Explore the vast range of titles available.

Sent to Cuba to visit the father he barely knows, Edver is surprised to meet a half-sister, Luza, whose plan to lure their cryptozoologist mother into coming there, too, turns dangerous.

Aims Understanding the role of invasive species in ecological communities, and how native and invaders interact to shape the composition, biodiversity, and structure of contemporary forests, is crucial for effective management and conservation action. This is especially important in tropical regions, for which the mechanisms and consequences of invasion remain understudied compared to temperate forests despite increasing research on the effects of invasives during recent decades. Here, we evaluate the roles of invasive species composition, topography, and habitat in shaping the composition and biodiversity of native tree communities in tropical forests. Location Puerto Rico, United States. Methods We analysed data from 188 permanent plots across closed‐canopy and post‐agricultural secondary forests. Multivariate analysis of variance and variation partitioning were used to quantify the contributions of invasive species composition (NMDS axes derived from species‐level densities [stems/ha]), habitat (forest type, soil type, forest age, historical land use), and topography (elevation, slope, aspect) to variation in native tree composition and biodiversity. Analyses were conducted island‐wide and within each of three forest types (dry, moist, and wet forests). Results Invasive species composition, habitat, and topography explained ~14% of the variation in native tree composition and ~39% of the variation in biodiversity. Invasive species composition, forest type, forest age, elevation, and slope were the primary characteristics accounting for such variation at both scales (island‐wide and within each forest type). The full models for native composition and biodiversity were significant at both scales. The relative importance of invasive species composition, habitat, and topography on the composition and biodiversity of native tree communities differed among forest types, but general patterns were the same, with habitat characteristics explaining the greatest amount of variation, followed by topography and invasive species composition. Main Conclusions Invasive species modify the composition and biodiversity of native trees in Puerto Rico. Combined with land‐use changes and habitat attributes, they have the potential to significantly alter the composition of tropical forests, with long‐term consequences for biodiversity management and conservation.

\"Without risking life or limb, readers can explore the wonders and beauty of the Amazon in this Where Is...? title\"-- Provided by publisher.

Understanding the role of alien species in forest communities, and how native and alien species interact to shape the composition and structure of contemporary forests, is of critical importance to invasion ecology and natural resource management. We used vegetation data collected over a 20‐year period in 341 permanent plots representing remnants of closed‐canopy forests and post‐agricultural secondary forests across Puerto Rico to compare changes in the composition and abundance of native and alien woody species in plots with and without aliens across different forest types and to assess whether aliens and natives show divergence or convergence regarding functional roles and ecological strategies. We also tested the applicability of Grime's CSR (competitive, stress‐tolerant, and ruderal strategies) theory to explain naturalization success. Species richness and abundance of natives are consistently lower in plots in which aliens are present compared with those without them. This negative association between aliens and natives has been consistent over the 20 years and across all forest types. Both native and total richness slightly increased over the 20 years, but the increase in native species richness was three times lower in plots with aliens relative to those without aliens. The CSR classification provided insight into the naturalization success of aliens. Corroborating the “join the locals” hypothesis, aliens use the same functional spaces as natives. The exception is in dry forests, where aliens and natives differ in the use of functional spaces, a result that corroborates the “try harder” hypothesis. Generally, aliens were better competitors compared with natives, and natives were more stress‐tolerant than aliens. Our combined results suggest that alien species may inhibit population growth or even drive local changes in native plant communities by transforming the assembly and dynamics of tropical forests. Ultimately, modifications linked to invasive species may have significant implications for local forests, affecting their regeneration and productivity. More definitive conclusions require additional plot censuses, and analyses of disturbance regimes and stand‐age structure to reveal the long‐term implications of alien species on regenerating tropical forests, including their vulnerability, resilience, and adaptive capacity to cope with various aspects of climate change.

