Tree Size Class Distributions Research Articles

Chronic browsing by an introduced mammalian herbivore in a tropical island alters species composition and functional traits of forest understory plant communities

AbstractMammalian herbivores have large‐scale impacts on vegetation, altering structure, and species composition, especially in tropical grasslands and savannas. However, there is limited understanding of the potential impacts of mammalian herbivores in tropical wet forests, where they are typically less abundant. We investigated the effects of an introduced mammalian herbivore chital (Axis axis) on vegetation structure, composition and leaf functional traits of tropical evergreen forests of the Andaman Islands, India. Across seven islands, representing a gradient of herbivore densities, increasing chital presence was associated with decreased understory richness, understory density and adult tree richness, but was not related to adult tree density or size class distributions. We also found a significant decrease in community level leaf palatability traits (specific leaf area decreased and leaf thickness increased) with increasing chital habitat use. This community level shift in leaf trait values was better explained by intraspecific variation in leaf traits across islands rather than changes in species composition. In summary, we show persistent long‐term impacts of an introduced mammalian herbivore on understory tropical tree communities although there is little impact on adult tree communities. Our results also show that functional traits of species can be altered in response to novel herbivory, even at herbivore densities where there are no detectable impacts on adult forest structure or composition. Such altered functional traits may potentially alter ecosystem functioning in these forests even without changes in vegetation structure.Abstract in Hindi is available with online material.

Dependência, pressão e recuperação de recursos florestais no Parque Nacional do Limpopo (Moçambique)

The general perception is that forest resources exploitation can cause the degradation and loss of resources and biodiversity, promoted by landscape fragmentation and pressure over habitats. But such assumption might not be adjusted to situations where long term exploitation by traditional communities is based on management strategies adapted to recovery, adjusting pressure to kept resources available. In this work, we assess the recovery of the Mopane woodlands considering different land use practices and stand development stages on areas explored by local communities. In detail, we want to explore: i) changes on stem size across plant comunities dominated by Mopane (Kirk ex Benth ex J. Leonard); ii) relationships between the variation in stem size across communities and the associated land use practices and vegetation stand development stage. To answer those questions, an inventory was carried out to collect data from 50 temporary circular plots of different sizes spatially nested, covering four stand development stages. Each nested circular plot was composed of a large plot (0.02 ha), an intermediate plot (0.04 ha), and an inner plot (0.01 ha) for counting stems of different DBH. Data was analysed using Excel, Two-Way Indicator Species Analysis (TWINSPAN) and CANOCO, and several parametric and non-parametric tests. TWINSPAN analysis, using stem counts, grouped the 1746 stems from 29 species (with Mopane as one species) into 5 communities and 10 sub-communities, based on indicator species and eigenvalues (level of stability). This study was carried out in the Limpopo National Park (LNP), in Mozambique, a conservation area established in 2001 and part of the Great Limpopo Transfrontier Park (GLTP) since 2002. Acording to the results, population structure (size class distribution of trees) of Mopane communities showed variation related to stand development stage, as expected. The initial stages show good regeneration, indicating that recovery is not hampered by the exploitation regime in use, a critical aspect once ecosystem dynamics of Mopane woodland has a deep influence on the way that local communities manage harvesting of Mopane products for different uses, and traditional uses do also have influence on recovery dynamics. So, management of such resource is critical to ensure sustainable resource use and guarantee provision for future generations. For that, a zonation of Mopane woodlands within the Park, considering different land uses, might enhance a quick system recovery on specific areas and contribute to woodland productivity, good quality products and reduce used areas, promoting habitat conservation.

Assessing fruit production and harvesting effects on Carapa procera DC. population, a threatened oil tree in Burkina Faso, West Africa

The exploitation of non-timber forest products contributes considerably to local livelihoods for subsistence in developing countries. The study aims to assess the structure and fruit production of C. procera natural populations in harvesting and non-harvesting sites and to compare the structure characteristics and fruits yields of the two sites.The study was carried out in Burkina Faso on both, harvesting and non-harvesting sites. Eighty fruits bearing trees (40 per site) were sampled, from each, all the fruits were counted. Dendrometric parameters were measured in 80 plots of 1000 m². In each plot, diameter at breast height (dbh) and total height of trees were measured. Density, basal area, mean diameter and height were computed for each site. Analyses of variance were performed to test differences between sites based on measured variables. Weibull theoretical model was used on size class distribution to analyze trees structure in both sites.The results showed that the production of fruits reaches a mean of 6462.73 ± 4237.51 fruits/ha and 9103.44 ± 7631.88 fruits/ha, respectively in non-harvesting and harvesting site. Significant differences (p < 0.05) were found for tree densities, basal area and tree height between sites with highest values in the harvesting site. The size class distribution of trees showed in both sites the existing of potential regeneration with the dominance of young trees (1 < c < 2) with some survival difficulties during the growth stages. C. procera populations exhibit a high potential of fruit production and natural regeneration but are influenced by pressures impact.

