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Litter Accumulation (litter + accumulation)
Selected AbstractsAssessing the effects of post-pine beetle forest litter on snow albedoHYDROLOGICAL PROCESSES, Issue 6 2010Rita Winkler Abstract The effect of forest litter on snow surface albedo has been subject to limited study, mainly in the hardwood-dominated forests of the northeastern United States. Given the recent pine beetle infestation in Western North America and associated increases in litter production, this study examines the effects of forest litter on snow surface albedo in the coniferous forests of south-central British Columbia. Measured changes in canopy transmittance provide an indication of canopy loss or total litterfall over the winter of 2007,2008. Relationships between percent litter cover, an index of albedo, snow depth, and snow ablation during the 2008 melt season are compared between a mature, young, and clearcut coniferous stand. Results indicate a strong feedback effect between canopy loss and subsequent enhanced shortwave transmittance, and litter accumulation on the snow surface from that canopy loss. However, this relationship is confounded by other variables concurrently affecting albedo. While results suggest that a relatively small percent litter cover can have a significant effect on albedo and ablation, further research is underway to extract the litter signal from that of other factors affecting albedo, particularly snow depth. Copyright © 2010 John Wiley & Sons, Ltd. [source] Californian mixed-conifer forests under unmanaged fire regimes in the Sierra San Pedro Mártir, Baja California, MexicoJOURNAL OF BIOGEOGRAPHY, Issue 1 2000R. A. Minnich Abstract Aim,This study appraises historical fire regimes for Californian mixed-conifer forests of the Sierra San Pedro Mártir (SSPM). The SSPM represents the last remaining mixed-conifer forest along the Pacific coast still subject to uncontrolled, periodic ground fire. Location,The SSPM is a north,south trending fault bound range, centred on 31°N latitude, 100 km SE of Ensenada, Baja California. Methods,We surveyed forests for composition, population structure, and historical dynamics both spatially and temporally over the past 65 years using repeat aerial photographs and ground sampling. Fire perimeter history was reconstructed based on time-series aerial photographs dating from 1942 to 1991 and interpretable back to 1925. A total of 256 1-ha sites randomly selected from aerial photographs were examined along a chronosequence for density and cover of canopy trees, density of snags and downed logs, and cover of non-conifer trees and shrubs. Twenty-four stands were sampled on-the-ground by a point-centred quarter method which yielded data on tree density, basal area, frequency, importance value, and shrub and herb cover. Results,Forests experience moderately intense understory fires that range in size to 6400 ha, as well as numerous smaller, low intensity burns with low cumulative spatial extent. SSPM forests average 25,45% cover and 65,145 trees per ha. Sapling densities were two to three times that of overstory trees. Size-age distributions of trees , 4 cm dbh indicate multi-age stands with steady-state dynamics. Stands are similar to Californian mixed conifer forests prior to the imposition of fire suppression policy. Livestock grazing does not appear to be suppressing conifer regeneration. Main conclusions,Our spatially-based reconstruction shows the open forest structure in SSPM to be a product of infrequent, intense surface fires with fire rotation periods of 52 years, rather than frequent, low intensity fires at intervals of 4,20 years proposed from California fire-scar dendrochronology (FSD) studies. Ground fires in SSPM were intense enough to kill pole-size trees and a significant number of overstory trees. We attribute long fire intervals to the gradual build-up of subcontinuous shrub cover, conifer recruitment and litter accumulation. Differences from photo interpretation and FSD estimates are due to assumptions made with respect to site-based (point) sampling of fire, and nonfractal fire intensities along fire size frequency distributions. Fire return intervals determined by FSD give undue importance to local burns which collectively use up little fuel, cover little area, and have little demographic impact on forests. [source] Demographic variation and population viability in Gentianella campestris: effects of grassland management and environmental stochasticityJOURNAL OF ECOLOGY, Issue 3 2001Tommy Lennartsson Summary 1,Transition matrix models were used to evaluate the effects of environmental stochasticity and four different methods of grassland management on dynamics and viability of a population of the biennial Gentianella campestris (Gentianaceae) in species-rich grassland. Data were collected between 1990 and 1995. 2,Continuous summer grazing, the prevailing management strategy in Scandinavian grasslands, resulted in high recruitment of new plants, mainly because litter accumulation was prevented and gaps were created by trampling. Trampling and repeated grazing, however, caused damage which reduced seed production. Lambda for the average matrix was c. 0.77, and a stochastic matrix model yielded an extinction probability for the total population of c. 0.08 within 50 years. 3,Mowing in mid-July (used as a conservation tool) increased seed production, but litter accumulation following re-growth of the vegetation prevented establishment. Lambda and extinction risk were similar to continuous grazing. 4,Mowing in October (another conservation tool) promoted recruitment because of low litter accumulation, but the seed output decreased because plant growth was impaired by tall vegetation. Lambda was 0.64, while the extinction probability was very high (c. 0.98 within 50 years). 5,Mid-July mowing followed by autumn grazing (the historical management regime) yielded high values for both seed production and establishment of rosettes. Lambda was 0.94 and the probability of extinction within 50 years was below detection level. 