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9 Close-to-nature forest management in Europe

Compatible with managing forests as complex adaptive forest ecosystems?

Jürgen Bauhus, Klaus J. Puettmann and Christian Kühne

What is close-to-nature forest management?

Close-to-nature forest management (CTNFM) is a production system that devel-

oped from concepts of multifunctional forest management. The main historical

and philosophical roots of close-to-nature forest management include Möller

(1922), who first described the ‘Dauerwald’ (perpetual forest) approach as an

alternative to the conventional even-aged forest management focused on conifer

monocultures. Earlier, Karl Gayer (1886) had already promoted mixed uneven-

aged forests as an ecologically more stable alternative to even-aged monocultures.

Another important influence in the development of this system came from Leibun-

dgut in Switzerland, who emphasized that silvicultural practices should not be

forced into specific themes but instead should accentuate the natural development

of forests (Schütz, 2001). This agreed well with Möller’s suggestions to employ all

suitable forest structures in forest management, and not to carry out the Dauer-

wald approach in a rigid systematic way (Möller, 1922).

While the Dauerwald and later the close-to-nature movement still show that

their origin and applications were strongly influenced by practitioners who had to

address specific management situations and goals, Möller (1922) developed a con-

ceptual basis for this approach early on. His writings represent an early attempt

to describe what is now known as the ecosystem concept (Huss, 1990; Thomasius,

1996). It is important to note that Möller developed his ideas before ecosystem

ecology became of major interest to the science community. This explains what

now appears as an incomplete understanding of ecosystems in his writings. Philo-

sophically, Möller’s view of ecosystems as an organism suggests close linkages with

Clements’ view of ecosystems as meta-organism dynamics (Clements, 1936) and

with the Gaia hypothesis, which views the whole globe as a super-organism; both

of which imply top-down control mechanisms (Levin, 1998). This view expressed

itself in the idea of bringing together productivity, diversity and especially continu-

ity and stability of forest conditions. Möller and his followers believed that simul-

taneously emphasizing these attributes would provide forests with the capacity

for self-regeneration and self-regulation. While this appears to be philosophically

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aligned with the concept of self-organization of complex adaptive systems, several

philosophical distinctions are already evident. For example, complexity science

suggests that self-organization originates from a bottom-up approach, rather than

from top-down control. Several other distinctions, such as the emphasis of close-

to-nature forest management on continuity and stability, rather than on system

dynamics as highlighted in complexity science, are discussed in detail below. In

addressing the title question, we will specifically focus on the characteristics of

complex adaptive systems (Chapters 1 and 2), including openness, heterogeneity

and diversity, hierarchy, uncertainty, self-organization and adaptation.

The management settings of the main proponents of CTNFM lead to an

emphasis on stability, productivity, diversity and continuity of forest conditions,

which resulted in attempts to integrate multiple forest management goals at small

spatial scales, ideally within individual forest stands. This is in contrast to a segre-

gated forest management approach, such as the TRIAD concept, which comprises

separate areas in the landscape for wood production and biodiversity conservation

functions, in addition to areas of less intensive, multiple use forestry (Seymour and

Hunter, 1992). The attempt to simultaneously integrate multiple forest functions

at smaller scales, typically forest stands, has led to an emphasis on mixed-spe-

cies and uneven-aged forests across the landscape as a way to provide for wood

production, recreation, biodiversity, aesthetic values, and so on. More recently, a

stronger consideration of conservation goals has prompted the integration of per-

manent or semi-permanent structural elements of old forests at the stand level (e.g.

Gustafsson et al., 2012). Whereas the emphasis on managing forest at small spatial

scales and on maintaining mixed-species and uneven-aged forests everywhere may

appear to lead to homogenous forest landscapes, the situation in Central Europe

today is quite variable, due in part to the diversity in land ownership and manage-

ment histories.

Pro Silva, a non-governmental organization, serves as an umbrella for national

non-governmental organizations promoting close-to-nature forest management in

Europe. Pro Silva is now 23 years old, but its ideas and several national organi-

zations are several decades older. For a long time, the close-to-nature approach

was only practiced by a minority of mostly private landowners. Their main goals

of providing a stable supply of high value wood from small stands holdings had a

strong influence on the development of CTNFM practices. The large windstorms

in the early 1990s, in combination with public pressures concerned with biodi-

versity issues and budget limitations, raised interest in alternative management

regimes, specifically in CNTFM. Other ownerships with a wider set of manage-

ment settings and goals subsequently endorsed close-to-nature, or a derivative

thereof, as their official management approach (Hockenjos, 1999).

Members of Pro Silva agree to management that is guided by well-accepted

principles; see, for example, Pro Silva (1999). In addition to these private hold-

ings, many public forest owners, including city and state forests, have based their

management on principles of CTFNM (e.g. Lower Saxony Ministry for Nutrition,

Agriculture, Consumer Protection and Regional Development, 2007). Today,

CTNFM is a prominent paradigm in central Europe, shared by many forest

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owners as well as governmental and environmental organizations (e.g. NABU,

2008). Its principles form the basis for certification standards of the Forest Steward-

ship Council (FSC) as well as the Programme for the Endorsement of Forest Certi-

fication Schemes (PEFC) for Central Europe. In addition, a common assumption

by many forest practitioners, forest administrations and policy makers in central

Europe is that CTNFM is the most suitable approach to cope with future climate

change (e.g. Reif et al., 2010).

Due to its origin and wide-spread application, CTNFM cannot be regarded as

an approach with a single commonly agreed definition and a well-defined, estab-

lished scientific basis (e.g. Pommerening and Murphy, 2004). Instead, it is defined

by a set of general principles that are derived from the common goal of managing

for high value wood production. The widespread application of these principles

accommodates local conditions and challenges, as different managers and agen-

cies will emphasize different principles in different situations. Here, we provide

a short description of the main principles and rationales of CTNFM, discuss the

strength and limitations of these, and analyze how these principles relate to the

concept of managing complex adaptive systems (see Table 1).

The principles and rationales of close-to-nature forest management

Forest development types and site adapted species composition

Description. The species composition of forest stands is commonly planned on the

basis of so-called forest development types. Based on the spatially explicit analysis

of site conditions, the desired forest functions (e.g. high value wood production, soil

conservation, water protection, recreation) or conservation status, one or multiple

forest development types are selected as target stand conditions, which are assumed

to provide the desired future forest functions (e.g. Niedersächsische Landesforsten,

2004). Forest development types serve as guides for future silvicultural activities

to direct the development of forest stand condition towards desired states, typi-

cally defined as fully stocked, multi-age, mixed species stands (Larsen and Nielsen,

2007). Forest development types are comprised of site adapted tree species with

physiological niches compatible with current or predicted future site conditions

(based on climate change predictions), high growth and value potential and little

or acceptable production risks (Frischbier et al., 2010). Depending on landowner

objectives, stand composition may comprise exclusively native species based on the

potentially natural vegetation. Alternatively, it may include a variable amount of

non-native or exotic species to promote the production function, or – increasingly

important – to promote the resistance of forests to future stresses and disturbances.

