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PubMed2005

Microbial community structure and density under different tree species in an acid forest soil (Morvan, France).

Overexploitation of forests to increase wood production has led to the replacement of native forest by large areas of monospecific tree plantations. In the present study, the effects of different monospecific tree cover plantations on density and composition of the indigenous soil microbial community are described. The experimental site of "Breuil-Chenue" in the Morvan (France) was the site of a comparison of a similar mineral soil under Norway spruce (Picea abies), Douglas fir (Pseudotuga menziesii), oak (Quercus sessiflora), and native forest [mixed stand dominated by oak and beech (Fagus sylvatica)]. Sampling was performed during winter (February) at three depths (0-5, 5-10, and 10-15 cm). Abundance of microorganisms was estimated via microbial biomass measurements, using the fumigation-extraction method. The genetic structure of microbial communities was investigated using the bacterial- and fungal-automated ribosomal intergenic spacer analysis (B-ARISA and F-ARISA, respectively) DNA fingerprint. Only small differences in microbial biomass were observed between tree species, the highest values being recorded under oak forest and the lowest under Douglas fir. B- and F-ARISA community profiles of the different tree covers clustered separately, but noticeable similarities were observed for soils under Douglas fir and oak. A significant stratification was revealed under each tree species by a decrease in microbial biomass with increasing depths and by distinct microbial communities for each soil layer. Differences in density and community composition according to tree species and depth were related to soil physicochemical characteristics and organic matter composition.

Bacteria↗
PubMed2003

Impact of fencing on the recovery of the ground flora on heavily eroded slopes of a deciduous forest.

This paper seeks to outline early stages in the recovery of forest ground flora on eroded slopes impacted by recreation activities and to suggest how these data might be applied in the formulation of management policies for forest recreation areas. Based on a fencing experiment in the Sonian Forest near Brussels, we investigated whether, over a 6-year period, the vegetation was able to recover after having been destroyed by recreation use. Short-term trends in overall species composition were already observable during this 6-year study. Species recovery on eroded hills was related to slope, aspect, and soil type. During the considered time scale, the proportion of hemicryptophytes and the number of ancient forest species increased significantly. A downward trend was detected for Ellenberg's nitrogen and temperature indexes and for the proportion of therophytes and pioneer plants of disturbed places. Changes in species' frequencies suggest six recovery strategies: early, late, expanding, disappearing, transient, and fluctuating species. Aside from seedling reproduction from overstory influences, Luzula sylvatica appeared to be the most resilient of the species identified in the study since this species has the highest global frequency in our sampling plots and has increased its cover during the study period. Study results indicate that (1) protection from recreation has initiated the recovery of species in the herb layer, but (2) it may take a long time before vegetation previously present in the ground flora may recover in both density and species composition.

Conservation of Natural Resources↗
PubMed2005

Learning machines applied to potential forest distribution.

The clearing of forests to obtain land for pasture and agriculture and the replacement of autochthonous species by other faster-growing varieties of trees for timber have both led to the loss of vast areas of forest worldwide. At present, many developed countries are attempting to reverse these effects, establishing policies for the restoration of older woodland systems. Reforestation is a complex matter, planned and carried out by experts who need objective information regarding the type of forest that can be sustained in each area. This information is obtained by drawing up feasibility models constructed using statistical methods that make use of the information provided by morphological and environmental variables (height, gradient, rainfall, etc.) that partially condition the presence or absence of a specific kind of forestation in an area. The aim of this work is to construct a set of feasibility models for woodland located in the basin of the River Liébana (NW Spain), to serve as a support tool for the experts entrusted with carrying out the reforestation project. The techniques used are multilayer perceptron neural networks and support vector machines. Their results will be compared to the results obtained by traditional techniques (such as discriminant analysis and logistic regression) by measuring the degree of fit between each model and the existing distribution of woodlands. The interpretation and problems of the feasibility models are commented on in the Discussion section.

Artificial Intelligence↗
PubMed2003

Changing role of non-timber forest products (NTFP) in rural household economy: the case of Sinharaja World Heritage site in Sri Lanka.

