PARENT SESSION
Oral Session #22: Plant function and response to stress. Presiding: K. Miyanishi.
Tuesday, August 7, 2001. 8:00 AM to 11:45 AM. Hall of Ideas P&Q.
A quantitative comparison of two extremes in chaparral shrub phenology.
Thwing, Lisa1, Mahall, Bruce1, 1
ABSTRACT- We compared quantitative phenology and PDXPPs of a fully deciduous shrub, Styrax officinalis, with those of an evergreen shrub, Arctostaphylos glauca in shared microsites in southern Californian chaparral during a multi-year drought. Twig elongation and leaf production began during early spring for both species, but S. officinalis leaves matured more quickly. S. officinalis leaf senescence occurred mostly in August and September. A. glauca leaf senescence occurred throughout the year, especially coinciding with leaf production. Both leaf development and leaf senescence were more synchronous for S. officinalis than for A. glauca. Inflorescence bud development and flowering occurred simultaneously with leaf development for S. offincinalis. A. glauca inflorescence bud development occurred during leaf production; however, flower and seed production occurred 6-9 months later. PDXPPs were similar for the two species during most months of the year; however, small but significant differences on 9 of 25 occasiions suggested important differences in root architecture between these two species. S. officinalis appears to have somewhat phreatophytic roots, while A. glauca appears to have primarily shallow roots. Results of watering experiments support these hypotheses. During multi-year drought, S. officinalis changed little, producing nearly the same numbers of leaves per year with minimal shoot death. In contrast, A. glauca plants underwent extensive changes: older leaves were retained longer, fewer leaves, flowers, and fruits were produced, and significant numbers of twigs died. The ecological implications of these differences will be discussed.
KEY WORDS: Arctostaphylos, Styrax, drought, shrub morphology