IMPACT OF DEFORESTATION ON SOIL
Study By: Henok Kassa and others
Presentation By: Reese Norton
Site Information
Case Study
Site
- Study area encompasses the upper Gacheb catchment (collection of water through a natural drainage area)
- Located in headwaters of White Neil in SW Ethiopia
- Altitude ranges from 1000 - 2600 m a.s.l.
- Average temperature ranges from 13 - 27 degrees C
- Annual rainy season from March to November
- Vegetation includes both upper and lower canopy trees
Issues Addressed
Human Caused Issues
- How does deforestation affect different land types?
- What is the impact on soil fertility?
- What is the best land type from preserving the current ecosystem?
DEFORESTATION: trees are completely or selectively removed to create farmland
SOIL FERTILITY: ability of soil to sustain plant growth by providing necessary nutrients
AGROFORESTRY: mixture of woody plants, agricultural plants, and/or livestock
Definitions
Data Collection
Research Methods
- Soil samples taken in both April and May of 2013
- Creation of topographic maps in order to fully understand land features and landscape
- 5 stud sites selected from 3 land-use types (forest, agroforestry, cropland)
- A total of 360 samples were collected
FOREST: 20-40 cm, 40-60 cm, and 40-80 cm equal average depth of nutrients and clay particles
AGROFORESTRY: sites selected free from animal manure to avoid misinformation
CROPLAND: soil depth of 0-20 cm to emulate average cropland plow
3 Land Types
Land Type Contrast
- Soil chemical characteristics higher in forest and agroforestry than cropland
- Most cropland topsoil are sandy and low in soil organic carbon
- Topsoil bulk density differs about 0.01 among all sites
- Topsoil pH ranges from 5.4 - 6.4
- Organic compound content ranges from 3.6% - 8.2%
- Soil organic carbon loss from forest to agroforest then from agroforest to cropland
Results
- Forest and agroforest similar in soil content
- Cropland experiences less soil content
- Cropland has greater loss in soil substances
Overview
Findings
Discussion
- Reports differing soil characteristics between woodland and cultivated land
- Identifies distinctions in soil organic carbon between low, middle, and high elevations (soil carbon increases with altitude)
- Low temperatures at higher altitudes maintain low soil organic matter decomposition
- Higher topsoil and subsoil nitrogen levels in forest and agroforest
- Organic carbon loss in soil due to human impact caused rapid decline
Answers
Conclusion
- Available phosphorus content in all three land types are below crucial levels
- Organic carbon and nitrogen stocks higher in forest and agroforest at all three elevations
- Cropland has low soil organic carbon and nitrogen stocks
- Human impact and deforestation has caused loss of organic carbon and nitrogen in soil of all three land types
- It is important to strengthen agroforestry as the main agricultural strategy in order to sustain agricultural production in this specific terrain
- Precautions still need to be taken in order to sustain and protect these ecosystems
Citation
Kassa, Henok, et al. “Impact of Deforestation on Soil Fertility, Soil Carbon and Nitrogen Stocks: the Case of the Gacheb Catchment in the White Nile Basin, Ethiopia.” Agriculture, Ecosystems & Environment , vol. 247, Sept. 2017, pp. 273–282.
https://doi.org/https://doi.org/10.1016/j.agee.2017.06.034.