INTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 1 2010
Manuel A. S. Graça
Abstract We tested the hypotheses that (1) plant defenses against consumers increase in the tropics, and that these differences in quality are perceived by detritivores; and (2) microbial conditioning of leaf litter is important for the feeding ecology of shredders from both geographical regions. We compared quality parameters of 8 tree species from Portugal and 8 from Venezuela. The tropical leaves were tougher, but did not differ from temperate leaves in terms of N, C: N, and polyphenols. In multiple-choice experiments, shredders from Portugal (Sericostoma vittatum and Chaetopteryx lusitanica) and from Venezuela (Nectopsyche argentata and Phylloicus priapulus) discriminated among conditioned leaves, preferentially consuming softer leaves. In another set of experiments, all shredders preferentially fed on conditioned rather than unconditioned leaves, grew faster when fed conditioned than unconditioned leaves and fed more on temperate than tropical leaves. We conclude that leaf litter from the tropics is a low-quality resource compared to leaves in temperate systems, because of differences in toughness, and that tropical shredders benefit from microbial colonization, as previously demonstrated for temperate systems. We suggest that leaf toughness could be one explanation for the reported paucity of shredders in some tropical streams. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Bioassay and Identification of Root Exudates of Three Fruit Tree Species

JOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 3 2007
Jiang-Hong Zhang
Abstract A laboratory bioassay was designed to determine the allelopathic potential of root exudates of three fruit tree species on apple germination. The results showed that root exudates of apple (Malus pumila L.) and peach (Prunus persica L.), each at concentrations of 0.02 and 0.2 mg/L, inhibited germination and radicle growth of apple seeds by 56.7%, 60.7%, 51.5%, and 59.3%, respectively. The corresponding shoot growth inhibition rate was 49.5%, 46.7%, 36.4%, and 44%, respectively. Root exudates of jujube (Ziziphus jujuba Mill.) had no significant effect on apple seeds. Qualitative determination of root exudates of apple, peach, and jujube tree was developed with gas chromatography-mass spectrometry. The root exudates of apple seedlings mainly contain organic acids, glycol, esters, and benzenphenol derivatives. Peach root exudates contained phenolic acids and benzenphenol derivatives in addition to two unidentified compounds. The root exudates of jujube did not contain any phenolic acids. [source]

The Effect of Seed Mass and Gap Size on Seed Fate of Tropical Rain Forest Tree Species in Guyana

PLANT BIOLOGY, Issue 2 2004
L. H. van Ulft
Abstract: For eleven tree species, differing in seed mass, germination success (emergence success for two small-seeded species) and the causes of failure to germinate were studied in the forest understorey and in logging gaps in the tropical rain forests of Guyana. In the forest understorey, germination success increased with seed mass. However, as gap size increased the difference between smaller and larger seeded species diminished because germination success of smaller-seeded species increased slightly, while that of larger-seeded species decreased dramatically. The negative effect of gap size on germination success of larger-seeded species was caused by an increased risk of desiccation with gap size, which was a far more important seed mortality agent for larger than for smaller-seeded species. Generally, seeds of smaller-seeded species suffered more from insect predation and were removed at higher rates than larger-seeded species. On the other hand, larger-seeded species were eaten more by mammals than smaller-seeded species. It is concluded that logging can result in shifts in the species composition in the tropical rain forests of Guyana which are dominated by species with large seeds, since germination success of larger-seeded species is dramatically reduced in large logging gaps. [source]

Litter Decomposition Within the Canopy and Forest Floor of Three Tree Species in a Tropical Lowland Rain forest, Costa Rica

BIOTROPICA, Issue 3 2010
Catherine L. Cardelús
ABSTRACT The rain forest canopy hosts a large percentage of the world's plant biodiversity, which is maintained, in large part, by internal nutrient cycling. This is the first study to examine the effects of site (canopy, forest floor) and tree species (Dipteryx panamensis, Lecythis ampla, Hyeronima alchorneoides) on decay rates of a common substrate and in situ leaf litter in a tropical forest in Costa Rica. Decay rates were slower for both substrates within the canopy than on the forest floor. The slower rate of mass loss of the common substrate in the canopy was due to differences in microclimate between sites. Canopy litter decay rates were negatively correlated with litter lignin:P ratios, while forest floor decay rates were negatively correlated with lignin concentrations, indicating that the control of litter decay rates in the canopy is P availability while that of the forest floor is carbon quality. The slower cycling rates within the canopy are consistent with lower foliar nutrient concentrations of epiphytes compared with forest floor-rooted plants. Litter decay rates, but not common substrate decay rates, varied among tree species. The lack of variation in common substrate decay among tree species eliminated microclimatic variation as a possible cause for differences in litter decay and points to variation in litter quality, nutrient availability and decomposer community of tree species as the causal factors. The host tree contribution to canopy nutrient cycling via litter quality and inputs may influence the quality and quantity of canopy soil resources. Abstract in Spanish is available at http://www.blackwell-synergy.com/loi/btp [source]

Performance Trade-offs Driven by Morphological Plasticity Contribute to Habitat Specialization of Bornean Tree Species

BIOTROPICA, Issue 4 2009
Daisy H. Dent
ABSTRACT Growth-survival trade-offs play an important role in niche differentiation of tropical tree species in relation to light-gradient partitioning. However, the mechanisms that determine differential species performance in response to light and soil resource availability are poorly understood. To examine responses to light and soil nutrient availability, we grew seedlings of five tropical tree species for 12 mo at < 2 and 18 percent full sunlight and in two soil types representing natural contrasts in nutrient availability within a lowland dipterocarp forest in North Borneo. We chose two specialists of nutrient-rich and nutrient-poor soils, respectively, and one habitat generalist. Across all species, growth was higher in high than low light and on more nutrient rich soil. Although species differed in growth rates, the ranking of species, in terms of growth, was consistent across the four treatments. Nutrient-rich soils improved seedling survival and increased growth of three species even under low light. Slower-growing species increased root allocation and reduced specific leaf area (SLA) and leaf area ratio (LAR) in response to decreased nutrient supply. All species increased LAR in response to low light. Maximum growth rates were negatively correlated with survival in the most resource-limited environment. Nutrient-poor soil specialists had low maximum growth rates but high survival at low resource availability. Specialists of nutrient-rich soils, plus the habitat generalist, had the opposite suite of traits. Fitness component trade-offs may be driven by both light and belowground resource availability. These trade-offs contribute to differentiation of tropical tree species among habitats defined by edaphic variation. [source]

