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opencc-zeroJan 2022View details →

Not all trees can make a forest: tree species composition and competition control forest encroachment in a tropical savanna

Forest encroachment into savannas is a widespread phenomenon, the rate of which may depend on soil conditions, species composition, or changes in stand structure. As savanna specialist trees are replaced by generalist species, rates of stand development may increase. Because generalists can persist in forests, they are likely to grow more quickly and survive longer in dense stands, compared to savanna specialists. Furthermore, the faster growth rates of generalists may allow them to overtop and outcompete savanna specialists, causing rapid species turnover. We measured growth and survival of 6147 individuals of 112 species of savanna and generalist tree species over a period of 10 years in an ecological reserve in Assis, São Paulo State, Brazil. We modeled growth and mortality as a function of soil texture and nutrients, tree size, competitive neighborhood, and membership in savanna or generalist (species which can persist in forests and savannas) functional groups. Tree growth and survival was strongly influenced by competition, as estimated by the basal area of trees taller than a focal tree. At the stand level, savanna species are unable to contribute basal area growth in closed stands, while generalist species continue to increase in basal area even at high stand basal area. This phenomenon is driven by differences in growth and mortality. Generalists grew faster than savanna species, both in height and diameter. This difference in growth rates led to savanna species becoming suppressed more rapidly than generalists. When suppressed, savanna species were more than twice as likely to die than were generalists. Soils had inconsistent and mostly weak effects which were difficult to separate from gradients of stand structure. Synthesis: We demonstrate that the presence of generalist trees accelerates rates of basal area accumulation due to their greater growth rates and tolerance of shading. Generalists outcompete savanna trees by growing faster in the open and overtopping savanna specialists. Due to the slow growth and high mortality of savanna species in the shade, they are unable to form closed-canopy stands. Accounting for differences among functional types and development of vegetation structure is critical for modeling forest encroachment.

opencc-zeroJan 2022View details →

Lianas and trees exhibit divergent intrinsic water-use efficiency along elevational gradients in South American and African tropical forests

Elevational gradients provide excellent opportunities to explore long-term morphological and physiological responses of plants to environmental change. We determined the difference in the elevational pattern of foliar carbon isotope composition (δ13C) between lianas and trees, and assessed whether this difference arises from changes in photosynthesis or stomatal conductance. We also explored the pattern of nutrient limitations with the elevation of these two growth forms. We conducted inventories of lianas and trees using standardized techniques along elevational gradients in Ecuador and Rwanda. We determined the values of several foliar traits including δ13C and chemical traits in dominant liana and tree species. We set up Bayesian linear mixed-effect models to quantify the effects of elevation and these two growth forms, and the difference of the effect of elevation between the two growth forms on each of the foliar traits. We found consistent growth form specific divergences in foliar δ13C and carbon to nitrogen ratio (C:N) responses to elevation. While we noted a meaningful increase in foliar δ13C and C:N with elevation for trees, lianas did not exhibit such a trend. Foliar δ13C and C:N remained relatively constant for lianas along the transects. The physiological processes at the basis of foliar carbon isotope fractionation shift differently in lianas and trees along elevation. Lianas operate at relatively constant intrinsic water- and nitrogen- use efficiencies with elevation as opposed to trees. Altogether, the study suggests the existence of a functional divergence of water and nutrient use strategies between lianas and trees along tropical elevational transects.

opencc-zeroJan 2022View details →

Data for: The interplay of environmental cues and wood density in the vegetative and reproductive phenology of seasonally dry tropical forest trees

The great phenological diversification characteristic of seasonally dry tropical forests (SDTF) suggests that these patterns result from a complex interplay between exogenous (e.g., climatic) and endogenous (e.g., morphological, physiological, anatomical) factors. Based on the well-established relationships of wood density with water-storing capacity and cavitation vulnerability in woody plants, we hypothesized differential vegetative and reproductive phenological responses to environmental cues for hardwood and softwood species. To test this hypothesis, we compared phenological patterns of pairs of conspecific populations of 10 species differing in wood density, occurring in two localities with slightly different climatic regimes, and evaluated the influence of three environmental variables (rainfall, photoperiod, temperature) on them. Our results, based on the assessment of the overlap of the phenological curves of conspecific populations occurring in different sites and on linear modeling, showed different effects of the environmental factors on phenophase attributes, depending on wood density of the study species, thus supporting our hypothesis. Leaf out in softwood species took place in the dry season, they shed the foliage at the first signs of drought, and once leafless, they flowered and fruited shortly after. By contrast, hardwood species bore leaves and flowers in the rainy season, shed their leaves several months after the rain ceased, and produced fruits during the dry season. We conclude that the role of environmental variables in cueing growth and reproduction cycles in SDTF tree species is interrelated with their wood density, a key endogenous factor crucially linked to plant hydraulics in these water-limited ecosystems.

