Article

Forest biomass, productivity and carbon cycling along a rainfall gradient in West Africa

Authors:
  • CSIR-Forestry Research Institute of Ghana
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Abstract

Net primary productivity (NPP) is one of the most important parameters in describing the functioning of any ecosystem and yet it arguably remains a poorly quantified and understood component of carbon cycling in tropical forests, especially outside of the Americas. We provide the first comprehensive analysis of NPP and its carbon allocation to woody, canopy and root growth components at contrasting lowland West African forests spanning a rainfall gradient. Using a standardised methodology to study evergreen (EF), semi-deciduous (SDF), dry forests (DF) and woody savanna (WS), we find that (i) climate is more closely related with above and belowground C stocks than with NPP (ii) total NPP is highest in the SDF site, then the EF followed by the DF and WS and that (iii) different forest types have distinct carbon allocation patterns whereby SDF allocate in excess of 50% to canopy production and the DF and WS sites allocate 40-50% to woody production. Furthermore, we find that (iv) compared with canopy and root growth rates the woody growth rate of these forests is a poor proxy for their overall productivity and that (v) residence time is the primary driver in the productivity-allocation-turnover chain for the observed spatial differences in woody, leaf and root biomass across the rainfall gradient. Through a systematic assessment of forest productivity we demonstrate the importance of directly measuring the main components of above and belowground NPP and encourage the establishment of more permanent carbon intensive monitoring plots across the tropics.

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... Fire management through the timing of prescribed fires offers a potential tool to control greenhouse gas emissions. Shifting prescribed burns from late to earlier growing season has been proposed to reduce greenhouse gas emissions (Lipsett- Moore et al., 2018;Russell-Smith et al., 2003). Lower carbon emissions following early-growing-season burns is linked to less plant biomass and litter burned compared with later in the growing season (Russell-Smith et al., 2003;Russell-Smith et al., 2021); however, other factors such as the higher water content of fuel can also influence greenhouse gas emissions, for example, methane (Laris, 2021). ...
... Lower carbon emissions following early-growing-season burns is linked to less plant biomass and litter burned compared with later in the growing season (Russell-Smith et al., 2003;Russell-Smith et al., 2021); however, other factors such as the higher water content of fuel can also influence greenhouse gas emissions, for example, methane (Laris, 2021). A pan-savanna study across 50 countries calculated that shifting from late-to early-growing-season fires reduced carbon-equivalent nitrous oxide and methane emissions by 89.4 Mt CO 2 -e year À1 (Lipsett- Moore et al., 2018). Reducing greenhouse gas emissions through fire management can be sold as part of voluntary carbon market schemes (Russell-Smith et al., 2015). ...
... Reducing greenhouse gas emissions through fire management can be sold as part of voluntary carbon market schemes (Russell-Smith et al., 2015). Wildlife protected areas regularly manage vegetation by prescribed burning, shifting the timing of burning has been proposed as a potential source of financial revenue for wildlife conservation (Lipsett- Moore et al., 2018;Russell-Smith et al., 2021;Tear et al., 2021). ...
Article
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Fire is fundamental to the functioning of tropical savannas and routinely used as a management tool. Shifting prescribed burning from later to earlier in the growing season has the potential to reduce greenhouse gas emissions. However, large uncertainties surround the impact of seasonal burning on longer term plant and soil carbon sequestration. In this study, we quantify ecosystem carbon storage across burn seasons and histories in a wet-to-mesic Guinea tropical savanna in Mole National Park, Ghana. Aboveground (plant and litter) and belowground (soil plus roots) carbon storage was quantified across four burning seasons and histories: recent (<3 years) early-season burns, recent late-season burns, old (>4 years) late-season burns, and long-unburned (>15 years) sites. We found that recent late-season burns significantly lowered belowground carbon storage to a depth of 17 cm compared with all other burn seasons and histories. Belowground carbon was 1.2 kg C m À2 , or 27% lower, for recent late-season burns compared with prescribed early-season burns. However, in older late-season burns sites, belowground carbon "recovered" after 4-13 burn years to comparable storage as long-unburned and early-season burn sites. For most aboveground carbon pools, there was no significant difference in carbon storage across burn seasons and histories, except higher aboveground tree carbon in long-unburned sites. We suggest that observed changes in belowground carbon are likely due to the turnover and production of root carbon. Prescribed early-season burning is promoted to reduce greenhouse gas emissions and our findings affirm that early-season burning has limited impact on plant and soil carbon stocks compared with long-unburned sites. While early-season burning regimes will have some patches that become late-season wildfires, our results suggest on balance early-season burning regimes are a low-risk land management practice in reducing plant and soil carbon storage losses and sustaining a patch-mosaicked landscape with multiple other ecosystem service benefits for savannas. Joana Awuah and Stuart W. Smith contributed equally to the work reported here.
... In addition to demographic dynamics along succession, changes in absolute NPP and relative NPP allocation to canopy, stem and root along secondary succession have drawn even less research attention (Becknell et al. 2021), despite being a key element of ecosystem functioning (Moore et al. 2017). Litter-, wood-, and fine root production collectively account for approximately 80% of total NPP (Riutta et al. 2018). ...
... Litter-, wood-, and fine root production collectively account for approximately 80% of total NPP (Riutta et al. 2018). Tree growth rates (i.e. the rate of carbon (C) accumulation in wood) and litter production have frequently been quantified and used as proxies for forest NPP (Aryal et al. 2014;Poorter et al. 2016;Suarez et al. 2019), while fine root production is rarely quantified and integrated into NPP estimates (Brown and Lugo 1990;Moore et al. 2017). In contrast to litter-and fine root production, wood production represents a long-term C sink. ...
... Total NPP and NPP allocation show variation across tropical forests, indicating significant differences in tropical forest functioning, resource use, and allocation (Malhi et al. 2011;Suarez et al. 2019). Previous studies showed variation of the total NPP and NPP allocation along a rainfall gradient (Moore et al. 2017), disturbance gradient (Riutta et al. 2018), edaphic gradient (Bukombe et al., in review), 50 and successional gradient (Anderson-teixeira et al. 2016;Poorter et al. 2016). However, studies along secondary succession have either deduced NPP from standing biomass (Anderson-teixeira et al. 2016;Poorter et al. 2016), investigated only aboveground NPP (Brown and Lugo 1990;Becknell et al. 2021), or only broadly distinguished NPP between secondary and pristine forests (Nyirambangutse et al. 2016). ...
Thesis
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Loss of tropical forests due to agriculture expansion constitutes the most pressing environmental issues of the 21st century and is at the center of biodiversity and climate crisis. In central Africa, this results mostly from subsistence agriculture. With Sub-Saharan Africa's expected rapid population growth, the deforestation trend is likely to increase. However, allowing the tropical degraded land to regenerate naturally represents an opportunity to restore tropical forest characteristics efficiently and at a low cost, while mitigating global climate change. We used the space-for-time chronosequences approach to investigate how a central Congo basin forest recover from shifting cultivation disturbances. Specifically, we examined along a successional gradient the recovery rates of biodiversity, biogeochemical cycles, and dynamics of lowland forest of the Yoko forest reserve in the central Congo basin, Democratic Republic of the Congo. I showed that lowland forest of the central Congo basin recover biodiversity, carbon stocks and biogeochemical cycles as do the other tropical forests. However, in comparison with forests of the Amazon basin, I showed that carbon stocks recover in the central Congo basin at a relatively slow pace. Additionally, despite high atmospheric nitrogen deposition in the central Congo, nitrogen cycle still recover from conservative in young secondary to open cycle in old growth forests. Finally, I showed that secondary forest dynamics are determined by the rate of replacement of plants functional groups along secondary succession. Overall, the results imply that while allowing tropical secondary forests to regenerate naturally, we should protect old-growth forests for the reason that: (1) they store important biodiversity; and (2) store carbon stocks with long recovery trajectory.
... Six plots were established within the Bobiri Forest Reserve, located in the moist semi deciduous forest zone. Additionally, five plots are located within the Kogyae Strict Nature Reserve, which covers the dry forest to savanna transition zone of Ghana (Moore et al. 2018). For the purpose of this study, two plots were selected from each forest site for data collection. ...
... Fine-root production was calculated using both changes in biomass and dead roots in a decision matrix, and the trend suggests that fineroot production estimates were greatly influenced by changes in biomass increment rather than root mortality (Table 3). We speculate that the fine root production estimates obtained for the studied sites could be related to the total productivity of the sites (Litton et al. 2007;Moore et al. 2018). A synthesis study by Litton et al (2007) showed that carbon fluxes to different plant components, including belowground production, increased linearly with increasing total productivity of forests across the globe. ...
... A synthesis study by Litton et al (2007) showed that carbon fluxes to different plant components, including belowground production, increased linearly with increasing total productivity of forests across the globe. In fact, Moore et al. (2018) working along the same gradient also reported a positive correlation between fine root production and total net primary productivity. This suggests that the wet forest could have higher Fig. 3 Smoothing curves for soil moisture; soil temperature, rainfall and air temperature. ...
Article
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Key message Fine-root biomass relates to environmental variables differently along a rainfall gradient in Ghana. Abstract Understanding changes in root dynamics in response to environmental factors is crucial for projections of climate change, yet information on controls of root dynamics is limited in the tropics. This study quantified fine-root dynamics along a rainfall gradient in Ghana, ranging from dry to wet evergreen forests. Fine-root biomass and necromass were estimated by the sequential coring method for a year and analyzed in relation to measured environmental factors (rainfall, soil moisture content, air temperature and soil temperature). Overall, fine-root biomass increased along the gradient with the highest estimate found in the wet forest site. Mean annual fine root production ranged from 276.60 to 348.95 gm⁻² year⁻¹ across the different forest types. Fine-root turnover rates ranged from 2.3 to 3.1 year⁻¹, and roots tended to turn over faster in the dry than in the moist and wet forest sites. There was a non-linear but significant relationship between fine-root biomass and soil moisture content in the wet forest. None of the environmental factors related to fine-root biomass in the moist forest. However, there was a significant non-linear relationship between rainfall and fine-root biomass in the dry forest site. These results suggest that environmental factors influence fine-root biomass differently across the three forest types. Therefore, future studies should focus on a comprehensive measurement of environmental controls to deepen our understanding of fine root dynamics.
... To compare our intact forest plot measurements with other semideciduous forests in Ghana, we added the total and allocation patterns of forest NPP from Moore et al. (2017). This study followed the same Global Ecosystems Monitoring (GEM) protocol (Marthews et al., 2012) and monitored two semideciduous, one hectare forest plots located within 5 km of each other within the Bobiri Forest Reserve. ...
... Mean total NPP measured in the intact (17.6 ± 2.1 Mg C ha −1 year −1 ) and logged (17.7 ± 1.6 Mg C ha −1 year −1 ) forest plots were among the highest values reported for tropical forest, though similarly high values were reported by Moore et al. (2017) for a different semideciduous forest site in Ghana (Table S1). Remarkably, the NPP of the cocoa farms was similar to that of intact forest, and in many cases was higher, with an average across our monitored farms of 18.8 ± 2.5 Mg C ha −1 year −1 . ...
... Also, our HANPP estimates are based on the NPP measures of only one intact forest plot that was measured in close proximity. To assess the effect of this assumption, we compared our forest measures with a similar study (Moore et al., 2017) and found our estimates to be within 5%. Therefore, we feel our forest NPP values to be within a reasonable range for calculating locally relevant HANPP measures. ...