Comparing the Dispersal of Large-seeded Tree Species by Frugivore Assemblages in Tropical Montane Forest in Africa

BIOTROPICA, Issue 4 2009
Nicole D. Gross-Camp
ABSTRACT We examined frugivore visitation and seed dispersal of five large-seeded (, 5 mm) tree species in tropical montane forest based on their occurrence in frugivorous primate diets: Ekebergia capensis, Olea capensis, Parinari excelsa, Prunus africana, and Syzygium guineense. A total of 21 frugivores in five assemblages (i.e., chimpanzees, cercopithecines, large-bodied birds, small-bodied birds, and squirrels) were observed over the study period (August 2006 and October,April 2007). We observed seed dispersal in four of five tree species studied; no dispersal was observed for P. excelsa. Frugivore assemblages did not visit tree species equally. Primates spent the most time in trees and had the largest group size. Large-bodied birds (LB) and chimpanzees dispersed the highest number of seeds per minute. LB and cercopithecines potentially dispersed the greatest number of seeds for E. capensis, and chimpanzees for S. guineense. Our analyses indicated that the mean fruiting duration of the focal tree, time in the tree, and number of species present are important predictor variables for seed dispersal by small- and large-bodied birds, and cercopithecines. The number of fruiting trees in the immediate vicinity of the focal tree further predicted seed dispersal for small-bodied birds (SB). Large-bodied birdseed dispersal also was predicted by time in tree by SB, and the number of individuals for SB and cercopithecines. Cercopithecines (CS) were further explained by the time in tree and number of species (SB & LB), and number of individuals for CS. Our study highlights the complexity of describing the relative importance of a frugivore assemblage to the dispersal of a tree species seeds. [source]

Inner-crown Microenvironments of Two Emergent Tree Species in a Lowland Wet Forest,

BIOTROPICA, Issue 2 2005
Catherine L. Cardelús
ABSTRACT Vascular epiphyte communities, comprising up to 25 percent of tropical forest flora, contribute to plant diversity and thus ecosystem-level processes; however, one of the proximal determinants of those communities, microclimate, is little studied. Here we present the first comprehensive study of microclimates in the inner crowns of two emergent tree species, Hyeronima alchorneoides and Lecythis ampla, at La Selva Biological Station, Costa Rica. We examined photon flux density, temperature, vapor pressure, and humidity in inner-crown branches during the wet and dry seasons and during the wet-season leafless phase of Lecythis. In both seasons, the percentage daily PFD in foliated Lecythis crowns (9%, wet season; 11%, dry season) was significantly higher than in Hyeronima crowns (5%, both seasons), with the leafless wet-season PFD of Lecythis reaching 23 percent of full sun. Temperature and vapor pressure varied less in Hyeronima than in Lecythis crowns during the dry season. Microenvironmental conditions for epiphytes within Hyeronima crowns were more spatially and temporally homogeneous and were more buffered from ambient conditions than within Lecythis crowns. Growing conditions within the crowns of the same trees and among different trees were measurably different and are likely to affect the structure and composition of the resident epiphyte communities. RESUMEN Las epífitas vasculares representan el 25 por ciento de la flora vascular en bosques tropicales. Sin embargo, existe poca información sobre el microclima en que estas plantas habitan. Comparamos flujo fotosintético (PFD), temperatura, presión de vapor y humedad en las ramas interiores de dos especies de árboles emergentes, Hyeronima alchorneoides y Lecythis ampla, en la Estación Biológica La Selva, Costa Rica. En cada estación, se encontró una diferencia significativa entre el por ciento PFD en el dosel de Lecythis (9%, estación lluviosa; 11%, estación seca) y el por ciento PFD registrado en Hyeronima (5.6%, los dos estaciones), con por ciento PFD de Lecythis en la época sin hojas llegando a 23 por ciento. Las copas de Hyeronima mostraron menos variación en temperatura y presión de vapor que las copas de Lecythis durante la época seca. El microclima en el dosel de Hyeronima fue más homogéneo espacialmente y temporalmente y más regulado en comparación con el microclima en Lecythis. Las condiciones de crecer en el dosel de un árbol y entre diferentes árboles son diferentes, y probablemente afectan la estructura y composición de las comunidades de epífitas. [source]

Impact of Cotyledon and Leaf Removal on Seedling Survival in Three Tree Species with Contrasting Cotyledon Functions1

BIOTROPICA, Issue 3 2003
Kaoru Kitajima
ABSTRACT The relative importance of cotyledons and leaves for seedling survival was evaluated using a factorial field experiment on three neotropical tree species with contrasting cotyledon functional morphologies (photosynthetic, epigeal reserve vs. hypogeal reserve). In all species, cotyledon and leaf removal shortly after leaf expansion had additive negative effects on seedling survival over 7 weeks. Carbon supplies from cotyledons and other carbohydrate reserves apparently enhanced ability of seedlings to cope with herbivory and disease. [source]

Mating System Parameters in a Tropical Tree Species, Shorea leprosula Miq. (Dipterocarpaceae), from Malaysian Lowland Dipterocarp Forest,

BIOTROPICA, Issue 4a 2000
S. L. Lee
First page of article [source]

Influence of Forest Type and Tree Species on Canopy-Dwelling Beetles in Budongo Forest, Uganda,

BIOTROPICA, Issue 3 2000
Thomas Wagner
ABSTRACT Beetles were collected on 64 trees of four species (Cynometra alexandri C. H. Wright, Rinorea beniemis (Welwitsch ex Olivier) Kuntze, Teclea nobilis Delile, and Trichilia rubescens Olivier) in Budongo Forest, Uganda, using an insecticidal fogging technique. Selected tree species were abundant, taxonomically not closely related, and different in the shape of leaves, growth form, and size, with heights between 7 and 35 m. Trees were fogged in an old primary forest stand, in an area of secondary forest where selective logging was performed, and in a swamp forest. Eight conspecific trees per forest type were fogged. A total of 29,736 beetles were collected from all trees that could be assigned to 1433 (morpho)-species; 41.6 percent were singletons and 89.6 percent of species were found with less than ten individuals. Abundant beetle taxa included Latridiidae (N= 4093), Chrysomelidae (3952), Staphylinidae (2931), Apioninae (2621), and Curculionidae (2457). Most species-rich groups were Staphylinidae (N= 196 spp.), Curculionidae (189), and Chrysomelidae (148). Abundance increased in the order: primary < secondary < swamp forest. Due to the relatively high dominance of some species in the secondary forest, species richness increased in the order: secondary < primary < swamp forest. Beta diversity measures and factor analysis showed distinct differences among forest types but higher similarity of beetle communities on different tree species within one forest type. The taxonomic distribution of beetles in the secondary forest was more heterogeneous than in the primary forest. Analyses of the data revealed low host specificity even for phytophagous beetles, underlining the importance of habitat structure and chance effects on the spatial distribution of beetles in the canopy of Budongo Forest. [source]