This paper examines the modified patterns of utilizing non-timber forest products (NTFP) and associated behavioral changes around tropical forest areas in the context of conservation-related objectives and other commercially driven objectives. Our study introduces a conceptual framework based on the household production theory and tests empirically the hypotheses drawn at Sinharaja World Heritage in Sri Lanka. The results show that conditions introduced by forest conservation programs and the spread of small-scale commercial tea cultivation are transforming the economy around Sinharaja. The process is an economically rational one where resident communities decide upon their actions based on the opportunity cost of time involved with NTFP in the absence of observable prices. Although the process, overall, has led to a decline in the role of NTFP in the household economy, its impact over different NTFP are not uniform, leaving sustained demand for certain NTFP. This situation calls for a multifaceted approach in forest management programs to address the various household needs fulfilled by NTFP-based activities.

Commerce↗
PubMed2005

The impact of NTFP sales on rural households' cash income in India's dry deciduous forest.

In recent years, researchers and policy makers have recognized that nontimber forest products (NTFPs) extracted from forests by rural people can make a significant contribution to their well-being and to the local economy. This study presents and discusses data that describe the contribution of NTFPs to cash income in the dry deciduous forests of Orissa and Jharkhand, India. In its focus on cash income, this study sheds light on how the sale of NTFPs and products that use NTFPs as inputs contribute to the rural economy. From analysis of a unique data set that was collected over the course of a year, the study finds that the contribution of NTFPs to cash income varies across ecological settings, seasons, income level, and caste. Such variation should inform where and when to apply NTFP forest access and management policies.

Commerce↗
PubMed2005

Forest and farmland conservation effects of Oregon's (USA) land-use planning program.

Oregon's land-use planning program is often cited as an exemplary approach to forest and farmland conservation, but analyses of its effectiveness are limited. This article examines Oregon's land-use planning program using detailed spatial data describing building densities in western Oregon. An empirical model describes changes in building densities on forest and agricultural lands from 1974 to 1994, as a function of a gravity index of land's commuting distance to cities of various sizes, topographic characteristics, and zoning adopted under Oregon's land-use planning program. The effectiveness of Oregon's land-use planning program is evaluated based on the statistical significance of zoning variables and by computing estimated areas of forest and agricultural lands falling into undeveloped, low-density developed, and developed building density categories, with and without land-use zoning in effect. Results suggest that Oregon's land-use planning program has provided a measurable degree of protection to forest and agricultural lands since its implementation.

Agriculture↗
PubMed2005

Tree structure and diversity in human-impacted littoral forests, madagascar.

This research surveyed human-impacted littoral forests in southeastern Madagascar to determine (i) how forest structural features, indicative of human impact, are related to total, utilitarian, and endemic tree diversity; (ii) the distribution, abundance, and demographics of tree species groups (i.e., total, useful, endemic) across the landscape; and (iii) the amount of basal area available per human use category. We also use these data to consider issues of sustainable use and how human impact may influence littoral forest tree community composition across the landscape. Within 22 transects of 400 m2 each, we recorded a total of 135 tree species and 2155 individuals. Seventy-nine species (58%) were utilitarian and 56 (42%) were nonutilitarian species. Of the 2155 individuals, 1827 (84%) trees were utilitarian species. We recorded 23 endemic species (17% of the total species) and 17 (74%) of these were utilitarian species. Basal area was significantly correlated with Shannon Weiner Index values for total (r = 0.64, P < 0.01), utilitarian (r = 0.58, P < 0.01), and endemic tree diversity (r = 0.85, P < 0.01). Basal area was significantly correlated with the Simpson's index values for the endemic species (r = 0.74, P < 0.01). These correlations suggest that endemic tree species, of high global conservation value, may be the species group most influenced by changes in forest structure. Utilitarian species constituted 84% of the total basal area. The use category contributing the highest amount of basal area to the landscape was firewood. The results presented herein demonstrate that the landscape of southeastern Madagascar, commonly perceived as degraded, retains high value for both global conservation purposes and for local livelihoods. Thus, valuable opportunities may exist for developing conservation incentives that leverage both global and local conservation needs.

Conservation of Natural Resources↗
PubMed2000

Forest Protection and Reforestation in Costa Rica: Evaluation of a Clean Development Mechanism Prototype.

