Seeing Central African forests through their largest trees
Bastin, J.F. ; Barbier, N. ; Réjou-Méchain, M. ; Fayolle, A. ; Gourlet-Fleury, S. ; Maniatis, D. ; Haulleville, T. De; Baya, F. ; Beeckman, H. ; Beina, D. ; Couteron, P. ; Chuyong, G. ; Dauby, G. ; Doucet, J.L. ; Droissart, V. ; Dufrêne, M. ; Ewango, C.E.N. ; Gillet, F. ; Gonmadje, C.H. ; Hart, T. ; Kavali, T. ; Kenfack, D. ; Libalah, M. ; Malhi, Y. ; Makana, J.R. ; Pélissier, R. ; Ploton, P. ; Serckx, S. ; Sonké, B. ; Stevart, T. ; Thomas, D.W. ; Cannière, C. De; Bogaert, J. - \ 2015
Scientific Reports 5 (2015). - ISSN 2045-2322 - 8 p.
tropical forest - biomass - size - distributions - diversity - dynamics
Large tropical trees and a few dominant species were recently identified as the main structuring elements of tropical forests. However, such result did not translate yet into quantitative approaches which are essential to understand, predict and monitor forest functions and composition over large, often poorly accessible territories. Here we show that the above-ground biomass (AGB) of the whole forest can be predicted from a few large trees and that the relationship is proved strikingly stable in 175 1-ha plots investigated across 8 sites spanning Central Africa. We designed a generic model predicting AGB with an error of 14% when based on only 5% of the stems, which points to universality in forest structural properties. For the first time in Africa, we identified some dominant species that disproportionally contribute to forest AGB with 1.5% of recorded species accounting for over 50% of the stock of AGB. Consequently, focusing on large trees and dominant species provides precise information on the whole forest stand. This offers new perspectives for understanding the functioning of tropical forests and opens new doors for the development of innovative monitoring strategies.
Visualization of the stem water content of two genera with secondary phloem produced by successive cambia through Magnetic Resonance Imaging (MRI)
Robert, E.M.R. ; Schmitz, N. ; Copini, P. ; Gerkema, E. ; Vergeldt, F.J. ; Windt, C.W. ; Beeckman, H. ; Koedam, N. ; As, H. van - \ 2014
The Journal of Plant Hydraulics 1 (2014). - ISSN 2268-4565 - 8 p.
Shrubs and trees with secondary phloem tissue produced by successive cambia mainly occur in habitats characterized by a periodical or continuous lack of water availability. The amount of this secondary phloem tissue in stems of Avicennia trees rises with increasing soil water salinity and decreasing inundation frequency. Hence, increased water storage in secondary phloem tissue produced by successive cambia was put forward to be advantageous in harsh environmental conditions. It was however never tested whether the secondary phloem cells over the entire stem of woody species showing this wood anatomical feature are indeed water-filled as expected. In this preliminary and pioneering study, we use magnetic resonance imaging (MRI) to visualize the stem water content of three species with successive cambia, the mangroves Avicennia marina and A. officinalis and the non-mangrove Bougainvillea spectabilis. Measurements were conducted in living plants. We tested the hypothesis that not only the outermost phloem tissue has high water content but also the secondary phloem tissues over the entire stem from the bark inward to the pith, herewith serving as water storage sites. We can conclude that all secondary phloem tissue of both Bougainvillea and Avicennia has high water contents. This aligns with the contribution of secondary phloem tissue produced by successive cambia to ecological success in conditions of physiological drought. Further study should however be done to understand the mechanisms through which this secondary phloem tissue contributes to the water household of plants in conditions of water shortage.
Conventional tree height-diameter relationships significantly overestimate aboveground carbon stocks in the Central Congo Basin
Kearsley, E. ; Haulleville, T. de; Hufkens, K. ; Kidimbu, A. ; Toirambe, B. ; Baert, G. ; Huygens, D. ; Kebede, Y. ; Defourny, P. ; Bogaert, J. ; Beeckman, H. ; Steppe, K. ; Boeckx, P. ; Verbeeck, H. - \ 2013
Nature Communications 4 (2013). - ISSN 2041-1723
tropical forests - landscape-scale - central-africa - live biomass - land-use - climate - deforestation - emissions - impacts - regions
Policies to reduce emissions from deforestation and forest degradation largely depend on accurate estimates of tropical forest carbon stocks. Here we present the first field-based carbon stock data for the Central Congo Basin in Yangambi, Democratic Republic of Congo. We find an average aboveground carbon stock of 162 +/- 20 Mg C ha(-1) for intact old-growth forest, which is significantly lower than stocks recorded in the outer regions of the Congo Basin. The best available tree height-diameter relationships derived for Central Africa do not render accurate canopy height estimates for our study area. Aboveground carbon stocks would be overestimated by 24% if these inaccurate relationships were used. The studied forests have a lower stature compared with forests in the outer regions of the basin, which confirms remotely sensed patterns. Additionally, we find an average soil carbon stock of 111 +/- 24 Mg C ha(-1), slightly influenced by the current land-use change.
