J.R. Healey

Hurricane effects on forest ecosystems in the Caribbean

Hurricanes are common, potentially catastrophic events for ecosystems in the Caribbean. We synthesize the work reported in this issue, together with the existing literature, to discuss effects of hurricanes on Caribbean ecosystems and to highlight priorities for future work. Comparisons of the impacts of hurricanes on different ecosystems are made difficult by the lack of detailed meteorological data, lack of prehurricane ecological data and differences between studies in types and timing of measurements made. Effects of recent hurricanes on Caribbean forest ecosystems include: defoliation, ranging from complete in lowland wet forest in Nicaragua after Hurricane Joan to negligible in parts of Jamaican montane forest after Hurricane Gilbert; felling of trees by uprooting and snapping (80% in Nicaragua to 14% in Jamaica); and tree mortality, which is rarely recorded and generally low (13% in the Yucatan following Hurricane Gilbert to 3% in Puerto Rican montane forests following Hurricane Hugo). Damage to individual trees varies with topographic location, stand characteristics, tree size (large ones uprooting and small ones snapping in Dominica during Hurricane David, but not in Jamaica), and species characteristics (such as wood density), but it is difficult to generalize about these factors. Effects on animal populations are both direct and through reductions in food supplies. Frugivorous and nectarivorous birds were more severely affected than insectivorous species in the Virgin Islands and Jamaica. There is little information about hurricane effects on insect populations, but populations of two species of walking sticks in Puerto Rico declined sharply after Hurricane Hugo. Numbers of adults of one frog species in Puerto Rico quadrupled after Hurricane Hugo, but numbers of juveniles were severely reduced by the storm. Effects of hurricanes on the physical environment include modified microclimates due to increased light penetration through defoliated canopies and landslides triggered by rainfall. Increased litterfall led to increases in some soil nutrients, and fine root biomass was drastically reduced in a Puerto Rican montane forest. Recovery of forest ecosystems from hurricanes depends on a combination of seedling growth and resprouting of canopy trees. In several studies, seed germination was promoted by higher light and/or higher temperature, but seedling mortality also increased. The relative importance of newly germinated seedlings, advance regeneration, and regrowth of damaged adults has not been studied. The few long-term studies of adult trees show the expected decline in the proportion of pioneer and intolerant species with time after disturbance. Hurricanes may be the most important factor controlling species composition and some aspects of ecosystem dynamics in the Caribbean; there is much still to be learned, and we suggest some priorities for future research.

Sprouting of trees in Jamaican montane forests after a hurricane

1 Forests in the Blue Mountains of Jamaica were damaged by Hurricane Gilbert which passed over the island on 12 September 1988. 2 In plots between 1300-1900 m, recorded 5-41 months after the hurricane, most stems (61.4% of 4949 living stems) and most species (44 of 47 common species) had sprouts. Comparing species, percent of stems sprouting ranged from 0 to 100%. 3 Broken stems sprouted proportionately more than intact stems; completely defoliated stems sprouted proportionately more than those not completely defoliated; there was no difference between uprooted and upright stems; and stems > 10 cm d.b.h. sprouted more frequently and produced more sprouts per stem, than those 30 sprouting stems, four sprouted more from below 2.5 m, five more from above 2.5 m and five had sprouts evenly distributed. For all species combined, approximately equal numbers of stems fell into each of these three categories. 6 Survivorship up to 41 months after the hurricane was higher in stems with sprouts than those without. 7 There was no simple relationship between the frequency of sprouting of species and microenvironments where seed germination and seedling establishment have been recorded. However, eight common species which have rarely been observed to germinate or establish (in a wide range of conditions) had high frequencies of sprouting. We propose that sprouting is an important mechanism by which many species maintain their presence in these forests.

