Spatial distribution patterns of two predominant emergent trees in a tropical rainforest in Sarawak,Malaysia

Spatial distribution patterns of two emergent tropical rainforest tree species (Dryobalanops aromatica & D. lanceolata) were examined in where they were dominant (17–20% of total basal area of canopy trees) in Sarawak, East Malaysia. Newly established seedlings (< 2 years old) were restricted to areas < 40 m from mother trees for both species, suggesting a limited seed dispersal. Seedling (< 1 cm in dbh) density was highest around conspecific adults ( 30 cm in dbh). Negative spatial patterns were observed between larger juveniles (1–5 cm in dbh) and conspecific adults for both species; the most dense populations of sapling (1–5 cm in dbh) and poles (5–30 cm in dbh) were found at a distance of 15–20 m from the nearest conspecific adult. Seedlings of both species were distributed randomly with respect to light conditions evaluated by a forest floor diffuse site factor and a canopy closure index. Saplings of both species, and poles of D. lanceolata, were distributed under more open conditions than expected from spatially random distributions, and from average light conditions of all species of the same size classes. Possible mechanisms for the observed distribution patterns and intermediate canopy dominance of Dryobalanops were discussed from the viewpoints of gap-dynamics and distance-dependent mortality.     

High tree alpha-diversity in Amazonian Ecuador

In a 1 ha square plot of terra firme forest at 260 m elevation in Amazonian Ecuador, all trees with diameter at breast height (dbh) 5 cm were studied. There were 1561 individuals, 473 species, 187 genera and 54 families. Of these, 693 individuals, 307 species, 138 genera and 46 families had a dbh 10 cm. This is the highest number of tree species ever recorded for a tropical rain forest sample of this size. In both dbh classes, the most species-rich families were: Fabaceae sensu lato (including Mimosaceae and Caesalpiniaceae), Lauraceae and Sapotaceae; the most species-rich genera, were Pouteria, Inga and Protium. The vertical space was partitioned among species: 166 species were found only in the 5–10 dbh cm class and were mostly sub-canopy treelets, and 307 species with dbh 10 cm were mostly large canopy trees.     

Effects of fire and selective logging on the tree species composition of lowland dipterocarp forest in East Kalimantan, Indonesia

Tree species composition (diameter at breast height (dbh) 10 cm) was studied in primary, selectively logged and heavily burnt forests in East Kalimantan, Indonesia. The number of trees, tree species, and the Fishers's- diversity index were determined for the first 15 years (burnt forest) and 25 years (selectively logged forest) after disturbance. Additionally the population structure of six common and typical Macaranga pioneer tree species was compared through time between selectively logged, burnt and primary forest. Both selectively logged and burnt forest showed a significant reduction in number of trees and tree species per surface area directly after disturbance. Fire especially affected dominant tree species, while for selective logging the opposite was observed. In selectively logged forest the number of trees, tree species and the Fishers's- index reached pre-disturbance levels within c. 15 years. For burnt forest, only the number of trees recovered to pre-disturbance levels. The number of tree species stayed constant after disturbance, while the Fishers's- index decreased. The six studied Macaranga pioneer tree species seedlings were present in all forest types. Their density seems to be unrelated to light levels in the forest understorey but strongly related to the number of mature parent trees. Their sapling densities were strongly related to light levels in the forest understorey. The studied Macaranga species formed an important part of both under- and over-storey in burnt forest 15 years after disturbance, while they were almost absent in the understorey and only moderately common in the overstorey of selectively logged forest.     

