Search

Effects of permanent (i.e., maintained) and temporary edges with north- and south-facing exposures were studied in sand pine (Pinus clausa var. clausa (Chapm. ex Engelm.) Vasey ex Sarg.) scrub, an open-canopied forest type in Ocala National Forest, Florida. On edges and interiors of four stands of each type, we measured canopy tree architecture in 5 m × 100 m plots and stand density and basal area in 5 m × 200 m plots. Edge effects were modest but often stronger on south- than north-facing edges and along permanent forest roads than temporary edges of clearcuts that were allowed to regrow. Compared with interior trees, those on edges were typically shorter, retained branches lower on their boles, oriented their first branches more towards the edge, and produced more asymmetrical crowns with the long axis extending into the opening; these trends were greater on south- than north-facing edges and along permanent than temporary edges. Contrary to expectations, there were no edge effects on total basal area, dead tree densities, proportions of sand pine trees with leaning trunks, directions of lean, or angles of lean. Instead of an edge effect, most trees leaned towards the southwest, which seems related to the northeastern origin of prevailing winds and wind gusts.

PREMISE To support large leaves, many woody plant species evolved a cost-effective way to thicken twigs. As an extension of E. J. H. Corner's rule that twig diameter increases with leaf size, we hypothesized that pith width also increases with leaf size. The benefit to the plant from the proposed relationship is that pith is a low-cost tissue that reduces the metabolic cost of large diameter twig production. METHODS Leaf sizes and cross-sectional areas of bark, xylem, and pith of 81 species of trees and shrubs growing in Gainesville, Florida were measured and compared with standardized major axis regressions of pairwise species trait values and phylogenetically independent contrasts. RESULTS Pith area increases with leaf size with or without accounting for phylogenetic relationships. In agreement with Corner's rule, overall twig diameter as well as bark and wood thickness also increase with leaf size. Thicker twigs showed more variation in relative pith, wood, and bark cross-sectional areas compared to thinner twigs. CONCLUSIONS Investments in pith, a tissue of low density found in the centers of twigs, provides a low-cost way to increase twig circumference and thereby space for attachment of large leaves while increasing the overall second moment of area of twigs, which increases their ability to biomechanically support large leaves.

Research Highlights: Tree size and wood characteristics influenced the susceptibility of five Amazonian timber tree species to heartwood decay and colonization by termites. Termites occurred in the heartwoods of 43% of the trees, with Coptotermes testaceus the most abundant species. Background and Objectives: Hollows and rotten cores in the stems of living trees have ecological and economic impacts in forests managed for timber. The decision on whether to cut or maintain hollow trees in such forests must account for the susceptibility of different tree species to decay. We investigated tree and wood characteristics of living trees of five commercial timber species in the eastern Amazon that influenced the likelihood of heartwood decay and the occurrence of termite nests inside the rotten cores. Materials and Methods: We used Pearson&rsquo, s correlations and one-way analysis of variance (ANOVA) to explore relationships among tree basal area and hollow area. We used principal components analysis (PCA) to analyze the variation of wood anatomical traits, followed by a linear regression to explore the relationships between PCA scores, and heartwood hollow area. We used a logistic model to investigate if the probability the occurrence of colonies of C. testaceus inside tree cores varied with tree and species characteristics. Results: Heartwood hollow areas increased with stem basal area. Larger hollows were more likely to occur in species with higher vessel and ray densities, and smaller diameter vessels. Termites occurred in the hollows of 43% of the trees sampled, with C. testaceus the most common (76%). The probability of encountering termite nests of C. testaceus varied among tree species and was positively related to wood density. Conclusions: This study shows that given the increased likelihood of stem hollows and rotten cores in large trees, tree selection criteria in managed tropical forests should include maximum cutting sizes that vary with the susceptibility of different tree species to stem decay.

Premise Many perennial herbaceous plants develop underground storage organs (USOs) that store carbohydrates, water, and minerals. The resprouting ability of plants is influenced by the availability of these materials and by the type of underground organ and number of viable buds. In this study, we illustrate the diversity of longleaf pine savanna species and their nonstructural carbohydrate (NSC) pools and concentrations. We also determined whether NSC concentrations by USO are good predictors of NSC pools in species with different types of underground structures. Methods We excavated in their entirety 1-4 individuals of each of 100 ground-layer pine savanna species, classified their USO types, and measured their NSC concentrations and NSC pools. Results The NSC concentrations in underground organs varied widely among the 100 species sampled. Surprisingly, the fibrous roots of Pityopsis graminifolia stored higher concentrations of NSCs than many species with USOs. The relationship between NSC concentrations and NSC pools was strong after controlling for underground biomass. Conclusions Our results revealed the high diversity of underground organs in pine savannas. It also showed that NSC concentrations in species with USOs reach high levels. Predictions of NSC pool sizes from NSC concentrations are interpretable, when corrections for underground biomass are considered. Research on underground organs would benefit from inclusion of morphological-anatomical analyses and phylogenetic controls to promote use of the data in broad-scale analyses.

Made available in DSpace on 2022-04-29T08:32:06Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-11-01 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) When an ecosystem undergoing restoration does not follow the desired trajectory, management interventions may be warranted. Where the initial steps towards restoration include tree planting at high densities, reduction of stand basal area (BA) by overstory thinning is a potential adaptive management tool to stimulate natural regeneration, although it can also damage young plants. We ask how tree regeneration in a restored tropical forest responds to different intensities of thinning. We applied two intensities of thinning to a 22-yr-old restored forest in southeastern Brazil and then sampled seedlings and saplings before and over an eight year period after thinning; unthinned plots were retained as controls. Thinning impacts on the woody understory were negligible, far below annual mortality in control plots. Positive responses to thinning were stronger in the treatment with low remaining basal area (ca. 30% below the reference forests), with increases in seedling density, numbers of recruits, and seedling-to-sapling and sapling-to-tree transitions. Understory dynamics were clearly intensified by gap opening, with a pulse of natural regeneration in the first years after thinning. These changes, however, were not simultaneous and did not usually persist over time. Rarefied richness of the understory increased over time after all treatments and changes in species composition of saplings were enhanced by thinning. Our study gives support to selective timber harvests from restored tropical forests insofar as thinning did not threaten the understory and stimulated natural regeneration. Frequency and intensity of thinning operations, however, should be locally adjusted based on monitoring data. Departamento de Ciência Florestal Solos e Ambiente Faculdade de Ciências Agronômicas Universidade Estadual Paulista “Júlio de Mesquita Filho”, Avenida Universitária, 3780, Altos do Paraíso Floresta Estadual de Assis Instituto de Pesquisas Ambientais, Caixa Postal 104 Department of Biology University of Florida, P.O. Box 118526 Departamento de Ciência Florestal Solos e Ambiente Faculdade de Ciências Agronômicas Universidade Estadual Paulista “Júlio de Mesquita Filho”, Avenida Universitária, 3780, Altos do Paraíso CNPq: #303402/2012 CNPq: #561771/2010-3 CAPES: 001

