Dynamic processes in the seconDary communities Grażyna Łaska
Politechnika Białostocka, Chair of Protection of Soil and Land Surface, Białystok, Poland
Abstract
Process of forest restoration after clear-cutting within the entire potential biochora is an example of secondary succession. The recreative secondary succession leading to recovery of a permanent climax community takes place when the process of transformation concerns small changes in the layer structure and floristic composition of the community but does not include irreversible changes in the habitat. The latter provides an opportunity to recover of the damaged structure of the tree stand and species composition of the original community. This process shows certain differences dependent on the fertility of habitats and biological properties of the main edificators, i.e. certain tree species determining the vertical structure of future tree stand. It has been established that the poorer the habitat the easier recovery of a permanent climax community in the process of recreative secondary succession. This regularity was observed mainly for communities growing in poor and dry pine stand habitats for which it is the easiest to reach a climax form and which have the greatest chance of returning to lost habitats.
Recreative secondary succession is also possible in medium-fertile or fertile habitats, however, it is more difficult there. The problem is related to the age of main edificators reproducing the future final community, and to the time needed to attain appropriate age and spatial structure of populations of particular tree species.
Supposedly a longer time required for reproduction of the final deciduous community implies a possibility of greater diversity of development towards new forms of communities in the process of creative secondary succession.
Creative secondary succession leads to the appearance of new forms of communities. As follows from the observations in the Knyszyn Forest, the communities occurring in medium-fertile habitats are easily subjected to spruce expansion which leads to the appearance of pine stand-like communities and in time can create new types of pine stand communities.
Introduction
The material presented comprises preliminary synthesis of results collected in 10 years of study devoted to identification and classification of secondary communities
(post-clear-cutting and young tree communities), according to the transformation they underwent. The aim of this report is not only a description of the floristic composition and structure of the communities renewing in the sites after clear-cuttings, but mainly the presentation, the directions and rate of such communities, development and factors determining the course and laws of their transformation. Explanation of the mechanisms of formation and development of communities after clear-cuttings is essential for determination of the course of the initial stages of secondary succession and directions of development of forest communities subjected to anthropopressure.
The area of study
Dynamic processes on sites after clear-cuttings was studied in the Knyszyn Forest, in the north-eastern Poland. The study was carried out in the communities representing three types of deciduous forests, known as hornbeam forests: linden-oak-hornbeam forest - Tilio-Carpinetum (Traczyk, 1962), oak-hornbeam forest - Melitti-Carpinetum (Czerwiński, 1978), and maple-linden forest - Aceri-Tilietum (Faber, 1936); and in three types of coniferous forests, known as pine and spruce stands: wet mixed - Querco-Piceetum (Mat et Pol, 1956), fresh mixed - Serratulo-Piceetum (Sokołowski, 1966) and high needle – Carici digitatae-Piceetum (Czerwiński, 1978). Observations were made in natural communities as well as in the communities appearing after clear- cutting, in young tree stands and in the secondary forest communities of each particular dynamic vegetation circle (Schwickerath, 1954).
The communities studied were selected as representing specific links in the vegetation developmental series (Pawłowski, Zarzycki, 1972). The associations of Tilio-Carpinetum and Querco-Piceetum are specific vegetation series which form characteristic physiocenoses of thawed-out basins in flat terrains with a shallow ground water table and occupy clay or dusty pluvial-gley soil. The associations of Aceri- Tilietum, Melitti-Carpinetum, Serratulo-Piceetum and Carici digitatae-Piceetum form physiocenoses characteristic of creviced glacial deposits - kames which are sandy- gravely hills with deep ground water table and whose presence is related to red and brown soils (leached or podzoiled soil in coniferous forest) (Czerwiński, 1995).
Methods
Phytosociological studies of secondary communities were conducted in the entire Knyszyn Forest in 1987-1997. The communities were described on the basis of 536 phytosociological records, including 97 taken at post-clear-cutting sites, 158 of young tree communities and 281 of secondary forest communities. The records were made according to the commonly accepted Braun-Blanquet method of 255 plots size 200 m2 (10 x 20 m) at post-clear-cutting sites and young tree communities, and of 281 plots size 400 m2 (20 x 20 m), at the secondary forest communities. Plots were chosen taking into account the time of clear-cutting, way of tree stand recovery - spontaneous or artificial, the age of renewing communities and the type of vegetation. The records were arranged in 72 tables of communities and organised in 5 synthetic tables of
constancy. The records were analysed by numerical syntaxonomy, using the Multi- Variate Statistical Package, version 2.1 – KCS.
