversity hotspot. An important proportion of deforested areas were converted to forest plantations. Araucaria angustifolia is a native tree to the Atlantic Forest, which has been largely exploited for wood production and is currently cultivated in commercial plantations. An important question is to what extent such native tree plantations can be managed to reduce biodiversity loss in a highly diverse and vulnerable forest region. We evaluated the effect of stand age, stand basal area, as a measure of stand density, and time since last logging on the density and richness of native tree regeneration in planted araucaria stands that were successively logged over 60 years, as well as the differences between successional groups in the response of plant density to stand variables. We also compared native tree species richness in planted araucaria stands to neighbouring native forest. Species richness was 71 in the planted stands (27 ha sampled) and 82 in native forest (18 ha sampled) which approximate the range of variation in species richness found in the native forests of the study area. The total abundance and species richness of native trees increased with stand age and time since last logging, but ecological groups differed in their response to such variables. Early secondary trees increased in abundance with stand age 3–8 times faster than climax or late secondary trees. Thus, the change in species composition is expected to continue for a long term. The difference in species richness between native forest and planted stands might be mainly explained by the difference in plant density. Therefore, species richness in plantations can contribute to local native tree diversity if practices that increase native tree density are implemented.

Para conservar una superficie representativa de los bosques subtropicales de Misiones (Argentina), ecosistema amenazado a nivel mundial, es necesario encontrar una solución económicamente viable a las superficies que hoy, y de acuerdo con la Ley 26331, sólo se pueden destinar al manejo sostenible del bosque nativo, así como a disminuir la deforestación en las áreas pasibles de ser reemplazadas (901617 ha y 477858 ha, respectivamente, de acuerdo con el último ordenamiento territorial realizado por la Provincia de Misiones). La deforestación, que ocurre desde mediados del siglo pasado, fue fomentada por políticas públicas de incentivos a actividades de producción intensivas como las plantaciones forestales u otros cultivos. Los bosques remanentes están degradados por la explotación de las principales especies nativas comerciales en ciclos de corta menores a 20 años, y la productividad maderera es más baja de lo necesario para sostener económicamente la actividad. En algunos casos, la productividad podría recuperarse con manejos post-extracción (e.g., el corte de bambúes y lianas), mientras que, en situaciones de mayor degradación, se necesitan acciones de manejo más intensivas como la escarificación de los suelos o la plantación de renovales de especies de alto valor comercial y rápido crecimiento que permitan turnos de corta de 30 años e incrementos de al menos 3 m³.ha^-1.año^-1. Asimismo, se necesita una política de control del comercio ilegal de madera nativa, que disminuye los precios y reduce la rentabilidad de productores responsables. Por otra parte, la obtención de madera debería complementarse con reducciones impositivas, por ejemplo, a través de la compensación por provisión de servicios ecosistémicos, o mediante otros tipos de usos, como el aprovechamiento de recursos no madereros. En el caso de pequeños y medianos productores, el gobierno y ONG deberían estimular la conservación del bosque por el uso de sus recursos y servicios ambientales, incentivar activamente la diversificación de la producción y brindar las herramientas que les permitan a los productores independizarse del cultivo intensivo de tabaco. Es necesario un mayor financiamiento directo a los productores para el manejo, así como a organismos dedicados a generar conocimiento que permita avances concretos en el manejo sostenible del bosque.

Tree physiological processes are affected not only by environmental conditions, but also by phenological leaf stages. During foliar expansion, rapid changes occur, such as the activation of metabolic processes that encompass a hydraulic link between xylem and phloem pathways at a whole-tree level. Daily and seasonal changes in stem diameter may reveal different temporal dynamics of water use and recharge in tree reservoirs. Foliar phenological patterns were studied in relation to stem dimensional changes in 10 canopy tree species with different phenological patterns (three deciduous, three brevideciduous and four evergreen species). Additionally, we assessed (i) daily sap flow fluctuations in branch and main stem, (ii) diurnal changes in sapwood volumetric water content and (iii) stem radius variations during leafless, expanding and mature leaves periods in three of the 10 tree species (two deciduous and one brevideciduous). During the leaf expansion phase, the diameter of trees decreased in all 10 species, with a larger impact on deciduous and brevideciduous species. For the subset of deciduous and brevideciduous species, the movement of long-distance water transport occurred first near the branches and then in the main stem during the leafless stage. Changes in stored water use and a decrease in the volumetric water content and the radius of the main stem during this period suggest that there is a contribution of water from internal stem reservoirs toward the construction of new leaves.

Phenology is a key ecosystem process that reflects climate–vegetation functioning, and is an indicator of global environmental changes. Recently, it has been suggested that land-use change and timber extraction promote differences in forest phenology. We use remote-sensing data to describe regional leaf phenological patterns in combination with field data from 131 plots in old-growth and disturbed forests distributed over subtropical forests of Argentina (54–65°W). We assessed how climate is related to phenological patterns, and analysed how changes in forest structural characteristics such as stock of above-ground biomass relate to the observed phenological signals across the gradient. We found that the first three axes of a principal component analysis explained 85% of the variation in phenological metrics across subtropical forests, ordering plots mainly along indicators of seasonality and productivity. At the regional scale, the relative importance of forest biomass in explaining variation in phenological patterns was about 15%. Climate showed the highest relative importance, with temperature and rainfall explaining Enhanced Vegetation Index metrics related to seasonality and productivity patterns (27% and 47%, respectively). Within forest types, climate explains the major fraction of variation in phenological patterns, suggesting that forest function may be particularly sensitive to climate change. We found that forest biomass contributed to explaining a proportion of leaf phenological variation within three of the five forest types studied, and this may be related to changes in species composition, probably as a result of forest use.