To assess the impacts of a low-intensity selective timber harvest on a palm community in Belize, we mapped logging infrastructure (i.e., roads, log landings, skid trails, and stumps) and measured palm regeneration 1 year after a timber harvest carried out using reduced-impact logging (RIL) practices. We sampled palms across a gradient of increasing harvest impact severity from areas not directly affected by logging, in felling gaps, on secondary and primary skid trails, and on log landings. We used generalised linear mixed-effect models fitted in a Bayesian framework and applied a non-metric multi-dimensional scaling of the ecological distances between sites to evaluate differences in palm seedling regeneration density and species composition, respectively. The harvest of an average of 2.5 trees ha−1 caused 0.4% of the forest to be converted to log landings, 0.7% and 3.6% to roads and skid trails, and 2.3% to felling gaps, which left 93.0% of the 350 ha harvest block with no direct impacts of logging. The difference in abundance and species composition of palm regeneration in unlogged areas compared to felling gaps and skid trails was small, but log landings had markedly lower densities. These results highlight that the impacts of selective logging are minor at least where harvest intensities are low and RIL practices are employed. If further reductions in canopy opening and soil disturbance are desired, we recommend that logs be cable-yarded (i.e., winched) the final 20 m to skid trails instead of driving to the tree stumps. We estimate that implementation of this practice would reduce total skid trail coverage from 3.6% to 2.9% and overall forest disturbance from 7.0% to 6.3%. However, further reductions in disturbance might be inimical to the maintenance of palms and will certainly not favour regeneration of light-demanding commercial timber species (e.g., Swietenia macrophylla).

Attempts to restore savannas are often thwarted by the resprouting of unwanted woody plants after they are top-killed by fire or mechanical treatments. In an effort to reduce stump sprouting of native to the region but invasive Quercus hemisphaerica (laurel oak) and Q. nigra (water oak) in an area being restored to longleaf pine (Pinus palustris) savanna, we treated 5–19 cm diameter stumps in ways opposite to the recommended practices for coppice management. Specifically, we created high stumps (1 m) and split half longitudinally (1 m-split); we also cut a sample at ground level (0 m), as recommended for coppice management. Over the 9-year observation period about 45% of the stumps died, with no treatment or species effects. Survival of individual sprouts was higher for Q. nigra than Q. hemisphaerica. In both species, sprouts from the 1 m stumps suffered the highest mortality rates, followed by the 0 m and 1 m-split treatments; number of sprouts per stump followed the same pattern (1 m > 0 m > 1 m-split). Root collar sprouts were more likely to survive than those that emerged higher on the stump or from rhizomes, and sprout mortality decreased with stump diameter in Q. nigra but not Q. hemisphaerica. Sprout survival decreased but sprout growth increased with canopy openness. About 40% of all sprouts were from rhizomes. Contrary to our expectation, wood decay was rare in all sprouts, regardless of their diameter or the height from which they emerged. These results confirm the benefits of treating stumps with herbicides to reduce unwanted trees in savannas undergoing restoration.

We compared stump sprouting by three common timber species in Suriname on the basis of sprout origins on stumps, sprout densities, and sprout height:diameter ratios. We then compared some leaf and stem functional traits of 15&ndash, 18-month-old resprouts and nearby conspecific saplings of the same height (0.5&ndash, 3.5 m) but unknown age. Stumps of Dicorynia guianensis Amsh. (29&ndash, 103 cm in diameter) produced the most sprouts (x = 9.2/stump), followed by the 50&ndash, 71 cm diameter stumps of Eperua falcata Amsh. (10.6/stump), and the 30&ndash, 78 cm diameter Qualea rosea Amsh. (5.9/stump), sprout density did not vary with stump diameter. Sprouts emerged from the lower, middle, and upper thirds of the stumps of all three species, but not from the vicinity of the exposed vascular cambium in Qualea. With increased resprout density, heights of the tallest sprout per stump tended to increase but height:diameter ratios increased only in Dicorynia. Compared to conspecific saplings, sprouts displayed higher height-diameter ratios, higher leaf-to-wood mass ratios (LWR), and lower wood densities, but did not differ in leaf mass per unit area (LMA) or leaf water contents. These acquisitive functional traits may reflect increased resprout access to water and nutrients via the extensive root system of the stump. That we did not encounter live stump sprouts from the previous round of selective logging, approximately 25 years before our study, suggests that stump sprouts in our study area grow rapidly but do not live long.

Large trees in the tropics are reportedly more vulnerable to droughts than their smaller neighbours. This pattern is of interest due to what it portends for forest structure, timber production, carbon sequestration and multiple other values given that intensified El Niño Southern Oscillation (ENSO) events are expected to increase the frequency and intensity of droughts in the Amazon region. What remains unclear is what characteristics of large trees render them especially vulnerable to drought-induced mortality and how this vulnerability changes with forest degradation. Using a large-scale, long-term silvicultural experiment in a transitional Amazonian forest in Bolivia, we disentangle the effects of stem diameter, tree height, crown exposure and logging-induced degradation on risks of drought-induced mortality during the 2004/2005 ENSO event. Overall, tree mortality increased in response to drought in both logged and unlogged plots. Tree height was a much stronger predictor of mortality than stem diameter. In unlogged plots, tree height but not crown exposure was positively associated with drought-induced mortality, whereas in logged plots, neither tree height nor crown exposure was associated with drought-induced mortality. Our results suggest that, at the scale of a site, hydraulic factors related to tree height, not air humidity, are a cause of elevated drought-induced mortality of large trees in unlogged plots. This article is part of a discussion meeting issue ‘The impact of the 2015/2016 El Niño on the terrestrial tropical carbon cycle: patterns, mechanisms and implications'.

Sea level rise elicits short- and long-term changes in coastal plant communities by altering the physical conditions that affect ecosystem processes and species distributions. While the effects of sea level rise on salt marshes and mangroves are well studied, we focus on its effects on coastal islands of freshwater forest in Florida's Big Bend region, extending a dataset initiated in 1992. In 2014–2015, we evaluated tree survival, regeneration, and understory composition in 13 previously established plots located along a tidal creek; 10 plots are on forest islands surrounded by salt marsh, and three are in continuous forest. Earlier studies found that salt stress from increased tidal flooding prevented tree regeneration in frequently flooded forest islands. Between 1992 and 2014, tidal flooding of forest islands increased by 22%–117%, corresponding with declines in tree species richness, regeneration, and survival of the dominant tree species, Sabal palmetto (cabbage palm) and Juniperus virginiana (southern red cedar). Rates of S. palmetto and J. virginiana mortality increased nonlinearly over time on the six most frequently flooded islands, while salt marsh herbs and shrubs replaced forest understory vegetation along a tidal flooding gradient. Frequencies of tidal flooding, rates of tree mortality, and understory composition in continuous forest stands remained relatively stable, but tree regeneration substantially declined. Long-term trends identified in this study demonstrate the effect of sea level rise on spatial and temporal community reassembly trajectories that are dynamically re-shaping the unique coastal landscape of the Big Bend.