Article
Terrestrial net primary productivity (NPP) is an important metric of ecosystem functioning; however, there is little empirical data on the NPP of human‐modified ecosystems, particularly smallholder, perennial crops like cocoa (Theobroma cacao), which are extensive across the tropics. Human appropriated NPP (HANPP) is a measure of the proportion of a natural system's NPP that has either been reduced through land‐use change or harvested directly and, previously, has been calculated to estimate the scale of the human impact on the biosphere. Additionally, human‐modification can create shifts in NPP allocation and decomposition, with concomitant impacts on the carbon cycle. This study presents the results of three years of intensive monitoring of forest and smallholder cocoa farms across disturbance, management intensity, distance from forest and farm age gradients. We measured among the highest reported NPP values in tropical forest, 17.57 ± 2.1 and 17.7 ± 1.6 Mg C ha⁻¹ yr⁻¹ for intact and logged forest respectively; however, the average NPP of cocoa farms was still higher, 18.8 ± 2.5 Mg C ha⁻¹ yr⁻¹, which we found was driven by cocoa pod production. We found a dramatic shift in litterfall residence times, where cocoa leaves decomposed more slowly than forest leaves and shade tree litterfall decomposed considerably faster, indicating significant changes in rates of nutrient cycling. The average HANPP value for all cocoa farms was 2.1 ± 1.1 Mg C ha⁻¹ yr⁻¹; however, depending on the density of shade trees it ranged from ‐4.6 to 5.2 Mg C ha⁻¹ yr⁻¹. Therefore, rather than being related to cocoa yield, HANPP was reduced by maintaining higher shade levels. Across our monitored farms 18.9% of farm NPP was harvested (i.e. whole cocoa pods) and only 1.1% (i.e. cocoa beans) was removed from the system; suggesting that the scale of HANPP in smallholder cocoa agroforestry systems is relatively small. This article is protected by copyright. All rights reserved.
... d-use changes, deforestation, is the one that influences most soil properties and functions (Martínez-Garza, Campo, Ricker, and Tobón, 2016;Veldkamp, Schmidt, Powers, and Corre, 2020). In the last few decades the knowledge of the carbon cycle in lowland tropical forest soils have increased significantly (Brienen et al., 2015b;Girardin et al., 2016;S. Moore et al., 2018) as well as for planted forest ( Wang and Huang, 2020). However, for tropical montane forests (TMF) there are large gaps in knowledge, and the carbon cycling dynamics are understudied (Moser et al., 2011), especially the soil carbon dynamics following clearance and recovery (Nyirambangutse et al., 2017;Soh et al., 2019). ...
... Equally, soil N stocks ranging from 16.4 ± 4.8 Mg N ha -1 in <10 years forest recovery regime to 20.1 ± 3.9 Mg N ha -1 in the old growth secondary forest Complex in Kenya. The nonsignificant change in soil C and N stocks over different recovery periods in the Mau forest complex from this study provide new information which contributes to knowledge on how the soil C and N stocks in the montane forests of East Africa respond to forest clearance and the following recovery stages which had not been widely reported in the montane tropical forest as similar studies focus on the tropical lowland forests (Moore et al., 2018). ...
Thesis
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Tropical montane forests are fragile ecosystems that provide a wide range of ecosystem services such as hydrological services, protection of biodiversity, and a contribution to climate change mitigation, yet they face degradation as well as losses due to deforestation. Deforestation poses a major threat yet whether these tropical montane forests recover from these changes is not well understood, especially for African montane forests. This study assessed rates of deforestation, and recovery using remote sensing of two important tropical montane forests of East Africa: the Mau Forest complex and the Mount Elgon forest. An in-depth study of aboveground biomass, species diversity and richness, and soil carbon and nitrogen stocks were conducted for the Mau forest complex. To conduct the detailed study, 47 forest plots were established to collect data subsequently used to calculate the rate of recovery of the aboveground biomass (AGB) and species recovery in 3 blocks of the Mau forest complex. From the same plots, soil samples were collected to assess the response of soil carbon (C) and nitrogen (N) stocks to 60 cm of soil depth from the different recovery stages. This study found that 21.9% (88,493 ha) of the 404,660 ha of the Mau forest Complex was lost at an annual rate of -0.82% yr-1 over the period between 1986-2017. However, 18.6% (75,438 ha) of the forest cover that was cleared during the same period and is currently undergoing recovery. In the Mt Elgon forest, 12.5% (27,201 ha) of 217,268 ha of the forest cover was lost to deforestation at an annual rate of -1.03 % yr-1 for the period between 1984 - 2017 and 27.2% (59,047 ha) of the forest cover that was lost is undergoing recovery. The analysis further revealed that for the Mau forest complex, agriculture (both smallholder and commercial) was the main driver of forest cover loss accounting for 81.5% (70,612 ha) of the deforestation, of which 13.2% was due to large scale and 68.3% was related to the smallholder farming. For the Mt Elgon forest, agriculture was also the main driver of forest loss accounting for 63.2% (24,077 ha) of deforestation followed by the expansion of human settlements that contributed to 14.7% (5,597 ha) of forest loss. For the aboveground biomass (AGB), it was found that AGB recovered rapidly in the first 20 years at an annual rate of 6.42 Mg ha-1, but the rate of recovery slowed to 4.67 Mg ha-1 at 25 years and 4.46 Mg ha-1, at 30 years of age. At 25 years, the mean AGB (198.32 ± 78.11 Mg ha-1) was statistically indistinguishable from the mean AGB in the old growth secondary forest (282.86 ± 71.64 Mg ha-1). Stem density, species diversity, and richness (i.e., Evenness index, Shannon’s index, and Simpson’s index) did not show any significant changes with the recovery stages of the secondary forest, although there existed a significant variation between the young secondary forests of age below 15 years from the old growth secondary forests. The study further found that, unlike the AGB and aboveground carbon (AGC), the soil C and N stocks were not significantly different across the recovery periods with mean soil C in the youngest forest 184.1 ± 41.0 Mg C ha-1 and old growth secondary forest as 217.9 ± 51.8 Mg C ha-1, the N stocks in the youngest forest was 16.4 ± 4.8 Mg N ha-1 and 20.1 ± 3.9 Mg N ha-1 for the old growth secondary forest. The findings of the study indicate that these tropical montane forests of East Africa are under threat resulting from forest clearance and deforestation. The forest AGB recovers after 25 years while the tree species richness and diversity, soil C and N stocks do not change significantly with the recovery stages. The effects of disturbances i.e., forest fire, charcoal burning, grazing (livestock), elephant damage, and fuelwood collection on the soil C and N stocks within the different recovery stages were not significantly different between old growth secondary forests and the other recovery stages. These findings contribute to the knowledge on the response of the tropical montane forest of East African to pressures of forest clearance and deforestation.
... Research on identifying potential drivers for C dynamics in tropical forests has mostly focused on climatic parametersthat is, precipitation and temperature (Moore et al., 2017;Tonin et al., 2017;Hofhansl et al., 2020), topographic patterns (de Castilho et al., 2006;Malhi et al., 2017;Jucker et al., 2018) or the effect of anthropogenic disturbance Ross et al., 2021). However, in many terrestrial ecosystems, soil parent material co-determines nutrient availability more so than other factors (Augusto et al., 2017) with strong consequences for C cycling (Vitousek, 1984;Fernández-Martínez et al., 2014;Wieder et al., 2015). ...
... This is why it is common practice in large-scale modeling studies to use fixed ratios of shoot : root biomass/C allocation and apply allometric equations relating above-to belowground biomass to estimate ecosystem C budgets (Mokany et al., 2006;Cleveland et al., 2013;Gherardi & Sala, 2020). As such, the potential impact of local edaphic parameters, such as differences in soil geochemical properties and parent material, on NPP allocation in tropical forests has often been ignored or considered of secondary importance (Moser et al., 2011;Moore et al., 2017). In part, this is due to the assumption that nutrient cycling in deeply developed tropical soils should be largely decoupled from soil parent material (Augusto et al., 2017;Doetterl et al., 2021a,b) and that nutrients get recycled quickly in semi-closed systems with rapid turnover of organic litter by microbial decomposers and uptake into vegetation (Krishna & Mohan, 2017;Giweta, 2020). ...
Article
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The lack of field‐based data in the tropics limits our mechanistic understanding of the drivers of net primary productivity (NPP) and allocation. Specifically, the role of local edaphic factors – such as soil parent material and topography controlling soil fertility as well as water and nutrient fluxes – remains unclear and introduces substantial uncertainty in understanding net ecosystem productivity and carbon (C) stocks. Using a combination of vegetation growth monitoring and soil geochemical properties, we found that soil fertility parameters reflecting the local parent material are the main drivers of NPP and C allocation patterns in tropical montane forests, resulting in significant differences in below‐ to aboveground biomass components across geochemical (soil) regions. Topography did not constrain the variability in C allocation and NPP. Soil organic C stocks showed no relation to C input in tropical forests. Instead, plant C input seemingly exceeded the maximum potential of these soils to stabilize C. We conclude that, even after many millennia of weathering and the presence of deeply developed soils, above‐ and belowground C allocation in tropical forests, as well as soil C stocks, vary substantially due to the geochemical properties that soils inherit from parent material.
... In this Article, we evaluate the climate responses of woody biomass growth throughout the global tropics (here defined as 30° N-30° S, including subtropics). We focus on woody biomass growth in tree stems, which constitutes a significant share of net productivity of tropical vegetation at local 13,14 to continental scales 15,16 , contributes to the main long-term carbon reservoir in tropical biomass 17 and determines the success of forest-based natural climate solutions 18 . Using a compilation of tropical tree-ring data, we test three hypotheses on the association between climate and annual woody biomass growth of trees (hereafter, 'tree growth') across tropical climate zones that vary in temperature and precipitation. ...
... Line graphs per climate response group are similar to those inFig. 2and show mean Pearson r correlation coefficients of 50-year RWI series with monthly T max (red) or PP (blue) for a 24-month period that covers the year of ring formation (months[1][2][3][4][5][6][7][8][9][10][11][12] and that prior to ring formation (months[13][14][15][16][17][18][19][20][21][22][23][24]. Bar graphs show the percentage of correct and incorrect assignments of the left out sites to climate response groups.Extended DataFig. ...
Article
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Interannual variability in the global land carbon sink is strongly related to variations in tropical temperature and rainfall. This association suggests an important role for moisture-driven fluctuations in tropical vegetation productivity, but empirical evidence to quantify the responsible ecological processes is missing. Such evidence can be obtained from tree-ring data that quantify variability in a major vegetation productivity component: woody biomass growth. Here we compile a pantropical tree-ring network to show that annual woody biomass growth increases primarily with dry-season precipitation and decreases with dry-season maximum temperature. The strength of these dry-season climate responses varies among sites, as reflected in four robust and distinct climate response groups of tropical tree growth derived from clustering. Using cluster and regression analyses, we find that dry-season climate responses are amplified in regions that are drier, hotter and more climatically variable. These amplification patterns suggest that projected global warming will probably aggravate drought-induced declines in annual tropical vegetation productivity. Our study reveals a previously underappreciated role of dry-season climate variability in driving the dynamics of tropical vegetation productivity and consequently in influencing the land carbon sink.
... The most common technique used to quantify fine root NPP is the ingrowth core mesh (Addo-Danso et al., 2016;Marthews et al., 2014;Metcalfe et al., 2007;Vogt et al., 1998). To date, high variability of fine root productivity has been recorded for different tropical forest types, which is driven by soil properties and climatic variables Kho et al., 2013;Metcalfe et al., 2008;Moore et al., 2018;Riutta et al., 2018;Violita et al., 2016), which is driven by soil properties and climatic variables. In lowland Amazon forest, fine root productivity is influenced by soil texture Silver et al., 2005). ...
... Araujo-Murakami et al., 2014;del Aguila-Pasquel et al., 2014;Girardin et al., 2014;Huaraca Huasco et al., 2014;Malhi et al., 2017;Moore et al., 2018;Riutta et al., 2018). NPP total was the sum of canopy productivity (estimated from canopy litterfall), wood productivity (stem and coarse wood productivity of stems ≥10 cm diameter at breast height, based on allometric equations), and fine root productivity. ...
