Shale Hills, GRAD STUDENT
The hydraulic architecture of a tree could contribute to its ability to tolerate drier soils by increasing resistance to xylem cavitation and improving the efficiency of water transport. This study examined six co-occurring tree species within three genera (3 congeneric contrasts; Carya glabra and C. tomentosa, Pinus strobus and P. virginiana, Quercus alba and Q. prinus) under naturally occurring soil moisture gradients. Within each genus, species differed significantly in distribution along gradients of soil moisture (P < 0.003), with one species preferentially occupying wetter sites and the other occupying drier sites. I hypothesized that hydraulic architecture might partially explain variation in the distribution of species. I measured a suite of hydraulic architecture parameters including maximum specific hydraulic conductivity (ks max), leaf specific hydraulic conductivity (LSC), and xylem vulnerability at three levels of percent loss of maximum hydraulic conductivity (P20, P50, and P70). The congeneric contrasts within oaks and within hickories showed no significant differences for any of the parameters. For pines, the species associated with drier sites, P. virginiana, was more resistant to cavitation, which was consistent with my hypothesis. In general, species that preferentially occurred on drier sites tended to have higher maximum specific conductivity (P = 0.0039), which was opposite the expected water-conserving strategy hypothesized for drought-adapted species. These results suggest that these measures of hydraulic architecture of stems in mature trees may play only a minor role in explaining species-level variation in distribution on the landscape. This research invites further investigation into other potential limiting factors that may be controlling tree species distribution in the hill and valley region of central Pennsylvania.
Wubbles, J. (2010): Tree species distribution in relation to stem hydraulic traits and soil moisture in a mixed hardwood forest in central Pennsylvania . Master of Science, Horticulture, The Pennsylvania State University, p. 39..
This Paper/Book acknowledges NSF CZO grant support.
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