Planting Seedlings in Tree Islands Versus Plantations as a Large-Scale Tropical Forest Restoration Strategy

background

This research compares the growth and mortality of 4 tree species (2 native to Costa Rica and 2 native to northwestern South America) in the reforestation of abandoned agricultural land in Costa Rica.

Research Goals & Methods

The study used two different approaches: plantation (entire 50 x 50m planted) and tree island (six patches of three sizes–small, medium and large– planted within a 50 x 50m area). The experiment was replicated in 12 different sites across a 100 km2 area. Over a period of 3 years, data was collected on seedling growth and survival, canopy cover, soil and foliar nutrients, soil compaction, and photosynthesis.

Conclusions & Takeaways

Overall, seedling survival was similar across treatments; however, seedling growth and canopy area was higher in plantations, with an overall height difference of 0.6 m recorded over 3 years. The authors link the decreased growth recorded in the tree islands to two possible factors: (1) a higher incidence of damage along the edge from ruderal vegetation clearing, and (2) a higher proportion of saplings exposed to the more stressful abiotic conditions along the edge. Survival, growth and canopy area were all site- and species-specific and greater rates were recorded for the two N-fixing species, Inga edulis and Erythrina poeppigiana. Measurements of soil and foliar nutrients did not vary significantly between the plantation and island designs; however, individual species growth and canopy cover did vary with soil and foliar nutrients. For the two non-N-fixing species (Terminalia Amazonia and Vochysia guatemalensis), foliar N was strongly correlated to canopy cover of Inga edulis. With regard to the measurements of photosynthesis, the leaf mass per unit area was higher in the islands, while efficient use of phosphorus was higher in plantations. The authors suggest that, while reforestation with tree islands is significantly cheaper and may have seedling survival rates comparable to plantations, the possible disadvantages must be carefully measured and site-specific methods should be used.