Modes of Dispersal

As a habitat dead wood is characterized by: (i) the limited duration of each habitat patch (e.g. a fallen trunk) and (ii) an unpredictable and heterogeneous distribution of habitat patches in space and time, influenced by twigs and branches falling, natural tree mortality factors (e.g. storms, drought) and in recent centuries by forest management cycles and landscape fragmentation. To persist in this highly dynamic context wood decay fungi need to be able to spread between sinking and rising habitat patches (Jonsson et al., 2005). They do so in two main ways, depending on whether or not they are confined within the woody resource— 'resource-unit-restricted' or 'non-resource-unit-restricted', respectively. Resource-unit-restricted fungi are disseminated in space and time via spores, whereas non-resource-unit-restricted fungi can spread both via spores and as mycelium growing out of the wood in search of new resources.

Fungi able to spread as mycelium from one resource in search of another have considerable advantages. They operate a variety of search strategies to optimize discovery of new resources (Boddy, 1993, 1999; Boddy and Jones, 2006; Chapter 1). On arrival at a new resource they can exert considerable inoculum potential—their carbon and mineral nutrient requirements are met by translocation through the established mycelium (Chapter 3), and they can attack resident fungi over a large front. Moreover, when new resources have been located and colonized, the fungi can reallocate biomass that is growing through soil in non-successful areas of search (Boddy, 1999; Boddy and Jones, 2006). Fungi that extend outside resources can also operate a 'sit and wait' strategy, whereby a

Table 1 Ecological strategies and life-history traits of fungal colonizers of angiosperm wood, through pioneer, early, late and final stages of decomposition

General category

Ecological

Subtype

Site and mode

Stage of

Life-history

Typical

Examples

References

strategy

of establishment

succession

strategya

lifespan of active mycelia

Primary: Involved in

Heart rot

Top rot

Wounds and

Pioneer to late

S

Many years

Fistulina hepatica,

Phillips and

lignocellulose

agents

broken

stage

Laetiporus

Burdekin

decomposition prior

branches

sulphureus,

(1982),

to colonization by

exposing

Pholiota

Rayner and

other fungi

heartwood, sapwood of dead branches, branch stubs, etc., engulfed as tree grows outwards

Ossicaulis lignatilis,

Volvariella bombycina

Boddy (1988), personal observations

Butt rot

Roots; latently present

Pioneer to late stage

S

Many years

Armillaria spp., Ganoderma adspersum, Heterobasidion annosum, Inonotus dryadeus, Pholiota squarrosa, Kretzschmaria deustab

Phillips and Burdekin

(1982), Rayner and Boddy (1988), Butin (1995), Woodward et al. (1998)

Pathogens

Root pathogens

Spores and mycelium via wounded roots, root grafts, subcortical growth and direct penetration

Pioneer to late stage

C, S

Many years

Armillaria spp., Collybia fusipes, Grifola frondosa, Heterobasidion annosum, Meripilus giganteus

Rayner and Boddy (1988), Butin (1995), Woodward et al. (1998), Fox (2000), Piou et al. (2002)

Wound parasites

Wounds

Pioneer

R, S

2-5 years

Chondrostereum purpureum, Trametes spp., Stereum

Rayner and Boddy (1988), Butin (1995)

sanguinolentum sanguinolentum

Latent colonizers/ endophytes of sap wood

Natural pruners Sites of entry of branches and twigs unconfirmed but probably various; propagules remain latent in functional sap wood for many years

Trunk colonizers As above

Canker formers As above

Ruderal primary colonizers

Wound colonizers

Felled wood and stumps

Freshly exposed wood as spores; some via insect vectors

Secondary. Involved in Resource unit Combative Exposed wood, lignocellulose restricted invaders via spores decomposition after colonization by primary and other secondary colonizers

Pioneer

R, S

Few months

VuiUeminia

Chapela and

to few years

comedens,

Boddy

Colpoma

(1988a),

cjuercinumh,

Rayner and

Peniophora spp.,

Boddy (1988),

Biscogniauxia

Fisher and

nummularis,

Petrini (1990),

Hypoxylon

Griffith and

fragiformeh,

Boddy (1990),

Stereum

Hirst (1995),

gausapatum

Boddy (2001)

Pioneer to late

S

Up to several

Biscogniauxia

Chapela (1989),

stage

years

nummularis,

Hendry et al.

Eutypa spinosah,

(1998, 2002),

Piptoporus

Danby (2000),

betulinus, Fomes

Baum et al.

fomentarius

(2003)

Pioneer to late

s

Few months

Biscogniauxia

Rayner and

stage

to several

nummularis,

Boddy (1988),

years

Eutypa spinosS,

Pinon and

Hypoxylon

Manion

mammatum,

(1991),

Neonectria spp.b

Hendry et al.

(1998, 2002)

Pioneer

R

Few months

Mostly non-

Rayner and

to few years

Basidiomycota

Boddy (1988)

Early to late stages

2-5 years

Chondrostereum purpureum, Cylindrobasidium evolvens Bjerkandera adusta, Phlebia radiata, Stereum hirsutum, Trametes spp.

Coates and Rayner

(1985a, 1985b, 1985c) Boddy and Rayner (1983), Coates and Rayner (1985a, 1985b, 1985c)

(Continued)

Table 1 (Continued)

General category Ecological Subtype strategy

Site and mode of establishment

Temporary Initially via mycoparasites specific fungal hosts

Defensive

Exposed wood via spores

Desiccation tolerant

Dead wood prone to desiccation, via spores

Heat and desiccation tolerant

Sun-baked wood, presumably via spores

Acid and polyphenol tolerant Late stage polypores and agarics

Heartwood rich in tannins, via spores Well-decayed wood, presumably via spores

Stage of

Life-history

Typical

Examples

References

succession

strategy3

lifespan of active mycelia

Early to late

C

2-5 years

Antrodiella sppv

Rayner et al.

stages

Lenzites betulina, Trametes gibbosa

Chapela et al.