Article
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Fine roots constitute a significant component of the net primary productivity (NPP) of forest ecosystems but are much less studied than above‐ground NPP. Comparisons across sites and regions are also hampered by inconsistent methodologies, especially in tropical areas. Here, we present a novel dataset of fine root biomass, productivity, residence time, and allocation in tropical old‐growth rainforest sites worldwide, measured using consistent methods, and examine how these variables are related to consistently determined soil and climatic characteristics. Our pantropical dataset spans intensive monitoring plots in lowland (wet, semi‐deciduous, deciduous) and montane tropical forests in South America, Africa, and Southeast Asia (n=47). Large spatial variation in fine root dynamics was observed across montane and lowland forest types. In lowland forests, we found a strong positive linear relationship between fine root productivity and sand content, this relationship was even stronger when we considered the fractional allocation of total NPP to fine roots, demonstrating that understanding allocation adds explanatory power to understanding fine root productivity and total NPP. Fine root residence time was a function of multiple factors: soil sand content, soil pH, and maximum water deficit, with longest residence times in acidic, sandy, and water‐stressed soils. In tropical montane forests, on the other hand, a different set of relationships prevailed, highlighting the very different nature of montane and lowland forest biomes. Root productivity was a strong positive linear function of mean annual temperature, root residence time was a strong positive function of soil nitrogen content in montane forests, and lastly decreasing soil P content increased allocation of productivity to fine roots. In contrast to the lowlands, environmental conditions were a better predictor for fine root productivity than for fractional allocation of total NPP to fine roots, suggesting that root productivity is a particularly strong driver of NPP allocation in tropical mountain regions.
... All studies presented in this thesis were conducted in the Kogyae Strict Nature Reserve (KSNR) (refer to the figure in Chapter 2) in the Ashanti Region of Ghana (7⁰15'52'' N and 1⁰04'47'' W). The dry forest and savanna woodlands of Kogyae have received particular scientific interest recently in the study of vegetation structure, fire ecology, plant physiology and carbon dynamics in the forestsavanna transition zone (Cardoso et al., 2016;Domingues et al., 2010;Moore et al., 2017;Torello-Raventos et al., 2013;Veenendaal et al.,2015). ...
... Kogyae is the only designated strict nature reserve in Ghana, being "devoted solely to scientic research" with entry by humans for tourism or other uses prohibited (Hagan, 1998). The dry forest and savanna woodlands of Kogyae have received particular scientic interest recently, in the study of vegetation structure, re ecology, plant physiology and carbon dynamics in the forest-savanna transition zone (Cardoso et al., 2016;Domingues et al., 2010;Moore et al., 2017;Torello-Raventos et al., 2013;Veenendaal et al., 2015). Kogyae is classied as category Ia protected area by the Inter-national Union for the Conservation of Nature (Ofori et al., 2014). ...
... At sites with a substantial and productive herbaceous layer (for example, savannas), above-ground herbaceous productivity Moore et al., 2018) is estimated through seasonal biomass harvest of sample quadrats (protected from grazing where necessary). Belowground herbaceous productivity is already incorporated into the fine root productivity estimates, which do not distinguish between trees and herbaceous plants. ...
... Furthermore, the wet-dry trend almost disappeared in woody growth, because drier forests invested disproportionately more in woody growth. Moore et al. (2018) reported a similar pattern along wet-dry gradients in Ghana, West Africa, though here the highest NPP was found in the centre of the gradient, possibly because of soil fertility effects. ...
Article
A rich understanding of the productivity, carbon and nutrient cycling of terrestrial ecosystems is essential in the context of understanding, modelling and managing the future response of the biosphere to global change. This need is particularly acute in tropical ecosystems, home to over 60% of global terrestrial productivity, over half of planetary biodiversity, and hotspots of anthropogenic pressure. In recent years there has been a surge of activity in collecting data on the carbon cycle, productivity, and plant functional traits of tropical ecosystems, most intensively through the Global Ecosystems Monitoring network (GEM). The GEM approach provides valuable insights by linking field-based ecosystem ecology with the needs of Earth system science. In this paper, we review and synthesize the context, history and recent scientific output from the GEM network. Key insights have emerged on the spatial and temporal variability of ecosystem productivity and on the role of temperature and drought stress on ecosystem function and resilience. New work across the network is now linking carbon cycling to nutrient cycling and plant functional traits, and subsequently to airborne remote sensing. We discuss some of the novel emerging patterns and practical and methodological challenges of this approach, and examine current and possible future directions, both within this network and as lessons for a more general terrestrial ecosystem observation scheme.
... In recent decades, as interest in forest C budgets has increased, many studies have investigated patterns and mechanisms of spatial variation in tropical forest AWP and AGB with abiotic and biotic factors (e.g. Levine et al., 2016;Malhi et al., 2017;Taylor et al., 2017;Moore et al., 2018;Sullivan et al., 2020) (methods summarized in Box 1). This research builds naturally on an older literature on forest structure and composition (e.g. ...
... resulting from damage when a neighboring tree falls). Relatively few studies have measured branchfall rates directly (but see Palace et al., 2008;Malhi et al., 2017;Moore et al., 2018), and spatiotemporal variability in branchfall is so high that sampling errors in such data are invariably large (Gora et al., 2019). Most AWP estimates from plot recensuses include only net increases in standing woody biomass without considering branch turnover, and thus are systematic underestimates. ...
Article
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Tropical forests vary widely in biomass carbon (C) stocks and fluxes even after controlling for forest age. A mechanistic understanding of this variation is critical to accurately predicting responses to global change. We review empirical studies of spatial variation in tropical forest biomass, productivity and woody residence time, focusing on mature forests. Woody productivity and biomass decrease from wet to dry forests and with elevation. Within lowland forests, productivity and biomass increase with temperature in wet forests, but decrease with temperature where water becomes limiting. Woody productivity increases with soil fertility, whereas residence time decreases, and biomass responses are variable, consistent with an overall unimodal relationship. Areas with higher disturbance rates and intensities have lower woody residence time and biomass. These environmental gradients all involve both direct effects of changing environments on forest C fluxes and shifts in functional composition – including changing abundances of lianas – that substantially mitigate or exacerbate direct effects. Biogeographic realms differ significantly and importantly in productivity and biomass, even after controlling for climate and biogeochemistry, further demonstrating the importance of plant species composition. Capturing these patterns in global vegetation models requires better mechanistic representation of water and nutrient limitation, plant compositional shifts and tree mortality.
... The trait sampling plots were located in the humid forest zone in Ankasa National Park (two plots of 1 ha each; latitude: 5.267, longitude: −2.693; 5.2710-2.692), in the semi-deciduous forest zone in Bobiri (two plots of 1 ha each; 6.691, −1.338; 6.704, −1.318) and on the dry forest zone in Kogyae Strict Wildlife Reserve (three plots of 1 ha each; 7.261, −1.150; 7.302, −1.180; 7.301, −1.164). For further details on site characteristics, plot biomass, productivity and carbon cycling of these plots see 67 . The following traits from the leaf, hydraulics and wood economics spectrum were collected: LA:SA, potential stem specific conductivity (kp), vessel lumen fraction (VLF), vessels diameter (VD), vessel density (pV), leaf area (Area L ), specific leaf area (SLA), leaf nitrogen(N L ) and phosphorus (P L ) content, leaf thickness (Thickness L ), photosynthetic capacity at maximum carbon assimilation rates (A max ) and at light saturated carbon assimilation rates (A sat ), adult maximum height (Height max ), wood density (WD), phenology, guild and nitrogen fixing capacity (Supplementary Table 2). ...
... Soil data was collected at the plot level between 2007 and 2013 (Supplementary Table 3). For further information on soil characteristics and sampling across the study area see Moore et al. 67 and the ForestPlots database (www.forestplots.net). We used the averaged soil characteristics (Supplementary Table 3) for the first 30 cm depth and carried a principal component analysis using the prcomp function of the stats package in R 76 . ...
Article
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Tropical ecosystems adapted to high water availability may be highly impacted by climatic changes that increase soil and atmospheric moisture deficits. Many tropical regions are experiencing significant changes in climatic conditions, which may induce strong shifts in taxonomic, functional and phylogenetic diversity of forest communities. However, it remains unclear if and to what extent tropical forests are shifting in these facets of diversity along climatic gradients in response to climate change. Here, we show that changes in climate affected all three facets of diversity in West Africa in recent decades. Taxonomic and functional diversity increased in wetter forests but tended to decrease in forests with drier climate. Phylogenetic diversity showed a large decrease along a wet-dry climatic gradient. Notably, we find that all three facets of diversity tended to be higher in wetter forests. Drier forests showed functional, taxonomic and phylogenetic homogenization. Understanding how different facets of diversity respond to a changing environment across climatic gradients is essential for effective long-term conservation of tropical forest ecosystems. Different aspects of biodiversity may not necessarily converge in their response to climate change. Here, the authors investigate 25-year shifts in taxonomic, functional and phylogenetic diversity of tropical forests along a spatial climate gradient in West Africa, showing that drier forests are less stable than wetter forests.
... With regard to one vegetation type (either forests or savannahs), significantly different estimates have been reported from different locations. For instance, Savannah-woodland had 5.9 Mg dry biomass/ha in central Burkina Faso, 132.0 Mg dry biomass/ha in southern Ghana but over 170.2 Mg dry biomass/ha in central Ghana (Koranteng, Adu-Poku, & Zawila-Niedzwiecki, 2017;Moore et al., 2018;Qasim et al., 2016). ...
... AGB showed significant differences between the vegetation types studied, being greatest in closed-canopy and riparian forests (>200 Mg/ha). The estimates for these two forest types are similar to those of semi-deciduous forest in central Nigeria and Ghana (Jibrin, Zubairu, Abdulkadir, Kaura, & Baminda, 2014;Moore et al., 2018, see Table 4). However, they are higher than values from riparian forest in two reserves in Burkina Faso (Qasim et al., 2016). ...
Article
Despite the increasing interest in the role of African savannah and woodlands on the global carbon cycle, little is known about the above‐ground biomass (AGB) and the factors affecting it in these ecosystems in West Africa. We estimated AGB in different vegetation types of a forest–savannah mosaic in Togo, and we investigated the relationship between AGB, structural and diversity attributes. We also assessed the effects of using the ≥5 or ≥10 cm diameter threshold on AGB estimates. We sampled tree diameter, height and species of all trees ≥5 cm diameter following standardised protocols in 160 plots of 50 × 20 m (50 × 10 m for riparian). Above‐ground biomass (AGB) (all trees ≥5 cm diameter) ranged from 6.2 Mg/ha in shrub savannah to 292 Mg/ha in riparian forest and showed significant differences between vegetation types. Differences in AGB were related to structural attributes, with little influence of diversity attributes. The effects of minimum tree diameter size (5 or 10 cm) on AGB estimates were negligible. At a landscape level, closed‐canopy and open forests stored important quantities of carbon. We highlight the importance of the forest–savannah mosaic as a large carbon pool, which could be released if converted to another land cover type.
... Seven plots were sampled along a rainfall gradient spanning from 1200 to 2100 mm of mean annual precipitation (Moore et al., 2018, Table 1). On the driest end, three plots were located at the Kogyae Strict Nature Reserve), a 330 km 2 protected area located in the north-eastern part of the Ashanti region. ...
... Two semi-deciduous forest plots were sampled at Bobiri Reserve (Table 1). Soils at Bobiri are thought to be of similar origin as in Kogyae, and there may be local depositional features, or other possibility includes heavy cation deposition from Saharan dust during the Harmattan winds in January and February (Moore et al., 2018). The two plots at the wettest end were located in Ankasa National Park, south-western Ghana. ...
Article
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Deconstructing functional trait variation and co-variation across a wide range of environmental conditions is necessary to increase the mechanistic understanding of community assembly processes and improve current parameterization of dynamic vegetation models. Here, we present a study that deconstructs leaf trait variation and co-variation into within-species, taxonomic-, and plot-environment components along three tropical environmental gradients in Peru, Brazil, and Ghana. To do so, we measured photosynthetic, chemical, and structural leaf traits using a standardized sampling protocol for more than 1,000 individuals belonging to 367 species. Variation associated with the taxonomic component (species + genus + family) for most traits was relatively consistent across environmental gradients, but within-species variation and plot-environment variation was strongly dependent on the environmental gradient. Trait-trait co-variation was strongly linked to the environmental gradient where traits were measured, although some traits had consistent co-variation components irrespective of gradient. Our results demonstrate that filtering along these tropical gradients is mostly expressed through trait taxonomic variation, but that trait co-variation is strongly dependent on the local environment, and thus global trait co-variation relationships might not always apply at smaller scales and may quickly change under future climate scenarios.