Structure,diversity, and regeneration of tropical dry deciduous forest of northern India

This study examined the impact of disturbance on the pattern of diversity, forest structure and regeneration of tree species in the Vindhyan dry tropical forest of India. A total of 1500 quadrats distributed over five, 3-ha permanent plots in five sites, differing in degree of disturbance, were used to enumerate and measure the tree species. A total of 65 species with 136,983 individuals were enumerated in the total 15-ha area for stems 30 cm height. The number of species and number of stems ranged from 12 to 50 and 8063–65331 per 3-ha area. The number of species and stems for trees 10 cm dbh ranged from 3 to 28 species, with a mean value of 16 species ha^–1, and from 16 to 477 stems, with a mean value of 256 stems ha^–1, respectively. The adult based PCA ordination indicated uniqueness of sites in terms of species composition and habitat characteristics. PCA ordination also showed uniqueness of sites in terms of seedling composition, but the seedling and adult distributions were not spatially associated. The distinct species composition at the different sites and at the two life-cycle stages on the same site is indicative of marked spatio-temporal dynamics of the dry tropical forest. The density–diameter semi-logarithmic curves ranged from a near linear to an overall concave appearance with a limited plateau in the mid-diameter ranges. The -diversity and its components decreased with increasing disturbance intensity, reflecting enhanced utilization pressure with increasing disturbance. The site-wise and species-wise regression analyses of the number of individuals in different stages of the species revealed that both the level of disturbance and the nature of species strongly affect the regeneration. In conclusion, although the forest is relatively species-poor, the differential species composition on different sites and the temporal dynamics lend a unique level of diversity to the tropical dry deciduous forest.     

Structure,composition and species diversity in an altitude-substrate matrix of rain forest tree communities on Mount Kinabalu,Borneo

We studied forest structure, composition and tree species diversity of eight plots in an environmental matrix of four altitudes (700, 1700, 2700 and 3100 m) and two types of geological substrates (ultrabasic and non-ultrabasic rocks) on Mount Kinabalu, Borneo. On both substrate series, forest stature, mean leaf area and tree species diversity (both 4.8 cm and 10 cm diameter at breast height [dbh]) decreased with altitude. The two forests on the different substrate series were similar at 700 m in structure, generic and familial composition and tree species diversity, but became dissimilar with increasing altitude. The decline in stature with altitude was steeper on the ultrabasic substrates than on the non-ultrabasic substrates, and tree species diversity was generally lower on ultrabasic substrates than on non-ultrabasic substrates at 1700 m. The forests on non-ultrabasic substrates at higher altitudes and those on ultrabasic substrates at the lower altitudes were similar in dbh versus tree height allometry, mean leaf area, and generic and familial composition at 1700 m. These contrasting patterns in forest structure and composition between the two substrate series suggested that altitudinal change was compressed on the ultrabasic substrates compared to the non-ultrabasic substrates. Tree species diversity was correlated with maximum tree height and estimated aboveground biomass, but was not with basal area, among the eight study sites. We suggest that forests with higher tree species diversity are characterized by greater biomass allocation to height growth relative to trunk diameter growth under more productive environment than forests with lower tree species diversity.     

Tree species distribution in canopy gaps and mature forest in an area of cloud forest of the Ibitipoca Range,south-eastern Brazil

The tree community of both canopy gaps and mature forest was surveyed in a 5 ha plot of cloud forest in the Ibitipoca Range, south-eastern Brazil, aiming at: (a) comparing the tree community structure of canopy gaps with that of three strata of the mature forest, and (b) relating the tree community structure of canopy gaps with environmental and biotic variables. All saplings of canopy trees with 1–5 m of height established in 31 canopy gaps found within the plot were identified and measured. Mature forest trees with dbh 3 cm were sampled in four 40×40 quadrats laid on the four soil sites recognised in the local soil catena. All surveyed trees were identified, measured and distributed into three forest strata: understorey (<5 m of height), sub-canopy (5.1–15 m) and canopy (15.1–30 m). The following variables were obtained for each gap: mode of formation, age, soil site, slope grade, size, canopy openness and abundance of bamboos and lianas. A detrended correspondence analysis indicated that the tree community structure of gaps in all soil sites was more similar to that of the mature forest understorey, suggesting that the bank of immatures plays an important role in rebuilding the forest canopy and that gap phases may be important for understorey shade-tolerant species. There was evidence of gap-dependence for establishment for only one canopy tree species. Both canonical correspondence analysis and correlation analysis demonstrated for a number of tree species that the distribution of their saplings in canopy gaps was significantly correlated with two variables: soil site and canopy openness. The future forest structure at each gap is probably highly influenced by both the present structure of the adjacent mature forest and the gap creation event.     

