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. standlevel 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 a median -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.Additional co-authors: T. F. Domingues, M. Drescher, P. M. Fearnside, M. B. Franca, N. M. Fyllas, G. Lopez-Gonzalez, A. Hladik, N. Higuchi, M. O. Hunter, Y. Iida, K. A. Salim, A. R. Kassim, M. Keller, J. Kemp, D. A. King, J. C. Lovett, B. S. Marimon, B. H. Marimon-Junior, E. Lenza, A. R. Marshall, D. J. Metcalfe, E. T. A. Mitchard, E. F. Moran, B.W. Nelson, R. Nilus, E. M. Nogueira, M. Palace, S. Patino, K. S.-H. Peh, M. T. Raventos, J. M. Reitsma, G. Saiz, F. Schrodt, B. Sonke, H. E. Taedoumg, S. Tan, H. Woll, and J. Lloy
Aboveground tropical tree biomass and carbon storage estimates commonly ignore tree height (<i>H</i>). We estimate the effect of incorporating <i>H</i> on tropics-wide forest biomass estimates in 327 plots across four continents using 42 656 <i>H</i> and diameter measurements and harvested trees from 20 sites to answer the following questions: <br><br> 1. What is the best <i>H</i>-model form and geographic unit to include in biomass models to minimise site-level uncertainty in estimates of destructive biomass? <br><br> 2. To what extent does including <i>H</i> estimates derived in (1) reduce uncertainty in biomass estimates across all 327 plots? <br><br> 3. What effect does accounting for <i>H</i> have on plot- and continental-scale forest biomass estimates? <br><br> The mean relative error in biomass estimates of destructively harvested trees when including <i>H</i> (mean 0.06), was half that when excluding <i>H</i> (mean 0.13). Power- and Weibull-<i>H</i> models provided the greatest reduction in uncertainty, with regional Weibull-<i>H</i> models preferred because they reduce uncertainty in smaller-diameter classes (≤40 cm <i>D</i>) 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 <i>H</i> reduces errors from 41.8 Mg ha<sup>−1</sup> (range 6.6 to 112.4) to 8.0 Mg ha<sup>−1</sup> (−2.5 to 23.0). For all plots, aboveground live biomass was −52.2 Mg ha<sup>−1</sup> (−82.0 to −20.3 bootstrapped 95% CI), or 13%, lower when including <i>H</i> 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 <i>H</i>. After accounting for variation in <i>H</i>, 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 km<sup>2</sup> and store 285 Pg C (estimate including <i>H</i>), then applying our regional relationships implies that carbon storage is overestimated by 35 Pg C (31–39 bootstrapped 95% CI) if <i>H</i> is ignored, assuming that the sampled plots are an unbiased statistical representation of all tropical forest in terms of biomass and height ...
-(Phenological behavior of woody species in a "cerrado" sensu stricto of Brasília, DF). In this study we followed the phenology of 19 woody species of a cerrado sensu stricto in the IBGE Ecological Reserve (15º55'06"-15º57'57" S and 47º51'22"-47º54'07" W), in Brasília, Federal District, Brazil. Phenological observations were made every fortnight between August 2000 and October 2003. The vegetation studied is a seasonal semi-deciduous wood savanna, where a hot wet season (from October through to April) is followed by a cool dry season (from May through to September). Vegetation canopy is reduced during the dry season and foliage cover reaches a minimum of 50% at the end of the dry season. Even though new leaves and flowers appear along the year, their production is intensified during the transition between the dry and wet seasons. According to the vegetative phenology, four groups were identified: four evergreen species with continuous growth, five evergreen species with seasonal growth, eight brevideciduous species and two deciduous species. The evergreen species with continuous growth produced leaves along the wet season, while the remaining groups produced leaves more intensely at the end of the dry season. Fruit maturation of autochoric and anemochoric species occurred within the dry season; zoochoric species dispersed seeds mainly during the wet season. Soil water availability seemed not to have restricted leaf production and reproduction of most species since the peak of flushing and blooming was at the end of the dry season. However, endogenous factors such as leaf longevity and internal water balance, as well as exogenous factors such as evaporative demand and irradiation seem to influence the phenological patterns observed in this vegetation.
