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ŠUMARSKI LIST 7-8/2018 str. 55     <-- 55 -->        PDF

and Rhabdocline pseudotsugae (Stephan 1981). In Croatia, large-scale problems with these pathogens were not found. Even though Douglas fir have shown slow initial growth, the quick further growth and development of this NNTS in Croatia in the plain, hilly and mountainous areas (eight different trials) support European research conclusions that Douglas-fir could be a very good silvicultural option (Dokuš 1972a, 1981, Dokuš et al. 1975, Dokuš and Gračan 1977, Orlić 1979, 1981, 1983, 1994, Orlić et al. 1985, 1997, Orlić and Ocvirek 1993, 1995, 1996, Komlenović et al. 1995, Perić et al. 2004, 2006a, 2006b, 2009, 2011). In addition, Douglas-fir provenances growing quickly are also the ones with better quality and less prone to frost and low temperatures; conversely, the ones growing slowly have a lower quality and are more sensitive to low temperatures (Orlić and Ocvirek 1996). Despite their good success, primary role of forest cultures of NNTS should be preparation of site for establishment of native tree species. Therefore, following good example of Dubravac et al. (2006) these should also be monitored with the aim of recording spontaneous appearance of native tree species.
In this respect the use of NNTS, especially those with low regeneration potential, can serve as a good solution for soil improvement thus preparing the site for more favourable native climax tree species. A good example of NNTS productivity and their special use for soil improvement is baldcypress (Taxodium distichum (L.) Rich.) forest culture (Management unit ”Mirna“, sub-compartment 4 b, 0.63 ha) located inside the special nature reserve “Motovunska šuma” (The Motovun forest). In here, even not used for soil improvement initialy, baldcypress has been very successful and it could be suitable and commercially interesting for introduction to similar sites.
3.2.2. New options in restoration of highly degraded areas and alternatives in the areas with frequent and severe drought events – Nove mogućnosti za sanaciju degradiranih i devastiranih šumskih površina i područja čestih i jakih suša
As the range and competitive potential of existing, native tree species decline with CC, NNTS may benefit due to greater ability to thrive in altered environmental conditions. Ehrenfeld (2010) stated that many NNT species have higher values of resource-acquisition traits (e.g. morphological, physiological, and chemical) related to performance than native tree species. Additionally, Willis et al. (2010) showed that NNTS may have greater ability to respond to novel climatic conditions by adjusting their phenology. Thorpe et al. (2006) believed that a new rationale for introduction of NNTS is their possible role in retention of the economic and environmental values associated with forest, especially in the drought-prone regions. Such areas are present in Croatia along the coast, where higher temperatures and more frequent occurrence of droughts and forest fires are predicted in the future. A need for restoration of such areas is constantly present, as well as the need for better silvicultural solutions. Cedrus atlantica is one of the NNTS that showed very good success in solving risks-related issues in plantations established in the coastal area (e.g. 55 year-old stand in forest area “Kontija”, management unit “Lim” - NNEXT 2016). Reforestation of degraded lands with a mix of NTS and NNTS is a promising method to re-establish trees and stabilize forests. This solution facilitates recovery of secondary native vegetation (Maestre and Cortina, 2004) and soil structure and diversity of soil microorganisms get the chance to recover (Hankin et al. 2015).
On the other hand, the use of NNTS on degraded areas, with degraded soils, can be suitable for some NNTS (Pilipović et al. 2003). The establishment of short rotation coppices (SRC) could be a first step in the restoration process. Besides vigorous growth and high biomass production, hybrid poplars are used in different systems of phytoremediation. Most often poplars are used to clean up sites and groundwater contaminated with Volatile Organic Compounds (VOCs), but they can also be used for the phytoremediation of heavy metals from the soil, uptake of contaminants present in groundwater (e.g. pesticides, fertilizers), nitrate phytoremediation, etc. (Felix et al. 2008). In addition, reforestation with black locust on sandy soils in northern Croatia (“Đurđevački pesci”) started at the end of the 19th century with the purpose of sand fixation and preparation of site conditions for natural regeneration of other species.
3.2.3. Possibilities of harmonisation and development of nursery production with needs in forestry practice – Mogućnosti usklađenja i razvoja rasadničke proizvodnje s potrebama u praksi
Seed stands/seed orchards for the production of FRM of NNTS in Croatia include Douglas-fir, black walnut, black locust, northern red oak, baldcypress (Ministry of Agriculture 2017). Nevertheless, data from the Supervision of nursery production of forest seedlings shows very low production of NNTS seedlings in Croatia in the last 25 years (Perić et al. 2008, 2009, 2010, 2013a, 2013b, 2014, 2017). Recently, NNTS FRM was partially covered by import, mainly of seeds (e.g. in 2015 around 30,000 kg of black walnut seeds and ca 3 kg of Douglas-fir seeds imported from the U.S.A.). According to the data of CFRI, in 2010-2015, 7 kg seeds of Douglas-fir were imported from the Netherlands, Austria, Slovenia, Hungary and France while 4,000 seedlings were imported from Austria. In the same period (only in 2011), eastern white pine seeds were imported from Slovenia (6 kg), while 183,600 seedlings of black walnut were imported from Hungary. These data clearly show both insignificant efforts of NNTS afforestation in Croatia, but low intensity of production of FRM of NNTS as well.