Predicting responses of vegetation to environmental factors in human-altered tropical ecosystems requires an understanding of the controls on plant population expansion across landscapes (i.e., long-distance dispersal) as well as of factors affecting recruitment at local scales (i.e., microsite conditions). We studied the roles of light availability, habitat type, soil disturbance, and seed dispersal in a selectively logged forest in lowland Bolivia where the exotic forage grass Urochloa (Panicum) maxima is abundant on roads and log landings but does not invade felling gaps or unlogged forest. Shade-house trials and seed addition experiments with U. maxima revealed that this C 4 grass thrives in high light but also grows in partial shade (10% full sun, but not 1% full sun), and that felling gaps, but not undisturbed forest, are suitable for grass establishment. To determine if seed dispersal by logging vehicles explains the discrepancy between actual and potential grass recruitment sites, we collected grass seeds that fell from trucks onto log landings located long distances (> 500 m) from established grass populations. Trucks dispersed an estimated 1800 alien grass seeds per log landing during the early dry season; automobiles also transported seeds of grass (135 seeds/vehicle). The seeds collected (and relative abundances) were the exotics U. (Panicum) maxima (97%) and Urocbloa (Brachiaria) brizantha (2%), and the pan-tropical weeds Sorghum halapense (1%) and Rottboellia cochinchinensis (0.2%). Grasses invade this forest where disturbance coincides with seed dispersal by motor vehicles, while dispersal limitation apparently prevents invasion of many sites otherwise suitable for grass recruitment (i.e., felling and natural gaps).

We test the hypotheses proposed by Gentry and Schnitzer that liana density and basal area in tropical forests vary negatively with mean annual precipitation (MAP) and positively with seasonality. Previous studies correlating liana abundance with these climatic variables have produced conflicting results, warranting a new analysis of drivers of liana abundance based on a different dataset. We compiled a pan-tropical dataset containing 28,953 lianas (Z2.5cmdiam.) from studies conducted at 13 Neotropical and 11 Paleotropical dry to wet lowland tropical forests. The ranges in MAP and dry season length (DSL) (number of months with mean rainfall o100mm) represented by these datasets were 860‐7250mm/yr and 0‐7mo, respectively. Pan-tropically, liana density and basal area decreased significantly with increasing annual rainfall and increased with increasing DSL, supporting the hypotheses of Gentry and Schnitzer. Our results suggest that much of the variation in liana density and basal area in the tropics can be accounted for by the relatively simple metrics of MAP and DSL.

A major impediment to the sustainable management of tropical dry forests in Bolivia is the scarcity of natural regeneration of commercial timber tree species. Where regeneration is present, true seedlings of many species are outnumbered by vegetative sprouts from roots, broken stems, and the stumps of felled trees. This study evaluates the importance of resprouts promoted by logging operations for the regeneration of commercially important canopy tree species. The objectives of the study were: (1) to characterize stump and root sprouting behaviors of canopy tree species harvested for timber; (2) to quantify the effect of logging on relative abundances and growth rates of stump sprouts, root sprouts, and true seedlings; (3) to relate the species-specific probabilities of stump sprouting to stump diameter and stump height; and (4) to explore how sprouting varies with the ecological requirements of canopy tree species. The study was carried out 1–5 years after logging of a privately owned land in a Bolivian tropical dry forest. Twenty-seven of the 31 species monitored resprouted at least occasionally, among which Centrolobium microchaete (Leguminosae-Fabaceae) and Zeyheria tuberculosa (Bignoniaceae) were the most frequent stump sprouters, and Acosmium cardenasii (Leguminosae-Fabaceae) and C. microchaete were the most frequent root sprouters. In all species the number of sprouts declined with increasing stump diameter and stump height. The probability of stump resprouting differed among species but did not vary consistently with stump diameter, except in Z. tuberculosa in which it declined. Approximately 45% of juveniles

SummaryWhile around 20% of the Amazonian forest has been cleared for pastures and agriculture, one fourth of the remaining forest is dedicated to wood production [1]. Most of these production forests have been or will be selectively harvested for commercial timber, but recent studies show that even soon after logging, harvested stands retain much of their tree-biomass carbon and biodiversity [2,3]. Comparing species richness of various animal taxa among logged and unlogged forests across the tropics, Burivalova et al. [4] found that despite some variability among taxa, biodiversity loss was generally explained by logging intensity (the number of trees extracted). Here, we use a network of 79 permanent sample plots (376 ha total) located at 10 sites across the Amazon Basin [5] to assess the main drivers of time-to-recovery of post-logging tree carbon (Table S1). Recovery time is of direct relevance to policies governing management practices (i.e., allowable volumes cut and cutting cycle lengths), and indirectly to forest-based climate change mitigation interventions.

Ilex VomitoriaAit. (Yaupon): A Native North American Source of a Caffeinated and Antioxidant-Rich Tea. Yaupon holly (Ilex vomitoria Ait.) is a caffeine-containing shrub native to the southeastern United States where its leaves and twigs were traditionally used to prepare a stimulating and healthful beverage by Amerindians and more recent colonists. For a variety of mostly socioeconomic and cultural reasons, widespread consumption of yaupon tea ceased by the late 19th century, but the species is widely used in ornamental horticulture. Given the environmental damage associated with other caffeine crops, we believe that disuse of this species is unfortunate, and we report on traits that consumers may consider valuable. We found that total foliar biomass, caffeine, and antioxidant production all increased with nitrogen fertilization in one common ornamental yaupon cultivar, ‘Nana.’ Increasing light availability was associated with increased antioxidant activity but not with the decreased caffeine production predicted by the carbon/nutrient balance hypothesis for secondary metabolite production. We also found the highest caffeine concentrations in another yaupon cultivar, ‘Pendula,’ but suggest that the wide range of chemical variation offered by wild-type yaupon populations renders them more suitable as sources for the development of high caffeine-producing varieties. The results of this study suggest that yaupon is a viable caffeine alternative for North Americans living within its range on the southeastern coastal plain.

We investigated the distribution of sand pine (Pinus clausa) seedlings in relation to the locations of hardwoods and palmettos that had resprouted in five recently clear-cut and one burned stand in sand pine scrub vegetation in Ocala National Forest (Florida, USA). We also studied how the shade and mechanical support provided by the taller resprouts affect the allometry and biomechanics of sand pine seedling stems. Although soil surface temperatures were higher and soil moisture contents (0–5 cm) were lower in open than in covered microsites, sand pine seedling densities did not vary in relation to proximity to resprouted hardwoods and palmettos. There was no apparent nurse plant effect on sand pine seedling distributions, but seedlings that grew up under the resprouts had larger whole stem flexibilities, greater height:diameter ratios, and less tapered stems. In response to the mechanical support and shade of neighboring plants, sand pine seedlings grow taller per unit investment in stem tissue, thereby shortening the period during which they presumably suffer from above-ground competition. This biomechanical plasticity increases the rates at which sand pine seedlings can overtop their resprouted competitors.