Community structure and regeneration status of Sal (Shorea robusta Gaertn.) forests of Dadeldhura district, Western Nepal

Community structure and regeneration are the determinant factors for the sustainability of forests. The present study aims to: (1) know the community structure and regeneration of Sal (Shorea robusta Gaertn.)-dominated community forests at two developmental stages (age of forests after community management) of Dadeldhura District of western Nepal and (2) know the impacts of management duration on forest regeneration. Vegetation data were collected from 105 square plots (100, 25 and 4 m2) applying a nested quadrat method. Forty-two tree species belonging 34 genera and 20 families and 41 shrub species belonging 35 genera and 24 families were recorded. Sal was the dominant species, while Dipterocarpaceae was the dominant family of the forests. Per hectare, there were 4408 plants, 15.4 m2 basal area, 15,905 seedlings, 1876 saplings and 1287 trees. Seedling, sapling and tree density and size class distribution curve indicate the satisfactory regeneration status of the forest with a stable population. Regeneration was affected by species richness, canopy cover, soil pH and nitrogen. Density and regeneration were higher in the forest at the developmental stage of 20 years than the forest at the developmental stage of 10 years.

How widespread are recruitment bottlenecks in fragmented populations of the savanna tree Banksia marginata (Proteaceae)?

Land clearing of habitat into smaller, isolated remnants is a major driver of plant and animal extinctions globally. In southeastern Australia, once widespread temperate savannas have been subjected to extensive land clearing since European settlement. Some small fragments have persisted, but declines in the dominant trees have been reported, with anecdotal observations of widespread recruitment bottlenecks and seed set failure. To test the hypothesis that populations of Banksia marginata are experiencing widespread recruitment bottlenecks, we examined tree size-class distribution and production of infructescences (cones) of 15 populations on the western plains of Victoria, Australia. We found no evidence of widespread recruitment bottlenecks or a failure to set seeds; most populations were recruiting, though we did find evidence of declining recruitment with population size, suggesting evidence of an Allee effect. The proportion of trees without cones varied between populations; three populations had large numbers of trees (> 40%) lacking mature fertile cones. Managers should focus on minimising threats to seedling survival and augment populations below 100 individuals to improve recruitment and maintain stand persistence in the landscape.

Tree Diversity, Stand Structure, and Community Composition in an Island Forest of Pulau Perhentian Besar, Terengganu

The Perhentian Island Archipelago comprising of 11 small islands is located in the state of Terengganu are among the biodiversity rich localities in Peninsular Malaysia. Perhentian Besar with approximately 867 hectares is one of the inhabited island and become the centre of tourism besides Perhentian Kecil. Island is well known as a place for many endemic and endangered living organism as previously demonstrated on other similar forested islands in Southeast Asia. However, there is little attention and effort of protection has been received by the terrestrial ecosystems that reside nearby the coastal. Thus, the present study investigates on tree diversity, stand structure and community composition in the island of Perhentian Besar, Terengganu. Forest plot of 0.5 hectare was established to analyze the floristic composition of tree taxa. The plot was divided into 10 subplots of 25m x 20m. All trees with 5cm diameter breast height (dbh) and above were tagged, measured for dbh size, recorded and identified. Voucher specimens were taken for further verification purposes. A total of 102 tree species were recorded comprising of 28 families and 65 genera. Rubiaceae had the highest number of species (11 species) and with regards to relative dominance, Shorea leprosula (Dipterocarpaceae) gave the highest importance value index (IVi) for species with a value of 8.45%. The Shannon-Weiner Diversity Index (H’) was considered high in the present study with 3.94 (H’max = 4.62) and the Evenness Index (E) value of 0.85 indicated that all species in the present study are almost equally abundant. The forest stand structure had a reverse J-shaped curve for tree size-class distributions as frequently observed in many natural forests, which indicated that the forest stand in the study site had a good recruitment patterns and also a main feature of matured forest in Peninsular Malaysia. The present study will help us to understand the pattern of tree species composition, diversity and forest ecosystem dynamic in Pulau Perhentian Besar.

