Relative Basal Area Research Articles

Mangrove community in an abandoned crick kiln: A structural and association analysis

Background: The presence of brick kiln along the Hoogly river sites of lower Bengal is very usual and this phenomenon is not only restricted to India alone but also to other south Asian countries. The abandoned brick kiln are important habitat for the formation of mangrove community due to tidal action, loose silty substratum and less anthropogenic interference. In this context, the aim of the present study is to visualize how the structural and association pattern regulate the community dynamics of a mangrove ecosystem. Materials and Methods: The entire study area was divided into 37 units (Quadrats of 27.31 sq m). Structural parameters like density, relative density, abundance, relative abundance, frequency, relative basal area were measured based on vegetation map, prepared through satellite image and ground truthing. Association indices (Ochiai, Dice and Jaccard) were measured based on 2X2 contingency/species association table. Results: Out of 10 species under 10 genera and 9 families found in the present habitat, Sonneratia caseolaris is the only mangrove tree species with 155 individuals along with other mangrove associates like Cryptocoryne ciliata, Crinum viviparum, Acanthus ilicifolius and Denis scandens. The high importance value index of Sonneratia caseolaris, Cryptocoryne ciliata, and Crinum viviparum indicated their significant role in community formation. The strong positive association of these 3 species also suggests helping in developing community in stressed environment. Conclusion: Identification of such potential mangrove habitat and study of their community dynamics would be helpful to find out the nature of mangrove establishment for future afforestation programme of threatened mangrove species.

Landscape patterns of species-level association between ground-beetles and overstory trees in boreal forests of western Canada (Coleoptera, Carabidae)

Spatial associations between species of trees and ground-beetles (Coleoptera: Carabidae) involve many indirect ecological processes, likely reflecting the function of numerous forest ecosystem components. Describing and quantifying these associations at the landscape scale is basic to the development of a surrogate-based framework for biodiversity monitoring and conservation. In this study, we used a systematic sampling grid covering 84 km2 of boreal mixedwood forest to characterize the ground-beetle assemblage associated with each tree species occurring on this landscape. Projecting the distribution of relative basal area of each tree species on the beetle ordination diagram suggests that the carabid community is structured by the same environmental factors that affects the distribution of trees, or perhaps even by trees per se. Interestingly beetle species are associated with tree species of the same rank order of abundance on this landscape, suggesting that conservation of less abundant trees will concomitantly foster conservation of less abundant beetle species. Landscape patterns of association described here are based on characteristics that can be directly linked to provincial forest inventories, providing a basis that is already available for use of tree species as biodiversity surrogates in boreal forest land management.

Comparative enumeration for dominant species in selected natural forests, North Central Province, Sri Lanka to be used in assessment of Carbon sequestration

With the increasing attention placed on climate change as the prime environmental hazard, more and more attention is on the forest ecosystems as sinks of carbon dioxide. At the International Convention on Climate Change in 1992 and subsequently the Kytoto Protocol Clean Development Mechanisms were introduced and one of its clauses was the trading of carbon between developing and developed countries. Despite the recognized potential of forests as an important sink to sequester carbon, accurate estimates of the carbon sequestration potential of different ecosystems or their component species are lacking especially in Sri Lanka. Out of the natural forests, the work done in this area on the dry zone forests is minimal.Monteith (1972 & 1977) showed that the rate of biomass production is directly proportional to the amount of radiation intercepted by the foliage canopy. The above relationship can be given as: W = e RI , Where, W is the amount of total biomass (above and belowground biomass) produced and RI is the amount of radiation intercepted by canopy. The proportionality constant, e is termed as Radiation Use Efficiency (RUE). In order to find the carbon sequestration of particular ecosystem it is imperative to find the radiation use efficiency of dominant species which is being taken as the Important Value Index. This study reports the findings of the comparative assessment of 3 forest ecosystems ie Padawiya Proposed Reserve, Weddakanda Proposed Reserve (PR) and Nagalakanda Proposed Reserve (PR) which are located in DL 1 a, DL 1 b and DL 1 c agro-ecological regions respectively for their dominant species. Padewiya PR lay on almost flat land and others are on isolated mountains. Elevation levels distributed between 55m to 210m from Mean Sea Level (MSL). Circular shape sample plots were located representing whole area and low, mid and high elevations.No of species and no of families were resulted as Padawiya PR 30, 17, Weddakanda PR 37, 18 and Nagalakanda PR 40, 25 respectively. Stem density (for all species) of Padawiya, Weddakanda PR, and Nagalakanda PR were recorded as 526, 1800 and 2038 stems ha-1. Basal area of the selected forest (for all species) was 35.0, 45.2 and 51.8 m2ha-1 respectivly. Relative density, relative basal area and relative frequency were calculated for each species. According to Important Value Index (IVI) dominant species are ranked as higher values are most dominant. Most dominant five species for Padawiya PR are Drypetes sepiaria, Syzygiyum cordifolium, Terminalia arjuna, Diospyros ovalifolia, and Wrightia angustifolia. Most dominant five species for Weddakanda PR are Drypetes sepiaria, Diospyros ebenum, Croton officinalis, Diospyros ovalifolia and Pterospermum suberifolium. As well as Mallotus walkerae, Drypetes sepiaria, Ficus tinctoria, Pterospermum suberifolium, and Glycosmis angustifolia are the most dominant species for Nagalakanda PR.