For example, forest development types for sub-montane sites in central Europe at

around 500 m elevation with approximately 800 mm precipitation and acidic soils

could include a) a highly natural, native European Beech (Fagus sylvatica) forest, with

few or no admixed species, b) a mixed sessile oak (Quercus petraea)-beech forest, or c)

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a mixed beech-conifer forest, where conifer species could include larch, Douglas fir,

Norway spruce or Silver fir. The tree species choice may be based on observations

of species performance in adjacent stands and empirical knowledge about compat-

ibility of species in mixtures in terms of competition for light and other resources.

The selected forest development types and target stand conditions are designed to

fully use the site potential without deteriorating site conditions, such as through lit-

ter of low decomposability which may acidify the surface soils. Ideally these species

should have the potential to regenerate naturally under the range of acceptable

stand conditions to facilitate the use of natural processes for future stand manage-

ment and maintenance of ecosystem functions (Röhrig et al., 2006).

The idea of forest development types resulted from the recognition that many

species have been cultivated on unsuitable sites in the past. In many areas, this

led to unstable forest ecosystems in regard to disturbances or undesired ecosystem

processes such as nutrient leaching (Puhe and Ulrich, 2001). The proportion of

forest stands composed of non-native species in the past federal forest inventory

in Germany is indicative of the historically developed forest composition that is

far from natural (Figure 9.1). These conditions are also part of the motivation for

application of CTNFM approaches.

The close-to-nature forest management movement has been a driving force in

recent decades to convert forests in composition and structure from mostly even-

aged forests dominated by non-native conifers (which have been highly suscep-

tible to disturbances) towards more broadleaved-dominated and uneven-aged

stands (e.g. Spiecker et al., 2004). The most suitable silvicultural opportunity for

conversion towards desired forest development types is during the regeneration

Figure 9.1 Naturalness of German forests as determined in the last federal forest inventory. Stands were classifi ed based on the proportion of tree species belonging to the potentially natural forest community. For this analysis, non-native forests con-tain species that are not part of the local natural vegetation community, although they may be native to other parts of Germany (BMELV, 2002). The potentially natural forest vegetation community is determined based on understorey plant composition, which is assumed to refl ect mostly soil and climatic conditions and to be little or not affected by past management (Tüxen, 1956).

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phase. Conversion practices often utilize advanced natural regeneration, if desir-

able species are present, or advance planting, to introduce desirable species. How-

ever, CTNFM also gained wide-scale recognition as an opportunity to respond

to unplanned natural disturbances. After several large-scale storms in the past

three decades, capacity and resources were insufficient for artificial regeneration

of many disturbed sites. Following a CTNFM approach, spontaneous successional

development of forests was permitted in many situations, even though this led

to species compositions in the natural regeneration that did not conform to the

intended forest development types (e.g. Schmidt-Schütz and Huss, 1998).

Critique of the principle and relationship to complex systems theory. The use of

site-adapted (rather than native) species is also discussed as an important strategy

to allow forests to adapt to climate change. However in this discussion, forest man-

agers focus more on adaptation to past and current site conditions and disturbance

regimes than on predictions of what will happen in the future (see also Figure 1.2 in

Chapter 1). This strategy is opposed by many environmental organizations, which

promote the exclusive use of native species (Reif et al., 2010). Their main argu-

ment is based on the importance of co-evolution; the idea being that native spe-

cies should have developed tighter ecological interactions with other forest organ-

isms than introduced species (Southwood, 1961). Such tight ecological coupling is

believed to favour resistance and adaptability to unexpected changes or extreme

events. However, history is telling a different story. There are no documented cases

of species being lost (or similar changes) that can be attributed to an introduced

tree species per se. In some cases, native species appear to benefit from their interac-

tions with introduced species (Goßner and Ammer, 2006) and introduced species,

such as Douglas-fir, are expected to better cope with increased drought events in

the future. On the other hand, there is ample evidence of native species struggling

to deal with the introduction of pest species or pathogens such as Ulmus sp. being

affected by Dutch Elm disease, Castanea sp. through chestnut blight, or currently

Fraxinus excelsior through the fungus Chalara fraxinea. Introduced tree species are,

however, not immune to introduced pests, such as Pinus strobus in Europe being

affected by white pine blister rust (McDonald and Hoff, 2001; Kirisits, 2007). Up

to now, there does not seem to be any scientific evidence that sole reliance on

native species will offer advantages with regard to potential adaptations to climate

change or to the supply of ecosystem services, compared with exotic species. Any

species may have a greater capacity to resist or recover quickly from unexpected

or extreme events, if these have been part of their historical natural disturbance

regime. Clearly, the perceived great advantage of native species is that they har-

bour more native biodiversity than exotics, and hence provide for more ecological

interactions within the ecosystem, but that may not always be the case (Goßner

and Ammer, 2006; Quine and Humphrey, 2010). Clearly, the decision about the

use of exotic tree species in the context of CTNFM will be a compromise between

landowner constraints and objectives, and political considerations.

The principle of using site-adapted species is primarily focused on local site

conditions and thus on the spatial scale of individual stands. It does not explicitly

consider landscape conditions. At the same time, in the long-term planning efforts

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of large forest owners such as state forests, this approach is guided by targets for

regional proportions of different tree species or forest types (e.g. Niedersächsische

Landesforsten, 2004). In practice, such regional level planning does account only

to a small extent for the goals and practices of other landowners, and thus cannot

provide specific goals regarding species composition and diversity of actual or for-

est development types at landscape scales.

The focus on local site conditions matches the emphasis on bottom-up regulation

of ecosystems as highlighted in complexity science. But, as described above, there

is no emphasis in CTNFM on cross-scale interactions, an important principle of

complex systems; for example, there is no tight linkage between local and landscape

or regional targets of species composition. The notion of forest development types

is nicely linked to the concept of self-organization, if the development types are

viewed in the broadest context, allowing for maximum flexibility. An example for

this can be seen in the reliance on spontaneous natural regeneration and succession

on disturbed sites following wind throw. However, reflecting the management set-

tings and goals of the landowners practicing CTNFM, the emphasis on target stand

structures associated with development types is not necessarily aligned with the

notion of adaptability and self-organization, which are important characteristics

of complex adaptive systems. Fully stocked uneven-aged and mixed-species stands

may have many advantages, but focusing on maintaining these conditions continu-

ously throughout the landscape suggests that landowners’ approach to achieving

their management goals is based (at least partially) on assumptions underlying a

static view of ecosystems. This contrasts with the dynamic view of complexity sci-

ence, often expressed as ‘stability is the exception, rather than the rule’.

