Search

After hurricane disturbances in tropical forests, the size structure and species composition are affected by immediate mortality, and subsequent recruitment and individual growth. Often, immediate post-disturbance stand-level data are presented but understanding of the components that affect changes in growth and longer-term responses to forest structure and composition are lacking. To answer questions about how mortality, recruitment, and growth change among successional Plant Functional Types (PFT) through time after a hurricane disturbance, we use long-term census data (1989–2014) collected in the Luquillo Experimental Forest, Puerto Rico. We developed an algorithm to fill missing diameter data from the long-term data set that was collected three months after Hurricane Hugo; and subsequently at five-year intervals. Both the immediate hurricane-induced mortality and subsequent mortality were lower in stems with larger diameters, but varied among successional PFTs Early, Mid, Late, and Palm. Tree growth rates were observed to decrease with time since the hurricane disturbance. Five years after the hurricane, mortality was minimal but then increased gradually with time. In contrast, recruitment was highest five years after the hurricane and then decreased with time. The palm Prestoea montana became the most abundant species in the forest after the hurricane, as it had the lowest immediate hurricane-induced and subsequent mortality, and the highest recruitment. Twenty-five years after the hurricane, the palm and the Late PFT dominate the forest after shifting species composition from pre-hurricane conditions.

Hurricanes commonly disturb and damage tropical forests. Hurricane frequency and intensity are predicted to change under the changing climate. The short-term impacts of hurricane disturbances to tropical forests have been widely studied, but the long-term impacts are rarely investigated. Modeling is critical to investigate the potential response of forests to future disturbances, particularly if the nature of the disturbances is changing with climate. Unfortunately, existing models of forest dynamics are not presently able to account for hurricane disturbances. Therefore, we implement the Hurricane Disturbance in the Ecosystem Demography model (ED2) (ED2-HuDi). The hurricane disturbance includes hurricane-induced immediate mortality and subsequent recovery modules. The parameterizations are based on observations at the Bisley Experimental Watersheds (BEW) in the Luquillo Experimental Forest in Puerto Rico. We add one new plant functional type (PFT) to the model – Palm, as palms cannot be categorized into one of the current existing PFTs and are known to be an abundant component of tropical forests worldwide. The model is calibrated with observations at BEW using the generalized likelihood uncertainty estimation (GLUE) approach. The optimal simulation obtained from GLUE has a mean relative error of −21 %, −12 %, and −15 % for stem density, basal area, and aboveground biomass, respectively. The optimal simulation also agrees well with the observation in terms of PFT composition (+1 %, −8 %, −2 %, and +9 % differences in the percentages of “Early”, “Mid”, “Late”, and “Palm” PFTs, respectively) and size structure of the forest (+0.8 % differences in the percentage of large stems). Lastly, using the optimal parameter set, we study the impact of forest initial condition on the recovery of the forest from a single hurricane disturbance. The results indicate that, compared to a no-hurricane scenario, a single hurricane disturbance has little impact on forest structure (+1 % change in the percentage of large stems) and composition ( % change in the percentage of each of the four PFTs) but leads to 5 % higher aboveground biomass after 80 years of succession. The assumption of a less severe hurricane disturbance leads to a 4 % increase in aboveground biomass.

Coastal wetlands are shrinking rapidly due to land-use activities. Accelerated sea-level rise (SLR) associated to the warming climate is also affecting coastal wetlands, particularly in islands with limited coastal plains. We analyzed coastal wetland changes in Puerto Rico by applying the Sea Level Affecting Marshes Model under two scenarios by 2100. We also analyzed mortality and recruitment in a freshwater swamp dominated by the tree Pterocarpus officinalis Jacq. in the context of landscape saltwater-intrusion and drought. Our results indicate mangroves and estuarine water would replace the areas currently covered by other saltwater and freshwater wetlands, and saltmarsh would encounter the most relative loss among wetland types. A moderate SLR of 1 m by 2100 allows expansion of mangroves but would decrease saltmarsh and freshwater wetlands. A 2-m SLR would decrease the distributions of all vegetated wetlands, mostly replaced by estuarine water. In the P. officinalis forest, saltwater-intrusion and drought increased tree mortality during 2003–2015 compared to 1994–2003. Saltwater intrusion had a more significant negative effect on tree recruitment than on mortality in this Pterocarpus forest. Coastal wetlands are facing challenges to their persistence at current locations due to accelerated SLR, limited coastal lands, and a modified hydrological regime.

