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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 permitted (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 cutting 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., cutting 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 cutting cycles of around 30 years and increments greater than 3 m3.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. [ABSTRACT FROM AUTHOR]

The area of tree plantations in the humid subtropical region of Northern Argentina has recently increased five folds. However, the impact of this land use change on evapotranspiration (ET), one of the main components of the hydrologic cycle, has not been evaluated. We studied the ET at tree and ecosystem levels for native forests and three tree plantations ( Pinus taeda , Araucaria angustifolia and Eucalyptus grandis ). Water consumption of individual trees was estimated using sap flow measurements. Ecosystem ET was characterized using both remote sensing derived data products (ET MODIS ) for 2000–2011 and scaling up from tree sap flow measurements to stand level. Canopy conductance ( g c ) was estimated using both sap flow measurements and ET MODIS data. At individual level, transpiration was positively related to the size of the tree, and the relationship was well described by an exponential function when all species (both native and cultivated trees) were included in the analysis. The average annual leaf area index was similar between native forest and tree plantations. The ET estimates obtained from scaling up sap flow measurements and from ET MODIS were relatively similar in most cases and differed by 4–34%, depending on the ecosystem. The tree plantations, regardless of density or age, did not show higher ET MODIS than native forests. The ET ranged from 1161 to 1389 mm per year across native forests and tree plantations according to remote sensing, representing 58–69% of the annual precipitation. Furthermore, the good agreement between ET estimates, with the exception of E. grandis , obtained using sap flow and remote sensing provide a good basis for predicting the effects of land conversion from native forest to most non-native tree plantations on regional ET. Monthly ET MODIS increased with increasing monthly air saturation deficit (ASD) up to 0.8 kPa, value at which ET MODIS did not increase further probably due to stomatal control and low values ​​of g c . Different negative exponential relationships between g c and ASD were obtained when g c was calculated by scaling up daily tree sap flow to ecosystem level. Canopy conductance (estimated by remote sensing) declined in a similar negative exponential fashion with increasing ASD, and no differences were observed across ecosystem types. The result of increasing the time step, from daily to monthly, and the spatial scale from individual tree to stand level, had the consequence to lower, even to eliminate differences in annual ET and g c among ecosystems in their responses to climate drivers. This suggests that the nature of ET regulation at individual and ecosystem levels could be different, which should be taken into account when predicting the effects of changes in land use on regional hydrology. [ABSTRACT FROM AUTHOR]

Physiological characteristics of saplings can be considered one of the most basic constraints on species distribution. The shade-tolerant arborescent palm Euterpe edulis Mart. is endemic to the Atlantic Forest of Argentina, Brazil and Paraguay. At a local scale, saplings of this species growing in native forests are absent in gaps. We tested the hypothesis whether sensitivity to photoinhibition or hydraulic architecture constrains the distribution of E. edulis saplings in sun-exposed forest environments. Using shade houses and field studies, we evaluated growth, survival, hydraulic traits and the susceptibility of Photosystem II to photoinhibition in E. edulis saplings under different growth irradiances. Survival rates in exposed sites in the field were very low (a median of 7%). All saplings exhibited photoinhibition when exposed to high radiation levels, but acclimation to a high radiation environment increased the rate of recovery. Petiole hydraulic conductivity was similar across treatments regardless of whether it was expressed per petiole cross-sectional area or per leaf area. At the plant level, investment in conductive tissues relative to leaf area (Huber values) increased with increasing irradiance. Under high irradiance conditions, plants experienced leaf water potentials close to the turgor-loss point, and leaf hydraulic conductance decreased by 79% relative to its maximum value. Euterpe edulis saplings were able to adjust their photosynthetic traits to different irradiance conditions, whereas hydraulic characteristics at the leaf level did not change across irradiance treatments. Our results indicate that uncoupling between water demand and supply to leaves apparently associated with high resistances to water flow at leaf insertion points, in addition to small stems with low water storage capacity, weak stomatal control and high vulnerability of leaves to hydraulic dysfunction, are the main ecophysiological constraints that prevent the growth and survival of E. edulis saplings in gaps in the native forest where native lianas and bamboos show aggressive growth. [ABSTRACT FROM PUBLISHER]