Demography and matrix analysis on a natural Pterocarya rhoifolia population developed along a mountain stream

The population structures and dynamics of a dominant riparian canopy species, Pterocarya rhoifolia (Juglandaceae), were analyzed based on the census data collected for the 7 years from 1989 through 1996. A study plot was established over an environmental gradient that included the lower hill-slope, river terrace, and low-level floodplain of a riparian area within a 2.8-ha cool-temperate forest stand. Spatial analyses of the demographic data showed that there were significant differences in recruitment, growth, and death processes among the three habitats. The slope and terrace habitats were the severest for the pre-reproductive stage and recruitment process, respectively. A topographically combined projection matrix was constructed for the life-history processes of the three subpopulations, which clearly revealed that the floodplain and terrace subpopulations constituted the mainland source populations, whereas the slope subpopulation was an island sink population. The whole Pterocarya population linked by seed flow showed an increase in population size (λ=1.052). The elasticity analysis showed that the sum of the elasticity values was zero, 0.14, and 0.85 in the slope, terrace and floodplain subpopulations, respectively. This fact clearly indicates that the role of the floodplain subpopulation as a source population is six times as large as that of the terrace subpopulation. Electronic Publication     

Tree species diversity in small, tropical riparian forest fragments in Belize, Central America

Tree species diversity was measured in a network of very small galleryforests within the Mountain Pine Ridge savanna in Belize. Research focussed onforest patches smaller than 1 ha in size (micro-forests) and linearstrips of trees along creeks lacking interior core zones with low understoreylight levels (tree thickets). Twenty-five micro-forests and 51 tree thicketsites were sampled throughout the savanna. A total of 144 morphospecies 5cm dbh (106 in micro-forests and 117 in tree thickets) werefound, which represents 1/5 of the approximately 700 native tree species in Belize.Most (85.3%) of the species encountered are typically found in tropical rainforests and few are restricted to savanna or riparian environments. Speciesaccumulated at a much faster rate in micro-forests than in tree thickets. Onlyone species, the palm Acoelorraphe wrightii, was extremelyabundant, accounting for almost 30% of all stems. Many of the species werepresent in very low densities: 19% of all species found in micro-forests and 42%of those found in tree thickets had on average one or fewer stems per hectare. Alarge proportion of species were also found infrequently across the landscape,being present in only 36% of micro-forests and at 52% of tree thicket sites. Theresults indicate that networks of very small forest patches can contain highnumbers of species and could therefore contribute to the maintenance of regionalbiodiversity.     

Diversity and structure of tropical rain forest of Tutuila,American Samoa: effects of site age and substrate

We report tree community diversity, guild composition, and forest structure from three 1.2 ha (100 m × 120 m) permanent forest research plots on Tutuila, American Samoa, an isolated volcanic island in the South Pacific Ocean. Plots were established in three habitat types of lowland hill forest: two in mature tracts that differed in substrate type (talus vs non-talus), and a third in a 30–40 year-old abandoned plantation on non-talus soil. We encountered a total of 57 tree species 10 cm dbh. Richness was similar across sites, but composition differed substantially. We were able to classify with confidence 24 tree species into four distinct guilds based on forest-type preference: early successional or persistent successional (disturbed forest), generalist (no preference), or mature-phase. Sample size limitations or interactions between site age and substrate precluded categorization of all species. Thirty-eight percent (9/24) of the tree species were successional, a result which contrasts sharply with data from (formerly) continental forest in Panama. Spatial distributions of 33 species revealed 17 species exhibiting clumping or hyperdispersion (i.e., regular spacing) in at least one site. Possible non-anthropogenic mechanisms promoting clumping in the plots were (a) topography (edaphic), (b) gap affiliation, (c) inefficient or altered patterns of propagule dispersal, and (d) lack of natural seedling predators. Forest structure differed across site type, with stem densities highest in regenerating forest; conversely, regenerating forest had the lowest basal areas. Steep talus forest sequestered the most carbon (344.3 Mg ha^–1), and secondary forest sustained only 42% of levels found in talus forest (145.5 Mg ha^–1). Mature forest on non-talus soil sequestered the majority of carbon in mid-sized trees (30–50 cm dbh). Future assessments of land-use cover and biomass will provide for a complete estimate of the carbon budget of Tutuila. Finally, the results of this study suggest that conservation of the native fauna is essential in retaining the potential for regeneration of native forest after large-scale disturbance.     

