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Forest Gaps (forest + gap)
Selected AbstractsCordia millenii: on the risk of local extinction?AFRICAN JOURNAL OF ECOLOGY, Issue 3 2009Fred Babweteera Abstract Selective logging of valuable tropical timber trees is a conservation concern because it threatens the long-term sustainability of forests. However, there is insufficient information regarding the postlogging recovery of harvested species. Here, I assessed the seed dispersal patterns, recruitment and abundance of Cordia millenii, a valuable timber tree in two Ugandan tropical rain forests that have been subjected to varying disturbance regimes. The aim was to determine the vulnerability of Cordia in these forests. The rate of seed dispersal was lower in the heavily disturbed Mabira Forest compared with the less disturbed Budongo Forest. Frugivores in Mabira were small-bodied individuals that spat seeds beneath fruiting trees, whereas 90% of the fruit in Budongo was consumed by large-bodied chimpanzees that disperse seeds over long distances. Juveniles of Cordia were not found in the closed forest, although they were found in forest gaps in Budongo but not Mabira. Mature tree density was higher in Budongo compared with Mabira. Lack of effective seed dispersal coupled with the inability of seedlings of Cordia to establish under closed canopy account for the arrested recruitment in Mabira. Enrichment planting in felling gaps is necessary to avoid local extinction of Cordia in forests without large vertebrates. Résumé L'abattage sélectif des espèces précieuses d'arbres tropicaux inquiète le milieu de la conservation parce qu'il menace la durabilité des forêts à long terme. Cependant, il n'y a pas assez d'informations au sujet de la restauration des espèces prélevées après l'abattage. Ici, j'ai évalué les schémas de dispersion des semences, le recrutement et l'abondance de Cordia millenii, une espèce d'arbre prisée, dans deux forêts tropicales pluviales d'Ouganda qui ont été soumises à des régimes de perturbation variables. Le but était de déterminer la vulnérabilité de Cordia dans ces forêts. Le taux de dispersion des graines était plus faible dans la forêt très perturbée de Mabira que dans la forêt de Budongo, moins dérangée. Les frugivores de Mabira étaient des individus de petite taille qui recrachaient les graines sous les arbres producteurs des fruits alors que 90% des fruits de Budongo étaient consommés par des chimpanzés qui peuvent disperser les semences sur le longues distances. On n'a pas trouvé de juvénile de Cordia dans la forêt fermée; on en trouvait dans des clairières dans la forêt de Budongo, mais pas dans celle de Mabira. La densité des arbres matures était plus haute à Budongo qu'à Mabira. Le manque de dispersion efficace des graines, coupléà l'incapacité des semences de Cordia de s'établir sous une canopée fermée, intervient dans l'arrêt du recrutement à Mabira. Il est nécessaire de pratiquer un enrichissement des plantations dans les clairières déboisées pour éviter l'extinction locale des Cordia dans les forêts qui n'abritent pas de grands vertébrés. [source] Size-dependence of growth and mortality influence the shade tolerance of trees in a lowland temperate rain forestJOURNAL OF ECOLOGY, Issue 4 2009Georges Kunstler Summary 1A trade-off between growth in high-light and survival in low-light of species is often proposed as a key mechanism underpinning the dynamics of trees in forest communities. Yet, growth and survival are known to depend on plant size and few studies have analysed how this trade-off can vary between juvenile life stages and the potential consequences of the trade-off for the differences in regeneration rate between species in mixed forests. 2We quantified growth and mortality for two different juvenile life stages , seedlings and saplings , of seven tree species common in temperate rain forests in New Zealand using data from field studies. We found strong evidence that the ranking of species for survival in shade and growth in full light was affected by size. There was a trade-off between seedling survival in low light and sapling height growth in high light, but no trade-offs were observed when considering other combinations of life stages (seedling growth vs. seedling survival, seedling growth vs. sapling survival, or sapling growth vs. sapling survival). 3We ran simulations with an individual-based forest dynamics model , SORTIE/NZ , to explore how the trade-off drives the differences in tree species regeneration success in gaps vs. under closed forest conditions. These simulations indicate that because species' ranks in shade tolerance varied with life stage, regeneration success was not predicted from knowledge of tree performance at a single life stage. For instance, high-light sapling growth was a strong determinant of regeneration success in forest gaps, but seedling growth was also influential. Under closed forest, regeneration success was primarily limited by low-light mortality at the seedling stage, but seedling growth and sapling survival were also influential. 