Over more than two decades of our research program, R.A.I.N. has funded dozens of experiments and observational studies.

Experiments and Observational Studies



R.A.I.N. has helped fund dozens of experiments and even more observational studies since 1998 as well as our efforts since 2002 at community outreach, described on the ABOUT page.  Here we list several of the main themes of our research.  Click on any theme for more in-depth description and photos.


Clearly, growing trees requires a lot of time!  However, much basic information was unknown at the beginning, yet was required for designing good long-term experiments.  Many basic data can be gathered quickly, so the projects have varied from short-term student studies to experiments that yield results for many years.  


Here are thumbnail sketches of a few of our projects, with links to more detailed information and photos.  You will see that we named some projects in Spanish -- we did this for the sake of our Costa Rican assistants!  The experiments and studies fall into categories within which they are arranged in approximately chronological order. 


These selected studies treat eight questions:

[click on the numbered title to access information and photos]



Our soils have been so deeply eroded that few trees can survive, much less grow.  We conduct tree trials (“Ensayos”) with seedlings produced in our own tree nursery and then out-planted into plots of degraded pasture on the farm.  Examples include Ensayo 1994, Ensayo 1996, and Ensayo 1998.  From dozens tried, only four native species and two non-natives consistently proved able to tolerate the degraded conditions at the farm. Some of the questions below involve deeper testing of the more successful species, such as Vochysia and Nicaraguan pine.

2. Does fertilizer or mulch help trees grow?  If so, does the benefit exceed the cost?

Soil infertility caused by erosion seems to call for chemical fertilizer or mulch/compost.  Our results however are either negative or equivocal.

3. Can other plants help target tree species grow?

When one kind of plant helps another kind to grow, “facilitation” occurs.  For example, local farmers know that if they intersperse legume trees among their coffee shrubs, they need less nitrogen fertilizer.  We tested for facilitation with several kinds of legumes in "Bloques’93" and in a new experiment called "Site Preparation" established in 2012.  Besides clicking on this theme to link to photos of Site Preparation, you can click on Nancy's 2012 letters to read about it.  Besides legumes, we also are testing facilitation by a non-legume tree that takes toxic aluminum out of the soil and by a grass that may help form terraces.

"Site preparation" experiment, 2012.  Here we are planting pilon, which might improve soil phosphorous.

"Site preparation" experiment, 2012.  Here we are planting pilon, which might improve soil phosphorous.

4.  Can we improve beneficial fungi in the soil so as to help target trees grow?

Soil erosion not only reduces nutritious minerals, but also can remove beneficial fungi called mycorrhizal fungi that most tropical trees need to grow well. These fungi establish a symbiosis in the tree roots that helps the trees gather important components from the soil.  Our studies included censuses of the fungi in the soils and in tree roots, and experiments to determine their role in restoration of trees to our pastures.  We were also concerned whether the different kind of fungi that pines have ("ectomycorrhizae") compete in the field with the kind that our other trees have ("arbuscular mycorrhizal fungi").

5. Do weedy ferns that invade the worst soils help improve the soil?

Several experiments determined that in some conditions, such as on high ridge-tops and in deep cattle trails, almost no tree seedlings survived to maturity.  After a few years, though, weedy ferns densely invaded these areas.  Although some evidence exists in the literature that the fern on the right, "helecho macho," may produce a toxin inhibiting other plants, we tested the alternative hypothesis.  We think that over many years the ferns may help improve the soil.  Our preliminary experiment tests this idea.

6.  Do pasture grasses compete with the tree seedlings? 

Once cattle are excluded from test plots, pasture grasses usually thrive and fill in.  We questioned the assumption that after tree planting, farmers have to control the grasses around tree seedlings because otherwise the grasses would outgrow and kill them in the first couple of years.  Alternatively, shade from grasses might help seedlings survive their first dry season, which can last up to three months.  We have done two experiments testing this alternative.


7.  Do some of the trees we try need more shade than is available in old cattle pastures?

We conducted two light experiments with seedlings, one under the shade of pioneer trees and another using different thicknesses of shade cloth.  Our results surprised us.


8.  How does the bird community change as tree regeneration proceeds?

We have censused birds in October every four years to see how our regenerated patches of forest affect the kind and the diversity of birds.  Non-restored neighboring pasture serves as a control.  The kinds of birds have changed even in the non-restored control pastures, perhaps due to changing climate.  In our restored areas, the diversity of birds has greatly increased from what it was in pasture.

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