Implications of Climatic Warming for Conservation of Native Trees and Shrubs in Florida

CONSERVATION BIOLOGY, Issue 4 2001
David W. Crumpacker
Climatic-envelope models are useful for simultaneous investigation of many plant species whose range-limiting mechanisms are poorly known. They are most effectively applied in regions with strong temperature and moisture gradients and low relief. Their required databases are often relatively easy to obtain. We provide an example involving the effect of six annual warming scenarios, ranging from +1° C to +2° C and from +10% to ,20% annual precipitation (some have greater warming in winter than in summer), on 117 native woody species in Florida (U.S.A.). Tree species at their southern range boundaries in several parts of Florida are likely to be negatively affected by as little as 1° C warming if it is greater in winter than in summer or is accompanied by a 20% decrease in annual precipitation. Potential species responses to an identical type of 1° C warming may be different for some conservation areas in the same region of Florida. Potentially extensive disruption of some major woody ecosystems is predicted under certain types of 1° C annual warming and under all types of 2° C annual warming that were investigated. Additional consideration of nonclimatic factors suggests that many potential effects on species and ecosystems are not underestimates of actual effects over a 100-year period of warming. We recommend monitoring for decreased fertility and viability of ecologically important, temperate woody species near their southern range limits in Florida. Early detection of such changes in fitness might then provide time for mitigations designed to alleviate more serious subsequent effects on biodiversity. Control of invasive, non-native plant species and prevention of their additional introduction, human-assisted translocation of native subtropical plant species into previously temperate parts of Florida, and restoration of more natural hydrological regimes are examples of potentially useful mitigations if climatic warming continues. Resumen: Los modelos de procesos ecológicos y los modelos empíricos han sido usados para relacionar predicciones de cambio climático con los efectos en especies de plantas y vegetación. Los modelos climáticos son útiles para la investigación simultánea de muchas especies de plantas cuyos mecanismos limitantes de rango son poco conocidos. Estos modelos son más eficientemente aplicados en regiones con gradientes de temperatura y humedad fuertes y con relieve bajo. Las bases de datos requeridas son a menudo relativamente fáciles de adquirir. Proveemos un ejemplo que involucra el efecto de seis escenarios anuales de calentamiento con un rango de +1° C a +2° C y de +10% a ,20% de precipitación anual (algunos con rangos de calentamiento mayores en el invierno que en el verano), en 117 especies leñosas nativas de Florida ( E.U.A.). Las especies de árboles en sus límites de rango al sur en diversas partes de Florida son más factibles de ser negativamente afectadas por tan poco como 1° C de calentamiento, si este es mayor en el invierno que en el verano o si es acompañado por una disminución de un 20% de precipitación anual. Las respuestas potenciales de las especies a un tipo idéntico de calentamiento de 1° C puede ser diferente para algunas áreas de conservación en la misma región de Florida. Se predicen perturbaciones potencialmente extensivas en algunos ecosistemas leñosos principales investigados bajo ciertos tipos de calentamiento anual de 1° C y bajo todos los tipos de calentamiento anual de 2° C. Las consideraciones adicionales de factores no climáticos sugieren que muchos efectos potenciales sobre las especies y ecosistemas no son subestimaciones de los efectos actuales sobre un período de calentamiento de 100 años. Se recomienda el monitoreo de la disminución de la fertilidad y viabilidad de especies leñosas templadas ecológicamente importantes cerca de los límites sureños de sus rangos en la Florida. La detección temprana de estos cambios en adaptabilidad pueden proveer tiempo para mitigaciones diseñadas para aliviar efectos posteriores más serios en la biodiversidad. Algunos ejemplos de mitigaciones potencialmente útiles en caso de que el calentamiento global continúe incluyen el control de especies de plantas invasoras no nativas y la prevención de su introducción adicional, la translocación asistida por humanos de plantas nativas subtropicales en partes previamente templadas de Florida y la restauración de regimenes hidrológicos más naturales. [source]

Impact of common European tree species on the chemical and physicochemical properties of fine earth: an unusual pattern

EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 1 2010
L. Mareschal
Case studies are necessary to assess the effects of changes to tree species on the physicochemical and chemical properties of soils. To achieve this, the fine earth under five tree species was investigated. This study was performed in the Breuil-Chenue experimental forest site located in the Morvan Mountains (France). This site contains two adjacent blocks with replicated stands. The native forest (old beech and oak coppice with standards) was partially clear-felled and replaced in 1976 with mono-specific plantations of European beech, Norway spruce, Laricio pine and Douglas fir. The same changes in soil properties were revealed in both blocks, thus confirming the tree species effect. The percentage of exchangeable acidity on the cation exchange capacity (CEC) was greater under spruce, Douglas fir and pine than under the other species. Spruce stands, and to a lesser extent those of Douglas fir and pine, had a less acidic soil pH than hardwood stands (which was unusual in view of the data in the literature) and smaller CEC values. The small quantities of carbon added to the soil under these tree species provide an explanation for these effects through a partial control of both CEC and pH. This case study thus demonstrated that the tree species effect was not unequivocal and different criteria are necessary for its interpretation. Tree species significantly influenced certain aspects of the chemical properties of topsoil and have the potential to have an impact on current soil fertility. [source]

Methane and nitrous oxide fluxes of soils in pure and mixed stands of European beech and Norway spruce

EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 5 2006
W. Borken
Summary Tree species can affect the sink and source strength of soils for atmospheric methane and nitrous oxide. Here we report soil methane (CH4) and nitrous oxide (N2O) fluxes of adjacent pure and mixed stands of beech and spruce at Solling, Germany. Mean CH4 uptake rates ranged between 18 and 48 ,g C m,2 hour,1 during 2.5 years and were about twice as great in both mixed and the pure beech stand as in the pure spruce stand. CH4 uptake was negatively correlated with the dry mass of the O horizon, suggesting that this diminishes the transport of atmospheric CH4 into the mineral soil. Mean N2O emission was rather small, ranging between 6 and 16 ,g N m,2 hour,1 in all stands. Forest type had a significant effect on N2O emission only in one mixed stand during the growing season. We removed the O horizon in additional plots to study its effect on gas fluxes over 1.5 years, but N2O emissions were not altered by this treatment. Surprisingly, CH4 uptake decreased in both mixed and the pure beech stands following the removal of the O horizon. The decrease in CH4 uptake coincided with an increase in the soil moisture content of the mineral soil. Hence, O horizons may maintain the gas diffusivity within the mineral soil by storing water which cannot penetrate into the mineral soil after rainfall. Our results indicate that conversion of beech forests to beech,spruce and pure spruce forests could decrease soil CH4 uptake, while the long-term effect on N2O emissions is expected to be rather small. [source]

THE FALL LINE: A PHYSIOGRAPHIC-FOREST VEGETATION BOUNDARY,

GEOGRAPHICAL REVIEW, Issue 4 2007
David Shankman
ABSTRACT. The range boundaries for many tree species in the southeastern United States correspond to the Fall Line that separates the Coastal Plain from the Appalachian Highlands. Trees in the Coastal Plain with northern range boundaries corresponding to the Fall Line occur exclusively in alluvial valleys created by lateral channel migration. These species grow mostly on lower bottomland sites characterized by a high water table, soils that are often saturated, and low annual water fluctuation. In contrast to the Coastal Plain, the southern Appalachian Highlands are occupied mostly by bedrock streams that have few sites suitable for the regeneration of these species. The Fall Line is also an approximate southern boundary for trees common in the southern Appalachians that typically occur on either dry, rocky ridgetops or in narrow stream valleys, habitats that are uncommon on the relatively flat Coastal Plain. The ranges for many trees in eastern North America are controlled by large-scale climatic patterns. Tree species with range boundaries corresponding to the Fall Line, however, are not approaching their physiological limits caused by progressively harsher climatic conditions or by competition. Instead, the Fall Line represents the approximate boundary of habitats suitable for regeneration. [source]

Prediction of Prosopis species invasion in Kenya using geographical information system techniques

AFRICAN JOURNAL OF ECOLOGY, Issue 3 2010
Gabriel M. Muturi
Abstract Tree species from Prosopis genus were widely planted for rehabilitation of degraded drylands of Kenya. However, they have invaded riverine ecosystems where they cause negative socio-economic and ecological impacts. GIS was used to estimate the reverine area threatened by Prosopis invasion in Kenya. Landsat satellite images, field surveys and past studies were also used to assess the resulting potential ecological impacts in the Turkwel ecosystem in Kenya. The study revealed that 3.0 to 27.7 million hectares are threatened by invasion, based on documented riverine forests width of 0.5,3 km. Image analysis showed that 34% of the sites under positive change were invaded, with most invasions occurring in natural forests and abandoned farms. Prosopis had overall occurrence of 39% in all the sampled sites in 2007, in contrast to 0% in 1990 that was reported in an earlier study. In these areas, Acacia tortilis occurrence dropped from 81% in 1990 to 43% in 2007, suggesting that Prosopis could be displacing it. Utilization of Prosopis for fodder, fuel wood and pods for animal feeds is recommended as a management tool to reverse the trend. The methods used in this study are also recommended for invasion prediction and management in other similar ecosystems. Résumé Pour la réhabilitation de zones arides dégradées au Kenya, on a abondamment planté trois espèces de Prosopis. Cependant, elles ont envahi des écosystèmes riverains où elles ont des impacts socioéconomiques et écologiques négatifs. On a utilisé un SIG pour estimer la superficie riveraine menacée par l'invasion des Prosopis au Kenya. Des images satellite Landsat, des études sur le terrain et les résultats de travaux antérieurs ont aussi été utilisés pour évaluer les éventuels impacts écologiques dans l'écosystème de Turkwel. L'étude a révélé qu'entre 3,0 et 27,7 millions d'hectares sont menacés d'invasion, si l'on se base sur la largeur de forêt riveraine documentée, qui est de 0,5 à 3 km. L'analyse des images a montré que 34% des sites en mutation positive étaient envahis, et que la plupart des invasions touchaient des forêts naturelles et des exploitations agricoles abandonnées. Les Prosopis avaient un taux d'occurrence global de 39% dans tous les sites échantillonnés en 2007, à comparer avec le chiffre de 0% rapporté en 1990 par une étude antérieure. Dans ces zones, la présence d'Acacia tortilis a chuté de 81% en 1990 à 43% en 2007, ce qui laisse penser que Prosopis pourrait être responsable de ce déplacement. On recommande d'utiliser Prosopis comme fourrage et bois de feu et de donner les gousses au bétail, ce qui serait une façon de les gérer pour inverser la tendance. Les méthodes utilisées dans cette étude sont aussi recommandées pour prédire et gérer les invasions dans des écosystèmes comparables. [source]

