Improve poorer and less fit soils with planted forest
Planted forests can make an important contribution to improving soil characteristics. By managing them responsibly, enabling them to perform their natural ecological functions for the health of ecosystems, the suitability of the land is simultaneously improved.
Vegetation cover, and in particular forests, plays a crucial role to contain soil degradation processes. Forests with longer growth cycles or, although shorter, with several growth cycles, tend to keep the soil more protected, for example, from the action of raindrops and the surface run-off of water that carries soil particles with it.
Contrary to the common belief, climate and topographic factors are the most prevalent in soil quality, far more than the type of species planted: the quantity, intensity and concentration of rainfall; relief; land preparation, for example; and the existence and abundance of vegetation cover.
For example, in eucalyptus-planted forests, an added value is related to the possibility that a plantation can be managed by several growth cycles – coppice regime – without the need to replant. Thus, after a first cut of the stand, up to two shoots per foot are usually allowed to thrive for another growth cycle. This technique avoids the need to prepare the land again for more than 30 years, which is usually necessary in each new planting. The rapid growth of shoots per foot and the maintenance of the root system already developed on the ground protect the soil from the direct action of raindrops and create barriers to surface run-off of water, thus helping prevent disaggregation, or rather, one of the soil erosion phases. The existence of vegetation cover reduces, in a way, the incidence of solar rays, preventing the surface layer of the soil from overheating and increasing evaporation during the hottest times of the year. It thus avoids soil disturbance, enhances its ecological balance and its protection by reducing the period of direct exposure to erosive agents.
The soil will be more akin to degradation in the planting and forest exploitation phase and to that end following the best forestry practices and the most appropriate timings, avoiding the rainiest periods, is paramount.
Plants and leaves (scraps) that remain in the soil from previous growth cycles of the stand also play a role in mitigating possible erosive effects: they help organic matter increase and create forest residual biomass. That is, they promote better conditions for soil microorganisms, which, in turn, promote the decomposition of organic matter and redistribute or recycle nutrients.
Cutting scraps and the foliage that falls during the growth cycle is important for soil conservation, as it protects it, but also as a source of organic matter and nutrients, essential for plant growth, and normal functioning of the soil biome and nutrient cycle. Since not all the nutritional needs of the plantation are covered by this procedure, duly fertilisation of the soil and stand with mineral or organic supplementation ensures long-term soil sustainability and fertility.
Forests and their products are fundamental to mitigating climate change effects, acting as carbon reservoirs. In these forest ecosystems, the soil also plays an important role due to its carbon sequestration and storage capacity, and in the particular case of eucalyptus, it can store up to 30 cm of soil depth, more than two-thirds of the total carbon retained in the stand.
Once again, special care is needed as regards forest management practices, such as the proper management of cut scraps, land preparation and logging practices, to minimize soil disturbance and allow the different resources in a forest ecosystem such as the planted species and its production, soil, water and biodiversity to function dynamically and harmoniously, as in a Tetris game.