... The mean fine root biomass of woody plants in the savanna woodlands at the foot of Mt. Kilimanjaro (1.0 Mg ha −1 ) was at the lower end of the range of values reported for other tropical savannas and dry forests (0.4 to 11.86 Mg ha −1 ) (Roy and Singh, 1994;Chen et al., 2003;February and Higgins, 2010;Moore et al., 2018). In the present study, we only consider woody roots, whereas most of the cited studies did not differentiate between woody and non-woody roots. ...
... Furthermore, fine root production in the savanna was also lower and fine root lifespan higher than the range of values given for other savannas and tropical dry forests (ca. 1.0 vs. 2.3 to 14.3 Mg ha −1 yr −1 and 0.97 yr compared to 0.07 to 0.38 yr, respectively) (Kummerow et al., 1990;Pandey and Singh, 1992;Chen et al., 2004;Moore et al., 2018). ...
Article
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Fine roots (≤2 mm) consume a large proportion of photosynthates and thus play a key role in the global carbon cycle, but our knowledge about fine root biomass, production, and turnover across environmental gradients is insufficient, especially in tropical ecosystems. Root system studies along elevation transects can produce valuable insights into root trait-environment relationships and may help to explore the evidence for a root economics spectrum (RES) that should represent a trait syndrome with a trade-off between resource acquisitive and conservative root traits. We studied fine root biomass, necromass, production, and mean fine root lifespan (the inverse of fine root turnover) of woody plants in six natural tropical ecosystems (savanna, four tropical mountain forest types, tropical alpine heathland) on the southern slope of Mt. Kilimanjaro (Tanzania) between 900 and 4,500 m a.s.l. Fine root biomass and necromass showed a unimodal pattern along the slope with a peak in the moist upper montane forest (~2,800 m), while fine root production varied little between savanna and upper montane forest to decrease toward the alpine zone. Root:shoot ratio (fine root biomass and production related to aboveground biomass) in the tropical montane forest increased exponentially with elevation, while it decreased with precipitation and soil nitrogen availability (decreasing soil C:N ratio). Mean fine root lifespan was lowest in the ecosystems with pronounced resource limitation (savanna at low elevation, alpine heathland at high elevation) and higher in the moist and cool forest belt (~1,800–3,700 m). The variation in root traits across the elevation gradient fits better with the concept of a multi-dimensional RES, as root tissue density and specific root length showed variable relations to each other, which does not agree with a simple trade-off between acquisitive and conservative root traits. In conclusion, despite large variation in fine root biomass, production, and morphology among the different plant species and ecosystems, a general belowground shift in carbohydrate partitioning is evident from 900 to 4,500 m a.s.l., suggesting that plant growth is increasingly limited by nutrient (probably N) shortage toward higher elevations.
... NPP values for the cocoa farms were then compared to NPP values collected for the conservation area forest plots (∼17 Mg C ha −1 yr −1 ) to generate an estimate of HANPP of the cocoa farms. While high, these values are comparable to several other tropical regions and other studies have confirmed that West Africa has very high NPP values (Moore et al., 2017). Further, this value sits within upper bounds calculated for synthesis studies of tropical forest NPP (Clark et al., 2001). ...
... These values are lower than those for our study which ranged from 10.59 to 11.05 Mg C ha −1 yr −1 . The high productivity noted in tropical forests of Ghana (Moore et al., 2017;Morel et al., 2019) could possibly explain these differences. ...
Article
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Quantifying human impact on the environment is increasingly important and particularly so in complex mosaic landscapes. Such landscapes are prolific in the developing world, notably in West African, small holder cocoa farming communities. Human Appropriated Net Primary Productivity (HANPP) is a metric which has been developed to quantify the human impact on the environment and has been used in a number of studies globally. However, most operationalization's of HANPP have been done on a coarse global scale or a very local scale, and few studies exist of complex mosaic landscapes. This study utilizes Unmanned Autonomous Vehicles (UAV), or drones, to classify land use and HANPP for three cocoa farming regions in Ghana's Central Region. The results of the study indicate while all regions differ in land use composition, the primary crop for all is cocoa, followed by palm and then land that was previously cultivated which has been left fallow. The average HANPP was 44% for all measured regions, calculated using net primary productivity (NPP) values of an adjacent natural tropical forest. The HANPP for the three regions studied was found to be approximately 6.69, 8.00, and 9.85 Mg C ha−1 yr−1. These values are higher than those that have been reported in some widely accepted global studies, and highlight the need for more regional and landscape scale studies to supplement global assessments of HANPP.
... We ran an initial spin-up simulation from bare ground (just seeds and a few seedlings for each PFT) for 500 yr to reach a steady state in which the number of plants, biomass, basal area and so on had minimal (<1%) year-to-year variation. We then compared the average of the last 100 yr of the model output with the forest inventory data from LuiKotale and published data from tropical African forests 12,37 . The model output compared reasonably well to the LuiKotale and central Africa data in terms of stems ha −1 , basal area, mean diameter and AGB (Supplementary Table 2). ...
... The simulated relative amounts of each PFT comprise a realistic mix of early-, mid-and late-successional types ( Supplementary Fig. 6). Modelled NPP (average 17.5 Mg ha −1 yr −1 ) compares reasonably with field measurements in tropical Africa (13-16 MgC ha −1 yr −1 ; ref. 37 ). ...
Article
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Large herbivores, such as elephants, can have important effects on ecosystems and biogeochemical cycles. Yet, the influence of elephants on the structure, productivity and carbon stocks in Africa’s rainforests remain largely unknown. Here, we quantify those effects by incorporating elephant disturbance in the Ecosystem Demography model, and verify the modelled effects by comparing them with forest inventory data from two lowland primary forests in Africa. We find that the reduction of forest stem density due to the presence of elephants leads to changes in the competition for light, water and space among trees. These changes favour the emergence of fewer and larger trees with higher wood density. Such a shift in African’s rainforest structure and species composition increases the long-term equilibrium of aboveground biomass. The shift also reduces the forest net primary productivity, given the trade-off between productivity and wood density. At a typical density of 0.5 to 1 animals per km², elephant disturbances increase aboveground biomass by 26–60 t ha⁻¹. Conversely, the extinction of forest elephants would result in a 7% decrease in the aboveground biomass in central African rainforests. These modelled results are confirmed by field inventory data. We speculate that the presence of forest elephants may have shaped the structure of Africa’s rainforests, which probably plays an important role in differentiating them from Amazonian rainforests.
... Along the aridity gradient, rainfall seasonality (Table S1), vegetation seasonality and deciduousness increased considerably toward the drier sites 10,61,65 , whereas LAI and tree density decreased toward the drier sites 64 . More information about the study sites, soil properties, hydrology and climate regime can be found at 10,30,84,85 . Forests in ANK and BOB have never burnt (to our knowledge), but KOG experiences wildfire roughly every decade 19,86 . ...
Article
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Tropical forests cover large areas of equatorial Africa and play a substantial role in the global carbon cycle. However, there has been a lack of biometric measurements to understand the forests’ gross and net primary productivity (GPP, NPP) and their allocation. Here we present a detailed field assessment of the carbon budget of multiple forest sites in Africa, by monitoring 14 one-hectare plots along an aridity gradient in Ghana, West Africa. When compared with an equivalent aridity gradient in Amazonia, the studied West African forests generally had higher productivity and lower carbon use efficiency (CUE). The West African aridity gradient consistently shows the highest NPP, CUE, GPP, and autotrophic respiration at a medium-aridity site, Bobiri. Notably, NPP and GPP of the site are the highest yet reported anywhere for intact forests. Widely used data products substantially underestimate productivity when compared to biometric measurements in Amazonia and Africa. Our analysis suggests that the high productivity of the African forests is linked to their large GPP allocation to canopy and semi-deciduous characteristics.
... In contrast, lower understorey vegetation biomass at higher altitudes may result from harsh environmental conditions, including low temperatures and frost that cause physiological stress to the plants, and can limit the growth of many vascular plant species at these elevations (Singh et al. 1994;Sharma et al. 2011). Furthermore, at higher elevations, the slow rate of organic matter decomposition can lead to excess humus accumulation, subsequently reducing soil productivity and decreasing vascular biomass production in the understorey (Berg and McClaugherty 2014;Parton et al. 2015;Korner, 2015;Moore et al. 2017;He et al. 2018). However, the increasing trend in bryophyte biomass production observed in our study can be attributed to their ability to thrive in the harsh, cold climatic conditions typical of higher elevations (Heegaard 2002;Brunn et al. 2006). ...
Article
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Forests, covering approximately thirty percent of the Earth’s total surface area, are the world’s largest carbon sink and a crucial player in mitigating climate change through carbon sequestration. However, human activities, both developmental and anthropogenic, have resulted in forest degradation, resulting in biodiversity loss, and increased carbon dioxide concentrations in the temperate Himalayan region, where reliable estimates of aboveground biomass and its variation across the landscape are currently lacking. The present study aims to assess aboveground biomass and carbon stocks along altitudinal gradients and overstorey types in the temperate Himalayan region. Across all altitudinal gradients and dominant overstorey composition types, total, tree, shrub, herb, and bryophytes biomass and carbon stocks on average were 372.7, 369.1, 2.76, 0.77 and 0.10 Mg ha􀀀 1, and 177.1, 175.3, 1.31, 0.37 and 0.05 Mg ha􀀀 1, respectively. The biomass and carbon stock of total and individual vegetation components differed significantly along the altitudinal gradients and overstorey composition types. Total and tree aboveground biomass and carbon stocks showed a consistent gradual increase along altitudinal gradients, peaking at middle elevations and declining thereafter at higher altitudes. The result highlighted the variation in biomass and carbon stocks in the temperate Himalayan region is influenced by factors such as the presence of individuals in large-diameter classes, higher stem densities with increased basal area, and forest management practices along altitudinal gradients. The study also emphasized the role of dominant overstorey composition types in biomass and carbon stock distribution in the temperate Himalayan region. However, tree, shrub, herb, and bryophyte biomass production responded differently for dominant composition types. Shrub and herb biomass along with their carbon stocks appeared to be positively associated with higher resource availability under deciduous broadleaf overstorey types, while the trees and bryophytes biomass and carbon stocks were found to be higher under coniferous stands. Mixedwood stands, on the other hand, were found to be intermediate between the pure stands, but had higher biomass and carbon stocks at higher altitudes. Therefore management interventions should aim at maintaining a diverse range of overstorey composition types for promoting the ecosystem functions and services of temperate Himalayan forest ecosystems.
... We investigate whether the field-observed high productivity is consistent with the leaf photosynthetic traits and other field measurements that were commonly simulated by models. This investigation was made possible by extensive field measurements of environmental variables, plant traits, and carbon fluxes at the study sites (23)(24)(25)(26). Objective (3): We attempt to account for the data-model discrepancy in the West African region by substituting model parameters with field measurements, according to several hypotheses listed below as to the cause of this discrepancy. ...
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Tropical forests dominate terrestrial photosynthesis, yet there are major contradictions in our understanding due to a lack of field studies, especially outside the tropical Americas. A recent field study indicated that West African forests have among the highest forests gross primary productivity (GPP) yet observed, contradicting models that rank them lower than Amazonian forests. Here, we explore possible reasons for this data-model mismatch. We found the in situ GPP measurements higher than multiple global GPP products at the studied sites in Ghana. The underestimation of GPP by models largely disappears when a standard photosynthesis model is informed by local field-measured values of (a) fractional absorbed photosynthetic radiation (fAPAR), and (b) photosynthetic traits. Satellites systematically underestimate fAPAR in the tropics due to cloud contamination issues. The study highlights the potential widespread underestimation of tropical forests GPP and carbon cycling and hints at the ways forward for model and input data improvement. Teaser West African forests are much more productive than predicted by remote sensing or modelling – we explain why this happens and its potential implications for global estimates of tropical forest productivity. Codes and data availability There are no potential conflicts of interest. All data and codes underlying the study are currently shared via Github (link here) which will be made available through Zenodo upon acceptance.
