Wood biophysical properties and the dynamics of water storage discharge and refilling were studied in the trunk of canopy tree species with diverse life history and functional traits in subtropical forests of northeast Argentina. Multiple techniques assessing capacitance and storage capacity were used simultaneously to improve our understanding of the functional significance of internal water sources in trunks of large trees. Sapwood capacitances of 10 tree species were characterized using pressure-volume relationships of sapwood samples obtained from the trunk. Frequency domain reflectometry was used to continuously monitor the volumetric water content in the main stems. Simultaneous sap flow measurements on branches and at the base of the tree trunk, as well as diurnal variations in trunk contraction and expansion, were used as additional measures of stem water storage use and refilling dynamics. All evidence indicates that tree trunk internal water storage contributes from 6 to 28% of the daily water budget of large trees depending on the species. The contribution of stored water in stems of trees to total daily transpiration was greater for deciduous species, which exhibited higher capacitance and lower sapwood density. A linear relationship across species was observed between wood density and growth rates with the higher wood density species (mostly evergreen) associated with lower growth rates and the lower wood density species (mostly deciduous) associated with higher growth rates. The large sapwood capacitance in deciduous species may help to avoid catastrophic embolism in xylem conduits. This may be a low-cost adaptation to avoid water deficits during peak water use at midday and under temporary drought periods and will contribute to higher growth rates in deciduous tree species compared with evergreen ones. Large capacitance appears to have a central role in the rapid growth patterns of deciduous species facilitating rapid canopy access as these species are less shade tolerant than evergreen species.

The canopy photosynthesis and carbon balance of the subtropical forests are not well studied compared to temperate and tropical forest ecosystems. The main objective of this study was to assess the seasonal dynamics of Normalized Difference Vegetation Index (NDVI) and potential canopy photosynthesis in relation to seasonal changes in leaf area index (LAI), chlorophyll concentration, and air temperatures of NE Argentina subtropical forests throughout the year. We included in the analysis several tree plantations (Pinus, OPEN ACCESSForests 2014, 5 288Eucalyptus and Araucaria species) that are known to have high productivity. Field studies in native forests and tree plantations were conducted; stem growth rates, LAI and leaf chlorophyll concentration were measured. MODIS satellite-derived LAI (1 km SIN Grid) and NDVI (250m SIN Grid) from February 2000 to 2012 were used as a proxy of seasonal dynamics of potential photosynthetic activity at the stand level. The remote sensing LAI of the subtropical forests decreased every year from 6 to 5 during the cold season, similar to field LAI measurements, when temperatures were 10 °C lower than during the summer. The yearly maximum NDVI values were observed during a few months in autumn and spring (March through May and November, respectively) because high and low air temperatures may have a small detrimental effect on photosynthetic activity during both the warm and the cold seasons. Leaf chlorophyll concentration was higher during the cold season than the warm season which may have a compensatory effect on the seasonal variation of the NDVI values. The NDVI of the subtropical forest stands remained high and fairly constant throughout the year (the intra-annual coefficient of variation was 1.9%), and were comparable to the values of high-yield tree plantations. These results suggest that the humid subtropical forests in NE Argentina potentially could maintain high canopy photosynthetic activity throughout the year and thus this ecosystem may be a large carbon sink.

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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.

Frost and drought are key stress factors limiting the growth and distribution of tree species. Resistance to stress involves energy costs that may result in trade-offs between different functional traits. Structures or mechanisms that can help to withstand stress imply differences in the carbon economy of the species. Although adaptive responses to frost and drought resistance are usually of a similar nature, they are rarely assessed simultaneously. We investigated these resistance mechanisms in 10 canopy tree species coexisting in the semi-deciduous subtropical forests of northern Argentina. We measured leaf lifespan, anatomical, photosynthetic and water relations traits and performed a thermal analysis in leaves to determined ice nucleation and tissue damage temperatures. Our results showed that evergreen and deciduous species have different adaptive responses to cope with freezing temperatures and water deficits. Evergreen species exhibited cold tolerance, while deciduous species were more resistant to hydraulic dysfunction and showed greater water transport efficiency. Further research is needed to elucidate resistance strategies to stress factors at the whole tree- and stand level, and possible links with hydraulic safety and efficiency among different phenological groups. This will allow us to predict the responses of subtropical forest species to changes in environmental conditions under climate change scenarios.

