Precios psicológicos

We suspect that just as plants and animals reside in or develop “communities” based on those species regularly found living together, truffle species and ectomy- corrhizal fungi do so too. Truffle communities are typically described based on fruit-body presence within certain forest types, and are often included as part of the total ectomycorrhizal fungus community. Ectomycorrhizal fungus communites are measured in several ways, including mushroom and truffle presence, production, species diversity, and, more recently, based on morphological and genetic DNA identification of ectomycorrhizal root tips sampled from soil. In this section we review general findings on the communities of ectomycorrhizal fungi in a variety of PNW forest settings. In a later section we focus on silviculture effects on truffle communities.

Comparison of fungal communities based on the occurrence of mushrooms and truffles with communities from DNA identification of ectomyorrhizal species on root tips has shown that the dominant ectomycorrhizal fungi of a site are not the most prolific mushroom and truffle producers (Brandrud and Timmermann 1998, Dahlberg et al. 1997, Gardes and Bruns 1996, Kårén and Nylund 1996, Yamada and Katsuya 2001). However, truffle abundance and mycorrhiza abundance of some individual species correspond (Luoma et al. 1997). Truffle and mushroom abun- dance can reveal changes in the fungal community that are related to environmental gradients (Luoma 1988, O’Dell et al. 1995b) and thereby serve as an indicator of the overall ectomycorrhizal fungus community response to environmental conditions.

Studies assessing mushroom and truffle communities in North America often focus on differences between vegetation types or forest age classes (e.g., Bills et al. 1986, Luoma 1988, Smith et al. 2002, Villeneuve et al. 1989). Miller (1983) presented data on ectomycorrhizal mushroom species richness in stands of different ages of western white pine (Pinus monticola); diversity was substantially higher in

175-year-old stands than in 15-year-old stands. Kranabetter et al. (2005) found strong differences between 20- and 225-year-old stands, including 12 late-seral-dependent species. They suggested that ectomycorrhizal fungus succession largely represents an accumulation of species with little species replacement as host stands age.

In the PNW, several studies of truffle communities have been reported (Colgan et al. 1999; Fogel 1976; Hunt and Trappe 1987; Luoma et al. 1991, 2004; North et al. 1997; Smith et al. 2002; Waters et al. 1994). In two studies (Fogel and Hunt 1979, North et al. 1997), mushroom biomass was compared with that of truffle biomass: the contribution of truffle biomass averaged from about half to more than twice as much as the mushroom biomass. At the H.J. Andrews Experimental Forest, over a range of stand-age classes, J. Smith et al. (2002) found that truffle biomass was about twice as much as mushroom biomass. Because epigeous mushrooms include substantial amounts of stems and caps whereas truffles are made up largely of spore-bearing tissue, the reproductive tissue in truffles would generally equal or exceed that in mushrooms.

Luoma (1988) and Luoma et al. (1991) described the community structure of truffle species along age and moisture gradients in the H.J. Andrews Experimental Forest. Maximum number of species was found in the mesic mature (≈175-year-old) stands. Although some species of truffles were restricted to the oldest stands, the truffle community changed more along the moisture gradient than by stand age class.

In a followup study, J. Smith et al. (2002) examined truffle and mushroom fruit- body production in stands of three age classes at the H.J. Andrews Experimental Forest: unmanaged old-growth (400+ yr), managed rotation-age (50 yr), and managed young (35 yr) Douglas-fir stands. About a third of the species were unique to an age class, and truffle biomass was more evenly distributed among species in old-growth stands.

Young managed stands may have a different composition of truffle species than old-growth or natural mature stands. Among western-hemlock-dominated forests of various ages studied across northwest Washington by North et al. (1997), the number of truffle species was highest in the old-growth stands. The total truffle biomass was much higher in the natural mature and old-growth stands than in the young managed stands. This was largely due to the presence of large clusters of the truffle

Elaphomyces granulatus in the older natural stands. A similar trend was found in

Pacific silver fir (Abies amabilis (Dougl.) Forbes) stands of western Washington. The annual production of truffles was only 1 kg/ha per year dry weight in 23-year- old stands, whereas in the 180-year-old stands, production was 380 kg/ha per year (Vogt et al. 1981).