... In contrast, lower understorey vegetation biomass at higher altitudes may result from harsh environmental conditions, including low temperatures and frost that cause physiological stress to the plants, and can limit the growth of many vascular plant species at these elevations (Singh et al. 1994;Sharma et al. 2011). Furthermore, at higher elevations, the slow rate of organic matter decomposition can lead to excess humus accumulation, subsequently reducing soil productivity and decreasing vascular biomass production in the understorey (Berg and McClaugherty 2014;Parton et al. 2015;Korner, 2015;Moore et al. 2017;He et al. 2018). However, the increasing trend in bryophyte biomass production observed in our study can be attributed to their ability to thrive in the harsh, cold climatic conditions typical of higher elevations (Heegaard 2002;Brunn et al. 2006). ...
... t N ha − 1 year − 1 ). This might result from the drier climate in tropical Africa (Fig. S6f), which is supported by findings of Moore et al. (2018) showing that NPP decreased from the humid to arid region in West Africa. Thus, the highest NPP in African tropical forests was calculated to be 53.69 ...
... We predicted that C residence time should be greater in (1) cooler systems due to lower soil temperatures and shorter growing seasons and (2) drier systems due to moisture limitations on microbial activity. Previous studies examining patterns of C residence time have found relationships of varying strengths with climate or latitude (Bird et al., 1996;Chen et al., 2013;Carvalhais et al., 2014;Moore et al., 2018), biome type (Zhou and Luo, 2008), soil properties (Telles et al., 2003), vegetation tissue quality (Adair et al., 2008;Bontti et al., 2009), and land use change (Sperow et al., 2016;Wu et al., 2020). Yet, there is still much uncertainty associated with trends in C residence time (Friend et al., 2014). ...
Article
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Future global changes will impact carbon (C) fluxes and pools in most terrestrial ecosystems and the feedback of terrestrial carbon cycling to atmospheric CO2. Determining the vulnerability of C in ecosystems to future environmental change is thus vital for targeted land management and policy. The C capacity of an ecosystem is a function of its C inputs (e.g., net primary productivity – NPP) and how long C remains in the system before being respired back to the atmosphere. The proportion of C capacity currently stored by an ecosystem (i.e., its C saturation) provides information about the potential for long-term C pools to be altered by environmental and land management regimes. We estimated C capacity, C saturation, NPP, and ecosystem C residence time in six US grasslands spanning temperature and precipitation gradients by integrating high temporal resolution C pool and flux data with a process-based C model. As expected, NPP across grasslands was strongly correlated with mean annual precipitation (MAP), yet C residence time was not related to MAP or mean annual temperature (MAT). We link soil temperature, soil moisture, and inherent C turnover rates (potentially due to microbial function and tissue quality) as determinants of carbon residence time. Overall, we found that intermediates between extremes in moisture and temperature had low C saturation, indicating that C in these grasslands may trend upwards and be buffered against global change impacts. Hot and dry grasslands had greatest C saturation due to both small C inputs through NPP and high C turnover rates during soil moisture conditions favorable for microbial activity. Additionally, leaching of soil C during monsoon events may lead to C loss. C saturation was also high in tallgrass prairie due to frequent fire that reduced inputs of aboveground plant material. Accordingly, we suggest that both hot, dry ecosystems and those frequently disturbed should be subject to careful land management and policy decisions to prevent losses of C stored in these systems.
... Furthermore, the desire of plantation farmers for a certain size allows trees to reach a specific size before harvest as their biomass accumulates rapidly with stand age [72]. Similar to this result are studies in semi-deciduous forest in West Africa [73,74] and for closed canopy and Riverine forest in Togo [18]. ...
Article
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Tropical landscapes comprise a variety of land cover (LC) types with characteristic canopy structure and tree species. Depending on the LC type, large-diameter trees and certain tree species can contribute disproportionately to aboveground biomass (AGB), and these patterns are not described at landscape-level in LC type specific studies. Therefore, we investigated the impact of large trees and tree species on AGB across a range of LC types in Taita Hills, Kenya. Data included 239 field plots from seven LC types: Montane forest, Plantation forest, Mixed forest, Riverine forest, Bushland, Grassland, and Cropland and homestead. Our results show that the contribution of large trees (DBH > 60 cm) on AGB was greatest in Riverine forest, Montane forest and Mixed forest (34–87%). Large trees were also common in Plantation forests and Cropland and homestead. Small trees (DBH < 20 cm) covered less than 10% of the total AGB in all forest types. In Grassland, and Cropland and homestead, smaller DBH classes made a greater contribution. Bushland differed from other classes as large trees were rare. Furthermore, the results show that each LC type had characteristic species with high AGB. In the Montane and Mixed forest, Albizia gummifera contributed 21.1% and 18.3% to AGB, respectively. Eucalyptus spp., exotic species planted in the area, were important in Mixed and Plantation forests. Newtonia hildebrandtii was the most important species in Riverine forests. In Bushland, Acacia mearnsii, species with invasive character, was abundant among trees with DBH < 30 cm. Vachellia tortillis, a common species in savannahs of East Africa, made the largest contribution in Grassland. Finally, in Cropland and homestead, Grevillea robusta was the most important species (>25% of AGB). Our results highlight the importance of conserving large trees and certain species to retain AGB stocks in the landscape. Furthermore, the results demonstrate that exotic tree species, even though invasive, can have large contribution to AGB.
... The conversion of savanna woodlands to maize fields represents a high impact on the fine root C stocks as it entails a 70% decrease of the fine root biomass. Our fine root biomass values for savanna were at the lower end of the range of values reported for other tropical savannas and dry forests (0.4-11.86 Mg ha −1 ) (Roy and Singh 1994;Chen et al. 2003;February and Higgins 2010;Moore et al. 2018). Differences might be due to the lower mean annual precipitation, the lower number of trees at our savannas and to its semi-natural condition, as they are subject to logging and burning pressure that has been intensifying during the last decades (Agrawala et al. 2003;Hemp and Hemp 2018). ...
Article
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Tropical forests are threatened by anthropogenic activities such as conversion into agricultural land, logging and fires. Land-use change and disturbance affect ecosystems not only aboveground, but also belowground including the ecosystems' carbon and nitrogen cycle. We studied the impact of different types of land-use change (intensive and traditional agroforestry, logging) and disturbance by fire on fine root biomass, dynamics, morphology, and related C and N fluxes to the soil via fine root litter across different ecosystems at different elevational zones at Mt. Kilimanjaro (Tanzania). We found a decrease in fine root biomass (80-90%), production (50%), and C and N fluxes to the soil via fine root litter (60-80%) at all elevation zones. The traditional agroforestry 'Chagga homegardens' (lower montane zone) showed enhanced fine root turnover rates, higher values of acquisitive root morphological traits, but similar stand fine root production, C and N fluxes compared to the natural forest. The decrease of C and N fluxes with forest disturbance was particularly strong at the upper montane zone (60 and 80% decrease, respectively), where several patches of Podocarpus forest had been disturbed by fire in the previous years. We conclude that changes on species composition, stand structure and land management practices resulting from land-use change and disturbance have a strong impact on the fine root system, modifying fine root biomass, production and the C and N supply to the soil from fine root litter, which strongly affects the ecosystems' C and N cycle in those East African tropical forest ecosystems.
... We used a carbon content of 47% to convert dry weight biomass estimates to AGC. belowground) is 9% less than the satellite-based estimate for the same location and period, as well as 9% less than N P P ag estimated from forest inventory data ( Figure 2b). It has to be noted that a substantial fraction of NPP of 21-32% of NPP is allocated belowground in comparable forests in Ghana (Moore et al., 2018). Simulated SOC 2m of 9.0 kgm −2 is 54% higher The simulated sink in baseline simulation with constant nutrient deposition are lower than the 95 th percentile for all decades. ...
Article
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Spatial redistribution of nutrients by atmospheric transport and deposition could theoretically act as a continental‐scale mechanism which counteracts declines in soil fertility caused by nutrient lock‐up in accumulating biomass in tropical forests in Central Africa. However, to what extent it affects carbon sinks in forests remains elusive. Here we use a terrestrial biosphere model to quantify the impact of changes in atmospheric nitrogen and phosphorus deposition on plant nutrition and biomass carbon sink at a typical lowland forest site in Central Africa. We find that the increase in nutrient deposition since the 1980s could have contributed to the carbon sink over the past four decades up to an extent which is similar to that from the combined effects of increasing atmospheric carbon dioxide and climate change. Furthermore, we find that the modelled carbon sink responds to changes in phosphorus deposition, but less so to nitrogen deposition. The pronounced response of ecosystem productivity to changes in nutrient deposition illustrates a potential mechanism that could control carbon sinks in Central Africa. Monitoring the quantity and quality of nutrient deposition is needed in this region, given the changes in nutrient deposition due to human land use.
... Predominantly, the tropical forest ecosystem is known for the highest carbon pool in its biomass compared with other biomes of the world [19][20][21][22][23][24]. Generally, the tropical biome is the most productive and accounts for over 60% of global terrestrial photosynthesis and one-third of global net primary productivity [25][26][27]. ...
Article
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Moist tropical forests have a significant role in provisioning and regulating ecosystem services. However, these forests are under threat of deforestation and forest degradation. In Ethiopia, the moist evergreen Afromontane forests have the potential for carbon storage and support a high diversity of plant species. However, it is under severe threat of deforestation and degradation.This investigation was conducted to obtain adequate information on the carbon stock potential of the moist Afromontane forest of southwestern Ethiopia. A comparison of carbon stock was conducted between disturbed and undisturbed forests. A systematic sampling design was applied for recording woody species and soil data. A total of 100 main plots of 400 m2 were laid to record trees and shrubs with a diameter at breast height (DBH) ≥ 5 cm. The soil data were collected from 1 m2 subplots established at the four corners and the center of each main plot. The DBH and height were measured to calculate the aboveground carbon of trees and shrubs with DBH ≥ 5 cm. A total of 68 tree and shrub species belonging to 59 genera and 33 families were recorded. The mean carbon stock density was 203.80 ± 12.38 t·ha–1 (aboveground carbon stock) and 40.76 ± 2.47 t·ha–1 (belowground carbon stock). The highest proportion of aboveground carbon (t·ha–1) (42.34%) was contributed by a few tree individuals with DBH > 70 cm. The soil organic carbon stock (SOCS) (t·ha–1) for the depth of 0–30 cm is ranging from 58.97 to 198.33 across plots; the mean is 117.16 ± 3.15. The carbon stored in the moist Afromontane forest indicates its huge potential for climate change mitigation. Therefore, for the enhancement of forest biodiversity and carbon sequestration effective conservation measure and sound management approach is essential.
... Surprisingly, leaf N contents of dominant species are often lower than those of rare species in natural communities (Han et al., 2011;He et al., 2006;Yuan and Chen, 2009). The leaf N content of herbs is typically higher than that of trees in forests and it is also higher in extremely arid regions with scarce resources than in resource-rich regions (Moore et al., 2018;Moreno-Martínez et al., 2018;Wright et al., 2005). Therefore, it is difficult to establish a positive relationship between leaf N content and ecosystem productivity. ...
Article
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At present, using plant traits to predict ecosystem functions is of great significance as trait-based ecology recasts classic ecological propositions. However, functional traits at the individual level do not predict higher-level aggregated ecosystem processes (e.g., gross primary productivity) accurately because vital contextual information on specific communities or ecosystems is not considered. Here, we integrate individual or species level plant traits with background information, such as total leaf mass, to form plant community traits that explain spatial variability in productivity. We use a systematic dataset of leaf nitrogen (N) content in 73 typical ecosystems of China that were classified based on community weighted mean leaf N content (Ncontent, mg g⁻¹) and the total leaf N reserves per land area (Nquantity, g m⁻²) to verify their variations at a large scale across biomes and their responses to changing environmental factors. The results showed that using plant community traits, even without factoring in climatic factors, explains 81% and 68% of the spatial variability in annual gross primary productivities and monthly gross primary productivities, respectively. In addition, both Ncontent and Nquantity were significantly affected by environmental factors (climatic and soil factors). Our findings highlight that two-dimensional plant community traits of content vs. quantity on land area can strengthen the predictability of variations of primary productivity and even other ecosystem functions.
