Measuring the health of Mt. Tam

Maintaining a healthy, vibrant and diverse Mt. Tam begins with understanding how key ecological resources are faring, and how we can better care for this iconic and beloved place.

One Tam partners and Bay Area scientists have come together to try to answer the question: How healthy are Mt. Tam's natural resources?

Plant Communities

Mt. Tam’s plant communities are in varying condition, depending on a number of factors such as disease, invasive species, and changes to the wildfire frequencies.

Mt. Tam’s iconic, sweeping grasslands vistas and stately open-canopy oak woodlands serve as habitat for numerous plants and animals, and hold tremendous biodiversity. Both these plant communities have been impacted by ecological succession as a result of alterations in natural disturbance regimes, and by the invasion of non-native plants. In addition, coast live oak woodlands are losing large trees due to Sudden Oak Death. Native grasslands are at 1% of their historic extent in the state, and Mt. Tam preserves some of the best examples of remnant grassland ecosystems in the region.

Coast redwood forests (Sequoia sempervirens) are another iconic vegetation type undergoing changes due to Sudden Oak Death, climate change, and invasion by non-native species. The One Tam area of focus has a small amount of old-growth redwood forests, but majority are second-growth, having been logged at some point in the past.

Sargent cypress (Cupressus sargentii), particularly the pygmy forest along San Geronimo Ridge, is a rare vegetation type that hosts several California Native Plant Society-listed and locally rare plant species. Unlike many of the other communities chosen as indicators, Sargent cypress appears to be relatively disease- and weed-free. Sargent cypress forests have been impacted by changes in the fire regime on Mt. Tam however, as the trees reproduce solely from seed, and largely depend on fire to open their cones.

Shrubland communities on Mt. Tam are made up of drought- and heat-tolerant, hard-leaved evergreen chaparral species such as chamise and manzanita, and also by coastal scrub, which is primarily comprised of salt-adapted, evergreen coyote brush (Baccharis pilularis) shrubs. The shrublands of Mt. Tam can be used as indicators of successional processes, disturbance, and habitat quality for terrestrial birds.

Learn more about the condition and trends of these plant communities through the links above.