HERBACEOUS RESPONSE TO CANOPY REMOVAL IN SOUTHWESTERN OAK WOODLANDS

An understanding of overstory-understory relationships in southwestern oak woodlands is important for predicting response of these systems t o disturbance or manipulation, The objective of this study was to eval uate the response of herbaceous plants to removal of the overstory in evergreen oak woodlands. Overstory plants were removed from 30 X 30 m plots in January 1993 and January 1994, and the response of herbaceous plants in these plots was compared to untreated controls for 5 and 4 years, respectively, The C-4 graminoid and total biomass increased aft er overstory removal to as much as 10 times greater than controls, rem ained at elevated levels the second year, declined in subsequent years to 3-7 times the production of controls, and increased slightly durin g the final year of the study (1997), Overstory removal was necessary but not sufficient to affect herbaceous dicot biomass, which increased relative to controls during years with above-average winter precipita tion. The C-3 graminoids did not respond to overstory removal.