Forest Structure Patterns Research Articles

Mixed-severity fire history at a forest-grassland ecotone in west central British Columbia, Canada.

This study examines spatially variable stand structure and fire-climate relationships at a low elevation forest-grassland ecotone in west central British Columbia, Canada. Fire history reconstructions were based on samples from 92 fire-scarred trees and stand demography from 27 plots collected over an area of about 7km2 . We documented historical chronologies of widespread fires and localized grassland fires between AD 1600 and 1900. Relationships between fire events, reconstructed values of the Palmer Drought Severity Index, and annual precipitation were examined using superposed epoch and bivariate event analyses. Widespread fires occurred during warm, dry years and were preceded by multiple anomalously dry, warm years. Localized fires that affected only grassland-proximal forests were more frequent than widespread fires. These localized fires showed a lagged, positive relationship with wetter conditions. The landscape pattern of forest structure provided further evidence of complex fire activity with multiple plots shown to have experienced low-, mixed-, and/or high-severity fires over the last four centuries. We concluded that this forest-grassland ecotone was characterized by fires of mixed severity, dominated by frequent, low-severity fires punctuated by widespread fires of moderate to high severity. This landscape-level variability in fire-climate relationships and patterns in forest structure has important implications for fire and grassland management in west central British Columbia and similar environments elsewhere. Forest restoration techniques such as prescribed fire and thinning are oftentimes applied at the forest-grassland ecotone on the basis that historically high frequency, low-severity fires defined the character of past fire activity. This study provides forest managers and policy makers with important information on mixed-severity fire activity at a low elevation forest-grassland ecotone, a crucial prerequisite for the effective management of these complex ecosystems.

Estructura y productividad de los manglares en la reserva de biosfera Ría Celestún, Yucatán, México

Una zona importante de distribución de manglares en Yucatán está asociada al sistema lagunar de la Reserva de la Biosfera Ría Celestún, localizada al noroeste de la Península. Los principales impactos hacia este ecosistema son la interrupción de flujos de agua, el crecimiento urbano no controlado, el cambio en el uso del suelo y la deforestación. El suelo de la región es cárstico y altamente permeable; al no existir ríos, la única fuente de agua son la precipitación pluvial (760 mm año-1) y las descargas de agua subterránea las cuales tienen su mayor influencia en la parte interna de la laguna, reflejándose en un gradiente de menor a mayor salinidad hacia la boca de la laguna que la conecta con el Golfo de México. Debido a este gradiente se observaron diferentes grados de estructura, dominancia de especies y productividad, registrándose las mayores estructuras y valores de caída de hojarasca de 4,09 g m2 día-1 en la parte interna y de 2,59 g m2 día-1 en la zona de la boca. Temporalmente la productividad de la laguna está relacionada con la variabilidad climática de la región (nortes, secas y lluvias). Los diferentes patrones de estructura y producción de hojarasca fueron determinados por características del suelo como la salinidad y del clima. Por lo tanto las estrategias de manejo deben considerar estos aspectos, así como la variabilidad espacial y temporal de la hidrología, ya que modificaciones, incluso pequeñas, de este aspecto producirían impactos negativos de mayor escala, sugiriendo la vulnerabilidad de este ecosistema a los cambios hidrológicos y ambientales climáticos.

Spaceborne potential for examining taiga-tundra ecotone form and vulnerability.

In the taiga-tundra ecotone (TTE), site-dependent forest structure characteristics can influence the subtle and heterogeneous structural changes that occur across the broad circumpolar extent. Such changes may be related to ecotone form, described by the horizontal and vertical patterns of forest structure (e.g., tree cover, density and height) within TTE forest patches, driven by local site conditions, and linked to ecotone dynamics. The unique circumstance of subtle, variable and widespread vegetation change warrants the application of spaceborne data including high-resolution (< 5m) spaceborne imagery (HRSI) across broad scales for examining TTE form and predicting dynamics. This study analyzes forest structure at the patch-scale in the TTE to provide a means to examine both vertical and horizontal components of ecotone form. We demonstrate the potential of spaceborne data for integrating forest height and density to assess TTE form at the scale of forest patches across the circumpolar biome by (1) mapping forest patches in study sites along the TTE in northern Siberia with a multi-resolution suite of spaceborne data, and (2) examining the uncertainty of forest patch height from this suite of data across sites of primarily diffuse TTE forms. Results demonstrate the opportunities for improving patch-scale spaceborne estimates of forest height, the vertical component of TTE form, with HRSI. The distribution of relative maximum height uncertainty based on prediction intervals is centered at ~40%, constraining the use of height for discerning differences in forest patches. We discuss this uncertainty in light of a conceptual model of general ecotone forms, and highlight how the uncertainty of spaceborne estimates of height can contribute to the uncertainty in identifying TTE forms. A focus on reducing the uncertainty of height estimates in forest patches may improve depiction of TTE form, which may help explain variable forest responses in the TTE to climate change and the vulnerability of portions of the TTE to forest structure change.

