Plant-soil feedbacks in a tornado-damaged Southern Appalachian forest: Field and greenhouse studies
Although plant-soil feedbacks (PSF) can greatly influence plant community structure and diversity, it remains unknown what role they play in ecosystem development and changes. Severe disturbances such as tornadoes may alter PSF due to abiotic changes to the soil, as well as the shifting plant community. We conducted a field transplant experiment in 2014 to follow up on a 2012 greenhouse study. Greenhouse studies reveal many important patterns and mechanisms in PSF. However, in many cases, applications to natural systems are limited by a lack of field experiments.
This field transplant experiment investigated a) the growth of common southern Appalachian tree seedlings in same-species and different-species soil, and b) potential differences in that relationship between intact forest and tornado-damaged patches. In April 2011, a severe (EF-3) tornado damaged several thousand hectares of mixed pine-oak forest in Northeast Georgia. We planted seedlings of two common species (Nyssa sylvatica and Pinus strobus) beneath mature trees of three species, in both intact forest areas and tornado-damaged patches. Seedlings grew in field conditions for one growing season, after which they were harvested for biomass.
In the field transplant study, the growth of neither seedling species (Pinus strobus and Nyssa sylvatica) was significantly affected by neighbor tree identity. PSF were neutral in both intact forest areas and tornado-damaged patches. Seedlings of both species grew more in tornado-damaged areas (Pinus 0.277 +/- 0.027g ; Nyssa 0.594 +/- 0.465g) than in intact forest areas (Pinus 0.087 +/- 0.049g, F(1,1)=12.094, p<0.01; Nyssa0.180 +/- 0.104g, F(1,1)= 21.399, p<0.01 ), but growth was not affected by proximity to same-species mature trees.
These field-based results contrast with the results from our 2012 greenhouse study, in which PSF for Nyssa sylvatica were negative in soil from intact forests, but neutral-positive in soil from tornado-damaged patches. The difference in the results from these two studies may indicate that field-based experiments with realistic environmental pressures are necessary to adequately apply PSF greenhouse studies to a natural system. The field study also indicates that other environmental factors (such as light availability) likely influence post-disturbance seedling growth more so than PSF.