... In the past, a few studies have indicated that the multispectral satellite images are useful and can assist in monitoring the structure, and composition of a forest type, its diversity, and spatial arrangements (Lepine et al., 2016;Shiklomanov et al., 2016;Ali et al., 2017;Middinti et al., 2017), before addressing any functional ecological and biophysical processes of an ecosystem (such as above-ground biomass (AGB), net primary production (NPP), evapotranspiration, energy exchange, and biomass allocation patterns). Tropical forests are considered as productive terrestrial environments with a maximum potential of carbon sink and NPP per unit area (Fearnside, 1996;Gaston et al., 1998;Chave et al., 2001;Clark et al., 2001;Malhi et al., 2004;Malhi et al., 2009;Bijalwan et al., 2010;Mohommad and Joshi, 2015;Anderson-Teixeira et al., 2016;Moore et al., 2018;Wallis et al., 2019;Wang et al., 2019). The structure of vegetation helps to facilitate suitable management practices and obtain higher rates of biomass production with maximum economic returns. ...
Book
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All the editors hope that the article (review/research) published in this book will help the policy makers, environmentalists, foresters, and young researchers to understand the carbon dynamics in the terrestrial ecosystem at the regional and/or global scale. Furthermore, the mitigation strategies suggested by the different authors will help in C reduction in the terrestrial ecosystem.
... In the past, a few studies have indicated that the multispectral satellite images are useful and can assist in monitoring the structure, and composition of a forest type, its diversity, and spatial arrangements (Lepine et al., 2016;Shiklomanov et al., 2016;Ali et al., 2017;Middinti et al., 2017), before addressing any functional ecological and biophysical processes of an ecosystem (such as above-ground biomass (AGB), net primary production (NPP), evapotranspiration, energy exchange, and biomass allocation patterns). Tropical forests are considered as productive terrestrial environments with a maximum potential of carbon sink and NPP per unit area (Fearnside, 1996;Gaston et al., 1998;Chave et al., 2001;Clark et al., 2001;Malhi et al., 2004;Malhi et al., 2009;Beer et al., 2010;Bijalwan et al., 2010;Mohommad and Joshi, 2015;Anderson-Teixeira et al., 2016;Poorter et al., 2016;Moore et al., 2018;Wallis et al., 2019;Wang et al., 2019). The structure of vegetation helps to facilitate suitable management practices and obtain higher rates of biomass production with maximum economic returns. ...
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In recent decades, degradation and loss of the world’s forest ecosystems have been key contributors to biodiversity loss and future climate change. This article analyzes plant diversity, biomass, carbon sequestration potential (CSP), and the net primary productivity (NPP) of four vegetation types viz., Dense mixed forest (DMF); Open mixed forest (OMF); Teak plantation (TP), and Sal mixed forest (SMF) in the dry tropical forest ecosystem of central India through remote sensing techniques together with physical ground observations during 2013–2018. The total C storage in trees varied from 16.02 to 47.15 Mg ha−1 in studied vegetation types with the highest in DMF and lowest in OMF. The total C storage in stem wood, branches, and foliage falls in the range of 52.93–78.30%, 9.49–22.99%, and 3.31–12.89% respectively. The total standing biomass varied from 83.77 to 111.21 Mg ha−1 and these variations are due to different vegetation types, with the highest in DMF followed by TP, SMF while the lowest was estimated in OMF. The net primary productivity (NPP) [above ground (AG) + below ground (BG)] varied from 7.61 to 9.94 Mg ha−1 yr−1 with mean values of 8.74 Mg ha−1 yr−1 where AG shares a maximum contribution of 77.66%. The total biomass production was distributed from 64.09 to 82.91% in AG and 17.08–35.91% in BG components. The present study outlines that the studied forest ecosystem has the substantial potential of carbon sequestration and a great possibility of mitigating local and global climate change.
... In the past, a few studies have indicated that the multispectral satellite images are useful and can assist in monitoring the structure, and composition of a forest type, its diversity, and spatial arrangements (Lepine et al., 2016;Shiklomanov et al., 2016;Ali et al., 2017;Middinti et al., 2017), before addressing any functional ecological and biophysical processes of an ecosystem (such as above-ground biomass (AGB), net primary production (NPP), evapotranspiration, energy exchange, and biomass allocation patterns). Tropical forests are considered as productive terrestrial environments with a maximum potential of carbon sink and NPP per unit area (Fearnside, 1996;Gaston et al., 1998;Chave et al., 2001;Clark et al., 2001;Malhi et al., 2004;Malhi et al., 2009;Beer et al., 2010;Bijalwan et al., 2010;Mohommad and Joshi, 2015;Anderson-Teixeira et al., 2016;Poorter et al., 2016;Moore et al., 2018;Wallis et al., 2019;Wang et al., 2019). The structure of vegetation helps to facilitate suitable management practices and obtain higher rates of biomass production with maximum economic returns. ...
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In recent decades, degradation and loss of the world's forest ecosystems have been key contributors to biodiversity loss and future climate change. This article analyzes plant diversity, biomass, carbon sequestration potential (CSP), and the net primary productivity (NPP) of four vegetation types viz., Dense mixed forest (DMF); Open mixed forest (OMF); Teak plantation (TP), and Sal mixed forest (SMF) in the dry tropical forest ecosystem of central India through remote sensing techniques together with physical ground observations during 2013-2018. The total C storage in trees varied from 16.02 to 47.15 Mg ha −1 in studied vegetation types with the highest in DMF and lowest in OMF. The total C storage in stem wood, branches, and foliage falls in the range of 52.93-78.30%, 9.49-22.99%, and 3.31-12.89% respectively. The total standing biomass varied from 83.77 to 111.21 Mg ha −1 and these variations are due to different vegetation types, with the highest in DMF followed by TP, SMF while the lowest was estimated in OMF. The net primary productivity (NPP) [aboveground (AG) + belowground (BG)] varied from 7.61 to 9.94 Mg ha −1 yr −1 with mean values of 8.74 Mg ha −1 yr −1 where AG shares a maximum contribution of 77.66%. The total biomass production was distributed from 64.09 to 82.91% in AG and 17.08-35.91% in BG components. The present study outlines that the studied forest ecosystem has the substantial potential of carbon sequestration and a great possibility of mitigating local and global climate change.
... As anticipated, we found that drought significantly reduced terrestrial productivity (Fig. 2a), which confirmed the conclusions derived from previous forest (Moore et al., 2018;Ogaya and Peñuelas, 2007) and grassland (Ansley et al., 2013;Jin et al., 2018) studies across spatial and temporal gradients (Gao et al., 2019;Song et al., 2019;Wilcox et al., 2017;Wu et al., 2011). One possible explanation was that, under drought stress, plant growth was constrained and the growth rate of dominant herbs was decreased in grasslands (Jin et al., 2018). ...
... In the past, a few studies have indicated that the multispectral satellite images are useful and can assist in monitoring the structure, and composition of a forest type, its diversity, and spatial arrangements (Lepine et al., 2016;Shiklomanov et al., 2016;Ali et al., 2017;Middinti et al., 2017), before addressing any functional ecological and biophysical processes of an ecosystem (such as above-ground biomass (AGB), net primary production (NPP), evapotranspiration, energy exchange, and biomass allocation patterns). Tropical forests are considered as productive terrestrial environments with a maximum potential of carbon sink and NPP per unit area (Fearnside, 1996;Gaston et al., 1998;Chave et al., 2001;Clark et al., 2001;Malhi et al., 2004;Malhi et al., 2009;Beer et al., 2010;Bijalwan et al., 2010;Mohommad and Joshi, 2015;Anderson-Teixeira et al., 2016;Poorter et al., 2016;Moore et al., 2018;Wallis et al., 2019;Wang et al., 2019). The structure of vegetation helps to facilitate suitable management practices and obtain higher rates of biomass production with maximum economic returns. ...
Article
Full-text available
In recent decades, degradation and loss of the world’s forest ecosystems have been key contributors to biodiversity loss and future climate change. This article analyzes plant diversity, biomass, carbon sequestration potential (CSP), and the net primary productivity (NPP) of four vegetation types viz., Dense mixed forest (DMF); Open mixed forest (OMF); Teak plantation (TP), and Sal mixed forest (SMF) in the dry tropical forest ecosystem of central India through remote sensing techniques together with physical ground observations during 2013–2018. The total C storage in trees varied from 16.02 to 47.15 Mg ha⁻¹ in studied vegetation types with the highest in DMF and lowest in OMF. The total C storage in stem wood, branches, and foliage falls in the range of 52.93–78.30%, 9.49–22.99%, and 3.31–12.89% respectively. The total standing biomass varied from 83.77 to 111.21 Mg ha⁻¹ and these variations are due to different vegetation types, with the highest in DMF followed by TP, SMF while the lowest was estimated in OMF. The net primary productivity (NPP) [aboveground (AG) + belowground (BG)] varied from 7.61 to 9.94 Mg ha⁻¹ yr⁻¹ with mean values of 8.74 Mg ha⁻¹ yr⁻¹ where AG shares a maximum contribution of 77.66%. The total biomass production was distributed from 64.09 to 82.91% in AG and 17.08–35.91% in BG components. The present study outlines that the studied forest ecosystem has the substantial potential of carbon sequestration and a great possibility of mitigating local and global climate change.
... As anticipated, we found that drought significantly reduced terrestrial productivity (Fig. 2a), which confirmed the conclusions derived from previous forest (Moore et al., 2018;Ogaya and Peñuelas, 2007) and grassland (Ansley et al., 2013;Jin et al., 2018) studies across spatial and temporal gradients (Gao et al., 2019;Song et al., 2019;Wilcox et al., 2017;Wu et al., 2011). One possible explanation was that, under drought stress, plant growth was constrained and the growth rate of dominant herbs was decreased in grasslands (Jin et al., 2018). ...
Article
Terrestrial productivity underpins ecosystem carbon (C) cycling and multi-trophic diversity. Despite the negative impacts of drought on terrestrial C cycling, our understanding of the responses of above- and belowground productivity to drought remains incomplete. Here, we synthesized the responses of terrestrial productivity and soil factors (e.g., soil moisture, soil pH, soil C, soil nitrogen (N), soil C:N, fungi:bacteria ratio, and microbial biomass C) to drought via a global meta-analysis of 734 observations from 107 studies. Our results revealed that the productivity variables above- and belowground (i.e., net primary productivity, aboveground net primary productivity, belowground net primary productivity, total biomass, aboveground biomass, root biomass, gross ecosystem productivity, and net ecosystem productivity) were decreased across all ecosystems. However, drought did not significantly affect litter mass across all ecosystems, and the responses of above- and belowground productivity to drought were non-uniform. Furthermore, the responses of these productivity variables to drought were more pronounced with drought intensity and duration, and consistent across ecosystem types and background climates. Drought significantly decreased soil moisture, soil C concentrations, soil C:N ratios, and microbial biomass C, whereas it enhanced soil pH values and fungi:bacteria ratios. Moreover, the negative effects of drought on above- and belowground productivity variables were correlated mostly with the response of soil pH to drought among all soil factors. Our study indicated that litter biomass, which mostly represents productivity levels via traditional ecosystem models, was not able to predict the responses of terrestrial ecosystem productivity to drought. The strong relationship between the responses of soil pH and terrestrial productivity to drought suggests that the incorporation of soil pH into Earth system models might facilitate the prediction of terrestrial C cycling and its feedbacks to drought.
... Indeed, although increasing deforestation rates are reported for South America and Africa ( FAO, 2010( FAO, , 2015, it is widely recognized that tropical forests play a significant role in mitigating climate change impacts through the removal of atmospheric carbon dioxide ( Pan et al., 2011 ;Vashum and Jayakumar, 2012 ;Baccini et al., 2017 ;Rahman et al., 2017 ;Daba and Soromessa, 2019 ). These forests account for one-third of global primary productivity ( Moore et al., 2018 ) and 50% of global carbon stocks ( Pan et al., 2011 ). Sustainable management of tropical species. ...
