Knowledge of species–habitat relationships is important in understanding vegetation patterns in forested landscapes [1
]. Those relationships are also an important topic within the framework of the assessment of protected areas and their effectiveness in the conservation of forest vegetation biodiversity [2
]. In Central Europe, studies on interactions between forest vegetation and environment have been focused on various parameters, such as the niche breadth of tree species under the soil nutrient [5
]; forest vegetation and land-use changes [6
]; forest vegetation to topographical-soil gradient [7
]; beech and spruce forest to soil chemical properties [8
]; and environmental controls of plant species richness [9
Deciduous temperate forest vegetation–environment relationships have been studied globally across various patterns along geographic and environmental gradients [11
The existing vegetation is a result of the complex interaction of historic and recent environments and human disturbance factors [16
]. Relationships between environment and plant community have often been studied in areas where human disturbance is minimal, such as in protected areas [17
]. Only a few studies have taken place in areas with human disturbance [18
]. Disturbance may sometimes override the site's influence, especially in forested areas where human disturbances have a long history and play a key role in land-use changes.
Broadleaf deciduous forests are the dominant natural vegetation of Central Europe [19
]. The most important broadleaf deciduous forests across Europe, especially Central Europe, are a mixture of either beech and oak forests or beech-dominated forests, and they are important from ecological and socio-economic points of view [20
]. This also applies to the forests of Slovakia, which mostly consist of broadleaf deciduous species (63%), although some forested areas at higher altitudes are dominated by coniferous tree species (37%). The dominant broadleaf deciduous species are European beech (Fagus sylvatica)
and Sessile oak (Quercus petraea
. Of those forests, 73% are managed and only 23% are not disturbed by human impact (e.g., forests in protected areas).
The concept of ecological species groups is useful in classifying natural communities, determining changes in vegetation, understanding vegetation distribution and environmental factors, estimating species niches, calibrating indicator values for species, modelling the potential distribution of species and plant communities, and assessing habitat quality [21
]. The challenge for research into intensively managed forests is to correctly classify forest stands into species groups, because the traditional phytosociological classification was created for forests with a minimal impact from forest management. For this reason, we used the ecological species groups (ESGs) concept as suggested by the study [22
]: ESGs are comprised of plants that repeatedly occur together when certain combinations of site factors occur under certain type of forest management. They are species that are perceived to have similar ecological requirements and tolerances as regards environmental stresses and limitations. ESGs are detected by their species composition and abundance patterns among sampling plots. ESG-associated species have similar environmental features. These groups help with the descriptions and the mapping of forest ecosystems in the field through their presence or absence and by the relative coverage of plants in each group.
Forest management consists of anthropogenic disturbances which are able to modulate ecological features [23
]. Forest management generally affects abiotic factors in deciduous forests [24
], such as microclimate [25
] and soil nutrients content and dynamics [27
]. Tree cutting and coppicing are the most widespread management regimes which affect forest composition, structure and recovery, especially in southern European deciduous forests [28
], where mature and old growth forests are rare. On the other hand, growth managed forests in Central Europe occupy a significant area and certain parts of them are both economically and environmentally valuable. Despite the ecological research mainly focusing on the remnants of primeval forests or forest habitats with lower human impact [29
], some local studies also deal with various aspects of managed temperate forests ecology [32
]. As indicated in some studies [35
], there are ESGs of herbaceous species in lowland coppice forests. Thus, we presumed that other types of forest management also create a basic ecological framework for ESGs of herbaceous species.
The main aim of this study was to investigate the relationship between forest herbaceous vegetation and environment in a forested landscape in the Western Carpathians (Slovakia). In this area, clear-cutting forest management has been in progress since the end of 18th century without any significant changes in land-use to present [37
]. This unifying long-term forest management enabled this study to focus on the natural drivers behind and the classification of ecological herbaceous species groups in managed temperate deciduous forests, in order to improve our understanding of the distribution of ESGs as a potential support tool for sustainable forest management.