Importance of demography and dispersal for the resilience and restoration of a critically endangered tropical conifer Araucaria nemorosa

Aims In situ species survival involves persistence at current sites and/or colonization of new locations. Determining the likelihood of these events requires an understanding of population dynamics and dispersal. We address these issues in populations of a critically endangered tropical conifer Araucaria nemorosa and provide conservation recommendations. Location Port Boise, island of Grand Terre, New Caledonia, Pacific Ocean. Methods We characterize the demographic structure of six populations of A. nemorosa based upon size class frequencies and relative basal area compared to competing angiosperm trees. Using genotype data from 280 adult individuals at seven microsatellite loci, we indirectly estimate dispersal distances and project a maximal dispersal envelope around the extant populations. Results Our survey detected marked differences in demographic parameters including the proportion of basal area occupied by A. nemorosa versus angiosperm trees (ranging from 25% to 77%), the size class frequency distributions of A. nemorosa and seedling densities (ranging from 500 to 37300 seedlings ha−1) among some populations. Wright’s genetic neighbourhood ranged from 22 to 876 trees, and historic gene dispersal ranged from 10.8 to 82.4 m, indicating that most seed dispersal is <100 m. Main conclusions This study indicates that the risk of recruitment failure in remnant populations of Araucaria nemorosa is low in most of the stands but is high in the inland population Forêt Nord. In situ natural regeneration appears to be constrained in this population, most likely as a consequence of competitive exclusion. Our results also suggest that the majority of seed dispersal is too short to allow A. nemorosa to disperse to new more hospitable sites within an ecologically relevant time-scale. Our findings have implications not only for this emblematic tree species but also for a wide range of fragmented and degraded plant species populations with limited dispersal that are vulnerable to competitive exclusion.

Forest structure, composition, and tree diversity response to a gradient of regeneration harvests in the mid-Cumberland Plateau escarpment region, USA

Upland hardwood stands on mesic, escarpment-oriented sites on the Cumberland Plateau region of northeastern Alabama provide a myriad management opportunities. Stands are primarily managed for Quercus, but the high species diversity allows for management that targets multiple species. Stand composition is unique in that dominant species include shade tolerant species such as Acer saccharum, intermediate tolerant Quercus spp. and Carya spp., and intolerant Liriodendron tulipifera. Three replications of five levels of disturbance were created to assess species compositional changes; disturbances included three levels of harvest intensity, a mid-story herbicide treatment, and a control. After eight growing seasons, there were no discernable differences in species richness, diversity or evenness. Importance values based on relative basal area and relative density also changed little, except for clearcuts where L. tulipifera greatly increased. An initial gradient in basal area, canopy cover, and light created by harvesting or thinning dissipated following five growing seasons. Options exist for future stand management, including promoting two-aged or uneven-aged systems. Maintenance of Quercus will require additional tending.