Burrowing species can be considered important ecosystem engineers that increase landscape heterogeneity, create subterranean shelters and provide foraging opportunities. We measured and described different aspects of giant armadillo (Priodontes maximus) excavations (size, age), and differences generated in relation to the surrounding environment (vegetation, humidity, temperature) in three sites of the Argentine Chaco Region. We used camera‐traps in two protected areas to monitor the use of burrows by other species and tested two primary and non‐mutually exclusive hypotheses: Giant armadillo burrows are used as thermal protection from temperature extremes and provide new foraging opportunities for other species. Greater litter cover and depth were recorded in giant armadillo burrows, and more bare ground in spoil piles, producing habitat heterogeneity. Burrows had higher humidity and more moderate temperatures, with lower temperatures during hot months and higher temperatures during cold months. Out of 48 vertebrate species recorded by camera‐traps, 27 taxa (17 mammals, 9 birds and one reptile) were recorded using burrows. White‐lipped peccaries (Tayassu peccari) and collared peccaries (Pecari tajacu) used burrows more frequently than other mammals. Medium‐sized carnivores such as Pampas fox (Lycalopex gymnocercus) and Geoffroy´s cat (Leopardus geoffroyii) tended to only investigate burrows, probably searching for prey. In no instances, animals other than giant armadillos were recorded staying inside burrows for more than a few seconds. Medium‐sized species interacted more frequently than large‐sized species, and smaller species used giant armadillo burrows less than larger ones, suggesting that the benefits provided by excavations to other species depend on their body weight. The probability of use of burrows decreases with time, suggesting that burrows provide a finite resource used opportunistically. Further reduction in the distribution of the giant armadillo is therefore likely to have effects on habitat heterogeneity and biodiversity, probably impacting the fitness of species that use their burrows as foraging sources.

Bosque Atlántico, extracción selectiva, Ley de Bosques, manejo post-extracción, productividad de madera, productos forestales no maderables, servicios ecosistémicos] A�������. Is sustainable forest harvesting possible in Misiones? The need for multi-scale management, research, high-impact interventions, and funding. To conserve a representative area of the subtropical forests of Misiones, a globally endangered ecosystem, it is necessary to find a viable economic solution for the areas destined under Law 26331 exclusively for sustainable management of native forest, and to reduce deforestation in the areas where replacement of native forest is permi�ed (901617 ha and 477858 ha, respectively, according to the latest land use planning by the Province of Misiones). Since the middle of the last century, public policies have provided incentives for plantations of trees and other crops, promoting deforestation. Remnant forests are degraded from exploitation of the principal commercial species in cu�ing cycles shorter than 20 years, and productivity of wood is now too low to be economically useful. Productivity can be improved through post-harvest management (e.g., cu�ing of bamboo and lianas), but on highly degraded sites more intensive management is needed, such as scarifying of soils or planting seedlings of high-value, fast-growing species to allow cu�ing cycles of around 30 years and increments greater than 3 m 3 .ha -1 .year -1 . Action is also needed to control illegal trade in native wood, which diminishes the prices and reduces the viability of socially and environmentally responsible enterprises. Moreover, sustainable management of the native forest should be accompanied by reductions in taxes, for example through payment for ecosystem services, or by other types of use, such as harvesting of non-timber forest products. In the case of small and medium property owners, governments and organizations should stimulate conservation of forest through forest resources and services use, actively encourage diversification of production, and offer tools that promote independence from intensive tobacco cultivation. Funding is needed both directly to producers (through laws) and to institutions that generate knowledge that permits concrete advances in sustainable forest management.