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Forest Canopy (forest + canopy)

Distribution by Scientific Domains

Life Sciences	71%
Earth and Environmental Science	12%

Distribution within Life Sciences

Ecology & Organismal Biology	29%
Plant Science	16%

Selected Abstracts

Colonization Strategies of Two Liana Species in a Tropical Dry Forest Canopy

BIOTROPICA, Issue 3 2007
Gerardo Avalos
ABSTRACT Lianas impose intense resource competition for light in the upper forest canopy by displaying dense foliage on top of tree crowns. Using repeated access with a construction crane, we studied the patterns of canopy colonization of the lianas Combretum fruticosum and Bonamia trichantha in a Neotropical dry forest in Panama. Combretum fruticosum flushed leaves just before the rainy season, and its standing leaf area quickly reached a peak in the early rainy season (May,June). In contrast, B. trichantha built up foliage area continuously throughout the rainy season and reached a peak in the late rainy season (November). Both species displayed the majority of leaves in full sun on the canopy surface, but C. fruticosum displayed a greater proportion of leaves (26%) in more shaded microsites than B. trichantha (12%). Self-shading within patches of liana leaves within the uppermost 40,50 cm of the canopy reduced light levels measured with photodiodes placed directly on leaves to 4,9 percent of light levels received by sun leaves. Many leaves of C. fruticosum acclimated to shade within a month following the strongly synchronized leaf flushing and persisted in deep shade. In contrast, B. trichantha produced short-lived leaves opportunistically in the sunniest locations. Species differences in degree of shade acclimation were also evident in terms of structural (leaf mass per area, and leaf toughness) and physiological characters (nitrogen content, leaf life span, and light compensation point). Contrasting leaf phenologies reflect differences in light exploitation and canopy colonization strategies of these two liana species. RESUMEN Las lianas imponen una competencia intensa por la luz en el dosel superior al desplegar un denso follaje encima de las copas de los árboles. Usando acceso repetido al dosel a través de una grúa de construcción, estudiamos los patrones de colonización del dosel de las lianas Combretum fruticosum y Bonamia trichantha en un bosque neotropical seco en Panamá. Combretum fruticosum produjo hojas nuevas justo antes de la estación lluviosa, y su área foliar total alcanzó rápidamente un pico a inicios de la estación lluviosa (mayo-junio). En contraste, B. trichantha construyó su área foliar de forma continua a través de la estación lluviosa alcanzando un pico al final de esta (noviembre). Ambas especies desplegaron la mayoría de sus hojas bajo alta irradiación en la superficie del dosel, aunque C. fruticosum desplegó una mayor proporción de follaje (26%) en micrositios más sombreados que B. trichantha (12%). El auto sombreo dentro de los parches de hojas de lianas dentro de los primeros 40-50 cm del dosel superior redujo el nivel de radiación medido con fotodiodos colocados directamente sobre las hojas a 4-9% de la luz recibida por las hojas de sol. Muchas hojas de C. fruticosum se aclimataron a la sombra luego de un mes después de la producción inicial de hojas altamente sincronizada y persistieron en sombra profunda. En contraste, B. trichantha produjo hojas de corta longevidad de forma oportunística bajo las condiciones de mayor irradiación. Las diferencias entre especies en el grado de aclimatación a la sombra fueron evidentes en términos de caracteres estructurales (masa foliar por unidad de área, y dureza foliar) y fisiológicos (contenido de nitrógeno, longevidad foliar, y punto de compensación lumínica). Estas fenologías foliares tan contrastantes reflejan diferencias en las estrategias de explotación de luz y colonización del dosel por parte de estas dos lianas. [source]

Forest canopy and community dynamics in a temperate old-growth evergreen broad-leaved forest, south-western Japan: a 7-year study of a 4-ha plot

JOURNAL OF ECOLOGY, Issue 5 2001
Masahiro Miura
Summary 1Forest canopy gap and community dynamics were studied in a 4-ha permanent plot of an old-growth evergreen broad-leaved forest dominated by Castanopsis cuspidata var. sieboldii and Distylium racemosum in the Tatera Forest Reserve, Tsushima Islands, south-western Japan. The forest was affected by a powerful typhoon in 1987 and was monitored from 1990 to 1997. 2In 1990, all woody stems , 5 cm diameter at breast height (d.b.h.) in the plot were identified, mapped and marked, and the state of 1600 5 m × 5 m contiguous quadrats used to locate canopy gaps. Gaps occupied 17.1% of the plot, which contained 4494 tree and shrub stems (total basal area 63.48 m2 ha,1). Gaps were re-censused in 1997 and both marked and newly recruited (, 5 cm d.b.h.) stems were recorded in 1992 and 1997. 3Over 7 years the rates of canopy gap formation and closure were 0.72% year,1 and 1.61% year,1, respectively, mortality and recruitment rates were 0.97% year,1 and 0.99% year,1, and the rates of loss and gain in basal area were 0.95% year,1 and 0.83% year,1. 4The mortality of stems was size-dependent, with those in middle size classes having the lowest rates. Mortality of stems was lower in canopy and higher in the understorey, while the proportion of stems killed by disturbances increased with height. 5Stems that died during the 7 years were predominantly located in newly created gaps, whereas stems were recruited into both established and new gaps. Deciduous broad-leaved species were largely restricted to gaps that remained open throughout the study. 6Both composition and structure of the forest changed in response to disturbance-related effects on canopy dynamics. [source]

A note on estimating urban roof runoff with a forest evaporation model

HYDROLOGICAL PROCESSES, Issue 8 2008
J. H. C. Gash
Abstract A model developed for estimating the evaporation of rainfall intercepted by forest canopies is applied to estimate measurements of the average runoff from the roofs of six houses made in a previous study of hydrological processes in an urban environment. The model is applied using values of the mean rates of wet canopy evaporation and rainfall derived previously for forests and an estimate of the roof storage capacity derived from the data collected in the previous study. Although the model prediction is sensitive to the value of storage capacity, close correlation between the modelled and measured runoff indicates that the model captures the essential processes. It is concluded that the process of evaporation from an urban roof is sufficiently similar to that from a forest canopy for forest evaporation models to be used to give a useful estimate of urban roof runoff. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Modeling volatile isoprenoid emissions , a story with split ends

