Forest Ecosystems (forest + ecosystem)

Distribution by Scientific Domains
Distribution within Life Sciences

Selected Abstracts

Invertebrates and the Restoration of a Forest Ecosystem: 30 Years of Research following Bauxite Mining in Western Australia

Jonathan D. Majer
Abstract Restoration needs to consider more than just soils and plants. The role of terrestrial invertebrates in the restoration of Alcoa's bauxite mines in the Jarrah (Eucalyptus marginata) forest of Western Australia has been the subject of over 20 individual studies. Projects range from arthropods in soil and leaf litter, to the understorey vegetation, and the tree canopy. Moreover, projects span a range of trophic groups, including decomposers (e.g., springtails and termites), predators (e.g., ants and spiders), and herbivores (e.g., true bugs and ants preying on seeds). Elucidation of recolonization trajectories uses both space-for-time substitutions and long-term regular sampling. Importantly, many studies are at species level rather than coarser taxonomic ranks. This paper provides an historical account and an integrated review of this research. The role of ants as seed predators and as indicators of ecosystem health is described. Successional data for other groups, when measured by species richness (ants, spiders, and hemipterans) and composition (ants and spiders), show their reassembly trajectories tracking toward unmined reference areas. Hemipteran species composition tracks the vegetation reassembly trajectory but not toward unmined reference areas. Studies also have revealed optimal sampling methods for surveying invertebrates and their rich biodiversity in southwestern Australia. In restored mine pits burnt to reduce fuel loads, the response of spiders to this additional disturbance was retrogression/alteration of the post-mining trajectory. Finally, attention is drawn to research areas receiving limited scrutiny to date, such as the contribution of terrestrial invertebrates to ecosystem function and taxonomic groups not yet studied. [source]

Maintaining Biodiversity in Forest Ecosystems

Kerry D. Woods
No abstract is available for this article. [source]

Global pattern of NPP to GPP ratio derived from MODIS data: effects of ecosystem type, geographical location and climate

GLOBAL ECOLOGY, Issue 3 2009
Yangjian Zhang
ABSTRACT Aim, To examine the global pattern of the net primary production (NPP)/gross primary production (GPP) ratio of the Earth's land area along geographical and climatic gradients. Location, The global planetary ecosystem. Methods, The 4-year average annual NPP/GPP ratio of the Earth's land area was calculated using 2000,03 Moderate Resolution Imaging Spectroradiometer (MODIS) data. The global pattern of the NPP/GPP ratio was investigated by comparing it among each typical terrestrial ecosystem and plotting it along a geographical and climatic gradient, including latitude, altitude, temperature and precipitation. Results, The global terrestrial ecosystem had an average NPP/GPP ratio value of 0.52 with minor variation from 2000 to 2003. However, the NPP/GPP ratio showed considerable spatial variation associated with ecosystem type, geographical location and climate. Densely vegetated ecosystems had a lower NPP/GPP ratio than sparsely vegetated ecosystems. Forest ecosystems had a lower NPP/GPP ratio than shrub and herbaceous ecosystems. Geographically, the NPP/GPP ratio increased with altitude. In the Southern Hemisphere, the NPP/GPP ratio decreased along latitude from 30° to 10° and it exhibited high fluctuation in the Northern Hemisphere. Climatically, the NPP/GPP ratio exhibited a decreasing trend along enhanced precipitation when it was less than 2300 mm year,1 and a static trend when the annual precipitation was over 2300 mm. The NPP/GPP ratio showed a decreasing trend along temperature when it was between ,20 °C and 10 °C, and showed an increasing trend along rising temperature when it was between ,10 °C and 20 °C. Within each ecosystem, the NPP/GPP ratio revealed a similar trend to the global trend along temperature and precipitation. Conclusions, The NPP/GPP ratio exhibited a pattern depending on the main climatic characteristics such as temperature and precipitation and geographical factors such as latitude and altitude. The findings of this research challenge the widely held assumption that the NPP/GPP ratio is consistent regardless of ecosystem type. [source]

Nitrogen balance in forest soils: nutritional limitation of plants under climate change stresses

H. Rennenberg
Abstract Forest ecosystems with low soil nitrogen (N) availability are characterized by direct competition for this growth-limiting resource between several players, i.e. various components of vegetation, such as old-growth trees, natural regeneration and understorey species, mycorrhizal fungi, free-living fungi and bacteria. With the increase in frequency and intensity of extreme climate events predicted in current climate change scenarios, also competition for N between plants and/or soil microorganisms will be affected. In this review, we summarize the present understanding of ecosystem N cycling in N-limited forests and its interaction with extreme climate events, such as heat, drought and flooding. More specifically, the impacts of environmental stresses on microbial release and consumption of bioavailable N, N uptake and competition between plants, as well as plant and microbial uptake are presented. Furthermore, the consequences of drying,wetting cycles on N cycling are discussed. Additionally, we highlight the current methodological difficulties that limit present understanding of N cycling in forest ecosystems and the need for interdisciplinary studies. [source]

Fine-root respiration in a loblolly pine (Pinus taeda L.) forest exposed to elevated CO2 and N fertilization

ABSTRACT Forest ecosystems release large amounts of carbon to the atmosphere from fine-root respiration (Rr), but the control of this flux and its temperature sensitivity (Q10) are poorly understood. We attempted to: (1) identify the factors limiting this flux using additions of glucose and an electron transport uncoupler (carbonyl cyanide m-chlorophenylhydrazone); and (2) improve yearly estimates of Rr by directly measuring its Q10in situ using temperature-controlled cuvettes buried around intact, attached roots. The proximal limits of Rr of loblolly pine (Pinus taeda L.) trees exposed to free-air CO2 enrichment (FACE) and N fertilization were seasonally variable; enzyme capacity limited Rr in the winter, and a combination of substrate supply and adenylate availability limited Rr in summer months. The limiting factors of Rr were not affected by elevated CO2 or N fertilization. Elevated CO2 increased annual stand-level Rr by 34% whereas the combination of elevated CO2 and N fertilization reduced Rr by 40%. Measurements of in situ Rr with high temporal resolution detected diel patterns that were correlated with canopy photosynthesis with a lag of 1 d or less as measured by eddy covariance, indicating a dynamic link between canopy photosynthesis and root respiration. These results suggest that Rr is coupled to daily canopy photosynthesis and increases with carbon allocation below ground. [source]

