Forest biomass and carbon stocks

The dissertation deals with the factors both physical and human that impact biomass levels in the case of seasonally dry tropical forests (SDTF) and discusses how the findings might help to improve REDD+ policy in Mexico. The central part of the dissertation is made up of three published articles. First, the study explores the extent to which aboveground biomass levels in the SDTF could be predicted using linear and non-linear relationships at regional (that is to say, multi-community) scale with physical variables such as altitude, slope, and insolation. Second, more complex modeling approaches are used to related aboveground biomass levels to local topographic variables, which are systematically replicated in the landscape, such as convexity/concavity of the terrain, in order to spatially predict standing biomass of SDTF within rural communities. Third, the dissertation addresses the intensification of current shifting agricultural practices in the study area and evaluates the impact of shifting cultivation on carbon stocks. This section considers how cultivation cycles can be optimized to promote a reduction in carbon emission. Finally, the results of the three empirical chapters are discussed, to evaluate how the results of the thesis could be used to support carbon enhancement projects by communities in Mexico.

A B S T R A C T Changes in structure and functioning of tree communities in response to forest fragmentation may alter tropical forest's capacity to store carbon and regulate climate. However, evidence for indirect effects of forest fragmentation on above – and belowground carbon pools through changes in forest biodiversity is scarce. Here we focus on understanding the relative importance of taxonomic and functional diversity and tree cover to explain above-and below-ground carbon stocks in coastal dune forest fragments. We surveyed tree species composition and structure in six coastal forest patches varying in size from 215 to 13350 ha, in Kwa-Zulu Natal, South Africa. For each fragment, we estimated carbon stocks of two pools, aboveground biomass (AGC) and soil organic carbon (SOC). We used structural equation models to test if and to what extent the effects of forest fragmentation on AGC and SOC were mediated by tree cover and taxonomic and functional diversity. Our results showed that forest fragmentation directly reduced AGC, but increased SOC. In contrast, forest fragmentation indirectly, through decreasing functional diversity, increased AGC, but decreased SOC. Small patches therefore had few tree species that were functional similar and had high AGC, but low SOC, which led to a negative relationship between species richness and AGC. Tree cover was not affected by fragmentation, and had a direct positive effect on AGC but not on SOC. Our results suggest that forest fragmentation simultaneously affect multiple processes which directly and indirectly affects carbon stocks of different pools. Fragmentation may trigger a process of biotic homogenization, in which a few species are positively related with carbon storage above-, but not below-ground.

The present study was aimed to anticipate how forest composition, regeneration, biomass production, and carbon storage vary in the ridge top forests of the high mountains of Garhwal Himalaya. For this purpose five major forest types—(a) Pinus wallichiana, (b) Quercus semecarpifolia, (c) Cedrus deodara, (d) Abies spectabilis, and (e) Betula utilis mixed forests—were selected on different ridge tops in the Bhagirathi Catchment Area of the Uttarkashi District of Garhwal Himalaya. The highest species richness (10 species) and stand density (804 ± 184.5 stems ha −1) were recorded in Abies spectabilis forests, whereas lowest species richness (4 species) and species density (428 ± 144.7 stems ha −1) were found in Quercus semecarpifolia forests. The total basal cover (TBC) values were maximum (91.1 ± 24.4 m 2 ha −1) in Cedrus deodara forests and minimum (26.5 ± 11.7 m 2 ha −1) in Pinus wallichiana forests. The highest total biomass density (TBD) (464.2 ± 152.5 Mg ha −1) and total carbon density (TCD; 208.9 ± 68.6 Mg C ha −1) values were recorded for Cedrus deodara forests; however, lowest TBD (283.4 ± 74.8 Mg ha −1) and TCD (127.5 ± 33.7 Mg C ha −1) values for Quercus semecarpifolia forests. Our study suggests that Abies spectabilis-dominated forests should be encouraged for biodiversity enrichment and reducing carbon emissions on ridge top forests of high mountains.

Forest types of Kumaun Himalaya were mapped using IRS-P6, AWiFS
satellite data and integrated with crown cover classes to generate forest
type cum crown cover map. A total of 25 categories of crown cover were
obtained in 12 forest types. Sampling in different crown cover classes was
carried out to measure mean stand biomass and mean crown cover in
each forest type. Regression equations were developed between ground
measured mean stand biomass and mean crown cover. Based on these
equations mean biomass for each crown cover class was estimated. Mean
biomass values were substituted for crown cover classes in forest type
cum crown cover map to prepare biomass maps for the aboveground
components of tree. Entire study area exhibited a total biomass of 22.18 x
7
10 ton, of which contribution of bole, branch, twig and foliage was: 66.6%, 20.9%, 8.4% and 4.7%, respectively. The total carbon stored in the
aboveground components of the tree layer existing in the study area was
7 11.16 x 10 ton. The estimates of biomass and carbon stock are relevant in context of climate change studies and further helpful to advocate forest conservation as a carbon sink in Himalayan region.