PLANT BIOLOGY, Issue 1 2008
R. Grote
Abstract Accurate prediction of plant-generated volatile isoprenoid fluxes is necessary for reliable estimation of atmospheric ozone and aerosol formation potentials. In recent years, significant progress has been made in understanding the environmental and physiological controls on isoprenoid emission and in scaling these emissions to canopy and landscape levels. We summarize recent developments and compare different approaches for simulating volatile isoprenoid emission and scaling up to whole forest canopies with complex architecture. We show that the current developments in modeling volatile isoprenoid emissions are "split-ended" with simultaneous but separated efforts in fine-tuning the empirical emission algorithms and in constructing process-based models. In modeling volatile isoprenoid emissions, simplified leaf-level emission algorithms (Guenther algorithms) are highly successful, particularly after scaling these models up to whole regions, where the influences of different ecosystem types, ontogenetic stages, and variations in environmental conditions on emission rates and dynamics partly cancel out. However, recent experimental evidence indicates important environmental effects yet unconsidered and emphasize, the importance of a highly dynamic plant acclimation in space and time. This suggests that current parameterizations are unlikely to hold in a globally changing and dynamic environment. Therefore, long-term predictions using empirical algorithms are not necessarily reliable. We show that process-based models have large potential to capture the influence of changing environmental conditions, in particular if the leaf models are linked with physiologically based whole-plant models. This combination is also promising in considering the possible feedback impacts of emissions on plant physiological status such as mitigation of thermal and oxidative stresses by volatile isoprenoids. It might be further worth while to incorporate main features of these approaches in regional empirically-based emission estimations thereby merging the "split ends". [source]

Tropical rainforest canopies and climate change

AUSTRAL ECOLOGY, Issue 1 2007
NIGEL E. STORK
Abstract There is less certainty about the impact of climate change on tropical rainforests than on temperate forests because of the comparative lack of background data and because few large scale experiments have been, and are being, carried out in tropical rainforests. Many of the factors critical to the future of tropical rainforests concern canopies, the key processes that take place there, and the roles and interactions of canopy biodiversity. In particular there are almost no data on how forest canopies and processes are changing with increased carbon dioxide levels. The implications of elevated carbon dioxide, climatic stress and related changes in water-use efficiency, nutrient availability and other such changes are discussed particularly with references to Australia's tropical rainforests. [source]

Morphological and Molecular Evidence of Arbuscular Mycorrhizal Fungal Associations in Costa Rican Epiphytic Bromeliads,

BIOTROPICA, Issue 2 2005
Annette R. Rowe
ABSTRACT Arbuscular mycorrhizal fungi influence the growth, morphology, and fitness of a variety of plant species, but little is known of the arbuscular mycorrhizal (AM) fungal associations of plant species in forest canopies. Plant species' associations with AM fungi are most often elucidated by examining the roots for fungal structures; however, morphological data may provide a limited resolution on a plant's mycorrhizal status. We combined a traditional staining technique with a molecular marker (the 18S ribosomal gene) to determine whether or not a variety of epiphytic bromeliads form arbuscular mycorrhizal fungal associations. Using these methods we show that the epiphytic bromeliad Vriesea werkleana forms arbuscular mycorrhizal fungal associations with members of the genus Glomus. AM fungal sequences of this plant species formed three distinct clades nested within a larger Glomus clade; two of the clades did not group with any previously sequenced lineage of Glomus. Novel clades may represent novel species. Although Vriesea werkleana is associated with multiple AM fungal species, each individual plant is colonized by a single lineage. The combination of morphological and molecular methods provides a practical approach to the characterization of the mycorrhizal status of epiphytic bromeliads, and perhaps other tropical epiphytes. [source]

Ground beetle responses to patch retention harvesting in high elevation forests of British Columbia

ECOGRAPHY, Issue 5 2004
Jeffrey P. Lemieux
The effect of a forest harvesting system whereby small (typically 0.1,2.0 ha) patches of standing timber are retained inside of harvests, was compared to conventional clearcutting for its effect on ground beetle assemblages. Two seasons of pitfall trapping entailed 46,451 trap days, and yielded 15,799 individuals of 28 species; abundance was dominated by four species comprising 92.4% of the catch. Most species were known to have wide geographic distributions in Canada and Alaska but many species seemed to respond to disturbance on a site-specific basis. Contrary to findings of similar studies, no species could be characterized as "mature-forest specialists", or "forest generalists". Forest patches and edge habitats immediately inside the forest canopy contained assemblages more closely related to mature forest than to cleared areas. Harvested areas with patches yielded catches distinct from typical clearcuts, based primarily on changes in abundance of one common species. Climatic regimes and landscape disturbance levels were the two important factors distinguishing our study from others, and we have suggested that these may influence the degree to which patches are an effective conservation tool. [source]

The underestimated importance of belowground carbon input for forest soil animal food webs

ECOLOGY LETTERS, Issue 8 2007
Melanie M. Pollierer
Abstract The present study investigated the relative importance of leaf and root carbon input for soil invertebrates. Experimental plots were established at the Swiss Canopy Crane (SCC) site where the forest canopy was enriched with 13C depleted CO2 at a target CO2 concentration of c. 540 p.p.m. We exchanged litter between labelled and unlabelled areas resulting in four treatments: (i) leaf litter and roots labelled, (ii) only leaf litter labelled, (iii) only roots labelled and (iv) unlabelled controls. In plots with only 13C-labelled roots most of the soil invertebrates studied were significantly depleted in 13C, e.g. earthworms, chilopods, gastropods, diplurans, collembolans, mites and isopods, indicating that these taxa predominantly obtain their carbon from belowground input. In plots with only 13C-labelled leaf litter only three taxa, including, e.g. juvenile Glomeris spp. (Diplopoda), were significantly depleted in 13C suggesting that the majority of soil invertebrates obtain its carbon from roots. This is in stark contrast to the view that decomposer food webs are based on litter input from aboveground. [source]

