Antillean dry forests have experienced high levels of human impact for almost five centuries. Economic changes in the second half of the 20th century have facilitated forest recovery in Puerto Rico. We quantified the extent of forest cover and the community composition of representative forest fragments in the subtropical dry forest life zone (sensu Holdridge, 1967) in southwestern Puerto Rico. Forest cover, which was largely eliminated by the 1940s, stood at 48% in the western dry forest life zone in 1993. Fragments varied in land-use history and supported from 1% to 86% of the reference species sampled in Guanica Forest, a 4000-ha protected area. Reference species were well represented in forest fragments, even those smaller than 1 ha, if they had never been completely cleared, but were uncommon in forests regenerating on previously cleared sites. The studied fragments are novel ecosystems which combine native and introduced elements; Leucaena leucocephala (Lam.) De Wit, an introduced legume, was the most common species, regardless of land-use history. (C) 2012 Elsevier B.V. All rights reserved.

The physiognomy of Caribbean dry forest is shorter, denser and contains a greater proportion of multi-stemmed trees than other neotropical dry forests. Our previous research, conducted after Hurricane Georges in 1998, has shown that dry forest trees sprout near the base following hurricane disturbance, even if the trees have not incurred structural damage. However, for these hurricane-induced sprouts to contribute to the physiognomy of the forest, they must grow and survive. We followed sprout dynamics and stem mortality on 1,407 stems from 1998, after Hurricane Georges, until 2005. The number of surviving sprouts and the proportion of sprouting stems decreased during the 7-year period, but the sprouting rate was still 3-fold higher and the proportion of sprouting stems 5-fold higher than before the hurricane. Mortality of non-sprouting stems (15.4%) was about the same as for sprouting stems (13.9%) after 7 years. The mean length of the dominant sprout surpassed 1.6 m by 2005, with over 13% of the dominant sprouts reaching subcanopy height. Sprout growth and survival varied among species. These results demonstrate that, despite some thinning, hurricane-induced sprouts survive and grow and that the unique physiognomic characteristic of Caribbean dry forests is related to hurricane disturbance.

Globally, dry forests represent a threatened ecosystem, and documentation of biodiversity in the few remaining remnants of dry forest is needed as a basis for conservation planning. Guanica forest, one of the best remaining representatives of subtropical dry forest habitat, supports the richest, and most complete native dry forest lizard community on the island of Puerto Rico. The lizard community there is comprised of 10 species, some of which are differentially distributed among coastal scrub, deciduous, and semi-ev green forest. Anolis cristatellus and Sphaerodactylus nicholsi are the most abundant in all forest types, while Anolis cooki, a threatened species, is restricted to coastal scrub habitat. Sphaerodactylus nicholsi was most abundant in habitats where leaf litter was deep, especially in humid ravines. These data on lizard community composition and abundance in a relatively undisturbed dry forest provide insights into dry forest community ecology and a reference against which other dry forest lizard communities in disturbed or otherwise impacted habitats can be compared.

The effects of habitat fragmentation on termite communities and wood decom- position rates were investigated in subtropical dry forest fragments in the southwestern region of Puerto Rico. The composition of the termite community and the abundance of individual ter- mite species were determined in small (<1 ha), medium (1-10 ha), and large (>10 ha) forest fragments and compared to a relatively undisturbed tract of contiguous dry forest (Guánica Commonwealth Forest). In a subset of these sites, wood bundles were set out for a period of 1 year in order to estimate rates of wood decomposition. The composition and structure of ter- mite communities did not differ significantly between the forest fragments and the contiguous forest site, while rates of wood decomposition for a representative dry forest tree species were significantly lower in the fragments. These results indicate the problems associated with in- ferring the response of an ecosystem process to habitat fragmentation based solely on the re- sponse exhibited by the community of organisms that mediates the process.

