Three scientifically-designed field assays and many informal trials on 27 native trees and 3 non-natives determined which can survive and grow in our degraded soils. Only a handful can.

What valuable or otherwise beneficial trees can grow in deeply eroded tropical soils?

For subjects of tests and field assays, we selected trees with specific benefits for humans, such as timber or fruit, and for wildlife, such as flowers, fruits, and seeds.

We preferred native species because introducing non-native organisms sometimes causes problems in ecosystems if they become invasive weeds.  The non-natives we tried were either recommended by local foresters or already widely established by Costa Rican farmers as shade trees for their coffee.

Four plots of Ensayo 94 (blue), and 15 each of Ensayo 96 (orange) and 98 (yellow).  Some of these are out of sight on the slope at left.

Ensayos (Tree Trials) 1994, 1996, 1998.  These three scientific tests determined the ability of many native trees and three non-natives to survive and grow in our degraded soils. We planted 90 seedlings of each tree species, three in each of 30 plots across the farm under varying conditions including deeply eroded "hellholes", ridges, valleys, and steep slopes

These formal trials were followed by less structured plantings of other species over the years, so that by now we have tested over 30 species. 

In all we have found only four natives and two non-native trees that have done well.  The natives, as seen in the panel below left to right, are one species of legume tree Inga spectabilis ('guaba caite'), two species in the genus Vochysia ('mayo blanco' and 'mayo colorado'), and Hyeronima oblonga ('pilon' or 'zapatero').  Except for the legume, these are not related to anything we are familiar with in the Temperate Zone.

The two non-natives that survive our conditions are another species of legume related to the native Inga, Inga edulis ('guaba chilillo', below left) and Pinus tecunumanii aka oocarpa (pine, below right).  The natural distributions of both of these come close to Costa Rica, however.  The pine is native to Central America as far south as Nicaragua, Costa Rica's immediate northern neighbor.  Inga edulis is native to South America and comes as close as Panama, Costa Rica's immediate eastern neighbor.

Only one of these six trees, the pine, is economically viable for a farmer as a harvestable crop in less than 20 years.  See Our story of pine, below.

Several scientific publications and oral presentations have emerged from this work, listed on our page PUBLICATIONS, among them a paper for the Food and Agriculture Organization of the United Nations and one in the journal Forest Ecology and Management in 2004, as well as a presentation in 2002 at an international conference.

Our story of pine

The pine may be key to restoring economic value to farms with a high proportion of deeply eroded and otherwise infertile soil.  This is the only tree that can survive in our hellholes and along high ridges. The left photo in the panel below shows an area in our degraded pasture eroded to bedrock--no, that's not a sand trap in a golf course, it's our Hellhole no.1!  The boxes drawn on the photo indicate the locations of two of 30 plots for Ensayo 1994, which included pine.  By five years after planting eight kinds of trees, only pine had survived in the hellhole (middle photo).  Similarly, only pine survived on high ridges (right).

Of the 87 pines in Ensayo 1994 (we lost one plot), only a few died.  Those fell in high winds once they got large. Some of these fallen logs were large enough to harvest when we brought in a portable sawmill in 2011 to thin the pines, which had been planted only 10' apart.  At 17 years old, many were so large that they crowded each other, so we had to remove one of the three pines in several plots.  The panel below shows sawing, cutting into planks in the field, hauling by horseback, and drying the high quality lumber.

Drying a large part of the lumber from only 10 pines.

Drying a large part of the lumber from only 10 pines.

The wood is dense, full of resin, and beautiful but somewhat difficult to work.  Project Administrator Eduer Sandi is a talented carpenter and made this bed and headboard for the farm house after the planks had seasoned for about a year.  Click on the photos to enlarge them.

Imagine the quantity and quality of wood coming from a few trees in another few years!  Some of our neighbors were involved in this harvest and told Project Director, Dr. Carpenter, with a chagrined smile: "When you planted trees back then, we thought you were crazy (loquita!).  But if we had done the same, we would be better off economically now."

Stand of three pines (left) in an Ensayo94 plot after 13 years of growth.

Wood is costly now because much of the available timber has been logged.  The fact that we could get a viable harvest in less than 20 years makes planting pine an economically viable option for small farmers with deeply eroded portions of land.  At Dr. Carpenter's presentation at the local farmers association, one person said that planting trees--if done right--could be a retirement investment.  Another pointed out that just having healthy patches of trees on their farms would increase land values in case they wanted to sell.

Our story of pine perhaps does not end with its potential value as a commodity.  Does it have ecological value as well?  We do not recommend large plantings of pine.  It is not a native species, and casual observation suggests that bird, insect, and understory plant diversity is low in pine plantations in our area.

On the other hand, by growing quickly, the crowns of the trees soon touch and form a closed canopy.  This layer along with the roots is likely to reduce erosion, yielding a valuable ecosystem service.

Furthermore, preliminary evidence suggests that pine may act as a nurse tree, facilitating the growth of at least one of our most difficult and valuable hardwood species, cristobal (Platymiscium).   If so, this is an important result, so we plan more definitive experiments to test this idea in the future. 

If pine proves to be a facilitator, then a farmer might plant pine to stabilize soils and get a harvestable crop in 15-20 years.  Meanwhile, he can plant hardwood seedlings under the pine canopy.  These trees will grow slowly at first.  However, after the pines are removed in thinning and harvesting, the hardwoods might grow faster.  The farmer then might get a slower-growing, even more valuable native timber crop, perhaps in his lifetime.

Cristobal sapling (left foreground) two years after planting as a seedling under a pine in Ensayo94, with Mancha the dog.

Cristobal sapling (left foreground) two years after planting as a seedling under a pine in Ensayo94, with Mancha the dog.