Showing papers by "Ariel E. Lugo published in 1999"

Soil oxygen availability and biogeochemistry along rainfall and topographic gradients in upland wet tropical forest soils

Abstract: We measured soil oxygen concentrations at 10 and 35 cm depths and indices of biogeochemical cycling in upland forest soils along a rainfall and elevation gradient (3500–5000 mm y−1; 350–1050 masl) and along topographic gradients (ridge to valley, ∼150 m) in the Luquillo Experimental Forest, Puerto Rico Along the rainfall gradient, soil O2 availability decreased significantly with increasing annual rainfall, and reached very low levels (<3%) in individual chambers for up to 25 consecutive weeks over 82 weeks of study Along localized topographic gradients, soil O2 concentrations were variable and decreased significantly from ridges to valleys In the valleys, up to 35% of the observations at 10–35 cm depth were <3% soil O2 Cross correlation analyses showed that soil O2 concentrations were significantly positively correlated along the topographic gradient, and were sensitive to rainfall and hydrologic output Soil O2 concentrations in valley soils were correlated with rainfall from the previous day, while ridge sites were correlated with cumulative rainfall inputs over 4 weeks Soils at the wettest point along the rainfall gradient had very high soil methane concentrations (3–24%) indicating a strong influence of anaerobic processes We measured net methane emission to the atmosphere at the wettest sites of the rainfall gradient, and in the valleys along topographic gradients Other measures of biogeochemical function such as soil organic matter content and P availability were sensitive to chronic O2 depletion along the rainfall gradient, but less sensitive to the variable soil O2 environment exhibited at lower elevations along topographic gradients

Deliberate Introductions of Species: Research Needs Benefits can be reaped, but risks are high

Abstract: The silent invasion of Hawaii by insects, disease organisms, snakes, weeds and other pests is the single greatest threat to Hawaii’s economy and natural environment.... Even one new pest-like the brown tree snake--could forever change the character of our islands. (Coordinating Group on Alien Pest Species 1996, P. 1). Reforestation in the tropics is so vastly behind deforestation that we cannot wait to fully appraise all the potential negative elements of domestication. Weediness is of consequence perhaps in Honolulu, but not in Addis or Delhi. (James Brewbaker, quoted by Hughes 1994, p. 244 ).

The Holdridge life zones of the conterminous United States in relation to ecosystem mapping

Abstract: Summary Aim Our main goals were to develop a map of the life zones for the conterminous United States, based on the Holdridge Life Zone system, as a tool for ecosystem mapping, and to compare the map of Holdridge life zones with other global vegetation classification and mapping efforts. Location The area of interest is the forty-eight contiguous states of the United States. Methods We wrote a PERL program for determining life zones from climatic data and linked it to the image processing workbench (IPW). The inputs were annual precipitation (Pann), biotemperature (Tbio), sea-level biotemperature (T0bio), and the frost line. The spatial resolution chosen for this study (2.5 arc-minute for classification, 4-km for mapping) was driven by the availability of current state-of-the-art, accurate and reliable precipitation data. We used the Precipitation-elevation Regressions on Independent Slopes Model, or PRISM, output for the contiguous United States downloaded from the Internet. The accepted standard data for air temperature surfaces were obtained from the Vegetation/Ecosystem Modelling and Analysis Project (VEMAP). This data set along with station data obtained from the National Climatic Data Center for the US, were used to develop all temperature surfaces at the same resolution as the Pann. Results The US contains thirty-eight life zones (34% of the world's life zones and 85% of the temperate ones) including one boreal, twelve cool temperate, twenty warm temperate, four subtropical, and one tropical. Seventy-four percent of the US falls in the ‘basal belt’, 18% is montane, 8% is subalpine, 1% is alpine, and < 0.1% is nival. The US ranges from superarid to superhumid, and the humid province is the largest (45% of the US). The most extensive life zone is the warm temperate moist forest, which covers 23% of the country. We compared the Holdridge life zone map with output from the BIOME model, Bailey's ecoregions, Kuchler potential vegetation, and land cover, all aggregated to four cover classes. Despite differences in the goals and methods for all these classification systems, there was a very good to excellent agreement among them for forests but poor for grasslands, shrublands, and nonvegetated lands. Main conclusions We consider the life zone approach to have many strengths for ecosystem mapping because it is based on climatic driving factors of ecosystem processes and recognizes ecophysiological responses of plants; it is hierarchical and allows for the use of other mapping criteria at the association and successional levels of analysis; it can be expanded or contracted without losing functional continuity among levels of ecological complexity; it is a relatively simple system based on few empirical data; and it uses objective mapping criteria.

Mangrove Ecosystem Research with Emphasis On Nutrient Cycling

Abstract: Mangroves are the subject of a struggle between those who want to maximize economic benefit through intensive uses of the system (sometimes at the cost of eliminating the biota in favor of urban or other developments) and those who advocate complete preservation of the ecosystem even at the exclusion of people. As tropical countries continue to develop economically, their governments must balance the various uses of mangroves and other coastal areas to assure sustainability of development. However, this will not be possible without a constant flux of scientific information on these ecosystems. Scientists must provide accurate information upon which resource managers and policy makers can base their decisions.