tropical forest


Boose, E.R., Serrano, M.I. & Foster, D.R. (2004) Landscape
and regional impacts of hurricanes in Puerto Rico. Ecological
Monographs, 74, 335–352.

Puerto Rico is subject to frequent and severe impacts from hurricanes, whose long-term ecological role must be assessed on a scale of centuries. In this study we applied a method for reconstructing hurricane disturbance regimes developed in an earlier study of hurricanes in New England. Patterns of actual wind damage from historical records were analyzed for 85 hurricanes since European settlement in 1508. A simple meteorological model (HURRECON) was used to reconstruct the impacts of 43 hurricanes since 1851. Long-term effects of topography on a landscape scale in the Luquillo Experimental Forest (LEF) were simulated with a simple topographic exposure model (EXPOS). Average return intervals across Puerto Rico for F0 damage (loss of leaves and branches) and F1 damage (scattered blowdowns, small gaps) on the Fujita scale were 4 and 6 years, respectively. At higher damage levels, a gradient was created by the direction of the storm tracks and the weakening of hurricanes over the interior mountains. Average return intervals for F2 damage (extensive blowdowns) and F3 damage (forests leveled) ranged from 15 to 33 years and 50 to 150 years, respectively, from east to west. In the LEF, the combination of steep topography and constrained peak wind directions created a complex mosaic of topographic exposure and protection, with average return intervals for F3 damage ranging from 50 years to .150 years. Actual forest damage was strongly dependent on land-use history and the effects of recent hurricanes. Annual and decadal timing of hurricanes varied widely. There was no clear centennial-scale trend in the number of major hurricanes over the historical period.


Exotic Earthworms Accelerate Plant Litter Decomposition in a Puerto Rican Pasture and a Wet Forest
Z. G. Liu and X. M. Zou
Ecological Applications
Vol. 12, No. 5 (Oct., 2002), pp. 1406-1417

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 CO2 evolution rates, soil microbial biomass, and physical and chemical soil properties between the controls and earthwormreduced 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.

Estimating soil turnover rate from tree uprooting during hurricanes in Puerto Rico

Lenart, Melanie T.; Falk, D.A.; Scatena, F.N.; Osterkamp, W.R. 2010. Estimating soil turnover rate from tree uprooting during hurricanes in Puerto Rico. Forest Ecology and Management. 259:1076-1084.

Soil turnover by tree uprooting in primary and secondary forests on the island of Puerto Rico was measured in 42 study plots in the months immediately after the passage of a Category 3 hurricane. Trunk basal area explained 61% of the variability of mound volume and 53% of the variability of mound area. The proportion of uprooted trees, the number of uprooted trees, or the proportion of uprooted basal area explained 84–85% of the variation in hurricane-created mound area. These same variables explain 79–85% of the variation in mound volume. The study indicates that the soil turnover period from tree uprooting by Puerto Rican hurricanes is between 1600 and 4800 years. These rates are faster than soil turnover by landslides and background treefall in the same area and provide a useful age constraint on soil profile development and soil carbon sequestration in these dynamic landscapes.

Natural disturbances and the hydrology of humid tropical forests

Scatena FN, Planos-Gutiérrez EO, Schellekens J. 2004. Natural disturbances
and the hydrology of humid tropical forests. In Forests,
Water, and People in the Humid Tropics, Bonell M, Bruijnzeel LA
(eds). Cambridge University Press: Cambridge; 5–28.