Hurricane-caused tree mortality in tropical dry forests occurs predominantly in early successional species. Consequently, hurricanes may accelerate succession in these forests. Forest regeneration, however, must be measured over an extended posthurricane time period to demonstrate this pattern. In this study, we recorded tree seedlings in 19 Florida Keys forests during May–August 1995, 3 years after Hurricane Andrew. For these forests—spanning a chronosequence from 14 to over 100 years since the most recent clearing—we used weighted averaging regression on relative abundances of pre-hurricane trees to calculate a successional age optimum for each species; and used weighted averaging calibration to calculate inferred successional ages for stands based on pre-hurricane trees and on posthurricane seedlings. To test the hypothesis that successional stage of seedlings exceeded successional stage of pre-hurricane trees, we compared inferred stand ages based on posthurricane seedlings with those based on pre-hurricane trees. Across the study area, inferred stand ages based on posthurricane seedlings were greater than those based on pre-hurricane trees (P < 0.005); however, more seedlings in the youngest stands were early successional than in older stands. Of 29 species present both as pre-hurricane trees and posthurricane seedlings, 23 had animal-dispersed seeds. These results provide evidence that: (1) hurricanes do not ‘reset’ succession, and may accelerate succession; and (2) a strong legacy of stand successional age influences seedling assemblages in these forests.

A tree species replacement sequence for dry broadleaved forests (tropical hardwood hammocks) in the upper Florida Keys was inferred from species abundances in stands abandoned from agriculture or other anthropogenic acitivities at different times in the past. Stands were sampled soon after Hurricane Andrew, with live and hurricane-killed trees recorded separately; thus it was also possible to assess the immediate effect of Hurricane Andrew on stand successional status. We used weighted averaging regression to calculate successional age optima and tolerances for all species, based on the species composition of the pre-hurricane stands. Then we used weighted averaging calibration to calculate and compare inferred successional ages for stands based on (1) the species composition of the pre-hurricane stands and (2) the hurricane-killed species assemblages. Species characteristic of the earliest stages of post-agricultural stand development remains a significant component of the forest for many years, but are gradually replaced by taxa not present, even as seedlings, during the first few decades. This compositional sequence of a century or more is characterized by the replacement of deciduous by evergreen species, which is hypothesized to be driven by increasing moisture storage capacity in the young organic soils. Mortality from Hurricane Andrew was concentrated among early-successional species, thus tending to amplify the long-term trend in species composition.

We studied the ecological characteristics of 45-50-yr-old subtropical dry forest stands in Puerto Rico that were growing on sites that had been deforested and used intensively for up to 128 yr. The study took place in the Guánica Commonwealth Forest. Our objective was to assess the long-term effects of previous land use on this forest--i.e., its species composition, structure, and functioning. Previous land-use types included houses, farmlands, and charcoal pits. Stands with these land uses were compared with a nearby mature forest stand. The speed and path of forest recovery after deforestation and land-use abandonment depended on the conditions of the land. Study areas where land uses had removed the forest canopy and altered soil conditions (houses and farmlands) required a longer time to recover and had a different species composition than study areas where land uses retained a forest canopy (charcoal pits). Different forest attributes recovered at different rates. Crown area index, stem density, and litterfall rate recovered faster than stemwood and root, biomass, tree height, and basal area. Where previous land uses removed the canopy, Leucaena leucocephala, a naturalized alien pioneer species, dominated the regrowth. Native species dominated abandoned charcoal pits and mature forest. The change in species composition, including the invasion of alien species, appears to be the most significant long-term effect of human use and modification of the landscape.

Dead wood is a substantial carbon stock in terrestrial forest ecosystems and hence a critical component of global carbon cycles. Given the limited amounts of dead wood biomass and carbon stock information for Caribbean forests, our objectives were to: (1) describe the relative contribution of down woody materials (DWM) to carbon stocks on the island of St. John; (2) compare these contributions among differing stand characteristics in subtropical moist and dry forests; and (3) compare down woody material carbon stocks on St. John to those observed in other tropical and temperate forests. Our results indicate that dead wood and litter comprise an average of 20 percent of total carbon stocks on St. John in both moist and dry forest life zones. Island-wide, dead wood biomass on the ground ranged from 4.55 to 28.11 Mg/ha. Coarse woody material biomass and carbon content were higher in moist forests than in dry forests. No other down woody material components differed between life zones or among vegetation categories (P > 0.05). Live tree density was positively correlated with fine woody material and litter in the moist forest life zone (R= 0.57 and 0.84, respectively) and snag basal area was positively correlated with total down woody material amounts (R= 0.50) in dry forest. Our study indicates that DWM are important contributors to the total biomass and, therefore, carbon budgets in subtropical systems, and that contributions of DWM on St. John appear to be comparable to values given for similar dry forest systems.

