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The influence of trees on the water cycle
Since childhood, we know that the simple leaf of a plant, the branches of trees, suckers, stems, among other aerial parts of plants, collaborate in stopping the blows provided by the precipitation of raindrops. These are distributed throughout the structure and shapes of the different trees. Those with small leaves lose the minimum of water by evaporation. Trees with broad, lancerolate, long leaves and with small thetics (stomata), with few surface areas and fibrous roots, form a water sponge around and within them. We call the mechanism that uses water, which is trapped or retained between the different parts of the trees, at some point. Approximately 100ml of water that falls on a tree, 10 to 20% slowly drains off to infiltrate or percolates between the soil profiles increasing the fertilization of the water table. Another part of it runs off the earth's surface and will contribute to increasing the flow of the rivers, which will flow into the sea, where the water evaporates and when condensing, it precipitates on the surface of the earth and thus fulfills the hydrological cycle of water.
Water quality, like stream flows, will be affected by soil conditions and plant cover. A wooded soil holds water between 5 to 8 times more than a grassland cover soil and between 10 to 15 times more than a bare soil or an eroded soil.
The freshwater harvest
As evidenced in the previous paragraph, trees and forests help to retain water. Due to their structure and composition, many forest-covered soils have a great capacity to retain water. What happens between the tree and the ground for the water to be retained? The observations shared with the farmers, give us to understand that the integration of biological, physical and chemical phenomena occurs in the freshwater harvest. We have learned a first biophysical phenomenon in the role played by leaf litter and humus (decomposed organic matter, biochemical process) from the decomposition of leaves, branches and fruits, which accumulates on the ground. In some forests it reaches 6 to 20 cm deep. As the litter opens and decomposes, nutrients are released enriching the surface layer of the earth. Leaf litter and humus protect the soil from the direct impact of water, helping to maintain water infiltration without disturbing the soil. After infiltrating, a part of the water runs off, another percolates on the soils. Here and depending on the diversity of crops and their biomass (total weight of organic matter (of life) of the trees) and their different levels of interception of water is that the beginning from the water harvest. An association of crops due to biomass difference will retain more water than a monoculture.
These water courses constitute the most important water resource, since they form rivers, streams, humidity spaces for the production of crops, streams, for the formation of rains and the maintenance of hydrographic basins.
Venezuela and its Hydrographic Basins
The natural area, limited by divisions, where both rainwater and waters coming from the snow-capped mountains are deposited and run towards a main drain that generally function as axes of a region, we call it hydrographic basins. The basins or receiving watersheds are part of the basins of the valleys, plateaus and mountains affected by the runoff that feeds the main drains. Any piece of land can be considered an integral part of a hydrographic basin. For example, almost the entire Venezuelan territory is made up of hydrographic basins. Five of them are international, which are part of other countries. Among them we have the Lake Maracaibo Basin; The Orinoco River Basin; The Rio Negro Basin of the Amazon; The Cuyuní Basin towards the Essequibo and the Paraguachón Basin (Venezuela and Colombia); The Río Negro Basin (of the Amazon) (Venezuela, Colombia and Brazil); The Cuyuní Basin towards the Essequibo (Venezuela-Guyana). Other important basins in Venezuela we have: in the east of the country, the Unare, Neverí, Manzanares, San Juan and Guarapicjhe basins. In the Center: the Cuencas del Tuy, Guapo, Lake Valencia and in the West: the Cuencas del Hueque, Tocuyo, Aroa, Yaracuy, Chama and Motatan; the rivers of all of them flow into the Caribbean Mara, except those of Lake Valencia.
These large areas could be seen, in turn, as a kind of puzzle integrated by smaller basins. As management units, sometimes we speak of micro-basins on several farms, and on the same farm we can have mini-basins or small freshwater harvesting spaces.
In Venezuela, in most western states of the Andean foothills and several mountain ranges, there are a good number of farms with shared micro and mini basins, which indicates that we cannot work in isolation since the management of one affects the others.
Production in freshwater harvest
We have pointed out the importance of freshwater harvest in the maintenance of hydrographic basins. It is understood that the different formations, such as the arrangements of trees and plants in the agrobiodiversity of a production system, regulate the different watersheds that run into it.We cannot maintain a hydrographic basin without its agrobiodiversity and, this , without the vital resource of water for its existence. There is an exact synergy and complementarity between ecosystems.
Let's understand what the producers and peasants of the states of Mérida, Barinas and Portuguesa in western Venezuela have taught us producing and harvesting water. The attached figure (# 18 Pág. 82 of the Book Proposed of Sustainable Rural Development of MANúñez 2002) presents the:
The family production unit of the Venezuelan Andean foothills considers the humidity gradient (water harvesting) and the preservation of the slope, where crop associations are also established in each of the specified specificities.
Peasant knowledge shows the arrangement of agrobiodiversity where at least 26 crops for different productive uses stand out, they teach us that this production is achieved according to the natural physical limitations expressed in the different degrees of slope. They instruct us that above a slope of 30 degrees we must maintain the forests to obtain the harvest of water produced there and provide us with the different humidity spaces that are considered in their production systems. These cultivation arrangements are given according to their seasonality, perenniality and short-cycle crops. Agricultural production systems, typical of countries that have sustained sustainable tropical agriculture for millennia. The peasant is also teaching us that he has dense and extensive agronomic knowledge of the different types of soils, agro-climatic conditions and eco-technologies, which together sustainably collaborate with the environment. There is efficient use of water based on the synergy and complementarity between the physical, chemical and biological properties of the agro-productive system not very well known by academia and university students. It is demonstrated that agrobiodiversity in its water harvest acts as an antidote to the preservation of the environment of the evaluated micro hydrographic basin.
The other contribution of the water harvest.
Understanding the meaning of being able to easily harvest water implies that the knowledge that this experience provides us, we must necessarily have the participation of farmers and producers who, in the end, are the ones who really have the most genuine and instructive knowledge. Here where we have demonstrated it with pride and dignity. It is about knowing how to obtain the ideas, criteria and different forms of wisdom, which they have possessed for their centuries of existence. It is also about respecting their different rationalities between their cultural, social and religious values that the Latin American peoples possess. Knowledge that has not disappeared, is maintained and is waiting to be valued and recognized.
In the production systems of tropical latitudes, we recognize that for their understanding and interpretation it is necessary among peasants to apply participatory methodologies that help us to organize and systematize the knowledge that through the different processes of reflection and action allow us to assess more objectively the knowledge and wisdom of our farmers. We affirm the most appropriate environmental education, it is the one that is received on the basis and interaction of environmental and cultural rationality expressed among the actors who develop it.
This accumulation of knowledge that we have presented here should call us to reflection because in them an endless number of criteria and ideas have to be given off, and more knowledge of extreme utility, which must be valued and assumed by the academy, the campuses universities and research institutions. For example among others we have; how the sustainable use of water can be produced and maintained; the integral management of forest resources, the implications of agrobiodiversity and the different eco-technologies in production systems. Bases of what to do agroecological in the new face that our agriculture demands. Which has to become the most dynamic part of our local economies, helping the new types of sustainable environmental societies that we must create and reorganize for the future of the new generations that are on the way and to substantially improve the quality and reason for life of our rural and urban sectors.