Understory spider assemblages from a cloud forest in Chiapas, Mexico, and their relationships to environmental variables

Cloud forests have high ecological complexity, but their reduced area and exploitation by human communities, make them one of the most endangered ecosystems in Mexico. The spider assemblages of a cloud forest reserve in Chiapas, Mexico, were studied to analyze influence of environmental variables (forest stand structure, temperature and relative humidity) and their temporal variation, on the distribution, abundance, species richness and assemblage structure of spiders. Ten parcels were established for the sampling of spiders and the recording of forest and climatic variables. Spider sampling took place during the dry and rainy seasons. Vegetation data were recorded at the end of the study (except canopy cover, which was registered at the end of each season). Some differences were found among parcels in forest stand structure, but only the density of seedlings showed a high correlation with spider abundance, seemingly seedlings (by its size and architecture) offered numerous supports for the understory spiders’ webs and then promote the settlement of weaver spiders. Also there were some correspondences between the similarity patterns of forest structure and spider assemblages, giving some evidence of a forest structure influence on the integration of spiders’ assemblages. Spider abundance was notoriously higher in the dry season. Other environmental variables had only weak effects on spider variables (abundance and species richness) and assemblage structure. The most abundant families were Tetragnathidae, Theridiidae and Linyphiidae, which were also among the dominant families in other tropical cloud forests, with the latter two also being among the most diverse. As complex ecosystems, tropical cloud forests seem to have complicated interactions with their inhabitant animals, not easy to elucidate.

Historical (1860) forest structure in ponderosa pine forests of the northern Front Range, Colorado

Management of many dry conifer forests in western North America is focused on promoting resilience to future wildfires, climate change, and land use impacts through restoration of historical patterns of forest structure and disturbance processes. Historical structural data provide models for past resilient conditions that inform the design of silvicultural treatments and help to assess the success of treatments at achieving desired conditions. We used dendrochronological data to reconstruct nonspatial and spatial forest structure at 1860 in fourteen 0.5 ha plots in lower elevation (∼1900–2100 m) ponderosa pine (Pinus ponderosa Douglas ex P. Lawson &amp; C. Lawson) forests across two study areas in northern Colorado. Fires recorded by trees in two or more plots from 1667 to 1859 occurred, on average, every 8–15 years depending on scale of analysis. The last fire recorded in two or more plots occurred in 1859. Reconstructed 1860 stand structures were very diverse, with tree densities ranging from 0 to 320 trees·ha−1, basal areas ranging from 0.0 to 17.1 m2·ha−1, and quadratic mean diameters ranging from 0.0 to 57.5 cm. All trees in 1860 were ponderosa pine. Trees were significantly aggregated in 62% of plots in which spatial patterns could be estimated, with 10% to 90% of trees mainly occurring in groups of two to eight (maximum, 26). Current stands based on living trees with a diameter at breast height of ≥4 cm are more dense (range, 175–1010 trees·ha−1) with generally increased basal areas (4.4 to 23.1 m2·ha−1) and smaller trees (quadratic mean diameters ranging from 15.7 to 28.2 cm) and contain greater proportions of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and Rocky Mountain juniper (Juniperus scopulorum Sarg.). This is the first study to provide detailed quantitative metrics to guide restoration prescription development, implementation, and evaluation in these and similar ponderosa pine forests in northern Colorado.