Influences of woody encroachment and restoration thinning on overstory savanna oak tree growth rates

Midwestern savannas historically covered >10 M ha in central North America, but are now rare due to agricultural conversion and anthropogenic modifications to disturbance regimes – particularly fire suppression. Throughout this range, Midwestern savannas are characterized by scattered overstory trees; however, with fire suppression, these systems are invaded by non-savanna trees. Restoration of encroached savannas involves removal of invading trees, yet little is known about the impacts of encroachment or encroachment removal on the relict savanna overstory trees, which define these systems. Here, we use tree ring analysis to investigate savanna tree growth rates in encroached, non-encroached, and experimentally restored Midwestern oak savannas in central Iowa. We found that woody encroachment led to pronounced declines in growth rate (ring width) of relict overstory white oak ( Quercus alba), relative to Q. alba trees in competition-free, open-grown conditions, or in an encroachment-free remnant woodland. To further understand effects of encroachment removal on relict Q. alba savanna trees, we conducted a large-scale restoration experiment, where encroaching trees were mechanically removed from four encroached savannas, with an additional four savannas retained as encroached controls. Restoration led to elevated tree growth rates, with these changes generally persistent through 7 years post-restoration (2003–2009). Over the course of this post-restoration study period, ring width, basal area increment, and relative basal area increased by 49%, 59%, and 55%, respectively, in trees from restored sites, relative to trees from encroached, control sites. These results suggest that woody encroachment has strong influence on overstory savanna trees, through increased competitive dynamics; however, woody encroachment removal may help to restore relict savanna tree growth rates, even after prolonged periods of encroachment (>40 years). To restore the oak savannas at our sites, and perhaps elsewhere, we advocate a three step process: (1) mechanical woody encroachment removal, (2) maintenance of the encroachment-free state through prescribed fire, and (3) promotion of a diverse understory layer, characteristic of oak savanna in our region. While promoting oak regeneration will be important for the long-term maintenance of these sites as oak savanna, relict savanna trees appear responsive to restoration and should maintain overstory conditions through the near-term.

Growing-Space Relationships in Young Even-Aged Northern Hardwood Stands Based on Individual-Tree and Plot-Level Measurements

Abstract The amount of growing space occupied by trees of given sizes and species is traditionally assessed on a plot basis, using observations from groups of trees growing within an area of fixed size. Our study combines individual-tree with plot-based observations of upper-canopy trees representing a range of shade tolerance (Fagus grandifolia ≥ Acer saccharum &gt; Betula alleghaniensis ≥ Fraxinus americana) in three young, fully stocked, even-aged northern hardwood stands. The amount of canopy growing space used by a stem of given size was described by the ratios of crown projection area and crown surface area to stem basal area. These variables were related to species, stand, and relative basal area using analysis of covariance. Both ratios were generally highest in the youngest (19 years) stand, intermediate in the mid-aged stand (24 years), and lowest in the oldest stand (29 years). A few differences were detected among species, with shade-tolerants having larger ratios. Allometric models were used in conjunction with plot density data to estimate canopy cover at the stand level. Considerable crown overlap was indicated among upper-canopy trees in all three stands. Estimates from tree-centered plots suggested that crowns occupied 1.81 ± 0.02 times the ground area in the youngest stand and 1.45 ± 0.03 times in the mid-aged and oldest stands; when corrected for sampling bias, these ratios were at least 1.30 and 0.96, respectively. Combining individual-tree with plot-level measurements afforded a comprehensive assessment of trends in growing-space occupancy not possible using either technique alone.

Multi-sensor data fusion for estimating forest species composition and abundance in northern Minnesota

The magnitude, duration, and frequency of forest disturbance caused by the spruce budworm and forest tent caterpillar in northern Minnesota and neighboring Ontario, Canada have increased over the last century due to a shift in forest species composition linked to historical fire suppression, forest management, and pesticide application that has fostered increased dominance of host tree species. Modeling approaches are currently being used to understand and forecast potential management effects in changing insect disturbance trends. However, detailed forest composition data needed for these efforts is often lacking. We used partial least squares (PLS) regression to integrate different combinations of satellite sensor data including Landsat, Radarsat-1, and PALSAR, as well as pixel-wise forest structure information derived from SPOT-5 sensor data (Wolter et al., 2009), to determine the best combination of sensor data for estimating near species-level proportional forest composition (12 types: 10 species and 2 genera). Single-sensor and various multi-sensor PLS models showed distinct species-dependent sensitivities to relative basal area (BA), with Landsat variables showing greatest overall sensitivity. However, best results were achieved using a combination of data from all these sensors, with several C-band (Radarsat-1) and L-band (PALSAR) variables showing sensitivity to the composition and abundance of specific species. Pixel-level forest structure estimates derived from SPOT-5 data were generally more sensitive to conifer species abundance (especially white pine) than to hardwood species composition. Relative BA models accounted for 68% (jack pine) to 98% (maple spp.) of the variation in ground data with RMSE values between 2.46% and 5.65% relative BA, respectively. Receiver operating characteristic (ROC) curves were used to determine the effective lower limits of usefulness of species relative BA estimates which ranged from 5.94% (jack pine) to 39.41% (black ash). These estimates were then used to produce a dominant forest species map for the study region with an overall accuracy of 78%. Most notably, this approach facilitated discrimination of aspen from paper birch as well as spruce and fir from other conifer species which is crucial for the study of forest tent caterpillar and spruce budworm dynamics in the Upper Midwest. We also demonstrate that PLS regression is an effective data fusion strategy for mapping composition of heterogeneous forests using satellite sensor data.

