Fetcher N.

Nitrogen Immobilization by Decomposing Woody Debris and the Recovery of Tropical Wet Forest from Hurricane Damage

Nitrogen Immobilization by Decomposing Woody Debris and the Recovery of Tropical Wet Forest from Hurricane Damage
J. K. Zimmerman, W. M. Pulliam, D. J. Lodge, V. Quiñones-Orfila, N. Fetcher, S. Guzmán-Grajales, J. A. Parrotta, C. E. Asbury, L. R. Walker and R. B. Waide
Oikos
Vol. 72, No. 3 (Apr., 1995), pp. 314-322

Abstract: 
Following damage caused by Hurricane Hugo (September 1989) we monitored inorganic nitrogen availability in soil twice in 1990, leaf area index in 1991 and 1993, and litter production from 1990 through 1992 in subtropical wet forest of eastern Puerto Rico. Experimental removal of litter and woody debris generated by the hurricane (plus any standing stocks present before the hurricane) increased soil nitrogen availability and above-ground productivity by as much as 40% compared to unmanipulated control plots. These increases were similar to those created by quarterly fertilization with inorganic nutrients. Approximately 85% of hurricane-generated debris was woody debris >5 cm diameter. Thus, it appeared that woody debris stimulated nutrient immobilization, resulting in depression of soil nitrogen availability and productivity in control plots. This was further suggested by simulations of an ecosystem model (CENTURY) calibrated for our site that indicated that only the large wood component of hurricane-generated debris was of sufficiently low quality and of great enough mass to cause the observed effects on productivity. The model predicted that nutrient immobilization by decaying wood should suppress net primary productivity for 13 yr and total live biomass for almost 30 yr following the hurricane. Our findings emphasize the substantial influence that woody debris has upon nutrient cycling and productivity in forest ecosystems through its effects on the activity of decomposers. We suggest that the manner in which woody debris regulates ecosystem function in different forests is significantly affected by disturbance regime.

Acclimation of tropical tree species to hurricane disturbance: ontogenetic differences

Wen, S.Y., Fetcher, N. & Zimmerman, J.K. (2008) Acclimation of tropical tree
species to hurricane disturbance: ontogenetic differences. Tree Physiology,
28, 935–946.

Abstract: 
We investigated acclimation responses of seedlings and saplings of the pioneer species Cecropia schreberiana Miq. and three non-pioneer species, Dacryodes excelsa Vahl, Prestoea acuminata (Willdenow) H.E. Moore var. montana (Graham) Henderson and Galeano, and Sloanea berteriana Choisy ex DC, following a hurricane disturbance in a lower montane wet forest in Puerto Rico. Measurements were made, shortly after passage of the hurricane, on leaves expanded before the hurricane (pre-hurricane leaves) and, at a later time, on recently matured leaves that developed after the hurricane (post-hurricane leaves) from both seedlings and saplings at sites that were severely damaged by the hurricane (disturbed sites) and at sites with little disturbance (undisturbed sites). Pre-hurricane leaves of the non-pioneer species had relatively low light-saturated photosynthetic rates (Amax) and stomatal conductance (gs); neither Amax nor gs responded greatly to the increase in irradiance that resulted from the disturbance, and there were few significant differences between seedlings and saplings. Pre-hurricane leaves of plants at undisturbed sites had low dark respiration rates per unit area (Rd) and light compensation points (LCP), whereas pre-hurricane leaves of plants at disturbed sites had significantly higher Rd and LCP. Post-hurricane leaves of plants at disturbed sites had significantly higher Amax and Rd than plants at undisturbed sites. Compared with seedlings, saplings had higher Amax and Rd and showed greater acclimation to the increase in irradiance that followed the disturbance. Post-hurricane leaves of the non-pioneer species had significantly lower Amax and were less responsive to changes in irradiance than the pioneer species C. schreberiana. Variation in Amax across light environments and stages was strongly related to differences in leaf mass per unit area (LMA), especially in the non-pioneer species. As indicated by Vcmax or Jmax per unit nitrogen, light acclimation of Amax was determined by leaf morphology (LMA) for the nonpioneer species and by both leaf morphology and leaf biochemistry for C. schreberiana. Ontogenetic changes in Amax were attributable to changes in leaf morphology. The ontogenetic component of variation in Amax across light environments and stages differed among species, ranging from 36 to 59% for the non-pioneer species (D. excelsa, 59.3%; P. acuminata var. montana, 44.7%; and S. berteriana, 36.3%) compared with only 17% in the pioneer species C. schreberiana.