opencc-zeroFeb 2022View details →

Weak effects of birds, bats and ants on their arthropod prey on pioneering tropical forest gap vegetation

The relative roles of plants competing for resources versus top-down control of vegetation by herbivores, in turn impacted by predators, during early stages of tropical forest succession remain poorly understood. Here we examine the impact of insectivorous birds, bats and ants exclusion on arthropods communities on replicated 5x5 m of pioneering early successional vegetation plots in lowland tropical forest gaps in Papua New Guinea. In plots from which focal taxa of predators were excluded we observed increased biomass of herbivorous and predatory arthropods, and increased density, and decreased diversity of herbivorous insects. However, changes in the biomass of plants, herbivores and arthropod predators were positively correlated or uncorrelated between these three trophic levels and also between individual arthropod orders. Arthropod abundance and biomass correlated strongly with the plant biomass irrespective of the arthropods' trophic position – a signal of bottom-up control. Patterns in herbivore specialization confirm lack of a strong top-down control and were largely unaffected by the exclusion of insectivorous birds, bats and ants. No changes of plant-herbivore interaction networks were detected except for decrease in modularity of the exclosure plots. Our results suggest weak top-down control of herbivores, limited compensation between arthropod and vertebrate predators, and limited intra-guild predation by birds, bats and ants. Possible explanations are strong bottom-up control, a low activity of the higher order predators, especially birds, possibly also bats, in gaps, and continuous influx of herbivores from surrounding mature forest matrix.

opencc-zeroApr 2022View details →

Return of forest structure and diversity in tropical restoration plantings

Stepping-stone restoration plantings can reconcile conservation goals and local land use needs in highly fragmented ecosystems. We explored how initial planting composition influences recruiting plant species density, diversity, abundance, and forest structure in a 13-year-old restoration experiment in Los Tuxtlas, Veracruz, Mexico. Treatments included 8 fenced plantings with animal-dispersed species, 8 plantings with wind-dispersed species, 8 unplanted plots to favor natural succession, and 8 plots in the primary forest as reference sites. We predicted that that by attracting more seed dispersers, animal-dispersed plantings would most closely resemble the primary forest. A census of trees taller than 2 m showed that while wind-dispersed plantings had more recruits, the animal-dispersed plantings most closely resembled the primary forest in pioneer abundance, species density and abundance of biotically-dispersed and abiotically-dispersed plants, individual tree basal area (m2/ha), and vertical structure. The wind-dispersed plantings more closely approximated the forest in non-pioneer abundance and community composition. However, restoration treatments were more similar to each other than to the primary forest and did not differ in plant diversity. Animal-dispersed and wind-dispersed plantings did not differ in non-pioneer species density and matched the primary forest in total plot basal area. Higher abundance of trees in wind-plantings is explained by lower establishment limitations, seed legacy effects, and rapid reproduction of a few planted species. As the experiment continues, we expect treatment effects on seed dispersers will more strongly influence the recruiting plant community, leading the animal-dispersed plantings to more closely resemble the primary forest in diversity and forest structure.

opencc-by-4.0May 2022View details →

Data for: "Above and below ground trait coordination in tree seedlings depend on the most limiting resource: A test comparing a wet and a dry tropical forest in Mexico" by L. Sanaphre-Villanueva, F. Pineda-Garcia, W. Dattilo, L. F. Pinzon-Perez, A. Ricaño Rocha, H. Paz.