Effects of two Ca fertilizer types on sugar maple vitality

Over the last decades, continuous signs of sugar maple ( Acer saccharum Marsh.) dieback in stands of northeastern North America have promoted the experimentation of corrective measures to restore sugar maple vitality. To verify the hypothesis that K–Mg antagonism may have limited the full response of sugar maple to dolomitic lime application in a previous experiment (CaMg(CO3)2, 12% Mg), two Ca fertilizers (CaCO3 and CaSO4·2H2O), having negligible Mg content, were applied at rates of 1, 2, and 4 t Ca·ha–1 on sugar maple trees adjacent to the limed area. After 3 years, most of the foliar nutrient concentrations of treated trees were improved, particularly Ca, for both Ca fertilizers, in line with published ranges for healthy sugar maple trees, except for Mg. Moreover, no persistent nutrient antagonism was observed. The crown dieback rate of treated sugar maple was ≤5.8% after 3 years, while it reached 12% for the controls. Also, relative basal area growth showed that both Ca sources can improve growth rate. Growth response following Ca treatments was, however, lower than for the former lime experiment after the same period of time. In this context, our results suggest that Mg nutrition could be more important for sugar maple in this ecosystem than initially thought.

Pre-impact forest composition and ongoing tree mortality associated with sudden oak death in the Big Sur region; California

Mixed-evergreen forests of central coastal California are being severely impacted by the recently introduced plant pathogen, Phytophthora ramorum. We collected forest plot data using a multi-scale sampling design to characterize pre-infestation forest composition and ongoing tree mortality along environmental and time-since-fire gradients. Vegetation pattern was described using trend surface analysis, spatial autocorrelation analysis and redundancy analysis. Species-environment associations were modeled using non-parametric multiplicative regression (NPMR). Tanoak ( Lithocarpus densiflorus) mortality was analyzed with respect to environmental and biotic factors using trend surface analysis and multivariate regression. Mixed-evergreen forest occurs throughout the Big Sur region but is most widespread in the north, on north facing slopes, at mid-elevations near the coast. Relative basal area of the dominant tree species changes fairly predictably from north to south and from coast to interior in relation to mapped patterns of precipitation, temperature factors and soil characteristics. Most dominant tree species sprout vigorously after fire. The forests experience a mixed-fire regime in this region ranging from low severity understory burns to high severity crown fires, with the latter increasing above the marine inversion layer and at more interior locations. Ceanothus spp. can dominate mixed-evergreen sites for several decades after severe fires. All of the dominant broadleaf evergreen tree species are hosts of P. ramorum, although not all will die from infection. Tanoak mortality decreases from northwest to southeast and is significantly correlated with climate, especially growing degree days and mean annual precipitation, and with basal area of the foliar host bay laurel ( Umbellularia californica) in a 0.5–1 ha neighborhood. Adaptive management of mixed-evergreen forest to mitigate P. ramorum impacts in the region will need to consider large local and regional variation in forest composition and the potentially strong interactions between climate, fire, forest composition and disease severity.

Changes in tree species diversity and dominance across a disturbance gradient in Nepalese Sal (Shorea robusta Gaertn. f.) forests

