Climate and fire drivers of forest composition and openness in the Changbai Mountains since the Late Glacial

Ongoing climate changes have a direct impact on forest growth;they also affect natural fire regimes,with further implications for forest composition.Understanding of how these will affect forests on decadal-to-centennial timescales is limited.Here we use reconstructions of past vegetation,fire regimes and climate during the Holocene to examine the relative importance of changes in climate and fire regimes for the abundance of key tree species in northeastern China.We reconstructed vegetation changes and fire regimes based on pollen and charcoal records from Gushantun peatland.We then used generalized linear modelling to investigate the impact of reconstructed changes in summer temperature,annual precipitation,background levels of fire,fire frequency and fire magnitude to identify the drivers of decadal-to-centennial changes in forest openness and composition.Changes in climate and fire regimes have independent impacts on the abundance of the key tree taxa.Climate variables are generally more important than fire variables in determining the abundance of individual taxa.Precipitation is the only determinant of forest openness,but summer temperature is more important than precipitation for individual tree taxa with warmer summers causing a decrease in cold-tolerant conifers and an increase in warmth-demanding broadleaved trees.Both background level and fire frequency have negative relationships with the abundance of most tree taxa;only Pinus increases as fire frequency increases.The magnitude of individual fires does not have a significant impact on species abundance on this timescale.Both climate and fire regime characteristics must be considered to understand changes in forest composition on the decadal-to-centennial timescale.There are differences,both in sign and magnitude,in the response of individual tree species to individual drivers.

Recovery Status and Livestock Use of a Kenyan Montane Forest a Decade after Cessation of Human Encroachment

Montane forest ecosystems support biodiversity and provide varied ecosystem services to adjacent and downstream human communities. However, human-induced disturbances are common in many of these ecosystems, threatening their capacity to sustain their functions. This study assessed the status of woody vegetation and livestock use of a Kenyan montane forest 10 years after government-sanctioned cessation of human encroachment. The findings can inform suitable interventions that support recovery of abandoned forest settlements subjected to continuous anthropogenic disturbances. Selected woody vegetation attributes and livestock disturbance indicators were assessed across three human-driven disturbance regimes (light, moderate and heavy) using stratified-systematic sampling technique. Data on the extent of community dependence on forest grazing were collected from 381 randomly selected forest adjacent households using semi-structured questionnaires. Information on the palatability of plants to livestock was obtained from Focus Group Discussions. Vegetation data were analyzed using linear mixed models, while descriptive analysis was applied on household survey data. A total of 33 woody plant species belonging to 22 families were identified, out of which 55% were perceived to be unpalatable to livestock. Species richness, species diversity, stem density and basal areas declined significantly with increasing levels of disturbance. Specifically, these attributes were 59% - 98% lower in heavily disturbed sites than in moderately and lightly disturbed sites. A vast majority (88%) of the sampled households grazed their livestock in the forest throughout the year. Evidence from this study indicates that intense past and ongoing anthropogenic disturbances caused significant negative effects on the forest vegetation condition, and lowered its capacity to recover. Forest managers should prioritize minimizing recurrent anthropogenic disturbances as the forest recovers to ensure successful succession and sustainable provision of ecosystem services.

Forest structure and anthropogenic pressures in the Pachmarhi biosphere reserve of India

A critical first step in establishing biosphere reserves--under the Man and Biosphere Programme of UNESCO--is to generate baseline information for future courses of action. The present study aims to assess the structure and composition of forests--along with anthro- pogenic pressures mounting on these forests in the buffer zone of one such biosphere reserves--the Pachmarhi bio- sphere reserve of India. The quadrat method was employed for sampling vegetation, and information on anthropogenic pressures was collected by conducting interviews with local people and forest officials and collecting it from secondary sources. A total of 39 tree species were sampled in 82 quadrats; of these 26 tree species were in standing stage, 25 in sapling, and 35 in seedling. Chloroxylon swi- etenia emerged as the most dominant tree species having highest importance value index, followed by Tectona grandis, Terminalia tomentosa, and Hardwickia binata. Nine tree species and their saplings, including Sterculia urens and Terminalia arjuna, were exploited so badly that they were only found in the seedlings stage. The unavail- ability of standing trees of 12 important tree species including Aegle marmelos and Phyllanthus emblicaindicates the intensity and gravity of anthropogenic pres- sures on these important tree species. If the present anthropogenic pressure continues, which has inhibited the regeneration of several tree species, then substantial neg- ative ecological and societal consequences can be expected.

Extrapolating plot-scale CO_(2) and ozone enrichment experimental results to novel conditions and scales using mechanistic modeling

Introduction:The Aspen-FACE experiment was an 11-year study of the effect of elevated CO_(2) and ozone(alone and in combination)on the growth of model aspen communities(pure aspen,aspen-birch,and aspen-maple)in the field in northern Wisconsin,USA.Uncertainty remains about how these short-term plotlevel responses might play out over broader temporal and spatial scales where climate change,competition,succession,and disturbances interact with tree-level responses.In this study,we used a new physiologybased approach(PnET-Succession v3.1)within the forest landscape model LANDIS-II to extrapolate the FACE results to broader temporal scales(and ultimately to landscape scale)by mechanistically accounting for the globally changing drivers of temperature,precipitation,CO_(2),and ozone.We added novel algorithms to the model to mechanistically simulate the effects of ozone on photosynthesis through ozone-induced impairment of stomatal control(i.e.,stomatal sluggishness)and damage of photosynthetic capacity at the chloroplast level.Results:We calibrated the model to empirical observations of competitive interactions on the elevated CO_(2) and O_(3) plots of the Aspen-FACE experiment and successfully validated it on the combined factor plots.We used the validated model to extend the Aspen-FACE experiment for 80 years.When only aspen clones competed,we found that clone 271 always dominated,although the ozone-tolerant clone was co-dominant when ozone was present.Under all treatments,when aspen clone 216 and birch competed,birch was always dominant or co-dominant,and when clone 216 and maple competed,clone 216 was dominant,although maple was able to grow steadily because of its shade tolerance.We also predicted long-term competitive outcomes for novel assemblages of taxa under each treatment and discovered that future composition and dominant taxa depend on treatment,and that short-term trends do not always persist in the long term.Conclusions:We identified the strengths and weaknesses of PnET-Succession v3.1 and conclude that it can generate potentially robust predictions of the effects of elevated CO_(2) and ozone at landscape scales because of its mechanistically motivated algorithms.These capabilities can be used to project forest dynamics under anticipated future conditions that have no historical analog with which to parameterize less mechanistic models.