Sea-level rise threatens low-lying coastal ecosystems globally. In Florida, USA, salinity stress due to increased tidal flooding contributes to the dramatic and well documented decline of species-rich coastal forest areas along the Gulf of Mexico. Here, we present the results of a study of coastal forest stand dynamics in thirteen 400 m² plots representing an elevation gradient of 0.58-1.1 m affected by tidal flooding and rising sea levels. We extended previously published data from 1992-2000 to 2005 to quantify the full magnitude of the 1998-2002 La Nina-associated drought. Populations of the dominant tree species, Sabal palmetto (cabbage palm), declined more rapidly during 2000-2005 than predicted from linear regressions based on the 1992-2000 data. Dramatic increases in Juniperus virginiana (Southern red cedar) and S. palmetto mortality during 2000-2005 as compared with 1995-2000 are apparently due to the combined effects of a major drought and ongoing sea-level rise. Additionally, coastal forest stands continued to decline in species richness with increased tidal flooding frequency and decreasing elevation. Stable isotope (H, O) analyses demonstrate that J. virginiana accesses fresher water sources more than S. palmetto. Carbon isotopes reveal increasing δ¹³C enrichment of S. palmetto and J. virginiana with increased tidal flooding and decreased elevation, demonstrating increasing water stress in both species. Coastal forests with frequent tidal flooding are unable to support species-rich forests or support regeneration of the most salt-tolerant tree species over time. Given that rates of sea-level rise are predicted to increase and periodic droughts are expected to intensify in the future due to global climate change, coastal forest communities are in jeopardy if their inland retreat is restricted.

Estimation of carbon losses from trees felled and incidentally-killed during selective logging of tropical forests is relatively straightforward and well-documented, but less is known about the fates of collaterally-damaged trees that initially survive. Tree response to logging damage is an important and overlooked ecological process potentially affecting 2–5% of all extant tropical trees. Here we report on the fates of damaged trees over the first 8-years after logging in a transitional Amazonian forest in Eastern Bolivia. Mortality rates of damaged trees peaked in the first year after logging, and then slowly declined to background rates by the end of the study, indicating that if a damaged tree survives 8 years, it then runs approximately the same annual mortality risk as an undamaged tree. Of all types of logging damage, crown damage reduced growth rates the most while inclined trees suffered the highest mortality rates. Neither wood density nor tree size conferred tolerance to damage, though species with bark exudates were less tolerant of damage. Surprisingly, damaged trees survived droughts better than undamaged trees, perhaps due to their proximity to felling gaps and concomitant reduced above- and below-ground competition or due to their reduced leaf areas and associated reductions in water stress. While this study only tests one interaction between an aspect of climate change and logging, we found a positive signal for forest resilience. This response should be considered amongst others in models of managed forests in climate change scenarios.

This chapter examines the pantropical patterns of liana abundance and species diversity and their correlates with climatic characteristics to gain insight into which processes are important for the distribution of tropical lianas. The analyses follow from the standard sampling protocol of liana diversity and abundance used by Alwyn Gentry in the 1980s and 1990s. The chapter examines how climatic conditions are associated with liana density and diversity, by analyzing old-growth continental forests at 850mm yr-1.To broaden the discussion of determinants of liana density and diversity beyond climatic factors, the authors comment on differences between temperate and tropical forests and between continental and island regions. The chapter focuses on sites in the Global Liana Database (GLD) from temperate forests in Australia, subtropical forest in Argentina, and an island in the Caribbean, and also reviews the available literature.

Biomechanical plasticity and within-species growth form diversity are traits that can facilitate invasion by non-native plant species. We support this argument with evidence from the invasion of coastal habitats in northern Florida, USA, by Schinus terebinthifolius and describe some of the consequences of this invasion for overtopped saltmarsh plants. In crowded stands, Schinus grows more like a vine than a tree, with stem height : diameter ratios nearly twice than those observed in open-grown individuals but with no changes in wood density or the modulus of elasticity of stem material. When extracted from the surrounding vegetation, the formerly crowded Schinus stems buckle under their own weight. Schinus crowns also extend much further over adjacent saltmarsh than crowns of Juniperus virginiana, the only other tree species abundant in the study site. Along forest edges, the above-ground biomass of saltmarsh plants overtopped by Schinus crowns was reduced by more than an order of magnitude. The biomechanical plasticity of Schinus allows it to adapt its growth form to suit habitat conditions and can dominate the edges of salt marshes as a sprawling shrub and maritime forests as either a free-standing tree or a woody vine, depending on stand crowding

A recent increase in published studies of lianas has been paralleled by a proliferation of protocols for censusing lianas. This article seeks to increase uniformity in liana inventories by providing specific recommendations for the determination of which taxa to include, the location of diameter measurement points on individual stems, the setting of minimum stem diameter cutoffs, the treatment of multiple-stemmed and rooted clonal groups, and the measurement of noncylindrical stems. Use of more uniform liana censusing protocols may facilitate comparison of independently collected data sets and further our understanding of global patterns in liana abundance, diversity, biomass, and dynamics.

We followed the establishment and growth response of 13 commercial tree species to canopy opening, above-ground biomass removal, and experimental burns of low and high intensities in a lowland dry forest in Bolivia. Three patterns of response to treatments were observed among the most abundant commercial tree species. (1) Shade-intolerant species regenerated mostly from seed and had the highest survival and growth rates following high-intensity burns. (2) Shade-tolerant species were abundant in gap control and plant removal treatments. Treatments had little effect on the height growth of these species. (3) Individuals of root sprouting species were most abundant following plant removal and low-intensity burn treatments. Treatments had little effect on the height growth of these species. The wide variation in species’ responses to gap treatments found in this study not only reinforces the concept that species are distributed along a continuum of shade-tolerance levels, but that other aspects of species’ biology, such as seed dispersal type or sprouting behavior, further differentiate regeneration strategies. The variety of regeneration strategies found among the species at this forest site will require a flexible management scheme that mixes more intensive silvicultural treatments such as prescribed burning with less intensive treatments.

Blanket condemnation of alien species in restoration efforts is counterproductive. Where their presence does not unduly threaten surrounding ecosystems, alien species can be tolerated or even used to good advantage, if they provide essential ecological or socioeconomic services. By speeding restoration or making it more effective, non-native species can provide economic and ecological payoffs. Risk is always an issue when alien species are involved, but greater risk taking is warranted where environmental conditions have been severely modified through human activity than where reassembly of a biological community is the sole goal of restoration.

Liana infestations can be a problem in forests managed for timber because lianas decrease rates of tree growth, damage tree boles, and inhibit tree regeneration. To determine the area from which lianas colonize tree crowns in a liana-rich moist lowland forest in a timber concession in the Department of Santa Cruz, Bolivia, we described “liana sheds” of individual canopy trees (the area under the crown and beyond its margins from which lianas colonize trees). In the same area we tested the hypothesis that pre-logging cutting of lianas in a harvested tree’s liana shed reduces post-logging liana infestations. Prior to logging, 73% of 570 trees >10 cm in DBH representing 12 commercial species, carried at least one liana >2 cm DBH. Liana-infested trees hosted an average of 9.3 lianas (±0.45 S.E., range: 1–68). The mean area of the crown covered by lianas was 35% (±29.7 S.E.) but some trees (10%) were completely covered by lianas. “Liana shed areas” were a function of crown area and varied among tree species. Most lianas on trees were rooted below the crown of their host (90%); the number of lianas decreased with increasing distance from the crown edge, but lianas colonized trees from as far as 8 m beyond the crown. Overall, there was a significant reduction in the number of lianas in 22 felling gaps 8 months after logging where lianas were cut before logging compared with 22 control gaps. In control gaps, the majority of climbing lianas sprouted from the prostrate stems of fallen canopy lianas (81%), including 3.1 km/ha of stems that were rooted along the ground before logging. Liana regeneration in gaps after pre-logging liana cutting occurred mainly by stump sprouting (41%) and sprouting from prostrate stems (48%). Pre-felling liana cutting reduced liana cover in felling gaps by 9% only but reduced liana basal area by 69%. The results of this study suggest that tree crown area, shape, and height are among the most important factors determining the likelihood of liana colonization of canopy trees and that pre-logging liana cutting reduces post-logging liana proliferation in logging gaps.

