Luquillo Experimental Forest Research Articles

Effects of Treefall Gaps on the Density of Land Snails in the Luquillo Experimental Forest of Puerto Rico

The effect of disturbance on land snail density in a montane subtropical wet forest was evaluated during wet (March-April) and dry (June) seasons by collecting specimens from quadrats positioned along transects that bisected treefall gaps in the Luquillo Experimental Forest of Puerto Rico. Atmospheric and litter temperature, relative humidity, litter and soil moisture, slope, and substrate type also were measured in each quadrat to determine the effect of these environmental parameters on the spatial distribution of the land snails during two sampling periods in 1989. Of the 34 species of snail known from the forest, only five occurred with sufficient frequency to permit statistical analysis. The abundances of three species (Austrosolenites alticola, Megalomastoma croceum, and Subulina octana) were not significantly different in gap versus nongap areas

Comparison of Tropical Tree Plantations with Secondary Forests of Similar Age

The structure and dynamics of small plantations of pine (Pinus caribaea; 4 and 18.5 yr old in 1980) and mahogany (Swietenia macrophylla; 17 and 49 yr old in 1980) were compared with those of paired secondary forest stands of similar age and growing adjacent to each other under similar edaphic and climatic conditions. The study was conducted in the Luquillo Experimental Forest between 1980 and 1984. Comparisons included a variety of demographic, production, and nutrient cycling characteristics of stands. Although the small unmanaged plantations had a lower number of species in understory than paired secondary forests, the understory of the older plantations developed high species richness, including many of native tree species. After 17 yr, native tree species invaded the overstory of plantations. After 50 years the species richness in the understory of a mahogany plantation approached that of its paired secondary forest. Plantation understories had important ecological roles, including high nutrient accumulation. Understory plant tissue, particularly leaf litter, had higher nutrient concentration in pine plantations than in paired secondary forests. Understory biomass in plantations accumulated a higher proportion of the total nutrient inventory in the stand than did the understory in paired secondary forests. Plantations had higher aboveground biomass and net aboveground biomass production than paired secondary forests. Higher root densities and biomass were found in secondary forests as were greater depth of root penetration, higher nutrient concentration in roots, and more microsites where roots grow, than paired plantations. These characteristics may improve the capacity of secondary forests relative to that of paired plantations to rapidly recapture nutrients that become available by mineralization and that could otherwise be lost through hydrological or gaseous pathways. Both forest types accumulated nutrients and mass, but secondary forests recirculated nutrients much faster than the plantations, which tended to store the nutrients. Plantations had higher leaf fall and total litterfall, had litterfall with lower nutrient concentrations, accumulated more nutrients in litter, decomposed more litter on an annual basis, exhibited more variation in the spatial distribution of litter mass, and had more month—to—month variation in litter storage than paired secondary forests. Litter of the secondary forests, on the other hand, had a faster nutrient turnover than plantation litter, though plantations retranslocated more nutrients before leaf fall than did secondary forests. Nutrient retranslocation increased with plantation age. Plantations, particularly pine plantations, produced more litter mass per unit nutrient return than did paired secondary forests. Total nutrient storage in soil gave the best correlation with nutrient use efficiency estimated as element: mass ratios in various compartments. Nutrient use efficiency ranked differently among forest pairs, depending upon which nutrient and ecosystem parameters were being compared. Because of high retranslocation of nutrients, and in spite of greater nutrient "need" to produce higher biomass, plantations had nutrient demands on soil similar to paired secondary forests. Among the ecosystem parameters measured, nutrients in leaf fall correlated best with differences in soil nutrients across stands. Nutrient concentrations in understory species appeared to be a sensitive indicator of whole—stand nutrient use efficiency. Some of the observations of the study could be attributed to intrinsic differences between small unmanaged plantations and secondary forests, but many could be explained by species differences (i.e., timing of leaf fall), age of plantation (i.e., accumulation of biomass or species), or the relative importance of angiosperms and gymnosperms (i.e., nutritional quality of litter). The study challenges the conventional dogma with respect to differences between plantations and native successional ecosystems and underscores the dangers of generalizing about all tropical tree plantations or all natural tropical forests, or even extrapolating from one sector of the ecosystem to another.

