2008 Annual Monitoring Report (pdf 10.9MB) - Bolsa Chica ...

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Bolsa Chica Lowlands Restoration Monitoring 2008 Annual Report Decaying/Transitional Vegetation This habitat was used to describe transitional vegetation communities exhibiting the effects of exposure to or inundation by regular tidal influence following long periods of freshwater influence or intermittent inundation. This included rampikes of dead eucalyptus and Myoporum trees that ring the Muted Pocket Marsh and presently provide roosting and perching habitat for a variety of birds. These trees will eventually decay and begin to fall into the marsh. This category was also used to describe large areas of Rabbit Island. Prior to the opening of the FTB to the ocean, Rabbit Island supported mostly non-native upland species at the highest elevations and was ringed by coastal salt marsh. Following the introduction of tidal influence, which at extreme tide submerges much of Rabbit Island, both the upland and salt marsh vegetation began to die. Much of Rabbit Island is now covered with the standing dead woody stalks of past marsh and upland vegetation, including broad expanses of dead hottentot fig (Carpobrotus edulis). It is anticipated that as the decaying vegetation decomposes, coastal salt marsh will gradually become established at the mid- to high salt marsh elevations and cordgrass and mudflats will dominate the lower marsh elevations. Decaying marsh and hottentot fig on Rabbit Island (left/center), dead salt marsh transitioning to mud flat following inundation of the west MTB (right). Small losses to salt marsh in the MTBs and Seasonal Ponds were mapped as decaying vegetation as well, due to prolonged inundation by tidal waters or seasonal freshwater ponding. This process had only begun in the MTBs and is expected to results in greater losses of marsh in the coming years as the MTBs are all opened to tidal influence. Non-Native Vegetation Non-native vegetation was mapped primarily on the eastern boundaries of the study area in association with various oil filed operations and staging areas, as well as residential areas that contribute escaped landscape plantings. Common species include: radish, black mustard, castor-bean (Ricinus communis), myoporum (Myoporum laetum), hottentot fig, and tumbleweed (Amaranthus albus). Notably, there is little to no occurrence of the highly invasive non-natives giant reed (Arundo donax) or pampas grass (Cortaderia selloana) within the study area. By May 2008 non-native vegetation, primarily hottentot fig and slender-leaved iceplant (Mesembryanthemum nodiflorum), had begun to colonize the created nest sites. Only areas that were infested to a high enough degree as to preclude nesting were mapped as non-native vegetation, however there was a regular scattering of these and some native species on the surface of all three nest sites. The areas immediately adjacent to the roads bordering the marshes often supported a narrow mix of roadside weeds and a few native species such as goldenbush (Isocoma menziesii). Unless these weed bands were more than about 3 m wide and monotypically non-native, these roadside areas were not called out as a distinct habitat, rather included in either the coastal salt marsh they were mixed with or the urban/developed road, as appropriate. Merkel & Associates, Inc. 27
Bolsa Chica Lowlands Restoration Monitoring 2008 Annual Report Salt Panne Salt panne in the Seasonal Ponds. The habitat covering the third largest area within the study area was unvegetated salt panne, primarily in the Seasonal Pond and Future Full Tidal Basin areas. These areas were historically subsided marsh plain inundated by seawater, but are currently inundated intermittently by primarily freshwater. These low permeability areas collect water during rainy months, and later dry by evaporation as conditions warm in spring and summer months. This leaves hypersaline conditions that are inhospitable to most marsh plants. Although pickleweed has colonized much of the salt panne areas or its margins, the areas lowest in elevation that pool water for extended periods remain unvegetated. Disturbed Salt Panne Due to the use of the salt panne habitat by various migratory birds, including western snowy plovers for nesting, it is relevant to call out large areas of salt panne that are disturbed. Generally, these areas are previously flat expanses that have been traversed by various trucks and equipment, primarily for contaminated sediment removal work. When disturbed during wet periods, this activity leaves the ground deeply rutted, less desirable to foraging and nesting birds, and of some concern in relation to harboring pests such as mosquitoes longer into the summer season. Disturbed salt panned made up only 3% of the total salt panne area. Disturbed salt panne in the Seasonal Ponds. Intertidal Sand Shoal This category refers to the depositional flood shoals present in the FTB inlet. The shoals were composed of unvegetated and unconsolidated sand that can be highly transitory in nature as they are chronically accreted and reworked by the tides and waves. Their mapped extent was fully dependent on the tidal elevation at the time of the aerial imagery collection. A more comprehensive assessment of the shoal is included in the bathymetric monitoring section of this report (see Section 2.2). Intertidal Mudflat This habitat included the unvegetated intertidal mudflats occurring below elevations at which vascular plant communities occur. This habitat occurred primarily on the borders of FTB, in portions of the Muted Pocket Marsh, and at the lower elevations of Rabbit Island where inundated salt marsh transitioned to mudflat after the opening of the inlet. Although the cordgrass bench on the east shore of the FTB is above the typical intertidal mudflat zone, it will also be mapped as intertidal mudflat until such time as marsh vegetation develops. Open Water Open water habitat included all tidal waters, all permanently inundated areas in the FTB, Muted Pocket Marsh, and Freeman Creek. Standing water in the Seasonal Ponds and FFTB areas were mapped as salt panne in consideration of their underlying, persistent substrate. This habitat covered the greatest acreage in 2008, due to the large expanses of open water in the FTB. As with mudflat and sand shoal, its mapped extent was dependent on the tidal elevation at the time of the aerial imagery collection. In Merkel & Associates, Inc. 28
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2008 Annual Monitoring Report (pdf 10.9MB) - Bolsa Chica ...

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