Disturbance is often touted as a management tool, as moderate disturbance is believed to enhance diversity; thus an understanding of frequent and fluctuating disturbance regimes in forests and their effects on stand structure, dominance and diversity is very crucial. Here, the effects of different disturbance regimes, along a gradient, on diversity and dominance of five Shorea robusta Gaertn. f.-dominated forests were investigated in 25 one-ha plots in Nepal. A total of 67 tree species were recorded; of which 41 species were encountered in least disturbed and 10 species in heavily disturbed forest. Significant variations among forests were observed for all measures of alpha diversity. Alpha diversity measures declined linearly along a disturbance gradient while dominance increased linearly. Relative basal area of S. robusta increased as the level of disturbance increased, which in turn produced more than two-fold higher important value index in heavily disturbed forest than the least disturbed forest. All alpha diversity measures declined in an order of three with increasing relative basal area of S. robusta. The similarity in species composition between each pair of disturbed forests was generally low (Jaccard’s similarity index < 57%), suggesting a higher Beta diversity. It can be concluded that diversity of Sal forests declines with increasing magnitude of disturbance, which in turn favors a higher dominance of S. robusta. Controlling the population of the dominant species, mainly S. robusta, is recommended to enhance diversity and to achieve multiple-use forest management objectives.

Silvicultural alternatives in an uneven-sized forest dominated by Picea abies

In this article, we report on the increments in basal area and tree diameter as well as the structural development observed in variously thinned plots that underwent either uneven- or even-sized treatment. The experimental forest was originally an uneven-sized mixed stand dominated by Picea abies. Twenty-eight randomized sample plots underwent each treatment, and the trees were monitored for 15 growing seasons after thinning. The uneven-sized plots retained a reverse J-shaped diameter distribution, but this was changed into a bell shape by low thinning in the even-sized plots. Absolute basal area increment was positively correlated with basal area in the even-sized treatment but not in the uneven-sized treatment. In the latter, all of the plots grew almost equally well, and only the basal area of broadleaves explained slightly positively the increment variation. Relative basal area increment was negatively correlated with basal area in both treatments. Additionally, the basal area of Scots pine was a positive explanatory variable in the relative increment variation in the even-sized treatment. For the dominant Norway spruce trees, diameter increment was negatively correlated with basal area in both treatments and, conversely, heavy removal increased the diameter increment. Relative basal area increment averaged 5% annually in uneven-sized plots representing the “target selection.” This was more than double the increment observed for the even-sized plots that represented the “prevailing practice.” Likewise, the diameter increment of Norway spruce trees was 48% greater in the uneven-sized compared to the even-sized plots.

Prevalence of Tree Regeneration by Sprouting and Seeding Along a Rainfall Gradient in Hawai'i

ABSTRACTDrought stress in tropical dry forests is thought to result in greater asexual regeneration via vegetative sprouting (e.g., basal, root, and branch layering) than occurs in moister tropical forests. We tested this hypothesis by examining the prevalence of tree sprouting and seeding in tropical forests located along a rainfall gradient on the island of Hawai'i. Additionally, we examined the potential for novel disturbance, feral pig Sus scrofa rooting and trampling, to alter patterns in tree regeneration mode. We found greater sprouting (in terms of relative density and basal area) in dry forests than in mesic and wet forests, supporting the hypothesis. We also found that feral pig disturbance is negatively correlated with the relative density and basal area of seedlings in wet forests, but is positively correlated with the relative importance of sprouting, and the richness and diversity of sprouting species. Our results suggest rainfall regimes may be an important factor controlling broad‐scale patterns in tree regeneration mode, and that exotic ungulates can significantly modify such patterns with potential consequences for the structure and dynamics of tree populations and communities.

Present-day expansion of American beech in northeastern hardwood forests: Does soil base status matter?

Recently, sugar maple ( Acer saccharum Marsh.) decline in northeastern North America has been regarded as a major factor structuring hardwood forests by favouring American beech ( Fagus grandifolia Ehrh.) in the understory of maple-dominated stands. To determine whether soil fertility differences associated with sugar maple decline may have promoted the expansion of American beech, we explored the relationships between the soil base status and the sapling and tree strata density and composition, using data from 426 permanent sample plots distributed throughout Quebec. Our results indicate that American beech is currently expanding in the sugar maple range of Quebec. The abundance and proportion of American beech in the sapling stratum are mainly associated with the proportion of American beech in the tree stratum, the relative basal area of dead sugar maple trees, and the base status of soils. In accordance with the many studies reporting on the high sensitivity of sugar maple to the acid–base status of soils and the decline of the sugar maple population, this study supports the hypothesis that soil base cation depletion, caused in part by atmospheric acid deposition, is among the main factors involved in the present-day expansion of American beech over a large area in Quebec.

