Cut trees carefully to improve soil, say scientists studying Zambian forests.
Researchers say cleared forest areas and topsoils in a forest in Zambia had more organic matter, which means better quality soil. It is important to understand soil quality in sub-Saharan Africa since it has a big impact on how well plants and trees are able to thrive.
Soil has different nutrients, and organic matter and carbon are the most important to help plants thrive.
Organic matter are compounds in soil that come from the remains of dead plants and animals. Over half (58%) of organic matter is just carbon, and the rest is water and other nutrients. Soil with more organic matter, and carbon therefore, keeps water for longer and has more other nutrients. Scientists do not know much about changes in organic matter and carbon in sub-Saharan African soils, even though they are so important for the growth of plants and trees.
In this study, the researchers wanted to find out how soil organic matter in a forest changed, and what determines the amounts.
They did their study in a forest in Zambia. They collected soil samples at the top (0-10 cm), middle (10-20 cm), and deep (20-30 cm) levels, and in different areas of the forest.
The researchers then tested the soils in a laboratory to check how much organic matter it contained. A laboratory is a building where scientists do the tests and experiments, often using precision equipment to measure specific parameters.
They also recorded other properties of the soil like its type, for instance sandy or clay-like.
Their results showed that the amount of organic matter was very different between different places, and at different depths.
Topsoil had the highest organic matter of up to 114 milligrams (mg) in a hectare, followed by deep soil (almost 100 mg per hectare). Middle soil had the lowest amount of up to 80 mg per hectare.
The researchers said places in the forest that were recently cleared had more organic matter than uncleared areas. They suggest that cutting trees in a forest, with careful management, could therefore increase soil organic matter.
The researchers also observed that soil colour changed from dark brown (topsoil) to yellowish brown (deep soil), and that sandy and clay soils had more organic matter.
Areas in the forest that were more exposed to sunlight had bigger and older trees, and more organic matter.
The researchers, who were based in Zambia and South Africa, said their methods could be adapted by others to assess soil quality in different places and at different depths.
Soil organic matter (SOM) is a key component of forest productivity and soil organic carbon stock. However, little is known about SOM and C variability in miombo woodlands which is a significant ecosystem in sub-Sahara African forests and vital for REDD+ strategies. In this study, nine edaphic factors were measured and used to analyse the variability of SOM in miombo woodland sites with different tree structures in Luanshya, Zambia. The findings showed a large variability of SOM stocks at different soil depths: 36.67 to 113.89 Mg ha-1 at 0–10 cm depth, 28.67 to 79.56 Mg ha-1 at 10–20 cm depth, and 31.89 to 98.56 Mg ha-1 at 20–30 cm depth. These SOM values at different depths also varied between miombo woodland sites of different successional stages, notably that areas affected by recent tree clearance had higher than average SOM content per layer (0–10 cm: +5.57%; 10–20 cm: +4.20%; 20–30 cm: +4.30%). Canonical correspondence analysis (CCA) revealed that the most significant environmental factors influencing SOM were woodland thinning by clearance, and silt content within soils. This study highlights that CCA can be used to show the relative importance of different forest successional stages as a function of management practices, as well as edaphic factors, in determining miombo soil SOM content. The results of this study are particularly relevant for addressing current REDD+ reforestation and management strategies that are aimed at increasing carbon stocks in the tropical forests of sub-Saharan Africa.
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