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Walnut trees and allelopathy

Kelsey Nosek
Ecology class, BIO 342, Biology Department, DePauw University
Fall semester 2010

Black walnut trees release juglone to inhibit germination or growth of surrounding plants.  My goal was to research the effects of juglone released by walnut trees on surrounding vegetation.

I hypothesized that the density of trees and saplings would be lower around walnut trees compared to other trees.

I collected data along Big Walnut Creek.  I paired each walnut tree with a box elder tree as a control.  I counted the number of trees and saplings within a 3 meter radius from the densest part of each tree's canopy.  

Results and Discussion
The data showed the opposite pattern from what I expected.  The density of trees and saplings was higher around walnut trees compared to box elder trees.  There are several possible explanations for these patterns.  Some plants may be tolerant of juglone.  Black walnut trees may vary in production of juglone.  Juglone may need to build up to a certain threshold for effective interference.  Microorganisms may decompose and ingest juglone as a source of energy, reducing the amount in the soil.  The canopy of black walnut trees is relatively open, allowing more sunlight to reach understory plants.