These data represent those published in “Above and below ground trait coordination in tree seedlings depend on the most limiting resource: A test comparing a wet and a dry tropical forest in Mexico” by L. Sanaphre-Villanueva, F. Pineda-Garcia, W. Dattilo, L. F. Pinzon-Perez, A. Ricaño Rocha, H. Paz. PeerJ. 2022.

opencc-zeroMay 2022View details →

Range-wide habitat use of the Harpy Eagle indicates four major tropical forest gaps in the Key Biodiversity Area network

Quantifying habitat use is important for understanding how animals meet their requirements for survival and provides information for conservation planning. Currently, assessments of range-wide habitat use that delimit species distributions are incomplete for many taxa. The Harpy Eagle (Harpia harpyja) is a raptor of conservation concern, widely distributed across Neotropical lowland forests, that currently faces threats from habitat loss and fragmentation. Here, we use penalized logistic regression to identify species-habitat associations and predict habitat suitability based on a new International Union for the Conservation of Nature range metric, termed Area of Habitat. From the species-habitat model, we performed a gap analysis to identify areas of high habitat suitability in regions with limited coverage in the Key Biodiversity Area (KBA) network. Range-wide habitat use indicated that Harpy Eagles prefer areas of 70-75% evergreen forest cover, low elevation, and high vegetation species richness. Conversely, Harpy Eagles avoid areas of >10% cultivated landcover and mosaic forest, and topographically complex areas. Our species-habitat model identified a large continuous area of potential habitat across the pan-Amazonia region, and a habitat corridor from the Chocó-Darién ecoregion of Colombia running north along the Caribbean coast of Central America. Little habitat was predicted across the Atlantic Forest biome, which is now severely degraded. The current KBA network covered 18% of medium to high Harpy Eagle habitat exceeding a target biodiversity area representation of 10%, based on species range size. Four major areas of high suitability habitat lacking coverage in the KBA network were identified in north and west Colombia, western Guyana, and north-west Brazil. We recommend these multiple gaps of habitat as new KBAs for strengthening the current KBA network. Modelled area of habitat estimates as described here are a useful tool for large-scale conservation planning and can be readily applied to many taxa.

opencc-zeroMay 2022View details →

Differential nutrient limitation and tree height control leaf physiology, supporting niche partitioning in tropical dipterocarp forests

Revealing the mechanisms of environmental niche partitioning within lowland tropical forests is important for understanding the drivers of current species distributions and potential vulnerability to environmental change. Tropical forest structure and species composition change across edaphic gradients in Borneo over short distances. However, our understanding of how edaphic conditions affect tree physiology and whether these relationships drive niche partitioning within Bornean forests remains incomplete. This study evaluated how leaf physiological function changes with nutrient availability across a fine-scale edaphic gradient and whether these relationships vary according to tree height. Furthermore, we tested whether intraspecific leaf trait variation allows generalist species to populate a wider range of environments. We measured leaf traits of 218 trees ranging in height from 4 to 66 m from 13 dipterocarp species within four tropical forest types (alluvial, mudstone, sandstone, kerangas) occurring along an < 5km edaphic gradient in North Borneo. The traits measured included saturating photosynthesis (Asat), maximum photosynthetic capacity (Vcmax), leaf dark respiration (Rleaf), leaf mass per area (LMA), leaf thickness, minimum stomatal conductance (gdark) and leaf nutrient concentrations (N, P, Ca, K, Mg). Across all species, leaf traits varied consistently in response to soil nutrient availability across forest types except Rleaf_mass, [Mg]leaf and [Ca]leaf. Changes in photosynthesis and respiration rates were related to different leaf nutrients across forest types, with greater nutrient-use efficiency in more nutrient-poor environments. Generalist species partially or fully compensated reductions in mass-based photosynthesis through increasing LMA in more nutrient-poor environments. Leaf traits also varied with tree height, except Vcmax_mass, but only in response to height-related modifications of leaf morphology (LMA and leaf thickness). These height-trait relationships did not vary across the edaphic gradient, except for Asat, [N]leaf, [P]leaf and [K]leaf. Our results highlight that modification of leaf physiological function and morphology act as important adaptations for Bornean dipterocarps in response to edaphic and vertical environmental gradients. Meanwhile, multiple nutrients appear to contribute to niche partitioning and could drive species distributions and high biodiversity within Bornean forest landscapes.

