| 1. |
- Cuni-Sanchez, Aida, et al.
(författare)
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High aboveground carbon stock of African tropical montane forests
- 2021
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 596:7873, s. 536-542
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Tidskriftsartikel (refereegranskat)abstract
- Tropical forests store 40–50per cent of terrestrial vegetation carbon. However, spatial variations in aboveground live tree biomass carbon (AGC) stocks remain poorly understood, in particular in tropical montane forests. Owing to climatic and soil changes with increasing elevation, AGC stocks are lower in tropical montane forests compared with lowland forests. Here we assemble and analyse a dataset of structurally intact old-growth forests (AfriMont) spanning 44 montane sites in 12 African countries. We find that montane sites in the AfriMont plot network have a mean AGC stock of 149.4megagrams of carbon per hectare (95% confidence interval 137.1–164.2), which is comparable to lowland forests in the African Tropical Rainforest Observation Network4 and about 70per cent and 32per cent higher than averages from plot networks in montane and lowland forests in the Neotropics, respectively. Notably, our results are two-thirds higher than the Intergovernmental Panel on Climate Change default values for these forests in Africa8. We find that the low stem density and high abundance of large trees of African lowland forests is mirrored in the montane forests sampled. This carbon store is endangered: we estimate that 0.8 million hectares of old-growth African montane forest have been lost since 2000. We provide country-specific montane forest AGC stock estimates modelled from our plot network to helpto guide forest conservation and reforestation interventions. Our findings highlight the need for conserving these biodiverse and carbon-rich ecosystems.
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| 2. |
- Nyirambangutse, Brigitte, 1982, et al.
(författare)
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Carbon stocks and dynamics at different successional stages in an Afromontane tropical forest
- 2017
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 14, s. 1285-1303
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Tidskriftsartikel (refereegranskat)abstract
- As a result of different types of disturbance, forests are a mixture of stands at different stages of ecological succession. Successional stage is likely to influence forest productivity and carbon storage, linking the degree of forest disturbance to the global carbon cycle and climate. Although tropical montane forests are an important part of tropical forest ecosystems (ca. 8%, elevation > 1000ma.s.l.), there are still significant knowledge gaps regarding the carbon dynamics and stocks of these forests, and how these differ between early (ES) and late successional (LS) stages. This study examines the carbon (C) stock, relative growth rate (RGR) and net primary production (NPP) of ES and LS forest stands in an Afromontane tropical rainforest using data from inventories of quantitatively important ecosystem compartments in fifteen 0.5ha plots in Nyungwe National Park in Rwanda. The total C stock was 35% larger in LS compared to ES plots due to significantly larger above-ground biomass (AGB; 185 and 76MgCh-1 in LS and ES plots), while the soil and root C stock (down to 45cm depth in the mineral soil) did not significantly differ between the two successional stages (178 and 204MgCh-1 in LS and ES plots). The main reasons for the difference in AGB were that ES trees had significantly lower stature and wood density compared to LS trees. However, ES and LS stands had similar total NPP (canopy, wood and roots of all plots ĝ1/4 9.4MgCh-1) due to counterbalancing effects of differences in AGB (higher in LS stands) and RGR (higher in ES stands). The AGB in the LS plots was considerably higher than the average value reported for old-growth tropical montane forest of south-east Asia and Central and South America at similar elevations and temperatures, and of the same magnitude as in tropical lowland forest of these regions. The results of this study highlight the importance of accounting for disturbance regimes and differences in wood density and allometry of tree species dominating at different successional stages in an attempt to quantify the C stock and sink strength of tropical montane forests and how they may differ among continents.
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| 3. |
- Nyirambangutse, Brigitte, 1982, et al.
