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HomeMy WebLinkAbout21 VegetationThe Lakes at Valley West Subdivision – Phases 1 and 2 Preliminary Plat Application Vegetation Exhibit A shows the boundaries of surface waters and wetlands that directly correspond to the limits of the major vegetation types that currently exist within the Lakes at Valley West property. A majority of the parcel outside the Baxter Creek corridor has been disturbed by previous development. A gravel pit was developed on the property in 2002. The gravel pit was later expanded between 2007 and 2008 to construct the current footprint of the lakes. The mitigation wetlands on the perimeter of the open water and palustrine wetland located southeast of the east lake were constructed concurrently. The existing major vegetation types are associated with the constructed mitigation lakes and wetlands, the historic Baxter Creek riparian corridor, and protected upland buffers. The Lakes encompass approximately eight acres of open water. The wetland fringe surrounding the open water (termed lacustrine) and the palustrine, emergent wetlands located southeast of the East Lake extend across over six acres. The upland areas that surround the lakes and wetland consist of historically cultivated and grazed pasture that was seeded post-construction with native upland species. Mitigation wetlands are required to be protected from development in perpetuity by the US Army Corps permit conditions. The Baxter Creek corridor, the Lakes, and the palustrine wetland will be protected from development within dedicated park and/or open space. Critical plant communities associated with the streambanks and woody overstory of the historic Baxter Creek corridor will be protected within 50-foot watercourse setbacks that have been in place since 2008. The 50-foot watercourse setback for Aajker Creek extends to The Lakes parcel. Development will be restricted within the watercourse setbacks. The Baxter Creek corridor encompasses few woody species along its length. Isolated thin-leaf alder and Bebb willow trees and shrubs are found in small clusters along the channel. No trees or herbaceous plants within the corridor will be impacted by the development. A pedestrian bridge will be constructed instead of a culvert to cross Baxter Creek, which will limit the extent of impacts. The bridge location will avoid impacts to any woody species. Impacts to the riverine fringe will be limited to the footprint of the bridge footings. Pedestrian trails will be located in the outer 10 feet of the watercourse setbacks limiting access to the channel. The Lakes and palustrine wetland were constructed in 2008 as part of the 404 permit mitigation requirements. The mitigation design included upland buffers that surround the lakes and palustrine wetland. The lacustrine fringe of the lakes and the palustrine wetland are separated from any road or building envelope by a 35- to 50-foot upland buffer. The 458 trees and shrubs The Lakes at Valley West Subdivision – Phases 1 and 2 Preliminary Plat Application planted in 2008 around the lakes and within the Baxter Creek watercourse setback are located within park and/or open space that will be protected from any development. The trees and shrubs have been staked and caged to prevent browsing. The trees and shrubs were manually watered the first year after planting to ensure survival. Invasive species will be managed annually in accordance with a Gallatin County Weed Management Plan submitted on behalf of The Lakes at Valley West. The park, open spaces, and boulevards will be landscaped based on city-approved planting plans and in accordance with the City of Bozeman tree guide. The master plan for the park and open space that will encompass the lakes and palustrine wetlands includes an extensive system of gravel trails, boardwalks, and sidewalks. Baxter Creek Riparian Corridor The Montana Natural Heritage Program list of plant species of concern for Gallatin County was reviewed for this assessment. None of the listed species were identified within the creek corridor, the only water of the US on the property that has not been disturbed by development. The streambanks of Baxter Creek are vegetated with sod forming herbaceous species dominated by Northwest Territory sedge (Carex utriculata) and Nebraska sedge (Carex nebrascensis). The upper bank slopes are vegetated with native and non-native grasses including redtop (Agrostis stolonifera), Western wheatgrass (Pascopyron smithii), fowl bluegrass (Poa palustris), and orchard grass (Dactylis glomerata). The woody overstory along the length of the corridor had been impacted historically by unrestricted cattle access. Isolated clusters of senescent speckled alder (Alnus incana), Bebb willow (Salix bebbiana, aka gray willow), peach-leaf willow (Salix amygdaloides), and balsam poplar (Populus balsamifera) line