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Forests, forestation and agroforestry: online informative and educational resources on their importance for environment and water resources (Part 2)

摘要


The article presents informative and educational resources on forestation, agroforestry and water resources, downloadable for free from the internet. In traditional agriculture, livestock, crops and trees were combined together; since the 1800s they have been progressively separated in order to maximize productivity, but this has exposed fields to wind and water erosion. On the contrary, in agroforestry systems, trees and shrubs protect the fields from the adverse effects of strong winds and rains, such as soil erosion and moisture loss. Whereas, for instance, grazing livestock may reduce wildfire risk in agroforestry systems. Agroforestry can be practiced even in lands too steep for cropping and may promote the best use of water and nutrients thanks to: complementary root distribution, hydraulic redistribution, improved water infiltration and common mycorrhizal networks. Afforestation in tropical drylands is often discouraged because a large number of mature trees may dry out the soil; whereas, the positive effect on groundwater recharge of a moderate tree cover has been neglected. In fact, water infiltration into the litter covered soil below trees is 5-10 times faster than in a bare soil. This is why agroforestry systems may contribute to reduce downstream flooding. Several documents describe the large scale afforestation, and creation of agroforestry systems being carried on in drylands of China and Africa. Different techniques may reduce the velocity of runoff during heavy rains, thus providing enough time for water infiltration into the soil. This is important for soil and water conservation, and the improvement of agricultural productivity. Dryland afforestation is limited, e.g. to riparian zones of rivers or lakes, while in drier areas plants with lower water requirement, such as herbs and shrubs, are grown. The mechanisms by which forests influence weather and climate include CO_2 sequestration, evapotranspiration, cloud formation. In addition, because of a lower albedo, the forests absorb more incoming solar energy than surrounding desert or snowy areas, which leads to higher temperatures. Some documents deal with urban forests seen as a chance to improve the quality of life of the quickly growing urban population. The article also presents a few strategies for reducing deforestation.

參考文獻


Scott D.F. and Prinsloo F.W. (2008). Longer-term effects of pine and eucalypt plantations on streamflow. https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2007WR006781%4010.1002/%28ISSN%291944-7973.LANDUSE1
Bayala J. and Prieto I., (2019). Water acquisition, sharing and redistribution by roots: applications to agroforestry systems. https://link.springer.com/article/10.1007/s11104-019-04173-z
Tobella A.B., et al., (2014). The effect of trees on preferential flow and soil infiltrability in an agroforestry parkland in semiarid Burkina Faso. https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2013WR015197
Tobella A.B. et al., (2019). Trees in African drylands can promote deep soil and groundwater recharge in a future climate with more intense rainfall https://onlinelibrary.wiley.com/doi/pdf/10.1002/ldr.3430
Wilcox B.P. and Y. Huang, (2010). Woody plant encroachment paradox: Rivers rebound as degraded grasslands convert to woodlands. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2009GL041929

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