Streams and rivers of the Luquillo Experimental Forest, Puerto Rico, have been the subject of extensive watershed and aquatic research since the 1980s. This research includes understanding stream export of nutrients and coarse particulate organic matter, physicochemical constituents, aquatic fauna populations and community structure. However, many of the streams and watersheds studied do not appear in standard scale maps. We document recent collaborative and multi-institutional work to improve hydrological network information and identify knowledge gaps. The methods used to delimit and densify stream networks include establishment and incorporation of an updated new vertical datum for Puerto Rico, LIDAR derived elevation, and a combination of visual-manual and automated digitalization processes. The outcomes of this collaborative effort have resulted in improved watershed delineation, densification of hydrologic networks to reflect the scale of on-going studies, and the identification of constraining factors such as unmapped roadways, culverts, and other features of the built environment that interrupt water flow and alter runoff pathways. This work contributes to enhanced knowledge for watershed management, including attributes of riparian areas, effects of road and channel intersections and ridge to reef initiatives with broad application to other watersheds.

Hurricanes can cause severe damage to tropical forests. To understand the nature of hurricane impacts, we analyze and compare immediate effects from category-4 hurricane María in 2017 and category-3 hurricane Hugo in 1989 at Bisley Experimental Watersheds (BEW) in the Luquillo Experimental Forest, Puerto Rico. We show that hurricane María caused lower mortality than hurricane Hugo, even though hurricane María was a stronger event with higher sustained wind. The lower mortality was due to the combination of lower accumulated cyclone energy at the site and more wind-resistant forest structure and composition at the time of disturbance. We compare our study site with a nearby location that has the same forest type, Luquillo Forest Dynamics Plot (LFDP), and describe the similarities and differences of mortality and impact factors between the two sites during the two events. During hurricane Hugo, LFDP experienced much lower mortality than BEW, even though the accumulated cyclone energy at LFDP was higher. The difference in mortality was due to contrasting forest structure and composition of the two sites. Our results demonstrate that forest structure and composition at the time of the disturbance were more critical to hurricane-induced mortality at the two sites than accumulated cyclone energy.

Hurricanes shape ecosystems. A broad range of forested ecosystems is particularly affected by hurricanes, thus creating the need for studies addressing the effects of these disturbances. There is a long history of hurricane and forest research on the Caribbean island of Puerto Rico. In this study, we present results from a systematic literature review of peer-reviewed articles regarding ecological research conducted in Puerto Rico on the topic of hurricanes and forests published from 1900 through 2017. We present a summary of cyclonic activity on the island during the study period and the results from the systematic literature review within this cyclonic context. We discuss findings in terms of aspects of forests studied, geographical distribution of study areas, and time scales at which research was conducted. These findings allow us to determine what was studied about hurricanes and forests, identify gaps in the information, and suggest possible areas of research and production of new knowledge that recent and future storms can bring. We conclude with recommendations identifying research needs and propose additional approaches to complement existing information. Our goal is to generate future knowledge from hurricane and forest research with the broadest applications possible.

Today there is a wide variety of approaches on how to determine when a river restoration project can be considered ecologically successful. The limited information on river restoration responses renders this practice a subjective component of river management. We aimed to contribute to this issue by assessing the ecological outcomes of a restoration project conducted in Quebrada Chiclana, a first-order tropical stream located in the headwaters of the Rio Piedras in the city of San Juan, Puerto Rico. We focused on the reforestation component of the restoration project using current structure and composition of riparian vegetation as an indicator of restoration success. Recovery of riparian vegetation was studied eight years after restoration using a forest succession approach. We conducted a vegetation census and measured structural variables on vegetation at restored and nearby reference areas. We encountered a riparian vegetation community composed of 35 tree and 84 non-tree species. The non-native trees tall albizia ( Albizia procera ) and African tuliptree ( Spathodea campanulata ) were the most abundant tree species within the study area. We observed 11 out of the 16 woody species initially proposed in the reforestation plan but with lower tree density than proposed. Even though we demonstrate that the river restoration project has not yet met its reforestation objectives, our results show recovery of the vegetation community in the impacted area has occurred through natural succession.