opencc-zeroDec 2021View details →

Data from: Forest loss and treeless matrices cause the functional impoverishment of sapling communities in old-growth forest patches across tropical regions

Landscape-level disturbances, such as forest loss, can profoundly alter the functional composition and diversity of biotic assemblages. In fact, the landscape-moderated functional trait selection (LMFTS) hypothesis states that landscape-level disturbances may act as environmental filters that select a set of species with disturbance-adapted attributes while causing the loss of species with disturbance-sensitive attributes, ultimately compromising ecosystem functioning. However, the impact of landscape patterns on the functional composition and diversity of tropical regenerating trees (saplings) is unknown. Using a multiscale approach to identify the best spatial scale (i.e. the scale of effect), we tested the effect of forest cover, matrix openness and forest patch density (fragmentation) on functional composition and functional diversity of tree saplings in old-growth forest patches (n = 59) in three Mexican rainforest regions with different degree of deforestation. For 368 species and ~23,000 individuals, we compiled information from global and national databases on six functional traits related to seed dispersal and plant establishment and calculated their community abundance-weighted mean (CWMs) and three complementary functional diversity indices. Forest loss and matrix openness reduced functional richness and evenness, but only in the two most deforested regions. Overall, fragmentation had contrasting effects on functional diversity and composition, but correlated negatively with some functional traits in the most deforested region. Importantly, in the regions with high-to-intermediate degree of deforestation, functional composition experienced major changes: maximum height, seed mass, fruit size and wood density decreased, and SLA increased, in forest patches surrounded by open matrices in highly deforested and fragmented landscapes. This caused a shift of community traits towards more disturbed-adapted attributes. Synthesis and applications. In agreement with the LMFTS hypothesis, our results confirm that landscape modifications in regions undergoing high and long-lasting deforestation greatly impoverish the functional composition and diversity of sapling communities. The shift from communities composed mainly by conservative attributes towards communities with a higher prevalence of disturbance-adapted attributes disrupts the future community structure and jeopardizes critical ecosystem functions. Management practices focused on preventing deforestation, increasing forest cover, and promoting treed matrices are necessary to preserve the functionality of these species-rich but increasingly threatened rainforests.

opencc-zeroDec 2021View details →

Phenological status of plants in the very tropical dry forests of Curaçao

Tropical dry plant formations comprise diverse forests found in areas that experience pronounced seasonal changes in precipitation. Across broad regions, variation in the amount and distribution of precipitation determine the availability of water, and thus differences in species composition and phenology. Within any given region hydrology and topographic position, and geologic substrate may underlie additional differences in forest attributes. Of these three factors, geologic substrate is the least understood but it has been suggested that its influence on tropical dry forests, and more broadly speaking tropical forests, results from a combination of mechanisms regulating the use of water and nutrients. Phenological studies at population, community, and system levels acknowledge the significance of plan phenology for different ecological processes. Thus, characterizing phenological patterns at multiple levels of biological organization as a function of geologic substrate is important to assess the diversity of behaviors, and ultimately vulnerability of tropical dry forests to climate change. A study conducted in Curaçao between September of 1992 to February of 1995 at three sites underlaing by different geologies provided a unique opportunity to investigate the extent to which plant phenology diverges in regions underlain by different geologies.

opencc-by-4.0May 2022View details →

Dataset: Substantial organic and particulate nitrogen and phosphorus export from geomorphologically stable African tropical forest landscapes

Raw chemical and stream data from the publication 'Substantial organic and particulate nitrogen and phosphorus export from geomophologically stable African tropical forest landscapes'.  Data shows dissolved and particulate nitrogen and phosphorus concentrations of stream waters of two forested first order streams withing the Congo Basin.

