Old-growth forests and silviculture in the Italian Alps


What is an old growth forest?


There are dozens of definitions of old-growth forests along with similar terms like pristine, climax and ancient forests (LUND, 2000).
According to PETERKEN (1996), old-growth forests develop during long periods of freedom from catastrophic disturbances. They are the climax forests of Clementsian terminology (CLEMENTS, 1916), but they are not static.
The concept of climax, a relatively stable community condition toward which succession proceeds, lost much of its value as ecologists began to describe climax vegetation as "varying continuously across a continuously varying landscape" (SPIES, 1997). It is now becoming widely accepted that the periodic destruction of single stands is a normal part of the forest life cycle.
In the absence of human activity, the destruction of forest stands is due to natural disturbances defined as "any relatively discrete event that changes the structure of the ecosystem, the community or the population, and hence modifies the physical and functional characteristics of the system" (PICKETT ET AL., 1989).
Natural disturbances can be characterized by frequency, by the area covered, and by magnitude. Disturbances can be divided into two categories: "minor disturbances" (which leave some of the pre-disturbance trees alive) and "major disturbances" or "stand-replacing disturbances" (OLIVER, 1981). The frequency of minor disturbances is higher than that of major disturbances. The latter's frequency is usually higher than the average life of a single individual and are described by Harper (HARPER, 1977) as "catastrophes". Following a disturbance, there are different stand development patterns and processes that occur depending on various environmental and site factors.
According to OLIVER and LARSON (1996), old-growth implies a uniformity of process. They describe "transition old-growth" as a stand that contains some trees which were established after the initial disturbance as well as large and numerous younger trees of allogenic origin, whereas "true old-growth" is described as a stand composed entirely of trees which have developed in the absence of allogenic processes.
Old-growth forests are "later stages in forest development that are often compositionally and always structurally distinct from earlier successional stages" (FRANKLIN & SPIES, 1991). Not all virgin forests are "old-growth" because this term refers only to the late successional stage of a virgin forest. Old-growth forests can also develop after human disturbance. The age at which stands develop old-growth characteristics varies widely according to forest type, climate, site conditions and disturbance regime (HUNTER & WHITE, 1997), and range between 150 years in the "boreal forests" and more than 300 years in the "temperate rain forests".
Another widely recognised characteristic of old-growth forests is that they remain relatively unmanaged by humans, indeed their structure and composition are determined mainly by natural events and natural disturbances are allowed to shape much of the forest.
The processes that take place in old-growth forests imply certain structural characteristics with significant ecological and aesthetic values: "large and old trees", coarse woody-debris, "laying dead trees", "snags", an abundance of dead organic material, and large and small canopy gaps formed by trees that have fallen. Their composition and structure change constantly as the individuals of each component species regenerate, grow and die.
Old-growth forests are very important from a variety of vantage points (PETERKEN, 1996): wildlife and plant habitats (richness in rare animal and vegetal species), scientific research (natural processes, environmental monitoring), aesthetic and cultural values, historical roots of nature conservation, and as a fundamental reference point for naturalistic silviculture aimed to better achieve a mix of environmental and commodity objectives (FRANKLIN, 1991).



Are there old-growth forests in the Italian Alps?


Old-growth forests are becoming increasingly rare. As a matter of fact, there are only three countries where a consistent number of these forests still exist: Canada, Russia and Brazil.
In Europe, and particularly in the Alps, past human activity has affected most forests. Indeed, the majority of forests in the Italian Alps have been modified by man in some way, either through direct periodic destruction of the forest or by more subtle forms of management and habitat manipulation.
Human activity, which peaked during the 19th century, has modified these forests in various ways: large forest areas have been destroyed, and the natural composition and structures of forests have been affected by logging, burning, grazing and clearing for agricultural purposes. Natural disturbance regimes have been replaced by disturbances of human origin linked to economic and social development.
Consequently, land-use and forest-use history are fundamental determinants in shaping vegetative composition and stand structure in forests, and this cultural legacy has important implications for the present-day structure and composition of forest ecosystems and for forest management. For this reason, it is very difficult to find stands with "old-growth properties" in the Italian Alps.
The few stands that do have these properties are small and, at any rate, demonstrate some evidence of past human activity.
Since the beginning of the 20th century, there has been a noticeable reduction in many human activities in these forests, such as the grazing of domestic animals and tree felling. As a result, many forests have developed naturally over the past few decades, even if their composition and structure still reflect human activity.



Old-growth forests and silviculture in the Italian Alps


Given the lack of old-growth forests in the Italian Alps, it is clearly important to study present-day forests that are no longer cultivated and to establish permanent plots where the natural dynamic of these forest stands can be observed in the absence of human intervention.
These areas can be usefully exploited as a reference point for forest management and for the application of a naturalistic silviculture and will provide an important opportunity to investigate natural disturbance processes, forest dynamics and other ecological and biological insights (FOSTER et al., 1996).



Some example of stands with "old growth properties" in the European Alps.

Fondo Valchiusella (Piemonte, Italy). Old silver fir protective stand

Swiss National Park (Engadina, Switzerland). It has been free from antropogenic disturbances since 1913.

Paneveggio (Trento, Italy). Previously managed stand with few human interventions during the last century

Derborence (Valais, Switzerland). Stand originated more than 200 years ago after a landslide.

Alev� (Piedmont, Italy). The largest pure Swiss stone pine stand in the Alps.

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