Two decades of compositional and structural change in deciduous old-growth forests of Indiana,USA

Aims Using a network of permanent plots, we determined how multiple old-growth forests changed over an 18–19-year period at a state-wide scale. This examination of change allowed us to assess how the compositional and structural stability of each forest varied with site characteristics (topography, physiography and productivity) and stochastic disturbance.Methods In 2011, we resampled 150 plots distributed across five old-growth hardwood forests in Indiana, USA that were originally sampled in 1992–1993. Within each plot, we relocated and remeasured the diameter at breast height (dbh) of all trees (≥10.0cm) present during the 1992–1993 sample, which allowed us to track their individual fates through time for growth and mortality calculations. Trees that grew to ≥10.0cm dbh since plot establishment were designated as ingrowth. The dbh and species of all saplings (stems ≥2.0cm but <10.0cm dbh) were also recorded. For each forest, we calculated density (stems ha^-1), basal area (BA; m 2 ha^-1) and importance value (relative density + relative BA)/2) of trees by species. For saplings, density per ha was calculated by species for each forest. We also calculated annual mortality rate (AMR) for three diameter classes (10–29.9, 30–59.9 and ≥60cm) and species richness (S), evenness (E) and Shannon–Weiner diversity (H?) for the tree and sapling layers. Differences between years were compared for each forest using paired t -tests and Wilcoxon signed rank tests.Important findings Although we observed commonality in changes across some sites, our results suggest that these forests differ in their rates and trajectories of change. Changes in total stand BA and density varied across sites and were influenced by past disturbance and mortality rates. We observed a general increase in the overstory dominance of Acer saccharum coupled with a general decrease in the dominance of Quercus section Lobatae (red oak group) species. Mortality of overstory trees present in 1992–1993 ranged from 27% to 49% over the study period (mean AMR 1.6–3.7%). Most sites experienced greater mortality of early and mid-successional species, but one site experienced heavy mortality of Fagus grandifolia, a shade-tolerant late-successional species. Shade tolerant species, A. saccharum in particular, dominated the sapling layer at most sites. However, recruitment of this species into larger size classes did not occur uniformly across all sites and the species was comparatively uncommon at one site. Overall, our results suggest that old-growth remnants, even within a single state, cannot be viewed as equivalent units with regard to research or management. Stochastic disturbance events and surrounding land use may have amplified effects on small scattered remnants. Therefore, continued monitoring of these rare, but biologically important forests is critical to their long-term management and protection.     

Effects of Logging on the Diversity of Lianas in a Lowland Tropical Rain Forest in Hainan Island, South China

Lianas are an integral part of tropical forest ecosystems, which usually respond strongly to severe disturbances, such as logging. To compare the effect of different logging systems on the lianas diversity in tropical rain forest, we recorded all lianas and trees ≥1 cm dbh in two 40-year-old forest sites after clear cutting (CC) and selective cutting (SC) as well as in an old-growth (OG) lowland tropical rain forest on Hainan Island in south China. Results showed that OG contained fewer liana stems and lower species richness (stems: 261, richness: 42 in 1 ha) than CC (606, 52) and SC (727, 50). However, OG had the highest Fisher's α diversity index (17.3) and species richness per stem (0.184). Species composition and dbh class distribution of lianas varied significantly with different logging systems. The mean liana dbh in OG (22.1 cm) were higher than those in CC (7.0 cm) and SC (10.4 cm). Stem twining was the most frequent climbing mechanism represented in the forest, as shown by the greatest species richness, abundance, basal area, and host tree number with this mechanism. The percent of host tree stems ≥4 cm dbh hosting at least one liana individual in SC (39%) was higher than CC (23%) and OG (19.5%). Large host trees (dbh≥60 cm) were more likely to be infested by lianas in SC and OG. Our study demonstrated that logging disturbance could significantly change the composition and structure of liana communities in the lowland tropical rain forest of south China.
     