Nutrients, diversity, and community structure of two phytotelm systems in a lower montane forest, Puerto Rico

Barbara A. Richardson
Summary 1. Bromeliad and heliconia phytotelmata in the same forest area were compared in terms of their animal assemblages, nutrient inputs, and plant architecture. 2. For all major elements, nutrient inputs from canopy-derived debris and rainfall in bromeliads were significantly lower than those derived from decaying flower parts and plant secretions in heliconia bracts. Bromeliads contained significantly fewer organisms per unit volume of water and unit dry weight of organic matter than did heliconia inflorescences. They also contained a significantly lower animal biomass (199 mg DW from 15 bromeliads, 527 mg DW from 15 heliconia inflorescences). 3. Species richness was independent of abundance, demonstrating that, at least for small container habitats, higher abundance does not necessarily lead to a greater species richness. Communities were remarkably similar in patterns of relative abundance and species richness (23 spp. in bromeliads, 21 spp. in heliconia), probably due to functional similarities in plant architecture, with the two most abundant species comprising 60,62% of the total community. Coefficients of similarity were low because of marked differences in species assemblages. 4. Some taxa were phytotelm generalists but most showed a preference for one particular habitat, indicating differential selection in the choice of oviposition sites and larval development within the forest ecosystem. In common with many island communities, species richness was lower than that reported for these phytotelm habitats in mainland central and south America. [source]

Gross rates of ammonification and nitrification at a nitrogen-saturated spruce (Picea abies (L.)Karst.) stand in southern Germany

P. Rosenkranz
We investigated the magnitudes of temporal and spatial variabilities of gross ammonification and nitrification, in an N-saturated temperate forest ecosystem. Forest soil gross ammonification, gross nitrification and heterotrophic soil respiration were measured in the forest floor and uppermost mineral layer over a period of 3 years. Total annual gross fluxes for the organic layer and uppermost mineral horizon (0,4 cm) were in the range of 800,980 kg N ha,1 year,1 for gross ammonification and 480,590 kg N ha,1 year,1 for gross nitrification. Annual heterotrophic soil respiration was 8000,8900 kg C ha,1 year,1. Highest soil C and N turnover rates occurred in summer, and a consistent pattern was observed throughout the observation period, with highest values for plots located at a clear-cut area and lowest values for plots located at an unmanaged, approximately 100-year-old, spruce control site. Soil moisture, soil temperature and substrate availability accounted for most of the observed variability of C and N turnover rates. Because gross rates of inorganic N production were more than an order of magnitude larger than ecosystem N losses along hydrological and gaseous pathways, our study underlines the importance of internal microbial N turnover processes for ecosystem N cycling and retention. [source]

Abandoned anthills of Formica polyctena and soil heterogeneity in a temperate deciduous forest: morphology and organic matter composition

S. M. Kristiansen
Summary Ants can modify the properties of soil when they build their nests. We have investigated the degree and persistency of changes of soil morphology and chemistry in abandoned anthills in a temperate, deciduous wood in Jutland, Denmark. For this purpose, we sampled surface soils (0,10 cm) from each of five abandoned anthills (Formica polyctena Förster) and adjacent undisturbed sites, where anthills covered about 0.5% of the surface area. In addition, one soil profile in an abandoned anthill was sampled for morphological descriptions. All samples were analysed for pH, C, N, lignin-derived phenol, and cellulosic and non-cellulosic carbohydrate concentrations. The results showed that soils under the anthills were enriched in organic matter, were yellower and showed features of Podzol degradation. Former Podzols had to be reclassified to Umbrisols or Arenosols, whereas anthills on Luvisols affected soil classification only at the subdivision level. The C/N ratio and soil pH were not significantly affected by the ants' activity. However, lignin-derived phenols and cellulosic polysaccharides were enriched inside the mounds by a factor of 6 and 7, respectively. This probably reflected collection of woody debris for nest construction while the nest was occupied, and large input of C from an increased root density. The degree of changes in the quality of the organic matter decreased with time since abandonment, but changes were still detectable within anthills left 20 years ago. As ant colonies are concentrated, and move regularly on a decadal timescale, formation of Formica anthills has an intrinsic influence on the heterogeneity of the soil within this forest ecosystem. [source]

Regional-scale measurements of CH4 exchange from a tall tower over a mixed temperate/boreal lowland and wetland forest

Cindy Werner
The biosphere,atmosphere exchange of methane (CH4) was estimated for a temperate/boreal lowland and wetland forest ecosystem in northern Wisconsin for 1997,1999 using the modified Bowen ratio (MBR) method. Gradients of CH4 and CO2 and CO2 flux were measured on the 447-m WLEF-TV tower as part of the Chequamegon Ecosystem,Atmosphere Study (ChEAS). No systematic diurnal variability was observed in regional CH4 fluxes measured using the MBR method. In all 3 years, regional CH4 emissions reached maximum values during June,August (24±14.4 mg m,2 day,1), coinciding with periods of maximum soil temperatures. In 1997 and 1998, the onset in CH4 emission was coincident with increases in ground temperatures following the melting of the snow cover. The onset of emission in 1999 lagged 100 days behind the 1997 and 1998 onsets, and was likely related to postdrought recovery of the regional water table to typical levels. The net regional emissions were 3.0, 3.1, and 2.1 g CH4 m,2 for 1997, 1998, and 1999, respectively. Annual emissions for wetland regions within the source area (28% of the land area) were 13.2, 13.8, and 10.3 g CH4 m,2 assuming moderate rates of oxidation of CH4 in upland regions in 1997, 1998, and 1999, respectively. Scaling these measurements to the Chequamegon Ecosystem (CNNF) and comparing with average wetland emissions between 40°N and 50°N suggests that wetlands in the CNNF emit approximately 40% less than average wetlands at this latitude. Differences in mean monthly air temperatures did not affect the magnitude of CH4 emissions; however, reduced precipitation and water table levels suppressed CH4 emission during 1999, suggesting that long-term climatic changes that reduce the water table will likely transform this landscape to a reduced source or possibly a sink for atmospheric CH4. [source]

Modelling night-time ecosystem respiration by a constrained source optimization method