Avoidance of clearfelling

Description. The avoidance of clearfelling and the focus on continuity of ecosystem

processes throughout forest developmental stages highlights the linkage of close-

to-nature forest management to other silvicultural approaches, especially continu-

ous cover forestry (Mason et al., 1999). Möller’s concept of forests as ‘organisms’

– that all elements are top-down controlled, interconnected and together provide

for a continuity of ecosystem processes – stood in strong contrast to clearfelling

practices common at the time, with a subsequent simplification in forest structure

and dominant functions and processes (e.g. Schütz et al., 2012). He linked the poor

growth of pine monocultures to the practice of clearfelling, which presumably led

to reductions in soil organic matter content in the sandy soils of north-eastern

Germany (Möller, 1922). Subsequently, this largely empirical knowledge has been

substantiated by many other studies that have demonstrated the potentially strong

impact of clearfelling on reducing ecosystem nutrient pools and fluxes (e.g. Swank

and Crossley, 1988), although the magnitude of this effect can be highly variable.

In addition, clearfelling is avoided under CTNFM for a number of other reasons,

such as the objective of shifting the focus from optimizing stand values to optimiz-

ing tree values. Given a range of tree sizes in even the most homogenous stand,

clearfelling results in individual trees being harvested prematurely (trees at the

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smaller end of size distributions) or post maturity (trees at the larger end of size dis-

tributions), that is, before or after trees have reached their optimal dimension and

value, respectively. Also, one aim of CTNFM is to produce and maintain valuable

timber in harvestable dimensions continuously in every stand. In addition, the

avoidance of clearfelling is associated with a reliance on natural regeneration and

associated savings in planting costs. The retained overstorey following harvesting

is presumed to have a positive influence not only on survival but also on the quality

development of advance regeneration (form and branch size). While this is gener-

ally observed for conifer advance growth, it is questionable whether such canopy

shading has a similarly beneficial influence on quality development in hardwood

regeneration (Leonhardt and Wagner, 2006). Thus, while, technically, large open-

ings can be allowed under special conditions, the obvious bias against them (e.g.

evident in expressions, such as continuous cover forestry) has meant that they are

practically never implemented.

Partially as a result of the CTNFM movement, many German states have imple-

mented forest laws that prohibit clearfelling. Varying by state, clearfellings are

defined as units larger than contiguous areas of 0.3 to 2.0 ha, where stocking vol-

umes are reduced to less than 40% of a fully stocked stand (Klose and Orf, 1998).

Clearing sites at the scale of clearfells is only permitted as salvage operation and to

‘clean up’ following disturbances, or where it serves the conservation of habitat or

species. These new laws encouraged landowners to limit harvesting operations to

partial harvests, including small gaps, strips and shelterwood cuttings.

Critique of the principle and relationship with complex systems

theory. Concerns have been voiced that cutting small-scale gaps as dominant

harvest operations to initiate regeneration will eventually reduce the proportion of

light demanding tree species, such as oaks (c.f. von Lüpke, 2008). These species are

of special interest for nature conservation, future economic interests and for their

potential to adapt to future climatic conditions (e.g. von Lüpke, 2004).

From the perspective of complexity science, the avoidance of clearfelling, which

is a strong and central principle of CTNFM, shows an emphasis on memory and

legacies. The retention of forest structures during forest harvesting has evolved as

a central concept of ecologically sustainable forest management (e.g. Gustafsson

et al., 2012). It helps ensure the maintenance of structural heterogeneity and eco-

logical interactions on site throughout the regeneration phase of forests, such as

in the form of mycorrhizal networks (Chapter 7). However, limiting regeneration

options to favour a selective set of mostly shade tolerant species has the potential

to decrease species diversity in the long term. Such trends in central European

forests have been attributed to the continuous maintenance of mid- to late-suc-

cessional conditions and a lack of diversity of anthropogenic disturbances (e.g.

Wohlgemuth et al., 2002, see also Swanson et al., 2010 for a similar discussion

in North America). It has been suggested that a greater variety of management

practices is likely to provide for greater biodiversity, especially if they are designed

to provide niches for a wider variety of species (Bunnell and Huggard, 1999;

Wohlgemuth et al., 2002). In the context of complexity science, these management

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limitations imposed by CTNFM appear to conflict with the notion of maintaining

or increasing the ability of forest ecosystems to adapt to changes in future condi-

tions, because species that depend on regular disturbance (wind-dispersed species,

long-lived seed bank species, resprouters) may be lost. An important question in

this context is whether avoidance of clearfelling in CTNFM actually influences the

extent, intensity and severity of natural disturbances and the ability of forests to

respond. If CTNFM does not reduce the occurrence and severity of natural dis-

turbance events, then the combination of partial harvests and natural disturbances

may still provide ample opportunities for a diversity of self-organization processes.

However, these will depend on how disturbed sites are treated silviculturally; for

example, CTNFM approaches encourage maintenance of early successional spe-

cies, when target species are planted or established as part of accelerating stand

development towards target structures.

Focus on ecosystem stability

Description. The popularity of close-to-nature forest management in Germany

increased considerably during the public debate about forest decline related to

acid rain and other atmospheric pollution in the 1980s (Schmidt, 2009) and fol-

lowing the large storm events of the early 1990s (Hockenjos, 1999). The large

research efforts triggered by the forest decline improved the understanding of for-

est ecosystems considerably. Specifically, it expanded the concept of ecosystem

stability to include development of plant and faunal communities and processes,

such as carbon and nutrient cycling (Puhe and Ulrich, 2001). Further, research

demonstrated that highly cultivated stand types created under traditional even-

aged management (i.e. large-scale coniferous monocultures) were very productive

in terms of forest biomass growth (Spiecker et al., 1996), but were also particu-

larly vulnerable to storms (Schütz et al., 2006) and predicted climatic extremes

(e.g. Kölling et al., 2009), or even destabilized the systems through nutrient

leaching and accelerated soil acidification (Puhe and Ulrich, 2001).