Structure, composition and regeneration of miombo woodlands within harvested and unharvested areas

Production of tobacco by small holder farmers in Zimbabwe after the year 2000 land reform programme impacted woodlands due to the widespread use of fuel wood instead of coal for tobacco curing, but impacts have been rarely quantified. We assessed the effect of fuel wood harvesting for tobacco curing on structure, composition and diversity in harvested and unharvested miombo woodlands in the central watershed of Zimbabwe. Tree size class distributions provide demographic information on regeneration and recovery from disturbances. Vegetation structure and plant species composition were assessed in thirty 20 × 20 m plots in each site. Tree basal area, canopy cover and height were significantly higher in the less disturbed unharvested compared with harvested site. Species composition differed between harvested and unharvested sites, with higher diversity in the harvested compared with unharvested site. Trees had reverse-J-shaped size class distribution curves for both stem diameter and height at the harvested site and bimodal distributions with fairly large densities in larger size classes at the unharvested site. Recruitment and regeneration were higher in the harvested than unharvested site. Our findings show that harvesting fuel wood for tobacco curing has negative effects on tree structure, but not yet the diversity of the miombo woodland, however the latter will likely negatively impact tree species favoured for harvesting over the medium-long term. When species composition was compared using NMDS ordination, the harvested and unharvested plots were distinctly separated. Because of the rotational time for miombo woodlands of >25 years, continuous harvesting of the woodland may permanently keep the trees small, failing to provide sufficient wood for tobacco curing. Therefore, there is need for the consideration of alternative or supplementary sources of energy such as solar, with a zero deforestation in the production chain of tobacco in the whole miombo eco-region.

The Current Forest Status and Plant Species Diversity in Sekelemariam State Forest, Ethiopia

The aim of this study was to explore the characteristic of structure; species composition and species diversity in Sekelemariam State forest to enhance the forest’s plant biodiversity conservation and management practices through minimize the illegal deforestation practices by the local communities. The floristic composition and relative dominance of trees were studied in 66 (10m x 20 m) sample plots. A systematic sampling of plot of (10 m x 20 m) in each site was done to take vegetation samples. The data of tree individuals have served to give insight into the stand density, basal area, and frequency number of DBH class ranges. There were a large number of DBH class ranges but there were low DBH values. The species composition of Sekelemariam State forest is low rich and diversity with moderate density. The dominant species of trees were Croton macrostachys, Cupressus lusitanica Mil and Albizzia schimperiana, respectively. The maximum and minimum IVI values of trees were 34.97 and 0.66 of Croton macrostachys and Terminalia schimperiana , respectively. The density of vegetation in study area increases with increasing of DBH and height classes; this implies that the predominance of plantation tree individuals as the local community had been logging large sized natural tree species. The DBH size class distribution of trees in Sekelemariam State forest is shown to be on L-shape curve, which is high abundance of small trees. Keywords: Species diversity, Species richness, DBH, Diversity Indices. DOI : 10.7176/JBAH/9-24-02 Publication date: December 31 st 2019

A spatio-temporal analysis of canopy dynamics and intra-stand competition in a riparian forest, south-eastern Australia

Widespread high stem density stands of riparian River Red Gum (Eucalyptus camaldulensis Dehnh.) (RRG) result from land management legacies in inland riverine ecosystems of Australia. These stands generally exhibit reduced structural complexity with many slender stems and few large trees. Higher competition for water among populations of RRG in dense stands may affect stand-level canopy condition, particularly when water is scarce. We investigated whether stem density and water availability affected canopy condition dynamics in RRG forests of Murray Valley National Park, New South Wales. We collected eight years of satellite derived Foliage Projective Cover (FPC) data (Landsat 5 TM (2008–2011) and Landsat 8 OLI (2013–2016)) encompassing some of the driest and wettest years on record in south-eastern Australia. We used Generalised Linear Mixed Effects Modelling to investigate the drivers of RRG canopy condition at the plot-level. Canopy condition dynamics were driven by different sets of variables under different climatic phases, with water availability at the plot and regional scale, as well as climate, being the primary drivers of trends in RRG canopy condition. Stem density was not found to be a significant predictor of overall RRG stand canopy condition, although results suggested that individuals in higher density stands have lower canopy condition on average. Live basal area (LBA) was positively correlated with FPC in all climatic phases, and stands with high LBA tended to have a greater abundance of large trees than low LBA stands. Research efforts should be made towards integrating site-specific tree size class distributions with remotely sensed metrics to guide management for biodiversity. Findings from this study provide a baseline understanding against which ecological restoration actions can be evaluated and a foundation upon which an ongoing monitoring program can be developed.

