Radial Increment of Beech (Fagus sylvatica L.) Is under a Strong Impact of Climate in the Continental Biogeographical Region of Croatia

Abstract

European beech (Fagus sylvatica L.) is an important component of forests in the alpine and continental biogeographical regions of Croatia. This study aimed to (1) analyze the long-term response of beech to climate, (2) identify potentially critical climatic conditions that could negatively affect the radial increment (RI) and vitality of beech, and (3) evaluate differences in the response of beech between the two biogeographical regions in Croatia. We used the 16 × 16 km Croatian ICP Forests Level 1 network. On a total of 25 plots, we cored between 5 and 24 trees for dendrochronological analysis. Tree-ring widths (TRW) were measured and standardized using cubic spline. TRW chronologies for the two regions were calculated and correlated to the temperature and precipitation data and Standardized Precipitation and Evapotranspiration Index (SPEI) using bootstrapped correlations. Continental region precipitation from April to August and alpine region precipitation from June to August were significantly important for RI. Temperature was less important for RI than precipitation in both regions, but the importance of the negative impact of above-average temperatures in the continental region and the positive impact of above-average precipitation in the alpine region has increased over the last two decades. A comparison with the 3-month SPEI confirmed the significant influence of high temperatures and the lack of precipitation in August on the RI of beech trees in both regions.

Declining Radial Growth in Major Western Carpathian Tree Species: Insights from Three Decades of Temperate Forest Monitoring

“…The observed decreasing trend for common beech ( Figure 3 ) was highly significant, even when compared to the data from the other investigated deciduous species. The sensitivity of beech to drought is well known [ 36 , 55 , 56 , 57 ]. Our findings indicated that after the droughts in 2000 and 2003, the RBAI decreased to a value under 2% and has not recovered yet.…”

“…We selected years with total summer precipitation (for June, July, and August) lower than normal in more than 90% of the total ICP Forests Level I plots. In subsequent analyses, we closely examined tree growth in the years 1990,1992,1993,1994,2000,2003,2012,2013,2015,2017,2019, and 2022 (Figure 2), many of which were used as negative pointer years in other recent European studies [36]. Map of active ICP Forests Level I plots and plots included into the analysis.…”