Background:The zone of transition (ZOT) between the Cerrado and the Amazon forest in southern Amazonia represents a unique and rapidly shrinking area due to land-use change. Aims: To compare the dynamics and above-ground biomass of vegetation located in the ZOT with core Amazon forest and to determine how ZOT dynamics differ within vegetation types for different tree diameter classes. Methods: Censuses of trees were conducted in seven plots in monodominant forest, semi-deciduous seasonal forest, gallery forest, cerrado sensu stricto and cerradão, in north-eastern Mato Grosso, Brazil from 1996 to 2010, including data for the 2005 drought year. Separate analyses of stem dynamics and biomass were carried out for two different diameter (d) classes: 5 ≤ d < 10 cm and d ≥ 10 cm. Results: For trees with d ≥ 10 cm the average mortality rate was 2.8% year −1 , with an estimated above-ground dry biomass of 210 Mg ha −1 . Trees with 5 ≤ d < 10 cm constituted only a small fraction of the total biomass store (ca. 10 Mg ha −1 ) and had a mortality rate of 7.4% year −1 and recruitment of 6.5% year −1 . Overall, mortality and recruitment in the ZOT were greater than in core Amazonian forests (1-2% year −1 ). Conclusions:The distinct vegetation formations of the southern Amazon ZOT are markedly more dynamic than core Amazonian forest. Continued long-term monitoring throughout the region is required to assess whether they also respond differently to climate change.
Tropical tree height-diameter (<i>H:D</i>) 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 <i>H</i> and <i>D</i> measurements encompassing 283 sites in 22 tropical countries. Utilising this database, our objectives were: <br><br> 1. to determine if <i>H:D</i> relationships differ by geographic region and forest type (wet to dry forests, including zones of tension where forest and savanna overlap).<br><br> 2. to ascertain if the <i>H:D</i> relationship is modulated by climate and/or forest structural characteristics (e.g. stand-level basal area, <i>A</i>).<br><br> 3. to develop <i>H:D</i> allometric equations and evaluate biases to reduce error in future local-to-global estimates of tropical forest biomass. <br><br> Annual precipitation coefficient of variation (<i>P</i><sub>V</sub>), dry season length (<i>S</i><sub>D</sub>), and mean annual air temperature (<i>T</i><sub>A</sub>) emerged as key drivers of variation in <i>H:D</i> relationships at the pantropical and region scales. Vegetation structure also played a role with trees in forests of a high <i>A</i> being, on average, taller at any given <i>D</i>. 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 <i>H:D</i> relationships, but with trees in the forests of much of the Amazon Basin and tropical Australia typically being shorter at any given <i>D</i> than their counterparts elsewhere. <br><br> The region-environment-structure model with the lowest Akaike's information criterion and lowest deviation estimated stand-level <i>H</i> across all plots to within a median –2.7 to 0.9% of the true value. Some of the plot-to-plot variability in <i>H:D</i> 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 <i>D</i>. Pantropical and continental-level models provided only poor estimates of <i>H</i>, especially when the roles of climate and stand structure in modulating <i>H:D</i> allometry were not simultaneously taken into account
-(Floristic composition and structure of woody vegetation in a cerrado rupestre, Cocalzinho de Goiás, Goiás State, Brazil). A vegetation survey of the woody species (at least 5 cm of trunk diameter at 30 cm above the ground) was conducted in a savanna on rocky soil (cerrado rupestre) in Cocalzinho de Goiás municipality, Goiás State, Brazil (15°48' S and 48°45' W). The objective was to compare the structure characteristics and the floristics of cerrado rupestre with those features found in cerrado stricto sensu areas occuring on deep soils in Central Brazil. The sample consisted in 1.0 hectare (ten plots, 20 × 50 m) in cerrado rupestre. The cerrado rupestre studied showed structural similarities with the physiognomy of open cerrado (cerrado ralo). The richness and the species diversity are similar with other Brazilian savanna (cerrado stricto sensu areas of Brazil Central). The floristic composition revealed species predominantly from other physiognomies from the cerrado stricto sensu and to a lesser extent, species from forest formations from the bioma and endemics from this rocky environment. The floristic richness and diversity is similar to other savanna areas of Central