Leaves can be both a hydraulic bottleneck and a safety valve against hydraulic catastrophic dysfunctions, and thus changes in traits related to water movement in leaves and associated costs may be critical for the success of plant growth. A 4-year fertilization experiment with nitrogen (N) and phosphorus (P) addition was done in a semideciduous Atlantic forest in northeastern Argentina. Saplings of five dominant canopy species were grown in similar gaps inside the forests (five control and five N + P addition plots). Leaf lifespan (LL), leaf mass per unit area (LMA), leaf and stem vulnerability to cavitation, leaf hydraulic conductance (Kleaf_area and Kleaf_mass) and leaf turgor loss point (TLP) were measured in the five species and in both treatments. Leaf lifespan tended to decrease with the addition of fertilizers, and LMA was significantly higher in plants with nutrient addition compared with individuals in control plots. The vulnerability to cavitation of leaves (P50leaf) either increased or decreased with the nutrient treatment depending on the species, but the average P50leaf did not change with nutrient addition. The P50leaf decreased linearly with increasing LMA and LL across species and treatments. These trade-offs have an important functional significance because more expensive (higher LMA) and less vulnerable leaves (lower P50leaf) are retained for a longer period of time. Osmotic potentials at TLP and at full turgor became more negative with decreasing P50leaf regardless of nutrient treatment. The Kleaf on a mass basis was negatively correlated with LMA and LL, indicating that there is a carbon cost associated with increased water transport that is compensated by a longer LL. The vulnerability to cavitation of stems and leaves were similar, particularly in fertilized plants. Leaves in the species studied may not function as safety valves at low water potentials to protect the hydraulic pathway from water stress-induced cavitation. The lack of rainfall seasonality in the subtropical forest studied probably does not act as a selective pressure to enhance hydraulic segmentation between leaves and stems. [ABSTRACT FROM AUTHOR]

A 4-year fertilization experiment with nitrogen (N) and phosphorus (P) was carried out in natural gaps of a subtropical forest in northeastern Argentina. Saplings of six dominant canopy species differing in shade tolerance were grown in five control and five N + P fertilized gaps. Hydraulic architectural traits such as wood density, the leaf area to sapwood area ratio (LA : SA), vulnerability to cavitation (P50) and specific and leaf-specific hydraulic conductivity were measured, as well as the relative growth rate, specific leaf area (SLA) and percentage of leaf damage by insect herbivores. Plant growth rates and resistance to drought-induced embolisms increased when nutrient limitations were removed. On average, the P50 of control plants was −1.1 MPa, while the P50 of fertilized plants was −1.6 MPa. Wood density and LA : SA decreased with N + P additions. A trade-off between vulnerability to cavitation and efficiency of water transport was not observed. The relative growth rate was positively related to the total leaf surface area per plant and negatively related to LA : SA, while P50 was positively related to SLA across species and treatments. Plants with higher growth rates and higher total leaf area in fertilized plots were able to avoid hydraulic dysfunction by becoming less vulnerable to cavitation (more negative P50). Two high-light-requiring species exhibited relatively low growth rates due to heavy herbivore damage. Contrary to expectations, shade-tolerant plants with relatively high resistance to hydraulic dysfunction and reduced herbivory damage were able to grow faster. These results suggest that during the initial phase of sapling establishment in gaps, species that were less vulnerable to cavitation and exhibited reduced herbivory damage had faster realized growth rates than less shade-tolerant species with higher potential growth rates. Finally, functional relationships between hydraulic traits and growth rate across species and treatments were maintained regardless of soil nutrient status. [ABSTRACT FROM AUTHOR]

Abstract: We studied developmental and environmental constraints on leaf dynamics, morphology and physiology in the monopodial tropical palm of the Atlantic Forest biome, Euterpe edulis. Plastic responses to light environments in terms of photosynthesis, leaf size, leaf life span, patterns of biomass allocation and growth were analysed. Plants were grown during 14 months in a shade house under four different growth irradiances. Plants of Euterpe edulis were able to adjust leaf demography and biomass allocation in the different light treatments. Leaf life span increased by 100 days with decreasing light levels while the rate of leaf production decreased, consistent with lower electron transport rates. At low light levels, adjustments in biomass allocation to leaf components allowed E. edulis to reduce self-shading and increase light interception. At high light plants allocated more biomass to roots, and the plants exhibited small leaf sizes when leaves were compared using an explicit ontogenetic analysis. Ontogeny constrained the maximum size that each consecutive leaf could achieve, while growth irradiance determined the rate of leaf production and other leaf traits. Consequently, there were both, developmental constraints and environmental determinants influencing leaf demography and morphology in E. edulis. The findings of this ecophysiological and demographic study are relevant to palms growing under natural conditions and help to explain the success of E. edulis in the forest understory and its absence from large gap openings. Our results not only confirm that E. edulis is a shade tolerant species, but also show that palms are able to acclimate to different growing condition as well as trees. [Copyright &y& Elsevier]