Disturbance Effects on the Seed Bank of Mexican Cloud Forest Fragments,

BIOTROPICA, Issue 3 2005
C. Alvarez-Aquino
ABSTRACT The density and floristic composition of the soil seed bank was assessed in six cloud forest fragments with different levels of human disturbance in central Veracruz, Mexico. A total of 8416 seeds germinated in 60 soil samples, at 5-cm depth, corresponding to 107 species, 85 genera, and 48 families. Significant differences were found among study sites in seed densities with values ranging from 873 to 3632/m2. Tree species contributed 20 percent of the total soil seed bank in four sites and herbs accounted for the majority of the species in each site. Among tree species, Trema micrantha displayed the highest seed density, accounting for 84 percent of the germinated seeds. In general, the tree species composition of the soil seed bank did not closely reflect the composition of the tree community. Results suggest that disturbance produced by human activities (trail use, selective cutting of trees, livestock) may influence the size and composition of the soil seed bank in forest fragments. Sites where human activity has been reduced showed the highest proportion of dormant seeds. RESUMEN La densidad y composición florística del banco de semillas del suelo se determinó en seis fragmentos de bosque de niebla con distinto nivel de alteración humana, en Veracruz, México. Un total de 8416 semillas germinaron en 60 muestras de suelo, correspondientes a 107 especies, 85 géneros y 48 familias. Se encontraron diferencias significativas entre los sitios de estudio, con valores desde 873 a 3632 semillas/m2. La mayoria de las especies fueron hierbas y en cuatro de los sitios las especies arbóreas contribuyeron un 20 por ciento al total de semillas del banco del suelo. Entre las especies arbóreas, Trema micrantha (L.) Blume (Ulmaceae) presentó la mayor densidad de semillas (84% de las semillas germinadas). En general, la composición de especies arbóreas en el banco del suelo no reflejó la composición de la comunidad de árboles en cada sitio. Los resultados sugieren que la alteración causada por actividad humana (uso de senderos, tala selectiva y pastoreo) puede influir en el tamaño y composición del banco de semillas del suelo en fragmentos de bosque. Los sitios donde la actividad humana es reducida tienen la mayor proporción de semillas latentes. [source]

Beyond Reaping the First Harvest: Management Objectives for Timber Production in the Brazilian Amazon

CONSERVATION BIOLOGY, Issue 4 2007
DANIEL J. ZARIN
manejo de bosques; producción sostenida; sustentabilidad; tala de impacto reducido Abstract:,Millions of hectares of future timber concessions are slated to be implemented within large public forests under the forest law passed in 2006 by the Brazilian Congress. Additional millions of hectares of large, privately owned forests and smaller areas of community forests are certified as well managed by the Forest Stewardship Council, based on certification standards that will be reviewed in 2007. Forest size and ownership are two key factors that influence management objectives and the capacity of forest managers to achieve them. Current best ecological practices for timber production from Brazil's native Amazon forests are limited to reduced-impact logging (RIL) systems that minimize the environmental impacts of harvest operations and that obey legal restrictions regarding minimum diameters, rare species, retention of seed trees, maximum logging intensity, preservation of riparian buffers, fire protection, and wildlife conservation. Compared with conventional, predatory harvesting that constitutes >90% of the region's timber production, RIL dramatically reduces logging damage and helps maintain forest cover and the presence of rare tree species, but current RIL guidelines do not assure that the volume of timber removed can be sustained in future harvests. We believe it is counterproductive to expect smallholders to subscribe to additional harvest limitations beyond RIL, that larger private forested landholdings managed for timber production should be sustainable with respect to the total volume of timber harvested per unit area per cutting cycle, and that large public forests should sustain volume production of individual harvested species. These additional requirements would improve the ecological sustainability of forest management and help create a stable forest-based sector of the region's economy, but would involve costs associated with lengthened cutting cycles, reduced harvest intensities, and/or postharvest silviculture to promote adequate growth and regeneration. Resumen:,Bajo la nueva ley forestal aprobada en 2006 por el Congreso Brasileño, millones de hectáreas de bosques públicos están destinadas a constituir futuras concesiones madereras. Millones de hectáreas adicionales de extensos bosques privados y áreas reducidas de bosques comunitarios están certificadas por el Forest Stewardship Council por su buen manejo, con base en estándares de certificación que serán revisados en 2007. La extensión y tenencia del bosque son dos factores clave que influyen en los objetivos de manejo y en la capacidad de los manejadores para alcanzarlos. Las mejores prácticas ecológicas actuales para la producción de madera en los bosques de la Amazonía Brasileña están limitadas a sistemas de tala de impacto reducido (TIR) que minimizan los impactos ambientales de las operaciones de cosecha y que obedecen restricciones legales en relación con los diámetros mínimos, las especies raras, la retención de árboles semilla, la máxima intensidad de tala, la preservación de amortiguamientos ribereños, la protección del fuego y la conservación de vida silvestre. En comparación con la cosecha convencional, depredadora, mediante la cual se obtiene >90% de la producción de madera en la región, la TIR dramáticamente reduce el daño y ayuda a mantener la cobertura del bosque y la presencia de especies de árboles raras, pero los actuales lineamientos de TIR no aseguran que el volumen de madera removida pueda ser sostenido en futuras cosechas. Consideramos que es contraproducente esperar que los pequeños propietarios suscriban límites a la cosecha más allá de la TIR; que los bosques privados manejados para la producción de madera debieran ser sustentables respecto al volumen total de madera cosechada por unidad de área por ciclo de corte; y que los bosques públicos deberían sustentar el volumen de producción de especies individuales. Estos requerimientos adicionales mejorarían la sustentabilidad ecológica del manejo de bosques y ayudaría a crear un sector forestal estable en la economía regional, pero implicarían costos asociados con la prolongación de los ciclos de corte, la reducción de las intensidades de cosecha y/o la silvicultura postcosecha para promover el crecimiento adecuado y la regeneración. [source]

Effects of the Surrounding Matrix on Tree Recruitment in Amazonian Forest Fragments

CONSERVATION BIOLOGY, Issue 3 2006
HENRIQUE E. M. NASCIMENTO
efectos de borde; especies pioneras; fragmentación de bosques; bosque lluvioso Abstract:,Little is known about how the surrounding modified matrix affects tree recruitment in fragmented forests. We contrasted effects of two different matrix types, Vismia - and Cecropia -dominated regrowth, on recruitment of pioneer tree species in forest fragments in central Amazonia. Our analyses were based on 22, 1-ha plots in seven experimental forest fragments ranging in size from 1 to 100 ha. By 13 to 17 years after fragmentation, the population density of pioneer trees was significantly higher in plots surrounded by Vismia regrowth than in plots surrounded by Cecropia regrowth, and the species composition and dominance of pioneers differed markedly between the two matrix types. Cecropia sciadophylla was the most abundant pioneer in fragments surrounded by Cecropia regrowth (constituting nearly 50% of all pioneer trees), whereas densities of species in Vismia -surrounded fragments were distributed more evenly. Thus the surrounding matrix had a strong influence on patterns of tree recruitment in Amazonian forest fragments. Resumen:,Se conoce poco del efecto de la matriz modificada circundante sobre el reclutamiento de árboles en bosques fragmentados. Contrastamos los efectos de dos tipos diferentes de matriz, vegetación secundaria dominada por Vismia- y Cecropia-, sobre el reclutamiento de especies de árboles pioneros en fragmentos de bosque en la Amazonía central. Nuestros análisis se basaron en 22 parcelas de 1 ha en siete fragmentos de bosque experimentales que varían entre 1 y 1000 ha. Entre 13 y 17 años después de la fragmentación, la densidad poblacional de árboles pioneros era significativamente mayor en parcelas rodeados por Vismia que en las parcelas rodeadas por Cecropia, y la composición y dominancia de especies pioneras fueron marcadamente diferentes en cada tipo de matriz. Cecropia sciadophylla fue la pionera más abundante en fragmentos rodeados por Cecropia (constituyó casi 50% de todos los árboles pioneros), mientras que las densidades de especies en los fragmentos rodeados por Vismia se distribuyeron más homogéneamente. Por lo tanto, la matriz circundante tiene una fuerte influencia sobre los patrones de reclutamiento de árboles en fragmentos de bosque Amazónicos. [source]

