Invasive Plant Species
Invasive, non-native plant species possess particular qualities like fast growth, high seed production, and rapid maturation that—when combined with a lack of the natural predators and diseases that controlled them in their native environment—allow them to rapidly grow and spread. Mt. Tam is an important natural refuge in a largely urbanized area, but being near human development also means that it faces a continuous barrage of invasive, non-native plant species. In many areas across Mt. Tam, these invaders are altering fire regimes, impacting normal hydrological processes, and deteriorating the habitats of native plants and animals, including rare, threatened, and endangered species.
Wetlands, Seeps, Springs, & Streams
Mt. Tam’s seasonal wetlands, marshes, seeps, springs, ponds, and streams provide precious water in an otherwise relatively arid environment. This network of riparian corridors and other wet areas support several rare plants, and offer water, food, and refuge to creatures across the whole mountain. Bothin Marsh is home to threatened and endangered species like the California clapper rail and salt marsh harvest mouse. Redwood and Lagunitas Creeks support endangered coho salmon and threatened steelhead trout and California red-legged frogs. All of these habitats are threatened by invasive species, drought, and alterations to that have been made to the landscape and its hydrology.
Scrub & Chaparral
Dense patches of scrub and chaparral make even the driest and rockiest parts of Mt. Tam biologically rich. Close to the coast, fragrant shrub species like California sagebrush signal the dry season by shedding many of their leaves, while the foliage of other species are adapted to tolerate high winds and salt spray. Chaparral that grows on the mountain’s harsh serpentine soils is also home to many rare and endemic plants. Important to many species of songbirds, reptiles, and insects, these fire-dependent shrublands are under threat from decades of fire suppression and invasive plant species.
Mt. Tam’s wide array of microclimates and relatively high air quality support a remarkable diversity of lichens. The rare Methuselah’s beard (Usnea longissimia) is one of the 284 known lichen species on Mt. Tam, and there are still many more areas left to be surveyed. The California state lichen, lace lichen (Ramalina menziesii), also grows in oak woodlands and Douglas-fir forests around the mountain.
In nature, all things are connected. A plant, even one that is small or unglamorous, may provide vital food or shelter to other creatures. Its roots may stabilize the shifting earth below. If a plant species becomes very rare, it may no longer be able to fill these important roles, and its risk of extinction can become quite high. A remarkable 49 rare plants have been identified on Mt. Tam. Striking green serpentine rock outcrops visible across the mountain’s landscape hint at what makes it such a treasure trove of rare and endemic species, as rare plant communities are often found in areas with unusual geology and soils.
The deep, extensive root systems of perennial grasses allow them to survive dry California summers, with some individual plants living for 100 years or more. On Mt. Tam, stands of purple needle grass, blue wild rye, Idaho fescue, California oatgrass, and other species make up a rich and diverse ecosystem often brightly colored by wildflowers. Once common over large swaths of the California coast, only a tiny fraction of native grasslands remain as a result of farming, land development, and invasive species.
Forests & Woodlands
Oak woodlands carpeted with grasses and wildflowers, towering old-growth redwood groves, thick stands of Douglas-fir, and twisted Sargent cypress trees—all of these iconic habitats give Mt. Tam the sense of place and beauty we know and love. Numerous species of birds and mammals, including nesting threatened Northern Spotted Owls and Townsend’s big-eared bats also depend on these habitats. Mt. Tam’s forests are under threat from climate change and also from Sudden Oak Death, which has killed large numbers of oak trees across the mountain.
Mt. Tam hosts a truly remarkable array of plants for an area its size. The influence of the sea and coastal fog to the west, dry heat of the inland-facing slopes, cool valleys, and sunny ridge tops all help make Mt. Tam a biodiversity powerhouse. Learn more about the plant communities on Mt. Tam through the links below.
- One Tam Plant Species List
- Marin County Biodiversity Management Plan
- MMWD Biodiversity Management Plan
- MMWD Plant Lists and Guides
- Mt. Tamalpais Biodiversity Watershed Symposium (2009)
- California Native Plant Society, Marin Chapter
One Tam Plants and Fungi Photo Gallery