Coastal Scrub Zone

Coastal scrub represents the dominant vegetation type in the upland portion of YLR, covering most of the upland slopes. It takes various forms, with differing species composition and cover ranging from dense to sparse with numerous open areas. Overall, coyote brush (Baccharis pilularis) is most abundant; other abundant shrubs include poison oak (Toxicodendron diversilobum) lizard tail (Eriophyllum staechadifolii), and sticky monkeyflower (Mimulus aurantiacus). Native herbs such as soap plant (Chorogalum pomeridianum), California hedge nettle (Stachys bullata), Pacific sanicle (Sanicula crassicaulis), and yarrow (Achillea millefolium) grow in some open areas; other openings have weedy exotics such as poison hemlock (Conium maculatum), Italian thistle (Carduus pycnocephalus), rattail fescue (Vulpia myuros var. myuros), soft chess (Bromus hordeaceus), and wild radish (Raphanus sativus). Many of the larger openings in particular are dominated by dense stands of poison hemlock.

The coastal bluffs facing the ocean and lagoon mouth support a variety of typical coastal wet scrub species. These species are adapted to salt spray, strong winds, and cliff erosion. The adaptations include succulent leaves that reduce evaporation, low growing mats which survive the winds, and extensive root systems that provide firm anchorage and water absorption during the dry summers.

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Coastal Strand Zone

The coastal strand is found at south end of the YLR, just inland from the unvegetated beach on the more stable sandy substrate to the east of the open lagoon waters. Exposed to extreme conditions of wind and salt spray, it is characterized by light to moderate low-lying vegetative cover with much bare sand. Dominant plants include the native beach-bur (Ambrosia chamissonis) and small native herbs such as beach evening-primrose (Camissonia cheiranthifolia ssp. cheiranthifolia), beach morning glory (Calystegia soldanella), willow dock (Rumex salicifolius var. crassus), pink sand verbena (Abronia umbellata ssp. umbellata), yellow sand verbena (Abronia latifolia), California poppy (Eschscholzia californica), and fragrant everlasting (Gnaphalium canescens ssp. beneolens). The non-native cut-leaved plantain (Plantago coronopus) and ripgut grass (Bromus diandrus) are also relatively abundant and widespread. Slightly inland along the lagoon border is a dense patch of the native rhizomatous perennial grass saltgrass (Distichlis spicata), intermixed with creeping wild rye (Leymus triticoides).

The coastal strand community has a relatively high proportion of native species. At present, the coastal strand is vulnerable to surfer trespass and some areas have been damaged by trampling. There are also problems with weed encroachment.

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Coastal Saltwater Marsh Zone

The coastal salt marsh is dominated by pickleweed (Salicornia virginica), which forms a monoculture 1 to 2 ft high. It borders the open water of the lagoon continuously throughout the YLR, except at the lower end near the ocean. The pickleweed also extends up both arms of the lowland beyond the upper end of open water. A narrow strip of Pacific silverweed (Potentialla anserine spp. pacifica) grows on inland side, between the pickleweed and the base of the slope. Species in this community are early-successional species due to fluctuating salinities caused by periodic sandbar breaching at the mouth, inundation by sea water during winter storms, and inputs of fresh water during irrigation of the adjacent agricultural fields.

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Freshwater Marsh Zone

Three types of freshwater marsh occur at YLR (cattail marsh, bur-reed marsh, Pacific oenanthe marsh). They occupy the central portion of the two arms of the lowland, extending inland from the lagoon.

The cattail marsh grows in the central portion of the east arm of the lowland, just inland from the pickleweed marsh. It is characterized by a dense cover of tall emergent monocots dominated by southern cattail (Typha domingensis). California tule (Scirpus californicus) and broad-leaved cattail grow (Typha latifolia) in the marsh as well.

The bur-reed marsh grows just inland from the pickleweed marsh in the central portion of the west arm of the lowland. The tall emergent monocot Greene's bur-reed (Sparganium erectum ssp. stoloniferum) forms a dense stand. A small amount of broad-leaved cattail is also found there.

Freshwater marsh dominated by the rhizomatous perennial herb Pacific oenanthe (Oenanthe sarmentosa) occurs in each arm of the lowland, upstream from the cattail marsh in the east arm and the bur-reed marsh (as well as a patch of arroyo willow riparian forest) in the west arm. Broad-leaved cattail grows scattered through the marsh.
                                                                                                                        
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Riparian Zone

Several stands of central coast arroyo willow riparian forest are found in the YLR, both in the lowlands and extending onto upland slopes in some areas. The forest is characterized by dense, often impenetrable thickets of arroyo willow (Salix lasiolepis) with only a few understory species such as Pacific blackberry (Rubus ursinus) and American stinging nettle (Urtica dioica ssp. Gracilis). A large, continuous stand grows in the east arm, extending to the edge of the coastal terrace. The stands form four large patches in the west arm; the northernmost patch has been invaded by the non-native cape ivy (Delairea odorata). This habitat is a breeding area for several terrestrial bird species and might be getting overly dense for that purpose.
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Coastal Scrub-Grassland Zone

The coastal scrub-grassland vegetation type is found mainly on the ridge separating the two arms of the lagoon and on a smaller spur ridge to the southwest, west of the main lagoon. In these areas, patches of shrubs, primarily coyote brush, are found interspersed with relatively large areas dominated by grasses and herbs. Native species include the wood rose (Rosa gymnocarpa), purple needlegrass (Nassella pulchra), coast buckwheat (Eriogonum latifolium), soap plant (Chlorogalum pomeridianum), California aster (Lessingia filaginifolia var. californica), and yarrow. The non-native six-weeks fescue (Vulpia myuros), ripgut grass, soft chess, slender wild oat (Avena barbata), English plantain (Plantago lanceolata), bur-clover (Medicago polymorpha), Italian thistle, and smooth cat's ear (Hypochaeris glabra) also occur.

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