Significance of Dead Wood for Biodiversity Conservation and Close to Nature Forestry

Peter Zach, Ján Kulfan

Institute of Forest Ecology, Slovak Academy of Sciences, Zvolen

This presenration is to show how fascinating the world around dead wood is

and what we can learn from it

Definition (Read et al., 2000)

• (1) deadwood – wood which no longer fulfils any function for the tree

• (2) dead wood – wood that no longer contains living cells

• (3) coarse woody debris – CWD –

an American expression which refers to dead wood with diameter of more than

2.5 cm

Ecological significance of dead wood

In a forest ecosystem:

• wood (together with soil) amounts to the most significant sources of organic material and mineral elements

• improves physical, chemical and biological properties of soils

• retains water and keeps moisture and regulates the temperature, contributes to a formation of typical forest micro- and mesoclimates

• provides habitat, nutritions or food to a variety of organisms, namely to obligate and facultative saproxylic species, some of which play an important role in its decomposition and mineralization (e.g. fungi, insects)

• increases species richness (number of species) and diversity of organisms

• limits the risk of soil erosion and stabilise litter on steep slopes

• indicates a forest ecosystem quality (disturbace, exploatation)

Decomposition of wood

• cellulose (40-62% of dry weight of wood according to tree species) – fungi, bacteria and a few insects are able to decompose (hydrolyse) cellulose

• hemicelluloses (actice participation of xylophagous insects)

• lignin (18-38%) – only highly specialised fungi, bacteria and some protozoans are most significant, but a very limited number of insects can also digest lignin with help of fungal and bacterial symbionts in their digestive tracts

• secondary components (2-3%, starch, soluble sugars,etc.)

Concentrations of main mineral elements (μg.cm-3) in oak branches during the decomposition and

mineralization process (Swift, 1977 in Dajoz, 2000)

Elements N P K Ca Mg

Fresh wood 1,057 69.5 767 1,935 146

Wood with fungi 1,304 54.4 141 3,871 118

Wood with fungi and animals

710 27.8 20.9 1,777 58.3

From fresh wood to wood mould

• levels of organic nitrogen are low in healthy wood, they rise in decaying wood and are the highest in wood mould (the same with nitric nitrogen, ammoniacal nitrogen)

• the C/N ratio, which is very high in fresh (healthy) wood, gradually falls and is the lowest in wood mould

Chemical composition of wood without decay, decaying wood and wood mould in chestnut trees (Kelner, 1967 in Dajoz, 2000)

Organic nitrogen

(%)

Ammoniacal nitrogen

(%)

Nitric nitrogen

(%)

Carbon

(%)

Organic matter

(%)

Ash

(%)

C/N

(%)

Healthy wood

0.24 28 12 41.2 97.9 2.1 171.7

Dry rot 0.31 0 32 48 98.6 1.4 154.8

Damp rot 0.47 0 56 48.9 97.8 2.2 104

Wood mould

0.77-0.99 16-20 64-88 40.5-43.8

87-94.8 1.3-5.2 44.2-51.3

Soil 0.33 - - 0.65 - - 2.2

SURFACE

20 cm

40 cm

Moisture of substrate (% weight) in tree cavities

Calculation: (weight of water in substrate/dry weight of substrate)*100

Collecting date: April 30, 2002

Number of samples: n = 9, sample size N = 18

Substrate profile: surface layer - 20 cm - 40 cm deep

CAVITY

% w

eig

ht

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Dead wood

• provides one of the two or three greatest resources for animal species in a natural forest ecosystem (Charles Elton in The pattern of animal communities )

• if removed the forest fauna is impoverished by 20% (Kirby, Drake, 1993)

• In Central Europe every fifth to sixth beetle species depends on dead wood (Reiner, 1991)

Aromia moschata

Saproxylic beetles as indicators of a forest ecosystem quality

• Why? Saproxylic beetles strongly depend on CWD and take important part in its decomposition, they are restricted to various niches and do not migrate long distances, they are rich in species and in specimens and include significant bioindicary species, they can be collected through non-destructive methods, remnants of beetles in old (even fossil) wooden structures can also be identified.