The biomass of component parts of individuals of three dominant canopy tree species in the northern savannas of Australia was determined from field populations in World Heritage Kakadu National Park. Forty individual trees of Eucalyptus tetrodonta F. Muell., E. miniata Cunn. ex Schauer and E. papuana F.Muell., representing a range in size from 4 to 50 cm diameter at breast height (DBH), were felled for dry biomass of leaves, branches, woody stems and bark. Forty-seven other trees of E. tetrodonta and E. miniata were excavated for belowground biomass, by using trenching methods. The average proportion of aboveground biomass in foliage was 3–5%, to branches 20–32%, and trunk wood 77–59%, with little change over the size of a tree. Water content of foliage decreased with size of tree in all species, indicating an increasing xeromorphy as the trees age. Gross morphology of roots was bimorphic, with 70% of biomass at <20-cm soil depth, and large roots running horizontally on top of the shallow (0.3–1.4 m) ferricrete layer. There was no evidence of roots having access to water below this layer. Patterns of heights, percentage biomass allocation, percentage water content, and bark thickness of the three species were consistent with the rank order of their distributions across a topographic gradient, reflecting relative capacities to withstand drought, belowground competition and fire. By using tree diameter as the independent variable (x in cm DBH), allometric relationships were calculated to provide a method for calculating growth and productivity by using non-destructive repeat measures of sizes of trees. The total aboveground biomass (y in kg) of individual trees is y = 0.2068x2.3191 for E. tetrodonta, y = 0.1527x2.390 for E. miniata and y = 0.0356x2.8567 for E. papuana. Total belowground biomass per tree for E. tetrodonta is y = 31.150e0.0601x and for E. miniata, y = 28.753e0.0644x. As a tree grows, the aboveground biomass increases as a power function and belowground biomass as an exponential function of DBH, producing a decreasing proportion of total biomass below ground, e.g. the root/shoot ratio of E. tetrodonta is 0.50 for trees <10 cm DBH, 0.40 for trees 20 cm DBH, and 0.25 for trees 40–55 cm DBH. The overall proportion of total biomass below ground in Kakadu is well below 50%, contrary to the commonly accepted notion that the majority of biomass in savannas is below ground.

Given the variety of nesting locations (e.g., arboreal, epigeal, subterranean) and range of colony sizes exhibited by termites, a quantitative sampling scheme must incorporate multiple techniques in order to ascertain the abundance of all termite species in a particular area (Eggleton & Bignell 1995). A protocol for sampling the termite community of a subtropical dry forest is presented here. This protocol utilizes the colony as the sampling unit because, as a result of their reproductive division of labor, the effective population size of social insects is better represented by the abundance of colonies rather than the abundance of individuals. Previous studies investigating the abundance of termite colonies have been restricted to species that construct epigeal mounds (e.g., Redford 1984) or arboreal nests (e.g., McMahan 1996). Therefore, the main objective of this paper is to report the abundance of colonies for an assemblage of termite species with a variety of nest types. Colony densities for species belonging to the primitive family Kalotermitidae are presented here for the first time. The majority of southwestern Puerto Rico is classified as subtropical dry forest life zone (sensu Holdridge 1967) by Ewel & Whitmore (1973). Annual precipitation in this life zone is seasonal and ranges from 600 mm in the west to 1000 mm in the east. Guánica Commonwealth Forest, situated within the center of the dry forest life zone, represents one of the best remaining examples of subtropical dry forest in the world (Murphy & Lugo 1990). It is comprised of three major intergrading plant associations: coastal scrub forest, deciduous forest and semievergreen forest. Deciduous and coastal scrub forest account for most forest cover, with semievergreen forests restricted to ravines and sinkholes (Lugo et al. 1978). Therefore, two deciduous-forest sites and one coastal-scrub site were selected in order to characterize termite communities in this subtropical dry forest. The two deciduous-forest sites differed in their history of human disturbance. One of the deciduous-forest sites is a mosaic of recovering and relatively unimpacted forest stands while the other site is located in an area that has received a minimal amount of human disturbance over the past 60 years. This quantitative survey of the termites of Guánica Forest was conducted during the summer of 1997. Previous collections of termites from Puerto Rico (Jones & Scheffrahn, unpublished) documented 10 species (3 families, 8 genera) from th e islan d’s su btropical dry forest life zon e. Due to the variability in size and location of the termite colonies found in this region, two sampling regimes Tropical Ecology 41(1): 119-122, 2000 ISSN 0564-3295 © International Society for Tropical Ecology