Environmental signals for seed germination reflect habitat adaptations in four temperate Caryophyllaceae

FUNCTIONAL ECOLOGY, Issue 3 2008
F. Vandelook
Summary 1Requirements for dormancy break and seed germination are specific for all species and depend chiefly on phylogeny, geographical distribution, habitat preference and life cycle. Studying germination requirements of closely related species with a similar geographic distribution allows one to attribute variation in germination requirements to differences in habitat preference between the species. 2We investigated requirements for dormancy break and the effect of environmental signals on induction of germination in seeds of four closely related Caryophyllaceae species growing in a variety of habitats (Moehringia trinervia, Stellaria holostea, S. nemorum and S. graminea). The species studied depend on disturbances in the vegetation for seed germination and subsequent seedling establishment. 3Seedlings of all four species emerged both in summer and spring. Stellaria nemorum and M. trinervia, both growing in temperate forests, emerged mainly in summer under a closed forest canopy. Seeds of S. graminea, occurring in grasslands, did germinate in summer at an open site, but could not germinate under a closed forest canopy. Seedlings of S. holostea were observed in late summer when buried at an open site or in early spring when sown in a forest patch. 4Seeds of S. holostea and M. trinervia were completely dormant at dispersal in early summer, while germination was low in fresh seeds of S. graminea and S. nemorum. Dormancy was broken, to a certain extent, during all three after-ripening treatments applied (dry storage, cold and warm stratification). 5The effect of three gap-detection signals (light, fluctuating temperatures, nitrates) on germination of fresh and dry stored seeds was tested. Seeds of S. holostea only germinated in response to daily fluctuating temperatures. Although light was the most important signal affecting germination of S. graminea and M. trinervia, we also observed a positive effect of fluctuating temperatures and nitrates on germination. The effect of fluctuating temperatures on germination of S. nemorum was small in both light and dark incubated seeds. Seed germination in this species generally occurred in response to addition of light and nitrates. 6This study on dormancy breaking and germination requirements of the four species enabled us to expose, sometimes subtle, differences in germination requirements. These contrasting germination patterns were related to differences in the species' habitat preferences. [source]

Detection of a low-relief 18th-century British siege trench using LiDAR vegetation penetration capabilities at Fort Beauséjour,Fort Cumberland National Historic Site, Canada

GEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 5 2009
Koreen Millard
Airborne Light Detection and Ranging (LiDAR), a remote sensing data collection technique, has many applications in the field of archaeology, including aiding in the planning of field campaigns, mapping features beneath forest canopy, and providing an overview of broad, continuous features that may be indistinguishable on the ground. LiDAR was used to create a high-resolution digital elevation model (DEM) in a heavily vegetated area at Fort Beauséjour,Fort Cumberland National Historic Site, Canada. Previously undiscovered archaeological features were mapped that were related to the siege of the fort in 1755. Features that could not be distinguished on the ground or through aerial photography were identified by overlaying hillshades of the DEM created with artificial illumination from various angles. LiDAR provides accurate digital topographic models with the additional benefit of mapping vertical surfaces in accurate detail below the forest canopy. © 2009 Wiley Periodicals, Inc. [source]

Fine root dynamics in a loblolly pine forest are influenced by free-air-CO2 -enrichment: a six-year-minirhizotron study

GLOBAL CHANGE BIOLOGY, Issue 3 2008
SETH G. PRITCHARD
Abstract Efforts to characterize carbon (C) cycling among atmosphere, forest canopy, and soil C pools are hindered by poorly quantified fine root dynamics. We characterized the influence of free-air-CO2 -enrichment (ambient +200 ppm) on fine roots for a period of 6 years (Autumn 1998 through Autumn 2004) in an 18-year-old loblolly pine (Pinus taeda) plantation near Durham, NC, USA using minirhizotrons. Root production and mortality were synchronous processes that peaked most years during spring and early summer. Seasonality of fine root production and mortality was not influenced by atmospheric CO2 availability. Averaged over all 6 years of the study, CO2 enrichment increased average fine root standing crop (+23%), annual root length production (+25%), and annual root length mortality (+36%). Larger increase in mortality compared with production with CO2 enrichment is explained by shorter average fine root lifespans in elevated plots (500 days) compared with controls (574 days). The effects of CO2 -enrichment on fine root proliferation tended to shift from shallow (0,15 cm) to deeper soil depths (15,30) with increasing duration of the study. Diameters of fine roots were initially increased by CO2 -enrichment but this effect diminished over time. Averaged over 6 years, annual fine root NPP was estimated to be 163 g dw m,2 yr,1 in CO2 -enriched plots and 130 g dw m,2 yr,1 in control plots (P= 0.13) corresponding to an average annual additional input of fine root biomass to soil of 33 g m,2 yr,1 in CO2 -enriched plots. A lack of consistent CO2× year effects suggest that the positive effects of CO2 enrichment on fine root growth persisted 6 years following minirhizotron tube installation (8 years following initiation of the CO2 fumigation). Although CO2 -enrichment contributed to extra flow of C into soil in this experiment, the magnitude of the effect was small suggesting only modest potential for fine root processes to directly contribute to soil C storage in south-eastern pine forests. [source]