Effect of Topography on the Pattern of Trees in Tabonuco (Dacryodes excelsa) Dominated Rain Forest of Puerto Rico

The structure, composition, and spatial patterns of tree species in two adjacent watersheds of the Luquillo Experimental Forest, Puerto Rico were investigated. Both watersheds had the same vegetational characteristics. Dacryodes excelsa, Sloanea berteriana, and Guarea guidonia were the most important trees in the overstory. A profile diagram, chisquare criterion, and multivariate techniques showed the same result : trees were related significantly to topographic variables. Large trees, especially the dominant species, tabonuco, were associated significantly with ridges and slopes. Size-class distributions of individual species varied as a function of broad ecological factors such as topography and disturbance regime (...)

Hurricane Hugo: damage to a tropical rain forest in Puerto Rico

ABSTRACTHurricane Hugo of September 1989 caused severe damage to the rain forest in the north-rust corner of Puerto Rico. We assessed the severity of damage distributed in space, species, and size-classes of trees in the Bisley Watersheds of the Luquillo Experimental Forest. We analyzed pie- and post-hurricane data for vegetation from transects established in 1987 and 1988. The severity of damage was significantly greater in valleys than on ridges and slopes. All the species exceptDacryodes excelsa, Sloanea berteriana, andGuarea guidoniashowed 100% severe damage. Large trees (> 70 cm DBH) were highly susceptible to hurricane damage, but there was no clear pattern in the small size-classes.D. excelsa(tabonuco) was the most resistant to damage by the hurricane. Tabonuco which has extensive root-grafts and root anchorage to bedrock and subsurficial rocks, apparently can survive frequent hurricanes and continue as a dominant species in this montane tropical rain forest. The high frequency of hurricanes, which can override other ecological and topographic factors, may largely determine the overall spatial pattern of species in this rain forest.

Summary of Ecosystem-Level Effects of Caribbean Hurricanes

Effects of Hurricane Hugo on forest ecosystem processes in Puerto Rico and South Carolina are summarized from six research papers presented in this issue. Hurricanes are major catastrophic disturbances capable of altering ecosystemlevel processes in both the short and the long term. The high intensity, broad scale, and relatively high frequency of these storms makes them a major agent of catastrophic disturbance in the Caribbean and the Atlantic seaboard of the U.S.A. (Scatena & Larsen 1991). Although the return frequency of hurricanes for any given area is low (on the order of years or decades; Fig. 2 in Walker et al. 1991) relative to the lifespan of an individual investigator or a typical research project, the return time is shorter than the life span of a canopy tree or a forest ecosystem. Hurricanes have struck the Caribbean repeatedly within recorded history (Scatena & Larsen 1991, Walker et al. 1991), and have surely played a role in shaping plant population dynamics (e.g., Lugo et al. 1983), soil development (Scatena & Larsen 199 1) and nutrient cycling (Sanford et al. 199 1) over evolutionary time scales (thousands of years) in much of the Caribbean. Our paper summarizes the six preceding research papers in this issue, and focuses on the short-term changes in nutrient cycling induced by Hurricane Hugo, as well as the possible long-term consequences of such disturbances on tropical forests. Data on biomass and nutrient fluxes caused by Hurricane Gilbert in Quintana Roo, Mexico (Whigham et al. 1991, Plant Section, this issue) are included, but the discussion is primarily focused on two Long-Term Ecological Research sites funded by the National Science Foundation: the Luquillo Experimental Forest (LEF) in Puerto Rico and the North Inlet site in South Carolina. The processes summarized below are: hurricane litterfall and associated nutrient fluxes and exports; salinization of coastal soils from storm surge and associated changes in soil chemistry; fine root dynamics after disturbance; changes in soil nutrient pools and fertility; and, hurricane-induced changes in nitrogen (N) transformations and fluxes. DIRECT EFFECTS OF HURRICANE HUGO IN 1989, HURRICANE HUGO STRUCK NORTHEASTERN PUERTO RICO on 18 September with maximum sustained wind speeds of 166 kph, then struck the coast of South Carolina on 21 September with maximum sustained wind speeds of 217 kph. In addition, a storm surge associated with the hurricane inundated the coastal pine forest site in South Carolina. As a result of wind or wind plus salt stress, the forests were largely defoliated in both the Puerto Rican (Lodge et al. 1991, Walker 1991) and South Carolinian (Blood et al. 1991, Gardner et al. 1991) study sites. Consequently, a large amount of green leaves and wood were converted to necromass in all sites (Blood et al. 1991, Frangi & Lugo 1991, Lodge et al. 1991, Table 1). The forests in Quintana Roo, Mexico were similarly defoliated by winds of Hurricane Gilbert in 1988 (Whigham et al. 1991). In the LEF in Puerto Rico, the mass of fine litter resulting from Hurricane Hugo was ca 1000 g/m2 in tabonuco and palm forests, and 625 g/m2 in dwarf forest (Table 1, Lodge et al. 1991). The mass of litterfall resulting from Hurricane Hugo was 1.2 to 2.0 times the mean annual litterfall inputs in the LEF. In Mexico, Hurricane Gilbert induced a litterfall of 836 g/m2 leaves and 1600 g/m2 wood (Table 1; Whigham et al. 1991). In addition, wind structurally damaged or killed some of the trees in Puerto Rico (Frangi & Lugo 1991, Walker 1991), and South Carolina (Gardner et al. 1991). Damage to root systems was also apparent in both sites, though it is unclear to what extent the physical damage resulting from wind or salt stress was exacerbated by the drought of several months that followed the hurricane (Blood et al. 1991, Parrotta & Lodge 1991). ECOSYSTEM RESPONSES TO HURRICANE HUGO NUTRIENT CYCLING.-A large pulse of litterfall containing higher than normal concentrations of certain nutrients and labile carbon was deposited in all sites i Received 5 July 1991, revision accepted 15 July 1991.