Tree species diversity and forest structure in relation to microtopography in a tropical freshwater swamp forest in French Guiana

Diversity of tree association and forest structure were analysed in relation to microtopography and flooding intensity in a tropical freshwater swamp forest in the Sinnamary river basin, French Guiana. A 530-m-long vegetation transect was established through a hummock-hollow terrain. Nine 10 m× 50 m sample plots, perpendicular to the main transect, were located so that each was as microtopographically uniform as possible. Trees with dbh (diameter at 1.3 m) 10 cm were censused in all plots and trees with 2 cm dbh < 10 cm in three plots. Sixty tree species belonging to 39 genera and 30 families were recorded. The study area was divided into low and high sites according to microtopography and flooding intensity. According to the Czekanowski similarity matrix, the tree association in low, most frequently flooded, sites differed from that in the high sites under intermediate or low flooding intensity. The low sites had higher stand density and lower species richness than the high sites. Trees with dbh 10 cm in low sites were small and stand basal area (SBA) was about the same in low (69.6 m² ha^–1) and high (64.3 m² ha^–1) sites. The low areas were dominated by Pterocarpus officinalis (38% of stems with dbh 10 cm and 36% of SBA) and Malouetia tamaquarina (26 and 15%). Diospyros guianensis (13.4% of stems with dbh 10 cm and 6.1% of SBA), a Caraipa sp. (14.0 and 7.9%), Lecythis corrugata (6.6 and 3.5%) and emergent Caryocar microcarpum (0.9 and 13.9%) were abundant in high sites. Nodulated legume trees, P. officinalis, Hydrochorea corymbosa and Inga disticha, comprised 44% of stems in the low sites. The abundant nodulation suggests that symbiotic dinitrogen fixation may be an adaptation to N-depleted waterlogged soils. Other adaptive responses were litter accumulation between the buttresses of P. officinalis, which formed hummocks above surface water, and clonal growth habit of M. tamaquarina, which resulted in formation of monospecific groves in low sites.     

Tree species richness complementarity, disturbance and fragmentation in a Mexican tropical montane cloud forest

Tropical montane cloud forest exhibits great heterogeneity in speciescomposition and structure over short geographic distances. In central Veracruz,Mexico, the conservation priority of seven cloud forest fragments was assessedby considering differences in woody plant species richness and complementarityof species among sites, forest structure, tree mortality, and timber andfirewood extraction as indicators of anthropogenic disturbance. Densities oftrees 5 cm dbh (360–1700 trees/ha) weredifferent among the sites, but basal area (35.3–89.3m²/ha) did not differ among fragments. The number of dead trees rangedfrom 10–30 to 170–200 trees/ha. The fragments'species composition was different but complementary. The Morisita–Hornindex indicated low similarity between fragments. A non-parametric estimator ofspecies richness indicated that more sampling effort would be necessary tocomplete the inventory (15 additional trees and two understory shrub species).Unfortunately, most of the fragments are threatened with deforestation. The numberof cut trees was similar among sites (0–15 cut trees/0.1 ha).Sites with immediate need for conservation were close to settlements, with highnumbers of cut trees and no legal protection. The selected sites represent thevariety of situations that exist in the region. Given the high complementarityobserved between fragments, a regional conservation approach will be required topreserve the last repositories of part of the tremendous biodiversity of theonce continuous forest in this region.     