Key factors affecting diversity of saproxylic beetles : species richness

and number of specimens of specialists

• amount of decaynig wood – general factor

• diversity of dead tree parts (habitat heterogeneity) - number of dead trees of large diameter - presence of all stages of decay

• number of polypore species and fruting bodies

• distance to the nearest suitable habitats – every species has lower limit of how scattered its substrate can be before its population collapse – this distance increases with the size of clear-cut or thinning area (links to isolation effects)

• level of disturbance (forest exploatation – cutting, thinning the trees, and adverse affects) – larger clear-cut or intensively thinned areas cannot be recolonized by beetles

Dead wood amounts in primeval forests

• there are differences in dead wood amounts between different types of primeval forests

• primeval forests comparable in their site and environmental conditions show only minor fluctuations in their overall biomass (Saniga, 2001)

• if a particular primeval forest is considered proportion of dead wood may vary greatly within it according to the developmental phase (aggradation, optimum, disaggregation)

• 50-200 m3 of CWD in semi-natural and virgin forests (Albrechts, 1991)

• Western Carpathians: Boky (56,5 m3/ha, 14,7% of the whole amount of trees), Dobroc 1998 (184-412 m3/ha, 20-34% Badin 1997 (246-433 m3/ha, 27-37%), Polana (182,8 m3/ha, 32,9%) (Korpel, 1997, Saniga M., 2001)

Dead wood amounts in commercial forests

• they can be very low (none or up to 5 m3) as well as higher (over 100 m3 in extensively managed forests) and very high after disasters

• sufficient amounts can be derived from observations made in primeval forests combined with the results of experimental studies using indicator species or indicator groups

• sufficient amounts to stabilise populations of saproxylic beetles in commercial oak and spruce forests: 5-10 m3/ha in Germany (Ammer, 1994), but even some 30 m3/ha showed to be insufficient in spruce forests in Norway (Okland et al., 1996)

• sufficient amounts for the same purpose in an extensively managed oak forest in Germany: 40 m3 /ha (5% of the amount of living trees) (Haase, Topp, Zach, 1998)

How to support diversity of saproxylic beetles and that of a forest ecosystem

• to increase proportion of semi-natural forests

• to avoid monocultures everywhere where possible (conversion to mixed forests)

• to save large-diameter trees (diameter more than 40 cm) in different stages of decay and to support the existence of „special trees“ with basal hollows in tree trunks everywhere where possible

• to avoid extensive cutting over large areas, the same concerns extensive thinning of pioneer tree species

• to monitor dead wood amounts in order to predict unfavourable trends in their development and to integrate this monitoring in regular forest inventories

Monocultures of Norway spruce

A commercial spruce forest, Polana,central Slovakia

or mixed fir-beech forests ?

Badin nature reserve, central Slovakia

Obligate saproxylic Coleoptera in a natural and extensively managed fir-beech forest

(Badin, 1996-1997)based on catches in flight-interception traps

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All Coleoptera Scolytidae Cerambycidae

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All Coleoptera Scolytidae Cerambycidae

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cies

Natural forest Managed forest

Ancient oak tree

Central Slovakia

Old pasture woodlands

Central Slovakia

Any log left in a forest would help to increase species diversity. Unfortunately, not all organisms can be supported this way.

Upupa epops, Polana, W. Carpathians. Large forest areas have been lost in Slovakia in the past but, compared to Western Europe, this is not excessive. Still some 2,000000 ha remaining... Large-diameter logs in

Konigsforst, Cologne, Germany.

Problems

• avoidance of presence of dead wood by some foresters, landscapes owners and the public (forest hygiene, pests, easthetical aspects, risk to forest or park visitors, etc.)

• fragmentation of ownership in a forest sector

• protected areas (not state owned) – compensations to forest and landscape owners – Natura 2000

A wider discussion and closer co-operation is needed to approach or reach a consensus on dead wood matters between the forestry practices and nature conservation and the public