We conducted a silvicultural experiment to evaluate the effects of lianas on the stem diameter growth of Prioria copaifera (cativo), a valuable timber tree in Panama. Dalbergia brownei, a leguminous liana, is abundant in many riverine P. copaifera-dominated swamp forests in Panama’s easternmost province of Darien, particularly in logged areas. In a forest along the Balsas River, P. copaifera dominated the forest with 96.6% of the total arboreal basal area of 34.8 m2 ha−1 (trees≥10 cm dbh) while D. brownei comprised 96.9% of the total liana basal area of 3.4 m2 ha−1 (stems≥1 cm dbh). After classifying liana infestation as severe or minor for the crown of every tree ≥4 cm dbh in six 25 m ×25 m plots, we cut all lianas in three randomly chosen plots. Prior to treatment 53% of trees were severely infested, 31% had minor infestation, and 16% were liana-free. During the 5 years after treatment, mean annual diameter growth of cativo trees doubled in plots where all lianas were cut compared to control plots, regardless of severity of prior liana infestation. Prioria regeneration was scarce in heavily vine-infested forest compared to nearby permanent plots in forest with low liana infestation. At a cost of only 16 person-hours ha−1, these results suggest that a small investment in cutting lianas can greatly increase wood production in degraded cativo forests.

Gaps created by the death of one or more contiguous trees are common in mangrove forests but are poorly understood. In Kosrae, Federated States of Micronesia, where mangrove wood is harvested for local use, most natural gaps were < 50 m2, whereas most logging gaps were > 100 m2. Interior zones, where access is facilitated by roads, were the most heavily exploited. Although the forests contained 11 species, two species were primarily responsible for gap formation. Natural gaps were caused mainly by broken stems and large branches of Sonneratia alba trees, whereas logging gaps were created primarily by harvesting Rhizophora apiculata trees. Most natural gaps were formed by the fall of more than one tree or branch. Seedling densities were higher in logging gaps than in natural gaps and higher in gaps than under intact canopy. Bruguiera gymnorrhiza was the most common seedling species in gaps and under intact canopy. Relative rates of growth in height were faster in gaps than under intact canopy for R. apiculata and B. gymnorrhiza seedlings. Current harvesting practices on the island do not seem to be altering species richness, although R. apiculata may become less common as gaps are increasingly captured by B. gymnorrhiza.

We consider the mechanism of certification to encourage sustainable harvesting and best management practices of Iriartea deltoidea Ruiz and Pavon, in the context of current land use and agricultural management in Amazonian Ecuador. Interviews and observations with harvesters, storeowners, and furniture-makers provided information about current and potential markets for goods made from the palm. To understand the demographic variables that are critical for population stability, data from five plots in each of three different forest types (mature, secondary, and dissected) were collected. Matrix models were used to develop harvesting simulations through which biological constraints on sustainable harvesting were explored. These simulations suggest that sparing individuals 5–15 m tall when pastures are cleared and adding this palm to current agroforestry polycultures can improve the likelihood of sustainable harvesting for this species. Results showed that harvesting Iriartea could fit within current land use. Some forest colonists clear pastures to graze cattle, while others devote land to agriculture, including polycultures of annuals and perennials. In either case, palms can be left standing when forests are cleared. Swidden agriculture (slash and burn or slash and mulch) depends on a fallow period during which secondary forest may begin to regenerate. These secondary forests are ideal locations for extraction of forest products that fit within the cycle of fallow regeneration in areas near human settlements. Sparing Iriartea individuals 5–15 m tall could benefit agriculture, encourage the sustainability of future harvests, and help ensure the future of this palm as a part of the Amazonian landscape. Interviews with staff of governmental and non-governmental conservation organizations investigated the policy context for certification as a mechanism for conservation. Establishing guidelines for harvesting requires input from all stakeholders in the decision, not simply an ecological analysis. Such guidelines for certifying good management practices, if they are developed, should include provisions for monitoring unanticipated consequences of harvesting or changes in future environmental conditions. Transportation issues and stem drying processes need to be addressed if efforts to expand markets are to succeed. More generally, guidelines for management of forest resources can be improved by combining ecological and social research perspectives; the potential for carrying out such guidelines can be improved by incorporating the knowledge of local forest dwellers and NGOs.

Tree regeneration was compared in burned and unburned portions of a tropical dry forest (1110 mm ppt/year) and a tropical humid forest (1542 mm ppt/year) in southeastern Bolivia. Both forests burned 5 years prior to our study, and both forests were also lightly selectively logged ( intensity m 3 /ha ) —the dry forest during the 1970 and 1980s and the humid forest just prior to the wildfire. The objective of this study was to compare abundance, size, and mode (seedling or resprout) of tree regeneration in burned and unburned areas of these forests, focusing on the most common canopy tree species and the commercial timber species at each site. Regeneration of 13 species of trees was quantified in the humid forest and 12 species in the dry forest. Tree regeneration 20 cm tall was more abundant in the dry forest ( x =1807 stems/ha ) than in the wet forest (x=490 stems/ha ) . In both forests, resprouts were generally larger but less abundant than seedlings. In the dry forest, regeneration of the following commercial tree species was significantly more abundant in the burned areas: Cedrela fissilis, Anadenanthera colubrina, Astronium urundueva, and Centrolobium microchaete. However, Acosmium cardenasii, a canopy tree species not marketed for timber in Bolivia, represented the majority of regeneration (63%) in the dry forest and was equally abundant in burned and unburned areas (∼1100 stems/ha). In the humid forest, only one timber species, Aspidosperma rigidum, was more abundant in burned than unburned areas (51 vs. 0 stems/ha, respectively). Another timber species that is rarely harvested in the region, Pseudolmedia laevis, was significantly less abundant in the burned than unburned area (22 vs. 173 stems/ha, respectively). The results of this study suggest that controlled burning could increase the abundance of timber tree regeneration at the dry forest site and to a lesser extent at the humid forest site. No data were collected to assess the likelihood that this increased density of regeneration will result in increased harvestable timber. However, local forest management institutions do not presently appear capable or motivated to conduct fire management—whether for enhancing timber regeneration or for limiting the damage caused by accidental wildfires.

