Search Results - (Author, Cooperation:J. J. Ewel)

2011-06-10

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

Animals ; Conservation of Natural Resources/*methods ; Ecology/*methods ; *Ecosystem ; Extinction, Biological ; Introduced Species/*statistics & numerical data ; Species Specificity

1572-9680

agriculture ; climate ; fertility ; humid tropics ; life zones ; succession

Springer Online Journal Archives 1860-2000

Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Abstract Natural ecosystems, whose components are the results of natural selection, are sustainable; most are productive, responsive to pests, and retentive of nutrients. Thus, they are appropriate models on which to base the design of new systems of land use. Abiotic and biotic stressors are related non-linearly; the nadir of total stress being mid-way along a gradient of environmental harshness. Superimposing the stress functions on Holdridge's life zone chart yields four broad categories of environments for agriculture: climates where annual rainfall is similar to potential evapotranspiration, plus three other categories that are either too cold, too arid, or too wet. Extremely cold lands have no potential for agriculture. Lands that are arid or infertile can be used successfully, although the cost of compensating for environmental limitations increases exponentially with increasing abiotic stress. Grazing animals (which act as trophic buffers between people and environment) have proven successful in dry and infertile environments. The humid tropical lowlands epitomise environments of low abiotic stress but overwhelming biotic intricacy. Here it pays to imitate natural systems rather than struggle to impose simplicity on ecosystems that are inherently complex. The keys to success are to (i) channel productivity into outputs of nutritional and economic importance, (ii) maintain adequate diversity to compensate for losses in a system simple enough to be horticulturally manageable, (iii) manage plants and herbivores to facilitate associational resistance and not associational susceptibility, and (iv) use perennial plants to maintain soil fertility, guard against erosion, and make full use of resources.

Electronic Resource

1432-1939

Defoliation ; Diversity ; Herbivory ; Productivity ; Tropical

Springer Online Journal Archives 1860-2000

Biology

Summary Floristically rich and monospecific tropical plant communities both responded to partial defoliation with increases in rates of production of new leaf area. Even after 50% of the leaf area had been removed three times, the leaf area increments were still higher in defoliated plots than in controls. Mean leaf area increment after defoliation, on a leaf area per unit ground area basis, was 905 cm2 m-2 d-1 in diverse successional vegetation and 536 cm2 m-2 d-1 in a cassava monoculture. Although defoliation stimulated leaf area development, on a per unit ground area basis, in both the cassava monoculture and the successional vegetation, the effect was more pronounced in the successional vegetation. On a per unit leaf area basis, leaf area increments following defoliation in both the diverse successional vegetation and the monoculture were approximately five times those of controls. The diverse plant community continued to respond vigorously after repeated defoliation, while the amount of stimulation of leaf are development in the monoculture declined. Because of their ability to respond even after repeated defoliation, diverse communities may in the long term be more homeostatic with respect to leaf area than are monocultures. The enhanced responsiveness of the species-rich community was due to changes in plant species abundance and very rapid leaf area development by some species.

Electronic Resource

1573-5052

Forest regeneration ; Germination ; Seed input ; Seed rain: allochthonous ; Seed rain: autochthonous ; Soil seed bank ; Succession ; Tropics

Springer Online Journal Archives 1860-2000

Biology

Abstract Soil seed banks and current seed inputs each play a role in tropical succession. We compared the abundance and floristic composition of seeds from these two sources at a Costa Rican site by germinating seeds from the soil, measuring seed inputs for 3 yr, and monitoring the earliest colonists in a forest clearing. There were an estimated 6800 viable seeds/m2 in the soil of 3.3-yr-old vegetation, 9500 seeds/m2 in 11-yr-old vegetation, and 7000 seeds/m2 in a 75-yr-old forest. An estimated 10100 seeds/m2 fell on the soil surface of the young successional vegetation during 3 yr and 3700 seeds/m2 fell during that same time in the forest. Locally produced seeds accounted for about 75% of the seed input to the soil surface early in succession. Seeds dispersed out of young successional vegetation increased the quantity and species richness of the seed input and storage in an adjacent forest. Much of the species richness of the young successional vegetation resulted from seeds dispersed there from other communities by animals. Deforestation stimulated germination of most seeds in the surface soil of the old forest, including seeds of the dominant canopy tree. The recruitment of seedlings from the soil seed bank numerically overwhelmed that from post-disturbance seed rain and sprouts. We evaluated patterns of soil seed storage during succession and predicted the ability of vegetation of differing ages to respond to disturbance. Immediately after disturbance the number of seeds in the soil plummeted due to mortality, low inputs, and germination. As the vegetation regrew, the soil seed bank increased to a peak after 4 to 7 yr, then gradually decreased to its pre-disturbance size. High-frequency pulses of disturbance should result in reduced species richness, dominance by species with long-lived seeds, and fast recovery by seedling recruitment from the soil seed bank.

Electronic Resource

1573-5036

agroecosystems ; andept ; nutrient retention ; root biomass ; root surface area ; roots ; succession ; tropical

Springer Online Journal Archives 1860-2000

Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Abstract Fine and coarse root mass and fine root surface area were studied during 5 yr following the felling and burning of a tropical forest near Turrialba, Costa Rica. Five experimental ecosystems were established: 1) natural successional vegetation, 2) successional vegetation enriched by seed applications, 3) imitation of succession (built by substituting investigator-selected species for natural colonizers), 4) monocultures (two maize crops followed by cassava andCordia alliodora), and 5) a bare plot. Fine roots grew rapidly in all treatments during the first 15 wk, at which time there were 75 gm−2 in the monoculture and 140 gm−2 in the enriched and natural successions. Subsequent growth was slower, and fine-root mass decreased during the first dry season. After 5 yr coarse root mass to a depth of 85 cm was about 800, 1370, and 1530 gm−2 in the succession, enriched succession and imitation of succession, respectively. At the final harvest, the 3.5 yr-oldC. alliodora plantation had 1000 g m−2 of coarse-root biomass. Roots 〈1 mm in diameter were concentrated in the upper 5 cm of soil and accounted for most fine-root surface area. Total fine-root surface area was greatest in the enriched successional vegetation and usually lowest in the monoculture.

Electronic Resource

1573-5036

Andept ; Germination ; Manganese ; Seed traps ; Seedling growth ; Steam sterilization

Springer Online Journal Archives 1860-2000

Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Summary Steam sterilization of a Typic Dystrandept in Costa Rica resulted in a six-fold increase in extractable Mn, to levels often considered toxic. Seeds of eight species, comprised of six successional taxa and two cultivars (soybean,Glycine max and raddish,Raphanus sativus) were planted in the sterilized soil and in unsterilized soil after delays of 1, 8, 15, and 28 days. Germination and mortality were not different in the two soils, indicating that steamsterilized soil can safely be used in seed traps. Six species (including both cultivars) grew better in unsterilized soil, but two of the native taxa (Phytolacca rivinoides andBocconia frutescens) grew significantly faster in sterilized soil.

Electronic Resource