Chun-Ta Lai
Abstract One of the main challenges to quantifying ecosystem carbon budgets is properly quantifying the magnitude of night-time ecosystem respiration. Inverse Lagrangian dispersion analysis provides a promising approach to addressing such a problem when measured mean CO2 concentration profiles and nocturnal velocity statistics are available. An inverse method, termed ,Constrained Source Optimization' or CSO, which couples a localized near-field theory (LNF) of turbulent dispersion to respiratory sources, is developed to estimate seasonal and annual components of ecosystem respiration. A key advantage to the proposed method is that the effects of variable leaf area density on flow statistics are explicitly resolved via higher-order closure principles. In CSO, the source distribution was computed after optimizing key physiological parameters to recover the measured mean concentration profile in a least-square fashion. The proposed method was field-tested using 1 year of 30-min mean CO2 concentration and CO2 flux measurements collected within a 17-year-old (in 1999) even-aged loblolly pine (Pinus taeda L.) stand in central North Carolina. Eddy-covariance flux measurements conditioned on large friction velocity, leaf-level porometry and forest-floor respiration chamber measurements were used to assess the performance of the CSO model. The CSO approach produced reasonable estimates of ecosystem respiration, which permits estimation of ecosystem gross primary production when combined with daytime net ecosystem exchange (NEE) measurements. We employed the CSO approach in modelling annual respiration of above-ground plant components (c. 214 g C m,2 year,1) and forest floor (c. 989 g C m,2 year,1) for estimating gross primary production (c. 1800 g C m,2 year,1) with a NEE of c. 605 g C m,2 year,1 for this pine forest ecosystem. We conclude that the CSO approach can utilise routine CO2 concentration profile measurements to corroborate forest carbon balance estimates from eddy-covariance NEE and chamber-based component flux measurements. [source]

Birds and army ants in a fragment of the Atlantic Forest of Brazil

Christiana M. A. Faria
ABSTRACT Little is known about the birds associated with army-ant swarms in the Brazilian Atlantic forest. Our objectives were to locate and monitor army-ant swarms in the Atlantic rainforest of Brazil and to identify the species of birds that attended the swarms and exhibited bivouac-checking behavior. From July 2004 to August 2005, we located 49 swarms of army ants, including 28 Eciton burchelli, 19 Labidus praedator, and 2 Eciton vagans swarms. No birds were present at 17 (35%) swarms. At 32 swarms where birds were present, 22 (69%) were E. burchelli swarms and 10 (31%) were L. praedator swarms. No birds were observed at the two E. vagans swarms. We identified 66 species of birds attending the swarms, but only 43 species were observed foraging on prey flushed by the ants. Eighteen of these species had not been previously reported to forage in association with army-ant swarms. Most birds observed during our study attended army-ant swarms opportunistically, with White-shouldered Fire-eyes (Pyriglena leucoptera) the only obligate ant follower. Our observations suggest that the arthropods and other organisms flushed by army ants represent an important food resource for several species of birds in the Atlantic forest ecosystem. RESUMEN Se conoce poco sobre las aves asociadas con los enjambres de las hormigas soldado en el bosque Atlántico de Brasil. Nuestros objetivos fueron de localizar y monitorear los enjambres de las hormigas soldado en el bosque húmedo del Atlántico en Brasil e identificar las especies de aves que se encontraban junto con los enjambres y que chequeaban a los vivaques de las hormigas. Desde Julio 2004 hasta Agosto 2005, localizamos 49 enjambres de hormigas soldado, incluyendo a 28 enjambres de Eciton burchelli, 19 de Labidus praedator, y dos de Eciton vagans. No detectamos aves en 17 (35%) de los enjambres. En 32 enjambres donde encontramos aves, 22 (69%) eran enjambres de E. burchelli y 10 (31%) eran enjambres de L. praedator. No observamos aves en los dos enjambres de E. vagans. Identificamos 66 especies de aves junto con los enjambres, pero solo 43 especies fueron observadas comiendo las presas ahuyentadas por las hormigas. Dieciocho de estas especies no habían sido anteriormente reportadas forrajeando en conjunto con los enjambres de las hormigas soldado. La mayoría de las aves observadas durante nuestro estudio forrajeaban junto con las hormigas de manera oportunística, con Pyriglena leucoptera siendo la única especie que forrajeaba obligatoriamente con las hormigas soldado. Nuestras observaciones sugieren que los artrópodos y otros organismos que son ahuyentados por las hormigas soldado representan un recurso de comida para una variedad de especies de aves en el ecosistema del bosque Atlántico. [source]

Spatial variability of O layer thickness and humus forms under different pine beech,forest transformation stages in NE Germany

Oliver Bens
Abstract Spatial variability of humus layer (O layer) thicknesses can have important impacts upon soil water dynamics, nutrient storage and availability, as well as plant growth. The purpose of the present study was to elucidate the impact of forest-transformation practices on the spatial variability of O layer thicknesses. The study focused on the Kahlenberg forest area (NE Germany) with stands of Scots pine (Pinus sylvestris) and European beech (Fagus sylvatica) of different age structures that form a transformation chronosequence from pure Scots pine stands towards pure European beech stands. Topsoil profiles including both, the O layer and the uppermost humic mineral soil horizon were excavated at intervals of 0.4 m along 15,20 m long transects, and spatial variability of O layer thicknesses was quantified by variogram analysis. The correlation lengths of total O layer thickness increased in the sequence consisting of pure pine stand (3.1 m) , older mixed stand (3.7 m) , pure beech stand (4.5 m), with the exception of the younger mixed stand, for which no correlation lengths of total O layer thickness could be determined. The degree of spatial correlation, i.e., the percentage of the total variance which can be described by variograms, was highest for the two monospecies stands, whereas this percentage was distinctly lower for the two mixed stands. A similar minimum for the two mixed stands was observed for the correlation lengths of the Oh horizon. These results suggest that the spatial structures of forest-transformation stands may be interpreted in terms of a disturbance (in the form of the underplanting of beech trees). After this disturbance, the forest ecosystem requires at least 100 y to again reach relative equilibrium. These findings are in line with the results of other soil-related investigations at these sites. Räumliche Variabilität der Humuslagenmächtigkeit und Humusformen in verschiedenen Stadien des Waldumbaus von Kiefer zu Buche in NO-Deutschland Die räumliche Variabilität der Humusauflagenmächtigkeit kann einen bedeutenden Einfluss auf die Bodenwasserdynamik, Nährstoffspeicherung und -verfügbarkeit sowie das Pflanzenwachstum haben. Ziel dieser Studie war es, die Auswirkungen von Waldumbaumaßnahmen auf die räumliche Verteilung der Auflagehumusmächtigkeiten zu untersuchen. Im Forstrevier Kahlenberg, mit Beständen von Kiefer (Pinus sylvestris) und Buche (Fagus sylvatica) unterschiedlichen Alters, welche eine Transformations-Chronosequenz von einem Kiefern-Reinbestand hin zu einem reinen Buchenbestand darstellen, wurden Humusprofile entlang von 15,20 m langen Transekten in Abständen von 0,4 m aufgenommen. Die räumliche Variabilität der Mächtigkeiten der Auflagehumushorizonte wurde durch Variogramm-Analysen quantifiziert. Die Korrelationslängen der Mächtigkeiten des gesamten Auflagehumus stiegen in der Reihenfolge reiner Kiefernbestand (3,1 m) , älterer Mischbestand (3,7 m) , reiner Buchenbestand (4,5 m) an. Aus dieser Reihe fällt der jüngere Mischbestand heraus; für ihn konnten keine Korrelationslängen ermittelt werden. Der Grad der räumlichen Korrelation, d. h. der Anteil der gesamten Varianz, der durch Variogramme beschrieben wird, ist für die beiden Reinbestände am höchsten, während er für die beiden Mischbestände deutlich geringer ist. Ein ähnliches Minimum für die beiden Mischbestände ergibt sich, wenn nur die Korrelationslängen der Oh-Mächtigkeiten betrachtet werden. Diese Ergebnisse deuten darauf hin, dass die räumlichen Strukturen von Waldumbaubeständen im Sinne einer Störung gedeutet werden können (wobei die Umbaumaßnahme und der Unterbau mit Buchen die Störung darstellt). Diese Störung dauert offenbar mindestens 100 a an. Dieser Befund stimmt mit den Ergebnissen aus Studien zu weiteren relevanten Bodeneigenschaften an Forststandorten im nordostdeutschen Tiefland überein. [source]