Predicting canopy macrolichen diversity and abundance within old-growth inland temperate rainforests

Windward slopes of the inland mountain ranges in British Columbia support a unique inland temperate rainforest (ITR) ecosystem. Increasing fragmentation and the loss of old ITR stands have highlighted the need for determining conservation biology priorities among remaining old forest stands. We have addressed this issue by surveying foliose macrolichens within 53 old ITR stands in British Columbia's 135,000 ha very wet-cool interior-cedar hemlock (ICHvk2) biogeoclimatic subzone in the upper Fraser River watershed. Study plots were stratified by leading tree species and by “wet” versus “dry” relative soil moisture conditions. Other plot variables included: temperature, precipitation, incident solar loading, and canopy openness. Ordination plots showed a distinct assemblage of foliose cyanolichens, including Lobaria pulmonaria, Lobaria retigera, Sticta fuliginosa, Nephroma isidiosum, Nephroma occultum, and Pseudocyphellaria anomala, whose abundance was correlated with increasing relative soil moisture, temperature, canopy openness, precipitation, and basal area of spruce. Logistic regression models similarly identified relative soil moisture and temperature in all parsimonious models. Leading tree species, in combination with “wet” relative soil moisture and/or temperature, were important factors explaining the presence or absence of five ( Cavernularia hultenii, L. retigera, N. occultum, Platismatia norvegica, and Sticta oroborealis) of the eight modeled old-growth associate lichen species. This combination of conditions favouring the development of canopy lichen communities in old forests was best expressed in low elevation water receiving sites. We hypothesize that groundwater availability in these sites promotes species richness and abundance of canopy lichens by creating more favourable conditions for growth, and by reducing fire return intervals which allows for the accumulation of rare species over time. Historically, forests in these wet “toe-slope” positions were disproportionately targeted for logging. Their conservation should now be a high priority, given their disproportionate significance to maintaining canopy lichen diversity in the present-day landscapes.

Estimating Tree Survival: A Study Based on the Estonian Forest Research Plots Network

Tree survival, as affected by tree and stand variables, was studied using the Estonian database of permanent forest research plots. The tree survival was examined on the basis of remeasurements during the period 1995–2004, covering the most common forest types and all age groups. In this study, the infl uence of 35 tree and stand variables on tree survival probability was analyzed using the data of 31 097 trees from 236 research plots. For estimating individual tree survival probability, a logistic model using the logit-transformation was applied. Tree relative height had the greatest effect on tree survival. However, different factors were included into the logistic model for different development stages: tree relative height, tree relative diameter, relative basal area of larger trees and relative sparsity of a stand for young stands; tree relative height, relative basal area of larger trees and stand density for middle-aged and maturing stands; and tree relative height and stand density for mature and overmature stands. The models can be used as preliminary sub-components for elaboration of a new individual tree based growth simulator.

Experiments for alternative management of forest reserves: effects of partial cutting on stem growth and mortality of large oaks

Although protected forests are usually kept as free of human disturbance as possible, careful cutting may favour biodiversity in such areas. However, the use of heavy machinery during cutting operations may have a negative impact on protected forests. The large oaks ( Quercus spp.) found in many temperate nature reserves have a rich associated biodiversity. In 25 conservation forests in Sweden, the basal area growth and mortality of 250 large oaks (31–110 cm DBH) were compared between plots that were partially cut to promote the growth and survival of oaks and undisturbed plots. Each forest had one treatment plot (1 ha) and one undisturbed reference plot (1 ha) with similar levels of canopy cover. In 2002–2003, about 25% of the basal area was harvested in treatment plots, thereby increasing canopy openness from 14% to 33%. Cutting increased the mean relative basal area growth of large oaks (49% by plot, 22% by tree) after four seasons (P = 0.026). However, in nine forests, the growth rate was not higher in the treated plot than in the reference plot. Mortality, apparently due to cutting, was recorded only in one forest, where 18 large oaks died. Tree condition (percentage of dead large branches in crown) was the best (negative) predictor of growth rate, and openness around oak crown was also a (positive) predictor. Partial cutting favoured the growth of oaks and may be recommended, but a “hands-off” policy is also effective for these conservation forests.

