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Juniper seed dispersal

Briana White
Ecology class, BIO 342, Biology Department, DePauw University
Fall semester 2009

Effective seed dispersal is important for plants.  The "directed seed dispersal" hypothesis states that seeds are dispersed to locations where seedlings have higher survivorship.  This pattern is important for recovery of vegetation in disturbed ecosystems, such as the Quarry Bottom.  

I hypothesized that the distribution pattern of juniper saplings and sycamore trees would indicate that directed dispersal of seeds by birds is occurring.

I collected data on 487 juniper trees in a one hectare plot in the Quarry Bottom.  I measured height, location (under another tree or in the open), distance, and compass direction from trunk, and canopy area of adjacent trees.

More juniper trees were located underneath sycamore trees than in other locations.  More junipers were clustered in the northeastern quadrant relative to a sycamore tree.  More juniper saplings were clustered in the inner canopy of a sycamore tree compared to the outer canopy of a sycamore tree. 

My results provide support for the "directed seed dispersal" hypothesis.  Sycamore trees may serve as perches for birds, which then deposit juniper seeds non-randomly.  Survival of juniper saplings is higher under sycamore trees.  Juniper saplings are clustered within the protected inner canopy of sycamore trees.  Juniper seeds appear to be delivered to locations where seedling survival is likely to be high.