Damage and responsiveness of Jamaican montane tree species after disturbance by a hurricane

A severe hurricane affected Jamaican montane rain forests in 1988. We made local and widespread measurements of tree condition in three periods: prehurricane 1974- 1984 (preh.); hurricane 1984-1989 (h.); and post-hurricane 1989-1992 (post-h.). In the h. period, 7.22% of stems and 4.72% of the total basal area died; crown loss was the most frequent cause of mortality. Among individual tree species, the hurricane caused a large range in mortality (0-26%) and non-fatal damage. Post-h. mortality was greater than mor- tality in the h. period, and varied among species. Post-h. stem growth rates (all species combined) were more than double the prehurricane rates, but species showed a considerable range from no significant increase to eight times greater. We classified 20 common tree species using damage scores (normalized h. mortality, plus normalized change in mortality from preh. to post-h., plus normalized complete crown loss in h.) and response scores (normalized change, preh. to post-h., in recruitment to the ?3 cm dbh size class, plus normalized change in growth rate from preh. to post-h., plus normalized frequency of sprouts). Species were assigned to one of four groups: resistant (11 species), with low damage and low response; susceptible (5 species), with high damage and low response; resilient (1 species), with high damage and high response; and usurpers (3 species), with low damage and high responsiveness. The grouping of species was broadly related to their regeneration requirements. Most species with seedlings usually found under closed canopy were resistant; three of the four species with seedlings usually found on landslides were also resistant. Species with seedlings most frequently found in gaps included resilient, susceptible, and usurper species, but were not usually resistant. It is likely that the three species classified as usurpers will increase their relative abun- dance in the forest in the next decades and that Cyathea pubescens, which was very susceptible, will decrease in relative abundance of adults. Most of the other species are likely to have small changes in their relative abundances. Thus, at present, hurricanes have few long-term effects on the forests, although a change in the disturbance regime may alter this.

Nitrogen and phosphorus fertilization of Jamaican montane forest trees

Plots in the Jamaican montane forest were fertilized with nitrogen or with phosphorus to test the hypothesis that growth of trees in this natural forest is limited by the supply of N and P from the soil. Once a year from 1983 to 1986, urea was added to one plot (at 150 kg N ha −1 y −1 ) and triple superphosphate was added to another (at 50 kg P ha −1 y −1 ). In each of these plots and in two control plots, foliage of four common tree species was collected immediately before each fertilizer addition. Trunk growth was measured in 105 individuals. Foliar N concentrations were not significantly higher in trees fertilized with N compared to control trees. In Dendropanax cf. pendulus and Hedyosmum arborescens fertilization with N resulted in lower P concentrations but only after the third year of fertilization, possibly due to dilution by increased leaf production. Mean trunk diameter growth was significantly higher in the N-fertilized trees than in controls. Mean foliar P concentrations were higher in Podocarpus urbanii and Clethra occidentalis following fertilization with P, but only after two years of fertilization. Trunk diameter growth was greater in the P fertilized plot. Thus growth in some Jamaican montane forest trees was limited by the natural supplies of N and of P.

Does community forest management provide global environmental benefits and improve local welfare

Global financial donors have invested billions of dollars in “Sustainable Forest Management” to conserve forests and the ecosystem services they provide. A major contributing mechanism, community forest management (CFM), aims to provide global environmental benefits (reduce deforestation, maintain biodiversity), while also improving local human welfare (alleviate poverty). We have systematically reviewed available evidence of CFM effectiveness and consider the implications of our findings for future investment in CFM programs. There is evidence of CFM being associated with greater tree density and basal area but not with other indicators of global environmental benefits. We found no data on local human welfare amenable to meta-analysis. Poor study design, variable reporting of study methodology or context, and lack of common indicators make evidence synthesis difficult. Given the policy interest in and the planned donor expenditure on CFM, evaluation must be improved so that informed decisions can be made...

Remediation of metal polluted mine soil with compost: co-composting versus incorporation.

Trace element contamination of post-industrial sites represents a major environmental problem and sustainable management options for remediating them are required. This study compared two strategies for immobilizing trace elements (Cu, Pb, Zn, and As) in mine spoil: (1) co-composting contaminated soil with organic wastes and (2) conventional incorporation of mature compost into contaminated soil. Sequential chemical extraction of the soil was performed to determine temporal changes in trace element fractionation and bioavailability during composting and plant growth. We show that mine spoil can be co-composted successfully and this action causes significant shifts in metal availability. However, co-composting did not lead to significant differences in metal partitioning in soil or in plant metal uptake compared with simply mixing mine spoil with mature compost. Both treatments promoted plant growth and reduced metal accumulation in plants. We conclude that co-composting provides little additional benefit for remediating trace-element-polluted soil compared with incorporation of compost.

