Creating the Right Mosaic
Imagine flying in a helicopter over a forest and then looking out the window: At first, you think you see a solid green landscape. The trees seem identical. But keep looking and you notice differences: Smaller and larger trees and plants are mixed together. Leaf colors, and shapes, vary. Wild plants, and even bare areas, follow sections with thick growth, tall trees. What you’re looking at is a well-managed plantation forest, which is one that contains a “mosaic” of different plants.
Why is this significant? A forestry mosaic promotes better water balance in the soil, which supports the forest. It also maintains the water balance for the entire region, including many communities.
In southeastern Brazil, plantations have been experiencing higher mean annual temperatures, stronger rainfall and more frequent droughts. Forestry professionals need to prepare plants to adapt to these extreme conditions, so they continue to grow under water stress. This resilience can be achieved by respecting basic principles of hydrology.
Professor of Silviculture Sciences at the University of São Paulo (USP), in Brazil
The most important hydrological sign of sustainable forest management is what’s called “the watershed water balance.” A watershed region is an area that drains into a common water system, such as a river. The watershed water balance is the result of what water sources enter the region, such as precipitation and groundwater, versus what water sources exit it, such as evaporation, runoff and groundwater. The right balance can be reached by creating a forestry mosaic.
Let’s return to the helicopter view of a plantation forest. Now we notice the first piece of the mosaic: The fastest-growing trees, like Eucalypts, are planted in areas with low slopes and deep clay soil; these areas naturally have higher water levels. Steep areas, and those with sandy soil, tend to have limited water, so pines and other slower-growing plants are planted there. The mixture of plant types means fewer water-use conflicts in the same area.
The mosaic also includes a mix of plants throughout the plantation, even in areas with higher water levels. These less productive plants add biodiversity, and they balance the water needs of their thirstier neighbors. And, finally, the native plants and undeveloped land in the mosaic promote environmental conservation. More native forest leads to strength for the area’s entire ecosystem. It’s estimated that water levels may stabilize when 30 to 40 percent native vegetation exists in a plantation.
Other actions support water management in these plantation forests. One is planting specially bred plants in these areas that better withstand drought. Another strategy is to reduce the plants’ Leaf Area Index (LAI), so they can adapt to drought-like conditions. These are also valuable practices. But we can start with managing the overall mosaic – because we must respect regional water limits, and the limits of what an area of land can produce. When we do, we honor both plantations and people in these regions, and we’ll make certain both will have enough water.