Notholithocarpus densiflorus (Hook. & Arn.) Manos, Cannon & S.H. Oh (Fagaceae) (tanoak) needs immediate conservation attention due to the threat posed by Phytophthora ramorum Werres, de Cock & Man in't Veld, the water mold responsible for sudden oak death. This article explains the significant cultural value of tanoak and the seriousness of the sudden oak death threat. Current efforts to limit the spread of P. ramorum are not working adequately to prevent pathogen spread and maintain healthy ecosystems. The heartland of tanoak's distribution in northern California is at risk. I advocate for a collaborative process with tribal leadership to identify areas with mature tanoaks where traditional indigenous burning practices can be tested in combination with best management practices informed by western science. New approaches are needed to tend to tanoaks despite the sudden oak death pathogen and other threats.

Tanoaks, Notholithocarpus densiflorus (Hook. & Arn.) Manos, Cannon & S. H. Oh, are being killed by sudden oak death, caused by the pathogen Phytophthora ramorum Werres, de Cock & Man in't Veld. However, very little is known about the basic ecology of the species. Here we investigate the pollination ecology of tanoaks using insect-visitor observations along with a pollinator-exclusion study. Insect-visitor observations were conducted by citizen-scientist volunteers at three different sites in the Midpeninsula Regional Open Space District lands in the Coast Range of California in 2009. Pollinator exclusions were conducted over two years (2009, 2010), using veil bags to prevent insects from reaching female flowers at the Blodgett Forest Research Station in the Sierra Nevada foothills. Microsatellite markers were used to infer selfing or outcrossing for the developing acorns. The citizen scientists observed 148 insect visitors to tanoak flowers over 11.5 hours of observation (in 65 observation periods). Pollinator exclusion resulted in lower fruit set and higher rates of selfing. The data suggest that tanoak is primarily an insect-pollinated species, though some level of wind pollination is likely. There is a diverse community of insects visiting tanoak flowers. In order to understand the importance of tanoaks to the native insect community, future research needs to focus on identifying the composition of the insect community, and the extent to which they rely on tanoak pollen and nectar as a food source.

Invasive plant pathogens are often recognized as serious threats to the maintenance of biodiversity affecting both structure and function of ecosystems. Here, we investigate the potential impact of the invasive pathogen Phytophthora ramorum Werres, de Cock & Man in't Veld by using physical girdling of tanoak, Notholithocarpus densiflorus (Hook. & Arn.) Manos, Cannon & S. H. Oh (Fagaceae), as a surrogate for the disease and to test for changes on the hyphal abundance of ectomycorrhizal fungi. In this study, the flow of phloem to the roots of girdled trees was severed by cutting two narrow incisions (about 10 cm distant) through the inner bark around the circumference of the stem of each tree (fully-girdled), or by cutting two narrow incisions half of the circumference of the tree (half-girdled), to compare with untreated (non-girdled) trees. The hyphal abundance of two common and ecologically important ectomycorrhizal genera (Cenococcum and Tricholoma) was estimated from the roots and surrounding soil using real-time PCR quantification (TaqMan) assay. A significant decrease in the hyphal abundance from soil was observed in girdled tree plots. In contrast, no similar decrease in the root hyphal abundance was observed. Ectomycorrhizal fungi have a major impact on ecosystem function through their control over decomposition, nutrient acquisition, and mobilization and regulation of succession in plant communities. Given their important function, the decline in EM abundance of tanoak infected by P. ramorum will likely disrupt the function and structure of these forests.

Important physical characteristics, morphological attributes, physiological functions, and genetic properties of mutant tanoak, Notholithocarpus densiflorus f. attenuato-dentatus (Fagaceae), and normal tanoak, Notholithocarpus densiflorus (Hook. & Arn.) Manos, Cannon & S. H. Oh, were studied on the Challenge Experimental Forest in Yuba Co., California in an attempt to explain the cause of the mutation and to determine where in the tree it was manifest. Leaves, stomata, trichomes, foliar nutrients, photosynthesis, transpiration, internal moisture stress, DNA, and genetics (metabolonics) all were examined in detail. In some instances, the plant part or the process favored the mutant; in others, the normal tanoak exceeded. Susceptibility to Phytophthora ramorum, the sudden oak death pathogen (SOD) was similar. No all-encompassing functional difference for either type was indicated, other than the size and shape of the leaves and the metabolites in them. We know the two tanoak types differ genetically, but more complete genomic analysis is needed to pinpoint the cause of the mutation. Some thought-provoking enigmas concerning the morphology and physiology of tanoak are presented along with the status (number of plants and location) of the rare mutant.

Notholithocarpus densiflorus (Hook. & Arn.) Manos, Cannon, & S. H. Oh (Fagaceae), common name tanoak, has a reputation as a “difficult to work with” hardwood species that has been viewed at different times in history as everything from a valuable resource for edible acorns to an annoying “weed” tree that interferes with commercial forest management. This paper explores the complex character of the species from a wood products point of view and discusses the possibility of developing it as a valuable forest-products resource.

