Results of renewal management up to the present day
We can consider the following factors as fundamental indicators of the changes in the condition of the forests in the NP:
long-term modifications of the tree species composition
the development of the spatial representation of types of forest stands on the whole NP territory.
The comparison of the modification of the tree species composition (table 1) is based on the data included in the Forest Management Plans – the condition up to 1-1-1992 and up to 1-1-2003. The data for the condition of the forests in 2003 was recalculated for all owners of forested lands so that it is comparable with the entry data from 1992. Because the first Forest Management Plan was produced using the standard age class method and the second plan used the operative inventarisation method, there are some small differences between the data, but which do not change the long-term trends.
The relatively high growth of the representation of hornbeam in the forest stands is caused by the underestimation of its numbers when the first Forest Management Plan was produced. The hornbeams frequently formed the second layer in the forest stands with a main layer of pines which were mature and ready for felling and the forest inventory concentrated on the pines. The majority of these stands has been renewed in a careful way and now comprises a mixture of hornbeam, oak, lime and other deciduous trees and display age and spatial differentiation. The same statistical problem was noted with all kinds of maple, which grow scattered throughout the national park, but were often not recorded at all when using the standard age class method (maples are represented in the forest stand groups at less than 1%). The current (higher) representation of maples is not only due to actively introducing them into the forest stands, but due to counting them more effectively.
On the other hand there has been a relatively low growth in the representation of beech, even though beeches have made up around 40% of the young trees planted in the forests since 1993 (around 12 ha per year). Because the proportion of beech in the artificial renewal (including underplanting) has been increased in the last 5 years, we expect to see a significant increase in their representation in the next operative inventarisation in 2012.
The significant fall in the representation of spruce and pine correlates with the long-term active management. In the case of the pines this fall represents the situation where the old pines were of a felling age, were carefully removed and the space was then occupied by a height and age differentiated mix of deciduous trees and the formation of clear-cut areas is very sporadic. More often we are talking about underplanting more open parts of the forest stands with tree species of the target composition. We also cannot forget about the calamity situation which happened in December, 1995, when many areas of pole stage and small pole-stage pine stands were broken or destroyed by the large quantities of wet snow which fell. These pine stands had previously been neglected for a long time and the intensity of tending of these stands was very low (in the early stages the overtopping trees had not been removed, and the stands were too dense and full of very slim-trunked and unstable pines. All of these plots were renewed with a mixture of the target tree species, which reflect the locality conditions. In this way the pine monocultures were strongly reduced and divided up, especially in the IInd and IIIrd zones of the NP, to such an extent which even the most ambitious plans for systematic reconstruction of the forest stands could hope for. A similar but smaller snow catastrophe situation which happened in January 2006 also helped to speed up the further reconstruction of the pine monocultures which were planted here between 1970 and 1980.
The second and equally important indicator is the changes in the areas covered by different types of forest stands (table 2). Here we can clearly see the notable long-term growth in the areas covered by forest stands of the target types as a result of the long-term implementation of the principles of renewal management – long-term support (release) of the target tree species in the mix with conifers, supporting the lower storeys in the forest stands (forming a spatial structure), leaving rotting wood of the target tree species in the forest etc. The target stand types are deliberately monitored separately – on territories where the whole stand will be left to spontaneous development processes (Diagram 1) and in the buffer zones, which will be further cultivated according to the principles of near-natural forest management.By 2006 a total of 2070 ha of the forests of the target types (40% of the forests in the NP) had already been included in the category of forests which will be permanently left to spontaneous development. We cannot observe a long-term growth in the area covered by transition forest types as this is only a “flow” stage or classification unit. What is important for the forest management results is the growth in the target forest types and the reduction of the coniferous and false acacia stand types. The reduction of the false acacia stands is a slow process due to the demanding and expensive measures needed to convert the false acacia woods. The renewal areas must have all of the acacia shoots growing from roots and stumps removed. The cultures which are planted to replace the false acacias are then filled with acacias shoots which came from the neighbouring stands which still contain false acacias every year until the new forest stands develop a closed structure (which takes 10 – 12 years on the dry localities in Podyjí NP). Even though the false acacia stand types cover a relatively small area, their transformation will take longer than the transformation of the coniferous forest stands, which cover a much larger area of the NP.
If the current trends in renewal management are maintained the target condition – 75% of near-natural forests left to spontaneous development – will be reached in the period between 2025 and 2030. Up to 2006 near-natural communities which are left to spontaneous development cover 41% of the forested area of the NP.
Table 01 – Changes in the tree species composition in the period between 1991 and 2003
Table 02 – Development of the areas covered by forest stand types