4Synthesis. Growth-survival trade-offs can be strongly affected by the size of the individual analysed, resulting in completely different rankings of the shade tolerance of species across different juvenile life stages. Performance of both seedlings and saplings influenced regeneration success, highlighting the need to consider growth-survival trade-offs and the shade-tolerance strategies of tree species over a large range of juvenile sizes. [source] High population differentiation and unusual haplotype structure in a shade-intolerant pioneer tree species, Zanthoxylum ailanthoides (Rutaceae) revealed by analysis of DNA polymorphism at four nuclear lociMOLECULAR ECOLOGY, Issue 10 2008K. KAMIYA Abstract Differences in demographic history, life-history traits, and breeding systems affect nucleotide variation patterns. It is expected that shade-intolerant pioneer tree species have different patterns of genetic polymorphism and population structure than climax species. We studied patterns of nucleotide polymorphism at four putative starch pathway loci (agpSA, agpSB, agpL, and GBSSI) in Zanthoxylum ailanthoides, a shade-intolerant pioneer tree species that occupies forest gaps in warm-temperate forests of East Asia. Genetic diversity was lower within each population than among populations, and differentiation among populations was high across the loci (FST = 0.32,0.64), as expected from the insect-pollinated breeding system and the metapopulation structure of this pioneer species. Numbers of haplotypes were smaller than those expected from the observed numbers of segregating sites. Single haplotypes accounted for more than 47% of all the sampled genes at the respective loci. These variation patterns were incompatible with neutral predictions for populations of a finite island model. Complex population dynamics, such as bottleneck and/or admixture, in the history of this pioneer tree species might have resulted in the observed patterns of genetic variation and population structure, which are different from those of climax wind-pollinated tree species, such as conifers. In contrast to the other loci investigated in this study, agpL showed nearly no variation in Z. ailanthoides (one singleton only), but there was some extent of variation in a closely related species, Zanthoxylum schinifolium. This suggests possibly a recent selective sweep at or near the locus in Z. ailanthoides. [source] Gap-crossing movements predict species occupancy in Amazonian forest fragmentsOIKOS, Issue 2 2009Alexander C. Lees In fragmented landscapes, species persistence within isolated habitat patches is governed by a myriad of species life-history, habitat patch and landscape characteristics. We investigated the inter-specific variation in non-forest gap-crossing abilities of an entire tropical forest-dependent avifauna. We then related this measure of dispersal ability to species life-history characteristics and occupancy data from 31 variable-sized forest patches sampled within the same fragmented forest landscape. A total of 5436 gap-crossing movements of 231 forest-dependent bird species were observed across ten linear forest gaps of varying widths, adjacent to large areas of undisturbed forest. Species persistence in isolated fragments was strongly linked to gap-crossing ability. The most capable gap-crossers were medium to large-bodied species in the large insectivore, frugivore and granivore guilds, matching the most prevalent subset of species in small forest patches. However, some competent gap-crossing species failed to occur in small patches, and minimum forest-patch area requirements were more important in determining patch occupancy for these species. Narrow forest gaps (4,70 m) created by roads and power-lines may become territory boundaries, thereby eliminating home-range gap-crossing movements for many forest species, but permit rarer dispersal events. Wider gaps (>70 m) may inhibit gap-crossing behaviour for all but the most vagile species. Although patch size and quality may be the most important factors in structuring species assemblages in forest fragments, our results show that the degree of patch isolation and permeability of the surrounding matrix also explain which species can persist in forest isolates. Reducing the number and width of forest-dividing gaps; maintaining and/or creating forest corridors and increasing matrix permeability through the creation and maintenance of ,stepping-stone' structures will maximise the species retention in fragmented tropical forest landscapes. [source] Changes in forest understory associated with Juniperus encroachment in Oklahoma, USAAPPLIED VEGETATION SCIENCE, Issue 3 2010Paul Van Els Abstract Question: Does understory vegetation cover and richness decline along a gradient of increasing Juniperus virginiana midstory canopy cover and is that decline best correlated with litter accumulation? Location: Cross Timbers Forest in Payne County, OK, USA. Methods: We measured vegetation in forest gaps as well as forest areas