Hansen EM, Goheen EM.. Phellinus weirii and other native root pathogens as determinants of forest structure and process in western North America. Annu Rev Phytopathol 38: 515-539

Department of Botany and Plant Pathology, Oregon State University, Corvallis, Oregon 97331
Annual Review of Phytopathology (Impact Factor: 9.62). 02/2000; 38:515-539. DOI: 10.1146/annurev.phyto.38.1.515
Source: PubMed


The population structure and ecological roles of the indigenous pathogen Phellinus weirii, cause of laminated root rot in conifer forests of western North America, are examined. This pathogen kills trees in slowly expanding mortality centers, creating gaps in the forest canopy. It is widespread, locally abundant, and very long-lived. It is among the most important disturbance agents in the long intervals between stand-replacing events such as wildfire or harvest in these ecosystems and shapes the structure and composition of both wild and managed forests. Trees are infected and killed regardless of individual vigor. Management of public lands is changing dramatically, with renewed emphasis on natural forest structures and processes but pathogens, especially root rot fungi, remain a significant challenge to "ecosystem management."

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    • "Thinnings, for example, are well known to increase tree resistance to insect pests such as bark beetles (reviewed by Fettig et al. (2007) and Coops et al. (2009)) or spruce budworms (e.g., Bauce and Fuentealba 2013). The impacts of thinning on the resistance against fungi are less studied, and in the case of root pathogens, the results remain controversial (Waring et al. 1987; Entry et al. 1991; Hansen and Goheen 2000). To our knowledge, the question of whether harvesting of the surrounding trees can mitigate the dieback of mature ash trees has not been addressed. "
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    ABSTRACT: The European ash (Fraxinus excelsior L.) dieback is an acute forest pathology problem caused by the invasive ascomycete Hymenoscyphus fraxineus (T. Kowalski) Baral, Queloz, Hosoya. There are no practical solutions yet, but selection for resistant genotypes and intensive care have been highlighted as options. Our aim was to assess the disease mitigation potential of silvicultural harvests, which influence stress levels in retained trees. We annually monitored 577 retention trees on Estonian cut areas for 13 years, including 9 years impacted by the dieback. Sixty-five percent of the trees survived and 15% retained healthy crown, despite all sampled trees being infected. The damage was smallest in the trees retained near precut edges. Former forest-interior trees that were left in central parts of the cut areas suffered high initial damage but smaller disease progression than trees near postcut edges. Tree size and secondary infection by Armillaria spp. were not related to disease progression, but rapid decline was observed in the region with the highest density of ash trees retained. Our results indicate a significant silvicultural potential for tree resistance. Ash trees tend to be healthiest in open conditions, which probably inhibit the pathogen and provide better resources for the tree. Location near precut edges is an important tree retention criterion, which can mitigate initial harvest-induced stress. © 2015, National Research Council of Canada. All rights Reserved.
    No preview · Article · Jun 2015 · Canadian Journal of Forest Research
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    • "New methods yielding rapid woody sample identifications could facilitate determinations of biological activities, interactions, and ecological roles of microorganisms, insects, and other invertebrates that interact with wood in living and dead trees or coarse woody debris on the forest floor. Organisms associated with wood in forest ecosystems are involved in such activities as wood decomposition, nutrient cycling, and other functional niches that affect forest stand structure, dynamics, and ecosystem processes (Andrews and Harris, 2000; Hansen and Goheen, 2000; Whipps, 2001). Many microbes have effects on forest health and ecosystem functions because they include causal agents of tree mortality, forest diseases, wood decay, and lumber defects of importance in ecosystem and timber management, and in the manufacture of forest products. "

    Full-text · Dataset · Mar 2013
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    • "On the positive side are various types of mycorrhizal associations that aid in mineral uptake, as well as several other beneficial aspects, including soil structure formation and maintenance (Miller and Jastrow, 2000). On the negative side are a variety of root-borne pathogens that may severely impact plant populations and, in some instances indirectly contribute to major shifts in ecosystem viability (e.g., Hansen and Goheen, 2000). With this understanding of the ecological importance of fungal root endophytes in ecosystems today it is reasonable to anticipate a similar abundance, diversity, and biological impact of fungal root endophytes in ancient plant communities. "
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    ABSTRACT: A distinctive fungal endophyte, Cashhickia acuminata nov. gen. et sp., is described from permineralized calamite roots from the Upper Pennsylvanian Grand-Croix cherts of France. Heavily infected roots contain numerous intracellular hyphae in the outer cortex that arise from a meshwork-like mycelium extending between cortical cells. All intracellular hyphae are oriented toward the root center; none occur on the inner periclinal host cell walls. Other roots of the same type show localized infection by this fungus in which isolated cortical cells contain or give rise to intracellular fungal growth. Within the cortical cells are host responses in the form of callosities that indicate the roots were alive at the time of infection. Other endophytes are present in the same host tissue but are less frequent. The discovery of this association provides the first detailed account on the morphology of a Carboniferous fungal root endophyte, as well as the spatial distribution within the host, and infection pathways within the cortical tissues.
    Full-text · Article · Dec 2012 · Review of Palaeobotany and Palynology
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