Assessing the general patterns of forest structure: quantifying tree and forest allometric scaling relationships in theUnitedStates

AbstractAimUnderstanding the drivers of forest structure, function and change is a fundamental problem in both theoretical ecology and applied forestry for carbon mapping and monitoring. An important component of forest ecology research often utilizes allometric equations to scale up local measurements to predict large‐scale forest and ecosystem‐level properties. However, both applied and theoretical allometries in forest ecology (such as metabolic scaling theory,MST) assume that many scaling relationships are insensitive to broad‐scale climate gradients or species life histories. We aim to test these assumptions by mapping continental‐scale forest allometry across environmental gradients in theUnitedStates.LocationUnitedStates.MethodsWe fit exponents to two allometric relationships inc. 100,000ForestInventoryAnalysis (FIA) field plots: (1) the relationship between the height of an individual tree and its diameter, and (2) plot‐level tree size distributions. We compare fitted exponents to environmental and life‐history variables, such as climate, topography and forest structure, in an attempt to explain allometric variability and deviations from theoretically predicted allometries.ResultsWe find that the structural allometry of forests varies strongly as a function of location in theUnitedStates. Allometric exponents appear to asymptote at approximately whereMSTtheory predicts with increasing forest height, while deviations fromMSTare partially explained as a function of environmentally driven recruitment limitations and successional status.Main conclusionsWhile we find support for invariant tree and stand allometric scaling relationships in forests that are in steady state with regard to demography and resources, we also find considerable spatial variability in forest allometric relationships when steady‐state conditions are violated. These findings suggest that extensions of metabolic scaling theory should incorporate variation in demographic dynamics in younger successional forests, and factors influencing recruitment limitation.

Typhoon Disturbance Mediates Elevational Patterns of Forest Structure, but not Species Diversity, in Humid Monsoon Asia

Understanding factors controlling ecosystem structure and function is key to predicting the effects of climate change on vegetation distribution and carbon sequestration. Cyclones play a large role in structuring ecosystems and cyclone intensity is expected to increase on a warming planet. The effects of cyclones on broad-scale ecosystem patterns could be substantial but are poorly understood. This study assessed forest structure and biodiversity patterns across an elevation gradient (300–3000 m) in mountainous, humid forests of Taiwan, an island experiencing an average of 3–6 typhoons (regional name of cyclones) annually, and contrasted those patterns with a gradient within the Wuyi Mountains of China (500–2100 m), where the climate is similar to Taiwan but typhoon occurrence is rare and effects are generally minimal. In both Taiwan and the Wuyi Mountains, tree species richness and diversity decreased with increasing elevation. Tree size and stature decrease from low to high elevations in the typhoon-protected Wuyi Mountains. In contrast, the biomass and stature of forests in Taiwan increased from low to high elevations. The relationship between forest stature and climate was also contrasting in relation to typhoon disturbance in that we found decreasing tree height and basal area with increasing temperature in Taiwan, but not in the Wuyi Mountains. The more than twofold increase in tree height and biomass with increasing elevations reported here for subtropical humid forests of Taiwan is a unique pattern that highlights the potential role of cyclones in driving elevational patterns of forest structure. Climate change-induced alterations in tropical cyclone regimes may affect elevational patterns of forest structure and carbon sequestration in regions experiencing frequent cyclones.

Ecological restoration and fine-scale forest structure regulation in southwestern ponderosa pine forests

Fine-scale forest patterns are an important component of forest ecosystem complexity and spatial pattern objectives are an increasingly common component of contemporary silviculture prescriptions in dry fire-adapted forests of North America. Despite their importance, questions remain regarding the assessment of silvicultural treatments designed to meet spatial objectives. We initiated a replicated silvicultural assessment of two forest management approaches commonly applied in dense ponderosa pine forests of the Southwest United States: historical evidence-based ecological restoration guidelines (ERG) and northern goshawk (Accipiter gentilis) foraging area management recommendations (GMR). We compared stand-level characteristics, global tree location point patterns and tree group-level attributes resulting from the marking of these approaches to current forest conditions and patterns of historical forest remnants in six, 2.02ha stem mapped plots. We also assessed group-level Vegetative Structural Stage (VSS; a classification of fine-scale forest structural development used to regulate fine-scale spatial patterns in these forests). ERG and GMR-based treatments significantly reduced densities and basal area from the current condition, but did not significantly differ in density from historical forest remnant estimates. GMR-based treatments retained greater stand level basal area than ERG-based treatments, primarily in large, 28–48cm tree diameter classes. GMR-based treatments approximated global tree location point patterns of forest remnants better than ERG-based treatments, primarily due to a 5–6m minimum spacing of residual trees, but also likely due to specific aspects of ERG-based marking techniques. Despite this difference, both treatments resulted in group-level characteristics similar to those exhibited by historical forest remnants. Both treatments significantly altered group-level VSS area and reduced variation of tree diameters within classified VSS groups.Our study provides insight how tree marking techniques using historical forest remnants may have important effects on resulting fine-scale forest structure patterns. We also demonstrate how the use of global point or group-level pattern assessment methods can affect the evaluation of fine-scale spatial pattern objectives. Our analysis of VSS group characteristics highlights implementation and assessment issues associated with group-level spatial pattern identification, classification and regulation. We conclude that group-level classification and regulation is not necessary for maintaining fine-scale spatial patterns in complex ponderosa pine ecosystems subject to frequent fire disturbances and changing future climate conditions and societal demands. Both ERG and GMR-based approaches applied in this study may have utility in maintaining fine-scale spatial heterogeneity and promoting resiliency in Southwest ponderosa pine forests.