Dendrochronology in the dry tropics: the Ethiopian case
Wils, T. ; Sass-Klaassen, U. ; Eshetu, Z. ; Bräuning, A. ; Gebrenirstos, A. ; Couralet, C. ; Robertson, I. ; Touchan, R. ; Koprowski, M. ; Conway, D. ; Briffa, K.R. ; Beeckman, H. - \ 2011
Trees-Structure and Function 25 (2011)3. - ISSN 0931-1890 - p. 345 - 354.
climate-growth relationships - tree-ring analysis - pterocarpus-angolensis - rhizophora-mucronata - isotope ratios - stable carbon - africa - forests - dynamics - reconstruction
Dendrochronology is developing outside temperate and boreal regions. Over the past decade substantial progress has been made in Mediterranean and wet tropical regions. However, research in dry tropical regions, notably those of sub-Saharan Africa, has remained fragmentary. Here, we try to identify the unique challenges and opportunities of dendrochronology in the dry tropics. First, we briefly review the status of dendrochronology outside temperate and boreal regions with an emphasis on sub- Saharan Africa. Subsequently, we focus upon one of those areas where dendrochronology in the dry tropics is at the forefront of scientific advance: Ethiopia. A detailed review of tree ring studies in the lowlands and highlands highlights the complexity of ring formation and made us identify four major types of growth ring expression: anatomically notdistinct rings, multiple rings per year, annual rings and multiple missing rings. This complex tree growth behaviour is associated with large-scale variations in precipitation regime (unimodal to multimodal) and relatively small-scale variations in tree sensitivity to water availability. Literature results are used to develop a scheme that can be used to predict differences in growth ring formation along gradients in these two factors. Because of the exceptional growth sensitivity of and the importance of local site conditions (topography, biological factors, etc.) for most trees sampled, those growing at the limits of their ecological amplitude are prone to possess multiple rings per year or multiple missing rings. In such circumstances, site selection should not always take place at the limits of the ecological amplitude of a species, but may sometimes have to be diverted to more mesic environments. Successful studies are now appearing, such as those reporting correlations between tree ring chronologies and Blue Nile river flows.
Nature and periodicity of growth rings in two Bangladeshi mangrove species
Chowdhury, Q. ; Schmitz, N. ; Verheyden, A. ; Sass-Klaassen, U. ; Koedam, N. ; Beeckman, H. - \ 2008
Iawa Journal 29 (2008)3. - ISSN 0928-1541 - p. 265 - 276.
avicennia-marina - rhizophora-mucronata - red mangrove - gazi bay - rainfall - phenology - salinity - climate - trees - management
Nature and periodicity of growth rings were investigated in Sonneratia opetala and Heritiera fomes, two Bangladeshi mangrove species. From both species we collected three stem discs in the natural forest reserve of the Sundarbans. In addition, three discs were sampled from plantation-grown S. apetala trees of known age. Sanded stem discs revealed distinct growth rings but no periodic fluctuations in vessel variables (vessel density, vessel diameter, vessel grouping), which were measured at high resolution along a transect from pith to bark. The number of growth rings in plantation-grown S. apetala trees corresponded with the documented tree age, hence strongly suggesting the growth rings to be annual. Within species, the annual nature of the rings was further supported by a good match between the tree-ring series. The similar mean curves of S. apetala and H. fomes, growing at the same site in the Sundarbans, pointed to the presence of an external factor influencing their 1, Growth. A combination of precipitation and temperature was suggested influencing substrate salinity and phenological events. It became evident that tree-ring research in combination with the analysis of vessel patterns is a valuable tool to further investigate the complex interactions between tree growth and site ecology in mangrove forests.