Quercus geminata

Abstract: Several hurricanes struck Florida, U.S. in 2004 and 2005 causing widespread damage to urban and rural areas. We measured the impacts of five of these hurricanes on the urban forest and combined these results with four other hurricanes to present an assessment of wind resistance for southeastern United States coastal plain tree species. Urban forest loss was positively correlated with wind speed. Tree species demonstrating the highest survival in winds were sand live oak (Quercus geminata), American holly (Ilex opaca), southern magnolia (Magnolia grandiflora), live oak (Quercus virgin- iana), wax myrtle (Myrica cerifera), sweetgum (Liquidambar styraciflua), crapemyrtle (Lagerstroemia indica), dogwood (Cornus florida), and sabal palm (Sabal palmetto). In a statistical comparison of sand live oak, live oak, and laurel oak (Quercus laurifolia) survival after four panhandle hurricanes, laurel oak had significantly poorer survival than both live oak and sand live oak. Among all species, larger trees lost more branches than medium and smaller trees. Leaf loss had a positive relationship with survival; losing leaves during the hurricane meant higher survival. Trees growing in groups or clusters had greater survival than those growing as individual trees. Tree species with higher wood density had greater survival. Tree species categorized as having dense crowns lost more branches than those with moderate and open crowns; however, contrary to the literature, dense-crowned species survived best. A survey of arborists, scientists, and urban foresters ranked species for their wind resistance. Using our results from hurricane measurements and incorporating results from the survey and the scientific literature, we have developed lists of relative wind resistance for tree species in the southeastern coastal plain. These lists should be used with caution with the knowledge that no species and no tree is completely windproof. In addition, local considerations such as soil, cultural practices, tree age and health, and other urban forest conditions need to be taken into account.

Abstract: The unabated increase in global atmospheric CO2 is expected to induce physiological changes in plants, including reduced foliar nitrogen, which are likely to affect herbivore densities. This study employs a field-based CO2 enrichment experiment at Kennedy Space Center, Florida, to examine plant-herbivore (insect) interactions inside eight open-topped chambers with elevated CO2 (710 ppm) and eight control chambers with ambient CO2. In elevated CO2 we found decreased herbivore densities per 100 leaves, especially of leaf miners, across all five plant species we examined: the oak trees Quercus myrtifolia, Q. geminata, and Q. chapmanii, the nitrogen-fixing vine Galactia elliottii and the shrub Vaccinium myrsinites. Both direct and indirect effects of lowered plant nitrogen may influence this decrease in herbivore densities. Direct effects of lowered nitrogen resulted in increased host-plant related death and an increase in compensatory feeding: per capita herbivore leaf consumption in elevated CO2 was higher than in ambient CO2. Indirectly, compensatory feeding may have prolonged herbivore development and increased exposure to natural enemies. For all leaf miners we examined, mortality from natural enemies increased in elevated CO2. These increases in host-plant induced mortality and in attack rates by natural enemies decreased leaf miner survivorship, causing a reduction in leaf miner density per 100 leaves. Despite increased leaf production in elevated CO2 from the carbon fertilization effect, absolute herbivore abundance per chamber was also reduced in elevated CO2. Because insects cause premature leaf abscission, we also thought that leaf abscission would be decreased in elevated CO2. However, for all plant species, leaf abscission was increased in elevated CO2, suggesting a direct effect of CO2 on leaf abscission that outweighs the indirect effects of reduced insect densities on leaf abscission.

Abstract: We observed and quantified leaf miner distribution on Quercus geminata in order to determine its relation to leaf abscission and the effects of leaf abscission on larvae. A leaf—mining moth, Stilbosis quadricustatella, exhibited a clumped distribution of mines among leaves of the evergreen oak Quercus geminata. Mines tended to be on large, peripheral, and undamaged leaves so that leaves were often multiply minded. Mined leaves, especially those with multiple mines, tended to abscise early. Unless miners in an abscised leaf were very near to pupation, abscission killed them. Premature leaf fall was by far the largest source of larval mortality for this moth. A preliminary analysis suggested that the clumping of miners was no more favorable to the tree (in terms of number of leaves abscised early) than to the insect.

Abstract: Leaf-mining Stilbosis quadricustatella larvae are distributed non-randomly within leaves of their host plants, sand live oak (Quercus geminata) and water oak (Q. nigra), in north Florida. Fewer mines are found together on the same side of the mid-vein than separated, on opposite sides of the mid-vein. Larvae do not normally cross the mid-vein but create small blotch-like mines along subsidiary veins. Investigations of the usual mortality factors acting on these leaf-miner populations, including competition, parasitism, and predation, revealed no significant differences in these factors between mines separated by the mid-vein and those on the same side of the leaf. However, early leaf abscission, which kills the larvae present in the leaf, occurs significantly more frequently in cases where larvae are clustered on one leaf side. The reasons for this differential leaf abscission are not yet clear.