Soil is composed of minerals, soil organic material (SOM), water, and air, according to the Montana State University’s soil scientists, Ann McCauley. The actual composition of these various components within soil has a big influence on the porosity; i.e., the composition affects the movement of water into and through the soil (McCauley, 2005), and the movement of water into and through soil is absolutely necessary for productive crops, and healthy ecosystems. The binding together of soil particles is called “aggregation” and when water passed into the soil aggregation, if it is healthy, will keep the porosity and water movement slow and productive, which “improves fertility and carbon sequestration in the soil” (avoiding erosion at the
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In Brazil, a group of researchers investigated the influence that tree density had on “deep water uptake, soil water dynamics and evapotranspiration” (Oliveira, et al, 2005). Because Brazil has vast topical savannas and there have been changes in the kinds of vegetation grown in the savannas, the team of researchers sought to learn the influence that trees have on soil dynamics in those areas. They chose two adjacent ecosystems in central Brazil for their study; the two were chosen because they have similar soil types (high clay content) but one had grassy vegetation with small shrubs, and the other was a “semi-closed canopy vegetation” ecosystem – about 70% covered by trees – with trees that were about 5 to 9 meters (Oliveira, p. 575). Fire had not impacted either ecosystem for 27 years, the authors explain.
The results of the three-year survey showed that during the dry season (in the years 1996-1998) 82% of the water used by the tree-covered canopy ecosystem (cerrado denso) was extracted from the deep clay soil and 67% of the water used by the grass-dominated ecosystem (campo sujo) came from deep soil water (Oliveira, p. 574). This research provides evidence that deep roots “appear to play an exceptionally important role in providing water for vegetation” (Oliveira, p. 579), albeit the canopied ecosystem (cerrado denso) used more soil water than campo sujo. (Oliveira, p. 580). Overall, this study shows that two