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Transcript

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

AGROFORESTRY

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.

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