Water savings in mature deciduous forest trees under elevated CO2

GLOBAL CHANGE BIOLOGY, Issue 12 2007
SEBASTIAN LEUZINGER
Abstract Stomatal conductance of plants exposed to elevated CO2 is often reduced. Whether this leads to water savings in tall forest-trees under future CO2 concentrations is largely unknown but could have significant implications for climate and hydrology. We used three different sets of measurements (sap flow, soil moisture and canopy temperature) to quantify potential water savings under elevated CO2 in a ca. 35 m tall, ca. 100 years old mixed deciduous forest. Part of the forest canopy was exposed to 540 ppm CO2 during daylight hours using free air CO2 enrichment (FACE) and the Swiss Canopy Crane (SCC). Across species and a wide range of weather conditions, sap flow was reduced by 14% in trees subjected to elevated CO2, yielding ca. 10% reduction in evapotranspiration. This signal is likely to diminish as atmospheric feedback through reduced moistening of the air comes into play at landscape scale. Vapour pressure deficit (VPD)-sap flow response curves show that the CO2 effect is greatest at low VPD, and that sap flow saturation tends to occur at lower VPD in CO2 -treated trees. Matching stomatal response data, the CO2 effect was largely produced by Carpinus and Fagus, with Quercus contributing little. In line with these findings, soil moisture at 10 cm depth decreased at a slower rate under high-CO2 trees than under control trees during rainless periods, with a reversal of this trend during prolonged drought when CO2 -treated trees take advantage from initial water savings. High-resolution thermal images taken at different heights above the forest canopy did detect reduced water loss through altered energy balance only at <5 m distance (0.44 K leaf warming of CO2 -treated Fagus trees). Short discontinuations of CO2 supply during morning hours had no measurable canopy temperature effects, most likely because the stomatal effects were small compared with the aerodynamic constraints in these dense, broad-leaved canopies. Hence, on a seasonal basis, these data suggest a <10% reduction in water consumption in this type of forest when the atmosphere reaches 540% ppm CO2. [source]

Canopy recovery after drought dieback in holm-oak Mediterranean forests of Catalonia (NE Spain)

GLOBAL CHANGE BIOLOGY, Issue 12 2004
Francisco Lloret
Abstract Climate change is likely to produce more frequent and longer droughts in the Mediterranean region, like that of 1994, which produced important changes in the Quercus ilex forests, with up to 76% of the trees showing complete canopy dieback. At the landscape level, a mosaic of responses to the drought was observed, linked to the distribution of lithological substrates. Damage to the dominant tree species (Q. ilex) and the most common understorey shrub (Erica arborea) was more noticeable on the compact substrates (breccia) than on the fissured ones (schist). This result was consistent with observations documenting deeper root penetration in schist than in breccia materials, allowing the plants growing on fissured substrates to use water from deeper soil levels. Smaller plants were more vulnerable to drought than larger plants in the trees, but not in the shrubs. Overall, Q. ilex was more affected than E. arborea. The resilience of the system was evaluated from the canopy recovery 1 year after the episode. Stump and crown resprouting was fairly extensive, but the damage pattern in relation to substrate, plant size, and species remained similar. The effect of recurrent drought episodes was studied on vegetation patches of Q. ilex located on mountain slopes and surrounded by bare rock. We observed that plants that resprouted weakly after a previous drought in 1985 were more likely to die or to produce poor regeneration in 1995 than plants that had resprouted vigorously. Vegetation patches located on the lower part of the slope were also less damaged than patches situated uphill. The study provides evidence of relevant changes in forest canopy as a consequence of extreme climate events. The distribution of this effect across the landscape is mediated by lithological substrate, causing patchy patterns. The results also support the hypothesis that recurrent droughts can produce a progressive loss of resilience, by depleting the ability of surviving plants to regenerate. [source]

A note on estimating urban roof runoff with a forest evaporation model

Simulating soil-water movement under a hedgerow surrounding a bottomland reveals the importance of transpiration in water balance

HYDROLOGICAL PROCESSES, Issue 5 2008
Z. Thomas
Abstract The objective of this study was to quantify components of the water balance related to root-water uptake in the soil below a hedgerow. At this local scale, a two-dimensional (2D) flow domain in the x,z plane 6 m long and 1·55 m deep was considered. An attempt was made to estimate transpiration using a simulation model. The SWMS-2D model was modified and used to simulate temporally and spatially heterogeneous boundary conditions. A function with a variable spatial distribution of root-water uptake was considered, and model calibration was performed by adjusting this root-water uptake distribution. Observed data from a previous field study were compared against model predictions. During the validation step, satisfactory agreement was obtained, as the difference between observed and modelled pressure head values was less than 50 cm for 80% of the study data. Hedge transpiration capacity is a significant component of soil-water balance in the summer, when predicted transpiration reaches about 5·6 mm day,1. One of the most important findings is that hedge transpiration is nearly twice that of a forest canopy. In addition, soil-water content is significantly different whether downslope or upslope depending on the root-water uptake. The high transpiration rate was mainly due to the presence of a shallow water table below the hedgerow trees. Soil-water content was not a limiting factor for transpiration in this context, as it could be in one with a much deeper water table. Hedgerow tree transpiration exerts a strong impact not only on water content within the vadose zone but also on the water-table profile along the transect. Results obtained at the local scale reveal that the global impact of hedges at the catchment scale has been underestimated in the past. Transpiration rate exerts a major influence on water balance at both the seasonal and annual scales for watersheds with a dense network of hedgerows. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Estimating fog deposition at a Puerto Rican elfin cloud forest site: comparison of the water budget and eddy covariance methods

