tropical rainforest

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.

Protozoa from aboveground and ground soils of a tropical rain forest in Puerto Rico

Bamforth S (2007) Protozoa from aboveground and ground soils
of tropical rain forest in Puerto Rico. Pedobiologia 50:515–525

Abstract: 
forests, but little is known about the protozoa that stimulate bacterial activity and turnover. I examined litter and ground soils, epiphytic bryophyte soils on tree trunks and branches, and adventitious roots of lianas attached to tree trunks, within 2m above ground in the Luquillo Experimental Forest, within the Caribbean National Forest, Puerto Rico. Amoebae numbered 69,000–170,000, ciliates 1000–25,000, and testate amoebae 58,000–190,000 g1 dry wt. of litter, but were reduced by 0.25–0.5 of these abundances in the underlying soils. In the aboveground soils, amoebae numbered 64,000–145,000, ciliates 1000–8000, and testate amoebae 84,000–367,000 g1 dry wt. of soil. Eighty species of ciliates and 104 species of testate amoebae were found. About 50% of the individuals in ciliate and 33% in testate amoebae populations were small r-selected species, illustrating that functional differences between species determine community composition. Although protozoan numbers are best described as ‘‘protozoan potential’’ because many individuals may be dormant, the high moisture content of tropical rain forest litter and soils suggest almost continually connected soil water films (necessary for protozoan transport), and together with the large numbers and biodiversity of protozoa, suggest that a major proportion of these protozoa contribute to the bacterial decomposition channel of organic matter. & 2006 Elsevier GmbH. All rights reserved.

Modelling rainfall interception by a lowland tropical rain forest in northeastern Puerto Rico

Schellekensa, J.; Scatenab,F.N.; Bruijnzeela,L.A.; Wickela,A.J. 1999. Modelling rainfall interception by a lowland tropical rain forest in northeastern Puerto Rico. Journal of Hydrology 225 :168-184.

Abstract: 
Recent surveys of tropical forest water use suggest that rainfall interception by the canopy is largest in wet maritime locations. To investigate the underlying processes at one such location—the Luquillo Experimental Forest in eastern Puerto Rico—66 days of detailed throughfall and above-canopy climatic data were collected in 1996 and analysed using the Rutter and Gash models of rainfall interception. Throughfall occurred on 80% of the days distributed over 80 rainfall events. Measured interception loss was 50% of gross precipitation. When Penman–Monteith based estimates for the wet canopy evaporation rate (0.11 mm h21 on average) and a canopy storage of 1.15 mm were used, both models severely underestimated measured interception loss. A detailed analysis of four storms using the Rutter model showed that optimizing the model for the wet canopy evaporation component yielded much better results than increasing the canopy storage capacity. However, the Rutter model failed to properly estimate throughfall amounts during an exceptionally large event. The analytical model, on the other hand, was capable of representing interception during the extreme event, but once again optimizing wet canopy evaporation rates produced a much better fit than optimizing the canopy storage capacity. As such, the present results support the idea that it is primarily a high rate of evaporation from a wet canopy that is responsible for the observed high interception losses.

Effects of Hurricane Disturbance on Groundwater Chemistry and Riparian Function in a Tropical Rain Forest

Effects of Hurricane Disturbance on Groundwater Chemistry and Riparian Function in a Tropical Rain Forest
William H. McDowell, Claire P. McSwiney and William B. Bowden
Biotropica
Vol. 28, No. 4, Part A. Special Issue: Long Term Responses of Caribbean Ecosystems to Disturbances (Dec., 1996), pp. 577-584

Abstract: 
The long-term response of shallow groundwater chemistry to the canopy disturbance and defoliation associated with Hurricane Hugo was studied at two sites in the Luquillo Experimental Forest, Puerto Rico. The sites differed in bedrock type, dominant vegetation, and availability of pre-hurricane data. At the primary study site, the Bisley catchment, hurricane disturbance resulted in increased concentrations of NO3 -, NH4 +, dissolved organic N, base cations, Cl-, and SiO2 in groundwater within 5 mo of the hurricane. The largest relative change in concentration occurred for K+, which increased from 0.7 to as high as 13 mg/L, concentrations were still 1.3 mg/L 5.5 yr after the hurricane. Most other solutes had returned to background levels within 1-2 yr of the hurricane. At the secondary study site, the Icacos catchment, NO3 - concentrations peaked at 1.1 mg/L one yr after the hurricane and decreased to nearly zero 5.5 yr after the hurricane. At both sites, NO3 - concentrations were higher in upslope wells than in those closer to the stream. Overall, riparian processes appear to reduce but not eliminate hydrologic losses of N following catastrophic disturbance. The nature of the long-term biogeochemical response to disturbance in this tropical rain forest ecosystem is similar to that observed in some montane temperate forests, and the time course of recovery appears to be associated with the speed with which vegetation regrows following disturbance.

C and N dynamics in the riparian and hyporheic zones of a tropical stream, Luquillo Mountains, Puerto Rico

C and N Dynamics in the Riparian and Hyporheic Zones of a Tropical Stream, Luquillo Mountains, Puerto Rico
Tamara J. Chestnut and William H. McDowell
Journal of the North American Benthological Society
Vol. 19, No. 2 (Jun., 2000), pp. 199-214

Abstract: 
Hydrologic and chemical characteristics were determined for both riparian and hyporheic subsurface flow along a 100-m reach of a sandy-bottom tributary of the Rio Icacos in the Luquillo Experimental Forest, Puerto Rico. Hydrologic data (vertical hydraulic gradient and hydraulic conductivity of streambed sediments) and the topographic and morphological features of the watershed indicated diffuse inputs of groundwater from the near-stream riparian zone along this site. Cumulative groundwater discharge, determined by tracer dilution techniques, was ∼1.5 L/s or 10% of the total stream discharge. Spatial heterogeneity in hydrologic and chemical properties of riparian and hyporheic sediments was large. Hydraulic conductivity explained much of the variation in NH<sub>4</sub>-N and dissolved organic carbon (DOC) concentrations, with highest concentrations in sites having low conductivity. A mass-balance approach was used to examine the influence of the near-stream zone on nutrient transport and retention. Outwelling riparian groundwater had the potential to increase stream N concentrations by up to 84% and DOC concentrations by up to 38% along our 100-m reach. Because stream concentrations were constant downstream despite this input, we conclude that significant N and C retention or loss were occurring in the near-stream zone. Lotic ecosystems and their associated riparian groundwater can have a quantitatively significant impact on the nutrient budgets of tropical headwater catchments.
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