Facultative and Obligate Trees in a Mesic Savanna: Fire Effects on Savanna Structure Imply Contrasting Strategies of Eco-Taxonomic Groups.

Fire is a major determinant of savanna tree communities and, as such, manipulation of fire frequency is an important management tool. Resolving the effects of fire management on tree size class distributions can help managers predict and plan for short-term ecological and economic outcomes, reveal different strategies by which woody plants cope with frequent fire, and help us predict vegetation changes under future fire scenarios. Savanna structure and size class distribution are strongly influenced by the ability of suppressed tree resprouts to escape stem death by frequent fire. A widespread assumption is that resprouts have an imperative to escape fire to reach sexual maturity in the canopy and thereby ensure long-term species viability. We use a census of Australian mesic savanna tree communities subjected to annual, triennial, and fire exclusion (unburnt) fire treatments to ask how fire frequency affects size class distributions within and between eco-taxonomic groups of species. Total tree densities did not significantly differ, but were highest in the triennial (7,610 ± se 1,162 trees ha−1) and unburnt fire treatments (7,051 ± se 578 trees ha−1) and lowest in the annual fire treatment (6,168 ± se 523 trees ha−1). This was caused by increased sapling densities in the triennial and unburnt fire treatments, predominantly of Acacia and pantropical genera. Eucalypts (Eucalyptus and Corymbia spp.) dominated the canopy across all fire treatments indicating relatively greater success in recruiting to larger sizes than other species groups. However, in the sub-canopy size classes eucalypts co-dominated with, and in some size classes were outnumbered by, pantropicals and Acacia, regardless of fire treatment. We hypothesize that such results are caused by fundamental differences in woody plant strategies, in particular sexual reproduction, that have not been widely recognized in Australian savannas.

One shape fits all, but only in the aggregate: Diversity in sub‐stand scale diameter distributions

AbstractQuestionsTo what extent are the sub‐stand size class distributions at the neighbourhood patch scale masked at the stand level via spatial smoothing? What are the implications for naturalness assessment of obscuring, at the stand level, structures that arise from endogenous processes at the neighbourhood scale?LocationElborz Mountains, south of the Caspian Sea, Iran.MethodsNatural uneven‐aged old‐growth Oriental beech (Fagus orientalis) forest subject to fine‐scale disturbances was stem‐mapped in a 1.2‐ha plot of live trees &gt;7.5 cm DBH; neighbourhoods were delineated across multiple scales using the tree‐centred floating neighbourhood approach of spatial tessellation to connect trees to their natural neighbours. Cluster analysis was used to identify an optimal number of recurring diameter distribution types (DDT) based on the proportion of trees in each of the five size classes. The richness of DDTs was assessed and the extent of DDTs was modelled as a function of tree size.ResultsThe number of member trees and spatial extent increased with neighbourhood scale. While the stand‐level tree size class distribution exhibited a rotated sigmoid shape, the nine most distinct DDTs were characterized by four different distribution shapes (negative exponential, increasing‐q, rotated sigmoid and unimodal) and varied considerably in the abundance of trees in different size classes. Each individual tree contributed to at least three of the nine DDTs, which were nonetheless spatially distinct and varied in extent with size class composition. As expected, all metrics exhibited spatial smoothing (i.e., increasing homogeneity with increasing scale) as small, heterogeneous tree neighbourhoods were expanded into larger neighbourhoods with more similar average composition, which converged on a rotated sigmoid shape at the broadest scale.ConclusionsThe stand‐level rotated sigmoid distribution reflected spatial smoothing across more heterogeneous fine‐scale tree neighbourhood patches. Further studies are needed to assess if a better measure of natural forest structure may be the diversity of sub‐stand structures and the contribution of individual trees to that diversity, rather than an aggregated metric that averages across the hallmark heterogeneity of neighbourhood dynamics.