Effects of Hurricane Hugo on Manilkara bidentata, a Primary Tree Species in the Luqillo Experimental Forest of Puerto Rico

Changes in the population structure and recruitment characteristics of Manilkara bidentata populations were investigated at two sites (El Verde & Bisley) in the Luquillo Experimental Forest (LEF), at one month and nine months after Hurricane Hugo. Fatal damage occurred to 4 percent of the trees at the El Verde site. Severe damage to mature trees disrupted seed production. Sixty percent of the young seedling population was destroyed, mainly as a result of burial by litter. For surviving seedlings, the posthurricane growth rate (in height) of old seedlings was 2 cm/mo, 17 times greater than that under prehurricane conditions. The prehurricane population of young seedlings had a large number of individuals and a long transition period (over 14 yr); whereas, the posthurricane population had fewer individuals and a shorter transition period (less than 2 yr). Increased growth rates of seedlings were related to increased light at the forest floor. The recruitment rate of the Manilkara population from the seedling size class into the sapling size class was greater than that under prehurricane conditions. Rapid adjustment to posthurricane conditions, high tree survival, and increased number of seedlings recruited into larger size classes may increase the abundance of Manilkara trees in the forest. These adaptations are especially significant in the LEF and other forests which experience frequent hurricane disturbances. Based upon the effects of Hurricane Hugo, it appears that hurricanes play an important role in releasing suppressed seedling growth of Manilkara populations and that hurricanes may contribute to the abundance of Manilkara trees in the LEF.

Tree Damage and Recovery From Hurricane Hugo in Luquillo Experimental Forest, Puerto Rico

Hurricane Hugo struck Puerto Rico on 18 September 1989 with maximum sustained winds of over 166 km/hr (Scatena & Larsen 1991) and caused severe defoliation of 56 percent of the trees in study plots at El Verde in the Luquillo Experimental Forest (LEF). Some trees were uprooted (9%) or had trunks that snapped (11%), but overall mortality was low (7%). Damage was patchy on twenty 300 m2 plots with most damage occurring on north-facing sites. Tall trees and trees with large diameters were most likely to be uprooted, but successional status of trees was not a good predictor of the amount of damage the trees sustained. Recovery patterns varied among species but refoliation was rapid. Widespread sprouting and minimal breakage of large branches will probably lead to the recovery of most trees.