(författare)
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Carbon stocks and dynamics at different successional stages in an Afromontane tropical forest
- 2016
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Ingår i: Biogeosciences Discussions. - : Copernicus GmbH. - 1810-6277. ; , s. 1-39
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- As a result of different types of disturbance, forests are a mixture of stands at different stages of ecological succession. Successional stage is likely to influence forest productivity and carbon storage, linking the degree of forest disturbance to the global carbon cycle and climate. Although tropical montane forests are an important part of tropical forest ecosystems (c. 8%, elevation > 1000 m a.s.l.), there are still significant knowledge gaps regarding the carbon dynamics and 15 stocks of these forests, and how these differ between early (ES) and late successional (LS) stages. This study examines the carbon (C) stock, relative growth rate (RGR), and net primary production (NPP) of ES and LS forest stands in an Afromontane tropical rainforest using data from inventories of quantitatively important ecosystem compartments in fifteen 0.5 ha plots in Nyungwe National Park in Rwanda. The total C stock was 35% larger in LS compared to ES plots due to significantly larger above ground biomass (AGB; 185 and 76 Mg C ha-1 20 in LS and ES plots, respectively), while the soil and root C stock (down to 45 cm depth in the mineral soil) did not significantly differ between the two successional stages (178 and 204 Mg C ha-1 in LS and ES plots, respectively). The main reasons for the difference in AGB were that ES trees had significantly lower stature and wood density compared to LS trees. However, ES and LS stands had similar total NPP (canopy, wood and roots of all plots ~ 9.4 Mg C ha-1) due to counterbalancing effects of differences in AGB (higher in LS stands) and RGR (higher in ES stands). The AGB in the LS 25 plots was considerably higher than the average value reported for old-growth tropical montane forest of Southeast Asia and central and South America at similar elevations and temperatures, and of the same magnitude as in tropical lowland forest of different regions. The results of this study highlight the importance of accounting for disturbance regimes and differences in wood density and allometry of tree species dominating at different successional stages in attempts to quantify the C stock and sink strength of 30 tropical montane forests and how it may differ among continents.
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| 4. |
- Nyirambangutse, Brigitte, 1982, et al.
(författare)
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Spatial Variation of Above Ground Biomass and Diversity of Trees in Nyungwe Montane Rain Forest in Rwanda
- 2012
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Ingår i: http://www.eci.ox.ac.uk/africa/downloads/poster-abstracts.pdf.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Tropical rainforest plays an important role in the global terrestrial carbon cycle. This zone is undergoing rapid deforestation and degradation due to clearance for croplands, cattle pasture, logging and shifting cultivation. Few tropical forest sites have been the object of forest C cycle studies in detail. The lack of field data on the status of carbon stock and fluxes in central Africa is evident, which together with the high diversity of tree species contributes to the uncertainties in understanding the source/sink relationship of tropical African forests. A study has therefore been initiated to address questions on biodiversity (plant species), carbon fluxes and stocks and scaling of results to whole forests. The study aims at answering the following research questions: Is high diversity connected to high carbon stocks? Is variation in vegetation structure linked to the variation in carbon storage? Are nutrients, climate, disturbances (fire, logging) or topography important determinant factors for carbon storage and biodiversity? The study will be conducted in Nyungwe montane rain forest gazetted as a National Park to protect its extensive floral and faunal diversity covering an area of 970km2. Nyungwe is located in Southwest Rwanda (2o17´-2o50´S, 29o07´-29o26A´E). The forest is ranging between 1600-2950 m.a.s.l. and is one of the most biologically important rainforest in Albertine Rift region in terms of Biodiversity. Nyungwe consists of a mixture of primary and secondary forest. It supports a richness of plant and animal life. More than 260 species of trees and shrubs have been found at Nyungwe, including species endemic to the Albertine Rift. Nyungwe is also one of the most important sites for bird. 260 bird species have been found, some are endemic to the Albertine Rift. Thirteen species of primates populate the forest, including chimpanzees. The forest has a climate with a mean annual temperature of 15.5oC and rainfall averages 1744 mm/yr, with July and August being the only months when rainfall drops. Many forms of human disturbance occur in the forest, including fires, tree cutting, gold mining, honey collection, trapping, and poaching. In this study an east-westerly transect of experimental plots is to be set up where different types of forest occur on approximately the same altitude 2400-2500 m.a.s.l. primary forests stands, secondary forests stands and plantations in the buffer zones. We are sampling within the two plant communities with the highest relative density of Syzygium guineense (18.2 %) representing primary forest and Macaranga kilimandscharica (17.5 %) representing secondary forest and in the two most frequently occurring genus in the buffer zone: Eucalyptus and Pinus. We will describe forest C dynamics in different live biomass components (aboveground and belowground live biomass) and soil organic matter divided into two components: litter and humus. Finally we will investigate fluxes between Carbon pools on live over-story and under-story of trees, shrubs, herbs, and its fine roots. An outline of the study, together with results from an initial measurement campaign on spatial diversity of trees species and above ground biomass, is currently being compiled and will be reported.