Results
The results enabled identification of the forms of post-clear-cutting and young tree communities originating from the same natural community and allowed their classification in respect of the direction and rate of development of post-clear-cutting vegetation and the factors determining the course and rules of floristic changes.
Identification of secondary post-clear-cutting and young tree communities Results of numerical analysis revealed significant differences in the communities studied related to the habitat conditions as well as the structure and floristic composition. Taking into regard the initial natural communities, the following identification of syntaxons was made:
Post-clear-cutting communities:
• post-clear-cutting community from the Aceri-Tilietum circle with Stellaria holostea;
• post-clear-cutting community from the Tilio-Carpinetum circle - Agrostis-Rubus idaeus;
• post-clear-cutting communities from the circles of Melitti-Carpinetum, Serratulo- Piceetum, Carici digitatae-Piceetum, Querco-Piceetum - Calamagrostis arundinacea.
Young tree communities:
• young tree community from the circles of Aceri-Tilietum and Tilio-Carpinetum – Corylus-Agrostis.
• young tree communities from the Tilio-Carpinetum circle – Betula-Stellaria, Quercus- Stellaria, Betula-Agrostis, Picea-Agrostis.
• young tree communities from the circles of Tilio-Carpinetum and Querco-Piceetum - Pinus-Oxalis.
• young tree communities from the circles of Melitti-Carpinetum, Serratulo-Piceetum, Carici digitatae-Piceetum - Betula-Calamagrostis arundinacea, Betula-Descham- psia, Pinus-Calamagostris, Larix-Calamagostris.
Directions and stages of development of post-clear-cutting and young-tree communities.
In the first years after clear-cutting, the secondary succession is an ordered and directional process. In the first phases (0.5 to 5 years) it leads to the appearance of post- clear-cutting communities (see Fig. 1). At this stage, character of the final community can hardly be determined. Its prediction is the more difficult, the younger clear-cutting, and depends significantly on the habitat transformations caused by man (the way of cutting, soil cultivation, soil preparation for forestation, introduction of tree species foreign to a given habitat).
In the most fertile type of oak-hornbeam forest Aceri-Tilietum the communities forming after clear-cutting (with Stellaria holostea) are the least different from the natural communities in respect of the species composition (see Fig. 2, Photo 1). An undergrowth is mainly formed by eutrophic oak-hornbeam forest species from the order Fagetalia and class Querco-Fagetea, with a small contribution of the species from the classes: Epilobietea-Angustifolii, Molinio-Arrhenatheretea, and some accom- panying species.
In the communities from circle Tilio-Carpinetum a transformation of the habitat after clear-cutting may lead to development of post-clear-cutting communities dominated by clearing species from Epilobietea-Angustifolii class with a large contribution of Rubus idaeus and a large group of grasses, mainly from the genus Agrostis (Agrostis-Rubus idaeus), but with a reduced contribution of hornbeam species (see Fig. 2, Photo 1).
In the oak-hornbeam communities of Melitti-Carpinetum and pine stand communities Serratulo-Piceetum, Carici digitatae-Piceetum and Querco-Piceetum, the typical component of tree stands is pine, whereas the undergrowth is made by oak-hornbeam and pinewood species occurring at a similar constancy or pinewood species are dominant. A certain species composition in combination with deep habitat transformation as the result of clear-cutting may lead to development of post-clear- cutting communities of pinewood character (with Calamagrostis arundinacea) (see Fig. 3, Photo 2). Older post-clear-cutting sites are colonised by heliophilous and pioneer woody species at an increasing number of pinewood species from the class Vaccinio-Piceetea.
A subsequent stage in development of post-clear-cutting vegetation is the achievement of density by young trees and formation of the structure of young tree community (see Fig. 1). At this developmental stage, dynamic processes can lead to restoration of the initial oak-hornbeam forest or pine stand communities as the result of recreative secondary succession or create new kinds of communities as the result of creative secondary succession. The final result significantly depends on whether the further development of vegetation is spontaneous or a given clear-cutting is subjected to procedures aiming at artificial pine reafforestation.