Tropical land-use changes can have profound influence on earthworms that play important roles in regulating soil processes. Converting tropical forests to pastures often drastically increases the abundance of exotic earthworm populations such as Pontoscolex corethrurus. We initiated this study to examine the influence of exotic earthworms on the decomposition of plant leaves and roots in a tropical pasture and a wet forest of Puerto Rico. We employed two treatments: control with natural earthworm population, and earthworm reduction using an electroshocking technique. Decomposition rates of plant leaves on the ground surface and root materials within the surface mineral soil were estimated using a litterbag technique. To understand the role that exotic earthworms play in altering plant litter decomposition, we also compared soil CO2evolution rates, soil microbial biomass, and physical and chemical soil properties between the controls and earthworm-reduced plots during a one-year period. Earthworm populations in the electroshocked enclosures were reduced by 85% and 87% as compared with pasture and forest controls by the end of the experiment. Earthworm reduction significantly decreased the annual decay rates of plant leaves but had no effects on those of plant roots in both pasture and forest sites. Although the control plots had less mass remaining on every litterbag collecting date, significant treatment effects on leaf decomposition occurred only after 240 d in both sites. The decay rates were greater when organic materials had low carbon to nitrogen or phosphorus ratios. Soil respiration was also decreased in the earthworm-reduced plots. In contrast, soil microbial biomass C was not affected by earthworm reduction. Furthermore, there were no significant differences between the two treatments in soil bulk density, moisture content, pH, or temperature at either site. Our results suggest that exotic earthworms may accelerate leaf litter decomposition by elevating rates of litter consumption/digestion or microbial activity, rather than by improving soil physical/chemical conditions or altering microbial biomass.

We studied the ecological characteristics of 45–50‐yr‐old subtropical dry forest stands in Puerto Rico that were growing on sites that had been deforested and used intensively for up to 128 yr. The study took place in the Guánica Commonwealth Forest. Our objective was to assess the long‐term effects of previous land use on this forest—i.e., its species composition, structure, and functioning. Previous land‐use types included houses, farmlands, and charcoal pits. Stands with these land uses were compared with a nearby mature forest stand. The speed and path of forest recovery after deforestation and land‐use abandonment depended on the conditions of the land. Study areas where land uses had removed the forest canopy and altered soil conditions (houses and farmlands) required a longer time to recover and had a different species composition than study areas where land uses retained a forest canopy (charcoal pits). Different forest attributes recovered at different rates. Crown area index, stem density, and litterfall rate recovered faster than stemwood and root, biomass, tree height, and basal area. Where previous land uses removed the canopy, Leucaena leucocephala, a naturalized alien pioneer species, dominated the regrowth. Native species dominated abandoned charcoal pits and mature forest. The change in species composition, including the invasion of alien species, appears to be the most significant long‐term effect of human use and modification of the landscape. RESUMEN Estudiamos las características ecológicas de rodales de un bosque seco subtropical en Puerto Rico que tenían 45‐50 años de recuperación después de haber sido usados intensamente durante 128 años. El estudio se realizó en el Bosque Estatal de Guánica. Nuestro objetivo fue el de evaluar los efectos a largo plazo de los distintos tipos de usos del terreno en la composición de especies, la estructura y el funcionamiento. Los usos de terreno en el pasado incluyeron viviendas, terrenos agrícolas y carboneras. Estos rodales fueron comparados con un rodal de bosque maduro en un área cercana. La rápidez de recuperación y la manera en cómo sucede depende de las condiciones del terreno después de ser abandonado. Las áreas de estudio en las que se había removido el dosel y alterado las condiciones del suelo (casas y terrenos agrícolas) necesitaron más tiempo para recuperarse y reflejaron una composición de suelo diferente a las áreas de estudio donde el dosel se mantuvo (carboneras). Los diferentes atributos forestales se recuperaban a ritmos diferentes. El índice del área foliar de la copa, la densidad de tallos y la caída de hojarasca se recuperaron más rápido que la biomasa de tallos y raíces, la altura de los árboles y el área basal. La especie pionera naturalizada, Leucaena leucocephala (Lam.) de Wit‐Fabaceae, fue la especie dominante en los bosques donde se habia removido el dosel. Las especies nativas dominaban las carboneras abandonadas y el bosque maduro. El cambio en la composición de especies e incluso la invasión de especies foráneas, parece ser el efecto a largo plazo más significativo del uso humano y de la modificación del paisaje.