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| 5. |
- Nyirambangutse, Brigitte, 1982, et al.
(författare)
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Variation in leaf litter production and resorption of nutrients in abundant tree species in Nyungwe Afromontane tropical rainforest in Rwanda
- 2014
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Ingår i: EGU General Assembly 2014, held 27 April - 2 May, 2014 in Vienna, Austria, id.14278.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- African tropical rainforests play many roles from local to global scale as providers of resources and ecosystem services. Although covering 30% of the global rainforest, only few studies aiming to better understand the storage and fluxes of carbon and nutrients in these forests have been conducted. To answer questions related to these issues, we have established 15 permanent 0.5 ha plots where we compare carbon and nutrient fluxes of primary and secondary forest tree communities in a tropical montane forest in central Africa. The studies are conducted in Nyungwe montane tropical rain forest gazetted as a National Park to protect its extensive floral and faunal diversity covering an area of 970 km2. Nyungwe is located in Southwest Rwanda (2o17'-2o50'S, 29o07'-29o26A'E). The forest is ranging between 1600-2950 m.a.s.l. and is one of the most biologically important rainforest in Albertine Rift region in terms of Biodiversity. Nyungwe consists of a mixture of primary and secondary forest communities supporting a richness of plant and animal life. More than 260 species of trees and shrubs have been found in Nyungwe, including species endemic to the Albertine Rift. The forest has a climate with a mean annual temperature of 15.5oC and annual rainfall of ca 1850 mm yr-1, with July and August being the only months when rainfall drops. A part of this study is focusing on the dynamics of nutrients through leaf turnover. This turnover of leaves is regulated to maximize the carbon gain through canopy photosynthesis and resource-use efficiency of the plant. It is known that about half of leaf nitrogen is invested in photosynthetic apparatus and that there normally is a strong correlation between the photosynthetic capacity and leaf nitrogen per unit area. Hence leaf nitrogen is an important factor for canopy photosynthesis. However, leaves are produced, senesce and fall. Some nitrogen in the leaf is lost when leaves senesce but other is resorbed. The resorption of nitrogen, phosphorus and other nutrients is being studied to analyse the nutrient saving efficiency of different species within the primary and secondary forest communities. This is made by analyzing the nutrient content within fresh and fallen leaves of most abundant pioneer and climax species. Results from litterfall patterns as well as foliar, litter and soil carbon and nutrients are currently being compiled and will be reported.
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| 6. |
- Ziegler, Camille, et al.
(författare)
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Contrasting Dependencies of Photosynthetic Capacity on Leaf Nitrogen in Early- and Late-Successional Tropical Montane Tree Species
- 2020
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Ingår i: Frontiers in Plant Science. - : Frontiers Media SA. - 1664-462X. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- Differences in photosynthetic capacity among tree species and tree functional types are currently assumed to be largely driven by variation in leaf nutrient content, particularly nitrogen (N). However, recent studies indicate that leaf N content is often a poor predictor of variation in photosynthetic capacity in tropical trees. In this study, we explored the relative importance of area-based total leaf N content (N-tot) and within-leaf N allocation to photosynthetic capacity versus light-harvesting in controlling the variation in photosynthetic capacity (i.e.V-cmax,J(max)) among mature trees of 12 species belonging to either early (ES) or late successional (LS) groups growing in a tropical montane rainforest in Rwanda, Central Africa. Photosynthetic capacity at a common leaf temperature of 25x2da;C (i.e. maximum rates of Rubisco carboxylation,V(cmax25)and of electron transport,J(max25)) was higher in ES than in LS species (+ 58% and 68% forV(cmax25)andJ(max25), respectively). While N(tot)did not significantly differ between successional groups, the photosynthetic dependency on N(tot)was markedly different. In ES species,V(cmax25)was strongly and positively related to N(tot)but this was not the case in LS species. However, there was no significant trade-off between relative leaf N investments in compounds maximizing photosynthetic capacity versus compounds maximizing light harvesting. Both leaf dark respiration at 25x2da;C (+ 33%) and, more surprisingly, apparent photosynthetic quantum yield (+ 35%) was higher in ES than in LS species. Moreover, R(d25)was positively related to N(tot)for both ES and LS species. Our results imply that efforts to quantify carbon fluxes of tropical montane rainforests would be improved if they considered contrasting within-leaf N allocation and photosynthetic N(tot)dependencies between species with different successional strategies.
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