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Description
Mediterranean ecosystems worldwide are threatened by development, non-native species invasion and changes in disturbance regimes. Restoration of degraded ecosystems is challenging due to a lack of information on effective techniques and the inherent complexity of the systems. Southern California's Mediterranean-climate grasslands are particularly threatened and important as biodiversity hotspots, so research into restoration of degraded grasslands is urgently needed. This grassland restoration study on San Clemente Island tested the effects of herbicide, irrigation and seeding on species composition of two grassland areas (one highly invaded and one native dominated) after burning. Non-native grasses were successfully controlled in some sites with the herbicide treatment, both alone and in combination with other treatments. This control led to complex interactions between and among other functional groups (specifically Native forbs and Non-native forbs), burns and years, but overall, suppression of the Non-native grass functional group led to decreased competition pressure on both Native and Non-native forb functional groups. The addition of seeds to the plots also receiving irrigation and herbicide boosted Native forb cover, a result not seen in the absence of Non-native grass control. Irrigation treatments resulted in weak effects, indicating that it may be a poor restoration technique, particularly if it is not combined with Non-native grass suppression and native seed addition. Year two results were strikingly different from year one, highlighting the importance of multiple years of monitoring after the completion of restoration treatments.
