Root, ground cover, and litterfall dynamics within canopy gaps in a slash pine (Pinus elliottii Engelm.) dominated forest

Abstract

We studied root, ground cover, and litterfall responses to canopy gap formation (approximately 2000 m2) in a slash pine (Pinus elliottii Engelm.) stand in southern Georgia. Artificial gaps were created in October, 1995, by girdling trees to simulate an outbreak of southern pine beetle (Dendroctonus frontalis Zimm.). Post-treatment changes in root growth and mortality (measured with minirhizotrons), changes in understory vegetative cover, and litterfall collections were used to characterize above- and below-ground responses to gap formation. We expected to detect the presence of a root gap, mirroring above-ground canopy gaps, which would become less prominent as ground cover increased. We found that dead root length increased after girdling, from 0.012 cm dead roots cm−2 in November of 1995 to 0.12 cm cm−2 in March of 1997. Mortality increased at 0-25 cm soil depth in response to girdling, but root production was stimulated as well, compensating for gap-induced mortality of girdled trees. Consequently, there were no marked changes in live root length, nor did any root gap form. Concomitant increases and understory vegetative cover suggest that the absence of a root gap was due primarily to rapid response of understory vegetation. Ground cover increased dramatically in gaps, from ~15% at gap center in the summer before treatment to ~90% the second summer after treatment, and diminished with increasing distance from gap center. As expected, needle and bark litterfall increased beneath girdled trees. We conclude that when disturbance is restricted to canopy trees, ground cover rapidly responds to the increase in space, and probably increased resource availability. No root gap formed due to the rapid proliferation of extant and newly established vegetation.