In case of spontaneous shaping of young tree communities the following mechanisms of vegetation transformation were established. In habitats from Aceri- Tilietum and Tilio-Carpinetum circles the oak-hornbeam character of felling sites can establish. If natural restoration is weak, the shrub layer is formed by abundantly growing Betula pendula while an undergrowth may be dominated by expansively regenerating hornbeam species (Betula-Stellaria) (see Fig. 2, Photo 3). Otherwise the receding or removed birch trees may be replaced by natural recovery of tree stand, including particularly dynamically developing hazel (Corylus-Agrostis) or naturally or artificially recovering oaks (Quercus-Stellaria) (see Fig. 2, Photo 3). In young tree communities a well developed shrub layer determines changes in the light conditions which restricts the presence of heliophilous and pioneer woody species and leads to a change in the floristic composition of young tree communities. The shade-loving and shade-tolerating hornbeam species become increasingly abundant. Their dynamic
development may determine the course of transformations into the final oak-hornbeam community.
In certain Tilio-Carpinetum habitats abundantly growing grass herbal layer may significantly restrict regeneration of oak-hornbeam species. At the stage of young tree community development, Betula pendula rises to a dominant position in the shrub layer, and the herbal layer is composed of numerous grass species of Agrostis genus. Consequently, a new type of post-clear-cutting community develops (Betula- Agrostis) characterised by an abundant shrub layer and grass type vegetation (see Fig.
2). Apart from birch trees, the shrub layer includes natural regenerations of spruce trees (the constancy in herbal layer 100%). Greater expansion of spruce trees and their considerable contribution to young tree community may determine the development of the young tree community Picea-Agrostis (see Fig. 2).
Different tendencies in vegetation transformation were noted in the sites with artificial reafforestation of pine stand in Tilio-Carpinetum habitats (see Fig. 2). A compact layer of young pine trees significantly restricts an access of light to the floor and thus limits herbal layer development. As the result a characteristic type of much shaded young tree community - Pinus-Oxalis - is formed. Similar relations were found in the Querco-Piceetum habitat (see Fig. 2).
The process of spontaneous shaping of young tree communities in the hornbeam habitats of Melitti-Carpinetum and pine stand habitats Serratulo-Piceetum, Carici digitatae-Piceetum is of a bit different character. The pinewood type of post clear-cutting communities is preserved. In the young tree community, herbal layer is dominated by Calamagrostis arundinacea accompanied by Deschampsia caespitosa or other Agrostis genus species, developing into different variants, depending on the type of habitat. In the shrub layer Betula pendula dominates, and a qualitatively different type of young tree community - Betula-Calamagrostis or Betula-Deschampsia is formed (see Fig. 3, Photo 4). A general tendency to become a pine stand type community, while preserving a considerable number of oak-hornbeam forest species in the composition of Betula-Calamagrostis and Betula-Deschampsia communities, may indicate renewal of the initial natural communities as the result of recreative secondary succession (see Fig. 3).
The direction of changes in young tree communities with artificial pine stand re-afforestation in habitats of Melitti-Carpinetum, Serratulo-Piceetum and Carici digitatae-Piceetum circle is different than in the habitat of Tilio-Carpinetum. In the former habitats, apart from artificially grown pine, reed grass is still a dominant component of the herbal layer which provides good conditions for other kinds of grass (Agrostis, Poa, Festuca) and pinewood species. This leads to formation of a new type of young tree community - Pinus-Calamagrostis (see Fig. 3, Photo 4). Moreover, frequently apart from abundant grass (Calamagrostis arundinacea and Agrostis tenuis) an important component of these habitats becomes artificially introduced Larix decidua.
This leads to formation of an artificially initiated type of young tree community Larix- Calamagrostis, characterised by medium-development of the shrub layer (cover coefficient 31%) and mostly grass-like vegetation (see Fig. 3).
Predominant contribution of pinewood elements to the species composition
of the above communities determines the direction of dynamic processes towards formation of pine stand communities (Melitti-Carpinetum habitat) in the process of creative secondary succession or renewal of pine stand communities (in pine stand habitats) as the result of recreative secondary succession (see Fig. 3).