The resilience of a global sample of ecosystems to an increase in drought conditions is assessed, comparing data from the early twenty-first with the late twentieth century; results indicate a cross-ecosystem capacity for tolerating low precipitation and responding to high precipitation during recent warm drought and yet suggest a threshold to resilience with prolonged warm drought. The early twenty-first century has seen a global increase in drought conditions. These authors describe the response of plant communities in a global sample of ecosystems to drought stress as a measure of ecosystem resilience, comparing data from the early twenty-first century with the late twentieth century. They find a common range of water-use efficiency values across timescales and locations, with the increases in dry years this century not yet compromising the ability to lower water-use efficiency in response to wetter years. This work will help provide an understanding of how vegetation production will respond to the altered hydroclimatic conditions predicted with climate change, important when making decisions about food production and resource management. Climate change is predicted to increase both drought frequency and duration, and when coupled with substantial warming, will establish a new hydroclimatological model for many regions1. Large-scale, warm droughts have recently occurred in North America, Africa, Europe, Amazonia and Australia, resulting in major effects on terrestrial ecosystems, carbon balance and food security2,3. Here we compare the functional response of above-ground net primary production to contrasting hydroclimatic periods in the late twentieth century (1975–1998), and drier, warmer conditions in the early twenty-first century (2000–2009) in the Northern and Southern Hemispheres. We find a common ecosystem water-use efficiency (WUEe: above-ground net primary production/evapotranspiration) across biomes ranging from grassland to forest that indicates an intrinsic system sensitivity to water availability across rainfall regimes, regardless of hydroclimatic conditions. We found higher WUEe in drier years that increased significantly with drought to a maximum WUEe across all biomes; and a minimum native state in wetter years that was common across hydroclimatic periods. This indicates biome-scale resilience to the interannual variability associated with the early twenty-first century drought—that is, the capacity to tolerate low, annual precipitation and to respond to subsequent periods of favourable water balance. These findings provide a conceptual model of ecosystem properties at the decadal scale applicable to the widespread altered hydroclimatic conditions that are predicted for later this century. Understanding the hydroclimatic threshold that will break down ecosystem resilience and alter maximum WUEe may allow us to predict land-surface consequences as large regions become more arid, starting with water-limited, low-productivity grasslands.

From islands with no permanent flowing streams to those with navigable inland waters, the insular Caribbean contains a great range of conditions regarding the access to freshwater resources. Because of the variation in topography and size, the ability of islands to retain freshwater also varies widely. The usage of freshwater in this region is being led by two major drivers: (1) the demands of basic water needs from an increasing urban population, and (2) those of tourism-based economies that demand water for recreation and aesthetic uses. Formal and informal freshwater management and conservation approaches vary from those being implemented at an individual level based on cultural practices, to those based on government programs. Although most islands have integrated watershed resources practices at some level, economic investment in infrastructure and social governance of water and environment need further evaluation and development. In this overview paper, a description of the natural environment associated to freshwater resources in the insular Caribbean is presented, noting also economic and climatic constraints. Opportunities for improvement in the management of Caribbean freshwater resources are discussed in light of the particular regional environmental context.

When landmasses and shapes. we look If (e.g., at it is a countries) a map, thematic we expect reflecting map; this to see is, their a the map actual portrayed that sizes dislandmasses (e.g., countries) reflecting their actual sizes and shapes. If t is a thematic ma ; hi is, a p that d splays information about a specific theme; the different units are colored according to the information displayed (what is known as a choropleth map), or with symbols representing either quantitative or qualitative information (for example, a proportional symbol map). In the case of the insular Caribbean, logically, the Greater Antilles occupy a larger extent than the Lesser Antilles and the small islands in the northern Caribbean (Map 1). Oftentimes, geographic patterns displayed on regional maps are not easily discernible, particularly for those islands with smaller sizes (this will depend, of course, on the scale and extent of the map). This can be problematic because the information, and ultimately the message that wants to be conveyed through a map, can be overlooked or missed due to the inherent size differences.