Ecological stability in the context of CTNFM relates mostly to factors that

are currently or predicted to become the most important disturbances in Cen-

tral Europe, including wind storms (Schelhaas et al., 2003), insect outbreaks, in

particular bark beetles feeding in coniferous trees (Jönsson et al., 2011) and snow

damage (Nykänen et al., 1997). These disturbances typically interact with each

other; for example, bark beetles often follow wind or snow damage in Norway

spruce or Scots pine forests (Bakke, 1983). The development and maintenance

of ecologically stable forests focuses, therefore, on the physical stability of trees

and stands and on the reduction in the susceptibility to insect outbreaks. As is

described in Chapter 1, ecological stability is closely linked to resistance, resilience

and adaptability. The former refers to the ability of the ecosystem to withstand

the forces of disturbances and to maintain structure, composition and processes,

that is, to minimize disturbance severity. Silvicultural approaches as elements

of CTNFM aiming to increase resistance typically employ the use of compara-

tively ‘storm-resistant’ tree species. Also, tending schemes are specifically aimed

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at developing forest stands with a high collective (stand) and individual tree stabil-

ity (Klädtke and Abetz, 2010). For example, mixed-species forests that include

deep-rooted species are more wind-firm than monocultures of shallow-rooted spe-

cies (Knoke et al., 2008). However, this increased stability may be only detectable

when assessing whole stands and is not necessarily found for shallow-rooted trees

within mixed stands (von Lüpke and Spellmann, 1999). Collective stand stability

is further pursued through spacing and thinning practices aimed at reducing the

height at which certain target diameters are being reached. Tree height has been

identified as the most important single predictor of wind damage in forests (e.g.

Albrecht et al., 2012). Hence, reducing the length of production cycles is viewed

by forest practitioners as an important element of silvicultural strategies to avoid

or minimize storm damage as well as other risks (Reif et al., 2010). Consequently,

managed forest stands are likely to become increasingly young at the time of final

harvest. The production cycle is further reduced through recent trends showing

improved growth of forests in Central Europe (Spiecker et al., 1996). However,

reduced production cycles and consequently lower stocking volumes contrast with

other goals of CTNFM and nature conservation NGOs (Reif et al., 2010), which

emphasize the values of fully stocked and older stands. Therefore, reduction in

production cycle length is contested amongst followers of CTNFM.

The preferred methods in CTNFM to increase ecological stability with regard

to insect pest outbreaks focus on development of mixed-species stands, increasing

diversity and abundance of antagonists to pest species, and reducing the rate of

spread of pests (e.g. Jactel and Brockerhoff, 2007; Dulaurent et al., 2012), as well

as on modifications in stand structures that create less favourable microclimatic or

soil conditions for pest species (e.g. Heiermann and Schütz, 2008).

An interesting question is whether forests managed under CTNFM principles

have been less affected by disturbances. Large-scale disturbances have certainly

been a major factor shaping forests in Central Europe (Scheelhas et al., 2003).

For example, in the German State of Baden-Württemberg, the average amount

of unplanned harvesting (largely from storms and insect outbreaks) in state forests

typically constitutes more than one third of the total harvested volume. However,

for the same region, single tree selection forests (Plenterwald) have been affected

by disturbances to a much smaller degree (Lenk and Kenk, 2007). The volume

of unplanned harvests after disturbances for these forests was 21% for the period

1953–2001, compared with 36% for all state forests. Of course, these figures

have to be viewed with caution. Single tree selection forests could easily be biased

towards sites that are less susceptible to disturbances and hence have permitted

this type of forest management in the past.

In the context of forest management, the notion of adaptability is typically dis-

cussed in terms of re-establishment of forest conditions and associated provision

of ecosystem services. For CTNFM this is often assessed as the (re-)development

of forests towards a desired tree species composition and size distribution. In this

regard, CTNFM places particular value on the continual presence of advance

regeneration, which normally survives the most common disturbances in central

Europe, such as wind throw and insects outbreaks.

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Critique of the principle and relationship with complex systems

theory. Despite the prominence of the central principle of close-to-nature for-

est management to develop or maintain forest stands that ‘are stable in the face

of biotic and abiotic disturbances’ (Davies et al., 2008), limitations of viewing

ecosystem as stable are well recognized within the CTNFM community (e.g.

Schütz et al., 2012). As viewed within CTNFM, this principle implies a heavy

reliance on resistance, with less emphasis on resilience, adaptability and realign-

ment (Stephens et al., 2010). In contrast, complexity science emphasizes the

importance of the latter two principles, as stability is considered the exception

rather than the rule in forest ecosystems. In this context, fully stocked uneven-

aged mixed stands can be viewed as a stable domain that is desirable and ideally

maintained on all sites. However, research in old-growth forests suggested that

it is only a temporary phase and only one component of a natural forest devel-

opment cycle (e.g. Leibundgut, 1978). Nevertheless, through repeated manage-

ment inputs and in absence of major disturbances, CTNFM efforts have been

quite successful in maintaining ecosystems in this phase for relatively long peri-

ods. Thus, much of the management activity in CTNFM is aimed at minimizing

variability in stand conditions at larger spatial scales, to ensure a continuity of

ecosystem services and economic gains at small spatial scales. In contrast, com-

plexity science suggests that there is much value in variability and changes which

are likely to favour what Holling and Gunderson (2002) called ‘creativity’ in for-

est dynamics. Especially extreme events provide ecosystems with opportunities

to adapt to new conditions (Holling and Gunderson, 2002). A discussion of the

panarchy cycle (for a detailed description, see Holling and Gunderson, 2002)

highlights this point. In this context, CTNFM can be viewed as an attempt to

prevent larger-scale release and reorganization periods through repeated inter-

vention at small scales. The avoidance of clearcutting and the associated amount

of residual trees after harvest operations can be viewed as an emphasis on lega-

cies and memory in a smaller nested cycle. If successful, CTNFM continuously

eliminates the ‘back loop’ (release and reorganization) phases, through mini-

mizing impacts of wind storms and insect outbreaks. However, in the panar-

chy cycle, the back loop is also considered important for maximizing ‘creative’

changes that are likely to increase the ecological resilience of forests to possible

future increase of such disturbances. As such, Holling and Gunderson (2002)

suggest that these processes are crucial for ecosystem’s ability to adapt to future

perturbations. Consequently, complexity science places a strong emphasis on

these phases, when external forces or variability can more easily influence eco-

systems, leading to novel combinations of components, including more extreme

events (Drever et al., 2006).

The brief discussion of the panarchy cycle highlights the issue about risks

associated with reductions in disturbance frequencies and intensities through

CTNFM (see above). However, whether CTNFM has been successful at reduc-

ing the occurrence and severity of disturbances, perhaps below the background

level of natural disturbances typical for a particular region, is extremely difficult

to answer.