Regularities in development of structure and floristic composition of secondary communities
Results of the studies proved that the floristic composition of post-clear- cutting and young tree communities and the direction of vegetation transformation during succession depend to a significant degree on the habitat conditions and floristic
Fig. 1. Regularities in development of structure and floristic composition of secondary communities.
Fig. 2. The directions and stages of development of post-clear-cutting and young tree communities from the circles of Aceri-Tilietum, Tilio-Carpinetum and Querco-Piceetum.
compositions of natural initial phytocenoses which determine the species composition of particular communities. However, it has been established that irrespective of the type of habitat in early phases of forest development there is some ecological uniformity of anthropogenically transformed communities. Floristic similarity of oak-hornbeam and pinewood post-clear-cutting sites in an early stage of development permits formulation of general regularities of structural and compositional deve-lopment of secondary communities (Łaska, 1996). The young tree and post-clear-cutting communities are found to be characterised by the following features (see Photos 1-4):
• the initially non-forest stage of forest development and simplified vertical structure;
• dynamic sequence of quantitative and qualitative changes in the contri- bution of particular groups of species in the floristic composition of the communities.
In early stages of development (6 months to 5 years), the post-clear-cutting communities are characterised by enhanced invasion of non-forest species. Changes in vegetation at this stage depend significantly on the age of clear-cuttings. The degree disturbances of post-clear-cutting communities is the greater the younger the clear- cutting (Łaska, 1996).
The young tree communities (8 to 15 years old) are characterised by a strong competition among the phytocenoses components. Greater migration abilities of non- forest components (pioneer woody, anemochoria) than the surviving or recovering permanent components of oak-hornbeam and pine stand phytocenoses (heavy-seed, vegetative reproduction) frequently determine the dominance of the former and their much longer preservation in the species composition and structure of the secondary Fig. 3. The directions and stages of development of post-clear-cuting and young tree communities
from the circles of Melitti-Carpinetum, Serratulo-Piceetum and Carici digitatae-Piceetum.
community. In the case of much trouble in elimination of foreign species, in the oldest young-tree communities (15 to 20 year old) a new form of communities start to appear, or when the species typical of the original community have higher competitive abilities - the natural initial community starts to recover (Łaska, 1996). The fact of creation of new vegetation units as the consequence of another direction of transformations - post clear-cutting hornbeam communities into pine stand communities as the result of creative secondary succession - was noted for young-tree communities Pinus- Oxalis, Pinus-Calamagrostis, Larix-Calamagrostis (Fig. 2-3). Restoration of the initial natural community as the result of recreative secondary succession was observed for young-tree communities Corylus-Agrostis, Betula-Stellaria, Quercus-Stellaria, Betula- Agrostis, Picea-Agrostis, Betula-Calamagrostis, Betula-Deschampsia (see Fig. 2-3).
References
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POST-CLEAR-CUTTING COMMUNITIES with STELLARIA HOLOSTEA from the Aceri-Tilietum circle
AGROSTIS-RUBUS from the Tilio-Carpinetum circle
photo 1. Post-clear-cutting communities from the circles of Aceri-Tilietum and Tilio- Carpinetum.
POST-CLEAR-CUTTING COMMUNITIES
with CALAMAGROSTIS ARYNDINACEA from the Melitti-Carpinetum circle
with CALAMAGROSTIS ARYNDINACEA from the Serratulo-Piceetum circle
photo 2. Post-clear-cutting communities from the circles of Melitti-Carpinetum and Serratulo-Piceetum.
YOUNG-TREE COMMUNITES
BETULA-STELLARIA from the Tilio-Carpinetum circle
QUERCUS-STELLARIA from the Tilio-Carpinetum circle
photo 3. Young-tree communities from the Tilio-Carpinetum circle.
YOUNG-TREE COMMUNITIES
BETULA-CALMAGROSTIS from the Melitti-Carpinetum circle
PINUS-CALAMAGROSTIS from the Serratulo-Piceetum circle
photo 4. Young-tree communities from the circles of Melitti-Carpinetum and Serratulo- Piceetum.