Data for: Elevated inbreeding in Heliconia tortuosa is determined by tropical forest stand age, isolation, and loss of hummingbird functional diversity

Forest conversion and habitat loss are major threats to biological diversity. Forest regeneration can mitigate the negative effects of old growth forest loss on species diversity, but less is known about the extent to which forest loss reduces genetic diversity in remnant populations and whether secondary forests play a role in the maintenance of genetic diversity. We quantified genetic diversity in a tropical hummingbird-pollinated understory herb, Heliconia tortuosa, across a landscape mosaic of primary and secondary forest regrowth. Using microsatellite genotypes from >850 adult and juvenile plants within 33 forest patches and extensive bird surveys, we examined the effect of contemporary and historical landscape features including forest age (primary vs. secondary forest), stand isolation, and pollinator assemblages on genetic diversity and levels of inbreeding in H. tortuosa. We found that inbreeding was up to 3x higher in secondary forest, and this effect was amplified with reductions in primary forest in the surrounding landscape through reduced observed heterozygosity in isolated fragments. Inbreeding in forest patches was negatively correlated with the local frequency of specialist long-distance foraging traplining hummingbirds. Traplining hummingbirds therefore appear to facilitate mating among unrelated plants - an inference we tested using empirically parameterized simulations. Higher levels of inbreeding in H. tortuosa are therefore associated with reduced functional diversity of hummingbirds in secondary forests and forest patches isolated from primary forests. Our findings suggest a cryptic consequence of primary forest loss and secondary forest regeneration through the disruption of mutualistic interactions resulting in the erosion of genetic diversity in a common understory plant.

Litter decomposition rates across tropical montane and lowland forests are controlled foremost by climate

The "hierarchy of factors" hypothesis states that decomposition rates are controlled primarily by climatic, followed by biological and soil variables. Tropical montane forests (TMF) are globally important ecosystems, yet there have been limited efforts to provide a biome-scale characterization of litter decomposition. We designed a common litter decomposition experiment replicated in 23 tropical montane sites across the Americas, Asia, and Africa and combined these results with a previous study of 23 sites in tropical lowland forests (TLF). Specifically, we investigated (1) spatial heterogeneity in decomposition, (2) the relative importance of biological factors that affect leaf and wood decomposition in TMF and, (3) the role of climate in determining leaf litter decomposition rates within and across the TMF and TLF biomes. Litterbags of two mesh sizes containing Laurus nobilis leaves or birchwood popsicle sticks were spatially dispersed and incubated in TMF sites, for 3 and 7 months on the soil surface and at 10-15 cm depth. The within-site replication demonstrated spatial variability in mass loss. Within TMF, litter type was the predominant biological factor influencing decomposition (leaves > wood), with mesh and burial effects playing a minor role. When comparing across TMF and TLF, climate was the predominant control over decomposition, but the Yasso07 global model (based on mean annual temperature and precipitation) only modestly predicted decomposition rate. Differences in controlling factors between biomes suggest that TMF, with their high rates of carbon storage, must be explicitly considered when developing theory and models to elucidate carbon cycling rates in the tropics.

Size-dependent intraspecific variation in wood traits has little impact on aboveground carbon estimates in a tropical forest landscape

There is increasing evidence that intraspecific trait variation plays a role in governing rates of ecosystem functioning. While wood traits such as wood specific gravity (WSG) and wood carbon concentration (WCC) are key drivers of forest aboveground carbon (AGC) stocks, the sources of intraspecific variation in these wood traits and the consequences of this variation on AGC are poorly known, especially in the tropics. Here, we investigated intraspecific variation in wood specific gravity (WSG) and wood carbon concentration (WCC) from 556 individual trees belonging to 15 species that well characterize different successional stages of seasonal evergreen forests in Southeast Asia. Specifically, we tested the contribution of individual or species characteristics (tree size, growth rate and regeneration guilds) and local environmental conditions (topographic wetness index and successional stages) to intraspecific variation in WSG and WCC, and assessed the consequences of intraspecific variation in these wood traits on AGC estimates in 14 permanent forest plots established along a successional gradient in Khao Yai National park, Thailand. We found that tree size was the main driver of intraspecific variation in WSG and WCC as tree sizes increased from 10−100 cm in diameter, WSG increased by 7.3%, while WCC increased by 2.4% in heartwood, 1.6% and 2.7% in sapwood without and with volatile carbon included. There was no effect of the topographic wetness and other local environment condition in wood traits led to a slight overestimation of AGC in young secondary forests (+0.09 to +1.29%) and a small underestimation in older forests (-0.86 to -2.87%), but overall AGC estimates (13 of 14 forest plots) remained within error margins (the 95% interval). Our study provides evidence that tree size variation translates into intraspecific variability in wood traits, whereas local environmental conditions related to topography successional stages had no effect on wood trait variability. While size-dependent variation in WSG and WCC have largely been undocumented and thus ignored in forest carbon assessment approaches, we highlight that it has a limited impact on AGC estimates, indicating that it does not invalidate current forest carbon stock estimation approaches.