Improving predictions of tropical forest response to climate change through integration of field studies and ecosystem modeling.

Tropical forests play a critical role in carbon and water cycles at a global scale. Rapid climate change is anticipated in tropical regions over the coming decades and, under a warmer and drier climate, tropical forests are likely to be net sources of carbon rather than sinks. However, our understanding of tropical forest response and feedback to climate change is very limited. Efforts to model climate change impacts on carbon fluxes in tropical forests have not reached a consensus. Here, we use the Ecosystem Demography model (ED2) to predict carbon fluxes of a Puerto Rican tropical forest under realistic climate change scenarios. We parameterized ED2 with species-specific tree physiological data using the Predictive Ecosystem Analyzer workflow and projected the fate of this ecosystem under five future climate scenarios. The model successfully captured interannual variability in the dynamics of this tropical forest. Model predictions closely followed observed values across a wide range of metrics including aboveground biomass, tree diameter growth, tree size class distributions, and leaf area index. Under a future warming and drying climate scenario, the model predicted reductions in carbon storage and tree growth, together with large shifts in forest community composition and structure. Such rapid changes in climate led the forest to transition from a sink to a source of carbon. Growth respiration and root allocation parameters were responsible for the highest fraction of predictive uncertainty in modeled biomass, highlighting the need to target these processes in future data collection. Our study is the first effort to rely on Bayesian model calibration and synthesis to elucidate the key physiological parameters that drive uncertainty in tropical forests responses to climatic change. We propose a new path forward for model-data synthesis that can substantially reduce uncertainty in our ability to model tropical forest responses to future climate.

Patterns of vegetation composition across levels of canopy disturbance in temperate forests of west Himalaya, India

Abstract This study analyses the impacts of canopy disturbance on vegetation compositional attributes of two characteristic temperate forests (i.e., mixed broad-leaf and banj-oak forests) in west Himalayan part of India. Following the standard approaches, quantitative information on compositional attributes of forest vegetation was generated and analyzed. Considerable changes in these attributes were revealed across different levels of canopy disturbance in both forests. In particular, tree density and total basal area (TBA) exhibited significant decline from undegraded to degraded stands. Among others, seedling and sapling density of mixed broad-leaf forest was affected adversely by increased level of canopy disturbance. However, herb density in this forest increased significantly with increasing levels of disturbance; the same was not true for banj-oak forest. A significant decline in relative frequency and density of native herbaceous species was apparent towards degraded stands, implying that the disturbed sites in both forests created an opportunity for the establishment and proliferation of non-natives. However, with significant increase in relative density of non-native herbs, the degraded stands of banj-oak forest emerged as critically vulnerable to non-native proliferation. The patterns of tree size class distribution in both forests also exhibited certain trends across canopy disturbance, which suggested possible future changes in composition. In particular, the patterns of common tree associates (i.e., Myrica esculenta and Rhododendron arboreum) in banj-oak forest and Pinus roxburghii in mixed broad-leaf forest were indicative of likely compositional changes in near future. The study concludes that: (i) compositional attributes of both mixed broad-leaf and banj-oak forests were sensitive to increasing levels of canopy disturbance, (ii) mixed broad-leaf forest exhibited greater sensitivity to canopy disturbance at recruitment levels, (iii) increased canopy disturbance led to establishment and proliferation of non-native species in the herbaceous layer of both forests, and (iv) banj-oak forest exhibited high vulnerability to non-native proliferation at degraded stage.

Multi-scale heterogeneity in vegetation and soil carbon in exurban residential land of southeastern Michigan, USA.