In Europe, there have been some classifications of natural forest habitats developed traditionally (since of the beginning of the 20th century). Phytosociological classification (the so-called Zurich–Montpellier approach) is the well-known and widely applying classification system of natural plant communities [42
]. Specifically, geobiocenology has been used in Central and East Europe as a classification system focused on natural forests [54
]. Recently, CORINE [55
] and EUNIS [56
] classification systems have been developed. The newest classification system of natural habitats based on vegetation mapping is a classification system under Natura 2000 European network [57
], which is developed in detail in some European countries by creating of national catalogues of natural habitats (in Slovakia, see [68
]). Many studies [58
] have analyzed the impact of various environmental variables on plant species in the natural forests of Slovakia, but only 23% of forests in Slovakia are non-managed natural or semi-natural forests. However, most of our understanding of forest vegetation–site relationships in Slovakia comes from studies performed within forest ecosystems that are relatively undisturbed by humans or from investigations into the effects of particular management strategies on a small scale [64
]. If we take into account a human impact on forest ecosystems, including land-use change and modifications in the structure of the landscape, it is important to identify the primary driving forces of diversity, not only in undisturbed ecosystems, but also across entire landscapes that have been actively and intensively managed for many years [66
]. The need for research into the intensively managed forests will grow with the decrease of natural forests in the future, because some of the natural forests in Slovakia are not included in protected areas. In unmanaged forests in strictly protected areas with similar altitude and soil composition, the expected traditional vegetation unit would be predominantly habitats of Acidophilous oak forests, Asperulo-Fagetum beech forests, Luzulo-Fagetum beech forests, and Medio-European limestone beech forests [68
]. These vegetation units of forest natural habitats can only be used for mapping and research of natural forests, because the definition of these units is based on both natural structure and species diversity. Our research indicates that when these traditional units of natural forests are disturbed by clear-cutting forest management, it may revert or regenerate into a different vegetation types, such as identified ESGs in the study area.
On the base of TWINSPAN we have identified five species groups and established a list of diagnostic species. This species grouping was not consistent with the traditionally recognized units in the territory of the Western Carpathians [69
]. The author of the study [70
] found relationships between traditionally used vegetation units in Slovakia and vegetation units created by numerical classifications, but these were in natural or near-natural forest stands. The fact that the numerical classification vegetation units were not consistent with the traditional vegetation units was identified by the study [71
]. ESG 1 was statistically similar to Luzulo-fagion
and ESG 2 was also similar to Eu-fagenion
, but there were no accurate classifications because some diagnostic species were missing. ESG 3 and ESG 5 were very similar to Caricipilosae-Carpinenionbetuli
, but ESG 5 had no typical diagnostic species, Moehringia trinervia
. Only ESG 4 was relatively well classified by floristic composition and ecology as Tilio-Acerion
The main problems with the inclusion of traditional vegetation units were: (1) We did not choose ideal forest stands; (2) we did not carry out research into natural forest stands, but we chose intensively managed forest landscapes, because they are the predominant type of forest in Central Europe, especially in Slovakia; (3) the forest stands have been without the direct influence of management for five years, but they were near the stands where management had a direct influence (logging, path or forest road). An example of this influence was the high amount of Urtica dioica, which is not a typical forest herb.
Altitude and soil chemistry played a major role in the ecological species groupings. The highest variation of vegetation was explained by altitude, K and pH [9
]. Study of [5
] revealed Mg, K and Ca as limiting factors for plant growth in temperature beech forests. These results were expected in accordance with general knowledge on abiotic factors importance in managed forests [72
] and local knowledge in Slovakia [73
Altitude had a major role in explaining the variance in vegetation [75
]. On the high-altitude forest stands only a few species are capable of growth in the characteristically harsh climate, which has lower temperatures, higher wind speeds and more drastic changes in the type and amount of precipitation. Altitude is generally known as an important factor in natural forest vegetation distribution in temperate mountains in the form of forest vegetation zones [77
]. But, in managed forests, vegetation zonation is disturbed by both human activities including forest management practice and climate change impacts [78
Soil pH played a major role in the separation of ESG 1. It was one of the most important factors affecting the plant community and showed the important role of pH in the separation of species groups [18
]. The pH only had a minor role in a few studies [79
]. Soil organic C played a major role in the separation of ESG 4. It had a high absorption capability, which increased the soil´s exchange capacity and therefore its fertility levels. It was an important factor in the variety of deciduous forest in China [81
]. Calcium was an important factor in the separation of ESG 3 and ESG 4. Plants use calcium to activate certain enzymes and to send signals that coordinate cellular activities, and it is also responsible for holding together the cell walls. Calcium played a significant role in the separation of species and species groups [58
]. Potassium played a major role in the separation of ESG 3. The presence of potassium in the soil makes it easy to transform the water and nutrients in the soil, and it plays a major role in the regulation of photosynthesis, carbohydrate transport, protein synthesis and other phyto-sociological processes. Study [21
] showed the importance of potassium in the separation of species groups as well. Authors of the study [82
] found potassium as one of the effective factors in the distribution of vegetation types. Magnesium was an important micronutrient in the separation of ESG 4. It is necessary for normal plant growth and has an important role in photosynthesis. Thus, our results are in accordance with the study by [82
], which clearly indicated the important role of magnesium in the separation of species groups.