Highly-replicated soil, topography and vegetation sampling across an old-growth tropical rain forest landscape

Here we present data from highly-replicated sampling of soil, topography, and vegetation across an old-growth tropical rainforest landscape at the La Selva Biological Station, Costa Rica. Samples were taken at 100 x 50 m spacing using an existing surveyed grid system. The 573-ha sample area spanned a variety of soil, topographic and vegetation conditions, including flat terraces on old alluvial soil, ridge tops and steep slopes on residual soil, riparian habitats and fresh-water swamps. At each of 1170 grid points we established a circular 0.01 ha quadrat (radius = 5.64 m). We sampled soil at 30-50 cm depth with a soil augur and collected a sample for subsequent analysis. We measured slope angle with a clinometer and slope direction with a compass. We measured stem diameter to +1 mm with a synthetic fabric diameter tape for all stems >10 cm diameter (N= 5236) at 1.3 m from the ground or to ~ 6 m height if there were basal irregularities. We classified stems to life form (tree, palm, liana), and identified all trees and palms to species or morphospecies (N=266; lianas were not identified to species). We collected vouchers from all trees that we could not positively identify in the field (N=920). As a whole the data set presents an integrated view of soil, topography and vegetation across a mesoscale old-growth tropical rain forest landscape. The data have been used to refine a reserve-wide soils map for La Selva, and for a variety of papers analyzing the interactions of soil, topography and species distributions at landscape scales (see the 10 papers listed in the Related Works section below). There are no restrictions at all on the use of these data, and we think they will be useful for teaching and analysis projects as well as further original research applications. The data also provide a detailed benchmark of the status of old-growth vegetation in 1993-95 for one of the most intensively studied tropical rain forest landscapes in the world. Because the data are accurately georeferenced and detailed metadata on all methods are provided, this study could be repeated at any time to assess the trajectory of vegetation changes at La Selva, particularly in relation to local disturbances and changing regional and global climates.

opencc-zeroJul 2022View details →

Are fine roots 'leaves underground' in terms of allometry? A test in a tropical forest successional series in southwest China

Fine roots have been hypothesized to be "leaves underground" in terms of vascular network, but this hypothesis has rarely been tested within the framework of metabolic scaling theory (MST). We measured average fine-root (diameter < 1 mm) mass (M), surface area (A), volume (V), diameter (D) and length (L) for 216 soil cores from 24 plots across four successional stages in tropical forests of Xishuangbanna (southwest China), and examined eight scaling relationships between these variables at the individual root scale. We tested whether fine-root allometries conformed to MST's model for leaf (MSTl) or model (MSTw) for woody organs (e.g. trunk). We also assessed the relative effects of environmental factors, tree size, species composition and diversity, and stand structural factors on allometric relationships using structural equation models (SEMs). Our results showed that: 1) Fine-root scaling exponents rarely conformed to MSTl's predictions. 2) The scaling exponents between fine-root M, A, V and D all conformed to MSTw's predictions in later successional forests, but showed greater deviation towards early successional stage. 3) The scaling exponents associated with fine-root length differed markedly from MSTw's predictions. 4) Changes of some fine-root scaling exponents across successional stage were mainly affected by tree size or soil fertility, and species composition affected allometry only indirectly via tree size. Our results suggested that the allometries of individual fine roots largely conform to the scaling rules governing woody organs instead of leaves, probably because leaves are nearly two-dimensional objects while the other two are three-dimensional. We showed that MSTw can well predict some fine-root allometries in later successional forests, suggesting great potential of utilizing MSTw to better estimate fine-root biomass and productivity. However, the present MSTw still needs to be improved for predicting the scaling relationships concerning fine-root length, and also for better quantifying allometric exponents in earlier successional forests.

opencc-zeroSep 2022View details →

Chronic browsing by an introduced mammalian herbivore in a tropical island alters species composition and functional traits of forest understory plant communities