Humid tropical forests are highly dynamic ecosystems that are affected by a wide array of environmental processes and disturbances (Figure 19.1). Quantifying the magnitude, frequency, and impacts of natural disturbances is essential for designing hydraulic structures, developing water management strategies, and distinguishing between natural variation and man-made influences. A disturbance can be defined as any discrete event that transfers mass and energy from one part of a system to another in a manner that disrupts ecosystem, community, or population structure and changes resource availability or the physical environment (see White and Pickett 1985 for a detailed discussion). Natural disturbances can be driven by both external factors – hurricanes, meteor impacts, etc. – and the biological properties of the system such as senescence, pathogens, etc. The natural disturbances specified by the United Nations in the International Decade of Natural Disaster Reduction were earthquakes, windstorms, tsunamis, floods, landslides, volcanic eruptions, wildfires, grasshopper and locust infestations, drought, and desertification (Board on Natural Disasters, 1999). Additional natural disturbances known to affect the hydrology of humid tropical forests are tree falls, pathogens, exotic invasions and meteor impacts. Quantifying the effects of disturbances on landform morphology and ecosystem development have been major themes in geomorphology and ecology (Wolman and Miller, 1960, Connell, 1978). This approach has led to the paradigm that landscapes are structured by the processes acting upon them (O’Neill et al., 1986, Urban et al., 1987, Scatena, 1995). It is now generally recognised that the ability of a disturbance to affect the morphology of a landscape or the structure of an ecosystem depends on: (1) the type of disturbance (e.g., flood, fire, landslide, biologic, anthropogenic etc.); (2) the force exerted (e.g. wind velocity and duration, rainfall magnitude and intensity, earthquake magnitude etc.); (3) the ecosystem component that is impacted directly (e.g. soil, biomass, leaf area etc.); (4) the area affected and the spatial distribution of impacts; (5) the return period or frequency of the event; (6) the condition of the system at the time of the disturbance (e.g. structure, regeneration phase, time since last disturbance); and (7) the magnitude of the constructive or restorative processes that occur between disturbances.

Short-Term Disappearance of Foliar Litter in Three Species Before and After a Hurricane'

Short-Term Disappearance of Foliar Litter in Three Species before and after a Hurricane
Neal H. Sullivan, William B. Bowden and William H. McDowell
Vol. 31, No. 3 (Sep., 1999), pp. 382-393

Litter disappearance was examined before (1989) and after (1990) Hurricane Hugo in the Luquillo Experimental Forest, Puerto Rico using mesh litterbags containing abscised Cyrilla racemiflora or Dacryodes excelsa leaves or fresh Prestoea montana leaves. Biomass and nitrogen dynamics were compared among: (i) species; (ii) mid- and high elevation forest types; (iii) riparian and upland sites; and (iv) pre- and post-hurricane disturbed environments. Biomass disappearance was compared using multiple regression and negative exponential models in which the slopes were estimates of the decomposition rates subsequent to apparent leaching losses and the y-intercepts were indices of initial mass losses (leaching). Cyrilla racemiflora leaves with low nitrogen (0.39%) and high lignin (22.1%) content decayed at a low rate and immobilized available nitrogen. Dacryodes excelsa leaves had moderate nitrogen (0.67%) and lignin (16.6%) content, decayed at moderate rates, and maintained the initial nitrogen mass. Prestoea montana foliage had high nitrogen (1.76%) and moderate lignin (16.7%) content and rapidly lost both mass and nitrogen. There were no significant differences in litter disappearance and nitrogen dynamics among forest types and slope positions. Initial mass loss of C. racemiflora leaves was lower in 1990 but the subsequent decomposition rate did not change. Initial mass losses and the overall decomposition rates were lower in 1990 than in 1989 for Dacryodes excelsa. Dacryodes excelsa and C. racemiflora litter immobilized nitrogen in 1990 but released 10-15 percent of their initial nitrogen in 1989, whereas P. montana released nitrogen in both years (25-40%). Observed differences in litter disappearance rates between years may have been due to differences in the timing of precipitation. Foliar litter inputs during post-hurricane recovery of vegetation in Puerto Rico may serve to immobilize and conserve site nitrogen.

At What Temporal Scales Does Disturbance Affect Belowground Nutrient Pools?