The trajectory of hurricane-induced succession was evaluated in a network of forest plots measured immediately before and 3mo, 5, 10, and 15yr after the direct impact of a Category 4 hurricane. Comparisons of forest structure, composition, and aboveground nutrients pools were made through time, and between species, lifehistory groups and geomorphic settings. The hurricane reduced aboveground biomass by 50 percent, causing an immediate decrease in stem density and diversity indices among all geomorphic settings. After 15yr, basal area and aboveground biomass returned to pre-hurricane levels, while species richness, diversity indices, and stem densities exceeded pre-hurricane levels. Differences in species composition among geomorphic settings had not returned after 15yr but differences in stem densities and structure were beginning to emerge. Significant differences were observed in the nutrient concentration of the three species that comprised the most aboveground biomass, and between species categorized as secondary high-light species and primary, low-light species. Species whose abundance was negatively correlated with the mature forest dominant also had distinct nutrient concentrations. When total aboveground nutrient pools were compared over time, differences in leaf nutrients among species were hidden by similarities in wood nutrient concentrations and the biomass dominance of a few species. The observed successional trajectory indicates that changes in species composition contributed to fast recovery of aboveground biomass and nutrient pools, while the influence of geomorphic setting on species composition occurs at time scales 415yr of succession.

A BSTRACT. — Riparian zones are dynamic areas adjacent to flowing freshwater that connect aquatic and terrestrial environments. We measured individual tree distances relative to two permanent streams in the Luquillo Forest Dynamics Plot, Puerto Rico, to determine if tree species exhibit distinct affinities for riparian zones in a mid-montane tropical forest. In addition, we also calculated stem density, species richness, and diversity indices in 20 x 20 m randomly selected quadrats at different distances from the streams. We found that no single species in the study site was predominantly associated with riparian zones; however, almost all species were represented by a few stems in close proximity to streams. Multivariate (Fuzzy Set Ordination) ordination of plot species composition in relation to distance to streams indicated that there is greater variation in species composition closer to streams, and less variation in species composition farther from streams. This study suggests that in mid-montane wet forest, riparian zones include all tree species found throughout the forest landscape. R ESUMEN. — Las zonas riberenas son areas de gran dinamismo adyacentes a cuerpos de agua dulce que conectan a los ambientes terrestres con los acuaticos. Para determinar si hay especies de arboles que se encuentran exclusivamente asociadas a la zona riberena en un bosque humedo de montana, medimos la distancia de arboles individuales en relacion a dos quebradas permanentes en la Parcela de Dinamica Poblacional del Bosque de Luquillo, Puerto Rico. Tambien calculamos cantidad de tallos, riqueza de especies e indice de diversidad en cuadrantes 20 x 20 m que estaban a diferentes distancias de las quebradas. No encontramos especies que estuvieran exclusivamente en las zonas riberenas, sin embargo, casi todas las especies estaban representadas cerca de las quebradas. Encontramos una densidad mas alta de arboles cerca de las quebradas. Un analisis de ordenacion multivariado (Fuzzy Set Ordination) a base de composicion de especies y distancia a las quebradas de cuadrantes 20 x 20 m indico que la composicion de especies en cuadrantes cerca de las quebradas era mas variada que la composicion de especies de los cuadrantes a distancias mayores de 50 metros de las quebradas. Este estudio sugiere que en bosques humedos de montana las zonas riberenas incluyen todas las especies de arboles que se encuentran en el paisaje.

Temperate headwater streams with closed canopies rely on inputs of terrestrially derived organic matter to provide the major energy basis for their food webs. Microbial colonization, or conditioning, makes leaf litter more nutritional and palatable to stream detritivores, but few studies have investigated the relative importance of litter source to macroshredders in tropical streams. We determined the source (terrestrial, aquatic, or aerial), quantity, and species composition of allochthonous inputs into the Quebrada Prieta, a tropical headwater stream in Puerto Rico, as a first step toward understanding the importance of conditioning history to rates of tropical leaf-litter processing by decapod consumers. Fresh leaves of 4 common species of leaves were treated by exposing them to different conditions for 2 wk. These exposure treatments (conditioning histories) represented routes by which leaves might enter streams and included submersion (aquatic input), incubation on the streambank soil (terrestrial input), and suspension above the ground (aerial input). Conditioned leaves were placed in small experimental microcosms with or without shrimp (Xiphocaris elongata) for 20 d. Shrimp significantly increased the rate of decomposition of all leaf species independent of conditioning history. Conditioning history had little effect on breakdown rates independent of the presence of shrimp. One species (Rourea surinamensis) had faster mass loss when the leaves were conditioned as aquatic inputs rather than as terrestrial or aerial inputs. Our results indicate that conditioning history has little effect on the ability of some macroconsumers to alter detrital foodweb dynamics in tropical streams. Tropical stream ecosystems may function differently from temperate ecosystems because of the dominance of large detritivores such as shrimps.