Abstract The present study was aimed to anticipate how forest composition, regeneration, biomass production, and carbon storage vary in the ridge top forests of the high mountains of Garhwal Himalaya. For this purpose five major forest types—(a) Pinus wallichiana, (b) Quercus semecarpifolia, (c) Cedrus deodara, (d) Abies spectabilis, and (e) Betula utilis mixed forests—were selected on different ridge tops in the Bhagirathi Catchment Area of the Uttarkashi District of Garhwal Himalaya. The highest species richness (10 species) and stand density (804 ± 184.5 stems ha−1) were recorded in Abies spectabilis forests, whereas lowest species richness (4 species) and species density (428 ± 144.7 stems ha−1) were found in Quercus semecarpifolia forests. The total basal cover (TBC) values were maximum (91.1 ± 24.4 m2 ha−1) in Cedrus deodara forests and minimum (26.5 ± 11.7 m2 ha−1) in Pinus wallichiana forests. The highest total biomass density (TBD) (464.2 ± 152.5 Mg ha−1) and total carbon density (TCD; 208.9 ± 68.6 Mg C ha−1) values were recorded for Cedrus deodara forests; however, lowest TBD (283.4 ± 74.8 Mg ha−1) and TCD (127.5 ± 33.7 Mg C ha−1) values for Quercus semecarpifolia forests. Our study suggests that Abies spectabilis-dominated forests should be encouraged for biodiversity enrichment and reducing carbon emissions on ridge top forests of high mountains.

As land use change (LUC), including deforestation, is a patchy process, estimating the impact of LUC on carbon emissions requires spatially accurate underlying data on biomass distribution and change. The methods currently adopted to estimate the spatial variation of above-and below-ground biomass in tropical forests, in particular the Brazilian Amazon, are usually based on remote sensing analyses coupled with field datasets, which tend to be relatively scarce and often limited in their spatial distribution. There are notable differences among the resulting biomass maps found in the literature. These differences subsequently result in relatively high uncertainties in the carbon emissions calculated from land use change, and have a larger impact when biomass maps are coded into biomass classes referring to specific ranges of biomass values. In this paper we analyze the differences among recently-published biomass maps of the Amazon region, including the official information used by the Brazilian government for its communication to the United Nation Framework on Climate Change Convention of the United Nations. The estimated average pre-deforestation biomass in Climatic Change

There is increasing demand for agricultural commodities that are produced in a climate-friendly manner. At the same time, in many or most tropical countries there is need for intensification of agricultural production to increase yields and incomes, and this usually requires higher external inputs that may cause additional greenhouse gas emissions. Here we investigate if production methods that have a beneficial effect on the climate (are climate-friendly) are compatible with increased inputs and yields for traditional, shaded cocoa (Theobroma cacao) production systems (locally known as cabrucas) in southern Bahia, Brazil. We use two easily measurable and manageable dimensions of climate friendliness, namely the carbon (C) stocks in the large trees and the C footprint as related to on-farm agrochemical and fuel use. Through interviews and field inventories in 26 cabruca farms representing a range of production practices and intensities, we identify the combinations of management practices, yields, C stocks and C footprints typically found in the region. We find that yield levels up to the highest encountered yield of 585 kg ha−1, or twice the current regional average of 285 kg ha−1, are compatible with an aboveground C stock in the large shade trees (>30 cm diameter at breast height) of up to 65 Mg ha−1 and up to 55 % shade. Higher C stocks and shade levels are generally associated with yields below the regional average. Input-related C emissions increased non-linearly with increasing yield, but even the highest encountered yields were compatible with low (<0.25 kg CO2e kg−1 of cocoa) to medium (<0.5 kg CO2e kg−1 of cocoa) input-related emission levels. Cocoa yields responded positively to increased fertilizer applications, provided that other factors, including shade levels, were not limiting. Consequently, the highest input-related emissions (>1 kg CO2e kg−1 of cocoa) were related to large fertilizer applications that did not proportionately increase yields. We conclude that doubling the cocoa output from southern Bahia, where cabrucas are the predominant form of growing cocoa, is compatible with climate-friendly production practices, measured by local standards. We suggest that the presented methodology can be used to identify opportunities for climate-friendly intensification of tree crops more generally, thereby increasing the contribution of commodity production to global climate change mitigation.

Carbon-centric conservation strategies such as the United Nation’s program to Reduce CO2 Emissions from Deforestation and Degradation (REDD+), are expected to simultaneously reduce net global CO2 emissions and mitigate species extinctions in regions with high endemism and diversity, such as the Tropical Andes Biodiversity Hotspot. Using data from the northern Andes, we show, however, that carbon-focused conservation strategies may potentially lead to increased risks of species extinctions if there is displacement (i.e., “leakage”) of land-use changes from forests with large aboveground biomass stocks but relatively poor species richness and low levels of endemism, to forests with lower biomass stocks but higher species richness and endemism, as are found in the Andean highlands (especially low-biomass non-tree growth forms such as herbs and epiphytes that are often overlooked in biological inventories). We conclude that despite the considerable potential benefits of REDD+ and other carbon-centric conservation strategies, there is still a need to develop mechanisms to safeguard against possible negative effects on biodiversity in situations where carbon stocks do not covary positively with species diversity and endemism.