Norway spruce responses to drought forcing in areas affected by forest decline

Petr Čermák,Miroslav Trnka,Michal Rybníček,Tomáš Kolář,Tomáš Žid

doi:10.5424/fs/2019283-14868

Abstract

Aim of study: To assess the crown condition and radial growth of Norway spruce in plots with an increasing frequency and strength of drought during the last decades.Area of the study: Northern Moravia, Czech Republic.Materials and methods: Crown condition assessment and dendrochronology analysis were used.Main results: Tree-ring width (TRW) was significantly influenced by previous autumn and current summer climate. The temporal variability of the growth-climate relationship shows that the impact of water sufficiency (precipitation, relative soil water content, drought index) markedly increased mainly during the 2000s and the 2010s. Most climate-growth relationships were significant only in the last two or three decades. The observed crown conditions and their relationships with TRW also indicate stress intensification during the same period. Our results suggest that water availability was the main factor affecting radial growth and the occurrence of negative pointer years and was probably also the factor triggering the decline.Research highlights: In these current site and climate conditions, the silviculture of Norway spruce is extremely risky in the study area. Our results have also shown that the observed climate change is too dynamic for long-term forest plans, especially with regard to recommended forest species composition.Keywords: defoliation; Picea abies; tree-ring width; precipitation; PDSI; available soil water.

Highlights

Tree mortality usually involves complex processes and multiple interactions among disturbance agents and stress factors occurring at different time scales (Franklin et al, 1987; Trumbore et al, 2015).Tree death can be caused by abiotic stress factors interacting with different biotic factors, resulting in forest decline (Manion, 1991; Manion & Lachance, 1992; Sturrock et al 2011)
Drought often affects radial growth almost immediately, while foliage reduction becomes visible months later (Dobbertin, 2006). This reaction asynchronicity could be the reason we did not identify any relationships between defoliation and the mean tree-ring width index (TRWi) in recent years
Our results show that precipitation in the current summer months and the related AWR and Palmer drought severity index (PDSI) are significant mainly in moving intervals ending at the end of the 1990s or the beginning of the 2000s (Fig. 6)

Summary

Introduction

Tree mortality usually involves complex processes and multiple interactions among disturbance agents and stress factors occurring at different time scales (Franklin et al, 1987; Trumbore et al, 2015). Tree death can be caused by abiotic stress factors interacting with different biotic factors, resulting in forest decline (Manion, 1991; Manion & Lachance, 1992; Sturrock et al 2011). Drought is an important and frequent causal factor of forest decline; it can function as a predisposing, inciting or contributing factor (Sinclair, 1967). Forest resilience to drought mainly depends on drought intensity, but it may depend on tree species or specific functional traits (Greenwood et al, 2017); it can vary from one individual to another (Gazol et al, 2017; Camarero et al, 2018). During recent decades, droughttriggered forest declines have appeared in different forest types and climate zones. Allen et al (2010)

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