HYDROLOGICAL PROCESSES, Issue 13 2006
F. Holwerda
Abstract The deposition of fog to a wind-exposed 3 m tall Puerto Rican cloud forest at 1010 m elevation was studied using the water budget and eddy covariance methods. Fog deposition was calculated from the water budget as throughfall plus stemflow plus interception loss minus rainfall corrected for wind-induced loss and effect of slope. The eddy covariance method was used to calculate the turbulent liquid cloud water flux from instantaneous turbulent deviations of the surface-normal wind component and cloud liquid water content as measured at 4 m above the forest canopy. Fog deposition rates according to the water budget under rain-free conditions (0·11 ± 0·05 mm h,1) and rainy conditions (0·24 ± 0·13 mm h,1) were about three to six times the eddy-covariance-based estimate (0·04 ± 0·002 mm h,1). Under rain-free conditions, water-budget-based fog deposition rates were positively correlated with horizontal fluxes of liquid cloud water (as calculated from wind speed and liquid water content data). Under rainy conditions, the correlation became very poor, presumably because of errors in the corrected rainfall amounts and very high spatial variability in throughfall. It was demonstrated that the turbulent liquid cloud water fluxes as measured at 4 m above the forest could be only ,40% of the fluxes at the canopy level itself due to condensation of moisture in air moving upslope. Other factors, which may have contributed to the discrepancy in results obtained with the two methods, were related to effects of footprint mismatch and methodological problems with rainfall measurements under the prevailing windy conditions. Best estimates of annual fog deposition amounted to ,770 mm year,1 for the summit cloud forest just below the ridge top (according to the water budget method) and ,785 mm year,1 for the cloud forest on the lower windward slope (using the eddy-covariance-based deposition rate corrected for estimated vertical flux divergence). Copyright © 2006 John Wiley & Sons, Ltd. [source]

Anthropogenic disturbance and the formation of oak savanna in central Kentucky, USA

JOURNAL OF BIOGEOGRAPHY, Issue 5 2008
Ryan W. McEwan
Abstract Aim, To deepen understanding of the factors that influenced the formation of oak savanna in central Kentucky, USA. Particular attention was focused on the link between historical disturbance and the formation of savanna ecosystem structure. Location, Central Kentucky, USA. Methods, We used dendrochronological analysis of tree-ring samples to understand the historical growth environment of remnant savanna stems. We used release detection and branch-establishment dates to evaluate changes in tree growth and the establishment of savanna physiognomy. We contrasted our growth chronology with reference chronologies for regional tree growth, climate and human population dynamics. Results, Trees growing in Kentucky Inner Bluegrass Region (IBR) savanna remnants exhibited a period of suppression, extending from the establishment date of the tree to release events that occurred c. 1800. This release resulted in a tripling of the annual radial growth rate from levels typical of oaks suppressed under a forest canopy (< 1 mm year,1) to levels typical of open-grown stems (3 mm year,1). The growth releases in savanna trees coincided with low branch establishment. Over the release period, climatic conditions remained relatively constant and growth in regional forest trees was even; however, the growth increase in savanna stems was strongly correlated with a marked increase in Euro-American population density in the region. Main conclusions, Our data suggest that trees growing in savanna remnants originated in the understorey of a closed canopy forest. We hypothesize that Euro-American land clearing to create pasturelands released these trees from light competition and resulted in the savanna physiognomy that is apparent in remnant stands in the IBR. Although our data suggest that savanna trees originated in a forest understorey, this system structure itself may have been a result of an unprecedented lack of Native American activity in the region due to population loss associated with pandemics brought to North America by Euro-Americans. We present a hypothetical model that links human population dynamics, land-use activities and ecosystem structure. Our model focuses on the following three land-use eras: Native American habitation/utilization; land abandonment; and Euro-American land clearance. Ecological understanding of historical dynamics in other ecosystems of eastern North America may be enhanced through recognition of these eras. [source]

The ecological impacts of a migratory bat aggregation on its seasonal roost in Kasanka National Park, Zambia

AFRICAN JOURNAL OF ECOLOGY, Issue 1 2010
James W. Byng
Abstract The ecological impacts of migratory species on their seasonal environments are poorly known. The effects of several million straw-coloured fruit bats (Eidolon helvum), which migrate seasonally to Kasanka National Park, Zambia each year, on the small area of mushitu,swamp' forest in which they roost, were investigated. The structure of the mushitu forest was profoundly altered by the presence of E. helvum, with increased roost tree mortality, lowering and opening of the forest canopy and a decrease in tree basal area. Eidolon helvum are also thought to increase the severity of fires within their roost site because the structural changes result in a drier microclimate. The effects of increased nitrogen and phosphorous input were less apparent. These findings suggest that the ecological impact of this migratory bat species on its seasonal environment could ultimately threaten the long-term viability of its seasonal roost. Résumé Les impacts écologiques des espèces migratrices sur leurs environnements saisonniers sont peu connus. Les effets de plusieurs millions de roussettes paillées africaines Eidolon helvum qui, chaque année, migrent de façon saisonnière vers le Parc National de Kasanka, en Zambie, furent étudiés dans la petite zone de forêt marécageuse àmushitu où elles se perchent. La structure de la forêt àmushituétait profondément modifiée par la présence d'E. helvum, qui augmentait la mortalité des arbres servant de perchoirs, qui faisait baisser la hauteur et la densité de la canopée et entraînait une diminution de la surface basale des arbres. On pense aussi que la présence d'E. helvum augmente la gravité des feux dans les sites de repos parce que les changements structurels aboutissent à un microclimat plus sec. Les effets de l'apport accru en azote et en phosphore étaient moins apparents. Ces découvertes suggèrent que l'impact écologique de cette espèce de chauve-souris migratrice sur son environnement saisonnier pourrait, à long terme, menacer la viabilité de ses lieux de repos saisonniers. [source]

Abiotic and biotic drivers of seedling survival in a hurricane-impacted tropical forest