Abstract: Chusquea ramosissima is a semelparous woody bamboo growing in the understory of the semideciduous Atlantic Forest that increases in abundance after disturbance and consequently has profound effects on vegetation dynamics. Flowering and death of C. ramosissima may open a window of opportunity leaving space vacant for the recruitment of tree seedlings. We describe the flowering pattern and seedling demography of this species at different spatio-temporal scales between the years 2001 and 2009, and evaluate if tree seedling abundance of canopy species increased after the flowering event. At a landscape scale, flowering sites were interspersed with sites that did not flower. At a local scale, the flowering extended over 5 years, with flowering and non-flowering culms intermingled, also in small patches (i.e., 4 m2). Seeds germinated soon after flowering and die-back. Four successive seedling cohorts were studied. Mortality rate was high during the first 4 months after seedling emergence but several fast-growing seedlings were able to become established successfully. At the end of the study, 10%–20% of the initial number of bamboo seedlings in each cohort survived. Seedling abundance of tree canopy species was similar in flowering and non-flowering sites. C. ramosissima was able to re-colonize and perpetuate in sites it previously occupied. The coexistence of flowering and non-flowering culms at different spatio-temporal scales and clonal growth by rhizomes, together with the successful bamboo seedlings establishment, enhanced bamboo persistence in gaps and disturbed sites. Flowering and death of C. ramosissima did not facilitate seedling growth of canopy tree species. [Copyright &y& Elsevier]

Plasticity in hydraulic architecture of five dominant Atlantic forest species differing in light requirements and growth rates was evaluated in saplings grown at different irradiances to determine if hydraulic architecture changes in coordination with photosynthetic capacity. Saplings were grown in shade-houses at 10, 30, 45 and 65% of full solar irradiance for 4 months. In four of the five species, maximum relative growth rates were observed at intermediate irradiances (30 and 40% of full sun). Slow-growing species had lower maximum electron transport rates (ETRmax) than fast-growing species. A positive correlation between ETRmax and maximum leaf hydraulic conductivity (KL) was found across species, suggesting that species-specific stem hydraulic capacity and photosynthetic capacity were linked. Species with relatively high growth rates, such as Cedrela fissilis Vell., Patagonula americana L. and Cordia trichotoma (Vell.) Arrab. Ex Stend, exhibited increased KL and specific hydraulic conductivity (KS) with increased growth irradiance. In contrast, KS and KL did not vary with irradiance in the slower-growing and more shade-tolerant species Balfourodendron riedelianum (Engl.) Engl. and Lonchocarpus leucanthus Burkart, despite a relatively large irradiance-induced variation in ETRmax. A correlation between KS and ETRmax was observed in fast-growing species in different light regimes, suggesting that they are capable of plastic changes in hydraulic architecture and increased water-transport efficiency in response to changes in light availability resulting from the creation of canopy gaps, which makes them more competitive in gaps and open habitats. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Intensive farming systems benefit from the additional ecosystem services provided by tree integration, which generate different growing conditions for the main crop. We studied yerba mate (Ilex paraguariensis) responses to growing conditions in monoculture (the conventional cropping system of yerba mate) and in three agroforestry systems: (1) yerba mate + Balfourodendron riedelianum ; (2) yerba mate + Peltophorum dubium ; and (3) yerba mate + Toona ciliata. Mainly, we focused on water relations and the hydraulic architecture of yerba mate. Agroforestry cropping systems provided a shade cover of around 34–45% and yielded as high as the conventional system. The shade cover influenced the allocation pattern to enhance leaf light capture, incrementing the leaf area to the sapwood area at the branch level. We also found a higher specific hydraulic conductivity in stems of yerba mate plants in consortium with T. ciliata than in the conventional cropping system, as well as higher resistance to water deficits due to lower vulnerability to embolism in the stems. During a severe drought, yerba mate plants had a similar stem and leaf water potential in both agricultural systems. Still, plants in monoculture had lower hydraulic safety margins and higher signs of leaf damage and mortality. This indicates that integrating trees into the yerba mate cultivation increases water stress resistance which would be beneficial to avoid restrictions on crop productivity under severe droughts induced by climate change. Plant resistance to drought is very important in the face of global warming that threatens agriculture. Integrating trees into Ilex paraguariensis cultivation provides additional ecosystem services and different growing conditions that the crop must acclimate. We found that plants in agroforestry systems are more resistant to water stress and have a greater safety margin than plants in monocultures, with similar yields. The incorporation of trees in this perennial crop can effectively be used to maintain productivity under water stress. [ABSTRACT FROM AUTHOR]