/ Costa Rica has recently established a program that provides funds for reforestation and forest protection on private lands, partly through the sale of carbon certificates to industrialized countries. Countries purchasing these carbon offsets hope one day to receive credit against their own commitments to limit emissions of greenhouse gases. Costa Rica has used the proceeds of the sale of carbon offsets to Norway to help finance this forest incentive program, called the Private Forestry Project, which pays thousands of participants to reforest or protect forest on their lands. The Private Forestry Project is accompanied by a monitoring program conducted by Costa Rican forest engineers that seeks to determine net carbon storage accomplished on these lands each year. The Private Forestry Project, which is officially registered as an Activity Implemented Jointly, is a possible model for bundled projects funded by the Clean Development Mechanism (CDM) established by the 1997 Kyoto Protocol to the UN Framework Convention on Climate Change. It also serves as an interesting example for the CDM because it was designed by a developing country host-not by an industrialized country investor. Accordingly, it reflects the particular "sustainable development" objectives of the host country or at least the host planners. Early experience in implementing the Private Forestry Project is evaluated in light of the main objectives of the CDM and its precursor-Activities Implemented Jointly. It is concluded that the project appears to meet the criteria of global cost-effectiveness and financing from non-ODA sources. The sustainable development implications of the project are specific to the region and would not necessarily match the ideals of all investing and developing countries. The project may be seen to achieve additional greenhouse gas abatement when compared against some (although not all) baselines.

Journal Article↗
PubMed2000

Development of a methodology for selecting criteria and indicators of sustainable forest management: a case study on participatory assessment.

This paper describes an application of multiple criteria analysis (MCA) in assessing criteria and indicators adapted for a particular forest management unit. The methods include: ranking, rating, and pairwise comparisons. These methods were used in a participatory decision-making environment where a team representing various stakeholders and professionals used their expert opinions and judgements in assessing different criteria and indicators (C&I) on the one hand, and how suitable and applicable they are to a forest management unit on the other. A forest concession located in Kalimantan, Indonesia, was used as the site for the case study. Results from the study show that the multicriteria methods are effective tools that can be used as structured decision aids to evaluate, prioritize, and select sets of C&I for a particular forest management unit. Ranking and rating approaches can be used as a screening tool to develop an initial list of C&I. Pairwise comparison, on the other hand, can be used as a finer filter to further reduce the list. In addition to using these three MCA methods, the study also examines two commonly used group decision-making techniques, the Delphi method and the nominal group technique. Feedback received from the participants indicates that the methods are transparent, easy to implement, and provide a convenient environment for participatory decision-making.

Journal Article↗
PubMed2003

Nitrogen limitation of growth and nutrient dynamics in a disturbed mangrove forest, Indian River Lagoon, Florida.

The objectives of this study were to determine effects of nutrient enrichment on plant growth, nutrient dynamics, and photosynthesis in a disturbed mangrove forest in an abandoned mosquito impoundment in Florida. Impounding altered the hydrology and soil chemistry of the site. In 1997, we established a factorial experiment along a tree-height gradient with three zones, i.e., fringe, transition, dwarf, and three fertilizer treatment levels, i.e., nitrogen (N), phosphorus (P), control, in Mosquito Impoundment 23 on the eastern side of Indian River. Transects traversed the forest perpendicular to the shoreline, from a Rhizophora mangle-dominated fringe through an Avicennia germinans stand of intermediate height, and into a scrub or dwarf stand of A. germinans in the hinterland. Growth rates increased significantly in response to N fertilization. Our growth data indicated that this site is N-limited along the tree-height gradient. After 2 years of N addition, dwarf trees resembled vigorously growing saplings. Addition of N also affected internal dynamics of N and P and caused increases in rates of photosynthesis. These findings contrast with results for a R. mangle-dominated forest in Belize where the fringe is N-limited, but the dwarf zone is P-limited and the transition zone is co-limited by N and P. This study demonstrated that patterns of nutrient limitation in mangrove ecosystems are complex, that not all processes respond similarly to the same nutrient, and that similar habitats are not limited by the same nutrient when different mangrove forests are compared.

Avicennia↗
PubMed2003

Regeneration of Rhizophora mangle in a Caribbean mangrove forest: interacting effects of canopy disturbance and a stem-boring beetle.