Hurricane Effects on Soil Organic Matter Dynamics and Forest Production in the Luquillo Experimental Forest, Puerto Rico: Results of Simulation Modeling

The forests and soils at Luquillo Experimental Forest (LEF), Puerto Rico, are frequently disturbed by hurricanes occurring at various frequencies and intensities. We have derived a forest version of the Century soil organic matter model to examine the impact of hurricanes on soil nutrient availability and pool sizes, and forest productivity in the tabonuco forest at Luquillo. The model adequately predicted aboveground plant production, soil carbon, and soil nitrogen levels for forest conditions existing before Hurricane Hugo. Simulations of Hurricane Hugo and of an historical sequence of hurricanes indicated a complex pattern of recovery, especially for the first 10 yr after the hurricanes. After repeated hurricanes, forest biomass was reduced, while forest productivity was enhanced. Soil organic matter, and phosphorus and nitrogen mineralization stabilized at higher levels for the LEF than for hurricane-free tabonuco forest, and organic soil phosphorus was substantially increased by hurricanes. Results from these simulations should be regarded as hypotheses. At present there is insufficient data to validate the results of hurricane model simulations.

Differential Seedling Responses to Litter After Hurricane Hugo in the Luquillo Experimental Forest, Puerto Rico

We studied the dynamics of the seedling community in the Luquillo Experimental Forest during one year following Hurricane Hugo, to look at the effect of three litter treatments (continuous litter removal, unaltered litter quantity [controll and continuous litter addition), on seedling emergence, growth, density, and mortality. Total seedling densities (for both newly emerged and established seedlings) were highest in the litter removal treatment, suggesting that litter is a major constraint to recruitment of seedlings. However, species differed in their responses to the three treatments: species characteristic of early succession (Chionanthus domingensis and Cecropia schreberiana ex. C. peltata) were densest in the litter removal treatment, while densities of species characteristic of late succession either did not increase (Sloanea berteriana) or declined (Dacryodes excelsa) in the litter removal treatment. Height growth was lowest and mortality generally highest for seedlings in the litter removal treatment. Variability in species responses to litter after the hurricane may lead to changes in the species composition of the forest.

The Effect of Hurricane Hugo on Bird Populations in the Luquillo Experimental Forest, Puerto Rico

Hurricane Hugo caused severe but short-term disruption of the avian community of a subtropical wet forest site in the Luquillo Mountains of Puerto Rico. Nectarivorous and frugivorous bird species were greatly reduced in numbers immediately after the hurricane. The single granivore species studied decreased in numbers more slowly. Insectivores and omnivores increased after the hurricane. All species except the granivore returned to their prehurricane abundance levels prior to the following breeding season, suggesting that population changes were a result of movement in search of food rather than mortality. Mist net captures and observations indicated that birds occupied a reduced vertical foraging range after the hurricane, and stomach contents from birds captured 6-10 months after the hurricane showed that different foods were being consumed. Fewer and different kinds of arthropods were found in stomachs after the hurricane. These findings, coupled with the frequent occurrence of hurricanes in the Caribbean, suggest that there is pressure on bird populations in this region to maintain plasticity in habitat and dietary requirements.

Post-Hurricane Hugo Increases in Atyid Shrimp Abundances in a Puerto Rican Montane Stream

We report the first data on changes in tropical stream biota resulting from a major hurricane. Beginning in January 1989, we trapped freshwater shrimp, Atya lanipes, along 1200 m of a montane stream in the Luquillo Experimental Forest, Puerto Rico. Prior to Hurricane Hugo, shrimp densities were greater in the headwaters than at mid- and low elevation. In October 1989, one month after the hurricane, shrimp densities were reduced on average by 50 percent in the headwaters (apparently from washout) and increased by 80 percent at mid-elevation. From December 1989 to May 1990 overall shrimp densities increased rapidly to the highest abundances ever recorded. These densities most likely resulted from increased numbers of shrimp that migrated upstream from riverine pools; and, from increased availability of unusually abundant food resources (decomposing leaves and algae) that increased recruitment of these generalized consumers. Benthic communities in forested, headwater streams are likely to be resilient after intermediate levels of disturbance, because rapid debris-dam formation increases retention of food resources and reduces washout of invertebrate consumers. However, storms generating greater stream flow and/or less wind than Hurricane Hugo could cause extensive, longer-lasting decreases of benthic-dwelling shrimp because of greater washout of both consumers and food supplies.