Low Recruitment of Trees Dispersed by Animals in African Forest Fragments

CONSERVATION BIOLOGY, Issue 6 2001
N. J. Cordeiro
We compared adult and juvenile trees in forest transects in a 3500,ha submontane forest with those in four forest fragments of 521, 30, 9, and 0.5 ha. Preliminary results show that recruitment of seedlings and juveniles of 31 animal-dispersed tree species was more than three times greater in continuous forest and large forest fragments (,30 ha) than in small forest fragments (,9 ha), whereas recruitment of eight wind- and gravity-dispersed trees of the forest interior was unaffected. Recruitment of 10 endemic, animal-dispersed tree species was 40 times lower in small fragments than in continuous forest or large fragments. Counts of diurnal primates and birds in all five sites indicated that frugivorous species have declined with decreasing fragment size. These results are consistent with the idea that loss of dispersal agents depresses tree recruitment in the course of forest fragmentation. Resumen: Investigamos los efectos de la fragmentación del bosque en la desaparición de animales frugívoros y el reclutamiento de árboles dispersados por animales y viento en parches de bosques de 80 años de edad en las montañas del este de Usambara, Tanzania. Comparamos árboles adultos y juveniles en transectos de bosque en un bosque submontañoso de 3500 ha con transectos de cuatro fragmentos de bosque de 521, 30, 9 y 0.5 ha. Los resultados preliminares muestran que el reclutamiento de plántulas y juveniles especies de árboles dispersados por animales fue tres veces mayor en el bosque continuo y fragmentos grandes (,30 ha) que en fragmentos pequeños (,9 ha), mientras que el reclutamiento de ocho árboles dispersados por viento y gravedad del interior del bosque no fue afectado. El reclutamiento de 10 especies endémicas de árboles dispersados por animales fue 40 veces menor en los fragmentos pequeños que en el bosque continuo o en los fragmentos grandes. Los conteos de primates diurnos y aves en los cinco sitios indican que las especies frugívoras han disminuido con la disminución del tamaño del fragmento. Estos resultados son consistentes con la idea de que la pérdida de los agentes dispersores deprime el reclutamiento de los árboles en el transcurso de la fragmentación del bosque. [source]

Perennialism and Poverty Reduction

DEVELOPMENT POLICY REVIEW, Issue 1 2004
Nigel D. Poole
This article, which is both conceptual and a synthesis of the literature, considers the research component of poverty alleviation strategies for people whose livelihoods depend significantly on tree and forest resources. Two policy approaches are contrasted: enhancing the utilisation of indigenous tree species within the household and the local economy, and integrating tree and forest-dependent peoples into the wider economy by promoting the commercialisation of conventional tree crop production. It is argued that the discussion is relevant for other poor peoples who depend on perennial production systems, and that the conclusions contribute to the wider debate about remoteness, market access, decentralisation and targeting in policy formulation, and globalisation. [source]

Spatiotemporal changes of beetle communities across a tree diversity gradient

DIVERSITY AND DISTRIBUTIONS, Issue 4 2009
Stephanie Sobek
Abstract Aim, Plant and arthropod diversity are often related, but data on the role of mature tree diversity on canopy insect communities are fragmentary. We compare species richness of canopy beetles across a tree diversity gradient ranging from mono-dominant beech to mixed stands within a deciduous forest, and analyse community composition changes across space and time. Location, Germany's largest exclusively deciduous forest, the Hainich National Park (Thuringia). Methods, We used flight interception traps to assess the beetle fauna of various tree species, and applied additive partitioning to examine spatiotemporal patterns of diversity. Results, Species richness of beetle communities increased across the tree diversity gradient from 99 to 181 species per forest stand. Intra- and interspecific spatial turnover among trees contributed more than temporal turnover among months to the total ,-beetle diversity of the sampled stands. However, due to parallel increases in the number of habitat generalists and the number of species in each feeding guild (herbivores, predators and fungivores), no proportional changes in community composition could be observed. If only beech trees were analysed across the gradient, patterns were similar but temporal (monthly) species turnover was higher compared to spatial turnover among trees and not related to tree diversity. Main conclusions, The changes in species richness and community composition across the gradient can be explained by habitat heterogeneity, which increased with the mix of tree species. We conclude that understanding temporal and spatial species turnover is the key to understanding biodiversity patterns. Mono-dominant beech stands are insufficient to conserve fully the regional species richness of the remaining semi-natural deciduous forest habitats in Central Europe, and analysing beech alone would have resulted in the misleading conclusion that temporal (monthly) turnover contributes more to beetle diversity than spatial turnover among different tree species or tree individuals. [source]

Overstorey tree species regulate colonization by native and exotic plants: a source of positive relationships between understorey diversity and invasibility

DIVERSITY AND DISTRIBUTIONS, Issue 4 2008
Kathleen S. Knight
ABSTRACT The North American woody species, Prunus serotina Ehrh., is an aggressive invader of forest understories in Europe. To better understand the plant invasion process, we assessed understorey plants and Prunus serotina seedlings that have colonized a 35-year-old replicated common-garden experiment of 14 tree species in south-western Poland. The density and size of established (> 1 year old) P. serotina seedlings varied among overstorey species and were related to variation in light availability and attributes of the understorey layer. In a multiple regression analysis, the density of established P. serotina seedlings was positively correlated with light availability and understorey species richness and negatively correlated with understorey species cover. These results suggest that woody invader success is adversely affected by overstorey shading and understorey competition for resources. Simultaneously, however, invader success may generally be positively associated with understorey species richness because both native and invasive plant colonization respond similarly to environmental conditions, including those influenced by overstorey tree species. Identification of characteristics of forests that increase their susceptibility to invasion may allow managers to target efforts to detect invasives and to restore forests to states that may be less invasible. [source]

