The effect of Soil and Canopy Heterogeneity on Seedling Recruitment in Restored Tropical Pasture
Social Sciences
Environmental Studies 199
This study evaluated the heterogeneity of soil and canopy conditions in degraded
pasture in Costa Rica that had been restored using three strategies: passive restoration (control),
planting tree nuclei (islands), and planting tree plantations. I hypothesized that (1) there would
be highest habitat heterogeneity in the island treatment and (2) this heterogeneity would result in
higher seedling recruitment. I collected soil samples and took hemispheric photographs and
calculated the coefficients of variation of soil nutrients and canopy structure to quantify
heterogeneity. The field team sampled tree seedlings across a belt transect in each plot to assess
the abundance and richness of recruits. I found that although soil nutrients were heterogeneous
within treatments, their variability is not related to differences in tree planting strategies.
However, planting tree nuclei resulted in a more heterogeneous canopy than the other two
treatments. The heterogeneity of canopy conditions did not translate directly into higher seedling
recruitment, possibly due to dispersal or seed bank limitations. Seedling recruitment (richness and
abundance) was similar in island and plantation treatments and lower in control treatments. This
may be because established trees serve to shade out competitive grasses and indirectly facilitate
seedling establishment. Planting tree islands and plantations seem to equally induce natural
processes of succession by means of seedling recruitment. Therefore, tree islands may be used as
a cheaper alternative to tree plantations when restoring degraded tropical land.