We examined the effect of disturbances of varying intensity on the dominant modes of regeneration among woody plants in tropical dry forest in lowland Bolivia. Seed survival and density, mortality, height, crown area, and basal diameters of seedlings and sprouts were compared among four treatments of varying disturbance intensity (high-intensity burn, low-intensity burn, plant removal, and harvesting gap) over a period of 18 months following treatments. High- and low-intensity burns reduced densities of viable seed by an average of 94 and 50%, respectively. Tree seedlings were more abundant than tree sprouts in all treatments. There were few differences in seedling density among treatments. Sprouts were most common in the plant removal and low-intensity burn treatments than in harvesting gap and high-intensity burn treatments. Seedling mortality was higher than sprout mortality during the first year following treatments. Sprouts were taller, had more stems per individual, larger crown areas, and larger basal diameters than seedlings. Origin of sprout differed among treatments. Eighteen months following treatments, 85% of individuals >2.5 m tall were sprouts. Most seedlings >2.5 m tall after 18 months had established in high-intensity burn treatments. Sprouting individuals dominated regeneration after all treatments, however, in high-intensity burn treatments, sprouts were relatively less dominant due to smaller sprouts and larger seedlings after high-intensity burns.

Natural forest management in the tropics is often impeded by scarcity of advanced regeneration of commercial species. To supplement natural regeneration in a forest managed by a community in the Selva Maya of Mexico, nursery-grown Swietenia macrophylla seedlings were planted in multiple-tree felling gaps, known as bosquetes. Remnant trees are often left standing in gaps for cultural and economic reasons or due to their official protected status. We focus on these purposefully retained trees and their impacts on planted seedlings. Sampled bosquetes were 400–1800 m2, of which remnant trees covered a mean of 29%. Seedling height growth rates over the first 18 months after out-planting more than doubled with increased canopy openness from 0.09 m year−1 under medium cover to 0.22 m year−1 in full sun. Liana infestations and shoot tip damage were most frequent on seedlings in the open, but, contrary to our expectations, height growth rates were 0.14 m year−1 faster for liana-infested seedlings than non-infested and did not differ between damaged and undamaged seedlings. Apparently the more rapid height growth of well-illuminated seedlings more than compensated for the effects of lianas or shoot tip damage. Despite the abundance of remnant trees and their negative effects on seedling growth, enrichment planting in bosquetes has potential for community-based natural forest management in the tropics in supplementing natural regeneration of commercial species. One obvious recommendation is to leave fewer remnant trees, especially those of commercial species that are non-merchantable due to stem defects and trees retained for no apparent reason, which together constituted half of the remnant crown cover in the sampled bosquetes. Finally, given the rapid growth of lianas and understory palms in large canopy gaps, at least the most vigorous of the planted seedlings should be tended for at least two years.

[Extract] It is important to moderate the often exaggerated expectations about the potential for carbon payments to secure tropical forest conservation, but pessimism also needs to be kept in check. On the pessimistic side, Fisher et al. (Front Ecol Environ 2011; 9[6]: 329–34) estimated that the opportunity costs of conserving forests in Southeast Asia range between US$9860 and US$12 750 per hectare from logging and a further US$11 240 per hectare from subsequent conversion to oil-palm (Elaeis guineensis) plantations. We agree with the authors that these costs exceed any likely payments from international programs for Reducing Emissions from Deforestation and Forest Degradation and enhancement of carbon stocks (REDD+), but we do not think that these figures apply generally across Southeast Asia.

UNLABELLED • PREMISE OF THE STUDY In ecosystems maintained by low-intensity surface fires, tree bark thickness is a determinant of fire-survival because it protects underlying tissues from heat damage. However, it has been unclear whether relatively thick bark i S: maintained at all heights or only near the ground where damage is most likely.• METHODS We studied six Quercus species from the red and white clades, with three species characteristic of fire-maintained savannas and three species characteristic of forests with infrequent fire. Inner and outer bark (secondary phloem and rhytidome, respectively) thicknesses were measured at intervals from 10 to 300 cm above the ground. We used linear mixed-effects models to test for relationships among height, habitat, and clade on relative thickness (stem proportion) of total, inner, and outer bark. Bark moisture and tissue density were measured for each species at 10 cm.• KEY RESULTS Absolute and relative total bark thickness declined with height, with no difference in height-related changes between habitat groups. Relative outer bark thickness showed a height-by-habitat interaction. There was a clade effect on relative thickness, but no interaction with height. Moisture contents were higher in inner than outer bark, and red oaks had denser bark than white oaks, but neither trait differed by habitat.• CONCLUSIONS Quercus species characteristic of fire-prone habitats invest more in outer bark near the ground where heat damage to outer tissues is most likely. Future investigations of bark should consider the height at which measurements are made and distinguish between inner and outer bark.

La gestion des forêts tropicales et les décisions de politique leur ayant trait sont bloquées par un manque d'informations sûres sur les réponses des forêts à la récolte du bois aux autres interventions sylviculturelles. Bien que les données brutes nécessaires provenant des lots d'échantillons (PSPs) existent à priori, les résultats pertinents sont en géneral indisponibles dû à une carence de capacités analytiques au sein des institutions recelant les données, ou à un manque de motivations pour rendre les données disponibles. Quand la déficience analytique est la cause de l'obstacle, les accords de partage des données collaboratives allant au delà du partage d'analyse de données à des partis extérieurs peut fournir des options équitables et efficaces à court et à long terme. Le simple partage d'analyse de données PSP avec des scientifiques établis des pays extra-tropicaux peut résoudre des problèmes à court terme mais ne peut pas préparer la communauté des scientifiques dans les pays tropicaux à faire face aux défis de la recherche future. Le but de tels accords collaboratifs satisfaisant les besoins et les désirs des différentes parties prenantes est compliqué par des différences culturelles et institutionnelles, mais le progrès sur ce terrain est néanmoins évident.

Summary 1. Bark is crucial to trees because it protects their stems against fire and other hazards and because of its importance for assimilate transport, water relationships and repair. We evaluate size-dependent changes in bark thickness for 50 woody species from a moist forest and 50 species from a dry forest in Bolivia and relate bark thickness to their other bark characteristics, species life-history strategies and wood properties. 2. For 71% of the evaluated species, the allometric coefficient describing the relationship between bark thickness and stem diameter was significantly

Lianas are a conspicuous component of many forests, particularly in the tropics. Lianas also compete intensely with trees for belowground resources – primarily water and nutrients. Liana publication rate was extremely low until the 1980s, after which it began a rapid rise. The increase in liana abundance will motivate forest managers to more actively manage lianas in timber-producing forests. Lianas can be used to test basic ecological theory on the factors controlling plant species distribution, the maintenance of species diversity, plant competition, and large-scale structural change in tropical forests. The causes and consequences of increasing liana abundance and biomass will likely become an active area of future study. A deeper understanding of liana life-history strategies and how these strategies enable lianas to compete successfully with trees may reveal the causes of increasing liana abundance and biomass, and the ways in which these increases will alter future tropical forest dynamics.

