Aim: To test the extent to which the vertical structure of tropical forests is determined by environment, forest structure or biogeographical history. Location: Pan-tropical. Methods: Using height ...and diameter data from 20,497 trees in 112 non-contiguous plots, asymptotic maximum height (H AM ) and height—diameter relationships were computed with nonlinear mixed effects (NLME) models to: (1) test for environmental and structural causes of differences among plots, and (2) test if there were continental differences once environment and structure were accounted for; persistence of differences may imply the importance of biogeography for vertical forest structure. NLME analyses for floristic subsets of data (only/excluding Fabaceae and only/excluding Dipterocarpaceae individuals) were used to examine whether family-level patterns revealed biogeographical explanations of cross-continental differences. Results: H AM and allometry were significantly different amongst continents. H AM was greatest in Asian forests (58.3 ± 7.5 m, 95% CI), followed by forests in Africa (45.1 ± 2.6 m), America (35.8 ± 6.0 m) and Australia (35.0 ± 7.4 m), and height—diameter relationships varied similarly; for a given diameter, stems were tallest in Asia, followed by Africa, America and Australia. Precipitation seasonality, basal area, stem density, solar radiation and wood density each explained some variation in allometry and H AM yet continental differences persisted even after these were accounted for. Analyses using floristic subsets showed that significant continental differences in H AM and allometry persisted in all cases. Main conclusions: Tree allometry and maximum height are altered by environmental conditions, forest structure and wood density. Yet, even after accounting for these, tropical forest architecture varies significantly from continent to continent. The greater stature of tropical forests in Asia is not directly determined by the dominance of the family Dipterocarpaceae, as on average non-dipterocarps are equally tall. We hypothesise that dominant large-statured families create conditions in which only tall species can compete, thus perpetuating a forest dominated by tall individuals from diverse families.
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Aboveground tropical tree biomass and carbon storage estimates commonly ignore tree height (H). We estimate the effect of incorporating H on tropics-wide forest biomass estimates in 327 plots across ...four continents using 42 656 H and diameter measurements and harvested trees from 20 sites to answer the following questions: 1. What is the best H-model form and geographic unit to include in biomass models to minimise site-level uncertainty in estimates of destructive biomass? 2. To what extent does including H estimates derived in (1) reduce uncertainty in biomass estimates across all 327 plots? 3. What effect does accounting for H have on plot- and continental-scale forest biomass estimates? The mean relative error in biomass estimates of destructively harvested trees when including H (mean 0.06), was half that when excluding H (mean 0.13). Power- and Weibull-H models provided the greatest reduction in uncertainty, with regional Weibull-H models preferred because they reduce uncertainty in smaller-diameter classes (≤40 cm D) that store about one-third of biomass per hectare in most forests. Propagating the relationships from destructively harvested tree biomass to each of the 327 plots from across the tropics shows that including H reduces errors from 41.8 Mg ha−1 (range 6.6 to 112.4) to 8.0 Mg ha−1 (−2.5 to 23.0). For all plots, aboveground live biomass was −52.2 Mg ha−1 (−82.0 to −20.3 bootstrapped 95% CI), or 13%, lower when including H estimates, with the greatest relative reductions in estimated biomass in forests of the Brazilian Shield, east Africa, and Australia, and relatively little change in the Guiana Shield, central Africa and southeast Asia. Appreciably different stand structure was observed among regions across the tropical continents, with some storing significantly more biomass in small diameter stems, which affects selection of the best height models to reduce uncertainty and biomass reductions due to H. After accounting for variation in H, total biomass per hectare is greatest in Australia, the Guiana Shield, Asia, central and east Africa, and lowest in east-central Amazonia, W. Africa, W. Amazonia, and the Brazilian Shield (descending order). Thus, if tropical forests span 1668 million km2 and store 285 Pg C (estimate including H), then applying our regional relationships implies that carbon storage is overestimated by 35 Pg C (31–39 bootstrapped 95% CI) if H is ignored, assuming that the sampled plots are an unbiased statistical representation of all tropical forest in terms of biomass and height factors. Our results show that tree H is an important allometric factor that needs to be included in future forest biomass estimates to reduce error in estimates of tropical carbon stocks and emissions due to deforestation.
