MANAGING FOR BIODIVERSITY: WHY STEWARDSHIP MATTERS
Identifying and protecting areas that are important for biological diversity is only the first step towards conservation. Sound stewardship is vital to achieving the goals of the Conservation Lands Network. Each fine filter focus team identified management actions that are important for maintaining the viability of their conservation targets. These recommendations can be found at the end of Chapters 5 to 8 of the full report and under the Results tab above. Many of them are also captured in the Viability Summaries included in Chapter 9: Conservation Target Viability and available for individual download from the links below.
A brief overview of each of the viability factors considered is presented below, but the complete Viability Summary for each factor can be downloaded individually by clicking on the link provided.
1. Climate change: Vegetation exists in quasi-equilibrium with the local climate. As temperatures and water balance change over time, fire frequency, drought stress, insect outbreaks, and other mechanisms will change, affecting mortality and recruitment and thus the composition and structure of vegetation. Climate projections indicate a general increase in aridity, which may lead to an increase in shrublands at the expense of woodlands and forests.
2. Atmospheric nitrogen deposition: Air pollution delivers substantial amounts of reactive nitrogen to landscapes downwind of major urban and agricultural sources. This added nitrogen fertilizes ecosystems, and can lead to more intense weed invasions, increased grass biomass and fire intensity, and loss of native forbs. Low biomass vegetation types, especially those on nutrient-poor soils such as serpentine, are particularly susceptible. Appropriate grazing regimes are the only way to manage nitrogen deposition impacts over large areas; smaller areas can be managed by mowing and prescribed burns.
3. Fire: Fire is an inevitable factor in Bay Area landscapes, given a long dry season combined with frequent human and infrequent natural ignition sources. Many vegetation types are dependent on a certain frequency and intensity of fires. A lack of fire alters successional patterns leading to changes in vegetation types, and too-frequent fire can eliminate key plant species. Prescribed fire is an important management tool where it can be used safely. Fire management is especially complex near the urban/ wildland interface.
4. Ecological succession: Succession is the change in vegetation composition and structure as new species become established, or as existing species disappear. The dynamic nature of vegetation requires land managers to anticipate changes and determine when and where to intervene. Successional issues are particularly important in Cool and Moderate Grasslands, where rapid invasion by coyote brush, Douglas-fir, and other trees and shrubs can eliminate open habitat. Douglas-fir can also invade the understory of oak woodlands and montane hardwoods, eventually becoming the dominant species. Appropriate disturbance regimes (e.g., grazing, fire, and mechanical treatments) are essential to manage succession.
5. Flood and drought: Extremes of flood and drought are natural features of the Bay Area’s Mediterranean climate, with its cool rainy winters and warm dry summers. Every year has a summer drought lasting about six months, causing streams to naturally draw down, creating disconnected pools, and partially or fully drying wetlands. The accumulated water stress profoundly shapes local ecosystems, largely determining which plant species can grow. Big winter storms can saturate soils resulting in landslides and huge amounts of sediment and runoff into rivers and streams. Stream banks are overtopped and adjacent flatlands are flooded.
6. Landslides and erosion: Landslides and erosion create fresh geologic surfaces; deep, loose soils; and natural wetlands and ponds. They can also generate sediment that profoundly impacts streams. Heavy rains, fires, and earthquakes cause shallow landslides and high erosion rates in the mountains, which have steep, fault-riddled topography, weak rocks, and erosion-prone soils. Coastal bluffs are particularly susceptible to landslides, and continued shoreline retreat is inevitable with sea level rise. Going back to the Gold Rush, a legacy of poor land management, especially clearcut logging and poorly designed and maintained unpaved roads, still contributes to sediment.
7. Invasive plants: Non-native plants pose a significant threat to native vegetation. Bay Area grasslands have already been converted to a predominant cover of nonnative annual grasses and forbs, and invasions of shrubs such as broom and gorse threaten native grasslands, shrublands, and woodlands. Climate change is predicted to contribute to increased frequency and intensity of fires, leaving burned areas vulnerable to invasion by non-native species. Weed management is an ongoing process that requires a long-term commitment of resources for management.
8. Non-native animals: Many introduced animal species are now established in the Bay Area, causing disruptions in native plant and animal plant communities. For example, eastern grey squirrels compete with native squirrels for food and habitat, starlings monopolize nesting cavities, red fox prey upon native species (including endangered Clapper Rails), Argentine Ants displace native ants, and wild pigs root through and overturn meadows and grasslands. Once established, populations of non-native animals can explode in size and disperse to new areas, making them virtually impossible to eradicate.
9. Pathogens and disease: Pathogens such as viruses, bacteria, and fungi are present in all wild populations of plants and animals, and are normal causes of disease and mortality. But pathogenic diseases can become epidemics, spread rapidly, and cause high mortality. Emerging diseases such as Sudden Oak Death (SOD) and the chytrid fungus that is decimating amphibian populations worldwide have become particularly virulent; these and other diseases can pose major threats to the viability not only of host species, but of entire ecosystems.