Phylogenetic similarity and structure of Agaricomycotina communities across a forested landscape

Abstract The Agaricomycotina are a phylogenetically diverse group of fungi that includes both saprotrophic and mycorrhizal species, and that form species , rich communities in forest ecosystems. Most species are infrequently observed, and this hampers assessment of the role that environmental heterogeneity plays in determining local community composition and in driving ,-diversity. We used a combination of phenetic (TRFLP) and phylogenetic approaches [Unifrac and Net Relatedness Index (NRI)] to examine the compositional and phylogenetic similarity of Agaricomycotina communities in forest floor and surface soil of three widely distributed temperate upland forest ecosystems (one, xeric oak , dominated and two, mesic sugar maple dominated). Generally, forest floor and soil communities had similar phylogenetic diversity, but there was little overlap of species or evolutionary lineages between these two horizons. Forest floor communities were dominated by saprotrophic species, and were compositionally and phylogenetically similar in all three ecosystems. Mycorrhizal species represented 30% to 90% of soil community diversity, and these communities differed compositionally and phylogenetically between ecosystems. Estimates of NRI revealed significant phylogenetic clustering in both the forest floor and soil communities of only the xeric oak-dominated forest ecosystem, and may indicate that this ecosystem acts as a habitat filter. Our results suggest that environmental heterogeneity strongly influences the phylogenetic ,-diversity of soil inhabiting Agaricomycotina communities, but has only a small influence on forest floor ,-diversity. Moreover, our results suggest that the strength of community assembly processes, such as habitat filtering, may differ between temperate forest ecosystems. [source]

Effects of altered water regimes on forest root systems

How ecosystems adapt to climate changes depends in part on how individual trees allocate resources to their components. A review of research using tree seedlings provides some support for the hypothesis that some tree species respond to exposure to drought with increases in root,shoot ratios but little change in total root biomass. Limited research on mature trees over moderately long time periods (2,10 yr), has given mixed results with some studies also providing evidence for increases in root: shoot ratios. The Throughfall Displacement Experiment (TDE) was designed to simulate both an increase and a decrease of 33% in water inputs to a mature deciduous forest over a number of years. Belowground research on TDE was designed to examine four hypothesized responses to long-term decreases in water availability; (1) increases in fine-root biomass, (2) increases in fine root,foliage ratio, (3) altered rates of fine-root turnover (FRT), and (4) depth of rooting. Minirhizotron root elongation data from 1994 to 1998 were examined to evaluate the first three hypotheses. Differences across treatments in net fine-root production (using minirhizotron root elongation observations as indices of biomass production) were small and not significant. Periods of lower root production in the dry treatment were compensated for by higher growth during favorable periods. Although not statistically significant, both the highest production (20 to 60% higher) and mortality (18 to 34% higher) rates were found in the wet treatment, resulting in the highest index of FRT. After 5 yr, a clear picture of stand fine-root-system response to drought exposure has yet to emerge in this forest ecosystem. Our results provide little support for either an increase in net fine-root production or a shift towards an increasing root,shoot ratio with long-term drought exposure. One possible explanation for higher FRT rates in the wet treatment could be a positive relationship between FRT and nitrogen and other nutrient availability, as treatments have apparently resulted in increased immobilization of nutrients in the forest floor litter under drier conditions. Such hypotheses point to the continued need to study the interactions of water stress, nutrient availability and carbon-fixation efficiency in future long-term studies. [source]

Direct and indirect effects of elevated CO2 on leaf respiration in a forest ecosystem

J. G. Hamilton
Abstract We measured the short-term direct and long-term indirect effects of elevated CO2 on leaf dark respiration of loblolly pine (Pinus taeda) and sweetgum (Liquidambar styraciflua) in an intact forest ecosystem. Trees were exposed to ambient or ambient + 200 µmol mol,1 atmospheric CO2 using free-air carbon dioxide enrichment (FACE) technology. After correcting for measurement artefacts, a short-term 200 µmol mol,1 increase in CO2 reduced leaf respiration by 7,14% for sweetgum and had essentially no effect on loblolly pine. This direct suppression of respiration was independent of the CO2 concentration under which the trees were grown. Growth under elevated CO2 did not appear to have any long-term indirect effects on leaf maintenance respiration rates or the response of respiration to changes in temperature (Q10, R0). Also, we found no relationship between mass-based respiration rates and leaf total nitrogen concentrations. Leaf construction costs were unaffected by growth CO2 concentration, although leaf construction respiration decreased at elevated CO2 in both species for leaves at the top of the canopy. We conclude that elevated CO2 has little effect on leaf tissue respiration, and that the influence of elevated CO2 on plant respiratory carbon flux is primarily through increased biomass. [source]