Liana cutting is a commonly suggested silvicultural practice aimed at reducing the negative impacts of lianas on timber production, but few experimental studies have been conducted to evaluate the cost and efficiency of this practice. In this study, we estimated the cost of cutting lianas in 12 plots of 0.25 ha each in a densely liana-infested forest of lowland Bolivia, and evaluated the efficiency of this silvicultural treatment in terms of the proportion of lianas missed, the density of resprouting liana stumps, and the number of liana-infested trees after two years of an experimental liana treatment.The cost of cutting lianas in this forest by locally hired laborers was 23.6 (SE = 2.48) person-hours/ha. Considering local cost of labor and the U.S.–Bolivian currency exchange rate at the time of the study, this figure translates to ca $15/ha. Liana density decreased from 2471 (SE = 104.3) to 130 (SE = 24.2) liana stems ≥2 cm/ha immediately after cutting, because 5.5 percent of lianas were left uncut (missed). Slender lianas were missed more often than lianas with large-diameter stems. Liana species that grow 2–3 m before they start to twine were also frequently missed. Twenty-two percent of liana stumps ≥2 cm sprouted after cutting. Liana stumps with larger diameters sprouted more than stumps with smaller diameters. Most liana stumps produced only two sprouts. Two years after cutting, 78 percent of trees had no living lianas in their crowns, in contrast to only 13 percent liana-free trees in the control plots. Sixty-four percent of trees still had hanging dead lianas two years after cutting, but only 23 percent of trees were reinvaded by lianas using dead liana stems as trellises.Liana cutting can efficiently reduce the number of lianas in liana-infested forests, and the effects of cutting lianas last for at least two years; however, the treatment is expensive. Thus, we recommend that it is better to view liana cutting as a preventive activity to avoid liana infestation, rather than as a corrective measure after poor management. Liana cutting can be easily conducted along with other reduced-impact logging practices.

Water use patterns of two species of strangler fig, Ficus pertusa and F. trigonata, growing in a Venezuelan palm savanna were contrasted in terms of growth phase (epiphyte and tree) and season (dry and wet). The study was motivated by the question of how C3 hemiepiphytes accommodate the marked change in rooting environment associated with a life history of epiphytic establishment followed by substantial root development in the soil. During the dry season, stomatal opening in epiphytic plants occurred only during the early morning, maximum stomatal conductances were 5 to 10-fold lower, and midday leaf water potentials were 0.5–0.8 MPa higher (less negative) than in conspecific trees. Watering epiphytes of F. pertusa during the dry season led to stomatal conductances comparable to those exhibited by conspecific trees, but midday leaf water potentials were unchanged. During the rainy season, epiphytes had lower stomatal conductances than conspecific trees, but leaf water potentials were similar between the two growth phases. There were no differences in ∂13C between the two growth phases for leaves produced in either season. Substrate water availability differed between growth phases; tree roots extended down to the permanent water table, while roots of epiphytic plants were restricted to material accumulated behind the persistent leaf bases of their host palm tree, Copernicia tectorum. Epiphytic substrate moisture contents were variable during both seasons, indicating both the availability of some moisture during the dry season and the possibility of intermittent depletion during the rainy season. Epiphytic strangler figs appear to rely on a combination of strong stomatal control, maintenance of high leaf water potentials, and perhaps some degree of stem water storage to cope with the fluctuating water regime of the epiphytic environment.

Stranglers must undergo a transformation in growth form from epiphyte to tree to become reproductively mature and thus require developmental and/or physiological plasticity to cope with radical changes in their rooting environment. Differences in leaf structure and water relations between epiphytic-phase and free-standing individuals were marked in the five Ficus species examined. Epiphytic Ficus had several-fold higher specific leaf area (cm 2 g -1 ) and 2- to 4-fold lower stomatal densities than conspecific trees. Osmotic potentials at full saturation were, on average, 0.6 MPa higher (less negative) and the bulk modulus of elasticity approximately 50% lower in epiphytic plants than in conspecific trees. This resulted in leaves of epiphytic and tree individuals losing turgor at approximately the same relative water content, but at a substantially higher leaf water potential in the epiphytic plants. In contrast, differences in leaf structure and water relations between epiphytes and trees of Clusia minor and Coussapoa villosa were small. In greenhouse experiments, alteration of the water and nutrient supply to epiphytic F. tuerckheimmii plants did not lead to significant changes in leaf structure.

Six islands, each less than a hectare in area, were isolated in about 1913 from the mainland of central Panama by the rising waters of Gatun Lake. By 1980, the diversity of trees on all but one of these islands was far lower than on mainland plots of comparable size. A restricted subset of tree species has spread on these islands, notablyProtium panamense, Scheelea zonensis, Oenocarpus panamanus andSwartzia simplex. We constructed a null model to predict how chance would change tree diversity and the similarity of tree species compositions of different islands, assuming that each mature tree has equal chances of dying and/or reproducing, regardless of its species. This model cannot account for the diminished diversity of the changes in vegetation on these islands: some factors must be favoring a particular set of tree species.

Slash pine (Pinus elliottii var. elliottii Engelm.) seedlings (1-0) planted in a cutover stand dominated by 6-year-old coppiced hardwoods and woody vines benefited from reduction in root competition (by trenching) but not from increased light (by guy-wiring back overtopping trees).Over the 2-year experimental period there was no apparent effect of increasing canopy openness from 10% to 30% on pine seedling height, diameter, or aboveground biomass. In contrast, trenching resulted in increased foliar nitrogen and phosphorus concentrations, higher soil moisture contents,and a twofold increase in aboveground growth. The results support the use of site preparation and planting techniques that reduce root competition suffered by pine seedlings. South. J. Appl. For. 16(4):193-197

Relative effects of above-ground and below-ground competition from shrubs (Cornus racemosa and Rhus glabra) on the growth of tree seedlings (Acer rubrum and Fraxinus americana) were assessed with a field experiment in the Hudson Valley, New York. Shade on tree seedlings planted in clumps of shrubs was reduced by guy-wiring back overtopping shrub crowns. Root competition was reduced by cutting a 0.5 m deep slit around the seedlings and inserting root restriction cloth. We also applied a combined treatment to some seedlings and reserved others as controls. In the field with the most severely drained and nutrient-poor soil, reduction of root competition increased relative growth rates of the seedlings while opening the canopy had no effect. Trenching and shade reduction around tree seedlings planted in shrubs clumps in a more mesic old field with a stony silt loam soil increased relative growth rates only if the treatments were combined. In a wet field with alluvial soil, guy-wiring back overtopping shrubs greatly increased seedling growth but trenching alone had no effect. Tree encroachment into shrub-dominated stands can be reduced by both root and shoot competition, but the severity of competition in these arenas varies with site conditions; below-ground competition is intense where soil resources are limited whereas the effects of shade are relatively more severe on sites with good soil.