Permanent forest plots are sampling areas where tree identity, abundance and size are recorded periodically, in order to study how forests change with climate, natural disturbances, uses and management. So far, patterns of change observed with permanent plots in Argentina have been local or regional. To promote scientific collaborations between different research groups within and among regions of Argentina, we created the Network of Permanent Plots of Native Argentinian Forests (RAPP), which includes the regions of Bosques Andino-Patagónicos, Chaco Seco, Chaco Húmedo, Monte de Sierras y Bolsones, Monte de Llanuras y Mesetas, Selva Paranaense and Yungas. Here we synthesize and characterize the information of 317 permanent plots (328.9 ha) included in the RAPP, describing their geographic distribution, objectives, main methodological aspects, and characteristics of the forests where they are established (e.g., disturbance, land tenure, structure, species richness), and after that, discuss the complementarity between the RAPP and the national inventories of native forests. Permanent plots are established over a wide range of latitude (22.02-54.89° S) and elevation (19 a 2304 m a. s. l.), but they are mainly concentrated in Subtropics (Chaco Seco, Chaco Húmedo, Selva Paranaense, and Yungas) and in Bosques Andino-Patagónicos. In all plots, trees are taxonomically identified and different dasometric variables are remeasured, which are the basis for potential collaborations to answer ecological questions at a larger scale. We hope to continue incorporating working groups in the RAPP and encouraging the establishment of plots, mainly in regions with a low number of permanent plots such as Monte, Espinal, and Delta e Islas del Paraná. The goal is that the RAPP advances in the long-term study of all native forests in Argentina, achieving a greater national cover and more interactions among research teams. [ABSTRACT FROM AUTHOR]

Abstract: Many woody bamboo species are forest understory plants that become invasive after disturbance. They can grow rapidly forming a dense, nearly monospecific understory that inhibits tree regeneration. The principal aim of this study was to understand what functional traits of bamboos allow them to outcompete tree seedlings and saplings and become successful species in the semideciduous Atlantic Forests of northeastern Argentina. We studied leaf and whole-plant functional traits of two bamboo species of the genus Chusquea and five co-occurring saplings of common tree species growing under similar solar radiation and soil nutrient availabilities. Nutrient addition had no effect on bamboo or tree sapling survival and growth after two years. Tree species with high-light requirements had higher growth rates and developed relatively thin leaves with high photosynthetic capacity per unit leaf area and short leaf life-span when growing in gaps, but had lower survival rates in the understory. The opposite pattern was observed in shade-tolerant species that were able to survive in the understory but had lower photosynthetic capacity and growth than light-requiring species in gaps. Bamboos exhibited a high plasticity in functional traits and leaf characteristics that enabled them to grow rapidly in gaps (e.g., higher photosynthetic capacity per unit dry mass and clonal reproduction in gaps than in the understory) but at the same time to tolerate closed-canopy conditions (they had thinner leaves and a relatively longer leaf life-span in the understory compared to gaps). Photosynthetic capacity per unit dry mass was higher in bamboos than in trees. Bamboo plasticity in key functional traits, such as clonal reproduction at the plant level and leaves with a relatively low C cost and high photosynthesis rates, allows them to colonize disturbed forests with consequences at the community and ecosystem levels. Increasing disturbance in some forests worldwide will likely enhance bamboo invasion resulting in profound negative impacts on forest diversity, structure and function in the long term. [Copyright &y& Elsevier]