Pervasive threats within a protected area: conserving the endemic birds of São Tomé, West Africa

M. Dallimer
Abstract The importance of the rainforests on the island of São Tomé for biodiversity is well known. However, the area only recently received full legal protection as a National Park and currently few resources are available to enforce that legislation. With rapid economic development forecast for the island, active conservation efforts are essential. Here we study the distribution and density of the island's endemic bird species, including nine that are Globally Threatened, within the National Park. Sites, covering the full range of primary forest types, were surveyed using distance sampling methods. No introduced species were observed. The highest number of species, including eight Globally Threatened species, were found in lowland rainforest, although many were infrequently encountered. Higher altitude sites were less diverse, but supported some of the common endemic species at extremely high densities. The least diverse assemblage, with generally lower species population densities, occurred at the most accessible mid-altitude forest site. Distance from settlements was a key explanatory variable for the presence of all Globally Threatened species, indicating that human habitation has negative effects on the suitability of nearby forest habitats. This suggests that, as infrastructure improvements proceed, populations of endangered species will come under growing pressure. Integrating the needs of biodiversity conservation and development represents a major challenge for many biodiverse countries and on São Tomé, as elsewhere, may best be achieved by preserving the still intact functioning forest ecosystem. [source]

Landscape Heterogeneity and Diurnal Raptor Diversity in Honduras: The Role of Indigenous Shifting Cultivation,

BIOTROPICA, Issue 3 2001
David L. Anderson
ABSTRACT I studied the relationship between diurnal raptor diversity, density, and richness, and landscape heterogeneity in continuous primary forests and forests farmed by native Amerindians in the Río Plátano Biosphere Reserve of northeastern Honduras from January to June 1996 and 1997. I estimated landscape heterogeneity,the variability in naturally occurring and/or anthropogenic habitat mosaics,by mapping the extent and distribution of five human-modified and natural habitats in 24 1 km2 survey plots. I used the Shannon index to calculate landscape heterogeneity values for the respective plots based on the proportion of total area of each habitat within each plot. Diurnal raptor surveys from canopy-emergent viewpoints in these plots resulted in 137 observations of 18 species of raptors. Four species (Coragyps atratus, Ictinia plumbea, Leucopternis albicollis, and Buteo magnirostris) differed significantly in abundance among heterogeneity classes. Raptor diversity, density, and richness all increased directly with increasing landscape heterogeneity. Landscape heterogeneity was more important in explaining differences in raptor species diversity than the presence or extent of any single habitat or combination of habitats. In contrast to previous studies, my results indicate the importance of indigenous shifting cultivation in altering the naturally occurring patterns of habitat mosaics in lowland rain forest and its effect on bird species abundance and diversity in a rain forest ecosystem. RESUMES Estudié la relación entre la diversidad, densidad y la riqueza de especies de rapaces diurnas con la heterogeinidad de paisajes en bosques primaries contínues y bosques donde practican la agricultura migratoria indígenas de la Reserva de Biósfera del Río Plátano al noreste de Honduras entre los meses de enero a junio de 1996 y 1997. Evalué la heterogeneidad de paisajes-la variabilidad en mosaicos de hábitats naturales o antropogínicos-con mapas de cinco hábitats en 24 parcelas de 1 km2. Usé el Indice de Shannon para calcular valores de la heterogeneidad de cada parcela, basado en la proporción de cada hábitat. Desde el dosel, hice conteos de rapaces en las 24 parcelas que resukaron en 137 observaciones de 18 especies. Cuatro especies (Coragyps atratus, Ictinia plumbea, Leocopternis albicollis, y Buteo magnirostris) difirieron significativamente en abundancia entre los grupos de heterogeneidad del paisaje. La diversidad, densidad y riqueza de especies aumentaron conjuntamente con la heterogeneidad del paisaje. La heterogeneidad del paisaje rue mas importante para explicar la diversidad de rapaces que la presencia o el área de cualquier hábitat o combinación de hábitats. En contraste con estudios anteriores, mis resultados sugieron la importancia de la agricultura migratoria indigena en la alteracíon de mosaicos de hábitats naturales en los bosques hiimedos bajos, y su efecto en la abundancia y diversidad de aves de un ecosistema forestal. [source]

Ecohydrology of a semi-arid forest: partitioning among water balance components and its implications for predicted precipitation changes

ECOHYDROLOGY, Issue 2 2010
Naama Raz Yaseef
Abstract The distribution of precipitation inputs into different hydrological components of water-limited forest ecosystems determines water availability to trees and consequently forest productivity. We constructed a complete hydrological budget of a semi-arid pine forest (285 mm annual precipitation) by directly measuring its main components: precipitation (P), soil water content, evapotranspiration (ET, eddy covariance), tree transpiration (sap flux), soil evaporation (soil chambers), and intercepted precipitation (calculated). Our results indicated that on average for the 4-year study period, ET accounted for 94% of P, varying between 100% when P < 250 mm and 85% when P > 300 mm (with indications for losses to subsurface flow and soil moisture storage in wetter years). Direct measurements of the components of the ET flux demonstrated that both transpiration and soil evaporation were significant in this dry forest (45% and 36% of ET, respectively). Comparison between ecosystem ET (eddy covariance measurements) and the sum of its measured components showed good agreement on annual scales, but up to 30% discrepancies (in both directions) on shorter timescales. The pulsed storm pattern, characteristics of semi-arid climates, was sufficient to maintain the topsoil layer wet during the whole wet season. Only less often and intensive storms resulted in infiltration to the root zone, increasing water availability for uptake by deeper roots. Our results indicate that climate change predictions that link reduced precipitation with increased storm intensity may have a smaller effect on water availability to forest ecosystems than reduced precipitation alone, which could help forests' survival and maintain productivity even under drier conditions. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Trophic control of grassland production and biomass by pathogens

