Treesearch

We combined a detailed field study of forest canopy damage with calibrated Landsat 7 Enhanced Thematic Mapper Plus (ETM+) reflectance data and texture analysis to assess the sensitivity of basic broadband optical remote sensing to selective logging in Amazonia. Our field study encompassed measurements of ground damage and canopy gap fractions along a chronosequence of postharvest regrowth of 0.5–3.5 years. We found that canopy damage and regrowth rates varied according to the logging method used, either conventional logging or reduced impact logging. Areas used to stage felled trees prior...

A new false-colour-infrared image derived from biweekly 1993 and 1995 Advanced Very High Resolution Radiometer (AVHRR) data provides a snow-free and cloud-free base image for the interpretation of vegetation as part of a 1:7.5M-scale Circumpolar Arctic Vegetation Map (CAVM). A maximum-NDVI (Normalized DiVerence Vegetation Index) image prepared from the same data provides a circumpolar view of vegetation green-biomass density across the Arctic. This paper describes the remote sensing products, the environmental factors that control the principal vegetation patterns at this small scale, and...

Soil organic matter is the largest sink for N additions to forests. Species composition may affect soilNretention by altering the amount or proportion of added N stored in non-labile organic pools. We measured 15N tracer retention in labile and non-labile pools of surface (0–20 cm) mineral soils, 7 yr after the tracer was applied to a 9 yr-old Puerto Rican tree plantation with replicated stands of three species (two N-fixers, one Eucalyptus, Euc).

Soil organic matter is the largest sink for N additions to forests.Species composition may affect soilNretention by altering the amount or proportion of added N stored in non-labile organic pools. We measured 15N tracer retention in labile and non-labile pools of surface (0–20 cm) mineral soils, 7 yr after the tracer was applied to a 9 yr-old Puerto Rican tree plantation with replicated stands of three species.

Examination of the alkaloids of Solenopsis maboya Snelling and comparison with those previously found in S. Torresi Snelling, reveals a clear example of caste-specific alkaloid production in the queens and workers of each species. The queens of Solenopsis maboya contain a single piperidine while the workers produce a different piperidine along with two indolizidine isomers. In contrast, the queens of S. torresi contain a single indolizidine while the workers produce an unsaturated piperidine. In both species there is structural analogy between the bicyclic indolizidines and the monocyclic...

Nocturnal nuptial flights of ants were studied at Guaynabo and Guanica in the tropical island of Puerto Rico. A great proportion of the species had a high frequency of flights during the year with little seasonality in the frequency of flights. Flights were less frequent during the dry season. Nuptlal flights at Guaynabo occurred mostly during the post-sunset (18:30-22:30) and pre-dawn (04:00-06:00) hours. Few flights occurred between these two periods. The number of flights was fewer and flights on the average smaller in size in the Guanica dry forest than at Guaynabo. There was little...

With the vast amount of abandoned tropical land due to non- sustainable farming practices, tropical tree-plantations become an effective means in restoring soil productivity and preserving ecosystem biodiversity. Because earthworms are the dominant soil fauna in moist tropical regions and play an important role in improving soil fertility, understanding the mechanisms by which forest management practices affect the abundance and community structure of earthworms will be crucial in designing future reforestation programs. Forest management practices include site preparation, tree species...

The decomposition of plant residues is influenced by their chemical composition, the physical-chemical environment, and the decomposer organisms. Most studies interested in latitudinal gradients of decomposition have focused on substrate quality and climate effects on decomposition, and have excluded explicit recognition of the soil organisms involved in the process. To test whether soil fauna exhibit different effects under diverse climates or substrates, we quantified decomposition rates and N fluxes in control and fauna-excluded treatments with litterbags containing relatively high-quali...

This study develops two habitat-based approaches for evaluating instream-flow requirements within the Luquillo Experimental Forest in northeastern Puerto Rico. The analysis is restricted to instream-flow requirements in upland streams dominated by the common communities of freshwater decapods. In headwater streams, pool volume was the most consistent factor in predicting the abundance of common freshwater shrimp. In second- and third-order tributaries, both water depth and velocity can be used to define their habitats. The most common species of shrimp are reclusive during the day; at...