Ecosystem Development and Plant Succession on Landslides in the Caribbean

Ecosystem Development and Plant Succession on Landslides in the Caribbean
Lawrence R. Walker, Daniel J. Zarin, Ned Fetcher, Randall W. Myster and Arthur H. Johnson
Biotropica
Vol. 28, No. 4, Part A. Special Issue: Long Term Responses of Caribbean Ecosystems to Disturbances (Dec., 1996), pp. 566-576

Abstract: 
Landslides are common in mountainous regions of the Caribbean and are triggered by heavy rains and earthquakes, and often occur in association with human disturbances (e.g., roads). Spatially heterogeneous removal of both substrate and vegetation is responsible for a variety of patterns of ecosystem development and plant successional trajectories within Caribbean landslides. Soil nutrient pools in exposed mineral soils reach levels comparable to mature forest soils within 55 yr but soil organic matter recovers more slowly. Plant colonization of landslides depends on the availability of propagules and suitable sites for germination, soil stability, and the presence of residual or newly deposited soil organic matter and associated nutrients. Once initial colonization occurs, the rate and trajectory of plant succession on landslides is strongly affected by plant/plant interactions. We present two conceptual models of landslide succession that summarize the major processes and pathways of ecosystem development and plant succession on landslides. Additional work is needed to characterize interactions between spatially heterogeneous zones, controls over soil development, impacts of key plant species, and the role of animals on Caribbean landslides.

Natural disturbance and human land use as determinants of tropical forest dynamics: results from a forest simulator

Uriarte, M., C. D. Canham, J. Thompson, J. K. Zimmerman,
L. Murphy, A. M. Sabat, N. Fetcher, and B. L.
Haines. 2009. Natural disturbance and human land
use as determinants of tropical forest dynamics:
results from a forest simulator. Ecological Monographs
79:423–443.

Abstract: 
Forests are often subject to multiple, compounded disturbances, representing both natural and human-induced processes. Predicting forest dynamics requires that we consider how these disturbances interact to affect species demography. Here we present results of an individual-based, spatially explicit forest simulator that we developed to analyze the compounded effects of hurricane disturbance and land use legacies on the dynamics of a subtropical forest. We used data from the 16-ha Luquillo Forest Dynamics Plot in Puerto Rico, together with a reconstruction of historical wind damage, to parameterize the simulator. We used the model to ask two questions. (1) What are the implications of variation in hurricane frequency and severity for the long-term dynamics of forest composition, diversity, and structure? Both storm severity and frequency had striking effects on forest dynamics, composition, and structure. The periodicity of disturbance also played an important role, with periods of high hurricane activity fostering the establishment of species that may become rare in the absence of severe storms and quiescent periods allowing these species to reach reproductive size. Species responses to hurricane disturbance could not be predicted from their life history attributes. However, species perceived to be primary forest species exhibited low temporal variation in abundance through the simulations. (2) How do hurricanes and legacies from human land use interact to determine community structure and composition? Our results suggest that, over time, regardless of the storm regime, land use legacies will become less apparent but will lead to a forest community that contains a mixture of secondary and primary forest species formerly dominant in areas of different land use. In the long term, hurricane disturbance generated two communities with slightly greater similarity than those not subject to storms. Thus, the inclusion of hurricane disturbance does not alter the prediction that land use legacies in this tropical forest will diminish over time. Our simulations also highlight the contingent effects of human legacies on subsequent community dynamics, including the response to hurricane disturbance, therefore supporting the notion that compounded disturbances can interact in ways that cannot be predicted by the study of single disturbances. The widespread importance of land use as a large-scale disturbance makes it imperative that it be addressed as a fundamental ecological process.