Logging is an integral component of most conceptual models that relate human land-use and climate change to tropical deforestation via positive-feedbacks involving fire. Given that grass invasions can substantially alter fire regimes, we studied grass distributions in a tropical dry forest 1–5 yr after selective logging, and experimentally tested the effect of forest fire on populations of invasive grasses. In unlogged forests and in microhabitats created by selective logging we found a total of four alien and 16 native grass species. Grasses covered 2% of unlogged and 4% of logged forest, with grass cover in logged forest concentrated in areas directly disturbed by logging; log landings and roads had relatively greater grass cover (37% and 17%, respectively) than did skid trails (10%) and felling gaps (8%). Total grass cover and grass species richness increased with canopy openness and were greatest in sites most severely disturbed by logging. The grass flora of these disturbed areas was composed mostly of native ruderal species (e.g., Digitaria insularis , Leptochloa virgata ), a native bamboo ( Guadua paniculata ), and Urochloa ( Panicum ) maxima , a caespitose C 4 pasture grass introduced from Africa. Urochloa maxima formed monodominant stands (up to 91% cover and 2–3 m tall) and grew on 69% of log landings and 38% of roads. To better understand the potentially synergistic effects of logging and fire on the early stages of grass invasion, we tested the effect of a 12-ha experimental fire on U. maxima populations in a selectively logged forest. Three years after the fire, the area covered by alien grass in burned forest increased fourfold from 400 m 2 (pre-fire) to 1660 m 2 ; over the same period in a logged but unburned (control) area, U. maxima cover decreased from 398 m 2 to 276 m 2 . Increased canopy openness due to fire-induced tree mortality corresponded with the greater magnitude of grass invasion following fire. Selective logging of this dry forest on the southern edge of the Amazon Basin promotes alien grass invasion; when coupled with fire, the rate of invasion substantially increased. Recognition of the grass-promoting potential of selective logging is important for understanding the possible fates of tropical forests in fire-prone regions.

Silvicultural treatments are generally performed to improve yields of commercially valuable tree species by increasing their recruitment and growth rates. In this study we analyze the effects of three different sets of silvicultural treatments on the densities and growth rates of seedlings, saplings and poles of 23 commercial tree species in a moist tropical forest in Bolivia. The treatments vary in intensity of logging and silviculture application, and are compared to a control treatment. Silvicultural treatments applied were liberation of future crop trees from lianas and neighboring competing trees, soil scarification and stand refinements. Treatments were applied to twelve 27-ha plots. In each plot 4 transects were established to assess the density and growth of the regeneration of the 23 commercial species. Effects were measured 1 and 4 years after treatment application and were described using three ecological guilds; shade-tolerant species, partially shade-tolerant species, and long-lived pioneers. We found that the intensive silviculture treatment had the largest impact on the density and growth rates of the regeneration of the commercial species. Overall, the density of regeneration of the commercial species was higher in the control treatment than in the logged treatments 1 year after treatment application, but 3 years later these differences had disappeared. Nevertheless, there were marked shifts in densities when different size classes were considered. In nearly all treatments, the number seedlings decreased over time, while the number of saplings and poles increased. Overall shade-tolerant species were more abundant than the other two ecological guilds. Treatment had a positive effect on density only for long-lived pioneers. Growth of commercial tree regeneration was strongly affected by treatment and was highest in the intensive silvicultural treatment plots where growth of long-lived pioneers was twice that of shade-tolerant species and partial shade-tolerant species. Apart from silvicultural treatments and ecological guild, light availability had the strongest effect on growth rates. These results show that different silvicultural treatments have different effects on the regeneration of commercial tree species and that ecological guilds-specific treatments should be considered in management plans for sustainable timber production in tropical lowland forests.

Using reduced-impact timber-harvesting practices in legally logged tropical forests would reduce global carbon emissions by 0.16 Gt/year at a modest cost and with little risk of "leakage" (increased carbon emissions elsewhere).

Yaupon (Ilex vomitoria) is a caffeine-containing dioecious shrub native to the southeastern United States that was historically brewed into a stimulating beverage. We tested predictions of the carbon/nutrient balance (CNB) hypothesis by determining whether nitrogen availability and gender influence production of caffeine and related alkaloids as well as phenolic compounds in leaves of pot-grown yaupon plants fertilized with ammonium nitrate. The CNB hypothesis predicts that additional nitrogen should result in increased alkaloid concentrations and decreased phenolic concentrations. An extension of the CNB hypothesis to dioecious plants predicts that females have higher C/N ratios and therefore higher phenolic concentrations and lower alkaloid concentrations than male conspecifics. In our study, caffeine and total alkaloid concentrations were 5-10 times higher in fertilized than control plants but did not vary by gender. Nevertheless, an observed interaction between gender and fertilization suggests that females respond more to fertilization than males in caffeine production. In addition, fertilized plants not only contained higher concentrations of alkaloids and total nitrogen but also allocated a larger proportion of their nitrogen to alkaloid production than control plants. Total phenolic concentrations were higher in control females than control males as predicted by the CNB hypothesis, but did not vary by treatment nor were there differences by gender among fertilized plants. We also found high correlations between antioxidant capacity and both classes of phenolic compounds detected in our study (cinnamic acid derivatives and flavonoids) indicating that in addition to their putative defensive function against herbivores, phenolics protect yaupon from oxidative stress. Explanation of the inconsistencies between our data and predictions of the CNB hypothesis may benefit from a re-appraisal of the physiological mechanisms by which resource availability affects secondary metabolism as well as consideration of the selective pressures to which secondary metabolism responds.

Changes in climate and land use that interact synergistically to increase fire frequencies and intensities in tropical regions are predicted to drive forests to new grass-dominated stable states. To reveal the mechanisms for such a transition, we established 50 ha plots in a transitional forest in the southwestern Brazilian Amazon to different fire treatments (unburned, burned annually (B1 yr ) or at 3-year intervals (B3 yr )). Over an 8-year period since the commencement of these treatments, we documented: (i) the annual rate of pasture and native grass invasion in response to increasing fire frequency; (ii) the establishment of Brachiaria decumbens (an African C 4 grass) as a function of decreasing canopy cover and (iii) the effects of grass fine fuel on fire intensity. Grasses invaded approximately 200 m from the edge into the interiors of burned plots (B1 yr : 4.31 ha; B3 yr : 4.96 ha) but invaded less than 10 m into the unburned plot (0.33 ha). The probability of B. decumbens establishment increased with seed availability and decreased with leaf area index. Fine fuel loads along the forest edge were more than three times higher in grass-dominated areas, which resulted in especially intense fires. Our results indicate that synergies between fires and invasive C 4 grasses jeopardize the future of tropical forests.

Vines climb up. From a starting point in the forest understory, vines use the mechanical competence of neighboring plants in their ascent towards the bright sun of the forest canopy. Hemiepiphytes climb down. They begin life in the treetops and extend earthward to form permanent and often substantial connection with the soil (Figure 13.1). Vines and hemiepiphytes hold in common a period of mechanical dependence, yet the physiological consequences and constraints associated with this reliance upon external support differs substantially between the two groups. In vines, adaptations essential for effective climbing constrain their outward form and thus influence the uptake, transport, and storage of energy and materials. For hemiepiphytes, in contrast, the major constraints may not be the particular rigors associated with life as either an epiphyte or a tree, but rather in the plasticity required to succeed as both. Our discussion of tropical vine physiology is morphologically organized, considering in turn the function of stems, leaves, and roots. With hemiepiphytes, we focus primarily on the nature of the transition between the epiphytic and tree growth forms. We draw upon the roles of vines and hemiepiphytes in tropical forest communities only as such discussion provides insights into their physiology.