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Reliance on natural processes

Description. Close-to-nature forest management aims to minimize management

inputs and relies as much as possible on natural processes. This does not mean that

CTNFM approaches do not apply intensive management and active silvicultural

interventions. The reliance on natural processes is mainly focused on stages in

which silvicultural activities are not producing revenues, such as regeneration and

early stand development phases. For example, wherever possible, CTNFM relies

on natural regeneration, ideally of site-adapted species. Large-scale artificial regen-

eration through planting or sowing is generally avoided. Exceptions include the

conversion of stands dominated by species that are not site-adapted or to reforest

sites following large-scale disturbances. The last German federal forest inventory

revealed that, across all ownerships and management approaches, approximately

80% of forest stands in sapling stages or younger (up to 4 m tall trees) originated

from natural regeneration (BMELV, 2002). With the exception of forest domi-

nated by Douglas-fir and larch, natural regeneration was the most important form

of regeneration for all species, in particular in broadleaved forests.

Advantages of natural regeneration include primarily reduced establishment

costs and avoidance of problems due to distorted root systems, which may result

from planting of bare-root or container stock, in particular of species with tap

root systems (Nörr and Baumer, 2002). A further advantage of high densities and

multiple species in naturally regenerating stands is that natural selection processes

select for species and individuals best adapted to micro-site conditions (selection

filter of site conditions, e.g. drought years), which can be viewed as promoting

self-organisation of ecosystems. Also, natural regeneration established over long

periods from many parent trees ensures high genetic variation within seedling

populations (Finkeldey and Ziehe, 2004).

Under close-to-nature forest management, natural regeneration is mostly

achieved through reproduction methods that avoid large openings (Figure 9.2),

which favours a limited number of shade-tolerant species and discriminates

against light-demanding tree species (Wagner et al., 2011). The resulting extended

regeneration periods, which also conform with the aim to increase or maintain

resilience through the presence of advance growth (see above), may last up to four

decades in beech shelterwood systems or become a permanent feature in all-aged

Plenterforest. Extended establishment periods beneath the canopy of mature trees

protect seedling and saplings from frost and thus may reduce damages that lead to

reductions in tree quality, such as forking as result of bud damage (e.g. Kerr and

Boswell, 2001). The long regeneration periods, which are characterized by initially

fairly dark conditions in the understory, promote very shade-tolerant species such

as European beech (Fagus sylvatica) and Silver fir (Abies alba), which gain a growth

advantage over less shade-tolerant but (in full light) potentially more fast growing

species (e.g. Kühne and Bartsch, 2004).

As more landowners switched to natural regeneration of all tree species, it became

more and more obvious that herbivory by ungulates, mainly roe deer (Capreo-

lus capreolus) and red deer (Cervus elaphus), is a major factor limiting regeneration

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ionsuccess (Ammer et al., 2010). The requirement that population densities of browsing

wildlife species should permit natural regeneration of forest tree species is stated in

most German state forest laws. However, this issue did not receive as much attention

when practices were focused on monocultures, often of species not very palatable to

deer and when investments in regeneration could be justified, such as browse pro-

tection. Thus, CTNFM revived the long-standing discussion about increasing hunt-

ing pressures to reduce populations of herbivores. Recently, this topic gained even

further attention, as the current browsing situation in German forests is considered

by many to be a strong impediment to forests adapting to climate change (Ammer

et al., 2010). Under current conditions, regeneration layers are often missing species

deemed more suitable to future climates (e.g. oaks, fir), as these are particularly sus-

ceptible to browsing (Gill and Beardall, 2001).

After regeneration establishment, natural processes (such as self-thinning and

self-pruning) may also have to be complemented by active stand tending to ensure

the maintenance of species diversity and removal of undesired species and trees

(e.g. wolf trees). The reliance on self-thinning and self-pruning is most common in

young hardwood stands (Röhrig et al., 2006). Self-thinning involves a strong selec-

tion process, and tree numbers can decline by orders of magnitude before the first

silvicultural thinning entry occurs. For example, numbers of seedlings in naturally

Figure 9.2 Long regeneration periods beneath the shelter of mature trees that are harvested based on target diameters promote advance regeneration of shade-tolerant spe-cies, such as Silver fi r and Norway spruce.

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regenerated hardwood stands may decline from 100 000–200 000 germinants per

hectare to fewer than 1000 trees per hectare at 40 to 60 years, when the first crop

tree selection and associated thinning typically takes place (Pretzsch, 2009). Dur-

ing this process, asymmetric competition for light leads to size-dependent mortal-

ity of smaller, slower growing trees. Assuming that tree growth is related to genetic

fitness, self-thinning leads to selection for fitter plants and is expressed in higher

proportions of heterozygous individuals (e.g. Baker-Brosh, 1996). Hence, the reli-

ance of CTNFM on natural regeneration, often resulting in high seedling densities

and on self-thinning offers a large potential for natural selection to act and thus

promote adaptability of tree populations.

In contrast to hardwood stands, self-thinning in very dense, young conifer stands

is not commonly desirable. Here, high initial stand densities may lead to restricted

development of root systems, with long-lasting effects that may not even be rem-

edied by thinning, as has been shown for Norway spruce (Nielsen, 1990). Impaired

root development results in physically less stable trees, which is particularly critical

for shallow-rooted species, such as Norway spruce (Peltola et al., 2000). In addi-

tion, high densities in sapling and poles sized conifer stands may lead to smaller

branches, but not to improvement of stem quality through self-pruning (e.g. Hein

et al., 2008). Consequently, silvicultural approaches in conifer-dominated stands

do not typically rely on self-thinning, even in close-to-nature forest management,

but focus on promotion of tree and stand stability through spacing treatments

early in stand development.

Critique of the principle and relationship with complex systems

theory. The reliance on natural regeneration in the form of shade tolerant

advance growth restricts establishment and growth of many shade intolerant spe-

cies. In addition, exposure to root competition and shading through mature trees

may lead to restricted root development, with possible problems for the recovery

of structural roots in some species (Kühne et al., 2011). Consistent widespread

downplaying of the role of a large subset of species that potentially could be impor-

tant in determining the ecosystem’s response to disturbances or environmental

changes runs counter to the emphasis in complexity science on maintaining or

increasing the adaptive capacity of systems (Chapters 1 and 2). One may assume

that the likely recurrence of large-scale natural disturbances may provide ample

opportunities to promote these light demanding tree species and lead to land-

scapes with the full suite of species compositions (e.g. Schmidt-Schütz and Huss,

1998). However, this will only occur if seed-trees and propagules of all species have

been maintained within the landscape.