The subtropical dry forests of Puerto Rico are found mainly on the island’s southwest coast in the rain shadow of the central mountain system. Studies of the 4000-ha Guánica Forest have provided basic information on ecology and management potential. Even on the more favorable sites, the dry forests are smaller in stature and biomass, lower in biodiversity, lower in productivity, and more seasonally pulsed in tree growth, reproductive cycles, and organic matter turnover than forests in areas of higher and less seasonal rainfall. The limestone-based soils are primarily mollisols, characterized by high organic matter, low bulk density, and high pH. Soil nutrient contents are relatively high, but less than 2% of the P is in a readily available form. Nevertheless, because of the proportionately small nutrient inventory in biomass, it appears that the soil nutrient pool could sustain several rotations of aboveground biomass removal without depleting reserves to a level that would immediately jeopardize forest productivity. Relatively rapid recovery of a cut-over dry forest occurs if stump and root sprouts are allowed to survive. Because of sprouting, most plant species are reestablished within 3 years, and aboveground biomass accumulates to almost half of precut levels within 13 years. Chronically disturbed sites, however, are much slower to recover. On the basis of the available ecological data, we make recommendations concerning the conservation, utilization, and management of dry forests and offer suggestions concerning research needs.

Net aboveground primary production (NPP) at 725 m in elevation in the colorado forest (montane rain forest, sensu Beard; lower montane wet forest, sensu Holdridge) of the Luquillo Mountains of Puerto Rico averaged 7.60 t/ha yr on two 0.4-ha permanent plots and was determined by summing aboveground biomass accrual (0.59 t/ha yr), litterfall (6.80 t/ha yr), and herbivory (0.21 t/ha yr). The total leaf area index (trees, epiphytes, and ground vegetation) was 4.95 m2/i2, the aboveground woody volume and biomass, 220 m3/ha and 130 t/ha, respectively, and standing herbivory and the herbivory rate, 5.1 and 4.0 percent/yr, respectively. The mean standing crop of litter was 680 g/m2, with a turnover rate of 0.78 times per year. Of the structural features studied over a 600-m elevational gradient in the Luquillo Mountains, the number of trees per hectare, basal area, and soil organic matter increased with elevation; whereas, the specific leaf area, canopy height, range of tree diameters, forest volume and biomass, leaf area index, and species richness declined. Of the dynamic features studied, ingrowth and mortality of trees, tree growth (diameter, volume, and biomass growth), litterfall, loose litter, standing herbivory and herbivory rates, litter turnover, aboveground woody NPP, and total NPP all declined with an increase in aboveground elevation. The structural and floristic impoverishment of forests and changes in forest dynamics with ascent in the Luquillo Mountains reflect cooler temperatures, fog, and heavier rainfalls that interact to produce saturated soils and retard the mineralization of organic matter.