the banks of the creek. The 50- foot watercourse setback on the west side of the corridor was planted with clusters of native woody species in 2008 at the same time the Lakes were revegetated. The installed woody species are listed in the following section. West and East Lakes The West Lake was constructed within the footprint of a gravel pit excavated to provide pit run for the first phases of Valley West Subdivision. The East Lake is separated from the Baxter Creek corridor by a gravel fines trail and riverine and depression wetlands. The lacustrine fringe associated with the lakes is vegetated primarily with grass, grass-like, and forb herbaceous species. Sod mats salvaged from a non-jurisdictional wetland located north of the historic gravel pit were placed on approximately half of the perimeter of both lobes of the Lakes and around the fishing accesses in June 2008. The wetland sod mats contained toad rush (Juncus bufonius), lesser poverty rush (Juncus tenuis), common spikerush (Eleocharis palustris), Baltic rush (Juncus balticus), dagger-leaf rush (Juncus ensifolius), Nebraska sedge, beaked sedge, leafy The Lakes at Valley West Subdivision – Phases 1 and 2 Preliminary Plat Application tussock sedge (Carex aquatilis), hard stem club rush (Schoenoplectus acutus), common field mint (Mentha arvensis), fowl bluegrass, redtop, field meadow foxtail (Alopecurus pratensis), and yellow (Salix lutea) and Bebb willows. The lacustrine fringe of the lake was planted with 5,008 wetland tubelings in August 2008. The grass-like Carex and Juncus species were planted from 7- and 10-cubic inch tubelings and the forbs were planted from 4-cubic inch tubelings and bare-root plants. The water level in the Lakes was raised with the control structure after planting to ensure that there was sufficient inundation. The hydrophytic species included pale bulrush (Scirpus pallidus), hard stem club rush, lamp rush (Juncus effusus), Torrey’s rush (Juncus torreyi), duck potato (Sagittaria latifolia), and seep monkey-flower (Mimulus guttatus). A custom seed mix was planted on disturbed areas within the wetland in October 2008. The seeded species included tufted hairgrass (Deschampsia cespitosa), fowl bluegrass, slender wheatgrass (Elymus trachycaulus), fowl mannagrass (Glyceria striata), and lesser poverty rush. The wetland fringe surrounding the Lakes was planted with 458 trees and shrubs the last week of September 2008. Plant material sizes included 1-, 5-, and 10-gallon containers. The species included black cottonwood (Populus trichocarpa), quaking aspen (Populus tremuloides), yellow, Geyer, Booth, Bebb, and Pacific willows (Salix lutea, geyeriana, boothii, bebbiana, lasiandra, respectively), red-osier dogwood (Cornus stolenifera), golden currant (Ribes aureum), common chokecherry (Prunus virginiana), Wood’s rose (Rosa woodsii), common snowberry (Symphoricarpos albus), silverleaf buffaloberry (Shepherdia argentea), Western serviceberry (Amelanchier alnifolia), and American silverberry (Eleagnus communtata). The location of the trees and shrubs was based on the post-construction moisture regime, the moisture requirement for individual species, and topography. The trees and shrubs were planted in clusters to simulate a natural environment. The clusters were staked and caged to prevent browsing. The woody plants were watered manually in 2008. Ninety-six percent of the woody species planted survived through 2012. Upland Grassland The undisturbed vegetation cover on upland areas located outside the constructed mitigation wetlands and Baxter Creek riparian corridor is dominated by herbaceous grasses. The grasses include orchard grass, Kentucky bluegrass (Poa pratensis), smooth brome (Bromus inermis), meadow fescue (Festuca pratensis), field meadow foxtail, and common timothy (Phleum pratense). Upland areas disturbed during construction were seeded with a native upland mix consisting of slender wheatgrass, Canada wildrye (Elymus canadensis), Covar sheep fescue (Festuca ovina), Western wheatgrass, Canada bluegrass (Poa compressa), and Sodar streambank wheatgrass (Elymus lanceolatus). The species were selected to establish quickly and form a stable root mass that limits water and wind erosion. The seed mix was planted in October 2008. The Lakes at Valley West Subdivision – Phases 1 and 2 Preliminary Plat Application Invasive species on the site include Canadian thistle (Cirsium arvense), common mullein (Verbascum thapsus), and Mexican fireweed (Kochia scoparia). The only state classified noxious weed is Canadian thistle (Priority 2B) located primarily within the floodplain wetlands west of Baxter Creek. The thistle will be sprayed annually for at least three years. A map of the weed locations, revegetation details, revegetation costs, and weed management costs will be submitted to the Gallatin County Weed District as part of the Weed Management Plan.