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The establishment of native trees in exotic forest plantations can improve economic and ecological outcomes, and functional traits can help understanding differential responses of growth rates to stand variables. It is well known that growth rates can depend on functional traits and that the associations between functional traits and plant growth vary across ontogenetic stages. Here we studied if the response of growth rate to stand variables, that reflect ecological conditions, is associated with wood density, seed mass and height at maturity and if such relationships differ between saplings and seedlings. We measured the stem diameter increment over two years in 164 seedlings and 290 saplings of 30 tree species in 9 loblolly pine plantations in the Atlantic Forest, Argentina. The relationship between stem diameter increment and stand basal area, mean canopy openness and stand age was evaluated. The growth rate of saplings decreased with basal area and increased with canopy openness in species with wood density < 0.56 g.cm-3 or height at maturity > 23 m. No differences in growth rate response were found along seed mass. No consistent relationships between growth rate and stand variables were found in seedlings. We concluded that seedling growth rate is unrelated to stand variables while responsive species at sapling stage are those with low wood density or medium-high height at maturity. Silvicultural treatments reducing basal area can benefit the planted trees as well as unplanted saplings of medium-high valued native trees. [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]

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]

Abstract: Liana abundance and host tree colonization dynamics during a 10-year period were studied in a subtropical Atlantic Forest in Northeastern Argentina. The impact of liana and woody bamboo cutting on liana abundance and diversity, tree infestation and advanced tree regeneration (individuals >5cm and <10cm DBH) was assessed during the same time period. Six permanent 1ha plots (three control and three cutting plots) were located in the year 2000 in a native forest stand. Three plots were subjected to bamboo and liana cutting (BLC) and other three left as control (C). All lianas regardless of their diameters were cut. Liana abundance and basal area increased more than 50% after ten years in C plots, while the proportion of trees infested with lianas increased from 69% in 2000 to 83% in 2010 in the same plots. In this time period some trees species were able to shed their lianas but increased liana load was observed in other tree species which accounted for the increased proportion of infested trees. In BLC plots the proportion of infested trees was similar (about 60%) in 2000 and 2010, indicating a rapid liana colonization of trees after the treatment. Trees with short branch-free boles were rapidly re-infested compared to taller trees. Liana abundance and basal area were substantially lower in BLC compared to C plots, consistent with the relatively short period of colonization in the cutting plots. Tendriled lianas decreased more than twiners and scramblers. Liana richness and species evenness was not affected by the cutting treatment. Advance tree regeneration was partially affected: tree sapling abundance was similar between C and BLC plots but tree basal area was slightly lower in 2010 in C plots indicating that the treatment enhanced sapling growth. No differences in liana infestation on tree saplings were found between C and BLC plots in 2010. Our results indicate a rapid recovery of lianas after cutting, particularly for individuals smaller than 2.5cm DBH, and a substantial effect of this silvicultural treatment applied to enhance tree regeneration. Similar to other tropical forests, a relatively large increase in liana abundance and tree infestation, as observed in C plots, is occurring in this semideciduous forest. [Copyright &y& Elsevier]

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]