Abstract
Projecting trees species growth into future climate is subject to large uncertainties and it is of importance to quantify the different sources (e.g., site, climate model) to prioritize research efforts. This study quantifies and compares sites and climate model-induced uncertainties in projected Norway spruce growth from Denmark. We analyzed tree-rings from 340 Norway spruce trees sampled in 14 planted stands (1. Plantation; period 1950–1987) and additionally 36 trees from six trials in a common garden experiment (2. Common garden; period 1972–2012). Growth-climate correlations were estimated and multiple linear and nonlinear regression models relating growth with climate were tested. Tree growth was projected up to 2100 applying multiple linear or quadratic regression models based on the 15 Atmosphere-Ocean General Circulation Models (AOGCMs) of the Coupled Model Inter-comparison Project Phase 5 (CMIP5). The climate-growth models showed that summer drought and warm previous-year late-summer and early-autumn constrain growth. In some stands, warm springs affected growth positively. The projections of growth under future climates on average showed from no to slightly negative changes in growth compared to present growth rates. However, projections showed a very large variation, ranging from highly positive to highly negative growth changes. The uncertainties due to variation in site responses and in climate models were substantial. A lesser degree of uncertainty was related to the emission scenarios. Even though our projections on average suggest that Norway spruce may experience a growth reduction in the future, the tremendous variation in growth predictions due to differences between stands and climate models calls for further research and caution when projections are interpreted. These results also suggest that forest managers in general should avoid the use of Norway spruce on exposed and drought prone sites and as an additional resilience measure primarily use it in mixtures with other more climate tolerant species.
Highlights
Introduction(CMIP5) has integrated a larger number of more complex models including more external forces, running at higher resolution, and considering more scenarios and diagnostics compared with CMIP3 [3]
In the recent half century, spring temperature increased significantly in Norway spruce growth for several plantation stands if we considered the models with(Supplementary currentthat study high spring temperature seems to larger Akaike information criterion (AIC)-values
Our results show that different climate models based on the same emission scenario can lead to larger variations in projected growth responses compared to variation caused by different emission scenarios
Summary
(CMIP5) has integrated a larger number of more complex models including more external forces, running at higher resolution, and considering more scenarios and diagnostics compared with CMIP3 [3]. These scenarios have become important tools for assessing the impact of climate change, including forests ecosystems. Based on such frameworks, many studies have projected that climate change will lead to tree species distribution shifts [4,5,6,7], increases or decreases of growth [8,9,10] and changes in tree species composition [11]. Bias was showed in the study on 24 CMIP5 models by comparing the observed and simulated data during 1901–2005, as 12 models overestimated the warming trend by 1–3 ◦ C, and others underestimated the warming by
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