BRAY, JR., JAMES R., ABEL J. KINSER*, and BARBARA J. CRANDALL-STOTLER. Department of Plant Biology, Southern Illinois University, Carbondale, IL 62901. - Community Structure and Spore Bank Dynamics in the Fossombroniineae of South-central Texas.
Many species of the Fossombroniineae are adventives, occurring most
abundantly in either disturbed or seasonally dry habitats. Their
distribution within communities is generally patchy, with the patches
isolated from each other by denuded soil or more often by other
vegetation. Frequently, all patches of the community are comprised of
but a single species, but in some localities several species may
coexist. To investigate the spatial relationships among species as
well as infraspecific patch dynamics and establishment potential,
field studies were undertaken at Bastrop State Park near Austin, TX.
In year one of the study, patch distributions of Fossombronia
and Petalophyllum were mapped in eight randomly selected sites
within the park in the early spring growing season. To evaluate
microhabitat variation among these sites, soil pH, temperature at
patch surface, and intensity of red, far-red and blue radiation were
measured. Soil samples were systematically removed from each site for
subsequent spore bank analysis to assess the re-establishment
potential of each species. The eight sites were revisited and sampled
for spore bank analysis in midsummer of the following year to evaluate
the impact of seasonal changes on community structure. These studies
suggest that patches of the four taxa found within the sites are
clustered by species rather than being randomly mixed, with typically
no more than three species at any one site. In year one, only
F. foveolata and a few patches of Petalophyllum
germinated from the spore bank soil samples, while in year two, a
single patch of F. porphyrorhiza also developed. Such
germination events modify patch distributions but species composition
of each site seems to be consistent from year to year.
Key words: community mapping, establishment dynamics, Fossombroniineae, population structure