Regional-scale drivers of forest structure and function in northwestern Amazonia.

Field studies in Amazonia have found a relationship at continental scales between soil fertility and broad trends in forest structure and function. Little is known at regional scales, however, about how discrete patterns in forest structure or functional attributes map onto underlying edaphic or geological patterns. We collected airborne LiDAR (Light Detection and Ranging) data and VSWIR (Visible to Shortwave Infrared) imaging spectroscopy measurements over 600 km2 of northwestern Amazonian lowland forests. We also established 83 inventories of plant species composition and soil properties, distributed between two widespread geological formations. Using these data, we mapped forest structure and canopy reflectance, and compared them to patterns in plant species composition, soils, and underlying geology. We found that variations in soils and species composition explained up to 70% of variation in canopy height, and corresponded to profound changes in forest vertical profiles. We further found that soils and plant species composition explained more than 90% of the variation in canopy reflectance as measured by imaging spectroscopy, indicating edaphic and compositional control of canopy chemical properties. We last found that soils explained between 30% and 70% of the variation in gap frequency in these forests, depending on the height threshold used to define gaps. Our findings indicate that a relatively small number of edaphic and compositional variables, corresponding to underlying geology, may be responsible for variations in canopy structure and chemistry over large expanses of Amazonian forest.

Water balance and topography predict fire and forest structure patterns

Mountainous topography creates fine-scale environmental mosaics that vary in precipitation, temperature, insolation, and slope position. This mosaic in turn influences fuel accumulation and moisture and forest structure. We studied these the effects of varying environmental conditions across a 27,104ha landscape within Yosemite National Park, California, USA, on the number of fires and burn severity (measured from Landsat data for 1984–2010) and on canopy cover at two heights (>2m and 2–8m) and dominant tree height (measured with airborne LiDAR data). We used site water balance (actual evapotranspiration and climatic water deficit) and topography (slope position, slope, and insolation) as environmental predictors. Random forest modeling showed that environmental conditions predicted substantial portions of the variations in fire and forest structure: e.g., 85–93% of the variation in whether a location did not burn, burned once, or burned twice; 64% of the variation in the burn severity; and 72% of the variation in canopy cover >2m for unburned forests, 64% for once-burned forests, and 59% for twice-burned forests. Environmental conditions also predicted a substantial portion of forest structure following one and two fires, even though the post-fire forest structures were substantially different than pre-fire structures. This suggests a feedback mechanism in which local fire regimes and pre-fire forest structures are related to local environments, and their interaction produces post-fire structures also related to local environments. Among environmental predictors, water balance had the greatest explanatory power, followed by slope position, and then by slope and insolation. Managers could use our methods to help select reference areas that match environmental conditions, identify areas at risk for fires that endanger critical habitat or other resources, and identify climate analog areas to help anticipate and plan for climate change.