Charles E. Mitchell
Abstract Current theories of trophic regulation of ecosystem net primary production and plant biomass incorporate herbivores, but not plant pathogens. Obstacles to the incorporation of pathogens include a lack of data on pathogen effects on primary production, especially outside agricultural and forest ecosystems, and an apparent inability to quantify pathogen biomass. Here, I report the results of an experiment factorially excluding foliar fungal pathogens and insect herbivores from an intact grassland ecosystem. At peak in control plots, 8.9% of community leaf area was infected by pathogens. Disease reduction treatment dramatically increased root production and biomass by increasing leaf longevity and photosynthetic capacity. In contrast, herbivory reduction had no detectable effects at the ecosystem or leaf scale. Additionally, biomass of foliar fungal pathogens in the ecosystem was comparable with that of insect herbivores. These results identify pathogens as potential regulators of ecosystem processes and promote the incorporation of pathogens into trophic theory. [source]

Invasive and quarantine pests in forests in Slovakia1

EPPO BULLETIN, Issue 2 2006
Milan Zúbrik
Biological invasions of insects, plants, and fungal pest species often cause substantial disturbance to forest ecosystems and as well as severe socioeconomic impacts. Central Europe acts as a ,bridge' between Western and Eastern Europe both ecologically and as an important transit corridor for people. Human activity, including the movement of material goods, increases the risk of invasions. Some species introduced in the past have been established, becoming common and causing serious problems (such as Dreyfusia nordmannianae or Hyphantria cunea). The status, importance and spatial distribution in Slovakia of seven different forest pests recently introduced into Slovak forest ecosystems (Cameraria ohridella, Coleotechnites piceaella, Cryphonectria parasitica, Dothistroma septospora, Ips duplicatus, Parectopa robiniella, Phyllonorycter robiniellus) as well as two others not yet recorded in Slovakia (Anoplophora glabripennis, Phytophthora spp.) is discussed. [source]

Effects of oleoresins and monoterpenes on in vitro growth of fungi associated with pine decline in the Southern United States

L. G. Eckhardt
Summary As a means of exploring pine resistance to root disease and declines, the effects of host plant secondary metabolites on the growth of root colonizing fungi associated with three diseases/declines of southern pines , loblolly pine decline, littleleaf disease and annosum root rot were tested. The associated fungi ,Leptographium huntii, L. serpens, L. terebrantis, L. procerum, Heterobasidion annosum and Phytophthora cinnamomi, were grown in saturated atmospheres or in direct contact with, pure monoterpenes and crude oleoresin collected from the four southern pines (Pinus taeda, P. eschinata, P. palustris and P. elliotti) for 7 day. Fungal growth was measured at 3, 5 and 7 day. Root-infecting fungi differed significantly in sensitivity to crude oleoresin and pure monoterpenes. All fungi tested were inhibited, to some extent, by the resins tested. H. annosum and P. cinnamomi were strongly inhibited by all the monoterpenes tested. The ophiostomatoid fungi were significantly less affected by the compounds tested. L. huntii and L. serpens were less inhibited by monoterpenes than either L. terebrantis or L. procerum. These fungal growth studies show that the kind and amount of secondary metabolite produced by the host plant have a profound effect on tree pathogens. Alterations of tree physiology may have implications for defenses against tree pathogens as well as to the ecology and management of forest ecosystems. Difference in incidence of root disease observed in the field may be explained by the ability of the fungus to tolerate these host defense mechanisms. [source]

Below-ground carbon flux and partitioning: global patterns and response to temperature

C. M. Litton
Summary 1The fraction of gross primary production (GPP) that is total below-ground carbon flux (TBCF) and the fraction of TBCF that is below-ground net primary production (BNPP) represent globally significant C fluxes that are fundamental in regulating ecosystem C balance. However, global estimates of the partitioning of GPP to TBCF and of TBCF to BNPP, as well as the absolute size of these fluxes, remain highly uncertain. 2Efforts to model below-ground processes are hindered by methodological difficulties for estimating below-ground C cycling, the complexity of below-ground interactions, and an incomplete understanding of the response of GPP, TBCF and BNPP to climate change. Due to a paucity of available data, many terrestrial ecosystem models and ecosystem-level studies of whole stand C use efficiency rely on assumptions that: (i) C allocation patterns across large geographic, climatic and taxonomic scales are fixed; and (ii) c. 50% of TBCF is BNPP. 3Here, we examine available information on GPP, TBCF, BNPP, TBCF : GPP and BNPP : TBCF from a diverse global data base of forest ecosystems to understand patterns in below-ground C flux and partitioning, and their response to mean annual temperature (MAT). 4MAT and mean annual precipitation (MAP) covaried strongly across the global forest data base (37 mm increase in MAP for every 1 °C increase in MAT). In all analyses, however, MAT was the most important variable explaining observed patterns in below-ground C processes. 5GPP, TBCF and BNPP all increased linearly across the global scale range of MAT. TBCF : GPP increased significantly with MAT for temperate and tropical ecosystems (> 5 °C), but variability was high across the data set. BNPP : TBCF varied from 0·26 to 0·53 across the entire MAT gradient (,5 to 30 °C), with a much narrower range of 0·42 to 0·53 for temperate and tropical ecosystems (5 to 30 °C). 6Variability in the data sets was moderate and clear exceptions to the general patterns exist that likely relate to other factors important for determining below-ground C flux and partitioning, in particular water availability and nutrient supply. Still, our results highlight global patterns in below-ground C flux and partitioning in forests in response to MAT that in part confirm previously held assumptions. [source]

Nitrogen utilization by Hylocomium splendens in a boreal forest fertilization experiment

Summary 1Nitrogen uptake in the terricolous bryophyte Hylocomium splendens (Hedw.) B.S.G. was studied in a boreal forest long-term N-treatment experiment including control plots, N-addition plots (50 kg N ha,1 year,1 for 8 years) and recovery plots (50 kg N ha,1 year,1 for 5 years and thereafter no N addition for 3 years). 2A main objective was to explore whether the N treatments changed bryophyte uptake of different inorganic and organic N forms. In addition, we estimated the contribution of N from throughfall precipitation to the bryophyte N supply. 3The results demonstrated that bryophyte N uptake was similar in all the long-term N-treatment plots. Hylocomium splendens took up more 15N labelled than or glycine when these N forms were applied in situ by the spraying of solutions with N concentrations similar to those in precipitation. 4Analysis of the precipitation collected beneath the closed tree canopy from late May to early October revealed that it contributed 2·0 kg N ha,1 during the period studied, distributed between (78%), amino acid N (17%) and (5%). 5The study highlights that, in addition to analyses of and (normally included in standard environmental monitoring of precipitation), analysis of amino acid N must be performed to account fully for the precipitation N input to bryophytes in boreal forest ecosystems. [source]