Feed the Crop Not the Soil: Rethinking Phosphorus Management in the Food Chain

Society relies heavily on inorganic phosphorus (P) compounds throughout its food chain. This dependency is not only very inefficient and increasingly costly but is depleting finite global reserves of rock phosphate. It has also left a legacy of P accumulation in soils, sediments and wastes that is leaking into our surface waters and contributing to widespread eutrophication. We argue for a new, more precise but more challenging paradigm in P fertilizer management that seeks to develop more sustainable food chains that maintain P availability to crops and livestock but with reduced amounts of imported mineral P and improved soil function. This new strategy requires greater public awareness of the environmental consequences of dietary choice, better understanding of soil-plant-animal P dynamics, increased recovery of both used P and unutilized legacy soil P, and new innovative technologies to improve fertilizer P recovery. In combination, they are expected to deliver significant economic, environmental, and resource-protection gains, and contribute to future global P stewardship.

The cost of carbon retention by reduced impact logging.

Abstract Reduced impact logging (RIL) is one means of reducing the carbon emissions held responsible for global warming. It may also reduce other adverse logging effects. A study of RIL’s effects in Sabah, Malaysia, found 44% reduction of area logged within a tract, 22% reduction in timber yield per logged hectare, and 18% increase in cost per m 3 logged compared with conventional logging (CL). Estimated timber yield at the next harvest was 31% higher following RIL. Compared with unlogged forest, RIL damaged rattan, wildlife, soil and water quality values less than did CL. However, RIL’s environmental benefits per area of forest logged are considerably compromised by the greater logging area required for a given timber yield. Doing RIL in place of CL had a net cost per unit area at all rates of discount. Per m 3 of timber logged, RIL was beneficial without discounting, but had a net cost at a 2% discount rate and higher. The overall cost of RIL’s superior carbon retention varied with both discount rate and level of analysis, from negative price to more than US

The effects of secondary forest clearance and subsequent land-use on erosion losses and soil properties in the Blue Mountains of Jamaica

50 per megagram at a 10% discount rate. RIL appears most cost-effective on a per m 3 logged basis at low discount rates. However, at commonly applied discount rates (4% and above) RIL’s carbon price exceeds most published estimates for carbon prices.

Kinetics of soil microbial uptake of free amino acids

As pressure on land and forest resources increases, there is a growing need to assess and improve the sustainability of slash-and-burn agriculture in tropical uplands. On steep-hillslopes (24–32 ◦ ) in the forest buffer zone of the Blue Mountains of Jamaica, following clearance of secondary forest the relative impact on surface runoff, soil erosion and soil properties of three land-use treatments: maintained weed-free without cultivation (bare); cultivated with herbaceous crops (agriculture); and cultivated with herbaceous crops and intercropped with Calliandra calothyrsuscontour hedges (agroforestry) was assessed over a 5-year period and compared with an uncleared secondary forest control (forest). The forest provided good protection against surface runoff (which was consistently less than 0.2% of rainfall) and soil erosion losses (less than 500 kg ha −1 per year); agriculture caused a seven-fold increase in surface runoff and 21-fold increase in soil erosion. However, agroforestry was effective in conservation of water (45% reduction in runoff compared with agriculture) and soil (erosion reduced by 35%). The clearance of the secondary forest led to large changes in most measured soil properties. Over 5 years concentrations of organic matter declined by 31%, total N by 38%, exchangeable K by 47%, Ca by 43% and Mg by 56%; over the same period bulk density increased by 48%. Of the soil properties more subject to year-to-year fluctuations, after 5 years the concentration of available P was 36% less in cleared plots than in forest, exchangeable Na was 50% less and moisture content 43% less. Only total P concentration and pH were unaffected. Five years after forest clearance there was no good evidence that these changes had stabilised and very little difference in soil properties was found amongst the three land-use treatments. However, within the agroforestry plots, exchangeable K, Na and sand concentrations became higher under the hedgerows than between them (by 14, 9 and 8%, respectively), whilst clay concentration became higher between them (by 9%). The results indicate that this low-input, contour-tree-hedgerow technology is effective at soil and water conservation through the sieve-barrier effect and increased water infiltration (respectively) and has the potential to enhance the sustainability of this land-use system at a plot scale.