Beyond mean functional traits: Influence of functional trait profiles on forest structure, production, and mortality across the eastern US

Plant functional traits (PFTs) have increased in popularity in recent years to describe various ecosystems and biological phenomena while advancing general ecological principles. To date, few have investigated distributional attributes of individual PFTs and their relationship with key attributes and processes of forest ecosystems. The objective of this study was to quantify the distribution and contribution of various PFTs in determining forest structure, live tree production (volume and biomass), and tree mortality across the eastern US. In total, 16 metrics representing species specific gravity and their shade, flood, and drought tolerance were used to develop a PFT profile for over 23,000 permanent sample plots in the region. Spatial relationships were observed when analyzing not only the mean value of these traits but also measures of PFT complexity: the standard deviation, Shannon’s index (a measure of PFT diversity), and Gini coefficient (a measure of PFT inequality). Results from nonparametric random forests models indicated that variables which formed the PFT profile contributed to explaining broad-scale patterns in the variability in forest structure (volume and biomass of overstory live trees, maximum stand density index, and tree seedling abundance; R2 ranged from 0.09 to 0.78), production (volume [R2=0.16] and biomass accretion [R2=0.11]), and to a lesser degree, tree mortality. Despite the variability in the data employed and the variety of forest management regimes in these stands, this work demonstrates the utility of applying PFT profiles for understanding and predicting patterns of forest structure and production and their role in critical ecosystem processes such as carbon sequestration.

Examining the effect of diverse management strategies on landscape scale patterns of forest structure in Pennsylvania using novel remote sensing techniques

We used novel remote sensing techniques to compare the landscape-scale patterns of forest structure in Pennsylvania, USA under the management of four different agencies with varying primary objectives, including production forestry, wildlife habitat, recreation, and private ownership. We (i) developed a forest structure classification scheme using publicly available LiDAR and orthographic aerial imagery data, (ii) mapped the forest structure across twenty forested landscapes, and (iii) compared the landscape-scale forest structure patterns among the four forest management types. Our results indicate that different management philosophies and their associated forest management approaches have resulted in contrasting landscape-scale patterns of forest structure. Privately managed forests had shorter forests, higher densities of distinct patches, higher interspersion of patch types, and higher forest structure diversity at fine-scales (1.5 ha grain size) compared to forests lightly managed for recreation. Production forests under ecosystem management and forests managed for wildlife habitat exhibited intermediate patterns of forest structure. This variation in forest structure patterns among the forest managers is likely to have implications for wildlife habitat and other ecosystem services. Furthermore, greater emphasis is needed on encouraging private landowners to manage across property boundaries and providing the resources and tools to manage forests at the landscape scale.

Spatial pattern of forest structure mediated by topography in a steep mountain basin in West Tanzawa, Japan

In steep mountainous areas where geological activity is generally high, forest structure is controlled by ground–surface processes and topography, but this has rarely been investigated at the water catchment scale. Across a 306 ha basin covered with temperate forest on Mt Tanzawa, we conducted a field investigation of trees above 5 cm in diameter at breast height in 105 plots (0.01 ha) set at regular intervals. Total basal area (Total BA), basal area of the largest tree (MAX BA), and number of trees and species per unit area were examined in relation to topographical variables. Results showed that MAX BA was larger on main ridges and gentle slopes, whereas the number of trees was larger on branch ridges and on thin soils. Both MAX BA and number of trees significantly contributed to Total BA, although the former had a larger effect. Analyses for each species indicated that the higher value of MAX BA on main ridges was mainly explained by late-successional species. We suggest that ground stability controlled the spatial pattern of forest structure. We found a complex topographical niche differentiation among species: e.g., Fagus crenata, the most dominant and largest species, tended to occur on relatively flat ground at higher elevation, and its BA became larger around main ridges with deep soils. The most abundant species, Carpinus japonica, tended to occur on steep slopes and thin soils, and its BA was larger on north-facing slopes. Thus, complex topographical relief promotes habitat heterogeneity that underlines the biodiversity of the basin.

Spatial patterns of above-ground structure, biomass and composition in a network of six Andean elevation transects

Background: The Amazon to Andes transition zone provides large expanses of relatively pristine forest wilderness across environmental gradients. Such elevational gradients are an excellent natural laboratory for establishing long-term interactions between forest ecosystems and environmental parameters, which is valuable for understanding ecosystem responses to environmental change. Aims: This study presents data on elevational trends of forest structure (biomass, basal area, height, stem density), species richness, and composition from six elevational transects in the Andes. Methods: We analysed the spatial patterns of forest structure, above-ground biomass and composition from 76 permanent plots, ranging from lowland Amazonian rain forest to high-elevation cloud forests in Ecuador, Peru, and Bolivia. Results: Forest above-ground woody biomass stocks ranged from 247 Mg ha−1 (Peru, 210 m) to 86 Mg ha−1 (Peru, 3450 m), with significantly decreasing trends of tree height and biomass and an increasing trend of stem density with increasing elevation. We observed an increase in forest richness at three taxonomic levels at mid-elevation, followed by a decrease in richness within the cloud immersion zone. Conclusions: The transects show an increase in stem density, a decline in tree height and above-ground coarse wood biomass and a hump-shaped trend in species richness with increasing elevation. These results suggest that environmental change could lead to significant shifts in the properties of these ecosystems over time.