Current theory predicts that in low-density, seed-limited plant populations, seed predation will be more important than competition in determining the number of individuals that reach maturity. However, when plant density is high, competition for microsites suitable for establishment and growth is expected to have a relatively greater effect. This dichotomous perspective does not account for situations in which the risk of seed predation differs inside versus outside recruitment microsites. We report the results of a field experiment and sampling studies that demonstrate such an interaction between microsite quality and the risk of propagule predation in mangrove forests on the Caribbean coast of Panama, where it appears to play a key role in shaping the demography and dynamics of the mangrove, Rhizophora mangle. Rhizophora's water-borne propagules establish wherever they strand, but long-term sampling revealed that only those that do so in or near lightning-created canopy gaps survive and grow to maturity. These microsites afford better growth conditions than the surrounding understory and, as importantly, provide a refuge from predation by the scolytid beetle, Coccotrypes rhizophorae. This refuge effect was confirmed with a field experiment in which Rhizophora seedlings were planted at different positions relative to gap edges, from 5 m inside to 20 m outside the gap. Mortality due to beetle attack increased linearly from an average of 10% inside a gap to 72% at 20 m into the forest. The interaction between canopy disturbance and propagule predation may be having a large impact on the composition of our study forests. Being shade-tolerant, Rhizophora seedlings that escape or survive beetle attack can persist in the understory for years. However, the high rate of beetle-induced mortality effectively eliminates the contribution of advance regeneration by Rhizophora saplings to gap succession. This may explain why the shade-intolerant mangrove, Laguncularia racemosa, is able to co-dominate the canopy in low intertidal forests at our study sites.

Animals↗
PubMed2004

Successional changes in soil nitrogen availability, non-symbiotic nitrogen fixation and carbon/nitrogen ratios in southern Chilean forest ecosystems.

Vast areas of southern Chile are now covered by second-growth forests because of fire and logging. To study successional patterns after moderate-intensity, anthropogenic fire disturbance, we assessed differences in soil properties and N fluxes across a chronosequence of seven successional stands (2-130 years old). We examined current predictions of successional theory concerning changes in the N cycle in forest ecosystems. Seasonal fluctuations of net N mineralization (N(min)) in surface soil and N availability (N(a); N(a)=NH4+-N+NO3--N) in upper and deep soil horizons were positively correlated with monthly precipitation. In accordance with theoretical predictions, stand age was positively, but weakly related to both N(a) ( r(2)=0.282, P<0.001) and total N (N(tot); r(2)=0.192, P<0.01), and negatively related to soil C/N ratios ( r(2)=0.187, P<0.01) in surface soils. A weak linear increase in soil N(min) (upper plus deep soil horizons) was found across the chronosequence ( r(2)=0.124, P<0.022). N(min) occurred at modest rates in early successional stands, suggesting that soil disturbance did not impair microbial processes. The relationship between N fixation (N(fix)) in the litter layer and stand age best fitted a quadratic model ( r(2)=0.228, P<0.01). In contrast to documented successional trends for most temperate, tropical and Mediterranean forests, non-symbiotic N(fix) in the litter layer is a steady N input to unpolluted southern temperate forests during mid and late succession, which may compensate for hydrological losses of organic N from old-growth ecosystems.

Age Factors↗
PubMed2004

Competitive interactions among raptors in boreal forests.

We examined inter-specific interactions among goshawks ( Accipiter gentilis), common buzzards (Buteo buteo) and honey buzzards (Pernis apivorus) in western Finland in 1983-1996. Because goshawks are among the largest birds of prey species in boreal forests they may take over the nest of smaller and less-competitive forest-dwelling raptors when searching for suitable places for breeding. Accordingly, more than half of newly established goshawk territories were found on the territories previously occupied by the common buzzard and the honey buzzard. Otherwise, territory sharing between these species was rare. Fledgling production of honey buzzards was not associated with the presence of goshawks, probably owing to the almost 2 months later onset of breeding. This probably decreases competitive interactions between these two species. An intensive interference competition, instead, seemed to be evident between common buzzards and goshawks, because the fledgling production of common buzzards was decreased by 20% as a result of failures during incubation and nestling period in the vicinity (<1 km) of occupied goshawk nests. Similarly, territory occupancy of common buzzards till the next breeding season was significantly reduced in the presence of goshawks. Relatively high proportions of occupied buzzard territories (17%) in the study area were shared by breeding goshawks on the same territory. This suggests that although their diets are dissimilar they inhabit similar habitats and might compete for the available prime nesting habitats within forest landscapes. In addition, goshawks benefit from taking over the complete nests of other raptors, imposing upon the original owners of the nest, because building a large stick nest is probably energetically costly. As a large raptor, the goshawk apparently has a competitive advantage over smaller ones, and may have an ever-increasing impact on smaller birds of prey, if there is a lack of sheltered forests inducing competition for the available nest sites.

