Van der Steeg, R.  1999.  Factors that determine the presence of Enterolobium cyclocarpum.   Department of forestry, Wageningen Agricultural University.  47 p. AV-99-11

In former days there was a large area of tropical dry forests in Central America.  During the last centuries much of this area had been transformed into pasture.  Recently reforestation of these areas is getting more and more interesting.  Apart from planting, reforestation can be realised with the help of natural regeneration.

When doing this, it is important to know if reforestation with the help of natural regeneration is profitable.  For that I Looked at different factors which might influence the presence of Enterolobium cyclocarpum.  This was done in the Horizontes Experimental Forestry Station in Guanacaste, Costa Rica.  The factors that are being researched were the soil depth, the vegetation, the distance to the nearest mature tree and the posible influence of cattle.  With the help of the two samples test of Wilcoxon posible relations were tested.   After this it was investigated whether some of these factors are related with the size of the trees. This was done with the test of Kruskal-Wallis.  To test if the trees are related with their distance to the mature trees, the coefficient of aggregation was used.  For checking if the trees were clustered the chi-square test of goodness of fit was used.  Finallly the most important factor had to be found and this was done with the help of the Wald-statistic of the logistic regresión model.   this is a multivariable regression model and with the logistics regresión model it was posible to predict the presense of Enterolobium trees with the help of all factors.  Using map-making software the values of all factors were interpolate for the research area.  After that the chance of finding an Enterolobium in each plot was calculated with the help of a formula.

It turned out that there were positive relationships with tree-cober, shrub-cover and soil-depth and negative relationships with the grass-cover and number of droppings.  The most important factor measured was soil depth.  It turned out that the model of the logistic regression predicts too many trees.  Also the chance prediction map is too optimistic.  Possible reasons for this can be that the formula of the logistic regression model is not good enough.  Another reason might be that the map is not good due to the interpolation method used or because the data is not uniformly spread over the research area.  It is  also possible that there are other more important factors or the circumstances are different at the time of the establishment  of the tree.

A plantation  seems to give more profit that natural regeneration because it is unlikely that natural regeneration  will produce enough trees per ha to give more profit that the extra planting costs of a plantation.  When one has a area with deep soils and one uses cows for only a short period to spread the seeds, the regeneration probably will be more.  Other profitable tree-species are not taken into account for the calculation, and these species can give enough profit to make natural regeneration  more profitable.