Hydraulic traits were studied for six Nothofagus species from South America (Argentina and Chile), and for three of these species two populations were studied. The main goal was to determine if properties of the water conductive pathway in stems and leaves are functionally coordinated and to assess if leaves are more vulnerable to cavitation than stems, consistent with the theory of hydraulic segmentation along the vascular system of trees in ecosystems subject to seasonal drought. Vulnerability to cavitation, hydraulic conductivity of stems and leaves, leaf water potential, wood density and leaf water relations were examined. Large variations in vulnerability to cavitation of stems and leaves were observed across populations and species, but leaves were consistently more vulnerable than stems. Water potential at 50% loss of maximum hydraulic efficiency (P50) ranged from -0.94 to -2.44 MPa in leaves and from -2.6 to -5.3 MPa in stems across species and populations. Populations in the driest sites had sapwood and leaves more vulnerable to cavitation than those grown in the wettest sites. Stronger diurnal down-regulation in leaf hydraulic conductance compared with stem hydraulic conductivity apparently has the function to slow down potential water loss in stems and protect stem hydraulics from cavitation. Species-specific differences in wood density and leaf hydraulic conductance (KLeaf) were observed. Both traits were functionally related: species with higher wood density had lower KLeaf. Other stem and leaf hydraulic traits were functionally coordinated, resulting in Nothofagus species with an efficient delivery of water to the leaves. The integrity of the more expensive woody portion of the water transport pathway can thus be maintained at the expense of the replaceable portion (leaves) of the stem-leaf continuum under prolonged drought. Compensatory adjustments between hydraulic traits may help to decrease the rate of embolism formation in the trees more vulnerable to cavitation. [ABSTRACT FROM AUTHOR]

The article offers information on wood density (WD) and other wood mechanical and structural properties may have a strong functional relationship with demographic patterns and allometry of trees. Topics include the architectural traits and liana load were also determined, and the individual level, trees with greater hardness and toughness in branches died mostly uprooted, and trees with greater branch stiffness and susceptibility to colonization by lianas were mostly broken.

Leaf phenology responds sensitively to different environmental signals. Coordination between phenological phases and these signals allow species to adjust the optimal time for leaf expansion and growth, and to avoid possible damage caused by unfavorable environmental conditions. On the other hand, in deciduous species, tree height is another important factor, since the expansion and leafless events of canopy individuals determine the availability of light in lower heights. The objective of our work was to assess how environmental factors interact with leaf phenology in tree species of different leaf habits that coexist in the southern end of the semi-deciduous Atlantic Forest. For this purpose, the leaf phenology of 10 typical tree species of the canopy of the semi-deciduous Atlantic Forest in the province of Misiones was monitored. In deciduous and brevideciduous species, seasonal patterns were identified in the expansion and leafless phases linked to variations in temperature and photoperiod. In the evergreens, on the other hand, no clear association was found. The non-dominant deciduous trees advanced the expansion of leaves in comparison with the dominant ones. This would imply a strategy to optimize the capture of light and the gain of carbon at the beginning of the spring extending the season of growth. The phenology of deciduous species was closely coupled to environmental variables, which could generate, in these species, greater vulnerability to extreme events of environmental stress, such as low temperatures and water deficit. [ABSTRACT FROM AUTHOR]

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. Resistance to stress involves energy costs that result in trade-offs between different functional traits. In the semi-deciduous Atlantic Forest, species with different leaf habits coexist, but thus far, plant leaf strategies in this region remain poorly studied. We compared adaptive responses to cope with freezing temperatures and water deficits in canopy tree species. Different functional traits relationships showed that evergreen species exhibited cold tolerance, while deciduous species were more resistant to hydraulic dysfunction and showed greater water transport efficiency. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

There are numerous maps of the spontaneous vegetation of Argentina. However, a country-level map with enough detail to discriminate vegetation units within the phytogeographic provinces described by Cabrera (1976) is lacking. We analyzed vegetation descriptions published in recent decades, with special attention to those that produced physiognomic-floristic maps. As a result of this analysis, here we present a physiognomic-floristic map of spontaneous vegetation of Argentina that shows the heterogeneity within phytogeographic provinces. The map has 50 vegetation units as subdivisions of the phytogeographic ecotone and provinces early described, and a brief physiognomic-floristic description of each ecotone, province and vegetation unit. We propose a nomenclature of each vegetation unit based on dominant type of spontaneous vegetation and characteristic species and present digital cartographic material. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The development of the science and practice of restoration ecology in Argentina can be divided into three periods. The first was 1992-2004, characterized by isolated restoration efforts, mostly in arid and dry ecosystems, and engaging specific people in the academic, agro-technological, and private sectors as partially required by national regulations, but also inspired by the 1992 Earth Summit, the 1994 Amendments of the Constitutional Law, and environmental guidelines from investment entities. The second period of 2005-2010 showed significantly greater involvement in international networking and conference contributions. The current period from 2011-present has witnessed rapid advances and national integration. The country's network Red de Restauración Ecológica de Argentina ( REA) was founded in 2012, with seven subnational nodes. In 2014, the 2nd REA symposium was held to determine priority areas for restoration and to generate a National Plan. Public agencies, NGOs and volunteer groups are now actively engaged stakeholders. In 2013 Argentina became a founder member of SIACRE ( Sociedad Ibero-Americana y del Caribe para la Restauración Ecológica) and is organizing SIACRE's 4th international conference (April 2015; Buenos Aires). Restoration ecology in Argentina is ascendant because of long-term efforts related to strengthening democracy, people initiatives, and strong support from SIACRE, SER ( Society for Ecological Restoration), SER-Europe, and the national networks of Colombia, Brazil, Mexico, and Chile. Moreover, Argentina is now the first country to have updated its Civil Code by integrating the environment as a 'legal good,' which reinforces the citizens' rights to demand the implementation of degradation prevention and/or ecosystem restoration measures. [ABSTRACT FROM AUTHOR]