At What Temporal Scales Does Disturbance Affect Belowground Nutrient Pools?
Whendee L. Silver, Fred N. Scatena, Arthur H. Johnson, Thomas G. Siccama and Fiona Watt
Vol. 28, No. 4, Part A. Special Issue: Long Term Responses of Caribbean Ecosystems to Disturbances (Dec., 1996), pp. 441-457

We monitored the effects of both harvesting aboveground biomass and Hurricane Hugo on soil chemical and physical properties, and live and dead root biomass over 6 yr in a subtropical wet forest in Puerto Rico. Our goal was to determine how belowground processes changed at different temporal scales including the immediate period prior to revegetation (9 wk), the intermediate period of initial regrowth (9 mo), and the longer-term reorganization of the vegetation and biogeochemical cycling (6 yr). Harvesting resulted in temporary increases in the availability of exchangeable nutrients, but forest floor and soil nutrient pools had generally returned to pre-harvest values over a 9 wk period. Significant amounts of K moved through the soil over this time period, amounting to 29-46 kg/ha-1, and resulting in a reduction in the size of the exchangeable soil K pool. The hurricane deposited approximately 845 kg/ha-1 of forest floor mass and considerable nutrients on the soil surface, and increased soil NO3-N and exchangeable K pools, but in all cases, pool sizes had returned to pre-hurricane values within 9 mo. Examination of the data on an annual time step over the 6 yr period revealed an increase in soil cation pools and a significant decrease in soil pH. No change in soil organic matter was detected at any time step following the disturbances. Live fine root biomass was dramatically reduced as a result of the hurricane, and was only beginning to show signs of recovery near the end of the 6 yr experiment.

Hydrological Processes in a humid Tropical Rain Forest: A Combined Experimental and Modelling Approach

Schellekens, J. 2000. Hydrological processes in a humid tropical rain
forest: a combined experimental and modeling approach. Ph.D.
Thesis, Free University of Amsterdam, Amsterdam University
Press, 158 p.

With populations growing explosively in the tropical parts of the world, and the per capita water demands increasing where living standards improve, optimisation of water resources is becoming increasingly important [Bonell et al., 1993]. Similarly, the strong demands for industrial wood (pulpwood, saw and veneer logs), fuelwood and charcoal, require the establishment of large areas of fast-growing plantation forests, often on land that is currently not forested [Evans, 1992; Brown et al., 1997]. Coupled with (i) the continued indiscriminate clearing of the world’s tropical forests [Jepma, 1995; Nepstad et al., 1999] which in many areas serve as the traditional supplier of high quality water; (ii) the associated deterioration of soil and water quality due to erosion and pollution [Oldeman, 1994], plus (iii) the possibility of gradually less dependable precipitation inputs and (in certain ‘maritime’ tropical areas away from the equator) an increasing frequency of devastating hurricanes due to ‘global change’ [Wasser and Harger, 1992], a sound understanding of the hydrological functioning of tropical forests is arguably even more important nowadays than ever before [cf. Bruijnzeel, 1990, 2000a]. Bruijnzeel and Abdul Rahim [1992] suggested that in a time of dwindling resources, additional forest hydrological research in the humid tropics could best be carried out at a limited number of carefully selected data-rich key locations that could be loosely joined together in a network that captures the environmental variability encountered in the humid tropics. Furthermore, Bruijnzeel [1993] and Bonell and Balek [1993] considered a catchment-based approach to offer the best framework for such research as this allows for the integration of hydrological, geomorphological, pedological and ecological observations in a spatial context, particularly if supplemented by process studies and physicallybased distributed modelling.

Forest Floor Decomposition Following Hurricane Litter Inputs in Several Puerto Rican Forests

Rebecca Ostertag, Frederick N. Scatena, and Whendee L. Silver. 2003. Forest Floor Decomposition Following Hurricane Litter Inputs in Several Puerto Rican Forests. Ecosystems 6 :261-273.