The strong reliance on natural processes is linked to the concept of self-organi-

zation (Camazine et al., 2001), an important characteristic of complex adaptive

systems. In the case of CNTFM, however, self-organizing principles are utilized

in a limited context. Clear boundaries defined by management objectives are evi-

dent, for example, from the different utilization of self-thinning in deciduous and

in coniferous stands. The need for deviation from reliance on natural processes

and self-organization, and thus the implementation of management practices such

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as planting, thinning or pruning, will be decided by an assessment of whether or

not the stands are developing towards desired target structures and compositions.

This highlights how the focus on desired target structures and compositions can

subsume other aspects important for complex adaptive systems. How decisions to

plant, thin or prune affect the ability of ecosystems to respond to a variety of distur-

bances or environmental changes receives less attention in this context.

The importance of the emphasis on natural processes in terms of the public

acceptance of CTNFM cannot be underestimated (e.g. Edwards et al., 2012) and

is an indication of forests as open systems that cannot be separated from their

social context (Olsson et al., 2004). The general public acceptance of CTNFM

is at least partially due to a general positive perception of ‘nature’. In addition,

the emphasis on natural processes implies less reliance on social factors to ensure

adaptability of forest ecosystems. This is expressed in less costly remedies and

fewer external inputs, such as herbicides or fertilizer. In addition, this approach

requires less tolerance from the public in terms of accepting unsightly forest condi-

tions, such as recently clearfelled areas or perfectly aligned trees in monoculture

plantations. CTNFM also has high acceptance and is promoted by environmental

organizations (e.g. NABU, 2008).

Focus on the development of individual trees

Description. This principle is expressed in silvicultural practices that focus on

individual trees, specifically to benefit future crop trees. For example, harvesting

decisions are made on a tree-by-tree basis to ensure that trees are cut as close

to target diameters as possible. This ensures maximum value increment. Target

diameters are typically a function of size premiums, penalties for large diameters,

size-dependent growth rates and production risks (such as potential pathogens or

pests that increase with tree size and/or age) (e.g. Zell et al., 2004). Thus, target

diameters represent a tree’s economic optimum or economic maturity, when the

value increment culminates. It is important to note that the relatively long produc-

tion cycles and large dimensions are partially a result of using low interest rates in

economic calculations by many landowners in central Europe (often zero or less

than 2% or 3 %).

Through focusing silvicultural practices on individual trees, forest stands become

less important as management units. Instead, silvicultural interventions may be

focused on tending blocks that comprise multiple adjacent stands of variable ages,

compositions and structures. Using tending blocks also saves costs by concentrat-

ing management activities in one part of forest management districts, such as har-

vesting, log grading, road maintenance, regeneration, monitoring and tending

treatments. Also, operations are concentrated, leaving other parts of the forests

undisturbed. Tending efforts to optimize diameter and quality development of

individual trees often include frequent thinning operations during selected phases

of tree and stand development (e.g. Röhrig et al., 2006). Thus, typical CNTFM

operations may use tending blocks that comprise one fifth of management districts,

resulting in five-yearly return intervals for tending and harvesting operations. The

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frequent entries also highlight the importance of a good road infrastructure, espe-

cially in steeper terrain, which appears crucial for implementation of CTNFM.

Critique of the principle and relationship with complex systems

theory. The strong focus of CTNFM on the economic maturity of individual

trees has become a point of criticism. As has been pointed out, structural elements

important for wildlife habitat, such as habitat trees and standing or downed dead

wood, may be missing from forests managed under CTNFM, just as in forests

managed under the traditional even-aged monoculture paradigm (Bauhus et al.,

2009). Recent efforts push for increased integration of such structural elements

also in forests managed under CTNFM (Gustafsson et al., 2012, and see below).

However, the choice in scope and scale of these structural elements often appears

to be driven by specific wildlife habitat or biodiversity conservation concerns or

conditions found in nearby older forests. Whether these elements actually increase

the ability of ecosystems to respond to unexpected changes receives less attention.

For example, the size of retention patches may be driven by aspects of stability,

work safety, and so on, rather than ensuring that ecosystem processes are main-

tained at multiple spatial scales, which has been suggested as an important charac-

teristic of complex adaptive systems (Puettmann, 2011).

As mentioned above, in the absence of major disturbances, the avoidance of

clearfelling and associated use of single-tree or group cuttings leads to long regen-

eration periods. While this may allow many trees to participate in the regenera-

tion process (see above), it has also led to concerns that selection felling could lead

to a reduction in genetic variation and fitness, if the most vigorous trees with the

fastest diameter, which are harvested first, had no or only limited opportunities to

regenerate (e.g. Ziehe and Hattemer, 2002). However, the current understanding

of relationships between cutting systems, structural diversity of forests and genetic

diversity of tree species is not well developed. The general concern is that pref-

erential early removal of heterozygote individuals would affect allele frequencies

of uncommon alleles. These alleles, which are asymmetrically distributed, would

be discriminated against during target diameter harvesting and hence become

less frequent in the remaining stands, leading to lower frequencies of heterozy-

gote individuals in the following tree generation (Finkeldey and Ziehe, 2004). For

example, an inventory based on isozyme gene loci in Abies alba from Switzerland

and southern Germany showed slightly reduced levels of genetic variation in for-

ests managed under the CTNFM paradigm when compared with conventional

age-class forests (Konnert and Hussendörfer, 2001).

The focus on economic optimization of individual tree values highlights a shift

in scale of silvicultural interventions in close-to-nature forest management from

stands to smaller spatial scales, that is, single tree or small groups of trees (Schütz et

al., 2012). This is also reflected in various management practices, such as replacing

stand level rotation ages, which optimized the economic value of the whole stand,

with production cycles or target diameter harvesting. While the stand concept has

received much criticism (e.g. Puettmann et al., 2009), CTNFM has practically

replaced the focus on one spatial scale (stands) with that on another (trees). While

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smaller spatial scales inherently lend themselves better to bottom-up manage-

ment, complexity science strongly emphasizes the need for multi-scale approaches

(Chapters 1 and 2). Especially, concepts such as nonlinear feedback loops and

cross-scale linkages are hard to reconcile with the narrow focus on a single small

spatial scale. Further research is necessary to investigate whether optimizing value

and function at individual tree or small group scales will also result in optimal

accomplishment of stand and ownership or landscape level goals and especially

what the implications are for the adaptive capacity of ecosystems.

Mixed and uneven-aged, structurally diverse forests

Description. As mentioned above, recognition of the ecological value of mixed

species forests was one of the early motivations and inspirations for close-to-nature

forest management approaches. Since then, many studies in central Europe have

demonstrated that mixed species stands often have higher productivities than mono-

cultures and that they often offer greater economic and ecological stability (e.g.

