San Luis Valley Regional Habitat Conservation Plan Draft for Public Review
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2.2Riparian Vegetation CommunitiesThe San Luis Valley consists of a wide variety of vegetation communities and habitat types. The general vegetation communities are shown in Figure 3. The vegetation communities that are of primary interest in this HCP are the riparian and wetland areas found along the major streams, irrigation canals, and ditches on the Valley floor. Most of the documented habitat for the flycatcher and cuckoo occurs in dense willow patches along the Rio Grande and Conejos River; however, many smaller rivers and streams (such as Alamosa, Trinchera, and creeks on the Baca NWR) have not been surveyed. Riparian HabitatRiparian habitat in the Valley generally consists of a mosaic of woody trees and shrubs, wetlands, grasslands, and open water. The woody canopy includes stands of sandbar willow, peachleaf willow, crack willow, and broadleaf and narrowleaf cottonwood. In some areas, riparian vegetation is dominated by monotypic stands of either willow or cottonwood, while other areas support mixed stands of trees and shrubs (Stone, pers. comm. 2005; Lucero, pers. comm. 2005; Service 2003). Figure 3. Land Cover In addition to woody trees and shrubs, the riparian corridors in the Valley typically include wetlands and open water that are associated with irrigation and old oxbows, as well as wet meadows and grasslands that are often supported by irrigation and used for pasture. These ancillary habitat areas are generally found within the 100-year floodplain of major streams and rivers. This HCP does not address all wetland and riparian habitat types in the Valley. Outside of the woody riparian habitat areas that are the focus of this HCP, numerous areas throughout the Valley (such as the Monte Vista NWR and the wetlands in the Closed Basin) are renowned for their diverse open water, emergent wetland, and wet meadow habitat types. These areas, however, do not typically provide habitat for the covered species. Other Vegetation CommunitiesIn addition to riparian areas, the central Valley floor generally consists of irrigated cropland. Outside of those areas, the remainder of the Valley floor consists of rangeland and scrubland vegetated by native and introduced grasses, sedge and juncus species, greasewood, and rabbitbrush. The rim of the Valley supports scrubland dominated by sagebrush. The lower slopes of the surrounding mountains are vegetated by piñon-juniper communities, transitioning to pine, fir, and spruce forests at higher elevations. Riparian Habitat TypesFor the purposes of this HCP, riparian habitat in the Valley falls into three general categories (Figure 4):
These categories take into account land ownership and management, habitat quality, connectivity and continuity, and the known presence or absence of the covered species. These habitat types are used to explain the on-the-ground relationships between the covered activities and their impacts, typical habitat management practices, land ownership, and the value of various areas to the covered species. Given the conceptual nature of these categories, the distinctions between them are not always clear, have not been mapped, and are not quantified. Core Habitat AreasThese areas are protected from development, are managed to support or enhance wildlife habitat, and are known to support the covered species. Because of the combination of these factors, core habitat areas are considered the foundation for the conservation of covered species habitat in the Valley. Core habitat in the Valley is on the Alamosa NWR, the BLM’s McIntire-Simpson property, and several SWAs. Relationship to Recovery Plan Definitions – Core habitat areas in the Valley generally correspond with “occupied suitable habitat,” as defined in the Recovery Plan. Occupied suitable habitat is a riparian area with all the components needed to provide conditions suitable for breeding flycatchers, in which flycatchers are currently breeding or have established territories. In general, suitable breeding conditions are dense, mesic riparian shrub and tree communities 0.25 acre (0.1 hectare) or greater in size within floodplains large enough to accommodate Figure 4. Core and Buffer Habitat Concept Core Habitat Examples in the San Luis Valley – 13
riparian patches at least 33 feet (10 meters) wide (Service 2002a). Occupancy is confirmed by field surveys. These distinctions illustrate the range of habitat variability throughout the Valley that can still support the covered species. Because of this variability, these areas can provide a comparative baseline for nearby habitat areas that include similar habitat quality and components, but are not specifically managed to support or enhance wildlife habitat (e.g., secondary habitat areas). Buffer Habitat AreasThese areas contain general habitat structure and quality components that are similar to core habitat areas, are adjacent to or nearby core habitat areas, and provide an important buffer between core habitat areas and more intensively managed areas. Buffer habitat areas are privately owned, are not exclusively managed to support or enhance wildlife habitat, and may not be subject to any conservation or habitat management measures. Many of these areas are believed to provide potential habitat for the covered species, but have not been surveyed to confirm the presence or absence of the species. These areas have been, and continue to be, the focus of extensive private conservation efforts in the Valley. As of October 2011, more than 1,600 acres of riparian habitat, most of which has the potential to support the covered species, has been protected by conservation easements on private lands. Buffer Habitat Examples in the San Luis Valley –