Making Friends in the Rainforest: “Negrito” Adaptation to Risk and Uncertainty

The so-called negritos adapt not just to a tropical forest environment but also to an environment characterized by perturbations and fluctuations. As with other hunter-gatherers in the region and, indeed, throughout the world, they use both social and ecological methods to enhance their chances of survival in this changing environment: socially, they have developed networks of trading and marriage partners; ecologically, they maintain patches of key resources that are available for future harvesting. As evidenced in the case of the Batek (Orang Asli), patterns of forest structure and composition are sometimes direct outcomes of intentional resource concentration and enrichment strategies. While little of the above is controversial anthropologically, what has drawn some debate is the nature of the relationship with partner societies. Conventional wisdom posits relations of inequality between foragers and "others": foragers and farmers are often construed as hierarchical dyads where foragers supply products or labor to farmers in exchange for agricultural harvests and other trade goods. This kind of adaptation appears to be one of divergent specialization. However, there are cases, such as in the relationship between Batek and Semaq Beri, where both societies follow a roughly similar mode of adaptation, and specialization has not materialized. In sum, while not denying that hierarchy and inequality exist, I suggest that they have to be contextualized within a larger strand of relationships that includes both hierarchy and egality. Further, such relationships are part of the general portfolio of risk reduction strategies, following which access to widely scattered environmental resources, and passage from one location to another, is enhanced not by competing with and displacing neighbors but by maintaining a flexible regime of friendly exchange partners.

Linking the biological traits of boreal bryophytes to forest habitat change after partial harvesting

Biological traits are potentially important for understanding mechanisms of plant species responses to alteration of local habitat conditions through natural and anthropogenic disturbance. Forest harvesting is a prominent disturbance in the circumpolar boreal biome, influencing stand- and landscape-scale patterns of forest structure and biodiversity. We examined a range of variable retention harvesting intensities (10%, 50%, and 75% dispersed green-tree retention harvesting and unharvested controls) in terms of their effectiveness for maintaining mosses and liverworts with differing biological traits. Bryophytes were sampled in 20m radius plots 5–6years post-harvest in 24 forest stands (each 10ha) of two forest types (broadleaf-coniferous mixedwood, coniferous-dominated). We first examined the environmental factors that were the strongest predictors of species composition across the forest types and retention levels. We then used fourth-corner analysis to relate differences in the forest environment to species traits. Selected traits included bryophyte group, life form, habitat requirements, and reproductive and dispersal characteristics. The strongest predictors of species composition were ground-level moisture (estimated using growth of the moss Hylocomium splendens) and degree of canopy cover. Fourth-corner analysis showed that forest type, retention level, and their associated moisture conditions were closely related to the abundances of species characterized by different biological traits. Species with rare sporophyte production, larger spores, dioicous sexuality, or that require greater moisture or shade, were affiliated with higher retention and forest moisture. Reduced abundances of species with these traits after harvesting may detrimentally affect their capacity to disperse and re-establish, and suggests that moisture limitation is an important environmental filter that may restrict their representation at harvested sites. Coniferous-dominated forests supported higher abundances of several species types compared to mixed forests, including liverworts, acrocarpous mosses, and species that have greater moisture requirements, dioicous sexuality, or infrequent sporophyte production. This conveys the importance of coniferous forests as bryophyte habitat in mixedwood landscapes and the influence of canopy composition on regional species distributions. Understanding the tolerances of species exhibiting particular traits after harvesting may improve predictions about species extirpation risk and inform approaches to ensure their continued survival.

