Where has all the leaf litter gone?
Charlotte Buehler, Chad Byers, Summer Drake, and Vanessa Fox
Biology Department and Science Research Fellows Program, DePauw University
What affects the amount of leaf litter in a forest? There are very few leaves on the ground in forests at the Nature Park and there are fewer leaves in some parts of the forest than others. We have been testing various hypotheses to explore why these patterns exist. Does it depend on abundance of organisms that eat leaves, like earthworms, beetles, crickets, bacteria, or fungi? Or are abiotic conditions more important, like soil characteristics, moisture, or temperature? Or is it the palatability of leaves, like presence of more sugars in some leaves vs. presence of more toxic substances in other leaves (these are referred to as “lability” and “recalcitrance” in the literature!)? Our answers to these questions so far are no, no, and we don’t know yet. We used some interesting techniques, like pouring water containing a bunch of dissolved mustard onto the ground and waiting for earthworms to emerge out of the soil. We saw a few earthworms, but not enough to explain why there are so few leaves on the ground. We know that the soil in the forests contains a lot of calcium; this is so surprise since the underlying bedrock is composed of calcium-rich limestone (and the forests are in the vicinity of an old limestone quarry!). Calcium promotes more rapid decomposition of leaves than other nutrients in the soil. But this doesn’t explain why some forests in the Nature Park have fewer leaves than others, because the amount of calcium was similar across the board. Our latest hypothesis is that forest composition may be the most important factor contributing to differences in leaf litter among our sites.
Different parts of the forest are dominated by different species of trees; leaves from these trees may decompose faster or slower depending on their chemical make-up. We have just finished setting up a long-term experiment with mesh bags to test this hypothesis. During the summer, we collected fresh leaves from nine tree species. We placed 2 grams of air-dried leaves in each bag, with separate bags for each tree species. We will collect a subsample of bags at various times during the next year. We expect that some tree species will decompose faster than other tree species. If so, this may provide the missing link in understanding why leaf litter varies so much among the forests at the Nature Park.