The common edible fig is a subcanopy tree that has invaded many of the remnant riparian forests of California's Central Valley. Fig is unusual in its ability to invade low-light, low-disturbance, native-plant–dominated environments. Dendrochronology combined with regression and spatial analyses allowed us to empirically quantify the expansion rate and spatial pattern of the fig invasion into the native plant community at Caswell Memorial State Park (Ripon, CA) over a 70-year invasion period. Fig uses a combination of short-distance dispersal, which results in constant, linear expansion at source population sites and long-distance dispersal, which eventually leads to high recruitment of satellite populations in ideal environments. Although fig initially experienced a long lag in its invasion rate, at the time of this study, it was expanding at an exponential rate at the landscape scale in Caswell. We identified a number of characteristics intrinsic to the fig population (shade suppression, pollinator presence, highly specialized reproduction, and propagule pressure) as well as extrinsic characteristics of the receiving environment (hydrologic alteration from the construction of a dam, safe sites for juvenile recruitment, and target effects from environmental heterogeneity) that may have influenced the rate and pattern of fig invasion. The Central Valley riparian forests have been reduced to less than 6% of their original area, and invasive fig is a significant threat to the remaining fragments of this important vegetation community. We include suggestions for fig eradication based on knowledge gained in this study.
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