Seedling Survival

This past spring break I spent another week on Santa Rosa Island. This time  I re-measured the 329 tagged Torrey pines from July to determine their growth and survivorship. Seedling recruitment increased substantially, with 53 newly emerged seedlings in my demography plots. Despite having another year of drought, precipitation in the form of fog drip and the shading of larger Torrey pines has allowed over 70% of the seedlings I encountered in July to persist until now.

But moisture protection in the form of shading is a two-edged sword. It does protect the soil and plants from losing water in a dry Mediterranean climate, but it is also preventing much needed light from reaching the photosynthetic tissues of the younger pines. The result is that most seedlings under the canopy usually die within 2 or 3 years due to their lack of light.