Hurricanes affect ecosystem processes by altering resource availability and heterogeneity, but the spatial and temporal signatures of these events on biomass and nutrient cycling processes are not well understood. We examined mass and nutrient inputs of hurricane-derived litter in six tropical forests spanning three life zones in northeastern Puerto Rico after the passage of Hurricane Georges. We then followed the decomposition of forest floor mass and nutrient dynamics over 1 year in the three forests that experienced the greatest litter inputs (moist, tabonuco, and palm forests) to assess the length of time for which litter inputs influence regeneration and nutrient cycling processes. The 36-h disturbance event had litterfall rates that ranged from 0.55 to 0.93 times annual rates among the six forests; forest floor ranged between 1.2 and 2.5 times prehurricane standing stocks. The upperelevation forest sites had the lowest nonhurricane litterfall rates and experienced the lowest hurricane litterfall and the smallest relative increase in forest floor standing stocks. In the three intensively studied forests, the forest floor returned to prehurricane values very quickly, within 2–10 months. The palm forest had the slowest rate of decay (k  0.74  0.16 y–1), whereas the tabonuco forest and the moist forest had similar decay rates (1.04  0.12 and 1.09  0.14, respectively). In the moist forest, there were short-term increases in the concentrations of nitrogen (N), hosphorus (P), calcium (Ca), and magnesium (Mg) in litter, but in the other two forests nutrient concentrations generally decreased. The rapid disappearance of the hurricane inputs suggests that such pulses are quickly incorporated into nutrient cycles and may be one reason for the extraordinary resilience of these forests to wind disturbances.

Background and Catastrophic Tree Mortality in Tropical Moist, Wet, and Rain Forests

Background and Catastrophic Tree Mortality in Tropical Moist, Wet, and Rain Forests
Ariel E. Lugo and F. N. Scatena
Vol. 28, No. 4, Part A. Special Issue: Long Term Responses of Caribbean Ecosystems to Disturbances (Dec., 1996), pp. 585-599

The process of tree mortality has dimensions of intensity, spatial, and temporal scales that reflect the characteristics of endogenic processes (i.e., senescence) and exogenic disturbances (i.e., severity, frequency, duration, spatial scale, and points of interaction with the ecosystem). Tree mortality events expressed as percent of stems or biomass per unit area, range in intensity from background (<5% yr-1) to catastrophic (>5% yr-1), in spatial scale from local to massive, and in temporal scale from gradual to sudden (hours to weeks). Absolute annual rates of background tree mortality (biomass or stem ha-1 yr-1) can vary several fold depending on stand conditions and tend to increase with stem density. The ecological effects of a catastrophic, massive, and sudden tree mortality event contrast with those of background, local, and gradual tree mortality in terms of the direction of succession after the event, community dynamics, nutrient cycling, and possibly selection on trees. When standardized for the return frequency of disturbance events, area, and topography, the ranking of tree mortality events (trees ha-1 century-1) in the Luquillo Experimental Forest is: background > hurricanes > individual tree fall gaps > landslides. Estimates of vegetation turnover rates require long-term and spatial analysis to yield accurate results.

A nitrogen budget for late-successional hillslope tabonuco forest, Puerto Rico

A Nitrogen Budget for Late-Successional Hillslope Tabonuco Forest, Puerto Rico
Tamara J. Chestnut, Daniel J. Zarin, William H. McDowell and Michael Keller
Vol. 46, No. 1/3, New Perspectives on Nitrogen Recycling in the Temperate and Tropical Americas (Jul., 1999), pp. 85-108

Nitrogen budgets of late successional forested stands and watersheds provide baseline data against which the effects of small- and large-scale disturbances may be measured. Using previously published data and supplemental new data on gaseous N loss, we construct a N budget for hillslope tabonuco forest (HTF) stands in Puerto Rico. HTF stands are subject to frequent hurricanes and landslides; here, we focus on N fluxes in the late phase of inter-disturbance forest development. N inputs from atmospheric deposition (4-6 kg N/ha/yr) are exceeded by N outputs from groundwater, gaseous N loss, and particulate N loss (6.3-15.7 kg N/ha/yr). Late-successional HTF stands also sequester N in their aggrading biomass (8 kg N/ha/yr), creating a total budget imbalance of 8.3-19.7 kg N/ha/yr. We surmise that this imbalance may be accounted for by unmeasured inputs from above- and belowground N-fixation and/or slow depletion of the large N pool in soil organic matter. Spatial and temporal variability, especially that associated with gaseous exchange and soil organic matter N-mineralization, constrain the reliability of this N budget.
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