Ruth E. Sherman

Soil-plant interactions in a neotropical mangrove forest: iron, phosphorus and sulfur dynamics

Abstract We examined soil porewater concentrations of sulfate, alkalinity, phosphorus, nitrogen, and dissolved organic carbon and solid phase concentrations of pyrite in relation to mangrove species distributions along a 3.1-km-long transect that traversed a 47.1-km2 mangrove forest in the Dominican Republic. Iron, phosphorus, and sulfur dynamics are closely coupled to the activity of sulfate-reducing bacteria, the primary decomposers in anoxic soils of mangrove ecosystems. Patterns in the chemistry data suggested that sulfate reduction rates and storage of reduced sulfur were greater in the inland basin forest dominated by Laguncularia racemosa than the Rhizophora mangle dominated forest of the lower tidal region. The distribution of Laguncularia was significantly correlated with concentrations of total phosphorus (r= 0.99) and dissolved organic carbon (r= 0.86), alkalinity (r= 0.60), and the extent of sulfate depletion (r= 0.77) in the soil porewater and soil pyrite concentrations (r= 0.72) across the tidal gradient. Leaf tissue chemistry of Laguncularia was characterized by lower C:N and C:P ratios that could fuel the higher rates of decomposition in the Laguncularia-dominated forest. We suggest that a plant-soil-microbial feedback contributes to the spatial patterning of vegetation and soil variables across the intertidal zone of many mangrove forest communities.

Spatial Patterns of Biomass and Aboveground Net Primary Productivity in a Mangrove Ecosystem in the Dominican Republic

The objective of this study was to quantify spatial patterns in above- and belowground biomass, primary productivity, and growth efficiency along a tidal gradient in a 4700-ha mangrove forest in the Dominican Republic. We tested the hypothesis that spatial patterns of forest structure and growth following 50 years of development were associated with variations in the soil environment across the tidal gradient. Twenty-three plots were monitored from 1994 to 1998. Aboveground biomass and biomass accumulation were estimated by applying allometric regression equations derived from dimension analysis of trees harvested at our study site. Soil porewater salinity ranged from 5 to 38 g kg -1 across the tidal gradient, and most measurements of forest biomass and productivity were inversely related to salinity. Mean standing biomass (233 ± 16.0 Mg ha -1 ; range, 123.5-383.5), biomass increment (9.7 ± 1.0 Mg . ha -1 y -1 ; range, 3.7-18.1), annual litterfall rates (11.4 Mg . ha -1 yr -1 ; range, 10.2-12.8), leaf area index (LAI) (4.4 m 2 . m -2 ; range, 2.9-5.6), aboveground net primary productivity (ANPP) (19.7 Mg . ha -1 y -1 ; range, 15.6-25.0), and growth efficiency (1.6±0.2 kg . ha -1 y -1 ; range, 1.0-3.6) all showed an inverse linear relationship with salinity. Fine-root biomass (≤ 2 mm) (9.7 ± 1.2 Mg . ha -1 ; range, 2.7-13.8) showed a weak tendency to increase with salinity, and the ratio of root to aboveground biomass increased strongly with salinity. Our results suggest that physiological stresses associated with salinity, or with some combination of salinity and other covarying soil factors, control forest structure and growth along the tidal gradient. The higher allocation of carbon to belowground resources in more saline sites apparently contributed to reductions in ANPP along the tidal gradient.

Interrelationships between prey body size and growth of age-0 yellow perch

Abstract We conducted laboratory experiments in the summers of 1986 and 1987 to examine the effects of Daphnia pulex body size and ration level on growth of age-0 yellow perch Perca flavescens. Daphnia pulex rations were set at 25 and 40% of yellow perch dry weight. Specific growth rate tended to be higher for smaller fish and decreased with fish size at both ration levels. For the 25% ration, the highest growth rates, 0.023 to 0.024 g/d, were observed when yellow perch were fed meals of D. pulex between 1.4 and 1.8 mm long; growth declined for prey sizes outside this size range. For the 40% ration, no relationship was found between body length of D. pulex and specific growth rate; the mean specific growth rate for the 40% ration was the same as the peak rate for the 25% ration. Multiple-regression analysis was used to examine the dependence of specific growth rate of yellow perch on initial fish length, prey size, and temperature. For the 25% ration, prey size and the square of prey size were the only va...