Knoke et al., 2008; Pretzsch et al., 2010). Thus, this CTNFM principle and associ-

ated empirical knowledge and experimental evidence now have been integrated

in ecological research efforts investigating relationships between biodiversity and

ecosystem functioning. These efforts focus on two main hypotheses: a) ecosystem

productivity increases with the level of biodiversity and b) biodiversity enhances

ecosystem stability, which is interpreted as meaning that an increase in biodiver-

sity decreases the temporal variability of the provision of ecosystem services under

changing environmental conditions (Hooper et al., 2005; Loreau et al., 2002). The

latter is also called the ecological insurance concept and is based on the premise that

more diverse communities are better able to cope with new conditions when subject

to unpredictable stress or disturbance (Yachi and Loreau, 1999). For all these rea-

sons, the maintenance and further development of mixed-species forests is viewed

as one of the most important silvicultural strategies to facilitate forest ecosystems’

ability to adapt to climate change (Reif et al., 2010; Puettmann, 2011).

The general principles underlying productivity and stability of specific mixtures

in forestry are well researched, at least in two-species mixtures. However, great

uncertainty exists about the precise level and direction of interactions for specific

species combinations and site conditions (c.f. Pretzsch et al., 2010). For that rea-

son, silvicultural practices based on CTNFM (and other silvicultural approaches)

do not simply follow strategies to maximize tree species diversity, but rather aim

for specific mixtures of ‘compatible’ species, that is, selection and proportions of

species and their spatial distribution that maximize provision of ecosystem serv-

ices while minimizing tending efforts (Thomasius, 1996). For example, oaks and

other valuable hardwoods are cultivated with shade-tolerant, broadleaved trainer

species. Alternatively, conifers species (such as Norway spruce or Scots pine) are

mixed with shade tolerant broadleaves species to improve various aspects of bio-

diversity, nutrient cycling and productivity. Newer alternatives, such as cluster

plantings, provide for a long term mix of planted target and naturally regenerated

species (Figure 9.3).

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ionForests managed according to CTNFM principles typically have a high struc-

tural diversity with regards to different tree size classes and canopy layers at small

spatial scales. This is a direct consequence of the approaches outlined above,

including target diameter cutting, promotion of advance regeneration and spe-

cies mixtures. Assuming that biotic and abiotic disturbance agents affect trees of

specific size classes differently, diversity in tree sizes may offer a similar ‘insurance’

as species diversity (Brang et al., 2012). For example, large, thick barked trees are

likely to be more resistant to fires but they are also more susceptible to wind throw

than small trees of the same species. Other elements of structural diversity, such

as a diversity of differently sized dead wood, may provide more niches for a wider

variety of species (McElhinny et al., 2005). Also, a diversity of microsites in diverse

structured forests, such as microsites receiving different amount of sunlight, may

offer more regeneration opportunities than would otherwise be available (e.g. Sze-

wczyk and Szwagrzyk, 1996). Hence, in structurally diverse forests, it is more likely

that trees surviving specific disturbances may provide more legacy elements that

will facilitate self-organization than in less structurally diverse forests.

Figure 9.3 Planting of widely-spaced clusters of trees, such as oaks, to permit spontaneous regeneration of diverse tree communities between the clusters promotes the self-organization potential of forests when compared with conventional row planting.

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Critique of the principle and relationship with complex systems the-

ory. Increasing tree species’ diversity and stand structural attributes accords well

with the theory of complex systems of maintaining diverse and heterogeneous

elements to increase self-organization and adaptability of ecosystems. However,

much of the above considerations regarding mixing of species have been focused

on functional trait groups, that is, species traits that directly impact ecosystems

functions, such as timber production (Chapter 1). Less attention has been paid

to the mixing of species to maximize diversity of response type traits, meaning

traits that determine how species and ecosystems respond to perturbations, such

as different regeneration modes (with notable exceptions: Chapter 1; von Lüpke,

2009). This may be viewed as another indication of the relative importance of

economic factors under CTNFM and the underlying assumption of stable eco-

systems. In addition, the management of mixed-species stands has focused on

particular desired species combinations, deliberately excluding undesirable tree

species from the dynamic development of stands, and thus restricting the self-

organization of the system.

Another issue is the increasing pressure by conservation groups to restrict spe-

cies composition in CTNFM largely to native species (NABU, 2008). For example,

the enrichment of stands with non-native species, such as Douglas-fir (Pseudotsuga

menziesii) with a presumably high adaptive capacity towards future climatic condi-

tions, is discouraged (Reif et al., 2010). With the relatively low native tree species

diversity in central European forest, the desired adaptability to future conditions

may require a fresh look at introduced species. Clearly, assessing non-native tree

species as options to increase adaptive capacity of ecosystems will lead to chal-

lenges of the value of ‘naturalness’ under CTNFM (Reif et al, 2010).

Is close-to-nature forest management in central Europe compatible with managing forests as complex adaptive systems?

The question of whether close-to-nature forest management results in ecosystems

that are able to self-organize and adapt to changing conditions while providing the

desired ecosystem goods and services is at the heart of the previous discussion. It

is important to note that for a long time CTNFM was promoted by practitioners

without the benefit of a solid conceptual framework, such as is now available in

ecosystem ecology and complexity science. Clearly, many CTNFM principles and

practices, such as the emphasis on tree species diversity and structural heterogene-

ity at small spatial scales, can be viewed as an early attempt to apply principles that

are also embedded in complexity science (Chapters 1 and 2). Other aspects, such

as the emphasis on a limited set of spatial, temporal and hierarchical scales, the

focus on tree species diversity that emphasizes compatibility of growth pattern and

pays less attention to increasing the response type diversity (Chapter 1), as well as

limitations in terms of accepting the full suite of natural processes (such as larger-

scale disturbances), are not as closely aligned with characteristics and elements of

complex adaptive systems (Table 9.1).

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Differences in the view of hierarchical scales, an important concept in complex-

ity science, appear to show up in multiple dimensions of CTNFM. In complex-

ity science, the variety of scale – and especially cross-scale linkages and feedback

loops – are considered crucial for ecosystem adaptability; any silvicultural prac-

tice should be assessed on a variety of spatial and temporal scales using multiple

dimension, including ecological and social criteria. In contrast, most management

Table 9.1 Overview of the main principles of close-to-nature forest management and how they relate to characteristics of complex adaptive systems.