Exurban residential land (one housing unit per 0.2-16.2ha) is growing in importance as a human-dominated land use. Carbon storage in the soils and vegetation of exurban land is poorly known, as are the effects on C storage of choices made by developers and residents. We studied C storage in exurban yards in southeastern Michigan, USA, across a range of parcel sizes and different types of neighborhoods. We divided each residential parcel into ecological zones (EZ) characterized by vegetation, soil, and human behavior such as mowing, irrigation, and raking. We found a heterogeneous mixture of trees and shrubs, turfgrasses, mulched gardens, old-field vegetation, and impervious surfaces. The most extensive zone type was turfgrass with sparse woody vegetation (mean 26% of parcel area), followed by dense woody vegetation (mean 21% of parcel area). Areas of turfgrass with sparse woody vegetation had trees in larger size classes (> 50cm dbh) than did areas of dense woody vegetation. Using aerial photointerpretation, we scaled up C storage to neighborhoods. Varying C storage by neighborhood type resulted from differences in impervious area (8-26% of parcel area) and area of dense woody vegetation (11-28%). Averaged and multiplied across areas in differing neighborhood types, exurban residential land contained 5240±865g C/m2 in vegetation, highly sensitive to large trees, and 13 800±1290g C/m2 in soils (based on a combined sampling and modeling approach). These contents are greater than for agricultural land in the region, but lower than for mature forest stands. Compared with mature forests, exurban land contained more shrubs and less downed woody debris and it had similar tree size-class distributions up to 40cm dbh but far fewer trees in larger size classes. If the trees continue to grow, exurban residential land could sequester additional C for decades. Patterns and processes of C storage in exurban residential land were driven by land management practices that affect soil and vegetation, reflecting the choices of designers, developers, and residents. This study provides an example of human-mediated C storage in a coupled human-natural system.

Short-term Dynamics and the Effects of Biotic and Abiotic Factors on Plant Physiognomic Groups in a Hurricane-impacted Lower Montane Tropical Forest

We assessed the short-term effects of biotic (density, plant size) and abiotic factors (light), on the dynamics of physiognomically different plant groups (palms, tree ferns, lianas, and trees) in a hurricane-impacted tropical wet montane forest, John Crow Mountains, Jamaica. All plants ≥2 cm (dbh) found within 45, 25 × 25 m permanent sample plots (2.8125 ha), established according to a randomized block design along an elevation gradient, were tagged and measured (dbh) in 2006 and re-assessed in 2012 after Hurricane Dean (2007). Hemispheric light was measured in 2007 and 2008. Tree and liana size class distributions changed due to high mortality in the smallest size classes and their densities declined; however, palm and tree fern density remained unchanged. The dynamics of trees were only related to tree fern and liana dynamics (e.g., tree mortality was negatively related to liana recruitment etc.). Although pre- and posthurricane light was related to palm density and the density of the other plant groups, respectively, there were no significant changes in light. Tree survivorship increased with increasing dbh while posthurricane light and overall density influenced the growth and survivorship of tree species. Species importance value did not change, suggesting that direct regeneration may be the model of forest recovery following this small-scale disturbance. Over the short term, tree species showed life history trade-offs that aid species coexistence after this moderate/low disturbance event. Our study highlights that hurricanes with low impacts can have differential short- and possibly long-term effects on different plant groups.

A Comparison of Airborne Laser Scanning and Image Point Cloud Derived Tree Size Class Distribution Models in Boreal Ontario

Airborne Laser Scanning (ALS) metrics have been used to develop area-based forest inventories; these metrics generally include estimates of stand-level, per hectare values and mean tree attributes. Tree-based ALS inventories contain desirable information on individual tree dimensions and how much they vary within a stand. Adding size class distribution information to area-based inventories helps to bridge the gap between area- and tree-based inventories. This study examines the potential of ALS and stereo-imagery point clouds to predict size class distributions in a boreal forest. With an accurate digital terrain model, both ALS and imagery point clouds can be used to estimate size class distributions with comparable accuracy. Nonparametric imputations were generally superior to parametric imputations; this may be related to the limitation of using a unimodal Weibull function on a relatively small prediction unit (e.g., 400 m2).

Disentangling drivers of tree population size distributions

There are pressing needs to evaluate and manage the effects of biological invaders in forest ecosystems in the face of long-term changes and anthropogenic influences on these systems. Hence, disentangling the effects of different drivers is critical for understanding the relative importance of biological invaders on shaping future forest structure and composition, and how management of these invaders changes forest ecosystem functioning. We evaluated the effects of major drivers of changes in tree population structure in New Zealand forests using a national grid of permanent vegetation plots and long-term (>15year) ungulate exclosures. The long-term effects of disturbance and other drivers leave imprints in tree population dynamics and size class structure. For example, the effects of natural disturbance are expected to have different effects from those of browsing or folivorous animals. We quantified variation in tree size class distributions for common tree species, and plant functional groups defined by mammal diet selection, in 986 permanent forest plots and in 88 paired ungulate exclosure and control plots. Our analyses revealed that: (i) strong changes in size class distributions have occurred in recent decades, (ii) tree species selected or preferred by invasive ungulates (primarily red deer) demonstrate particularly strong shifts, (iii) inclusion of climate or soil variables into statistical models of exclosure effects on size class distributions were overwhelmed by temporal changes and effects of forest stand successional stage. These findings demonstrate that the effects of invasive herbivores can be distinguishable from other drivers such as disturbance or successional stage, and suggests that these changes will ultimately be manifested in altered forest community composition and ecosystem processes.

