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Report: Reforestation of pastures using bat seeds

Nearly one year into our project in Costa Rica, Gloriana Chaverri  reports about planting success and failure. 

Summary of the project

While efforts to curtail deforestation have had a major positive impact in many countries, one of the main problems ailing the recovery of biodiverse tropical ecosystems is that forest recovery tends to be relatively slow. Some of the reasons for this slow recovery include a lack of seed input into deforested areas, and competition with aggressive grasses that are used to feed cattle. The goal of our project is to try a new method of tropical forest recovery that may prove to be cost-effective compared with other current methods. We seek to use bat seeds, which are easily gathered by the thousands in natural roosts, and plant them in pasture areas that have been prepared in a manner that should reduce competition with aggressive species of grass.

First experiment

Our study is being conducted in disturbed habitats in the lowlands of southwestern Costa Rica. We have chosen cattle pastures located in Península de Osa, and owned by Osa Conservation (OC), a local NGO that is seeking the help of scientists to develop novel ways to quickly recover their deforested lands. OC acquired a land that was previously used as cattle pastures that contain only scattered trees and shrubs (Figure 1); after its purchase, the land has shown slow forest recovery even after cattle have been removed.

In our first trial conducted in September 2015, we planted a 20 x 80 m plot of abandoned pastureland at Osa Verde, the property managed by Osa Conservation. The plot had been mowed 3 days before we sowed bat seeds. In these plots, we had 4 treatments and 4 replicates per treatment. For the treatments we sowed either 300 or 1500 seeds collected from 5 bat roosts with Carollia perspicillata colonies. These seeds were either sown dispersed or clumped. After 10 months we have not seen growth of these seeds, probably because the grass started to grow very quickly, and aggressively, after it had been mowed .

Second experiment

Because the first seeding attempt was not successful, we conducted another trial where, in addition to cutting the grass, the soil was ploughed mechanically to destroy the aggressive grasses and hence reduce competition with bat seeds. We started this new trial in July 21st, 2016.

This new plot is smaller than the first, and we are attempting a broader approach: instead of trying out small scale treatments where the number of seeds differ, we have collected and planted as many seeds as possible. We are using 16 plots, each a size of 25 x 5 m. We have planted approximately 354053 seeds in each of 8 plots, and the other 8 were left as controls.

Marvin Lopez, the project’s field assistant, has visited the plot in 4 occasions, once per week. In addition to monitoring growth in the field, he has also planted a few seeds in a pot in his own house to determine if they were germinating. After 1 month we have not observed growth of the seedlings in the field, but we are confident that they are successfully germinating, albeit rather slow, based on data of germination in the pot. Therefore, because the terrain is not showing signs of rapid recovery of grasses, we believe at least some of the seedlings will survive.

The plots will continue to be monitored for at least 6 months. If we observe growth and establishment of bat seeds during this time, we will attempt a third experiment in April 2017; this month represents the beginning of the rainy season, therefore securing the germination of seeds within an area that can be safely mowed and ploughed. A larger plot will be selected this third time to secure the 2 ha originally proposed.  

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