Factors Limiting the Survival of Native Tree Seedlings used in Conservation Efforts at the Edges of Forest Fragments in Upland Madagascar

background

This study investigates the survival of tree seedlings 15 months after planting in grasslands along the edges of tropical forest fragments damaged by fire in four restoration treatments in upland Madagascar.

Research Goals & Methods

A total of 48 experimental plots were created in 3 similar grassland sites. At each plot, vegetation was stripped and the soil worked to a depth of 60 cm. In addition, 25 cm of vegetation surrounding each plot was removed on all sides, making a clearing of at least 1m2. Fertilizer treatments were applied. No maintenance was conducted on the plots over the course of the experiment. A total of 408 seedlings were planted; 207 survived the 15 month experiment. Increase distance from the forest lowered survival of all species at site 3 and of Rhus taratana at site 1.This was attributed to a gradation in microclimate and or soil conditions from the forest edge into the grassland.

Conclusions & Takeaways

Mixing soil from the forest into the experimental plots did not increase seedling survival. Fertilization lowered survival of Filicium decipiens and Olea lancea at the two hilltop sites and lowered the survival of Podocarpus madagascariensis at site 2. Fertilization resulted in increase in cover of shrubs and shading out the study species. The only significant effect of shading was the lowered survival of a light-demanding species, Dodonaea madagascariensis at site 1. Seedling survival was lower for most species except for O. lancea. This was because the species occured mostly on hilltops, suggesting that it is probably adapted to hilltop conditions. These findings have implications for future reforestation efforts. The distance from existing forest fragments must be taken into consideration when planning reforestation of tropical ecosystems, as a rate of successful tree establishment will most likely be higher in areas close to forest fragments than farther away.