TREES AND LIGHT


Ecological studies suggest that tree species that typically pioneer cleared forest can tolerate full sun but those that colonize in their shade cannot. True for our species?

What are the basic light requirements of the trees species we are trying?


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Shade requirements:  We planted seedlings under structures with different levels of shade to determine the shade requirements of four tree species.

We controlled the level of shade by varying the number of layers of shade cloth, from zero to three layers.  Compared to unobstructed light levels, these treatments represented 100%, 30%, 10%, and 3% of available light.

Contrary to expectations, seedlings characteristic of mature forest did better in full sun whereas seedlings characteristic of early open forest did better in shade, contrary to theoretical expectations. The best predictor of the shade requirements of a new species under trial is to talk with the local farmers!

Pilon sol y sombra:  One of the few species that did well in our Ensayo trials was pilon (Hieronyma oblonga).  We have done several subsequent experiments to determine how to improve its growth.  This one, “Sol y sombra” (“Sun and shade”) was designed by our Costa Rican field assistants and tested whether pilon grows better in shade or sun.

Pilon seedling in full sun.  In contrast, when planted in shade, leaves are dark green and have few red spots.

They planted pilon in plots exposed to full sun and plots shaded by weedy trees that had colonized one of our areas.  Those in shade grew more slowly but looked healthier than those in sun.  We could not distinguish the effects of shade on growth rates from possible effects of competition from the weedy trees, though.