An Introduction to Hurricanes in the Caribbean

THIS ISSUE OF BIOTROPICA brings together, for the first time, a collection of case studies that document the damage to natural ecosystems and the initial recovery process from three recent hurricanes in the Caribbean. The majority of papers address the impact of Hurricane Hugo (1989) and subsequent recovery during the year following the hurricane at three sites: St. John in the U.S. Virgin Islands, Puerto Rico, and South Carolina on the U.S. mainland (Fig. 1). Hurricane Hugo triggered a rapid increase in the level of hurricane research, in part because it passed over two Long-Term Ecological Research sites (Luquillo Experimental Forest, Puerto Rico and North Inlet, South Carolina) which had ecological data that allowed comparisons of prehurricane and posthurricane conditions. Benefits of such long-term studies include the ability to separate damage caused by the recent hurricane from previous damage; to not depend on reconstruction of damage scenarios from historical evidence; and, to begin studies of recovery immediately. Hurricane Hugo also provided an opportunity to contrast hurricane damage in different environments: tropical and temperate, humid and dry, island and continental. In addition to studies of Hurricane Hugo, we include studies of the effects of Hurricane Gilbert (1988) on Jamaica and Mexico, and Hurricane Joan (1988) on Nicaragua (Fig. 1). We have emphasized studies of terrestrial ecosystems; hurricane impacts on marine and coastal ecosystems have been examined elsewhere (Woodley et al. 1981, BenitoEspinal & Benito-Espinal 1991, Finkl & Pilkey 1991). Hurricanes are frequent, large-scale disturbances in the Caribbean. During the period 18711964, zero to eleven hurricanes per year (average = 4.6, median = 8) occurred in the Caribbean (Alaka 1976), resulting in, for example, a return time of 21 yr for the island of Puerto Rico (Salivia 1972). The strongest Caribbean hurricanes typically originate off the western coast of Africa, gain strength as they pass westward over the Atlantic Ocean, and rapidly deteriorate when they reach the mainland somewhere between Panama and New England. Weaker hurricanes and tropical storms (wind speeds 63-119 km/hr) have their origins throughout the Atlantic Ocean, Caribbean Sea, and Gulf of Mexico. With wind speeds of at least 119 km/hr and paths often tens of kilometers wide, hurricanes have a profound effect on plants, soils, animals, humans, and even landforms. Much attention is given to the destruction of property (Saffir 1991, Sparks 1991), and the loss of human lives in these storms. The effects of hurricanes on natural ecosystems (Fig. 2) have also been noted (e.g., Foster 1988) but are less understood. Studies in Puerto Rico suggest that hurricanes may have a major effect in structuring natural ecosystems in terms of age distribution of tropical forest trees (Doyle 1981, Weaver 1986, Lugo & Rivera-Batlle 1987), or biomass and species diversity (Crow 1980). These studies add to the accumulating evidence that suggests natural systems are largely organized by disturbance (Pickett & White 1985, Denslow 1987). The study of how natural ecosystems are altered by hurricanes and how they respond is essential to the understanding of how these systems are structured. Adding urgency to this study is the relationship between hurricanes and global climate change. Slight increases in surface water temperatures or periods of high rainfall in the I Received 28 July 1991, revision accepted 5 August 1991.

Changes in Light Availability Following Hurricane Hugo in a Subtropical Montane Forest in Puerto Rico

The changes in light availability in the understory of a subtropical wet forest (Luquillo Experimental Forest, Puerto Rico) were monitored after the passage of Hurricane Hugo on 18 September 1989. Gallium arsenide phosphide sensors were placed 1 m apart along a 32 m transect. Data were collected for periods of 7-10 d in October and December 1989, and in March, July, and November 1990. Daily histograms were generated for observations of photosynthetic photon flux density (PPFD) taken every two seconds. Mean total daily PPFD was calculated for each sensor in each data set. During the 14 mo after the passage of the hurricane, the PPFD showed a highly skewed distribution with most values 400 m2) treefall gaps. Median total daily PPFD fell to 0.8 mol m-2 d-' in November 1990 because of almost complete coverage of the transect by a canopy of Cecropia schreberiana Miq. ex. C. peltata. An analysis of semivariance was used to discern patterns of autocorrelation in total daily PPFD along the transect. Through March 1990 patches of high and low light separated by distances of 10-12 m were detected. By July 1990 the patchiness was replaced by a pattern that showed no autocorrelation at distances of 1 m or greater.