Relationship to Recovery Plan Definitions – Buffer habitat areas in the Valley generally correspond with two habitat types defined in the Recovery Plan: “Unoccupied suitable habitat” and “potentially suitable habitat.” Unoccupied suitable habitat appears to have physical, hydrological, and vegetation characteristics within the range of those found at occupied sites, but does not currently support breeding or territorial flycatchers. These areas, which occur primarily on private lands, have not been surveyed for flycatchers and, therefore, are assumed to be unoccupied. Potentially suitable habitat does not currently have all of the components needed to provide conditions suitable for nesting flycatchers (as described above), but which could – if managed accordingly – develop those components over time (Service 2002a). Marginal Habitat AreasThese areas are narrow, isolated, or edge habitat areas (such as ditches and outer edges of pasture) that may occasionally provide some aspect of habitat for the individual birds (i.e., migration, dispersal, and post-fledging); but do not provide high quality, sustainable habitat. Most of the covered activities occur in these areas, which define the interface between higher quality riparian habitat (i.e., secondary habitat areas) and human use areas. Marginal Habitat Examples in the San Luis Valley –
Relationship to Recovery Plan Definitions – Marginal habitat areas in the Valley generally correspond with two habitat types defined in the Recovery Plan: “restorable potential habitat” and “unsuitable habitat.” Restorable potential habitat are those areas that could have the appropriate hydrological and ecological characteristics to develop into suitable habitat if not for one or more major stressors (i.e., hydrological changes, mowing, grazing, and fire). Unsuitable habitat are those riparian and upland areas that are found where physical and hydrological conditions could not support the dense riparian shrub and tree vegetation used by breeding flycatchers and do not have the potential for developing into suitable habitat, even with extensive management (Service 2002a). Riparian Habitat MappingFor the purposes of this HCP, the existing woody willow and cottonwood components of riparian habitat was mapped along key drainages. Native woody riparian vegetation represents suitable nesting substrate for flycatchers and cuckoos. Mapping the native woody riparian vegetation serves as an index to the overall riparian habitat that includes the associated wet meadow, slow-moving water, and herbaceous understory that are important components of the covered species’ habitat. In 2005, Agro Engineering, Inc. developed baseline riparian habitat mapping specifically for this HCP. In 2008 and 2009, ERO Resources Corporation (ERO) expanded this mapping to include additional drainages, and updated the mapping to be consistent with 2009 aerial imagery. In 2011, riparian habitat in Mineral County was added. The riparian habitat mapping is focused exclusively on the woody willow and cottonwood areas along streams and rivers that are known to have the greatest potential to support nesting habitat for the covered species, and are the primary interest of this HCP. The mapping does not include the adjacent wetland or open water components of the 100-year floodplain that provide foraging habitat for the covered species. For this reason, the woody riparian mapping is intended to be an indicator for the primary habitat needs of the covered species and is the quantitative baseline for this HCP. The woody riparian habitat mapping provides the basis for all of the habitat acreages, most of the impact estimates, and all of the mitigation credits described in this HCP. The 100-year floodplain is intended to provide a frame of reference for the habitat mapping. While most of the woody riparian habitat is within the 100-year floodplain, a relatively small proportion of the designated floodplain areas contain sufficient nesting habitat for the covered species. Both the woody riparian mapping and the 100-year floodplain mapping are shown on Figure 5. The baseline riparian habitat mapping was based on aerial photography taken between 2002 and 2004 (some areas were mapped with 1998 imagery). Ten survey plots were randomly selected to broadly verify the accuracy of this mapping. The original baseline mapping included the Rio Grande, Conejos River, Saguache Creek, Sangre de Cristo Creek, and Rio San Antonio. In 2008, this mapping was expanded to also include smaller creeks and streams in Costilla and Conejos counties, such as Culebra Creek, Ute Creek, La Jara Creek, and the Alamosa River. In late 2009, the riparian mapping was updated with 2009 aerial imagery to reconcile any changes in habitat that may have occurred since the previous mapping (based on 1998-2004 imagery). This repeat mapping resulted in a 0.6 percent increase in habitat, most of which was attributed to mapping errors (omitting several peripheral patches) rather than actual habitat changes. Besides ensuring the accuracy of the riparian mapping data, this exercise also demonstrated the overall stability of the riparian system and its resilience to drought and the ongoing impacts of the covered activities. Riparian habitat mapping, along with the 100-year floodplain, are shown in Figure 2 and are quantified in Table 1. Table 1. Riparian habitat mapping elements.
The riparian habitat mapping is intended to be an indicator of the general riparian system, and is not intended to specifically define the limits of what is and what is not habitat, and should not be used for site-specific regulatory purposes. As described in Section 6, this mapping will be updated every 10 years to identify landscape-scale changes and trends, revisit impact assumptions, and subsequent mitigation requirements. Figure 5. Riparian Habitat | ||||||||||||||||||||||||||||||||||||||||||||||||