Selective cutting of woody species in a Mexican tropical dry forest: Incompatibility between use and conservation

A major challenge of forest management is to maintain the biodiversity and integrity of the forests while at the same time satisfying human needs through productive activities. While selective extraction of natural resources has less severe consequences on biodiversity and ecosystem function than complete removal of vegetation, such consequences need to be evaluated in detail. “Varas” or stems cut from small trees of tropical dry forests (TDF) in the Pacific Coast of Mexico have been used as plant support stakes in horticultural fields (mainly tomato crops) since the middle of the last century. In this study, we evaluated the effects of selective cutting of plant support stakes on the diversity of woody vegetation of a TDF in northwestern Mexico. Stakes were cut by local harvesters before our assessment of cutting effects. In each of three cutting treatments (T 0 = uncut, T 1 = one cut event, and T 2 = two cut events), we established three sampling plots each consisting of ten 50 m × 2 m parallel transects. All woody plants (stems ≥1.0 cm diameter at 1.3 m height, DBH) were identified and measured on each transect. Species richness ( S) decreased as the number of cuts increased (T 0 = 65 species, T 1 = 50 species, and T 2 = 38 species). The Simpson ( C) and the Shannon ( H′) diversity indices, as well as the rarefaction curves and non-parametric estimates of diversity (Chao1 and ACE) confirmed this tendency of change. Comparison of dominance–diversity curves showed that the woody plant community loses equitability with every additional stake cutting event. The total number of stake providing species did not vary notably across treatments (T 0 = 8 species, T 1 = 9 species, and T 2 = 7 species), but four species reduced their dominance considerably in T 2, while Croton septemnervius, the most used species, increased its abundance and relative basal area with each additional stake harvest, reaching a representation of more than 59% of total number of stems in T 2. The reduction in species diversity, changes in patterns of dominance, and the proliferation of species associated to disturbed sites suggest that current practices of selective cutting require adjustments to make this forest management application more consistent with local conservation of woody plant species diversity and community structure.

Growth–mortality relationships as indicators of life‐history strategies: a comparison of nine tree species in unmanaged European forests

Forest succession depends strongly on the life history strategies of individual trees. An important strategic element is the ability to survive unfavourable environmental conditions that result in strongly reduced tree growth. In this study, we investigated whether the relationship between growth and mortality differs among tree species and site conditions. We analysed 10 329 trees of nine tree species (Picea abies, Taxus baccata, Fagus sylvatica, Tilia cordata, Carpinus betulus, Fraxinus excelsior, Quercus robur, Betula spp. and Alnus glutinosa) from unmanaged forests of Europe: the continental Białowieża forest (Poland) and several oceanically influenced Swiss forest reserves. For each species, we calculated a set of flexible logistic regression models with the explanatory variables growth (as measured by relative basal area increment), tree size and site. We selected the species‐specific model with the highest goodness‐of‐fit and calculated its discriminatory power (area under the receiver operating characteristic curve, AUC) and calibration measures. Most models achieved at least a good discriminatory power (AUC&gt;0.7) and the AUC ranged from 0.62 to 0.87; calibration curves did not indicate any overfitting. Almost all growth–mortality relationships differed among species and sites, i.e. there is no universal growth–mortality relationship. Some species such as F. excelsior showed reduced survival probabilities for both unfavourable and very good growth conditions. We conclude that the growth–mortality relationships presented here can contribute to the life‐history classification of trees and that they should also help to improve projections of forest succession models.

The woodland vegetation of the Katavi-Rukwa ecosystem in western Tanzania

We describe tree diversity, forest community composition and vegetation structure in dry forest miombo woodland in the Katavi-Rukwa ecosystem of western Tanzania. Tree diversity was high (45 families, 117 genera, 229 species) and concentrated in the Fabaceae (30 genera, 73 species). A strong majority (75%) of 19,481 sampled trees were aggregated in just 12 genera spread among 11 families, with individuals in the genera Grewia (17.42%), Markhamia (13.20%) and Combretum (13.13%) dominating abundance. Assessing dominance in terms of a combined importance value (IV300, summed relative abundance, basal area and frequency), showed Terminalia sericea, Combretum adenogonium, and C. colinum as the dominant tree species. Thus, woodlands in this region are atypical of the miombo biome in which it is embedded with only six of fifty 0.1 ha quantitative plots dominated by species in one of the classic miombo genera ( Brachystegia, Julbernardia, or Isoberlinia). Ordination of data from these 50 plots revealed a diffuse structure of communities. Moreover, trees were found to be spatially clumped within, as well as among, plots. By documenting how the Katavi-Rukwa ecosystem is comprised of a patchwork of locally dominant common trees intermixed with a diverse assemblage of less common species, which have few specific associations with particular dominants, our study begins to fill an important gap in understanding composition and structure of dry forests that still occupy so much of southern-central Africa.