Assessing stand water use in four coastal wetland forests using sapflow techniques: annual estimates, errors and associated uncertainties

Forests comprise approximately 37% of the terrestrial land surface and influence global water cycling. However, very little attention has been directed towards understanding environmental impacts on stand water use (S) or in identifying rates of S from specific forested wetlands. Here, we use sapflow techniques to address two separate but linked objectives: (1) determine S in four, hydrologically distinctive South Carolina (USA) wetland forests from 2009–2010 and (2) describe potential error, uncertainty and stand-level variation associated with these assessments. Sapflow measurements were made from a number of tree species for approximately 2–8 months over 2 years to initiate the model, which was applied to canopy trees (DBH > 10–20 cm). We determined that S in three healthy forested wetlands varied from 1.97–3.97 mm day−1 or 355–687 mm year−1 when scaled. In contrast, saltwater intrusion impacted individual tree physiology and size class distributions on a fourth site, which decreased S to 0.61–1.13 mm day−1 or 110–196 mm year−1. The primary sources of error in estimations using sapflow probes would relate to calibration of probes and standardization relative to no flow periods and accounting for accurate sapflow attenuation with radial depth into the sapwood by species and site. Such inherent variation in water use among wetland forest stands makes small differences in S (<200 mm year−1) difficult to detect statistically through modelling, even though small differences may be important to local water cycling. These data also represent some of the first assessments of S from temperate, coastal forested wetlands along the Atlantic coast of the USA. Copyright © 2014 John Wiley & Sons, Ltd.

To What Extent Do Protected Areas Determine the Conservation of Native Flora? A Case Study in the Sudanian Zone of Burkina Faso

Natural vegetation contributes significantly to the daily needs of local people especially in the developing countries. This exerts a high pressure on freely accessible natural savannas and jeopardizes the conservation of protected areas. In Burkina Faso, conservation measures, such as the creation of protected forests, have been taken to safeguard the remaining indigenous vegetation. However, little is known about the effectiveness of these protected areas in conserving biodiversity. This study compared the diversity and structural characteristics of the vegetation communities in protected and unprotected areas in the Sudanian zone of Burkina Faso. A total of 208 species representing 41 families and 145 genera were found. Significant differences were found between the species richness in the north Sudanian sector for tree savannas and in the south Sudanian sector for the shrub savannas, tree savannas, savanna woodlands, and the woodlands of land use types. All tree size-class distributions in each vegetation type formed a reverse J-shaped curve, indicating vegetation dominated by juvenile individuals. Similarity in tree species composition between management regimes was found to be low, which reflects differences in habitat conditions, disturbance, and topography. Urgent measures are needed to ensure effective and efficient management and conservation of biodiversity in the protected areas of Burkina Faso.

Regeneration pattern and size-class distribution of indigenous woody species in exotic plantation in Pugu Forest Reserve, Tanzania.

Pugu Forest Reserve is among coastal forests in Tanzania which is highly degraded through exploitation. To conserve the forest, part of natural forest was cleared and established exotic plantation to provide forest resource needs for the nearby residents. However, the regeneration pattern of indigenous trees in the exotic plantation was not monitored. It was aimed at assessing diversity, population structure, size class distribution and natural regeneration pattern of indigenous trees in exotic tree plantation. Vegetation data was collected using nested plots established along transects on both exotic tree plantation and the natural forest. The diameter size classes for most trees were less than 25 cm with poor recruitment at lower size classes implying an unstable plant population structure. Significant difference existed on the abundance of indigenous plant species between those in exotic tree plantation and the natural forest. However, the indigenous plant species regenerated successfully in exotic tree plantation as it occurred in the natural forest. Conclusively, establishing exotic plantation through clearing natural forests required monitoring as a management strategy because indigenous woody plants recovered through natural regeneration and outcompeted exotic trees in the plantation. Key words: Pugu, exotic, indigenous, plantation, sizeclasses, regeneration.