Mixed-Forest Species Establishment in a Monodominant Forest in Central Africa: Implications for Tropical Forest Invasibility

Background

Traits of non-dominant mixed-forest tree species and their synergies for successful co-occurrence in monodominant Gilbertiodendron dewevrei forest have not yet been investigated. Here we compared the tree species diversity of the monodominant forest with its adjacent mixed forest and then determined which fitness proxies and life history traits of the mixed-forest tree species were most associated with successful co-existence in the monodominant forest.

Methodology/Principal Findings

We sampled all trees (diameter in breast height [dbh]≥10 cm) within 6×1 ha topographically homogenous areas of intact central African forest in SE Cameroon, three independent patches of G. dewevrei-dominated forest and three adjacent areas (450–800 m apart). Monodominant G. dewevrei forest had lower sample-controlled species richness, species density and population density than its adjacent mixed forest in terms of stems with dbh≥10 cm. Analysis of a suite of population-level characteristics, such as relative abundance and geographical distribution, and traits such as wood density, height, diameter at breast height, fruit/seed dispersal mechanism and light requirement–revealed after controlling for phylogeny, species that co-occur with G. dewevrei tend to have higher abundance in adjacent mixed forest, higher wood density and a lower light requirement.

Conclusions/Significance

Our results suggest that certain traits (wood density and light requirement) and population-level characteristics (relative abundance) may increase the invasibility of a tree species into a tropical closed-canopy system. Such knowledge may assist in the pre-emptive identification of invasive tree species.     

Diversity,structure and dynamics of a gallery forest in central Brazil

The structure and dynamics of approximately 64 ha of undisturbed gallery forest were studied over six years. Trees from 31 cm gbh (c. 10 cm dbh) were measured every three years from 1985. They were in 151 (10×20 m) permanent plots in the Gama forest in the Federal District of Brazil. Natural regeneration (individuals under 31 cm gbh) was measured in subplots (of 2×2 m, 5×5 m and 10×10 m) within the 200 m² plots. The total tree flora (gbh31 cm) consisted of 93 species, 81 genera and 44 families in 1985. The Leguminosae, Myrtaceae and Rubiaceae were the families richest in number of species. Most individuals and species were under 45 cm diameter and 20 m high while the maximum diameter per species ranged from 30 to 95 cm. The density structure of trees and natural regeneration was similar, in which the densities of c. 80% of the species represented less than 1% of the total density. The periodic mean annual diameter increment for trees from 10 cm dbh, was c. 0.25 cm/year. Variability was high with coefficients of variation c. 100% or more. The Gama community may maintain tree diversity and structure in undisturbed conditions. Regeneration of c. 80% of the species was found in the establishing phase (poles); the diameter structure was typical of native forests with the number of individuals decreasing with increasing size classes and showing little change over the six years; recruitment compensated for the mortality of most of the abundant species. The soils in Gama gallery forest were dystrophic with high aluminium content. Multivariate analysis suggested the stream, natural gaps and edges as the main causes of floristic differentiation at the community level.     

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.     

Tree diversity in primary forest and different land use systems in Central Sulawesi,Indonesia

We studied the tree communities in primary forest and three different land use systems (forest gardens, ca. 5-year-old secondary forests, cacao plantations) at 900–1200 m elevation in the environs of Lore Lindu National Park, Central Sulawesi. The primary forests had ca. 150 tree species 10 cm diameter at breast height (dbh) per hectare, which is unusually high for forests at this elevation in southeast Asia. Basal area in the primary forest was 140 m² ha^–1, one of the highest values ever recorded in tropical forests worldwide. Tree species richness declined gradually from primary forest to forest gardens, secondary forests, and cacao plantations. This decline was paralleled by shifts in tree family composition, with Lauraceae, Meliaceae, and Euphorbiaceae being predominant in primary forests, Euphorbiaceae, Rubiaceae and Myristicaeae dominating in the forest gardens and Euphorbiaceae, Urticaceae, and Ulmaceae in the secondary forests. Cacao plantations were composed almost exclusively of cacao trees and two species of legume shade trees. Forest gardens further differed from primary forests by a much lower density of understorey trees, while secondary forests had fewer species of commercial interest. Comparative studies of birds and butterflies demonstrated parallel declines of species richness, showing the importance of trees in structuring tropical forest habitats and in providing resources.     