without J. virginiana, at the inner and outer edge of J. virginiana canopies and near J. virginiana trunks (200 plots) and compared vegetation differences among location to light, litter, soil and microclimate variables. Results: Species richness (11 spp m,2 to 6 spp m,2) and summer vegetation cover (53.3% to 12.7%) declined with proximity to trunks. Regression indicated that richness declines (R2=0.08) and cover (R2=0.18) were best correlated with J. virginiana litter accumulation. Partial canonical correspondence analysis (pCCA) revealed two strong canonical axes, one related to litter/light and another to cover of Quercus spp. versus J. virginiana. Tree seedlings and woody vines dominated near J. virginiana. Forbs, graminoids and Quercus spp. seedlings were more common in areas without J. virginiana. Conclusions: Increasing J. virginiana and consequent litter additions alter understory biomass and composition and, through inhibiting Quercus spp. recruitment, may lead to changes in overstory composition. Decreases in herbaceous litter, which historically contributed to fuel accumulation, may have positive feedback effects on midstory encroachment by reducing the potential for prescribed burning. [source] Reduced-impact Logging has Little Effect on Temporal Activity of Frugivorous Bats (Chiroptera) in Lowland AmazoniaBIOTROPICA, Issue 3 2009Steven J. Presley ABSTRACT Reduced-impact logging (RIL) represents a viable option for sustainable use of Neotropical lowland forests while minimizing negative effects on local biodiversity. Many Neotropical bats of the family Phyllostomidae provide ecosystem services associated with pollination and seed dispersal that promote the regeneration of disturbed areas; therefore, effects of RIL on these species is of particular concern. We determined patterns of temporal activity, degree of temporal overlap of activity, and dispersion in peaks of activity for seven abundant species of frugivorous bat in Tapajós National Forest, Pará, Brazil. In addition, we evaluated the effects of RIL at a harvest level of 18.7 m3/ha and habitat physiognomy on temporal patterns of activity for these species. Bats were surveyed for four nights at each of 96 sites for a total sampling effort of 64,512 net-m-h. Sites were distributed among four experimental blocks, two blocks of unlogged forest and two blocks of forest subjected to RIL. Half of the sites in each management type were in forest gaps and half were in closed-canopy forest. In general, species exhibited similar patterns of activity, and greater than expected temporal overlap in activity among species. RIL and forest physiognomy had little effect on activity patterns of species. RIL in Amazonia removes fewer trees than do naturally occurring treefalls and such changes in habitat structure do not alter activity patterns of frugivorous bats. Evidence suggests that RIL does not have an appreciable adverse effect on frugivorous bats in Amazonia. RESUMO A exploração madeireira de impacto reduzido é uma opção viável para o uso sustentável de florestas de planícies tropicais, ao passo em que também minimizam os efeitos sobre a biodiversidade local e processos ecossistêmicos. Avaliações dos efeitos de regimes de derrubada de árvores geralmente se baseiam em respostas em nível populacional ou de comunidades e ignoram respostas comportamentais que podem ter consequências críticas em processos ecossistêmicos locais. Muitos dos morcegos neotropicais filostomídeos proporcionam serviços ecossistêmicos associados à polinização e dispersão de sementes, que promovem regeneração de áreas degradadas. Por esse motivo, os efeitos da exploração madeireira de impacto reduzido, sobre essas espécies, devem ter sua importância considerada. Nós avaliamos padrões temporais de atividade, grau de sobreposição temporal de atividade, e dispersão nos picos de atividade de sete espécies de morcegos frugívoros abundantes na Floresta Nacional de Tapajós, Pará, Brasil. Além disso, avaliamos os efeitos da exploração madeireira de impacto reduzido e da fisionomia de habitat (lacunas florestais e locais de dossel fechado) nos padrões temporais de atividade desses morcegos. Em geral, as espécies exibiram padrões de atividade similares, o que resulta em uma sobreposição temporal maior do que a esperada na atividade das espécies. A exploração madeireira de impacto reduzido e a fisionomia florestal tiveram pouco efeito nos padrões de atividades das espécies observadas. A exploração madeireira ora apresentada (2-4 árvores/ha) se propõe a um impacto menor que o associado às quedas naturais de árvores na Amazônia e aparenta não alterar a estrututra dos habitats de forma significativa à atividade das espécies de morcegos aqui estudadas. Consequentemente, não há evidências para acreditar que a exploração madeireira impacto reduzido possua efeitos adversos em espécies abundantes de morcegos frugívoros na Amazônia ou em suas capacidades de continuar a promover a regeneração de áreas degradadas via polinização ou dispersão de sementes. [source] | ||||||||||