Abstract
European beech (Fagus sylvatica L.) forests provide multiple essential ecosystem goods and services. The projected climatic conditions for the current century will significantly affect the vitality of European beech. The expected impact of climate change on forest ecosystems will be potentially stronger in southeast Europe than on the rest of the continent. Therefore, our aim was to use the long-term monitoring data of crown vitality indicators in Croatia to identify long-term trends, and to investigate the influence of current and previous year climate conditions and available site factors using defoliation (DEF) and defoliation change (ΔDEF) as response variables. The results reveal an increasing trend of DEF during the study period from 1996 to 2017. In contrast, no significant trend in annual ΔDEF was observed. The applied linear mixed effects models indicate a very strong influence of previous year drought on ΔDEF, while climate conditions have a weak or insignificant effect on DEF. The results suggest that site factors explain 25 to 30% DEF variance, while similar values of conditional and marginal R2 show a uniform influence of drought on ΔDEF. These results suggest that DEF represents the accumulated impact of location-specific stressful environmental conditions on tree vitality, while ΔDEF reflects intense stress and represents the current or recent status of tree vitality that could be more appropriate for analysing the effect of climate conditions on forest trees.
Highlights
Climate conditions influence the structure and function of forest ecosystems, and play an essential role in forest health [1,2]
There was a significant trend of increasing mean defoliation (DEF) by 0.39% annually over the study period (Figure 1)
Defoliation is widely accepted on as aitsproxy indicator of tree vitality and forest health, series are an important asset to explore the changes in forest ecosystem health across able to provide useful information on its status and trends
Summary
Climate conditions influence the structure and function of forest ecosystems, and play an essential role in forest health [1,2]. Global warming has indisputably caused climate change, which is a significant threat to forest ecosystems [3]. Vitality is a theoretical concept, it can be defined as the ability of a tree to assimilate, to survive stress, to react to changing conditions, and to reproduce [6]. Crown defoliation is a commonly used tree vitality indicator [8–10], which can be obtained costeffectively and relatively quickly in field surveys [11]. Defoliation is defined as leaf loss in the assessable crown, as compared to a reference tree, and is observed regardless of the cause of foliage loss [12]. Landmann [13] states that defoliation is an indicator of acute stress and subsequent recovery of forest ecosystems. To ensure data quality, training courses and repeated control assessments are regularly carried out on a national [17–19] and international level [20]
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