How Trees Protect Us During Prolonged Rainy Season – OpEd
A prolonged rainy season always pose danger to human lives and settlements. As PAGASA confirms that La Nina is unavoidable, we expect to have flooding, land and mudslides, excessive water run-off and loosening of soil surfaces.
The soil is like a sponge. If it exceeds its water holding capacity, it releases the water absorbed and often most of the soil with it. If you have trees within and around your community, you will not worry to0 much as those who have treeless properties.
Erratic rainfall could worsen with soil erosion and landslides, but with trees, this may not happen or will happen only to a little degree.
Trees contribute immensely in preserving soil. Far reaching roots hold soil in place and fight erosion. Trees absorb and store rainwater to as much as 200 liters per tree which reduce runoff and sediment deposit after storms. This helps the ground water supply recharge, prevents the transport of chemicals into streams and prevents flooding. Fallen leaves make excellent compost that enriches soil.
Trees can help reduce erosion by:
- Slowing wind and water flows;
- Holding soil together; and
- Increasing infiltration, and most importantly, acting as cushion or soil cover from the gazillions of raindrops.
When there are no trees to protect the soil, gully erosion occurs because: the shape of the terrain concentrates water flows over or through the land; and the soil is not cohesive enough to prevent soil loss.
Gully erosion is best controlled by by planting trees on higher ground around the gully area. Wherever possible, trees should be planted in conjunction with deep-rooted and fast growing grasses which will also use water, increase infiltration and control flow.
While slowing of water flow may not prevent gully erosion completely, it can dramatically reduce the rate of erosion. Diversion banks can take water elsewhere, but quite often this shifts the problem to a new site. Building a dam is an effective but expensive solution. Trees planted in and around the gully may help hold the soil together.
The closer to the gully, the wetter the soil will be, and may want to plant different species. To avoid scouring, plant small shrubs with flexible stems within the gully rather than trees.
Sheet and rill erosion can also happen if a property is treeless. To prevent this from happening, plant trees across the slope. The distance between the rows of trees planted across the slope affects slope length which in turn affects the rate of soil loss. Trees and shrubs can also be planted in strips along contours to check run-off.
Banks can be used to decrease slope length, but trees are much less susceptible to damage by floods than conventional banks and have the added bonus of increasing the rate of water infiltration.
Where banks are being used, trees can also be planted on them to provide bank stabilization. The steeper the slope, the faster water flows and the greater the chances of soil erosion.
While trees obviously cannot change slope steepness, they will slow down the rate of water flow when planted across the slope. Trees are most effective on steep slopes when used in conjunction with dams and contour and diversion banks for changing slope angles and increasing infiltration.
So save your life, save your property. Plant trees.