A comprehensive review of the forest-product literature reveals the many ways tanoak has been utilized. These uses have included fuel wood, lumber, railroad ties, flooring, and furniture, and as a source for leather- tanning chemicals. Early studies of the physical and mechanical properties of the wood show a similarity to many commercial hardwood species. However, tanoak has never gained the status of a preferred timber tree for forest products. This paper compiles what is known about the wood properties of tanoak and provides recommendations for successful lumber manufacturing. The risks and benefits of utilizing a species that is a known host for Phytophthora ramorum Werres, De Cock & Man in't Veld, the pathogen that causes sudden oak death, are also discussed from a forest-management point of view. As interest grows in developing local resources that require little transportation from source to end use, more opportunities for utilizing tanoak will likely emerge.

This paper offers a modern take on wild edible plants of the tanoak, Notholithocarpus densiflorus (Hook. & Arn.) Manos, Cannon & S. H. Oh (Fagaceae), ecosystem with instructions for gathering materials and preparing foods. We review the collection and processing of acorns, bay nuts, and foliage for herbal teas, along with specific recipes.

Tanoak, Notholithocarpus densiflorus (Hook. & Arn.) Manos, Cannon & S. H. Oh (Fagaceae), is an important component of mixed-evergreen forests and woodlands in coastal California and Oregon, with incursions into the Sierra Nevada and the Klamath Ranges. Sudden Oak Death (SOD) is causing severe dieback and mortality in tanoak and could transform these ecosystems in areas where the pathogen Phytophthora ramorum S. Werres, A.W.A.M. de Cock can become established. Knowledge of genetic diversity within the species is important for both disease resistance screening, conservation and replanting in sites with high mortality. Here we review what has been learned about the genetic structure within tanoak since SOD has caused disease epidemics in the species. We review published work on genetic structure at the species level and provide some re-analyses of these data that show divergence across the geographic range. We also review recently published data on genetic structure at a fine spatial scale that provides some guidelines for the selection of trees as seed sources. Finally, we interpret a range of seed provenancing strategies in the light of our knowledge of tanoak genetic diversity.

The geographic range of tanoak, Notholithocarpus densiflorus (Hook. & Arn.) Manos, Cannon & S. H. Oh (Fagaceae), encompasses tremendous physiographic variability, diverse plant communities, and complex disturbance regimes (e.g., development, timber harvest, and wildfire) that now also include serious threats posed by the invasive forest pathogen Phytophthora ramorum S. Werres, A.W.A.M. de Cock. Knowing where these disturbance factors interact is critical for developing comprehensive strategies for conserving the abundance, structure, and function of at-risk tanoak communities. In this study, we present a rule-based spatial model of the range-wide threat to tanoak populations from four disturbance factors that were parameterized to encode their additive effects and two-way interactions. Within a GIS, we mapped threats posed by silvicultural activities; disease caused by P. ramorum; human development; and altered fire regimes across the geographic range of tanoak, and we integrated spatially coinciding disturbances to quantify and map the additive and interacting threats to tanoak. We classified the majority of tanoak's range at low risk (3.7 million ha) from disturbance interactions, with smaller areas at intermediate (222,795 ha), and high (10,905 ha) risk. Elevated risk levels resulted from the interaction of disease and silviculture factors over small extents in northern California and southwest Oregon that included parts of Hoopa and Yurok tribal lands. Our results illustrate tanoak populations at risk from these interacting disturbances based on one set of hypothesized relationships. The model can be extended to other species affected by these factors, used as a guide for future research, and is a point of departure for developing a comprehensive understanding of threats to tanoak populations. Identifying the geographic location of disturbance interactions and risks to foundation species such as tanoak is critical for prioritizing and targeting conservation treatments with limited resources.

Non-native diseases of dominant tree species have diminished North American forest biodiversity, structure, and ecosystem function over the last 150 years. Since the mid-1990s, coastal California forests have suffered extensive decline of the endemic overstory tree tanoak, Notholithocarpus densiflorus (Hook. & Arn.) Manos, Cannon & S. H. Oh (Fagaceae), following the emergence of the exotic pathogen Phythophthora ramorum and the resulting disease sudden oak death. There are two central challenges to protecting tanoak: 1) the pathogen P. ramorum has multiple pathways of spread and is thus very difficult to eradicate, and 2) the low economic valuation of tanoak obscures the cultural and ecological importance of this species. However, both modeling and field studies have shown that pathogen-centric management and host-centric preventative treatments are effective methods to reduce rates of spread, local pathogen prevalence, and to increase protection of individual trees. These management strategies are not mutually exclusive, but we lack precise understanding of the timing and extent to apply each strategy in order to minimize disease and the subsequent accumulation of fuels, loss of obligate flora and fauna, or destruction of culturally important stands. Recent work identifying heritable disease resistance traits, ameliorative treatments that reduce pathogen populations, and silvicultural treatments that shift stand composition hold promise for increasing the resiliency of tanoak populations. We suggest distinct strategies for pathogen invaded and uninvaded areas, place these in the context of local management goals, and suggest a management strategy and associated research priorities to retain the biodiversity and cultural values associated with tanoak.