The Effect of Hurricane Hugo on Six Invertebrate Species in the Luquillo Experimental Forest of Puerto Rico

Although the importance of disturbance regimes in affecting ecosystem structure and function is becoming an accepted paradigm in ecology, the consequences of catastrophic events are poorly understood. On 18 September 1989 Hurricane Hugo struck Puerto Rico, with the center of the hurricane passing within ten kilometers of the Luquillo Experimental Forest. This provided a rare opportunity to document direct and indirect effects of a natural disturbance of high intensity, large scale, but low frequency on selected aspects of animal ecology. The densities and spatial distributions of six species of common invertebrates (four snails, Caracolus caracolla, Polydontes acutangula, Nenia tridens, and Gaeotis nigrolineata, and two walking sticks, Lamponius portoricensis and Agamemnon iphimedeia) in the tabonuco rain forest were estimated before and after the hurricane. Circular quadrats (radius = 5 m; area = 78.54 m2) were established at each of 40 points in the Bisley watersheds. Numbers of individuals of each species were counted during nighttime surveys and densities were compared before and after the hurricane via paired t-tests. Both species of walking stick and three of the four species of snail exhibited statistically significant reductions in density after the hurricane. Densities of N. tridens, G. nigrolineata, and A. iphimedeia were reduced to the point that no specimens were detected in posthurricane surveys. In fact, all species of invertebrates were so rare after the hurricane that comparisons of spatial distribution were only possible for C. caracolla, and its distribution was significantly less clumped after Hurricane Hugo (G-test). At the Bisley watersheds, all size categories of C. caracolla suffered similar reductions in density; no significant alteration in size distribution was detected after the hurricane (G-test).

The Impact of Hurricane Hugo on Forest Frogs in Puerto Rico

Hurricane Hugo caused extensive damage to the Luquillo Experimental Forest in September 1989. Individually marked Eleutherodactylus coqui were monitored in two study plots from January 1987 through October 1990. Survivorship estimates of adults for the period including the storm were within the normal range from previous years. Juveniles suffered severe reductions, primarily among the smaller size classes. By October 1990 adult population density had increased fourfold over prehurricane levels, although adults were smaller. Juvenile numbers also appeared to be increasing, but had not yet reached prehurricane densities. The rapid increase in density may have resulted from an increase in retreat sites and a decrease in invertebrate predators. Auditory censuses suggested that density changes for other species ranged from a 14 percent increase for the relatively common E. hedricki to an 83 percent decrease for the relatively rare E. richmondi.

Politics in Hobbes' mechanics: The social as enabling

We compared a non-spatial logistic regression model (LRM) with two spatial models, i.e., logistic mixed model (LMM) and geographically weighted logistic model (GWLM), to model/predict the occurrence of orographic cloud cover at the Luquillo Experimental Forest in north-eastern Puerto Rico. The cloud cover data were derived from two Landsat images on a relatively clear day and a relatively cloudy day, respectively. In these models, the response variable was binary with 0 representing non-cloudy areas and 1 representing cloudy areas. The covariates included slope, aspect, and the difference between elevation and lifting condensation level. The results indicated that the spatial LMM did not improve the prediction of probability of cloud cover over the non-spatial LRM. One possible explanation is that the LMM was not able to account for the anisotropy in the non-spatial LRM residuals. In contrast, the GWLM with the bandwidth close to the effective range of the semivariogram of the LRM residuals showed the best model fitting among the three types of models, resulting in the lowest Akaike Information Criterion (AIC) and sum of squared errors (SSE), and the smallest spatial autocorrelation and heterogeneity in the model residuals. The GWLM model coefficients were spatially nonstationary, ranging from negative to positive depending on locations. The significance of the covariates also varied spatially. Our study demonstrated that GWLM is a useful and effective tool to account for spatial heterogeneity in modeling/predicting the occurrence or probability of cloud cover, using the spatial data derived from satellite imagery and GIS.

Physical Aspects of Hurricane Hugo in Puerto Rico

On 18 September 1989 the western part of Hurricane Hugo crossed eastern Puerto Rico and the Luquillo Experimental Forest (LEF). Storm-facing slopes on the northeastern part of the island that were within 15 km of the eye and received greater than 200 mm of rain were most affected by the storm. In the LEF and nearby area, recurrence intervals associated with Hurricane Hugo were 50 yr for wind velocity, 10 to 31 yr for stream discharge, and 5 yr for rainfall intensity. To compare the magnitudes of the six hurricanes to pass over Puerto Rico since 1899, 3 indices were developed using the standardized values of the product of: the maximum sustained wind speed at San Juan squared and storm duration; the square of the product of the maximum sustained wind velocity at San Juan and the ratio of the distance between the hurricane eye and San Juan to the distance between the eye and percentage of average annual rainfall delivered by the storm. Based on these indices, Hurricane Hugo was of moderate intensity. However, because of the path of Hurricane Hugo, only one of these six storms (the 1932 storm) caused more damage to the LEF than Hurricane Hugo. Hurricanes of Hugo's magnitude are estimated to pass over the LEF once every