A non-native invasive grass increases soil carbon flux in a Hawaiian tropical dry forest

Abstract Non-native plants are invading terrestrial ecosystems across the globe, yet little is known about how invasions impact carbon (C) cycling or how these impacts will be influenced by climate change. We quantified the effect of a non-native C4 grass invasion on soil C pools and fluxes in a Hawaiian tropical dry forest over 2 years in which annual precipitation was average (Year 1) and ,60% higher than average (Year 2). Work was conducted in a series of forested plots where the grass understory was completely removed (removal plots) or left intact (grass plots) for 3 years before experiment initiation. We hypothesized that grass invasion would: (i) not change total soil C pools, (ii) increase the flux of C into and out of soils, and (iii) increase the sensitivity of soil C flux to variability in precipitation. In grass plots, grasses accounted for 25,34% of litter layer C and ,70% of fine root C. However, no differences were observed between treatments in the size of any soil C pools. Moreover, grass-derived C constituted a negligible fraction of the large mineral soil C pool (< 3%) despite being present in the system for ,50 years. Tree litterfall was ,45% lower in grass plots, but grass-derived litterfall more than compensated for this reduction in both years. Annual cumulative soil-surface CO2 efflux (Rsoil) was ,40% higher in grass plots in both years, and increased in both treatments by ,36% in the wetter Year 2. Despite minimal grass-derived mineral soil C, > 75% of Rsoil in grass plots was of C4 (i.e. grass) origin. These results demonstrate that grass invasion in forest ecosystems can increase the flux of C into and out of soils without changing total C pools, at least over the short term and as long as the native tree canopy remains intact, and that invasion-mediated changes in belowground C cycling are sensitive to precipitation. [source]

Trends and methodological impacts in soil CO2 efflux partitioning: A metaanalytical review

Abstract Partitioning soil carbon dioxide (CO2) efflux (RS) into autotrophic (RA; including plant roots and closely associated organisms) and heterotrophic (RH) components has received considerable attention, as differential responses of these components to environmental change have profound implications for the soil and ecosystem C balance. The increasing number of partitioning studies allows a more detailed analysis of experimental constraints than was previously possible. We present results of an exhaustive literature search of partitioning studies and analyse global trends in flux partitioning between biomes and ecosystem types by means of a metaanalysis. Across all data, an overall decline in the RH/RS ratio for increasing annual RS fluxes emerged. For forest ecosystems, boreal coniferous sites showed significantly higher (P<0.05) RH/RS ratios than temperate sites, while both temperate or tropical deciduous forests did not differ in ratios from any of the other forest types. While chronosequence studies report consistent declines in the RH/RS ratio with age, no difference could be detected for different age groups in the global data set. Different methodologies showed generally good agreement if the range of RS under which they had been measured was considered, with the exception of studies estimating RH by means of root mass regressions against RS, which resulted in consistently lower RH/RS estimates out of all methods included. Additionally, the time step over which fluxes were partitioned did not affect RH/RS ratios consistently. To put results into context, we review the most common techniques and point out the likely sources of errors associated with them. In order to improve soil CO2 efflux partitioning in future experiments, we include methodological recommendations, and also highlight the potential interactions between soil components that may be overlooked as a consequence of the partitioning process itself. [source]

Interannual climatic variation mediates elevated CO2 and O3 effects on forest growth

Abstract We analyzed growth data from model aspen (Populus tremuloides Michx.) forest ecosystems grown in elevated atmospheric carbon dioxide ([CO2]; 518 ,L L,1) and ozone concentrations ([O3]; 1.5 × background of 30,40 nL L,1 during daylight hours) for 7 years using free-air CO2 enrichment technology to determine how interannual variability in present-day climate might affect growth responses to either gas. We also tested whether growth effects of those gasses were sustained over time. Elevated [CO2] increased tree heights, diameters, and main stem volumes by 11%, 16%, and 20%, respectively, whereas elevated ozone [O3] decreased them by 11%, 8%, and 29%, respectively. Responses similar to these were found for stand volume and basal area. There were no growth responses to the combination of elevated [CO2+O3]. The elevated [CO2] growth stimulation was found to be decreasing, but relative growth rates varied considerably from year to year. Neither the variation in annual relative growth rates nor the apparent decline in CO2 growth response could be explained in terms of nitrogen or water limitations. Instead, growth responses to elevated [CO2] and [O3] interacted strongly with present-day interannual variability in climatic conditions. The amount of photosynthetically active radiation and temperature during specific times of the year coinciding with growth phenology explained 20,63% of the annual variation in growth response to elevated [CO2] and [O3]. Years with higher photosynthetic photon flux (PPF) during the month of July resulted in more positive growth responses to elevated [CO2] and more negative growth responses to elevated [O3]. Mean daily temperatures during the month of October affected growth in a similar fashion the following year. These results indicate that a several-year trend of increasingly cloudy summers and cool autumns were responsible for the decrease in CO2 growth response. [source]

Soil-atmospheric exchange of CO2, CH4, and N2O in three subtropical forest ecosystems in southern China

Abstract The magnitude, temporal, and spatial patterns of soil-atmospheric greenhouse gas (hereafter referred to as GHG) exchanges in forests near the Tropic of Cancer are still highly uncertain. To contribute towards an improvement of actual estimates, soil-atmospheric CO2, CH4, and N2O fluxes were measured in three successional subtropical forests at the Dinghushan Nature Reserve (hereafter referred to as DNR) in southern China. Soils in DNR forests behaved as N2O sources and CH4 sinks. Annual mean CO2, N2O, and CH4 fluxes (mean±SD) were 7.7±4.6 Mg CO2 -C ha,1 yr,1, 3.2±1.2 kg N2O-N ha,1 yr,1, and 3.4±0.9 kg CH4 -C ha,1 yr,1, respectively. The climate was warm and wet from April through September 2003 (the hot-humid season) and became cool and dry from October 2003 through March 2004 (the cool-dry season). The seasonality of soil CO2 emission coincided with the seasonal climate pattern, with high CO2 emission rates in the hot-humid season and low rates in the cool-dry season. In contrast, seasonal patterns of CH4 and N2O fluxes were not clear, although higher CH4 uptake rates were often observed in the cool-dry season and higher N2O emission rates were often observed in the hot-humid season. GHG fluxes measured at these three sites showed a clear increasing trend with the progressive succession. If this trend is representative at the regional scale, CO2 and N2O emissions and CH4 uptake in southern China may increase in the future in light of the projected change in forest age structure. Removal of surface litter reduced soil CO2 effluxes by 17,44% in the three forests but had no significant effect on CH4 absorption and N2O emission rates. This suggests that microbial CH4 uptake and N2O production was mainly related to the mineral soil rather than in the surface litter layer. [source]