JOURNAL OF ECOLOGY, Issue 6 2009
Liza S. Comita
Summary 1. ,Many forests experience periodic, large-scale disturbances, such as hurricanes and cyclones, which open the forest canopy, causing dramatic changes in understorey light conditions and seedling densities. Thus, in hurricane-impacted forests, large variations in abiotic and biotic conditions likely shape seedling dynamics, which in turn will contribute to patterns of forest recovery. 2. ,We monitored 13 836 seedlings of 82 tree and shrub species over 10 years following Hurricane Georges in 1998 in a subtropical, montane forest in Puerto Rico. We quantified changes in the biotic and abiotic environment of the understorey and linked seedling dynamics to changes in canopy openness and seedling density, and to spatial variation in soil type, topography and tree density. 3. ,Canopy openness was highest when first measured after Hurricane Georges and dropped significantly within c. 3 years, while seedling densities remained high for c. 5 years post-hurricane. When all species and census intervals were analysed together, generalized linear mixed effects models revealed that canopy openness, seedling and adult tree densities were significant drivers of seedling survival. 4. ,The relative importance of abiotic and biotic factors changed over time. Separate analyses for each census interval revealed that canopy openness was a significant predictor of survival only for the first census interval, with lower survival at the highest levels of canopy openness. The effect of conspecific seedling density was significant in all intervals except the first, and soil type only in the final census interval. 5. ,When grouping species into life-history guilds based on adult tree susceptibility to hurricane damage, we found clear differences among guilds in the effects of biotic and abiotic factors on seedling survival. Seedlings of hurricane-susceptible and intermediate guilds were more strongly influenced by canopy openness, while seedlings of the hurricane-resistant group were less affected by conspecific seedling density. Individual species-level analyses for 12 common species, however, showed considerable variation among species within guilds. 6. ,Synthesis. Our results suggest that hurricanes shape species composition by altering understorey conditions that differentially influence the success of seedlings. Thus, predicted increases in the intensity and frequency of hurricanes in the Caribbean will likely alter seedling dynamics and ultimately the species composition in hurricane-impacted forests. [source]

Occurrence and effects of Nosema fumiferanae infections on adult spruce budworm caught above and within the forest canopy

AGRICULTURAL AND FOREST ENTOMOLOGY, Issue 4 2007
Eldon S. Eveleigh
Abstract 1,Nosema fumiferanae infections in populations of both sexes of spruce budworm Choristoneura fumiferana moths, collected live above the forest canopy (canopy moths), within the tree crown (crown moths) and in drop trays (dead moths), were examined over a 5-year period in New Brunswick, Canada. 2,The incidence of infection and of moderate,heavy infections in canopy and crown moths of both sexes increased concomitantly with moth eclosion, indicating that N. fumiferanae retards larval/pupal development, with infected moths, particularly those having higher disease loads, emerging later in the season. 3,Infection rates differed among canopy, crown, and dead female, but not male, moths. Canopy (i.e. emigrating) females had a lower incidence of infection, lower incidence of moderate,heavy infections, and had longer forewings and higher dry weights, than crown females. These results suggest that N. fumiferanae infections negatively affect aspects of female, but not male, flight performance. Regardless of infection, forewing length and dry weight of both canopy and crown females declined over the moth flight period, but infected females in both moth types were smaller than their uninfected counterparts. Forewing lengths and dry weights of moderately,heavily infected females were most severely affected. 4,Despite high annual infection rates in parents, only a small percentage of offspring (second-instar larvae) that established feeding sites each spring were infected, indicating that high rates of horizontal transmission occurred annually throughout the larval period. 5,The present study indicates that whether N. fumiferanae infections are a debilitating sublethal factor in spruce budworm populations depends more on the disease load than on the overall incidence of infection. The potential importance of N. fumiferanae infections on various fitness parameters related to host dispersal is discussed. [source]

Population status and behaviours of the Samoan flying fox (Pteropus samoensis) on Tutuila Island, American Samoa

JOURNAL OF ZOOLOGY, Issue 3 2001
Anne P. Brooke
Abstract The small population and limited range of the Samoan flying fox Pteropus samoensis has generated concern regarding the survival of this large, diurnally active bat. During 1995,96, surveys were conducted monthly in six study valleys on Tutuila Island, American Samoa, to assess population size. The amount of diurnal and nocturnal activity was investigated to gauge the accuracy of diurnal surveys, and territorial behaviours were observed to determine how they influenced local dispersion. Individuals showed long-term fidelity to a series of roosts and small core areas that were used both nocturnally and diurnally. Territorial defence was observed only of temporary feeding territories in fruiting or flowering trees. Bats defended food resources by aerial patrols and extended aerial chases in which intruders were frequently bitten. Foraging movements changed seasonally, with up to 80% of individuals observed bypassing study valleys. The mean density of bats observed within the study valleys was 6.1 bats/km2 (range = 0.9,18.5 bats/km2). Pteropus samoensis were active both nocturnally and diurnally with greatest activity in late afternoon and evening, 16:00,22:00. Because bats were most active at night, it is probable that daytime surveys of flying bats undercount the number of individuals present. Greatest densities were found in valleys that were contiguous with large tracts of forest inaccessible to people. Most observations of roosting bats were of solitary males on dead branches that jutted above the forest canopy, while females and dependant young roosted below the canopy, hidden within vegetation. Adult male,female pairs were rarely seen together other than during the mating period in August,January. The population has increased following a ban on hunting, but reliance on mature forest makes long-term species survival dependant on protection of the limited mature forest remaining and continued hunting restrictions. [source]

Predicting invertebrate diversity from disturbance regimes in forest streams

OIKOS, Issue 1 2002
Russell G. Death
The link between substrate disturbance and stream invertebrate species richness is often complicated by the fact that substrate disturbance removes both invertebrates and periphyton (a potential food source). It is never clear whether disturbance acts directly on species diversity by removing animals or indirectly by reducing one of their food sources. To examine this relationship invertebrate diversity patterns were examined in 25 forest streams in Urewera National Park, New Zealand, where light attenuation from the forest canopy was postulated to limit periphyton biomass and remove the confounding influence of periphyton on the link between substrate disturbance and invertebrate diversity. Invertebrate species richness declined linearly with increasing substrate disturbance. Although periphyton biomass was comparatively low, species richness was more strongly related to periphyton biomass than to any disturbance measure. The highly mobile nature and terrestrial reproductive stage of many lotic invertebrates suggest that colonisation dynamics may have a more important influence on diversity patterns than monopolisation of resources for population growth. Although both the intermediate disturbance hypothesis and the dynamic equilibrium model encompass colonisation as a critical determinant of diversity both models also require a trade-off between the colonising and competitive ability of individual species; a phenomenon which does not appear to occur widely in lotic communities. Rather, it is postulated that resource levels will set an upper limit to the species richness of a benthic community that can be achieved through colonisation of taxa in the absence of disturbance, while disturbance removes taxa and resets the colonisation process. [source]