Principle Critique Relationship to complexity science

Site adapted Promotes ecological stability and Focus on local site conditions relatesspecies naturalness. Focus on native to bottom-up regulation and composition species may restrict adaptability self-organization of ecosystems. to future conditions/events. However, cross-scale interactions to the landscape level are largely ignored.Avoidance of Maintains structure and ecological Principle is in agreement withclearfelling processes of undisturbed forests emphasis on memory and legacies. (e.g. nutrient cycling). Facilitates If occurrence and severity of natural natural regeneration and focuses disturbance events are reduced, on development of individual trees. opportunities for self-organization Lack of disturbance may limit processes that require such large light-demanding tree species and disturbances are limited. reduce biodiversity. Focus on Reduced disturbances may Principle focuses on resistance andstability improve economic yields and less on resilience and adaptability provision of ecosystem services at of ecosystems. small spatial scales. Disturbance- dependent species may decline. Reliance on Reduces management inputs and Principle is linked to the concept ofnatural costs. Promotes natural selection self-organization, but clearprocesses processes. Improves public boundaries for stand development acceptance of forest management. are set by targeted stand structure and composition.Focus on Optimizing economic development Whereas smaller spatial scales lenddevelopment of individual trees. Reduced themselves better to bottom-upof individual regeneration opportunities for management, complexity sciencetrees shade-intolerant species and strongly emphasizes the need for reduced genetic diversity through multi-scale approaches. removal of fittest trees. Mixed and Higher productivities and greater Increasing tree species diversityuneven-aged, economic and ecological stability promotes diversity and heterogeneitystructurally than monocultures. that favours adaptive capacity ofdiverse forests ecosystems. Focus on functional types (e.g. compatibility of growth patterns), with less attention paid to response type traits, i.e. response to perturbations, limits adaptive capacity.

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activities under CTNFM are narrowly focused on trees and do not give the same

attention to larger spatial scales, such as a landscape or region.

For many management and conservation aspects, as well as elements of propa-

gation of pests and fire, these large-scale properties (such as distributions of tree

species and forest types, forest ages, areas under protection or conservation ease-

ments and viability of populations or species) are of particular importance. More

recently, such landscape considerations have also entered forest planning of large

public forest owners (Braunisch and Suchant, 2007) leading to substantial modi-

fications of close-to-nature forest management approaches; for example, the sub-

stantial reduction in stocking volumes in high elevations of the Black Forest to

increase habitat suitability for capercaillie.

A second aspect, which appears in the various sections above, is the accept-

ance of the inherent unpredictability of complex adaptive systems. On the one

hand, CTNFM embraces uncertainty and self-organization as it allows for natu-

ral processes to play out, such as natural regeneration and self-thinning. On the

other hand, CTNFM places firm boundaries on how to deal with uncertainty and

for the use and development of natural processes in managed forests, based on a

limited set of target stand structures and compositions, as evident in the emphasis

on forest development types and avoidance of larger-scale disturbances, such as

clearfelling.

Overall, the above discussion indicates that CTNFM already addresses many of

the characteristics of complex adaptive systems and has a great potential to benefit

from embracing complexity science as a conceptual framework. This framework

would allow researchers and foresters to assess how forest management practices

can be modified to improve ecosystems’ adaptive capacity and self-organization.

In the meantime, general claims about ecosystem adaptability should be viewed

with caution, such as claims that CTNFM is a suitable management option to pro-

vide for adaptation of forest to climate change (e.g. Schütz et al., 2012; see Brang

et al., 2012). These claims typically use traditional forest management as refer-

ence, and simply highlight the higher species and structural diversity at smaller

spatial scales without taking into consideration the highly uncertain future and the

ability of such an approach to be able to adapt to unknown future ecological and

socio-economic conditions. The apparent tradeoffs between adaptation to cur-

rent conditions and adaptability to future conditions (Puettmann, 2011; Chapter

1) suggest that a closer examination of CTNFM in terms of adaptability may be

beneficial in this context. Consequently, an analysis of ecosystem adaptability of

forests managed under CTNFM should be based on broad assessments that go

beyond specific goals and intentions of landowners and include landscape aspects,

such as natural disturbance patterns and the full suite of societal demands and

expectations.

Lastly, close-to-nature forest management poses numerous challenges as many

ecological interactions and processes and their responses to silvicultural treatments

and disturbances (such as climate change) are not well understood (Puettmann,

2011). The outcomes of any specific treatments or treatment intensities cannot

be predicted within tight boundaries. Hence, CTNFM with its relatively short

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history must be understood in the context of an adaptive management approach

that requires close observation and monitoring of outcomes and adjustment of the

approach as needed. Clearly, setting wider boundaries for future development of

forest ecosystems would probably provide more opportunities for diversification of

forests over the European landscapes. Less predictable development of forests and

landscapes, however, also require the willingness to adjust silvicultural concepts on

a continuous basis, and complexity science appears to provide a framework that

will facilitate this process.

Conclusion

Close-to-nature forest management (CTNFM) is widely held as an approach

that optimizes multiple forest functions at small spatial scales. Here we reviewed

the main principles of this approach, discussed their merits and limitations and

analysed to what extent they compared to principles expressed in complexity sci-

ence. The main principles of close-to-nature forest management reviewed here

comprise the use of site adapted tree species, development of mixed and uneven-

aged structurally diverse forests, avoidance of clearfelling, focus on stand stabil-

ity, reliance on natural processes and focusing on development of individual

trees. Many principles and practices of close-to-nature forest management, such

as the emphasis on diversity and structural heterogeneity, agree with principles

that are also embedded in complexity science. However, other aspects, such as

the emphasis on a limited set of spatial, temporal and hierarchical scales and

tight boundaries set for target structures and compositions, pay less attention

to increasing the response type diversity, and hence adaptability of forest eco-

systems are not as closely aligned with characteristics and elements of complex

adaptive systems. Although CTNFM embraces uncertainty and self-organiza-

tion as it allows for natural processes such as natural regeneration and self-thin-

ning, there is limited acceptance of the inherent unpredictability of complex

adaptive systems as evident in the emphasis on forest development types and

avoidance of larger-scale disturbances. We discuss such discrepancies in the

context of the different origins and goals of the two approaches. Our analysis

indicates that CTNFM could benefit from embracing complexity science as a

conceptual framework to assess the influence of its management practices and to

develop or adopt complementary approaches to promote the adaptive capacity

of forest ecosystems.

Acknowledgements

We are very grateful for the helpful and constructive suggestions for improve-

ment that we received for earlier versions of this chapter from Christian Messier,

Christian Ammer, Timo Kuuluvainen and Lluis Coll. Thanks to Ursula Eggert

for formatting the text and references. And we wish to thank the many colleagues

with whom we had the pleasure of discussing our views on close-to-nature forest

management and complex adaptive systems over the years.

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