Mammalian herbivores have large-scale impacts on vegetation, altering structure and species composition, especially in tropical grasslands and savannas. However, there is limited understanding of the potential impacts of mammalian herbivores in tropical wet forests, where they are typically less abundant. We investigated the effects of an introduced mammalian herbivore chital (Axis axis) on vegetation structure, composition and leaf functional traits of tropical evergreen forests of the Andaman Islands, India. Across seven islands, representing a gradient of herbivore densities, increasing chital presence was associated with decreased understory richness, understory density and adult tree richness, but was not related to adult tree density or size class distributions. We also found a significant decrease in community-level leaf palatability traits (specific leaf area decreased and leaf thickness increased) with increasing chital habitat use. This community-level shift in leaf trait values was better explained by intra-specific variation in leaf traits across islands rather than changes in species composition. In summary, we show persistent long-term impacts of an introduced mammalian herbivore on understory tropical tree communities although there is little impact on adult tree communities. Our results also show that functional traits of species can be altered in response to novel herbivory, even at herbivore densities where there are no detectable impacts on adult forest structure or composition. Such altered functional traits may potentially alter ecosystem functioning in these forests even without changes in vegetation structure.

opencc-zeroOct 2022View details →

Resilience of a tropical montane pine forest to fire and severe droughts

1. Higher temperatures, declining precipitation, changing cloud cover, and increased wildfires threaten tropical montane pine forests by overriding the environmental heterogeneity that typically buffers these systems from catastrophic fires. Severe fires threaten to overwhelm forest resilience and tip this biome into alternate vegetation states. 2. This study focused on long-term dynamics of montane Pinus occidentalis forests in the Cordillera Central, Dominican Republic, after a ~1000 km2 fire in 2005, the largest since 1965. We used long-term records to investigate climate before and after the fire and a 19-year dataset of pre- and post-fire vegetation change from a network of 55 permanent plots (20 small 0.05 ha plots and 35 large 0.1 ha plots) established in 1999 to model overstorey and understorey vegetation dynamics. 3. The 2005 fire was synchronized with the most extreme drought in the region in over 60 years. The fire burned from < 1600 to > 3000 m a.s.l. in elevation across windward and leeward slopes, creating a mosaic of low-, moderate-, and high-severity patches. Lower elevations, leeward slopes, and stands with a higher proportion of smaller pine trees all burned at higher severities. 4. Growth rates of trees that survived the fire remained lower than pre-fire rates 13 years after the fire. The highest mortality rates were soon after the fire and in the census immediately after the post-fire droughts. Post-fire pine seedling abundance was significantly greater in stands with higher basal area of live canopy trees and significantly reduced by increased shrub abundance in the understorey. Understorey composition recovered rapidly to pre-fire states in sites affected by low- and moderate-severity fires, but sites affected by high-severity fires remained dissimilar to pre-fire composition 13 years after the fire. Even though high-severity patches had persistently low pine regeneration, 100% of small plots and 96% of large plots had at least one pine sapling or canopy tree recruit by 2018. Shrub taxa survived the fire in higher numbers and recovered to pre-fire densities much faster than the pine, especially in high-severity burns. 5. Synthesis. Climate change has increased the likelihood of wildfires in tropical montane pine forests, with long-lasting effects on vegetation dynamics. However, this biome may prove resilient to increasingly severe fires in the near future, given the ongoing recovery of Pinus occidentalis forests in Hispaniola despite repeated severe droughts. Nevertheless, highly drought- and fire-resistant taxa (e.g. shrubs) may form alternate stable states in drier portions of tropical montane landscapes in the future as droughts and high-severity fires become more common.

opencc-by-sa-4.0Apr 2024View details →

Data for: "Different dry-wet pulses favor different functional strategies: a test using tropical dry forest tree species" by Vega-Ramos, Flor, Cifuentes Gómez, Lucas, Pineda-García, Fernando, Dawson, Todd, Paz, Horacio

These data represent those published in "Different dry-wet pulses favor different functional strategies: a test using tropical dry forest tree species" by Vega-Ramos, Flor, Cifuentes Gómez, Lucas, Pineda-García, Fernando, Dawson, Todd, Paz, Horacio