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West African Sudanian savanna ecosystems greatly contribute to local peoples’ livelihoods and climate change mitigation. Yet, the contribution of these ecosystems to carbon storage remains poorly documented due to the lack of accurate biomass predictive tools. Therefore, biomass allometric models developed at both the species-level and site-level may greatly improve carbon stock estimation. In this study, we developed allometric models for estimating aboveground biomass (AGB) at the tree component-, species- and site-levels in Burkina Faso. Five woody species with high socio-economic significance (Anogeissus leiocarpa, Combretum nigricans, Isoberlinia doka, Mitragyna inermis and Pterocarpus erinaceus) were selected at two forest sites based on their dominance in the savanna ecosystem. A total of 150 trees (30 trees per dominant species) spanning a wide range of diameter at breast height (DBH) were destructively sampled. Models to predict tree component biomass at the species-level were independently built with the Ordinary Least Squares (OLS) technique. Allometric models to predict tree total aboveground biomass (TAGB) for each species and all species were developed using both the OLS technique and the Seemingly Unrelated Regression (SUR) method. Biomass estimates were regressed with DBH as a single predictor, DBH and height (H) as interacted variables, and DBH, H and wood density (ρ) as three independent-input variables. The performance of the validated allometric models were compared with the generalized pantropical equation model for African tropical forests (Chave et al., 2014). The findings revealed that biomass predictors varied between the five species. The goodness-of-fit statistics revealed that both the OLS and SUR methods provide accurate biomass allometric equations, with the SUR method being the most accurate. The developed allometric models provide more accurate estimation of AGB than the pantropical model. Therefore, we recommend the use of these local models to improve the quantification of AGB and carbon stocks in Sudanian savanna ecosystems. Furthermore, the established species-specific and mixed-species allometric equations may constitute a useful tool for the monitoring, reporting and verification of carbon stocks within the REDD+ framework in Burkina Faso.
... Apart from very few NPP measurements in lowland forest plots (e.g. Moore et al. 2018), only one productivity assessment has been done in an African tropical montane forest (Rwanda; Nyirambangutse et al. 2017). Mount Kilimanjaro, in northern Tanzania, with a forest belt covering an elevation gradient of approx. ...
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Tropical forests represent the largest store of terrestrial biomass carbon (C) on earth and contribute over-proportionally to global terrestrial net primary productivity (NPP). How climate change is affecting NPP and C allocation to tree components in forests is not well understood. This is true for tropical forests, but particularly for African tropical forests. Studying forest ecosystems along elevation and related temperature and moisture gradients is one possible approach to address this question. However, the inclusion of belowground productivity data in such studies is scarce. On Mt. Kilimanjaro (Tanzania), we studied aboveground (wood increment, litter fall) and belowground (fine and coarse root) NPP along three elevation transects (c. 1800–3900 m a.s.l.) across four tropical montane forest types to derive C allocation to the major tree components. Total NPP declined continuously with elevation from 8.5 to 2.8 Mg C ha ⁻¹ year ⁻¹ due to significant decline in aboveground NPP, while fine root productivity (sequential coring approach) remained unvaried with around 2 Mg C ha ⁻¹ year ⁻¹ , indicating a marked shift in C allocation to belowground components with elevation. The C and N fluxes to the soil via root litter were far more important than leaf litter inputs in the subalpine Erica forest. Thus, the shift of C allocation to belowground organs with elevation at Mt. Kilimanjaro and other tropical forests suggests increasing nitrogen limitation of aboveground tree growth at higher elevations. Our results show that studying fine root productivity is crucial to understand climate effects on the carbon cycle in tropical forests.
... In Africa, forest and savanna cover approximately half of the continent's land surface (11% and 34%, respectively) and provide invaluable ecosystem services at local and global scales to millions of people (Grace et al., 2006;Lewis et al., 2009;Moore et al., 2017;Olsson & Ouattara, 2013;Parr et al., 2014). Global change threatens the provision of these ecosystem services by eroding forest and savanna ecosystem function through changes to the natural fire regime (Heubes et al., 2011;Scheiter et al., 2019;Seddon et al., 2016;Willis et al., 2013;van Nes et al., 2014). ...
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Global change is expected to increase savanna woody encroachment as well as fire spreading into forest. Forest–savanna ecotones are the frontier of these processes and can thus either mitigate or enhance the effects of global change. However, the ecology of the forest–savanna ecotone is poorly understood. In this study, we determined whether a distinct ecotonal tree community existed between forest and savanna. We then evaluated whether the ecotonal tree community was more likely to facilitate fire spreading into the forest, woody encroachment of the savanna or the stabilisation of both forest and savanna parts of the landscape. We sampled 28 vegetation transects across forest–savanna ecotones in a central African forest–savanna mosaic. We collected data on the size and species of all established (basal diameter >3 cm) trees in each transect. Split moving window dissimilarity analysis detected the location of borders delineating savanna, ecotone and forest tree communities. We assessed whether the ecotonal tree community was likely to facilitate fire spreading into the forest by burning experimental fires and evaluating shade and grass biomass along the transects. To decide whether the ecotone was likely to facilitate woody encroachment of the savanna, we evaluated if ecotonal tree species were forest pioneers. A compositionally distinct and spatially extensive ecotonal tree community existed between forest and savanna. The ecotonal tree community did not promote fire spreading into forest and instead acted as a fire buffer, shading out flammable grass biomass from the understorey and protecting the forest from 95% of savanna fires. The ecotone helped stabilise the forest–savanna mosaic by allowing the fire‐dependant savanna to burn without exposing the fire‐sensitive forest to lethal temperatures. The ecotonal tree community was comprised of many forest pioneer species that will promote woody encroachment in the savanna, especially if fire frequency is decreased. Synthesis. A distinct fire‐buffering ecotonal tree community in this forest–savanna mosaic landscape illustrated that savanna fires are unlikely to compromise forest integrity. Conversely, suppression of fire in this landscape will likely lead to loss of savanna as the ecotone becomes the frontier of woody encroachment. Regular burning is essential for the preservation of this forest–savanna mosaic.
... The soil carbon balance depends on the relationship between the addition of photosynthesized carbon by plants and carbon losses to the atmosphere resulting from the microbial oxidation of organic carbon into CO2 (King, 2011;Bhattacharya et al., 2016;Crowther et al., 2016). Studies have shown that the storage of organic carbon in soil and its dynamics are determined by factors such as climate, soil type and properties, plant cover, and management practices (Moore et al., 2018;Navarrete-Segueda et al., 2018;Shukla & Chakravarty, 2018). ...
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An increase in atmospheric CO2 levels and global climate changes have led to an increased focus on CO2 capture mechanisms. The in situ quantification and spatial patterns of forest carbon stocks can provide a better picture of the carbon cycle and a deeper understanding of the functions and services of forest ecosystems. This study aimed to determine the aboveground (tree trunks) and belowground (soil and fine roots, at four depths) carbon stocks in a tropical forest in Brazil and to evaluate the spatial patterns of carbon in the three different compartments and in the total stock. Census data from a semideciduous seasonal forest were used to estimate the aboveground carbon stock. The carbon stocks of soil and fine roots were sampled in 52 plots at depths of 0-20, 20-40, 40-60, and 60-80 cm, combined with the measured bulk density. The total estimated carbon stock was 267.52 Mg ha-1 , of which 35.23% was in aboveground biomass, 63.22% in soil, and 1.54% in roots. In the soil, a spatial pattern of the carbon stock was repeated at all depths analyzed, with a reduction in the amount of carbon as the depth increased. The carbon stock of the trees followed the same spatial pattern as the soil, indicating a relationship between these variables. In the fine roots, the carbon stock decreased with increasing depth, but the spatial gradient did not follow the same pattern as the soil and trees, which indicated that the root carbon stock was most likely influenced by other factors.
... Particularly, this ecosystem is known for its highest carbon pool when compared to other biomes of the world [1][2][3]. It is the most productive ecosystem accounting for over 60% of global terrestrial photosynthesis and one-third of global primary productivity [4]. Generally, the accumulation of a great deal of carbon stock in the aboveground biomass of tropical forests was verified [5,6]. ...
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Background: Application of allometric equations for quantifying forests aboveground biomass is a crucial step related to efforts of climate change mitigation. Generalized allometric equations have been applied for estimating biomass and carbon storage of forests. However, adopting a generalized allometric equation to estimate the biomass of different forests generates uncertainty due to environmental variation. Therefore, formulating species-specific allometric equations is important to accurately quantify the biomass. Montane moist forest ecosystem comprises high forest type which is mainly found in the southwestern part of Ethiopia. Yayu Coffee Forest Biosphere Reserve is categorized into Afromontane Rainforest vegetation types in this ecosystem. This study was aimed to formulate species-specific allometric equations for Albizia grandibracteata Tuab. and Trichilia dregeana Sond. using the semi-destructive method. Results: Allometric equations in form of power models were developed for each tree species by evaluating the statistical relationships of total aboveground biomass (TAGB) and dendrometric variables. TAGB was regressed against diameter at breast height (D), total height (H), and wood density (ρ) individually and in a combination. The allometric equations were selected based on model performance statistics. Equations with the higher coefficient of determination (adj.R2), lower residual standard error (RSE), and low Akaike information criterion (AIC) values were found best fitted. Relationships between TAGB and predictive variables were found statistically significant (p ≤ 0.001) for all selected equations. Higher bias was reported related to the application of pan-tropical or generalized allometric equations. Conclusions: Formulating species-specific allometric equations is found important for accurate tree biomass estimation and quantifying the carbon stock. The developed biomass regression models can be applied as a species-specific equation to the montane moist forest ecosystem of southwestern Ethiopia.
... Fine roots (traditionally defined as roots B 2 mm in diameter) are critical for the acquisition of water and mineral nutrients from soil (Bardgett et al. 2014). Fine roots also receive a substantial portion of fixed carbon (C), thus are an important component to net primary productivity (NPP) in forest biomes (McCormack et al. 2015;Moore et al. 2018). The key functions of fine roots in forest ecosystems are often related to their morphological traits such as mean root diameter (hereafter root diameter), specific root length (SRL), specific root area (SRA) and root tissue density (RTD) (Reich 2014;Roumet et al. 2016). ...
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Key functions of fine roots are often related to their morphological traits, yet little is known about the patterns and controls on fine-root morphological traits in the tropical forest biome. In this study, we consolidated data on key root morphological traits to describe patterns of root trait variation among different tropical regions and examined the relationships among root traits and climate and soil properties. We synthesized root traits (root diameter, specific root length (SRL), specific root area (SRA) and root tissue density (RTD)) from 59 site observations from nine countries in Africa, Asia, and Central and South America to determine the patterns and variation in root traits among different tropical regions. We also examined relationships among fine-root morphological traits, climate (mean annual precipitation, MAP; mean annual temperature, MAT) and soil properties (including available phosphorus (P), base saturation and clay content) using linear mixed-effects modelling. Plant fine-root morphological traits showed systematic variation among tropical regions—Africa, Asia and the Neotropics. Across the tropical biome, SRL was positively related to MAT, suggesting that in warmer tropical sites, plants tended to produce thinner roots with high SRL. Specific root length and SRA were positively related to base saturation, while soil available P explained some of the variation in SRL. This study demonstrates that soil properties, and to a lesser extent MAT, partially explain variation in key fine-root morphological traits across tropical forests. Importantly, we also identified wide variation in fine-root morphological trait values in the tropical biome that encompasses much of the variation seen worldwide. Consequently, attempts to predict tropical forest ecosystem functioning could improve significantly if regional differences in root traits are incorporated into process-based models.
... Among all kinds of biomass renewable energy sources, forest biomass is an excellent alternative to fossil fuels because of its huge content (accounting for 90% of the earth's fixed energy) and can be used in many ways. And forest biomass energy is a kind of efficient clean energy, its carbon dioxide emissions are almost zero, and the environmental benefits are very high [1]. Zhou et al. (2016) predicted that by 2020, China's forest biomass energy resources could be utilized by about 1.2 billion tons, replacing the standard coal by about 804 million tons, and the carbon dioxide emissions generated by forest biomass energy replacing fossil fuels would reach 17.13 tons [2]. ...