Animals↗
PubMed2004

Non-structural carbohydrate pools in a tropical forest.

The pool size of mobile, i.e. non-structural carbohydrates (NSC) in trees reflects the balance between net photosynthetic carbon uptake (source) and irreversible investments in structures or loss of carbon (sink). The seasonal variation of NSC concentration should reflect the sink/source relationship, provided all tissues from root to crown tops are considered. Using the Smithsonian canopy crane in Panama we studied NSC concentrations in a semi-deciduous tropical forest over 22 months. In the 9 most intensively studied species (out of the 17 investigated), we found higher NSC concentrations (starch, glucose, fructose, sucrose) across all species and organs in the dry season than in the wet season (NSC 7.2% vs 5.8% of dry matter in leaves, 8.8/6.0 in branches, 9.7/8.5 in stems, 8.3/6.4 in coarse and 3.9/2.2 in fine roots). Since this increase was due to starch only, we attribute this to drought-constrained growth (photosynthesis less affected by drought than sink activity). Species-specific phenological rhythms (leafing or fruiting) did not overturn these seasonal trends. Most of the stem volume (diameter at breast height around 40 cm) stores NSC. We present the first whole forest estimate of NSC pool size, assuming a 200 t ha(-1) forest biomass: 8% of this i.e. ca. 16 t ha(-1) is NSC, with ca. 13 t ha(-1) in stems and branches, ca. 0.5 and 2.8 t ha(-1) in leaves and roots. Starch alone (ca. 10.5 t ha(-1)) accounts for far more C than would be needed to replace the total leaf canopy without additional photosynthesis. NSC never passed through a period of significant depletion. Leaf flushing did not draw heavily upon NSC pools. Overall, the data imply a high carbon supply status of this forest and that growth during the dry season is not carbon limited. Rather, water shortage seems to limit carbon investment (new tissue formation) directly, leaving little leeway for a direct CO2 fertilization effects.

Carbohydrate Metabolism↗
PubMed2004

The direct and indirect effects of insectivory by birds in two contrasting Neotropical forests.

A goal among community ecologists is to predict when and where trophic cascades occur. For example, several studies have shown that forest birds can limit arthropod abundances on trees, but indirect effects of bird predation (i.e. decreased arthropod damage to trees) are not always observed and their context is not well understood. Because productivity is one factor that is expected to influence trophic cascades, we compared the extent to which birds indirectly limit herbivore damage to trees in two lowland Neotropical forests that differed in seasonality of leaf production and rainfall. We compared the effects of bird predation on local arthropod densities and on damage to foliage through a controlled experiment using bird exclosures in the canopy and understory of two forests. We found that birds decreased local arthropod densities and leaf damage in the canopy of the drier site during periods of high leaf production, but not in the wetter forest where leaf production was low and sporadic throughout the year. Birds had no effect on arthropod abundances and leaf damage in the understory where leaf production and turnover rates were low. In support of these experimental interpretations, although we observed that arthropod densities were similar at the two sites, bird densities and the rate at which birds captured arthropods were greater at the drier, seasonally productive site. The influence of top-down predation by birds in limiting herbivorous insects appears to be conditional and most important when the production and turnover of leaves are comparatively high.

Animals↗
PubMed2005

Regional variation in canopy transpiration of Central European beech forests.

