Effect of Exclosure Age on Carbon Sequestration Potential of Restorations in Tigray Region, N. Ethiopia

Samson Shimelse

doi:10.11648/j.ajbes.20170304.14

Abstract

Conversion of degraded free grazing lands into exclosures is one option to promote natural regeneration of plants and to restore degraded ecosystems in Ethiopia. The present study investigated the change in ecosystem carbon stocks (ECS) and the enhancement of plant species richness and diversity following the establishment of exclosures on free grazing lands in Tigray, Ethiopia. Exclosures of 10, 15, and 20 years old were selected and each exclosure was paired with an adjacent free grazing land. A total of 120 quadrants were sampled using a stratified preferential sampling design technique with flexible systematic model. The differences in carbon stocks and vegetation composition between an exclosure and free grazing lands were assessed using a paired t-test. Data analyses also included descriptive statistics, inferential statistics using one way ANOVA, t-test and Chi-square test. All exclosures displayed higher ECS, and plant species richness, diversity and aboveground standing biomass than the free grazing lands. Differences in ECS between exclosures and free grazing lands varied between 32.96 and 61.0 t. ha<sup>-1</sup> increasing with exclosure age. Over a period of 20 years, the carbon dioxide sequestered in the investigated exclosures was 223.88 t. ha<sup>-1</sup>. Differences in plant species richness and aboveground standing biomass between exclosures and free grazing lands also increased with exclosure age. The results of the present study confirm that establishment of exclosures on degraded free grazing lands in the Northern Highlands of Ethiopian is a viable option to restore ECS. The study showed that ECS in exclosures, in free grazing lands and the change in ECS following the establishment of exclosures on free grazing lands can be predicted using easily measurable biophysical and management-related indicators. Such information is necessary for the establishment of baseline information for carbon sequestration projects, for evaluation of whether exclosure establishment should be expanded, and for policymakers to take into account the value of exclosures in their management decisions. Although the study showed that exclosures are effective to restore ECS, expansion of exclosures would increase grazing pressure on the remaining free grazing area. Therefore, the decision to establish additional exclosures should also include an economical analysis and an evaluation of the social consequences of such a decision.

Highlights

Land degradation refers to worsening of land resources [1] and decreasing of the sustainable productive capacity of agricultural lands in the world [2]
A total of 142 plant species belonging to 118 genera and 52 families were identified (Table 7)
The results of the present study confirm that establishment of exclosures on degraded free grazing lands in the Northern Highlands of Ethiopian is a viable option to restore ecosystem carbon stocks (ECS)

Summary

Introduction

Land degradation refers to worsening of land resources [1] and decreasing of the sustainable productive capacity of agricultural lands in the world [2]. Land degradation is a severe problem across sub-Saharan Africa, and Ethiopia is among the most affected countries in this respect. Deforestation (37%), overgrazing (35%), inappropriate agricultural practices such as over-cultivation, fertilization and nutrient depletion (28%) and industrialization (1%) are major human-caused factors of land degradation in the world [3]. Rangeland degradation is a widespread problem throughout sub-Saharan Africa and its restoration is a challenge for the management of many semiarid areas [4]. Ethiopia rural population depending on agricultural land resources especially in developing countries, and is a cause of poverty [5]. Land degradation in Ethiopia is triggered by population expansion and over-exploitation of the natural resources and is a major threat to sustainable land uses [6]

Methods

Results

Conclusion