6,Log-linear analysis showed that the matrices differed significantly both between treatments and between years. The latter indicates environmental stochasticity, here caused by summer drought that increased the extinction risk. Lambda may be slightly underestimated because drought occurred in one out of five summers during the study period, which is high compared with the natural frequency. 7,We conclude that traditional grassland management is more favourable for G. campestris than the methods that prevail in Scandinavia today. This indicates a serious conservation problem, because grazing has replaced traditional management in many of the remaining semi-natural grasslands throughout Europe. [source] Shrubs as ecosystem engineers in a coastal dune: influences on plant populations, communities and ecosystemsJOURNAL OF VEGETATION SCIENCE, Issue 5 2010J. Hall Cushman Abstract Question: How do two shrubs with contrasting life-history characteristics influence abundance of dominant plant taxa, species richness and aboveground biomass of grasses and forbs, litter accumulation, nitrogen pools and mineralization rates? How are these shrubs , and thus their effects on populations, communities and ecosystems , distributed spatially across the landscape? Location: Coastal hind-dune system, Bodega Head, northern California. Methods: In each of 4 years, we compared vegetation, leaf litter and soil nitrogen under canopies of two native shrubs ,Ericameria ericoides and the nitrogen-fixing Lupinus chamissonis, with those in adjacent open dunes. Results: At the population level, density and cover of the native forb Claytonia perfoliata and the exotic grass Bromus diandrus were higher under shrubs than in shrub-free areas, whereas they were lower under shrubs for the exotic grass Vulpia bromoides. In contrast, cover of three native moss species was highest under Ericameria and equally low under Lupinus and shrub-free areas. At community level, species richness and aboveground biomass of herbaceous dicots was lower beneath shrubs, whereas no pattern emerged for grasses. At ecosystem level, areas beneath shrubs accumulated more leaf litter and had larger pools of soil ammonium and nitrate. Rates of nitrate mineralization were higher under Lupinus, followed by Ericameria and then open dune. At landscape level, the two shrubs , and their distinctive vegetation and soils , frequently had uniform spatial distributions, and the distance separating neighbouring shrubs increased as their combined sizes increased. Conclusions: Collectively, these data suggest that both shrubs serve as ecosystem engineers in this coastal dune, having influences at multiple levels of biological organization. Our data also suggest that intraspecific competition influenced the spatial distributions of these shrubs and thus altered the distribution of their effects throughout the landscape. [source] Strategic light manipulation as a restoration strategy to reduce alien grasses and encourage native regeneration in Hawaiian mesic forestsAPPLIED VEGETATION SCIENCE, Issue 3 2010S. McDaniel Abstract Question: Is there a light level at which alien grass biomass is reduced while still supporting growth and survival of native woody species, allowing for native species regeneration in abandoned pastures? Location: Island of Hawaii, USA. Methods: In a two-part study we examined the effect of light availability on common native woody and alien grass species found in secondary forests in Hawaii. A field survey was conducted to examine the relationship between light availability and canopy type (open pasture, planted canopy and secondary forest) on understory grass biomass and litter accumulation. We then experimentally manipulated light levels to determine the effect of light availability on growth and survival of six native woody species and three alien grasses. Low-light (5%), medium-light (10%) and high-light (20-30%) treatments were created using shade structures erected beneath the existing secondary koa canopy. Results: In the field survey, alien grass biomass was greatest under the open pasture and lowest in the secondary forest. There was a positive correlation between understory light availability and alien grass biomass. In the experimental study, large reductions in relative growth rates were documented for all of the grass species and four of the six woody species under the lowest light level. Although growth at 5% light is substantially reduced, survival is still high (84-100%), indicating that these species may persist under closed canopy. Conclusion: Low-light conditions result in the greatest reduction in alien grass biomass while creating an environment in which native woody species can grow and survive. [source] Changes in forest understory associated with Juniperus encroachment in Oklahoma, USAAPPLIED VEGETATION SCIENCE, Issue 3 2010Paul Van Els Abstract Question: Does understory vegetation cover and richness decline along a gradient of increasing Juniperus virginiana midstory canopy cover and is that decline best correlated with litter accumulation? Location: Cross Timbers Forest in Payne County, OK, USA. Methods: We measured vegetation in forest gaps as well as forest areas without J. virginiana, at the inner and outer edge of J. virginiana canopies and near J. virginiana trunks (200 plots) and compared vegetation differences among location to light, litter, soil and microclimate variables. Results: Species richness (11 spp m,2 to 6 spp m,2) and summer vegetation cover (53.3% to 12.7%) declined with proximity to trunks. Regression indicated that richness declines (R2=0.08) and cover (R2=0.18) were best correlated with J. virginiana litter accumulation. Partial canonical correspondence analysis (pCCA) revealed two strong canonical axes, one related to litter/light and another to cover of Quercus spp. versus J. virginiana. Tree seedlings and woody vines dominated near J. virginiana. Forbs, graminoids and Quercus spp. seedlings were more common in areas without J. virginiana. Conclusions: Increasing J. virginiana and consequent litter additions alter understory biomass and composition and, through inhibiting Quercus spp. recruitment, may lead to changes in overstory composition. Decreases in herbaceous litter, which historically contributed to fuel accumulation, may have positive feedback effects on midstory encroachment by reducing the potential for prescribed burning. 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