Stomatal regulation of transpiration constrains leaf water potential (ΨL) within species-specific ranges that presumably avoid excessive tension and embolism in the stem xylem upstream. However, the hydraulic resistance of leaves can be highly variable over short time scales, uncoupling tension in the xylem of leaves from that in the stems to which they are attached. We evaluated a suite of leaf and stem functional traits governing water relations in individuals of 11 lowland tropical forest tree species to determine the manner in which the traits were coordinated with stem xylem vulnerability to embolism. Stomatal regulation of ΨL was associated with minimum values of water potential in branches (Ψbr) whose functional significance was similar across species. Minimum values of Ψbr coincided with the bulk sapwood tissue osmotic potential at zero turgor derived from pressure–volume curves and with the transition from a linear to exponential increase in xylem embolism with increasing sapwood water deficits. Branch xylem pressure corresponding to 50% loss of hydraulic conductivity ( P 50) declined linearly with daily minimum Ψbr in a manner that caused the difference between Ψbr and P 50 to increase from 0.4 MPa in the species with the least negative Ψbr to 1.2 MPa in the species with the most negative Ψbr. Both branch P 50 and minimum Ψbr increased linearly with sapwood capacitance ( C) such that the difference between Ψbr and P 50, an estimate of the safety margin for avoiding runaway embolism, decreased with increasing sapwood C. The results implied a trade-off between maximizing water transport and minimizing the risk of xylem embolism, suggesting a prominent role for the buffering effect of C in preserving the integrity of xylem water transport. At the whole-tree level, discharge and recharge of internal C appeared to generate variations in apparent leaf-specific conductance to which stomata respond dynamically. [ABSTRACT FROM AUTHOR]

Leaf and whole plant-level functional traits were studied in five dominant woody savannah species from Central Brazil (Cerrado) to determine whether reduction of nutrient limitations in oligotrophic Cerrado soils affects carbon allocation, water relations and hydraulic architecture. Four treatments were used: control, N additions, P additions and N plus P additions. Fertilizers were applied twice yearly, from October 1998 to March 2004. Sixty-three months after the first nutrient addition, the total leaf area increment was significantly greater across all species in the N- and the N + P-fertilized plots than in the control and in the P-fertilized plots. Nitrogen fertilization significantly altered several components of hydraulic architecture: specific conductivity of terminal stems increased with N additions, whereas leaf-specific conductivity and wood density decreased in most cases. Average daily sap flow per individual was consistently higher with N and N + P additions compared to the control, but its relative increase was not as great as that of leaf area. Long-term additions of N and N + P caused midday ΨL to decline significantly by a mean of 0.6 MPa across all species because N-induced relative reductions in soil-to-leaf hydraulic conductance were greater than those of stomatal conductance and transpiration on a leaf area basis. Phosphorus-fertilized trees did not exhibit significant changes in midday ΨL. Analysis of xylem vulnerability curves indicated that N-fertilized trees were significantly less vulnerable to embolism than trees in control and P-fertilized plots. Thus, N-induced decreases in midday ΨL appeared to be almost entirely compensated by increases in resistance to embolism. Leaf tissue water relations characteristics also changed as a result of N-induced declines in minimum ΨL: osmotic potential at full turgor decreased and symplastic solute content on a dry matter basis increased linearly with declining midday ΨL across species and treatments. Despite being adapted to chronic nutrient limitations, Cerrado woody species apparently have the capacity to exploit increases in nutrient availability by allocating resources to maximize carbon gain and enhance growth. The cost of increased allocation to leaf area relative to water transport capacity involved increased total water loss per plant and a decrease in minimum leaf water potentials. However, the risk of increased embolism and turgor loss was relatively low as xylem vulnerability to embolism and leaf osmotic characteristics changed in parallel with changes in plant water status induced by N fertilization. [ABSTRACT FROM AUTHOR]