Sulfur transformations and pool sizes in tropical forest soils

Samples of A horizon soils collected along an elevational gradient within the Luquillo Experimental Forest in Puerto Rico, were examined for their capacity to adsorb sulfate, form organic S, and mobilize organic S that had been recently formed. Soil moisture, carbon. pH. and S pool sizes were assayed to determine factors regulating these processes. Samples were found to adsorb between 1.6 and 5.7 nmol S g −1 dry wt of added sulfate, while organic S formation potentials ranged from 0.7 to 3.6 nmol S g −1 dry wt. All soils within the gradient exhibited the capacity to mobilize organic S (between 27.3 and 56.9% 24h −1) as well as the capacity to accumulate organically bound S (0.7-1.8 nmol S g −1 24h −1). Total S ranged from 1231 to 353 μg S g −1 dry wt and organic S was the most abundant constituent. Carbon and moisture content were positively correlated with organic S formation potentials ( r = 0.71; P ⩽0.001; r = 0.80; P ⩽0.001; respectively), while total amounts of sulfate were positively correlated with organic S mobilization rates ( r = 0.85; P ⩽ 0.004).

Nutrients and mass in litter and top soil of ten tropical tree plantations

The importance of litter to nutrient and organic matter storage and the possible influence of species selection on soil fertility in ten stands each consisting of a separate tree species were examined in this study. The plantations had been grown under similar conditions in an arboretum in the Luquillo Experimental Forest, Puerto Rico. The species involved were: Anthocephalus chinensis, Eucalyptus × patentinervis, E. saligna, Hernandia sonora, Hibiscus elatus, Khaya nyasica, Pinus caribaea var. hondurensis, P. elliottii var. densa, Swietenia macrophylla, and Terminalia ivorensis. After 26 yr, litter mass ranged from 5 mg ha-1 in the H. sonora stand to 27.2 Mg ha-1 in the P. caribaea stand. Nutrients in the litter (N, P, K, Ca, and Mg) also varied widely, but stands were ranked in different order when ranked by nutrients in the litter than then ranked according to accumulation of mass. Only E. saligna and A. chinensis stands were ranked similarly in accumulation of both nutrients and mass, and the stand of H. elatus was ranked higher with respect to nutrient accumulation than to accumulation of mass. The nutrient concentration in standing leaf litter generally increased in the order of recently fallen <old intact< fragmented. Nutrient concentration of standing leaf litter appears to increase with age and depth in the litter layer. The amount of nutrients stored in the litter compartment of these plantations was in the same order of magnitude as the quantity of available nutrients in the top 10-cm of mineral soil. Total litter mass was negatively correlated with the mass-weighted concentration of N, K, and Mg. The same relationship was found for Ca in the leaf litter and N in the fine wood litter compartments. In some stands (notably P. caribaea, P. elliottii, and E. saligna), leaf litter derived from species other than the species planted in that particular stand had higher nutrient concentration than leaf litter from the planted species. Soils of the 10 stands were classified in the same soil series and had similar texture (clay soils). However, significantly different chemical characteristics were found. Results obtained by analysis of covariance and by limiting comparisons to adjacent stands with similar soil texture, indicate that different species have had different influences on the concentration of available nutrients in soil.

Hygrophoraceae of the Luquillo Mountains of Puerto Rico

Fourteen species in the Hygrophoraceae are described from the El Verde Research Area of the Luquillo Experimental Forest in Puerto Rico. Three new species of Hygrocybe are described: H. prieta (Sect. Eirmae ), H. melleofusca (Sect. Neohygrocybe ) and H. viridula (Sect. Coccineae ). A new variety, Camarophyllus umbrimts var. clarofulvus is described, and the new combination Hygrocybe subcaespitosa (Murr.) comb. nov. ( Hydrocybe subcaespitosa Murr.) is proposed.