OOS 32-4
Positive or neutral effects of non-native plant species in hybrid ecosystems: The use of songbirds and other observable wildlife as measures of ecosystem function
Scientists advocate a new impact-based assessment to prioritize established (i.e. not recently introduced) non-native plant species for either control or “acceptance” into otherwise native ecosystems. “Hybrid ecosystems” may be acceptable when a non-native species has neutral or positive effects on biodiversity, resilience, or ecosystem function. But few land managers can implement time and cost intensive research to measure these ecosystem attributes. We provide examples from vegetation and wildlife monitoring in three rare southern Californian habitats to demonstrate use of a relatively easy to measure parameter of ecosystem function, habitat provision, to assess impacts of non-native plant species and to reach our goal of providing habitat for birds and other wildlife. Over > 5 years we monitored all vegetation in needlegrass grasslands and in sites with both active and passive coastal sage scrub (CSS) restoration. In 2012 we initiated a study in riparian woodlands to assess impacts of a non-native ground layer species (Vinca major, periwinkle). During the wet and dry season annually, we trapped small mammals in all habitats over three consecutive nights per season. We surveyed birds using spot mapping (CSS) and qualitative surveys of two songbird species selected as indicators of habitat quality (grasslands).
Results/Conclusions
Non-native annual grasses (Avena and Bromus spp) had neutral effects in CSS restoration sites. Native shrubs colonized annual grass-dominated areas (32-45% total shrub cover after 2-3 yrs) and the hybrid developed into a native shrub-dominated ecosystem over time. Trends of increasing native bird species richness and small mammal species richness and abundance indicated that, without control of annual grasses, increasing shrub cover provided improved native wildlife habitat. Non-native annual grasses also had overall neutral effects on habitat for two grassland songbird species. Sturnella neglecta (Western Meadowlark) and Ammodramus savannarum (Grasshopeer Sparrow) populations persisted over seven years in grassland sites comprised of mixed native/non-native grass species. In the riparian woodland study, V. major had no negative effects on habitat provision for native small mammals. Captures from V. major-dominated ground layer sites were > two times those in sites without V. major; species richness in V. major-dominated ground layer sites was 1.75 times that of sites without V. major. Monitoring is ongoing, but thus far hybrid ecosystem concepts have stimulated us to view non-native species through a new lens to reduce workload and meet our goal of providing habitat for wildlife.