prilagođeno pretraživanje po punom tekstu

ŠUMARSKI LIST 7-8/2018 str. 54     <-- 54 -->        PDF

species is increasing. Research projects on growing Paulownia sp. in Croatia are in their initial phase (Drvodelić et al. 2016).
3.2. The use of NNTS as new silvicultural options for facing climate change and increasing ecological services of forest stands – Adaptacija na klimatske promjene i povećanje ekološke funkcije šumskih sastojina uporabom alohtonih vrsta kao novo šumskouzgojno rješenje
Climate change (CC) is expected to have a profound, but selective effect on forests in temperate and Mediterranean bioclimatic zones (Hlásny et al. 2014). Several studies conducted for the regions of Balkan and Central Europe have shown that CC might significantly affect future production and distribution range of main tree species (Kutnar and Kobler 2011; Stojanović et al. 2014). Forests fulfil multiple functions, but in light of expected CC it is uncertain if they will be able to cover all presumable needs. Indeed, forest trees populations generally contain a high genetic diversity (Porth and El-Kassaby 2014); nevertheless their abilities and adaptive capacities are limited (Lindner et al. 2010). Generally, species are not able to adapt to environmental conditions that do not coincide with genetically fixed physiological optimum. In the future, tree species that can adapt to specific local stand conditions will dominate the composition of forest stands, may they be native or non-native to Europe (Lindner et al. 2010). To guarantee resilience capacities of forests and woodlands to predicted CC a variety of species should be planted as mixed stands, and in the case of pure stand management a broad spectrum of genotypes enables the ecosystem to recover faster. Problematically, disturbances such as fire, windthrow or outbreak of pests and diseases affect species-poor stands more intense and may cause severe economic losses. In the worst case, large areas of land remain bare and exposed to erosion and degradation (EAA 2008). In that context, the use of NNTS may offer chances and opportunities for future forestry and help to adapt European forests to climate change as major challenge in the future (EAA 2008). Opportunities of the use of NNTS are shown in Figure 1.
The lack of natural regeneration of NNTS, in particular a certain sterility of Douglas-fir and eastern white pine could be advantageous in terms of reducing the need for silvicultural/control activities and lowering competition with natural regeneration of native species. In stands where Douglas-fir as individual trees or in small groups is recorded, problems with pollination can be detected. This phenomenon can be explained by high proportion of sterile seeds, by damages to female flowers caused by late frosts, as well as by damages of its seedling colonisations caused by game species or the invasive Hymenoptera species Megastigmus spermotrophus Wachtl. (Kinský and Šika 1987; Bušina 2007). Most studies performed by the CFRI on this topic focus rather on the survival of seedlings and saplings in recently established stands than on the regenerative potential of adult trees. However, an investigation carried out in Forest District Delnice and belonging to pilot study “Rogi” revealed that the natural regeneration of domestic European beech and silver fir was more prolific and even dominated the regeneration of introduced species such as Douglas-fir and eastern white pine (NNEXT 2016).
3.2.1. Enhancement of the catalogue of suitable species for forestry in terms of increase of diversity, reduce silvicultural risks and filling the stand gaps after disturbances – Povećanje broja prikladnih vrsta s ciljem poboljšanja bioraznolikosti, smanjenja šumskouzgojnih rizika i većih mogućnosti sanacije nakon šumskih šteta
Diverse climate scenarios highlight the enhancement of pests and diseases as a severe risk for forestry that has to be solved. Enrichment of stands with the aim of protection, biodiversity and stability is recognized as a target silvicultural option in some European countries. The management of Croatian forests should be performed according to the principles of sustainable management but climatic disturbances and pest damages raised two questions recently: (i) can native species adapt quickly enough and (ii) to what extent they can adapt to new conditions? Conversion of low productive coppice forests and degraded forests, together with broader possibilities of NNTS use in afforestation of abandoned agricultural land and other available areas refers to the possibility of using the improvement potential of NNTS species. The growing problems of management of native tree species, combined with the potential wider use of NNTS in relation to predicted CC should be the focus of further research. In addition, the existance of available land for afforestation in Croatia could be important (Tijardović & Perić 2013).
Thus, introduction of NNTS in Croatia is proposed in cases of significant tree mortality of native tree species (limited conditions due to CC), when they can serve as alternatives and could play a significant role in adaptation measures. Fraxinus pennsylvanica and F. americana L. are spreading spontaneously in Croatia, on areas where native Fraxinus angustifolia declined (Kremer and Borzan 2009). They found hybrids between these species, while hybrids with native F. angustifolia were not found pointing to the conclusion that this latter species could represent a good option for reforestation after forest dieback in the lowlands. Norway spruce dieback is one of the most pressing situations where different alternative species should be provided; in this respect, coastal Douglas-fir (Pseudotsuga menziesii menziesii) seems to be a good option to meet the future needs (Cremer et al. 2016). Though, Douglas-fir was badly affected by the fungal pathogens Phaeocrytopus gäumanni