Spatiotemporal analysis of growth dynamics under climate change across European unmanaged forests

Ing. Krešimir Begovič

Doctoral thesis

Abstract:

The past century has witnessed a global rise in greenhouse gas emissions and air temperatures, shifting hydroclimatic patterns, and increasing occurrence of climatic extremes. Disturbance regimes, as a key component shaping natural forest structure and driving individual tree growth dynamics, are concurrently changing rapidly with potentially dire consequences for forest ecosystem functioning and services, at the detriment of our socio-ecological systems. This Thesis aimed to disentangle the complex interactions between the intrinsic (i.e., physiological) and extrinsic (i.e., environmental) drivers of tree growth in order to explore contemporary forest dynamics and landscape structure in Central-Eastern and Southeastern European unmanaged forests under changing environmental conditions. Using an extensive dendrochronological database from a network of over 200 permanent study plots, robust information about individual tree growth dynamics and growth response to shifting climatic constraints was derived in order to assess the impact of environmental changes on secondary wood formation, spatiotemporal variability in climate-growth sensitivity, contemporary forest structure and landscape dynamics, and ecosystem functioning. At first, I examined the general climate-growth relationships of Norway spruce and silver fir in order to broaden the existing knowledge of growth-climate associations in mixed-species primary forests of the Dinaric Mountains (Chapter 4.1). Tree growth was mainly constrained by high temperatures and low precipitation and soil moisture during summer months in both species. I present strong evidence of the physiological weakening of Norway spruce trees under intensifying drought stress, that may lead to compositional shifts in favor of silver fir and carry major negative implications for the future development of the Dinaric primary mountain forests under increasing climatic and non-climatic perturbations. Secondly, I analyzed the spatiotemporal variation in radial growth patterns from the Western Carpathian primary spruce forests to explore how growth-longevity tradeoffs, disturbance dynamics and recent global warming influence large old trees development and forest biomass accumulation (Chapter 4.2). I demonstrate that life-growth histories (i.e., slow growth) and growth release events play an essential role for attaining multi-centennial lifespan in primary spruce forests and that, contrary to the general expectations, improving baseline conditions transcend age/size limitations for improved biomass accumulation, with significant implications for the future carbon sink role of primary mountain spruce forests. Lastly, I conducted a multi-parameter evaluation of drought impacts on Norway spruce and Scots pine growth across nature forest reserves in Czechia and Slovakia to infer conclusions about future resilience of Central European conifer forests under intensifying climatic constraints (Chapter 4.3). I show a clear dissociation of common growth patterns in temperature-limited Norway spruce mountain forests and increasingly moisture-limited Scots pine and Norway spruce montane and lowland sites, respectively, with a large site- and species-specific variability in growth sensitivity to shifting climatic constraints and response to extreme drought events, and pronounced legacy effects in wood formation during severe droughts. The empirical findings from these studies are used to infer robust and concise conclusions about tree growth and forest ecosystem dynamics, and provide general recommendations for forest managers and conservationists for ecosystem-based management strategies that could ensure the preservation of forest ecosystem functioning, long-term carbon storage and biodiversity under global climate change.

Keywords

dendrochronology, natural disturbance dynamics, primary forests, nature forest reserves, climate-growth relationships, growth-longevity tradeoffs, growth trends, drought legacy effects

Language used: English

Date on which the thesis was submitted / produced: 21. 1. 2023

Thesis defence

• Supervisor: prof. Ing. Miroslav Svoboda, Ph.D.

Czech University of Life Sciences Prague

Faculty of Forestry and Wood Sciences

Doctoral programme / field:
Forestry Engineering / Forest Biology