A new paradigm in leaf-level photosynthesis: direct and diffuse lights are not equal

PLANT CELL & ENVIRONMENT, Issue 1 2008
CRAIG R. BRODERSEN
ABSTRACT Global-change scenarios suggest a trend of increasing diffuse light due to expected increases in cloud cover. Canopy-level measurements of plant-community photosynthesis under diffuse light show increased productivity attributed to more uniform distribution of light within the forest canopy, yet the effect of the directional quality of light at the leaf level is unknown. Here we show that leaf-level photosynthesis in sun leaves of both C3 and C4 plants can be 10,15% higher under direct light compared to equivalent absorbed irradiances of diffuse light. High-light-grown leaves showed significant photosynthetic enhancement in direct light, while shade-adapted leaves showed no preference for direct or diffuse light at any irradiance. High-light-grown leaves with multiple palisade layers may be adapted to better utilize direct than diffuse light, while shade leaf structure does not appear to discriminate light based on its directionality. Based upon our measurements, it appears that leaf-level and canopy-level photosynthetic processes react differently to the directionality of light, and previously observed increases in canopy-level photosynthesis occur even though leaf-level photosynthesis decreases under diffuse light. [source]

Natural 15N abundance of epiphytes depends on the position within the forest canopy: source signals and isotope fractionation

PLANT CELL & ENVIRONMENT, Issue 4 2002
R. Wania
Abstract The natural 15N abundance (,15N) of epiphytes and its N sources were studied in the canopy of a lowland rainforest in Costa Rica. Vascular and non-vascular epiphytes and canopy soils were collected from four canopy zones and analysed for N contents and ,15N signals. In addition, the N concentrations and ,15N signatures of bulk precipitation, throughfall and stemflow were measured during the wet and the dry season. The ,15N values of epiphyte leaves decreased significantly from the lower zones (means of ,3·9 and ,4·3,) to the upper zones (means of ,5·4 and ,6·1,) of the canopy. In contrast, ,15N signatures of canopy soils (average ,0·3,) differed little between the zones. Bulk deposition was enriched in 15N (+4·3,) compared to all other potential N sources and was higher than throughfall and stemflow (+0·5 to ,1·3,). ,15N values of atmospheric deposition were inversely related to those of the epiphyte leaves, whereas N isotopic composition of canopy soils did not vary significantly. Consequently, it is concluded that the variations in foliar N isotope composition of epiphytes were not simply caused by utilization of isotopically different N sources, but by different 15N discrimination during N acquisition. [source]

Photosynthesis, light and nitrogen relationships in a young deciduous forest canopy under open-air CO2 enrichment

PLANT CELL & ENVIRONMENT, Issue 12 2001
Y. Takeuchi
Abstract Leaf photosynthesis (Ps), nitrogen (N) and light environment were measured on Populus tremuloides trees in a developing canopy under free-air CO2 enrichment in Wisconsin, USA. After 2 years of growth, the trees averaged 1·5 and 1·6 m tall under ambient and elevated CO2, respectively, at the beginning of the study period in 1999. They grew to 2·6 and 2·9 m, respectively, by the end of the 1999 growing season. Daily integrated photon flux from cloud-free days (PPFDday,sat) around the lowermost branches was 16·8 ± 0·8 and 8·7 ± 0·2% of values at the top for the ambient and elevated CO2 canopies, respectively. Elevated CO2 significantly decreased leaf N on a mass, but not on an area, basis. N per unit leaf area was related linearly to PPFDday,sat throughout the canopies, and elevated CO2 did not affect that relationship. Leaf Ps light-response curves responded differently to elevated CO2, depending upon canopy position. Elevated CO2 increased Pssat only in the upper (unshaded) canopy, whereas characteristics that would favour photosynthesis in shade were unaffected by elevated CO2. Consequently, estimated daily integrated Ps on cloud-free days (Psday,sat) was stimulated by elevated CO2 only in the upper canopy. Psday,sat of the lowermost branches was actually lower with elevated CO2 because of the darker light environment. The lack of CO2 stimulation at the mid- and lower canopy was probably related to significant down-regulation of photosynthetic capacity; there was no down-regulation of Ps in the upper canopy. The relationship between Psday,sat and leaf N indicated that N was not optimally allocated within the canopy in a manner that would maximize whole-canopy Ps or photosynthetic N use efficiency. Elevated CO2 had no effect on the optimization of canopy N allocation. [source]

Benefits of polyspecific associations for the Goeldi's monkey (Callimico goeldii)

AMERICAN JOURNAL OF PRIMATOLOGY, Issue 3 2001
Leila M. Porter
Abstract Polyspecific associations are an important component of Callimico goeldii behavior and ecology. On average, Callimico goeldii was found in proximity to or in vocal contact with Saguinus troops (S. fuscicollis and S. labiatus) during 53% of all time intervals sampled. Polyspecific associations varied considerably between seasons, however, with association rates peaking during the wet-season month of February (89%) and declining in the dry season, with the lowest rate (13%) in July. The primary benefits of associations appear to be an increased use of the lower and middle canopy, and an increase in feeding behaviors during the wet season. Thus, Callimico goeldii appear to benefit most from associations during the wet season when fruits are its principal food source. Fruits are eaten more in the forest canopy than in the understory; thus, an increase in height use likely permits an increase in the fruit resources on which Callimico goeldii can forage and feed. In addition, Saguinus groups, with their smaller home ranges, are likely to be more knowledgeable than Callimico goeldii about the location and abundance of ripe fruits in their home ranges. Thus, Callimico goeldii may parasitize Saguinus for their fruit knowledge by following them through their ranges. In the dry season, limited dietary overlap between Callimico goeldii and Saguinus groups is likely to make associations less beneficial for Callimico goeldii as they adopt different foraging and ranging strategies. Am. J. Primatol. 54:143,158, 2001. © 2001 Wiley-Liss, Inc. [source]

Oxidized nitrogen and ozone interaction with forests.

