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|Jazyk zpracování závěrečné práce:||Angličtina|
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|Název práce:||Coppice as a new perspective for an adaptive forest management|
|Abstrakt:||Increased frequency and intensity of drought events consequently affect oak high forests with the process of further decline, compromised growth and questionable natural regeneration. To overcome such difficulties, new adaptive strategies are required. Coppicing, as the oldest way of forest management might provide some solutions. In our study, we compared two contrasting management systems, coppice and high sessile oak (Quercus petraea (Matt.) Liebl) forests, both in initial and mature stages of forest development. Assimilation and photosynthetic efficiency - maximal quantum yield () - of young oaks were compared in coppice and high sessile oak stands of comparable age under different light intensity categories: under minimum light with values of indirect site factor (ISF) < 20%, in low light – 20%<ISF<25%, in medium light – 25%<ISF<30% and in the open, without mature canopy cover – ISF >30% during favourable and drought conditions. Measurements of maximal assimilation rates were performed during three consecutive growing seasons (2012, 2013 and 2014). Transpiration of the same young oak stands were monitored using the sap flow systems during the whole growing season of 2015. The study of transpiration was supplemented by leaf water potential (LWP) measurements during three measurement campaigns with contrasting weather conditions. Furthermore, dendrochronological study was conducted on a nearby adult high and aged coppice sessile oak forest stands. We analysed and projected climate-growth relationships and assessed the impact of the 21st century emission scenarios on the tree basal area increments and stand basal-area dynamics under different stand structures.
The quantum yield () in optimal conditions in seedlings was highest in the category of closed canopy, while in coppice sprouts in medium light category. During severe drought in 2013, the drop in efficiency of seedlings was evident in all categories, while in coppice sprouts no differences in efficiency were observed between favourable 2012 and 2013 with expressed drought stress, proving the advantage of young coppice sprouts over seedlings in this particular light category. Likewise, coppice sprouts transpired significantly higher than seedlings on the individual as well as stand level during entire growing season in 2015. Particularly high differences were observed between sprouts and seedlings during drought conditions. Coppice sprouts indicated less water limitations due to voluminous and already established deeper root system, confirmed by the leaf water potential measurements. Furthermore, dendrochronological study indicated, that stands experienced different long-term growth trends and also exhibit contrasting growth responses to climate and drought events. Higher radial growth rates were observed in coppice compared to high forest in first two decades after establishing the forests. Dendrochronological data and linear mixed-effects models show similar effects of precipitation for April-May (positive) for both, seed- and coppice-origin trees. Previous autumn and current June temperatures show significant negative correlations with the radial coppice growth. Nonetheless, trees from natural stands exhibited higher drought sensitivity and tend to increase radial growth after previous autumn temperature during the 20th century. The positive effect of warmer autumns, only confirmed in high stand, might be related to extending growing season, suggesting improved adaptive capacity to cope with impending warmer conditions.
Presented results attribute young coppices as one of the promising adaptable forest management alternative, with a better adaptive strategy on extreme sites, especially under water limiting conditions. Observed advantage according to growth rates in the studied coppice stands, persisted only during the first two decades and then gradually decreased. Conversion of aged coppice forests to high forest structures, as well as thinning of high stands, would enhance sessile oak forest adaptive capacity to cope with warming in drought-prone areas of central Europe.
|Klíčová slova:||transpiration, Coppice, high forest, seedlings, sessile oak, drought stress, quantum yield, sap flow, leaf water potential, dendrochronology, basal area increment, climate change, emission scenarios|
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