ABSTRACT
The attainment of green economy and low carbon climate resilient development in Kenya may be hindered by competing human interest on forests and other natural resources. Eastern Mau forest has experienced anthropogenic disturbance through encroachment and forest fires; that situation prompted the deployment of heterogeneous forest management. This study aimed at comparing the soil carbon stocks and soil CO2 effluxes in different forest management regimes on as well as how soil temperature and soil moisture impacts on carbon stocks and soil CO2 effluxes in the study area. The study was conducted between January and June 2016 in Sururu block of Eastern Mau forest reserve, Kenya. A nested experimental design was used in data collection; where thirty two sample plots were nested into four blocks (disturbed (fire) natural, undisturbed natural, plantation and glades) established on the basis of forest management types. Ina 10m2 plot, data was collected on soil carbon stocks, soil CO2 efflux and environmental controls (soil temperature and soil moisture). The results indicated that estimated soil carbon stocks were as follows: undisturbed natural (135.17± 35.99.0 Mg C-ha), disturbed natural forest by fire ( 134.52± 38.11 Mg C-ha) glades (122.4 ±64.9 Mg C-ha), and plantation forest (116.51± 39.77 Mg C-ha ). However, there were no significant differences in the mean carbon stocks between the four forest management regimes (F4, 16. =0.61, p=0.613). The mean soil CO2 efflux between the four forest management types was significantly difference (F1 32. =3.01, p=0.033). The soil CO2 efflux levels recorded were as follows; plantation forest (9.219 ± 3.067 g C M-2day-1), undisturbed natural forest (8.665 ± 4.818 g C M-2day-1), glades (8.592 ± 3.253 g C M-2day-1) and fire disturbed natural forest (7.198 ± 3.457 g C M-2day-1). Based on the results; forest disturbance impacts on soil stocks and therefore for Kenya to achieves its Nationally Determined Contribution (NDC) targets of reducing Green House Gases(GHG) emission by 30% relative to business as usual (BAU) emissions of 22 MtCO2e in 2030, natural forests and glades management regimes presented the best options. Therefore the use of natural forest management regimes in the conservation of soil carbon stocks and in reducing carbon dioxide efflux from the forests is recommended. Additionally a paradigm shift in forest management to include management for non wood forest products and service such as carbon stocks and climate stabilization is needed. Finally REDD+ process in Kenya should consider the carbon stored by forests in its reference level establishment.
CHAPTER ONE
INTRODUCTION
Background to the study
Forest soils are a major sink of terrestrial carbon containing more than double the amount of carbon found in forest tree biomass (Zheng et al., 2008, Scharlemann et al., 2014) and it plays a very important role in the global carbon cycle. However, large uncertainties in emission estimates exists due to inadequate data on the carbon density of forests such that it’s not possible to know whether forest is a net sink or source (Baccini et al., 2017) and consequently there is an urgent need for improved data sets that characterize the role of soils as a source or sink for carbon on a global scale due to its importance in assessing changes in atmospheric carbon dioxide concentrations and promoting conservation and sustainable management of the forest resources (Johnson and Curtis, 2001, Viet et al., 2017 ).
Traditionally forest management studies have focused on increasing the forest productivity and growing stock with little effort on the soil carbon dynamics. However with recent interest in reduction of the green house emission, attention on the role of forest soil in capturing and storing carbon has increased. Carbon dioxide (CO2) efflux from soil is the second largest carbon (C) efflux in most terrestrial ecosystems (Kuzyakov, 2006) and therefore measurements of soil CO2 efflux can be used as an indicator of forest ecosystem processes. These ecosystem processes includes metabolic activity in soil, persistence and decomposition of plant residue in soil and conversion of soil organic carbon to atmospheric CO2 (Ryan and Law, 2005). Frequent measurements of CO2 efflux can help to uncover environmental factors influencing heterotrophic respiration. To a large extent, temporal and spatial variation in soil CO2 and its components is driven by differences in soil temperature and moisture.