Floristic, structural and seed bank diversity of a dry Afromontane forest at Mafai, central Tanzania

Flora, vegetation and seed bank were studied in a dry Afromontane forest in the Kondoa Irangi Hills, Tanzania with the objective to obtain information necessary for the promotion of conservation of this forest, which is rapidly degenerating due to human pressure. A preliminary checklist of 104 vascular plants occurring in the forest is provided. Based on 27 plots, each of 400m², the forest had the following ecological features: mean tree density 408 stems·ha^–1; basal area 66.56m²·ha^–1; Shannon and Wiener diversity 2.6406; evenness 0.7585 and species richness 31 tree species per 1.08ha. The seed bank was dominated by woody species, including mature forest tree species, and had several species in common with the standing vegetation. The forest contains species that are phytogeographically linked to Madagascan, Western and Southern African floras and also species disjunctly distributed in this forest and the Eastern Arc Mountains of Tanzania. Correspondence Analysis of tree species based on size classes showed that the timber species had declining populations, indicating the possibility of genetic erosion, while other species showed expanding or interrupted populations. Some DBH-size classes (e.g. 145.0–189.9cm) have disappeared from the forest, presumably due to their selective removal. We recommend detailed integrated floristic and faunistic studies of the forest, targeting the ecologically sensitive indicators of habitat change such as orchids, birds, reptiles and amphibians. Finally, a proposal to conserve the forest under a community-based forest conservation scheme is put forward.     

Canopy dieback in lower montane forests of Alto Urimán,Venezuelan Guayana

Canopy dieback in patches was discovered in an otherwise undisturbed very humid lower montane forest on a quartzitic sandstone plateau of the middle Caroní river basin, Venezuela. The patches vary in size from about 0.1 to 2 ha (50 to 700 upper story dead trees per ha). Preliminary inventories were carried out at 3 selected sites comparing 4 dieback patches (M) with adjacent not affected (V) forests. In the M plots, 40 to 61% of all trees with dbh 10 cm were dead. They consisted mostly (81–100%) of the endemic tree species Terminalia quintalata of the upper story (dbh > 20 to 60 cm, height up to 30 m), which is much sparser in the V stands. Data on stand structure and species composition are presented. They seem to indicate a spatial variation in the density of Terminalia quintalata, but also of other dominant species, and reproductive problems of Terminalia, which is hardly present in the diameter classes below 10 cm dbh. V and M stands grow on similar soils with a perched high water table. They are practically free of clay and rich in humus. The exchange complex is dominated by H⁺. Low pH and dilution of base cations represent the main chemical stress factors. Different concepts of the dieback process are discussed, including cyclic reproductive patterns, nutrient sequestering and drought frequency.     

Population structure and dynamics oi Juniperus excelsa in Balouchistan,Pakistan

Abstract. 60 monospecific stands of Juniperus excelsa were sampled at four locations in Balouchistan. Density, basal area and height of individuals were recorded. Soils were analysed for selected physical and chemical characteristics and the degree of disturbance due to logging and burning was noted. The density of juniper trees (> 6 cm dbh) ranged from 56 to 332 stems / ha (average 174 stems / ha). Higher densities were recorded for relatively undisturbed stands and on west facing slopes. Density of seedlings and saplings (< 6 cm dbh) was strongly correlated with tree density and tree basal area. Among the edaphic variables CaC0₃ was correlated with juniper density and basal area. Diameter distributions within stands were mostly skewed and unimodal with gaps appearing in large size classes. The male to female ratio was close to 1. Cross-sections of 16 trees were used to determine age and growth rate. Number of rings in trees with 20 to 30 cm dbh ranged from 95 to 221 (x = 160 ± 38). Diameter and age were not related. Mean annual diameter increment ranged from 6 to 16 yr / cm x = 10 ± 3 yr / cm). It is concluded that size class gaps and low seedling / sapling densities are the consequence of anthropogenic disturbance.