Impact of an Extremely Dry Period on Tree Defoliation and Tree Mortality in Serbia

Abstract

This paper presents research results on forest decline in Serbia. The results were obtained through monitoring defoliation of 34 tree species at 130 sample plots during the period from 2004 to 2018. This research aimed to determine whether the occurrence of defoliation and tree mortality were caused by drought. Defoliation was assessed in 5% steps according to the International Co-operative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (ICP Forests) methodology. All the trees recorded as dead were singled out, and annual mortality rates were calculated. To determine changes in air temperature and precipitation regimes during the study period, we processed and analysed climatic data related to air temperature and precipitation throughout the year and in the growing season at 28 main weather stations in Serbia. Tree mortality patterns were established by classifying trees into three groups. The first group of trees exhibited a gradual increase in defoliation during the last few years of monitoring, with dying as the final outcome. The second group was characterised by sudden death of trees. The third group of trees reached a higher degree of defoliation immediately after the first monitoring year, and the trees died after several years. Tree mortality rates were compared between years using the Standardised Precipitation Evaporation Index (SPI) and the Standardised Precipitation Evapotranspiration Index (SPEI), the most common methods used to monitor drought. The most intensive forest decline was recorded during the period from 2013 to 2016, when the largest percentage of the total number of all trees died. According to the annual mortality rates calculated for the three observation periods (2004–2008, 2009–2013, and 2014–2018) the highest forest decline rate was recorded in the period from 2014 to 2018, with no statistically significant difference between broadleaved and coniferous tree species. As the sample of coniferous species was small, the number of sample plots should be increased in order to achieve better systematic forest condition monitoring in Serbia. The analysis of the relationship between defoliation and climatic parameters proved the correlation between them. It was noted that the forest decline in Serbia was preceded by an extremely dry period with high temperatures from 2011 to 2013, supporting the hypothesis that it was caused by drought. We therefore conclude that these unfavourable climatic conditions had serious and long-term consequences on forest ecosystems in Serbia.

Mites Associated with the European Spruce Bark Beetle Ips typographus (Linnaeus, 1758) in Europe, with New Evidence for the Fauna of Serbia

“…Biotic and abiotic disturbances associated with climate change currently pose the greatest threat to coniferous forests in Europe [1][2][3][4]. In Serbia, a sharp decline in coniferous forests has been observed since 2012 [5][6][7][8][9][10]. The main reason for this decline was droughts that occurred during growing seasons and caused damage of 116,290 m 3 with a percentage of 89% dead spruces and fir [11].…”

Evaluation of the Compound Effects of the 2022 Drought and Heatwave on Selected Forest Monitoring Sites in Hungary in Relation to Its Multi-Year Drought Legacy

“…When combined, air temperatures and precipitation clearly affected the changes in defoliation. The notion that losses in Serbia's forests were caused by drought and its aftermath is supported by the observations from 2004 to 2018 made by Češljar et al (2022) [34]. The highest forest decline rate was observed in the last period when comparing 2004-2008, 2009-2013, and 2014-2018, with no statistically significant difference between coniferous and broadleaved tree species.…”

Soil moisture and temperature dynamics in juvenile and mature forest as a result of tree growth, hydrometeorological forcings, and drought

“…It is also worth noting that trees in both forests are suffering from water stress. Unfavourable climatic conditions, most notably a lack of precipitation, rising air temperatures, and increasingly frequent and extended dry periods, have serious, but varying, long‐term implications for mixed forest ecosystems (Češljar et al, 2022; Niinemets & Valladares, 2006). In particular, juvenile plantations tend to be more sensitive to water stress due to high tree density and the adoption of genetic provenance with low drought tolerance, resulting in lower planting vigour and higher mortality ratio when compared to a naturally regenerated forest (Navarro‐Cerrillo et al, 2018).…”