Lending Nature a Hand

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The people in the tropics rely on the services and products that the tropical forest provides. Where the forest has been cleared for agricultural uses, over time when the agricultural activities have stopped, the forest will regenerate. However, this is a slow process.

Forests will regenerate but the process is a slow one. Marijke van Kuijk is a Dutch ecologist who has studied the regeneration of the tropical forest in Vietnam. He has also used two procedures to give nature a hand. One is the pruning of foliage to free up space for trees and the other is planting the desired tree species.

When the land is left to its own devices the development from agricultural plot to forest often stalls during the shrub stage as some plants and shrubs grow vigorously and become dominant. This means that many young trees do not receive enough light to grow.

One of Van Kuijk discoveries was that when foliage was pruned, the response of trees to the opening in the vegetation varied among species. This was related to the tree height, the leaf surface, the dimensions of the crown and the amount of light the trees needed.

The ideal size for the opening in the surrounding vegetation varies for each species and depends on the height and density of the vegetation. Van Kuijk used the PHOLIAGE model to predict tree growth accurately. This makes it possible to determine -- per tree and per forest -- the best timing, the best opening and the effects of cutting free.

The PHOLIAGE model can also be used when scheduling the planting of new trees. The success of planting depends on factors such as exposure to light by the existing vegetation, tree species, et cetera. In general, the calculations indicated that shade-tolerant species achieve maximum growth faster (with less intervention) than photophilic species.

There are circumstances when it is not desirable to open up the vegetation to such an extent that all tree species can reach their maximum growth. That can be at the expense of the existing forest and requires a lot of work. The PHOLIAGE model calculates the amount of growth increase per planting, given a particular opening size.

When the land is no longer being used for agricultural purposes, it will begin the slow process of returning to a more natural state, i.e., forest. What results from this return is known as a “secondary forest."

The secondary forest is, at first, composed of non-ligneous plants and shrubs, which is then followed within a few years by pioneer trees. Several decades later, the pioneers die off, giving the climax species the opportunity to grow and later form a forest.

This process, where species replace each other over time, is called “succession” and is the natural process by which a forest regenerates. Often this regeneration process stagnates during the early stages of succession. Non-ligneous plants and shrubs grow vigorously and become dominant, with young trees not receiving sufficient light to grow. This results in a scrub land of little biological, economic, social or cultural value.

The techniques that are applied in this project are well worth trying in other areas where the forest has been cut down and the land now sits abandoned.