Forest hydrologists have hypothesised that canopy transpiration (E(c)) of European temperate forests occurs at rather similar rates in stands with different tree species and hydrologic regimes. We tested this hypothesis by synchronously measuring xylem sap flow in four mature stands of Fagus sylvatica along a precipitation gradient with the aim (1) of exploring the regional variability of annual canopy transpiration (E(c(t))) in this species, and (2) of analysing the relationship between precipitation (P) and E(c(t)). E(c(t)) rates of 216, 225, 272 and 303 mm year(-1) corresponded to precipitation averages of 520, 710, 801 and 1,040 mm year(-1) in the four stands. We explored the regional variability of E(c(t)) in Central European colline to sub-montane beech stands in two meta-analyses based on (1) existing sap flow data on beech (n=5 observations), or (2) all canopy transpiration data on beech obtained by different techniques (sap flow, micrometeorological or soil water budget approaches, n=25). With a coefficient of variation (CV) of 20%, the regional variability of E(c(t)) (213-421 mm year(-1)) was smaller than the variation in corresponding precipitation (550-1,480 mm year(-1)). The mean E(c(t)) for beech was 289 (+/-58) mm year(-1) (n=25). A humped-shaped relationship between E(c(t)) and P, with a broad transpiration maximum in the precipitation range from ca. 700 to 1,000 mm year(-1), was found which may indicate soil moisture limitation of transpiration for P 1,000 mm year(-1). Thus, the precipitation level significantly influences canopy transpiration of humid temperate forests; however, the size of the P influence on E(c(t)) and, in part, the direction of its effect differ from forests in semi-arid or arid climates. European beech has the capacity to maintain high E(c) rates in both humid and partly dry summer climates (P<550 mm year(-1)).

Biological Transport↗
PubMed2005

The herb community of a tropical forest in central Panamá: dynamics and impact of mammalian herbivores.

Mammals are hypothesized to either promote plant diversity by preventing competitive exclusion or limit diversity by reducing the abundance of sensitive plant species through their activities as browsers or disturbance agents. Previous studies of herbivore impacts in plant communities have focused on tree species and ignored the herbaceous community. In an experiment in mature-phase, tropical moist forest sites in central Panamá, we studied the impact of excluding ground-dwelling mammals on the richness and abundance of herbs in 16, 30x45-m plots. Within each plot, we censused the herbaceous community in 28, 2x2-m subplots (1,792 m2 total area sampled). We identified over 54 species of herbs averaging 1.21 ramets m-2 and covering approximately 4.25% of the forest floor. Excluding mammals for 5 years had no impact on overall species richness. Within exclosures, however, there was a significant two-fold increase in the density of rare species. Overall herbaceous density and percent cover did not differ between exclosures and adjacent control plots, although cover did increase over time. Mammalian exclusion significantly increased the total cover of three-dominant herb species, Pharus latifolius, Calathea inocephala, and Adiantum lucidum, but did not affect their density. This study represents one of the most extensive herbaceous community censuses conducted in tropical forests and is among a few that quantify herbaceous distribution and abundance in terms of both density and cover. Additionally, this work represents the first community level test of mammalian impacts on the herbaceous community in a tropical forest to date. Our results suggest that ground dwelling mammals do not play a key role in altering the relative abundance patterns of tropical herbs in the short term. Furthermore, our results contrast sharply with prior studies on similar temporal and spatial scales that demonstrate mammals strongly alter tree seedling composition and reduce seedling density. Thus, we question the pervasiveness of top-down control on tropical plant communities and the paradigm that defaunation will inexorably lead to widespread, catastrophic shifts in plant communities.

Adiantum↗
PubMed2005

The direct and indirect effects of insectivory by birds in two contrasting Neotropical forests.

A goal among community ecologists is to predict when and where trophic cascades occur. For example, several studies have shown that forest birds can limit arthropod abundances on trees, but indirect effects of bird predation (i.e. decreased arthropod damage to trees) are not always observed and their context is not well understood. Because productivity is one factor that is expected to influence trophic cascades, we compared the extent to which birds indirectly limit herbivore damage to trees in two lowland Neotropical forests that differed in seasonality of leaf production and rainfall. We compared the effects of bird predation on local arthropod densities and on damage to foliage through a controlled experiment using bird exclosures in the canopy and understory of two forests. We found that birds decreased local arthropod densities and leaf damage in the canopy of the drier site during periods of high leaf production, but not in the wetter forest where leaf production was low and sporadic throughout the year. Birds had no effect on arthropod abundances and leaf damage in the understory where leaf production and turnover rates were low. In support of these experimental interpretations, although we observed that arthropod densities were similar at the two sites, bird densities and the rate at which birds captured arthropods were greater at the drier, seasonally productive site. The influence of top-down predation by birds in limiting herbivorous insects appears to be conditional and most important when the production and turnover of leaves are comparatively high.

Animals↗