Evidence of ectomycorrhizal fungus succession has also been drawn from observations of fruit-body occurrence as young stands age (Termorshuizen 1991). Generally, few species are present initially and species number gradually increases with stand age. Several studies of ectomycorrhizal fungus succession in birch (Betula spp.), spruce (Picea spp.), pine, and other types of forests (Deacon et al. 1983, Fleming et al. 1984, Fox 1986) indicate that some genera and species of ectomycorrhizal fungi consistently appear earlier in stand development than others (e.g., Thelephora spp. and Hebeloma spp. often appear before Russula spp. and

Amanita spp.).

Accurate baseline estimates of ectomycorrhizal fungus productivity and species diversity are necessary to effectively assess population changes over time. For example, Arnolds (1991) reported a serious decline in fruit-body production of mycorrhizal fungi over the preceding three decades. Mushrooms have been consumed in Europe for centuries, yet no prolonged decline had been noted previ- ously. Now accumulated experimental and field data show that a large number of ectomycorrhizal fungi were in decline owing to indirect effects of air pollution, particularly nitrogen, as well as loss of habitat (Arnolds 1991, Arnolds and Jansen 1992, Termorshuizen 1993).

The weight of truffles produced in a forest can be useful for interpreting roles of fungal species as a food source for animals or measuring the energy expended in an ecosystem for truffle reproduction. The sampled weight of truffles may underestimate actual truffle productivity because animals consume a portion of the fruit-bodies (Luoma et al. 2003). The degree of underestimation is most pronounced at periods of low productivity, when consumptive pressure on the available food resource is proportionally high (North et al. 1997).

Clearly, studies of sporocarp production of ectomycorrhizal fungi are incom- plete without comparable data for both truffle and mushroom taxa. When both mushroom and truffle species are simultaneously assessed, new understanding of overall diversity phenomena emerges. For example, our region has similar truffle production in spring and fall (Luoma et al. 2004, Smith et al. 2002). This constancy of truffle production has important implications to mycophagous mammals. Fungal diversity in the diet of such animals is nutritionally important (Claridge et al. 1999, Luoma et al. 2003, Maser et al. 1978). During spring in our region, mushroom production is often far less than truffle production (Cázares et al. 1999, Luoma et al. 2004, Smith et al. 2002). Animals that depend on fungi as major food items (Maser et al. 1978) could not rely on mushroom fungi for diet diversity during the spring. Quite possibly, population decline of some mycophagous animals could relate to decline in diversity of the fungal populations owing to habitat disturbance

or climate change (Claridge et al. 1996, Jacobs and Luoma in press). Disturbance, whether natural or from managment, can drastically alter populations of ectomy- corrhizal fungi (Amaranthus et al. 1994, 1996; Colgan 1997; Pilz and Perry 1984; Schoenberger and Perry 1982).

The functional importance of ectomycorrhizal fungus diversity is little explored, but different ectomycorrhizal fungus species differ in their response to substrate pH (Hung and Trappe 1983), seasonal or environmental change, providing benefits to their hosts (Trappe 1987) or nutritional value to mycophagists (Claridge and Cork 1994, Claridge and Trappe 2005, Fogel and Trappe 1978). Ectomycorrhizal fungus diversity can thus be inferred to provide resilience to forest systems: different species enhance fitness and growth of host trees at different seasons, in different niches in the soil, or in response to different perturbations, and provide necessary nutritional diversity to the diet of mammal mycophagists. High levels of ectomycorrhizal fungus diversity may provide both tree and forest with the functional diversity necessary to cope with changes in season, habitats, or climate. This belowground functional diversity may be linked to the ability of Douglas-fir to grow well over decades and centuries. Thus, maintenance of ectomycorrhizal fungus diversity is important for ecosystem health and resilience (Amaranthus and Luoma 1997, Perry et al. 1990).