Tropical tree height-diameter (H:D) relationships may vary by forest type and region making large-scale estimates of above-ground biomass subject to bias if they ignore these differences in stem ...allometry. We have therefore developed a new global tropical forest database consisting of 39 955 concurrent H and D measurements encompassing 283 sites in 22 tropical countries. Utilising this database, our objectives were: 1. to determine if H:D relationships differ by geographic region and forest type (wet to dry forests, including zones of tension where forest and savanna overlap). 2. to ascertain if the H:D relationship is modulated by climate and/or forest structural characteristics (e.g. stand-level basal area, A). 3. to develop H:D allometric equations and evaluate biases to reduce error in future local-to-global estimates of tropical forest biomass. Annual precipitation coefficient of variation (PV), dry season length (SD), and mean annual air temperature (TA) emerged as key drivers of variation in H:D relationships at the pantropical and region scales. Vegetation structure also played a role with trees in forests of a high A being, on average, taller at any given D. After the effects of environment and forest structure are taken into account, two main regional groups can be identified. Forests in Asia, Africa and the Guyana Shield all have, on average, similar H:D relationships, but with trees in the forests of much of the Amazon Basin and tropical Australia typically being shorter at any given D than their counterparts elsewhere. The region-environment-structure model with the lowest Akaike's information criterion and lowest deviation estimated stand-level H across all plots to within amedian −2.7 to 0.9% of the true value. Some of the plot-to-plot variability in H:D relationships not accounted for by this model could be attributed to variations in soil physical conditions. Other things being equal, trees tend to be more slender in the absence of soil physical constraints, especially at smaller D. Pantropical and continental-level models provided less robust estimates of H, especially when the roles of climate and stand structure in modulating H:D allometry were not simultaneously taken into account.
The Moderate Resolution Imaging Spectroradiometer Vegetation
Continuous Fields (MODIS VCF) Earth observation product is widely used to
estimate forest cover changes and to parameterize vegetation and ...Earth system
models and as a reference for validation or calibration where field data
are limited. However, although limited independent validations of MODIS VCF
have shown that MODIS VCF's accuracy decreases when estimating tree cover in
sparsely vegetated areas such as tropical savannas, no study has yet
assessed the impact this may have on the VCF-based tree cover data used by
many in their research. Using tropical forest and savanna inventory data
collected by the Tropical Biomes in Transition (TROBIT) project, we produce
a series of calibration scenarios that take into account (i) the spatial
disparity between the in situ plot size and the MODIS VCF pixel and (ii) the trees' spatial distribution within in situ plots. To identify if a
disparity also exists in products trained using VCF, we used a similar
approach to evaluate the finer-scale Landsat Tree Canopy Cover (TCC)
product. For MODIS VCF, we then applied our calibrations to areas identified
as forest or savanna in the International Geosphere-Biosphere Programme
(IGBP) land cover mapping product. All IGBP classes identified as “savanna”
show substantial increases in cover after calibration, indicating that the
most recent version of MODIS VCF consistently underestimates woody cover in
tropical savannas. We also found that these biases are propagated in the
finer-scale Landsat TCC. Our scenarios suggest that MODIS VCF accuracy can
vary substantially, with tree cover underestimation ranging from 0 % to 29 %. Models that use MODIS VCF as their benchmark could therefore be
underestimating the carbon uptake in forest–savanna areas and
misrepresenting forest–savanna dynamics. Because of the limited in situ plot
number, our results are designed to be used as an indicator of where the
product is potentially more or less reliable. Until more in situ data are
available to produce more accurate calibrations, we recommend caution when
using uncalibrated MODIS VCF data in tropical savannas.
Extensive areas of the Congo Basin forest are allocated to timber concessionaires. These forests also harbour and support village populations, including indigenous Baka people, who depend on forest ...foods obtained directly from trees (fruits, oils and caterpillars). Most food-producing
tree species are harvested by concessionaires for timber. We documented the availability and abundance of three food tree species around four villages and in two neighboring timber concessions in Cameroon. Data was used to determine the importance of timber concessions as sources of food for
local people to provide a foundation for governance arrangements that consider local needs for foods from timber trees. Discussions with concessionaires revealed that some of them have voluntarily refrained from extracting timber species of interest to villagers for their nontimber products.
This is either to avoid conflict with villagers, or because regulations have been promulgated to safeguard these resources. The interplay between internal village dynamics, regulations and their implementation by forest guards, and the actions of timber concessions create a complex arena for
addressing rights to forest resources. This paper provides information on the accessibility and availability of multiple use timber species as a foundation for negotiations and governance arrangements between concessionaires and local communities.
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To provide an inter-continental overview of the floristics and biogeography of drought-adapted tropical vegetation formations, we compiled a dataset of inventory plots in South America (n=93), Africa ...(n=84), and Asia (n=92) from savannas (subject to fire), seasonally dry tropical forests (not generally subject to fire), and moist forests (no fire). We analysed floristic similarity across vegetation formations within and between continents. Our dataset strongly suggests that different formations tend to be strongly clustered floristically by continent, and that among continents, superficially similar vegetation formations (e.g. savannas) are floristically highly dissimilar. Neotropical moist forest, savanna and seasonally dry tropical forest are floristically distinct, but elsewhere there is no clear floristic division of savanna and seasonally dry tropical forest, though moist and dry formations are separate. We suggest that because of their propensity to burn, many formations termed “dry forest” in Africa and Asia are best considered as savannas. The floristic differentiation of similar vegetation formations from different continents suggests that cross-continental generalisations of the ecology, biology and conservation of savannas and seasonally dry tropical forests may be difficult.
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Craterispermum parvifolium and C. robbrechtianum spp. nov. are described from the Lower Guinea Domain. Detailed descriptions and distribution maps are provided for each species, their conservation ...status is assessed and their taxonomic affinities are discussed. An identification key for the Craterispermum species of the Lower Guinea Domain is given.
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