Scale dependence of effective specialization: its analysis and implications for estimates of global insect species richness

DIVERSITY AND DISTRIBUTIONS, Issue 1 2007
Jon C. Gering
ABSTRACT Estimates of global insect species richness are sometimes based on effective specialization, a calculation used to estimate the number of insect species that is restricted to a particular tree species. Yet it is not clear how effective specialization is influenced by spatial scale or characteristics of the insect community itself (e.g. species richness). We investigated scale dependence and community predictors of effective specialization using 15,907 beetles (583 species) collected by insecticide fogging from the crowns of 96 trees (including 32 Quercus trees) located in Ohio and Indiana. Trees were distributed across 24 forest stands (,1 ha) nested within six sites (,10,100 km2) and two ecoregions (> 1000 km2). Using paired-sample randomization tests, we found that effective specialization (fk) exhibited negative scale-dependence in early (May,June 2000) and late (August,September 2000) sampling periods. Our average effective specialization (F) values , those that are comparable to Erwin's (1982) estimates , ranged from 19% to 97%, and increased as spatial scale decreased. We also found that beetle species richness and the number of shared beetle species across host trees were significant and consistent negative predictors of F. This shows that increases in spatial scale, species richness, and the number of trees (and/or tree species) all coincide with decreases in effective specialization. Collectively, our results indicate that estimates of global insect species richness based on effective specialization at a single spatial scale are overestimating the magnitude of global insect species richness. We propose that scale dependence should be promoted to a central concept in the research program on global estimates of species richness. [source]

Phytogeographical evidence for post-glacial dispersal limitation of European beech forest species

ECOGRAPHY, Issue 6 2009
Wolfgang Willner
The post-glacial migration of European beech Fagus sylvatica has been addressed by many studies using either genetic or fossil data or a combination of both. In contrast to this, only little is known about the migration history of beech forest understorey species. In a review of phytosociological literature, we identified 110 plant species which are closely associated with beech forest. We divided the distribution range of European beech forests into 40 geographical regions, and the presence or absence of each species was recorded for each region. We compared overall species numbers per region and numbers of narrow-range species (species present in <10 regions). A multiple regression model was used to test for the explanatory value of three potential diversity controls: range in elevation, soil type diversity, and distance to the nearest potential refuge area. A hierarchical cluster analysis of the narrow-range species was performed. The frequency of range sizes shows a U-shaped distribution, with 42 species occurring in <10 regions. The highest number of beech forest species is found in the southern Alps and adjacent regions, and species numbers decrease with increasing distance from these regions. With only narrow-range species taken into consideration, secondary maxima are found in Spain, the southern Apennines, the Carpathians, and Greece. Distance to the nearest potential refuge area is the strongest predictor of beech forest species richness, while altitudinal range and soil type diversity had little or no predictive value. The clusters of narrow-range species are in good concordance with the glacial refuge areas of beech and other temperate tree species as estimated in recent studies. These findings support the hypothesis that the distribution of many beech forest species is limited by post-glacial dispersal rather than by their environmental requirements. [source]

The relative importance of landscape and community features in the invasion of an exotic shrub in a fragmented landscape

ECOGRAPHY, Issue 2 2006
Anne M. Bartuszevige
Although invasive plants are recognized as a major ecological problem, little is known of the relative importance of plant community characteristics versus landscape context in determining invasibility of communities. We determined the relative importance of community and landscape features of 30 woodlots in influencing the invasion of Lonicera maackii. We sampled woodlots using the point-quarter method and calculated canopy openness and basal areas and densities of shrub, sapling and tree species, as well as woody species richness. We used aerial photos and ArcView GIS to calculate landscape parameters from the same woodlots using a buffer distance of 1500,m. We used logistic and linear regression analyses to determine the community and landscape factors that best explain L. maackii presence and density. We also tested whether woodlot invasion by L. maackii begins at woodlot edges. Presence of L. maackii was significantly explained only by distance from the nearest town (logistic regression, p=0.017); woodlots nearer town were more likely to be invaded. Among invaded woodlots, density of L. maackii was positively related to the amount of edge in the landscape (partial R2=0.592) and negatively related to total tree basal area (partial R2=0.134), number of native woody species (partial R2=0.054), and sapling shade tolerance index (partial R2=0.054). Lonicera maackii in woodlot interiors were not younger than those on the perimeters, leading us to reject the edge-first colonization model of invasion. Our findings reveal that landscape structure is of primary importance and community features of secondary importance in the invasion of L. maackii. This shrub is invading from multiple foci (towns) rather than an advancing front. Connectivity in the landscape (i.e. the number of corridors) did not promote invasion. However, edge habitat was important for invasion, probably due to increased propagule pressure. The community features associated with L. maackii invasion may be indicators of past disturbance. [source]

Spatial analysis of an invasion front of Acer platanoides: dynamic inferences from static data

ECOGRAPHY, Issue 3 2005
Wei Fang
It is an open question whether the invading tree species Acer platanoides is invading and displacing native trees within pre-existing forest stands, or merely preferentially occupying new stands of secondary forest growth at the edges of existing forests. Several threads of spatial pattern analyses were used to assess the invasibility of A. platanoides, and to link the invasion to the structure of a plant community in the deciduous forest of the northeastern United States. The analyses were based on maps of a contiguous 100×50 m area along an A. platanoides infestation gradient. The distribution of A. platanoides was highly aggregated and the population importance value increased from 28.1 to 38.5% according to mortality estimated from standing dead trees, while the distribution of native tree species was close to random and importance value of Quercus spp. decreased from 33.4 to 26.9% over time. The size distributions of each tree species across distance indicated that A. platanoides was progressively invading the interior of the forest while the native species (including A. rubrum) were not spreading back towards the A. platanoides monospecific patch. The null hypothesis of no invasibility was rejected based on quantile regressions. There were negative correlations between A. platanoides density and the densities of native species in different functional groups, and negative correlation of A. platanoides density and the species diversity in forest understory. The null hypothesis that A. platanoides invasion did not suppress native trees or understory was rejected based on Dutilleul's modified t-test for correlation, consistent with experimental results in the same study site. The combination of multiple spatial analyses of static data can be used to infer historical dynamical processes that shape a plant community structure. The concept of "envelop effects" was discussed and further developed. [source]