Brazil. In structural terms, the density and basal area are similar to values found in open cerrado vegetation. The limiting environmental conditions, mainly edaphics, do not result in expressive changes in floristic composition, richness, and species diversity, but promoted reduction in density and basal area of the wood species in the cerrado rupestre studied.Key words -Central Brazil, Cerrado, phytosociology, rocky soil environment RESUMO -(Composição florística e estrutura da vegetação arbustivo-arbórea em um cerrado rupestre, Cocalzinho de Goiás, Goiás). Foi realizado um levantamento da vegetação arbutivo-arbórea (indivíduos com diâmetro a 30 cm do solo ≥ 5 cm), em 1,0 hectare de cerrado rupestre (dez parcelas de 20 × 50 m), localizado em Cocalzinho de Goiás, Goiás, Brasil (15°48' S e 48°45' W). O objetivo foi avaliar e comparar as relações florísticas e as características estruturais deste cerrado sobre afloramentos rochosos com aquelas encontradas nos estudos já realizados em áreas de cerrado sentido restrito sobre solos profundos, localizados no Brasil Central. A composição florística do cerrado rupestre estudado é formada predominantemente por espécies das fitofisionomias do cerrado sentido restrito e em menor contribuição por espécies das formações florestais do bioma e espécies endêmicas de ambientes rupestres. A riqueza e a diversidade de espécies estão dentro dos limites normalmente encontrados para as áreas de cerrado sentido restrito do Brasil Central. Em termos estruturais, a densidade e área basal se assemelham aos valores registrados na subdivisão fitofisionômica de cerrado ralo. As condições ambientais limitantes, principalmente edáficas, não resultaram em mudanças expressivas na composição florística, riqueza e diversidade de espécies, mas refletiram em redução da densidade e área basal da vegetação arbustivo-arbó...
Abstract. Through interpretations of remote-sensing data and/or theoretical propositions, the idea that forest and savanna represent "alternative stable states" is gaining increasing acceptance. Filling an observational gap, we present detailed stratified floristic and structural analyses for forest and savanna stands located mostly within zones of transition (where both vegetation types occur in close proximity) in Africa, South America and Australia. Woody plant leaf area index variation was related to tree canopy cover in a similar way for both savanna and forest with substantial overlap between the two vegetation types. As total woody plant canopy cover increased, so did the relative contribution of middle and lower strata of woody vegetation. Herbaceous layer cover declined as woody cover increased. This pattern of understorey grasses and herbs progressively replaced by shrubs as the canopy closes over was found for both savanna and forests and on all continents. Thus, once subordinate woody canopy layers are taken into account, a less marked transition in woody plant cover across the savanna–forest-species discontinuum is observed compared to that inferred when trees of a basal diameter > 0.1 m are considered in isolation. This is especially the case for shrub-dominated savannas and in taller savannas approaching canopy closure. An increased contribution of forest species to the total subordinate cover is also observed as savanna stand canopy closure occurs. Despite similarities in canopy-cover characteristics, woody vegetation in Africa and Australia attained greater heights and stored a greater amount of above-ground biomass than in South America. Up to three times as much above-ground biomass is stored in forests compared to savannas under equivalent climatic conditions. Savanna–forest transition zones were also found to typically occur at higher precipitation regimes for South America than for Africa. Nevertheless, consistent across all three continents coexistence was found to be confined to a well-defined edaphic–climate envelope with soil and climate the key determinants of the relative location of forest and savanna stands. Moreover, when considered in conjunction with the appropriate water availability metrics, it emerges that soil exchangeable cations exert considerable control on woody canopy-cover extent as measured in our pan-continental (forest + savanna) data set. Taken together these observations do not lend support to the notion of alternate stable states mediated through fire feedbacks as the prime force shaping the distribution of the two dominant vegetation types of the tropical lands.
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