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 600 2004
I: Experimental observations, analysis of exchange with Douglas fir
Abstract Measurements of NOx and O3 exchange to and from a forest canopy are described with reference to canopy and ecosystem processes leading to emission of NO2. The soil below the forested measurement location is shown to be a net source of reactive oxidized nitrogen (as NO). It is shown that a large fraction (around 58% on average) of the emitted NO escapes out of the trunk space to react within and above the canopy. Fluxes of NO2 above the canopy are bi-directional, with large fluxes and most emission events taking place during the day. Deposition is shown to take place without significant changes in the vertical flux; however there appears to be rapid chemical reaction leading to significant flux divergence taking place during emission events. Above the top of the canopy (22 m), changes of 200% in the NO2 flux between 25 and 35 m are not uncommon. Ozone deposition to the forest system has been investigated. The flux is often related to stomatal deposition, but there are periods when large non-stomatal fluxes are observed. At night there is a large vertical divergence in the ozone flux above the canopy, probably related to reaction with NO from the forest soil. The reaction of O3 with volatile organic compounds is found, in general, to be negligible with respect to ozone concentrations and fluxes. Ozone is found to deposit mainly to leaf stomata during the day, with a small but not insignificant contribution from NO reaction. However, the nocturnal ozone budget for the forest changes significantly, with most of the measured deposition accounted for by soil uptake and reaction with NO. The resultant problems related to inadequate treatment of air chemistry when interpreting O3 fluxes in high NO emission environments are identified. Copyright © 2004 Royal Meteorological Society. [source]

Resilience of arboreal folivores to habitat damage by a severe tropical cyclone

AUSTRAL ECOLOGY, Issue 4 2008
ROBYN F. WILSON
Abstract Severe tropical cyclones greatly modify habitat of arboreal folivores by destroying forest canopy, reducing structure and complexity and defoliating remaining trees. We hypothesized that forest modification following severe Cyclone Larry would stress arboreal folivores of the Family Pseudocheiridae and be reflected in increased home ranges and a decrease in body condition. We conducted 19 pre-cyclone and 24 post-cyclone spotlighting surveys at a site with severe cyclone damage, and 18 post-cyclone surveys at a site with minor damage. We detected a greater number of lemuroid, Hemibelideus lemuroides and green, Pseudochirops archeri, ringtail possums as these possums remained in the severely damaged canopy and forest edge. In contrast, Herbert River ringtail possums, Pseudochirulus herbertensis, were detected in smaller numbers. We radio-tracked eight P. herbertensis before the cyclone, following two of these and nine new animals after the category 4 cyclone. No significant post-cyclone alteration in home range area or span was recorded in data pooled across the two sites or in limited post-cyclone data at the severely disturbed site, but a greater variability in home range was observed after cyclone (pooled across sites: 1.72 ± 0.77 ha; 197 ± 47 m) than before the cyclone (1.35 ± 0.30 ha; 196 ± 23 m). In contrast, pooled pre- and post-cyclone home range areas and spans were larger at the severely-disturbed site (2.08 ± 0.56 ha; 231 ± 32 m) than at the site with minor damage (0.68 ± 0.11 ha; 114 ± 25 m), suggesting resources were more widely spread at the former site. Post-cyclone home ranges were also larger at the severely damaged site (severe: 3.33 ± 1.36 ha, n = 3; minor: 0.52 ± 0.07 ha, n = 4). Condition of P. herbertensis (mass/tail length) did not differ significantly pre- and post-cyclone or between less and severely disturbed sites. These results and observations of breeding after cyclone suggest that possum populations may be resilient to severe cyclone damage under the relatively wet conditions experienced post-Cyclone Larry. [source]

Factors Affecting the Distribution and Abundance of Asplenium nidus L. in a Tropical Lowland Rain Forest in Peninsular Malaysia

BIOTROPICA, Issue 4 2010
Liwen Zhang
ABSTRACT Asplenium nidus is an abundant epiphytic fern of tropical rain forests in the Old World, where it plays an important ecological role in the forest canopy as host to diverse arthropod communities. We investigated the factors that determine the distribution and abundance of A. nidus in the canopy of an aseasonal lowland dipterocarp forest at Pasoh Forest Reserve, Malaysia. We found that A. nidus was more abundant in the understory, and on hosts with smooth bark and relatively flat branch angles. Ferns were found on a wide diversity and size range of host taxa. However, both host taxa and host diameter at breast height had a significant effect on A. nidus occupancy. Asplenium nidus had an aggregated spatial distribution at all scales within the study area. Spatial aggregation at larger scales appears to be driven by habitat preference, as A. nidus abundance was positively associated with swampy areas and negatively associated with hilly areas. At smaller scales, limited dispersal of their wind-dispersed spores most likely explains the aggregated distribution. Larger individuals occurred higher in the canopy and were more common in the hilly area. Thus, the distribution of A. nidus may represent a trade-off between the availability of suitable microsites for establishment in the understory and better growth conditions higher in the canopy. However, A. nidus is known to comprise a complex of cryptic species, and future studies should incorporate molecular techniques to elucidate the potential role of speciation in explaining these patterns. Abstract in Malaysian is available at http://www.blackwell-synergy.com/loi/btp [source]