Variation in mistletoe seed deposition: effects of intra- and interspecific host characteristics

ECOGRAPHY, Issue 2 2002
Juliann Eve Aukema
We investigated differences in host infection by a desert mistletoe, Phoradendron californicum, and examined one of the processes that contributes to these differences: variation in seed deposition among host individuals and species. In the Sonoran Desert, P. californicum parasitizes the sympatric leguminous trees Olneya tesota, Cercidium microphyllum, Prosopis velutina, Acacia constricta, and Acacia greggii. We hypothesized that seed deposition depends on host height and crown architecture. At a site in Arizona, frequency of infection did not reflect host relative abundance. Olneya tesota was parasitized at a higher frequency than expected from its abundance and maintained the highest mistletoe loads per individual host. In contrast, P. velutina was infected less frequently than expected. Infection frequency increased with host tree height for all hosts. Mistletoe seed deposition by avian dispersers differed among host species and was disproportionately high in O. tesota and P. velutina. Seed deposition was higher in infected than in non-infected host trees, and increased with tree height in O. tesota but not in C. microphyllum. We suspect that increased seed deposition with height in O. tesota may be due to the preference of seed-dispersing birds for higher perches. Some host tree species, such as C. microphyllum and A. constricta, probably received fewer mistletoe seeds because birds avoid hosts with dense and spiny crowns. Mistletoe populations are plant metapopulations in which host trees are patches and the frequency of infection in each host species/patch type is the result of interspecific differences in the balance between mistletoe colonization and extinction. From this perspective, our study of host use and seed dispersal is a metapopulation study of patch occupancy and propagule distribution among available patch types. Our seed-dispersal study demonstrates that the mechanisms that create pattern in patchy plant populations can be investigated in mistletoe systems. [source]

Soil water dynamics along a tree diversity gradient in a deciduous forest in Central Germany

ECOHYDROLOGY, Issue 3 2010
Inga Krämer
Abstract This study aimed to investigate whether soil water dynamics differ along a tree species diversity gradient. The 12 study plots in the Hainich National Park, Germany, were composed of up to 11 tree species. Fagus sylvatica formed the monospecific plots. Mixed forest plots consisted of a variable admixture of other broad-leaved deciduous tree species such as Tilia spp., Fraxinus excelsior, Carpinus betulus, and Acer pseudoplatanus. Volumetric soil water content and soil water potential were measured for about two and a half years. Overall patterns of soil water dynamics were similar in all study plots. However, during a desiccation period in summer 2006, significant correlations between soil water in the upper soil and tree species diversity of the 12 study plots were observed. At the beginning of this period, soil water was extracted at higher rates in the species-rich plots than in the beech-dominated plots. However, later during the desiccation period, when atmospheric evaporative demand was higher, only the beech-dominated stands were able to increase soil water extraction. In plots of high tree species diversity, soil water reserves were already low and soil water extraction reduced. Possible explanations for high water extraction rates in mixed species plots at the beginning of the desiccation period include species-specific characteristics such as high maximum water use rate of some species, enhanced exploitation of soil water resources in mixed stands (complementarity effect), and additional water use of the herb layer, which increased along the tree species diversity gradient. Copyright © 2010 John Wiley & Sons, Ltd. [source]

Host specificity of ambrosia and bark beetles (Col., Curculionidae: Scolytinae and Platypodinae) in a New Guinea rainforest

ECOLOGICAL ENTOMOLOGY, Issue 6 2007
JIRI HULCR
Abstract 1.,Bark and ambrosia beetles are crucial for woody biomass decomposition in tropical forests worldwide. Despite that, quantitative data on their host specificity are scarce. 2.,Bark and ambrosia beetles (Scolytinae and Platypodinae) were reared from 13 species of tropical trees representing 11 families from all major lineages of dicotyledonous plants. Standardised samples of beetle-infested twigs, branches, trunks, and roots were taken from three individuals of each tree species growing in a lowland tropical rainforest in Papua New Guinea. 3.,A total of 81 742 beetles from 74 species were reared, 67 of them identified. Local species richness of bark and ambrosia beetles was estimated at 80,92 species. 4.,Ambrosia beetles were broad generalists as 95% of species did not show any preference for a particular host species or clade. Similarity of ambrosia beetle communities from different tree species was not correlated with phylogenetic distances between tree species. Similarity of ambrosia beetle communities from individual conspecific trees was not higher than that from heterospecific trees and different parts of the trees hosted similar ambrosia beetle communities, as only a few species preferred particular tree parts. 5.,In contrast, phloeophagous bark beetles showed strict specificity to host plant genus or family. However, this guild was poor in species (12 species) and restricted to only three plant families (Moraceae, Myristicaceae, Sapindaceae). 6.,Local diversity of both bark and ambrosia beetles is not driven by the local diversity of trees in tropical forests, since ambrosia beetles display no host specificity and bark beetles are species poor and restricted to a few plant families. [source]

Community structure of arboreal caterpillars within and among four tree species of the eastern deciduous forest

ECOLOGICAL ENTOMOLOGY, Issue 6 2003
Keith S. Summerville
Abstract., 1.,A seasonally replicated experimental design was used to address the question of how differences within and among host tree species affect arboreal caterpillar communities. 2.,Seasonal variation influenced caterpillar community composition most significantly, and the similarity among caterpillar assemblages did not necessarily follow the pattern of phylogenetic relatedness among host trees. 3.,Species richness and abundance of caterpillars were higher on oaks and maples than on American beech. Diversity partitioning models revealed that , diversity was only occasionally greater or less than expected by chance alone. 4.,When , diversity was significant, values tended to be greater than expected by chance among replicate trees within each species and lower than expected by chance among the four tree species. 5.,Differences among trees appeared important for determining patterns of species presence/absence for rare species and influencing patterns of species dominance within caterpillar assemblages. Differences among tree species had a significant effect on overall lepidopteran community composition and mean species diversity (i.e. , diversity). 6.,Because , diversity of caterpillars among host trees was lower than expected by chance, host specificity within the Lepidoptera may be less prevalent than thought previously. [source]