(1995)

Early to late

S, C, R

Many years

Xylaria hypoxylon0

Coates and

stages

Chapela et al.

(1988)

Early to late

S, R

Several years

Auricularia

Theden (1961),

stages

auricula-judae, many corticoid fungi,

Neolentinus lepideus

Boddy and Rayner (1983), Boddy (2001), Heilmann-Clausen (2001)

Mid to late stages

S

Many years

Gloeophyllum spp., Trametes hirsuta, Pycnoporus cinnabarinus, Schizophyllum commune

Heilmann-Clausen

(2001), Huckfeldt et al. (2005)

Mid to late stages

s

Many years

Daedalea quercina, Hymenochaete rubiginosa

Rayner and

Boddy (1988)

Late to final

C, S, R

Several years

Lentinellus

Chapela et al.

stages

cochleatus, Ceriporia spp., Mycena spp., Pluteus spp.

(1988), Rayner and Boddy (1988), Heilmann-

P1 aiicpn

Clausen (2001)

Clausen (2001)

Non-resource restricted

Cord-formers

Tertiary: Not primarily involved in lignocellulose decomposition

Soil and litter fungi

Litter and humus colonizers

Ectomycorrhiza formers

Mycoparasites

Litter and humus colonizers

Felled and fallen

Early to final

C

Several years

Hypholoma

Chapter 1;

wood, and

stages

fasciculare,

Thompson

stumps, via

Lycoperdon spp.,

(1984), Coates

mycelia cords

Megacollybia

and Rayner

and spores

platyphylla,

(1985b,

Phallus

1985c),

impudicus,

Boddy (1993,

Phanerochaete

1999),

spp.

Heilmann-

Clausen

(2001)

All wood via

Late to final

S ± C ± R

Many years,

Clitocybe spp.,

Personal

mycelium, and

stages

though at

Collybia spp.,

observations,

invertebrate-

most

Marasmius spp.,

Swift and

carried spores

several

Lepiota spp.,

Boddy (1984)

years in

Trechispora spp.,

very

non-

decayed

Basidiomycota

wood

All wood via

Late to final

S ± C ± R

Few to many

Byssocorticium spp.,

Tedersoo et al.

mycelium

stages

years,

Lactarius

(2003)

though at

subdulcis,

most

Tomentella spp.,

several

Piloderma spp.

years in

very

decayed

wood

All wood,

Early to final

1-3 years

Achroomyces spp.,

Helfer (1991),

presumably

stages

Tremella spp.,

Zugmaier et

via spores

Hypomyces spp.b

al. (1994),

Hansen and

Knudsen

(1997)

Note: The classification into ecological strategies is not rigid, and categories sometimes overlap. For example, Piptoporus betulimus causes heart rot in Betula being latently present.

aMost common characteristics, though not necessarily for all examples.

bAscomycota.

large mycelial network waits for resources to land on it and then actively colonizes those resources, often with responses occurring elsewhere in the system (Boddy and Jones, 2006; Chapter 1). On the down-side, in the quest for new resources, non-resource-unit-restricted fungi risk loss of a large amount of biomass as a result of invertebrate grazing (Chapter 9), killing by other microorganisms and death in a harsh environment.

Sexual spores, as well as allowing genetic recombination, provide a means of long-distance spread, exceeding hundreds and possibly thousands of kilometres (e.g. Vilgalys and Sun, 1994; Hallenberg, 1995; Hallenberg and Kuffer, 2001). Sexual and asexual spores may also provide a means of dispersal in time as has been described in ectomycorrhizal communities (Baar et al., 1999; Kjoller and Bruns, 2003). Little is known of the role of resting spores in wood decay fungi, but several basidiomycetes, e.g. Piptoporus quercinus (Roberts, 2002), and members of the corticoid genera Botryobasidium and Trechispora (Eriksson et al., 1973-1988), are known to form thick-walled spores which most likely function as resting spores. In one species, Hyphodontia paradoxa, chlamydospores have been described as part of a drought resistant strategy, allowing the species to maintain its position in the fungal community of attached Quercus twigs and branches during desiccating conditions (Boddy and Rayner, 1983).

A major disadvantage of spatial dispersal by spores is that it is usually highly haphazard with small chance of landing on appropriate resources and encountering locally favourable conditions. In addition, the majority of liberated spores settle within a very short distance of the sporocarp (e.g. Norden and Larsson, 2000). Wind-borne spores have no active means of locating and settling on appropriate substrata, though variations in spore size and shape and the presence of protuberances may reflect adaptation to various establishment environments or animal vectors (Hallenberg and Parmasto, 1998; Norden et al., 1999). Some wood decay fungi have, however, evolved mutualistic relationships with invertebrates in which spores are transported to an appropriate location (Chapter 9). More haphazard dispersal over shorter distances is believed to be common in wood decay fungi, with various invertebrates and less commonly vertebrates functioning as dispersal vectors between resource units (Rayner and Boddy, 1988).

Germinating spores are faced with several obstacles before a reproductive mycelium can be established. They only have a small endogenous food reserve available for colonization (i.e. low inoculum potential), and gaining access to the resource often involves competitive/combative interactions (Chapter 7) with already established mycelia (Boddy, 2000). Hyphae developing from spores that are genetically identical (which is most likely if they are asexually derived) may act synergistically, but when they are genetically different somatic incompatibility is likely to result in competition rather than synergy (Coates and Rayner, 1985c).

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