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?

Grassland Birds

Summary

The overall condition of grassland-associated birds is Unknown.

Point Blue Conservation Science was unable to assess patterns of abundance from 1996 to 2013 because data were insufficient for grassland-associated birds (see References below). This is likely because the data are primarily from Marin Municipal Water District lands of which grassland acreage is low and because grassland birds naturally occur in relatively low densities.

The need for a standardized monitoring program that covers all One Tam agency lands was identified as a critical data gap through this health assessment process. Because grassland birds are declining both regionally and statewide, additional surveys should be implemented to determine the condition of grassland birds in the One Tam region.

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Abundance Patterns of Landbirds in the Marin Municipal Water District: 1996 to 2013

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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 Disease

Sudden Oak Death

Sudden Oak Death (SOD), caused by the introduced pathogen Phytophthora ramorum, was first documented in the United States on Marin Municipal Water District and State Park lands in Marin County in 1995 (Garbelotto & Rizzo, 2005). In the ensuing years, it has killed tens of thousands of trees on Mt. Tam. Vegetation mapping completed in 2004, 2009, and again in 2014 has tracked the rapid spread of the disease across watershed lands. The 2014 update found that over 90 percent of oak woodlands were affected by the disease. Overall, 84 percent of forested areas were impacted, though the degree to which they have been affected varies by the species composition of the forest and by tree canopy characteristics (AIS, 2015). 

The mortality rate exceeds 80 percent for tanoak (Notholithocarpus densiflorus) which has resulted in the transformation of thousands of acres where this species was once dominant in the canopy. Mortality rates are lower but still significant among coast live oaks (Quercus agrifolia), and black oaks (Q. kelloggii). Dozens of other native tree and shrub species also experience damage and/or lower levels of mortality. White oaks, including valley oaks (Q. lobata) and Oregon oak (Q. garryana), are not impacted (APHIS, 2013).

In addition to causing dramatic changes in habitat structure, dying and dead trees are increasing fuel loads. The effects of the loss of oak trees on species dependent on them for food and shelter (e.g., dusky-footed woodrat, acorn woodpecker) are not yet known (Nik et al., 2016).

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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?

Invasive Species

Non-native, Invasive Species on Mt. Tam

Non-native, invasive species in Marin County come in myriad forms, including water molds, plants, invertebrates, fish, amphibians, birds, and mammals. The major threats posed by invasive species include changes in fire frequency or intensity, groundwater depletion, changes to soil chemistry, competition with native species, and a loss of native species diversity (LCA, 2009).

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?

Fire

The Effects of Changed Fire Regimes on Mt. Tam

Mt. Tam has not seen a large, stand-replacing fire for over 70 years due to fire suppression policies and practices. While fire suppression is important for protecting local air quality and nearby property, the removal of fire is resulting, in part, in the succession of grasslands to shrublands, shrublands to woodlands, and woodlands to Douglas-fir (Pseudotsuga menziesii) dominated stands. Fire suppression also has implications for the regeneration of fire-dependent species, such as Sargent cypress (Cupressus sargentii) and Marin manzanita (Arctostaphylos virgata).

Disease Impacts

In addition to these direct impacts, changed fire regimes and fire suppression are interacting with other ecological stressors on Mt. Tam in a variety of ways. Higher fuel loads resulting from trees killed by Sudden Oak Death may increase the intensity of any fires that occur. Large fires burn hotly, and can kill large numbers of trees over a wide area. This both releases nutrients into the soil and increases the amount of light reaching the ground, conditions that can be exploited by non-native, invasive plant species (LCA, 2009).

Climate Change Considerations

Climate change is expected to generally cause an increase in wildfires, but underlying factors can combine in ways that make the specific effects difficult to predict. In general, drier and warmer conditions are more favorable to fires. Fire frequencies are projected to increase on the order of 20 percent for Mt. Tam under projected climate scenarios (Micheli et al., 2016).

Although models predict more intense fires, fire suppression policies will continue to maintain the mountain's fire regime in an altered state. This will likely lead to infrequent but large and intense wildland fires driven by extreme fire weather that will burn many acres despite efforts to control them.

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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?

Ecological Processes and Stressors

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?

Coast Redwood Communities

Summary

Old-growth coast redwood forest communities are doing well, but second-growth redwood forests, which make up the majority of the redwood forests on Mt. Tam are in Fair condition with an overall Declining trend.

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?

Open-canopy Oak Woodland Communities

Summary

Open-canopy oak woodlands are in Fair condition, with a Declining trend, mostly due to invasive species, Sudden Oak Death, and Douglas-fir (Pseudotsuga menziesii) encroachment.

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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?

Grassland Communities

Summary

Grassland communities on Mt. Tam are in Fair condition with a Declining trend. These areas have been relatively stable based on a recently assessed baseline for the total extent of grassland communities. However, Douglas-fir (Pseudotsuga menziesii) and coyote brush (Baccharis pilularis) recruitment into the edges and interior of some grassland patches mean that the overall patch size and number of large patches is below the desired condition. The presence and relative dominance of invasive, non-native grasses and forbs is further causing grassland habitat quality decline.

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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?

Shrubland Communities

Summary

Coastal scrub and chaparral communities are in Good condition with No Change in their overall trend. They have been stable and show no major negative signs from the impacts of ecological stressors that are affecting many of Mt. Tam’s other plant communities such as invasive species, or Douglas-fir (Pseudotsuga menziesii) encroachment. Their extent has remained fairly stable and the have a full complement of associated bird species.

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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?

Ecosystems

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