Earthworm effects on the incorporation of litter C and N into soil organic matter in a sugar maple forest

To examine the mechanisms of earthworm effects on forest soil C and N, we double-labeled leaf litter with 13C and 15N, applied it to sugar maple forest plots with and without earthworms, and traced isotopes into soil pools. The experimental design included forest plots with different earthworm community composition (dominated by Lumbricus terrestris or L. rubellus). Soil carbon pools were 37% lower in earthworm-invaded plots largely because of the elimination of the forest floor horizons, and mineral soil C:N was lower in earthworm plots despite the mixing of high C:N organic matter into soil by earthworms. Litter disappearance over the first winter-spring was highest in the L. terrestris (T) plots, but during the warm season, rapid loss of litter was observed in both L. rubellus (R) and T plots. After two years, 22.0% +/- 5.4% of 13C released from litter was recovered in soil with no significant differences among plots. Total recovery of added 13C (decaying litter plus soil) was much higher in no-worm (NW) plots (61-68%) than in R and T plots (20-29%) as much of the litter remained in the former whereas it had disappeared in the latter. Much higher percentage recovery of 15N than 13C was observed, with significantly lower values for T than R and NW plots. Higher overwinter earthworm activity in T plots contributed to lower soil N recovery. In earthworm-invaded plots isotope enrichment was highest in macroaggregates and microaggregates whereas in NW plots silt plus clay fractions were most enriched. The net effect of litter mixing and priming of recalcitrant soil organic matter (SOM), stabilization of SOM in soil aggregates, and alteration of the soil microbial community by earthworm activity results in loss of SOM and lowering of the C:N ratio. We suggest that earthworm stoichiometry plays a fundamental role in regulating C and N dynamics of forest SOM.

Linking community and national park development: A case from the Dominican Republic

National parks have complex relationships with local communities that impact both conservation success and community well-being. Integrated conservation and development projects have been a key approach to managing these relationships, although their effectiveness has been increasingly questioned. Park-people relationships of the Armando Bermudez National Park in the Dominican Republic were studied, focusing on forests, aquatic resources, community well-being and development, and ecotourism. The park, established in 1956, is well respected by the community, based on its long history and its role in protecting water resources that are critical to the community. However, management of riparian vegetation and local fisheries present challenges in terms of finding a balance between conservation and development. Hiking and trekking opportunities attract both national and international tourists to the park, and community members benefit from employment as tour guides and providing mule rentals. At the same time, tourism activities also present continuing challenges related to: (1) the distribution of tourism benefits between local people and outsiders, and within the local community, (2) maintaining the local economic benefits of tourism while protecting park resources, and (3) developing park- or conservation-related economic opportunities to complement tourism. The results highlight the need to develop site-specific strategies to manage park-people relationships through interdisciplinary analysis.

Vegetation-environment relationships in forest ecosystems of the Cordillera Central, Dominican Republic1

Abstract Sherman, R. E., P. H. Martin, and T. J. Fahey (Department of Natural Resources, Cornell University, Ithaca, NY 14853) Vegetation-environment relationships in forest ecosystems of the Cordillera Central, Dominican Republic. J. Torrey. Bot. Soc. 132: 293–310. 2005.—We examined forest vegetation-environment relationships in the central mountain range of Hispaniola to improve general understanding of tropical montane forests. Forest inventory data were collected in 1999 and 2000 from 245 plots established in the Armando Bermúdez and Carmen Ramírez National Parks, Dominican Republic, over an elevation range of 1,100–3,075 m. Average tree density (≥ 10 cm dbh), basal area, and dbh were highly variable across the elevation gradient; species richness declined significantly with elevation; and the canopy height of broadleaved stands declined whereas the height of stands dominated by the endemic pine, Pinus occidentalis Sw., was relatively constant across the elevation gradient. Four major forest associations were identified using TWINSPAN: a low elevation broadleaved forest; a pine-broadleaved mixed forest; a mid-elevation cloud forest; and a largely monospecific pine forest that extends from the cloud forests to the summits of the highest peaks and dominates the leeward slopes of the mountains. Species composition varied continuously along the elevation gradient up to 2,250 m; however, above 2,250 m there was an abrupt shift from cloud forest to monospecific pine forests. Temperature, humidity, and fire history appear to regulate the position of this boundary, probably reflecting the position of the trade wind inversion. Ordination and logistic regression indicated that disturbance history and topo-edaphic factors influenced individual species distributions.

Fire and vegetation dynamics in high-elevation neotropical montane forests of the Dominican Republic.

Abstract In March and April 2005, severe fires burned over 1000 km2 of tropical montane forests in the Cordillera Central, Dominican Republic. The fire burned through our network of permanent vegetation plots, which were established in 1999 to examine interactions among environment, vegetation, and disturbance. We used QuickBird satellite imagery combined with field surveys to map the extent and severity of the fire across the landscape. The fire burned through 96% of the pine forest but quickly extinguished at the pine–cloud forest boundary along most of the ecotone. Topographic factors and fire severity had no influence on fire behavior at the ecotone. These observations support our original hypothesis that fire maintains the abrupt boundary between the pine and cloud forest vegetation in these mountains. Vegetation structure and composition played a direct role in regulating fire spread and behavior in this landscape.