Extreme events (hurricanes, floods, and droughts) can influence upstream migration of macroinvertebrates and wash out benthic communities, thereby locally altering food webs and species interactions. We sampled palaemonid river shrimp (Macrobrachium spp.), dominant consumers in headwaters of the Luquillo Mountains of northeastern Puerto Rico, to determine their distributions along an elevational gradient (274–456 m asl) during a series of disturbances (Hurricane Hugo in 1989, a drought in 1994, and Hurricane Georges in 1998) that occurred over a 15-y period (1988−2002). We measured shrimp abundance 3 to 6 times/y in Quebrada Prieta in the Espiritu Santo drainage as part of the Luquillo Long-Term Ecological Research Program. In general, Macrobrachium abundance declined with elevation during most years. The lowest mean abundance of Macrobrachium occurred during the 1994 drought, the driest year in 28 y of record in the Espiritu Santo drainage. Macrobrachium increased in abundance for 6 y following t...

We show that tropical forest tree saplings with greater belowground carbon allocation have more breakage scars along their stems. We suggest the existence of alternative carbon allocation strategies in relation to physical damage in the forest understorey. “Tolerators” allocate more belowground, have enhanced resprouting ability and slower aboveground growth, whereas “escapers” allocate less belowground, are not well prepared for recovering from damage, but grow fast enough to escape from the damage-susceptible size class.

The science of ecology fundamentally aims to understand species and their relation to the environment. At sites where hurricane disturbance is part of the environmental context, permanent forest plots are critical to understand ecological vegetation dynamics through time. An overview of forest structure and species composition from two of the longest continuously measured tropical forest plots is presented. Long-term measurements, 72 years at the leeward site, and 25 years at windward site, of stem density are similar to initial and pre-hurricane values at both sites. For 10 years post-hurricane Hugo (1989), stem density increased at both sites. Following that increase period, stem density has remained at 1400 to 1600 stems/ha in the leeward site, and at 1200 stems/ha in the windward site. The forests had similar basal area values before hurricane Hugo in 1989, but these sites are following different patterns of basal area accumulation. The leeward forest site continues to accumulate and increase basal area with each successive measurement, currently above 50 m2/ha. The windward forest site maintains its basal area values close to an asymptote of 35 m2/ha. Currently, the most abundant species at both sites is the sierra palm. Ordinations to explore variation in tree species composition through time present the leeward site with a trajectory of directional change, while at the windward site, the composition of species seems to be converging to pre-hurricane conditions. The observed differences in forest structure and composition from sites differently affected by hurricane disturbance provide insight into how particular forest characteristics respond at shorter or longer time scales in relation to previous site conditions and intensity of disturbance effects.

Long-term research on the response of wet forests in the Luquillo Experimental Forest (LEF) to natural and anthropogenic disturbances yielded information useful for the management of these forests and to a better understanding of the functioning of tropical forests and how species composition changes under different disturbance regimes. We summarize studies on basal area removal, response to ionizing radiation, and the effects of hurricanes and landslides on forested watersheds. We also review studies on forested stream biota following hurricane, drought, and flooding events. This chapter also evaluates reforestation of degraded lands and recovery of forests after abandonment of paved roads. All the studies combined cover the major land cover changes that take place throughout the tropics and which require attention to conserve tropical biodiversity. These changes range from limited extractions of resources from forests to deforestation and conversion to pastures. When tropical forests are converted to pastures, more intensive management actions are needed to restore lands, including planting of introduced species capable of growing on degraded lands. Results from the LEF have demonstrated the high resistance and resilience of tropical forests and the success of plantings in the restoration of forest cover on degraded lands. In both streams and forests, species composition shifts from native to introduced species when anthropogenic disturbance regimes become prevalent over the natural disturbance regimes.