Forest Club model projects and sites

Secondary Forests

The overwhelming majority of taiga forests in European Russia have been severely altered in terms of structural and dynamic organization and are therefore classified as secondary forests. However, determining the exact share of secondary forest is difficult, especially in the absence of firm criteria for classification of primary and secondary stands. There is no consensus on the stages of restoration after a disturbance in which a forest should be classified as secondary, or to what extent a forest that has been disturbed by selective cutting should be called secondary. There are some fairly universal agreements - the first forest generation on a clearcut, on abandoned agricultural land, or on a quarry are all regarded as secondary. Even if a very narrow interpretation of secondary is used, it is clear that secondary forests form the general background condition in the taiga, with the exception only of the northernmost part of the territory. While primary stands of indigenous old-growth can be found selectively scattered, a sea of secondary forest surrounds them.

In Karelia, two-thirds of the forested area was harvested during the second half of the twentieth century (Gromtsev, 2000), with the situation in other regions more or less the same. Already at the latitude of the Leningrad, Vologda, and Kirov Regions, spontaneously reforested agricultural lands, abandoned during the period of collectivization and later, represent a significant share of the forest, and further south it may represent as much as 20-30 percent of the total forest area. Taking all of this together, a conservative estimate finds secondary forest makes up three-quarters of the forested land in the taiga of European Russia. With inclusion of even-aged spruce forests, formed as a consequence of selective cutting of pine (see Figure 26) or even-aged stands on gigantic fire scars, the share of secondary forest becomes even larger..

Fig. 20. Young birch forest on the site of a 30-year old clearcut. Arkhangelsk Region. Photo: A. Yaroshenko.

Secondary forests are very diverse, not only because of site differences but also due to variations in their history of human intervention. Still, it is possible to identify a few typical characteristics that distinguish them from intact taiga.

First and foremost, severe anthropogenic disturbances, leading to the death of the stand either in substantial parts or in its entirety, create stands with a significantly simplified spatial structure. The least architecturally complex forests are formed on the most severely disturbed parts (abandoned agricultural lands or clearcuts), with a very even canopy of secondary growth trees, most often birch and gray alder (Figure 21,a). Any older forest ecosystem fragments that might have survived the disturbance (such as pockets of undergrowth, residual small-diameter trees after clearcutting, stands or trees that happen to survive fire) add some complexity to the structure and composition of the new forest (Figure 21, b).

The evenness in structure and age is often carried over into the first re-growth layer, appearing under the canopy of pioneer deciduous species (see Figure 21, c). Intensive selective cutting in which all large-dimension trees are removed and mainly only undergrowth is retained also lead to the creation of simplified stands (Figure 21, d). In intact forests the main elements of spatial diversity of the stand and other forest layers at a particular site are connected with natural spontaneous disturbances; in secondary forests they are most often generated by diversity of technical interventions such as skid lines, landings and roads (Pautov, 1992; Yaroshenko et al., 1998).

The majority of inarguably secondary forests are characterized by a considerable mixture of pioneer deciduous tree species (birch, aspen, Gray Alder, Goat Willow), the seeds of which are easily carried over large distances by the wind and the seed production of mature trees is very large. Forests with an absolute domination of pioneer deciduous species are especially typical of the large (landscape size) clearcuts of the 1950's through 1980's. Then, the living conditions (microclimate, ground cover, etc.) of the trees were radically changed, while at the same time practically all sources of coniferous seeds were removed.

The simplified and homogeneous stand structure in secondary forests is associated with significant changes in other forest layers. Many microhabitats disappear under the forest canopy, such as fallen trees and features of micro-topography, formed when trees fall over along with their root systems. Also, the mosaic of gaps and illumination under the canopy is simplified. The result is a drastic reduction in the diversity of ecological conditions under the canopy, impoverishing the local flora and causing the gradual disappearance of individual species. It has been established that the disappearance of at least some species is connected not so much with the dramatic changes in ecological conditions that occur during the first years after a radical disturbance as with the simplification of the habitat diversity that follow the establishment of a closed secondary stand (Yaroshenko, et al., 1998). The restoration of the original structure of grasses and mosses is delayed in a similar fashion in comparison with the re-establishment of the original structure of the tree layer. Many forests in which the original stand structure has been restored following radical anthropogenic disturbances may still hold some characteristics typical of secondary forests such as the layer of grasses and mosses. We conclude that an assessment limited to the tree layer does not allow a full measurement of the degree of anthropogenic disturbance in a forest ecosystem or the degree to which its natural structural and dynamic organization has been restored.

Fig. 21. Secondary forest structures. See body text above.