Lack of Ecotypic Differentiation: Plant Response to Elevation, Population Origin, and Wind in the Luquillo Mountains, Puerto Rico

Fetcher, Ned; Cordero, Roberto A.; Voltzow, Janice 2000. Lack of Ecotypic Differentiation: Plant Response to Elevation, Population Origin, and Wind in the Luquillo Mountains, Puerto Rico. BIOTROPICA 32(2) :225-234 .

Abstract: 
How important is ecotypic differentiation along elevational gradients in the tropics? Reciprocal transplants of two shrubs, Clibadium erosum (Asteraceae) and Psychotria berteriana (Rubiaceae), and a palm, Prestoea acuminata var. montana (Palmaceae), were used to test for the effect of environment and population origin on growth and physiology in the Luquillo Experimental Forest of Puerto Rico. Two sites were used, one at Pico del Este (1000 m in cloud forest) and one at El Verde (350 m in lower montane rain forest). At the cloud forest site, plastic barriers were erected around a subset of the plants to examine if protection from wind affected survival or biomass accumulation. Survival of C. erosum and P. berteriana was not affected by site, population origin, or the presence of barriers. For P. acuminata var. montana, survival was higher for plants with barriers, but not affected by site and population origin. Plants of C. erosum and P. berteriana at El Verde grew larger than at Pico del Este, but there was no effect of population origin or barrier treatment on biomass accumulation for these species. For P. acuminata var. montana, there was no effect of environment, population origin, or barrier treatment on biomass accumulation. Light-saturated photosynthetic rate (Amax) of C. erosum, P. berteriana, and P. acuminata var. montana, as well as leaf anatomical characteristics of C. erosum, were unaffected by environment, population origin, and barrier treatment. On balance, there seems to be little evidence of ecotypic differentiation in these species along the gradient.

Modeling the spatial and temporal variability in climate and primary productivity across the Luquillo Mountains, Puerto Rico

Wanga, Hongqing; Halla, Charles A.S.; Scatenab, Frederick N.; Fetcherc, Ned; Wua, Wei 2003. Modeling the spatial and temporal variability in climate and primary productivity across the Luquillo Mountains, Puerto Rico.. Forest Ecology and Management 179 :69-94l.

Abstract: 
There are few studies that have examined the spatial variability of forest productivity over an entire tropical forested landscape. In this study, we used a spatially-explicit forest productivity model, TOPOPROD, which is based on the FORESTBGC model, to simulate spatial patterns of gross primary productivity (GPP), net primary productivity (NPP), and respiration over the entire Luquillo Experimental Forest (LEF) in the mountains of northeastern Puerto Rico.We modeled climate variables (e.g. solar insolation, temperature, rainfall and transpiration) using a topography-based climate model, TOPOCLIM. The simulated GPP ranged from 8 to 92 t C/ha per year with a mean of 51 t C/ha per year. The simulated NPP ranged from 0.5 to 24 t C/ha per year with a mean of 9.4 t C/ha per year. The simulated plant respiration ranged from 31 to 68 with a mean of 42 t C/ha per year. Simulated GPP and respiration declined with increased elevation whereas simulated NPP increased from low to middle elevation but decreased from middle to high elevations. Statistical analyses indicate that variation in solar insolation, which decreases with increase in elevation, is the most important factor controlling the spatial variation of forest productivity in the LEF. Validation with the limited spatial empirical data indicated that our simulations overestimated GPP by 2% for a middle elevation test site, and by 43% for a mountain peak site. Our simulations also overestimated NPP in the middle elevation Colorado forest and higher elevation Dwarf forest by 32 and 36%, respectively, but underestimated NPP in the Tabonuco and Palm forests at low to middle elevations by 9–15% and 18%, respectively. Simulated GPP and NPP would decrease under CO2 doubling as projected temperatures increase and precipitation decreases. Different forest types respond differently to potential climate change and CO2 doubling. Comparison with other tropical forests suggests that the LEF as a whole has higher GPP (51 tC/ha per year versus 40 t C/ha per year) but lower NPP (9.4 t C/ha per year versus 11 t C/ha per year) than other tropical rain forests.
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