ABSTRACTThe distribution of the nutrients N, P and K in soil and vegetation and their mobility through litterfall and decomposition in mature and successional stands of a subtropical dry forest were studied in Guánica, Puerto Rico. Soils of the Guánica forest have high total amounts of N (9100 kg/ha), P (1820 kg/ha), and K (7460 kg/ha). However, high extractable Ca (>4000 mg/g) and pH (> 7–8) may explain why only 1.3 and 25% of the total P and K, respectively, were extractable. Total ecosystem storage of N, P and K was 10,300, 1900 and 7700 kg/ha, respectively, of which vegetation stored only 10, 2 and 3%, respectively. Litterfall returned 26, 18 and 180% per year of the N, P and K stored in the ground litter compartment. Trees retranslocated about 30 and 65% of the N and P required to satisfy aboveground net primary production and immobilized P in dead roots. Slow leaf decomposition (7.3 yr for 95% decomposition) released K faster than mass, P as fast as mass, and ash and N slower than mass. The use efficiency of P by litterfall was high compared with other tropical forests, while that of N and K was similar to other tropical and temperate forests. Cutting and regrowth of vegetation resulted in differences in the nutrient concentration in litterfall and nutrient use efficiency of successional vegetation.

With the limited supplies of nutrients and water in the Lake Michigan sand-dune habitat, environmental factors which affect seedling growth also strongly affect survival. In this study, soil temperature, rainfall frequency, nutritional status of the soil, and species-specific water relations were studied as to their effects on the growth of Ptelea trifoliata L. seedlings. Root development was examined carefully since previous studies had indicated that root growth sufficient to reach a permanent water supply was critical for survival. Growth was stimulated by the temperature and soil-moisture conditions which occur in early spring. Fertilization, especially N and P, strongly stimulated growth. In addition, P. trifoliata produced adventitious roots when buried. Survival of seedlings was not enhanced by any adaptation to conserve water because plant resistances to water flow were typical of mesic species. Consequently, high transpiration rates occur in the sand-dune habitat, increasing the importance of good root growth. If adequate water is available, the high transpiration rates may help the seedling tolerate the high temperatures of this environment. Thus, Ptelea trifoliata seedlings possess no single characteristic that explains their ability to survive in the rigorous dune habitat, but possess many characteristics that contribute to their success.

(1) Changes in vegetation structure, species composition, and species dominance were studied over the first twenty-two months of succession after the cutting and burning of several mature tierra firme (i.e. non-flooded) forest sites in south Venezuela in the upper Rio Negro region of the Amazon Basin. To explain the observed succession, additional field investigations were undertaken. (2) Four months after burning the density of plants was less than 1 m-2. The density of successional woody plants, forbs, and grasses increased rapidly from the fourth to the tenth month of succession. There was little change in plant density between the tenth and twenty-second month, but a large change in vegetation height occurred during this time. By the twenty-second month a loose canopy of Cecropia spp. was present at 5 m height. (3) Many of the forest tree species sprouted from the stump when cut, but burning killed sprouts and significantly reduced the size of the seed bank. Nevertheless, the first successional woody colonizers established from seed which survived the burn. The first forb and grass colonizers established from seeds dispersed onto the site after the burn. (4) The common successional woody species had bator bird-dispersed seeds. Many forbs and grasses had wind-dispersed seeds. (5) Population densities were low during the first months of succession because of the low density of propagules and because the low rainfall during this time was not favourable for seedling germination or establishment. The rapid increase in plant density after about the fourth month occurred because the early colonizers had then begun to produce, and disperse locally, large numbers of seeds. (6) There were six distinct microhabitat types present on the sites after burning. Most species tested showed distinct microhabitat preferences.

An analysis of the energy inputs and outputs for conuco agriculture (i.e., shifting cultivation) and a comparison of productivity between conuco crops and successional vegetation was undertaken near the town of San Carlos de Rio Negro in southern Venezuela.

Aim Tropical dry forests in the Caribbean have an uniquely short, shrubby structure with a high proportion of multiple-stemmed trees compared to dry forests elsewhere in the Neotropics. Previous studies have shown that this structure can arise without the loss of main stems from cutting, grazing, or other human intervention. The Caribbean has a high frequency of hurricanes, so wind may also influence forest stature. Furthermore, these forests also tend to grow on soils with low amounts of available phosphorus, which may also influence structure. The objective of this study was to assess the role of high winds in structuring dry forest, and to determine whether soil nutrient pools influence forest response following hurricane disturbance.