In southern California, riparian areas are typically the only moist areas in an otherwise relatively dry environment. They provide breeding, foraging, dispersal, and refuge habitat for a host of invertebrates, fish, amphibians, reptiles, birds, and mammals. Healthy riparian areas also play a critical role in the movement of biota, sediment, water, and inorganic and organic materials throughout the environment.
Approximately 1,770 acres (716 hectares) of the Nature Reserve of Orange County classified as riparian are found in canyon and valley bottoms throughout the Ecological Health Assessment (EHA) Study Area. These habitats are the most sensitive to changes from drought, climate change, and human alterations to the environment.
It should be noted that hydrological conditions that once promoted and sustained some riparian and wetland populations may no longer exist because of alterations to watersheds via development (e.g., flood control measures) or drought-induced habitat type conversions. As a result, some plant and animal populations may not be able to readily reproduce, leading to long-term shifts in riparian and wetland community composition. Non-native polyphagous/Kuroshio shot hole borer beetles (Euwallacea sp.) and their symbiotic Fusarium fungal pathogen have caused significant die-off of willows and other species in nearby San Diego County.
Riparian areas within the EHA Study Area should be monitored for overall health and for signs of these stressors, including:
- Number of acres of late-successional native riparian habitat (characterized by a complex/layered structure that includes large floodplain trees in the overstory, understory trees and shrubs, and vines and ground cover such as Juncus spp., Carex spp., and Leymus spp.).
- Density of high-value trees (e.g., larger than 24 inches in diameter at breast height).
- Number of acres of woodland and forest habitat (ephemeral, intermittent, perennial).
- Riparian cover characteristics required for adequate sediment buffering and stream-channel shading.
- Presence and extent of priority non-native, invasive species.
- Corridor length, connectivity, and width.
- Fluvial geomorphic processes necessary to sustain long-term riparian succession and habitat formation.
- Changes in vegetation conditions over time.
Authors of the report State of the Regional Preserve System in Western San Diego County used two metrics to evaluate woody riparian habitat: percent conserved and ecological integrity. Aligning the metrics used in the EHA Study Area with those used for that report could provide a useful way to look at the health of these habitats on a more regional scale.