While there are many studies on a variety of aspects related to forestry in Africa, few studies have focused on soil carbon stocks (Maher et al., 2010, Pfeifer et al., 2012) and soil CO2 efflux. Soil CO2 efflux is an important parameter in carbon cycle and it is affected by environmental factors such as temperature, moisture and disturbance. Therefore changes in soil temperature or soil moisture could distort the equilibrium of soil carbon pool from being a net store/sink to net source of carbon. A study by Son et.al (2003) showed that soil CO2 evolution related with soil temperature. Separately Nouvellon et al (2008) in a study of soil respiration in a 3-year-old Eucalyptus plantation in coastal Congo observed that there was a maximum soil respiration at high soil water content. However, temperature has been reported as the single best predictor of soil respiration, but inclusion of moisture in the regression increase the predictive power of the model. Based on the above observation this study opines that a positive exponential relationship between soil CO2 evolution and soil temperature existed
Statement of the Problem
The carbon balance of tropical ecosystems remains uncertain, with top-down atmospheric studies suggesting an overall sink and bottom-up ecological approaches indicating a modest net source. The need to understand precisely what is happening in forest ecosystems is further amplified by the problems associated with increased levels of atmospheric CO2 and the major role the forests can play as major carbon sink and mitigating against climate change. East Mau forest reserve plays multiple roles for the current and future generation, but it has previously faced wide range of anthropogenic disturbances. In order to reverse on those negative trends a number of policy and restoration interventions were implemented. These intervention included a raft of forest management techniques geared at optimal resource management However, forest management affects carbon cycle within a forest ecosystem and therefore this study sought to understand how those operations impacted on carbon stocks and effluxes within East Mau forest reserve since no previous study have attempted to document and explain the effects of forest management on carbon dynamics.
Objectives of the Study
Broad objective
The broad objective of this study was to compare the soil carbon stocks and carbon dioxide effluxes in Eastern Mau Forest reserve subjected to different forest management regimes
Specific Objectives
1. To quantify soil carbon stocks under different forest management regimes
2. To quantify the effects of forest management on soil carbon efflux (soil respiration)
3. To assess the relationship between environmental controls (soil moisture and soil temperature) and soil carbon effluxes
Null Hypotheses
H1: Carbon stocks do not vary between undisturbed natural forest, disturbed (fire) natural forest, plantation and glades
H2: Soil carbon effluxes do not vary between undisturbed natural forest, disturbed (fire) natural forest, plantation and glades
H3: There is no significant relationship between environmental controls (soil moisture and soil temperature) and soil carbon effluxes
Justification of the Study
Changes in the forest ecosystems, interferes with vital ecosystem processes and forest productivity including carbon stocks and effluxes, therefore its critical to monitor changes in soil respiration as an indicator for soil carbon sequestration. The level of soil respiration in forest ecosystem is an indicator of ecosystem processes such as decomposition and microbial activities. In particular, decomposition leads to transfers of carbon from one pool to another and sometimes removal though emissions. Interestingly, heterotrophic respiration is influenced by environmental controls such as soil moisture and soil temperature among other factors. Therefore it is important to understand the level of these two factors in the soils at one particular time or season. Measurement of carbon dioxide efflux from the soil helps in assessing the effects of natural or artificial disturbance on the forest ecosystem. It is also important to measure soil temperature and moisture content in order to explain the resultant effluxes.
This study was driven by the need to understand the impacts of the forest management on soil carbon dynamics in the Eastern Mau forest reserve. The forest reserve is subjected to different forest management regimes due to varied past disturbance levels and as well as the existing resource types. These management activities are anticipated will have an effect of carbon dynamics such as carbon emission and sequestration. Better understanding of soil carbon stocks and flows is essential for better carbon management and climate change mitigation options such as REDD+, as well as to help parameterize global circulation models used to guide climate policy (Scharlemann et al., 2014). In Kenya the best available forest inventory data are largely outdated (Stiebert et al., 2012) and when coupled with the requirements of processes such as GHG reporting and accounting, Forest Reference Level (FRL) and REDD+ strategy development and implementation the need for recent data become a priority. Additionally the actualization of management regimes contained in Sururu Participatory Forest Management Plan (PFMP) and Forest Management Agreement signed between Kenya Forest Service and Mau Sururu and Likia Community Forest Association (MASULICOFA) especially on benefit sharing accrued from trading of forest carbon rights is dependent on updated information.
Scope of the Study
The study was conducted in Sururu forest block of Eastern Mau forest reserve located in Njoro division in Nakuru County. The study was undertaken between January and June, 2016, this period covered both the dry and wet season of the forest area. Measurement of soil carbon stocks was undertaken using Loss-on-ignition technique by analyzing soil samples collected between the depths of 0-10 cm while soil carbon dioxide effluxes measurement was done using soda lime method. Thermometer was used to measure soil temperature whereas proxy technique of collecting wet soil sample and oven drying it and the resultant difference in the two weights was used to determine soil moisture content. The above measurements were carried out during the dry and wet seasons of the study area in order to document seasonality.
Limitations and assumptions to the study
The study had a number of limitation that included; the absence of a weighing scale with higher sensitivity upto six decimal place within the University as well as the laboratory regulation on use of equipment and access by other students. Nevertheless the four decimal weighing scale within the Department of Biochemistry still provided accurate results while special arrangement by laboratory staff and other students solved mitigated on the access to the laboratory equipment challenge. This study assumed that no external interference occurred to the experimental chambers in the field.
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Item Type: Kenyan Topic | Size: 53 pages | Chapters: 1-5
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