Tropical montane cloud forest: environmental drivers of vegetation structure and ecosystem function

Tropical montane cloud forests (TMCF) are characterized by short trees, often twisted with multiple stems, with many stems per ground area, a large stem diameter to height ratio, and small, often thick leaves. These forests exhibit high root to shoot ratio, with a moderate leaf area index, low above-ground production, low leaf nutrient concentrations and often with luxuriant epiphytic growth. These traits of TMCF are caused by climatic conditions not geological substrate, and are particularly associated with frequent or persistent fog and low cloud. There are several reasons why fog might result in these features. Firstly, the fog and clouds reduce the amount of light received per unit area of ground and as closed-canopy forests absorb most of the light that reaches them the reduction in the total amount of light reduces growth. Secondly, the rate of photosynthesis per leaf area declines in comparison with that in the lowlands, which leads to less carbon fixation. Nitrogen supply limits growth in several of the few TMCFs where it has been investigated experimentally. High root : shoot biomass and production ratios are common in TMCF, and soils are often wet which may contribute to N limitation. Further study is needed to clarify the causes of several key features of TMCF ecosystems including high tree diameter : height ratio.

Lumbricid earthworm effects on incorporation of root and leaf litter into aggregates in a forest soil, New York State

Plant litter, microorganisms, and soil minerals assemble into aggregates in soils. Soil aggregates protect organic matter and are a primary site for storage of stabilized soil carbon, and thus many studies have evaluated how agriculture and soil disturbance affects aggregates. However, relatively little is known about aggregation in forest soils and the role of non-native earthworms. In a temperate forest where earthworm invasion has greatly reduced soil C stocks, we measured the abundance of aggregate fractions in plots with and without earthworms. We also quantified the flow of 13C from leaf litter and root litter into soil aggregates and evaluated how lumbricid earthworms affect this process. Macroaggregates comprised the majority of the bulk soil mass in these fine-textured soils both in the presence and absence of earthworms. The principal effect of earthworms on the composition of macroaggregates was to greatly reduce the proportion of both coarse POM and mineral-sorbed C in them. Earthworms also reduced the proportion of free microaggregates in soil. Two years after addition of isotope-labeled leaf litter most of the label was recovered in macroaggregates in the form of microaggregates held within them. Earthworms also greatly increased the proportion of root-derived C that was incorporated into macroaggegates, thereby apparently accelerating the process of root C incorporation into soil aggregates. However, much of the C incorporated into aggregates over a three-year time scale remained labile and was eventually mineralized. These observations indicate that earthworm effects on C mineralization may exceed effects on stabilization over longer time scales than for previous laboratory experiments.

The effects of acid deposition on the biogeochemical cycles of major nutrients in miniature red spruce ecosystems

As part of an experimental study of air pollution effects on tree growth and health, we combined process studies with an ecosystem approach to evaluate the effects of acidic deposition on soil acidification, nutrient cycling and proton fluxes in miniature red spruce ecosystems. Ninety red spruce saplings were transplanted into 1-m diameter pots containing reconstructed soil profiles and exposed to simulated acid rain treatments of pH 3.1, 4.1 and 5.1 for four consecutive growing seasons. All the principal fluxes of the major elements were measured.During the first year of treatments, the disturbance associated with the transplanting of the experimental trees masked any treatment effects by stimulating N mineralization rates and consequent high N03− cation, and H+ flux through the soil profile. In subsequent years, leaching of base cations and labile Al was accelerated in the most intensive acid treatment and corresponding declines in soil pH and exchangeable pools of Ca and Mg and increases in exchangeable Al concentrations were observed in the organic horizon. Leaching of Ca2+ and Mg2+ also was significantly higher in the pH 4.1 than in the pH 5.1 treatment. Flux of Ca from foliage and soil was increased in response to strong acid loading and root uptake increased to compensate for foliar Ca losses. In contrast, K cycling was dominated by root uptake and internal cycling and was relatively insensitive to strong acid inputs. Cation leaching induced by acidic deposition was responsible for the majority of H+ flux in the pH 3.1 treatment in the organic soil horizon whereas root uptake accounted for most of the H+ flux in the pH 4.1 and 5.1 treatments. Although no measurable effects on tree nutrition or health were observed, base cation leaching was significantly accelerated by acidic deposition, even at levels below that observed in the eastern U.S., warranting continued concern about acid deposition effects on the soil base status of forested ecosystems.