... Tropical rainforests are the most productive terrestrial ecosystems and account for the highest terrestrial net and gross primary production per unit area (Beer et al., 2010;Moore et al., 2018). In particular tropical montane forests store high amounts of biomass along their steep slopes (Spracklen and Righelato, 2014). ...
Article
Tropical montane forests, particularly Andean rainforest, are important ecosystems for regional carbon and water cycles as well as for biological diversity and speciation. Owing to their remoteness, however, ecological key-processes are less understood as in the tropical lowlands. Remote sensing allows modeling of variables related to spatial patterns of carbon stocks and fluxes (e.g., biomass) and ecosystem functioning (e.g., functional leaf traits). However, at a landscape scale most studies conducted so far are based on airborne remote sensing data which is often available only locally and for one time-point. In contrast, multispectral satellites at moderate spectral and spatial resolutions are able to provide spatially continuous and repeated observations. Here, we investigated the effectiveness of Landsat-8 imagery in modeling tropical montane forest biomass, its productivity and selected canopy traits. Topographical, spectral and textural metrics were derived as predictors. To train and validate the models, in-situ data was sampled in 54 permanent plots in forests of southern Ecuador distributed within three study sites at 1000 m, 2000 m and 3000 m a.s.l. We used partial least squares regressions to model and map all response variables. Along the whole elevation gradient biomass and productivity models explained 31%, 43%, 69% and 63% of variance in aboveground biomass, annual wood production, fine litter production and aboveground net primary production, respectively. Regression models of canopy traits measured as community weighted means explained 62%, 78%, 65% and 65% of variance in leaf toughness, specific leaf area, foliar N concentration, and foliar P concentration, respectively. Models at single study sites hardly explained variation in aboveground biomass and the annual wood production indicating that these measures are mainly determined by the change of forest types along with elevation. In contrast, the models of fine litter production and canopy traits explained between 8%-85% in variation depending on the study site. We found spectral metrics, in particular a vegetation index using the red and the green band to provide complementary information to topographical metrics. The model performances for estimating leaf toughness, biochemical canopy traits and related fine litter production all improved when adding spectral information. Our findings therefore revealed that differences in fine litter production and canopy traits in our study area are driven by local changes in vegetation edaphically induced by topography. We conclude that Landsat-derived metrics are useful in modeling fine litter production and biochemical canopy traits, in a topographically and ecologically complex tropical montane forest.
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The 2015–2016 El Niño event led to one of the most intense and hottest droughts for many tropical forests, profoundly impacting forest productivity. However, we know little about how this event affected the Cerrado, the largest savanna in South America. Here we report 5 years of productivity of the dominant vegetation types in Cerrado, savanna (cerrado) and transitional forest-savanna (cerradão), continuously tracked before, during, and after the El Niño. We carried out intensive monitoring between 2014 and 2019 of the productivity of key vegetation components (stems, leaves, roots). Before the El Niño total productivity was ~25 % higher in the cerradão compared to the cerrado. However, cerradão productivity declined strongly by 29 % during the El Niño event. The most impacted component was stem productivity, reducing by 58 %. By contrast, cerrado productivity varied little over the years, and while the most affected component was fine roots, declining by 38 % during the event, fine root productivity recovered soon after the El Niño. The two vegetation types also showed contrasting patterns in the allocation of productivity to canopy, wood, and fine-root production. Our findings demonstrate that cerradão can show low resistance and resilience to climatic disturbances due to the slow recovery of productivity. This suggests that the transitional Amazon-Cerrado ecosystems between South America’s largest biomes may be particularly vulnerable to drought enhanced by climate change.
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Tropical forests dominate terrestrial photosynthesis, yet there are major contradictions in our understanding due to a lack of field studies, especially outside the tropical Americas. A recent field study indicated that West African forests have among the highest forests gross primary productivity (GPP) yet observed, contradicting models that rank them lower than Amazonian forests. Here, we explore possible reasons for this data-model mismatch. We found the in situ GPP measurements higher than multiple global GPP products at the studied sites in Ghana. The underestimation of GPP by models largely disappears when a standard photosynthesis model is informed by local field-measured values of (a) fractional absorbed photosynthetic radiation (fAPAR), and (b) photosynthetic traits. Satellites systematically underestimate fAPAR in the tropics due to cloud contamination issues. The study highlights the potential widespread underestimation of tropical forests GPP and carbon cycling and hints at the ways forward for model and input data improvement.
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Tropical forests cover large areas of equatorial Africa and play a significant role in the global carbon cycle. However, there has been a lack of in-situ measurements to understand the forests' gross and net primary productivity (GPP and NPP) and their allocation. Here we present the first detailed field assessment of the carbon budget of multiple forest sites in Africa, by monitoring 14 one-hectare plots along an aridity gradient in Ghana. When compared with an equivalent aridity gradient in Amazonia using the same measurement protocol, the studied West African forests generally had higher GPP and NPP and lower carbon use efficiency (CUE). The West African aridity gradient consistently shows the highest NPP, CUE, GPP, and autotrophic respiration at a medium-aridity site, Bobiri. Notably, NPP and GPP of the site are the highest yet reported anywhere in the tropics using similar methods. Widely used data products (MODIS and FLUXCOM) substantially underestimate productivity when compared to in situ measurements, in Amazonia and especially in Africa. Our analysis suggests that the high productivity of the African forests is linked to their large GPP allocation to canopy and semi-deciduous characteristics, which may be a result of a seasonal climate coupled with high soil fertility.
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Aim: This study aimed to infer the allocation of belowground net primary productivity (BNPP) to sequential soil depths down to 2 m across the globe at a 1 km resolution and assess underlying environmental drivers. Location: Global. Time Period: Contemporary (1932-2017). Major Taxa Studied: Terrestrial plants. Methods: Global datasets including field net primary production (NPP, i.e., the difference between plant assimilated and respired carbon) from 725 soil profiles, root bio-mass and its depth distribution from 559 soil profiles were compiled and used to infer the depth distribution of BNPP across the globe and digitally map depth-resolved BNPP globally at 1 km resolution. Drivers of the depth distribution of BNPP were evaluated using machine learning-based models. Results: Global average BNPP allocated to the 0-20 cm soil layer is estimated to be 1.1 Mg C ha −1 yr −1 , accounting for ~60% of total BNPP. Across the globe, the depth distribution of BNPP varies largely, and more BNPP is allocated to deeper layers in hotter and drier regions. Edaphic, climatic and topographic properties (in order of importance) explain >80% of such variability; and the direction and magnitude of the influence of individual properties are soil depth-and biome-dependent. Main Conclusions: The findings suggest that mean annual temperature and precipitation are the two most important factors regulating BNPP across the globe. Soil properties such as soil actual evaporation and total nitrogen also play a vital role in regulating the depth distribution of BNPP. The maps of BNPP provide global benchmarks of depth- resolved BNPP for the prediction of whole-profile soil carbon dynamics across biomes.
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This article reports on a study conducted to assess the carbon storage potential of Bambusa vulgaris, the predominant bamboo species in Ghana. The study aimed to fill a knowledge gap on the potential of bamboo to sequester carbon for climate change mitigation in Ghana. Unlike previous studies that only focused on aboveground biomass, this study assessed belowground, litter, and coarse wood carbon pools. Allometric parameters and models were used to measure the aboveground biomass, while other carbon pools were directly measured. The results showed that the aboveground biomass of B. vulgaris had a carbon stock of 42.85 ± 9.32 Mg C ha⁻¹, which was 73% of the total biomass carbon stock. The carbon stocks of belowground, coarse wood and litter were 8.57, 3.02, and 4.25 Mg C ha⁻¹, respectively. The study also found that B. vulgaris had a high carbon dioxide sequestration potential of 215.39 Mg CO2e ha⁻¹ compared to 147–275 Mg CO2e ha⁻¹ for trees in general. The findings suggest that B. vulgaris could contribute to Ghana's transition to a low-carbon economy through carbon stock monitoring, reporting, and policy development to minimise the impact of climate change. Moreover, the inclusion of relevant carbon pools, including coarse wood and litter, in forest carbon estimates should be encouraged to provide a comprehensive understanding of the plant carbon cycle.
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Future global changes will impact carbon (C) fluxes and pools in most terrestrial ecosystems and the feedback of terrestrial carbon cycling to atmospheric CO2. Determining the vulnerability of ecosystems to future changes in C is thus vital for targeted land management and policy. The C capacity of an ecosystem (XC) is a function of its C inputs (e.g., net primary productivity – NPP) and how long C remains in the system before being respired back to the atmosphere (ecosystem C residence time – τE). The proportion of XC currently stored by an ecosystem (i.e., its C saturation – CSAT) provides information about the potential for long-term C pools to be altered by environmental and land management regimes. We estimated XC, CSAT, NPP, and τE in six US grasslands spanning temperature and precipitation gradients by integrating high temporal resolution C pool and flux data with a process-based C model. As expected, NPP across grasslands was strongly correlated with mean annual precipitation (MAP), while τE was primarily a function of mean annual temperature (MAT). We link soil temperature, soil moisture, and inherent C turnover rates (potentially due to differences in microbial function) as determinants of τE. Overall, we found that intermediates between extremes in moisture and temperature had low CSAT, indicating that ecosystem C in these systems may be buffered against global change impacts on XC. Hot and dry grasslands had greatest CSAT due to both small C inputs through NPP and high C turnover rates during periods of favorable soil conditions. CSAT also was high in tallgrass prairie due to frequent fire that reduced inputs of aboveground plant material. Accordingly, we suggest that both hot, dry ecosystems and those frequently disturbed should be subject to careful land management and policy decisions to prevent losses of C stored in these systems.
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[1] The key role of tropical forest belowground carbon stocks and fluxes is well recognised as one of the main components of the terrestrial ecosystem carbon cycle. This study presents the first detailed investigation of spatial and temporal patterns of fine root stocks and fluxes in tropical forests along an elevational gradient, ranging from the Peruvian Andes (3020 m) to lowland Amazonia (194 m), with mean annual temperatures of 11.8°C to 26.4 °C and annual rainfall values of 1900 to 1560 mm yr-1, respectively. Specifically, we analyse abiotic parameters controlling fine root dynamics, fine root growth characteristics, and seasonality of net primary productivity along the elevation gradient. Root and soil carbon stocks were measured by means of soil cores, and fine root productivity was recorded using rhizotron chambers and ingrowth cores. We find that mean annual fine root below ground net primary productivity in the montane forests (0–30 cm depth) ranged between 4.27±0.56 Mg C ha-1 yr-1 (1855 m) and 1.72±0.87 Mg C ha-1 yr-1 (3020 m). These values include a correction for finest roots (
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We report above-ground biomass (AGB), basal area, stem density and wood mass density estimates from 260 sample plots (mean size: 1.2 ha) in intact closed-canopy tropical forests across 12 African countries. Mean AGB is 395.7 Mg dry mass ha(-1) (95% CI: 14.3), substantially higher than Amazonian values, with the Congo Basin and contiguous forest region attaining AGB values (429 Mg ha(-1)) similar to those of Bornean forests, and significantly greater than East or West African forests. AGB therefore appears generally higher in palaeo- compared with neotropical forests. However, mean stem density is low (426 ± 11 stems ha(-1) greater than or equal to 100 mm diameter) compared with both Amazonian and Bornean forests (cf. approx. 600) and is the signature structural feature of African tropical forests. While spatial autocorrelation complicates analyses, AGB shows a positive relationship with rainfall in the driest nine months of the year, and an opposite association with the wettest three months of the year; a negative relationship with temperature; positive relationship with clay-rich soils; and negative relationships with C : N ratio (suggesting a positive soil phosphorus-AGB relationship), and soil fertility computed as the sum of base cations. The results indicate that AGB is mediated by both climate and soils, and suggest that the AGB of African closed-canopy tropical forests may be particularly sensitive to future precipitation and temperature changes.