Making Friends in the Rainforest: “Negrito” Adaptation to Risk and Uncertainty

The so-called negritos adapt not just to a tropical forest environment but also to an environment characterized by perturbations and fluctuations. As with other hunter-gatherers in the region and, indeed, throughout the world, they use both social and ecological methods to enhance their chances of survival in this changing environment: socially, they have developed networks of trading and marriage partners; ecologically, they maintain patches of key resources that are available for future harvesting. As evidenced in the case of the Batek (Orang Asli), patterns of forest structure and composition are sometimes direct outcomes of intentional resource concentration and enrichment strategies.

Multi‐scale patterns of forest structure and species composition in relation to climate in northeast China

Though a number of studies have focused on the factors that shape the structure and dynamics of temperate forests, little is known about whether these factors vary with spatial scale. In this study we investigated compositional and structural patterns of forests across three spatial scales (plot, local assemblages and regions) in northeast China and asked whether climatic variables shape these patterns. Using a systematic sampling design, we measured diameter at breast height (DBH) and height of trees, and recorded the abundances, percent of cover and heights of shrubs and herbs in 141 plots from 10 nature reserves. We found that summer temperature accounted for most of the variation in species composition, both within and among forest types. DBH, tree height and total basal area all increased significantly with summer temperature while stem density decreased. The DBH frequency distribution depended strongly on temperature (especially winter temperature) and varied among spatial scales, and it tended to be more left‐skewed as temperature increased. Taking together, our results suggest that a warming climate could lead to an increase in tree growth and the changes in size structure of temperate forests in northeast China. In particular, the proportion of large trees will in all likelihood increase while that of smaller trees will decrease. Shifts in forest structure in a warmed world will undoubtedly influence forest management practices, ecosystem dynamics, and species conservation.

Patterns of forest structure, competition and regeneration in southwestern white pine (Pinus strobiformis) forests

Pinus strobiformis (southwestern white pine, abbr. PIST), a species that comprises a small but significant component of the mixed-conifer forests of the U.S. Southwest, faces an increasing threat from white pine blister rust (Cronartium ribicola, abbr. WPBR). This potentially lethal, non-native fungal pathogen is windborne and, therefore, virtually impossible to control. However, silvicultural strategies, such as thinning, reintroduction of natural fire regimes, and encouraging natural selection for rust-resistant genotypes, show promise for maintaining or restoring infected stands. To expand ecological knowledge of the species and guide management, we surveyed PIST in mixed-conifer stands throughout Arizona and portions of New Mexico. We examined PIST forest structure, regeneration, and competitive interactions. We found that PIST occupied lower canopy positions in Pinus ponderosa-dominated plots, thereby supporting its classification as an intermediate shade-tolerant species. Plots where PIST was a dominant component showed evidence of succession towards more tolerant conifers. PIST regeneration occurred relatively rarely and was negatively associated with increasing understory plant cover and open conditions. Although PIST faced heavy tree competition, with Pseudotsuga menziesii the most important competitor, small suppressed trees showed evidence of persistence.

Age and Structure of Mature Knobcone Pine Forests in the Northern California Coast Range, USA

AbstractAn understanding of current structural conditions and disturbance history is a requisite for optimal management of forest ecosystems, especially for serotinous species such as knobcone pine (Pinus attenuataLemmon). Knobcone pine is widely distributed in California, yet little is known regarding age and forest structure patterns. In this study, we quantify forest conditions of 21 mature knobcone pine stands in the northern Mayacmas Mountains, north Coast Range, California, USA. Characterized by complex terrain, knobcone pine forests occur in small patches interspersed with chaparral and mixed evergreen forests. Stands displayed unimodal, bimodal, and diffuse age distributions with predominant stand ages ranging from 42 yr to 70 yr, although trees ranged from 17 yr to 98 yr old. Knobcone pine stands appear to have been maintained by stand replacing fires. However, stands with uneven-aged structures were produced through the persistence of residual trees and low intensity fires that created secondary cohorts. Stands varied in density, ranging from 503 stems ha−1to 2986 stems ha−1, with snags comprising 12 % to 40 % of total density. Wildfires that occurred from the 1930s to the 1960s, in addition to a large wildfire in 1981, created a heterogeneous landscape of knobcone pine forests. Older stands have lower canopy cover, high snag densities, and many trees with evidence of western gall rust (Peridermium harknessii) infections—signs that they are approaching their expected life spans. Risks and constraints associated with using stand replacing prescribed fire pose a challenge for managers of knobcone pine forests, and research may be needed to explore feasible treatment alternatives.