Evaluation of six process-based forest growth models using eddy-covariance measurements of CO2 and H2O fluxes at six forest sites in Europe

K. Kramer
Abstract Reliable models are required to assess the impacts of climate change on forest ecosystems. Precise and independent data are essential to assess this accuracy. The flux measurements collected by the EUROFLUX project over a wide range of forest types and climatic regions in Europe allow a critical testing of the process-based models which were developed in the LTEEF project. The ECOCRAFT project complements this with a wealth of independent plant physiological measurements. Thus, it was aimed in this study to test six process-based forest growth models against the flux measurements of six European forest types, taking advantage of a large database with plant physiological parameters. The reliability of both the flux data and parameter values itself was not under discussion in this study. The data provided by the researchers of the EUROFLUX sites, possibly with local corrections, were used with a minor gap-filling procedure to avoid the loss of many days with observations. The model performance is discussed based on their accuracy, generality and realism. Accuracy was evaluated based on the goodness-of-fit with observed values of daily net ecosystem exchange, gross primary production and ecosystem respiration (gC m,2 d,1), and transpiration (kg H2O m,2 d,1). Moreover, accuracy was also evaluated based on systematic and unsystematic errors. Generality was characterized by the applicability of the models to different European forest ecosystems. Reality was evaluated by comparing the modelled and observed responses of gross primary production, ecosystem respiration to radiation and temperature. The results indicated that: Accuracy. All models showed similar high correlation with the measured carbon flux data, and also low systematic and unsystematic prediction errors at one or more sites of flux measurements. The results were similar in the case of several models when the water fluxes were considered. Most models fulfilled the criteria of sufficient accuracy for the ability to predict the carbon and water exchange between forests and the atmosphere. Generality. Three models of six could be applied for both deciduous and coniferous forests. Furthermore, four models were applied both for boreal and temperate conditions. However, no severe water-limited conditions were encountered, and no year-to-year variability could be tested. Realism. Most models fulfil the criterion of realism that the relationships between the modelled phenomena (carbon and water exchange) and environment are described causally. Again several of the models were able to reproduce the responses of measurable variables such as gross primary production (GPP), ecosystem respiration and transpiration to environmental driving factors such as radiation and temperature. Stomatal conductance appears to be the most critical process causing differences in predicted fluxes of carbon and water between those models that accurately describe the annual totals of GPP, ecosystem respiration and transpiration. As a conclusion, several process-based models are available that produce accurate estimates of carbon and water fluxes at several forest sites of Europe. This considerable accuracy fulfils one requirement of models to be able to predict the impacts of climate change on the carbon balance of European forests. However, the generality of the models should be further evaluated by expanding the range of testing over both time and space. In addition, differences in behaviour between models at the process level indicate requirement of further model testing, with special emphasis on modelling stomatal conductance realistically. [source]

The role of local and regional processes in shaping dung beetle communities in tropical forest plantations in Borneo

GLOBAL ECOLOGY, Issue 4 2000
Andrew J. Davis
Abstract We examine whether rain forest dung beetle species found in plantations in Sabah, northern Borneo, tend to be endemic or geographically widespread. In addition, linear regressions of abundance vs. distance from a major river in primary rain forest are calculated to see if species found in plantation forest show affinity to one specific biotope (riverine vs. interior forest) in their natural habitat. Results show that 14 of the 40 species recorded from plantations are endemic to Borneo. Only edge-specialist endemic species are found in plantation forest, with no interior-forest specialists recorded. Data suggest that endemic species that are adapted to more exposed conditions in primary rain forest, such as riverine species, can in some instances tolerate man-made habitats. Twenty-nine species (±SE 4.0) per transect are recorded from plantation transects, whereas 44.2 (±1.7 SE) are recorded in primary rain forest. As species richness is much lower in plantations than natural forest, implying loss of biodiversity, we conclude that measures of biogeographic distinctiveness, whereby endemic species confer higher values, may be misleading unless they take into account edge-affinity. Local- as well as regional-distributional data may therefore be needed to interpret correctly patterns of species assemblages in derived forest ecosystems. [source]

Climate change and range expansion of an aggressive bark beetle: evidence of higher beetle reproduction in naïve host tree populations

Timothy J. Cudmore
Summary 1.,Hosts may evolve defences that make them less susceptible and suitable to herbivores impacting their fitness. Due to climate change-driven range expansion, herbivores are encountering naïve host populations with increasing frequency. 2.,Aggressive bark beetles are among the most important agents of disturbance in coniferous forest ecosystems. The presence of bark beetle outbreaks in areas with a historically unsuitable climate, in part a consequence of climate change, provided an opportunity to assess the hypothesis that the mountain pine beetle Dendroctonus ponderosae has higher reproductive success in lodgepole pine Pinus contorta trees growing in areas that have not previously experienced frequent outbreaks. 3.,We felled and sampled mountain pine beetle-killed trees from historically climatically suitable and unsuitable areas, i.e. areas with and without a historical probability of frequent outbreaks. Reproductive success was determined from a total of 166 trees from 14 stands. 4.,Brood productivity was significantly affected by climatic suitability class, such that mean brood production per female increased as historical climatic suitability decreased. 5.,Synthesis and applications. The current study demonstrates that the mountain pine beetle has higher reproductive success in areas where its host trees have not experienced frequent beetle epidemics, which includes much of the current outbreak area in north central British Columbia. This increased productivity of mountain pine beetle is likely to have been a key reason for the rapid population buildup that resulted in unprecedented host tree mortality over huge areas in western Canada. The outbreak thus provides an example of how climate change-driven range expansion of native forest insects can have potentially disastrous consequences. Since an increased reproductive success is likely to accelerate the progression of outbreaks, it is particularly critical to manage forests for the maintenance of a mosaic of species and age classes at the landscape level in areas where host tree populations are naïve to eruptive herbivores. [source]