Module 2 PROXIES - Tree growth
Impact of drought events on growth of Scots pine provenances
Taeger S, Zang C, Liesebach M, Schneck V, Menzel A (2013) Impact of climate and drought events on the growth of Scots pine (Pinus sylvestris L.) provenances. Forest Ecology and Management 307, 30–42.
We explored the growth response of Scots pine to temperature, precipitation, and drought events focusing on eleven provenances of the IUFRO 1982 international provenance trial. At two macro-climatically different sites in Germany we measured chronologies of tree-ring widths and annual height increment, and analyzed the data focusing on the impact of severe drought events on tree growth. Introducing the statistical method of archetypal analysis in the context of ecological questions, we were able to summarize our findings regarding overall growth performance and growth performance under drought conditions. Subsequently, a ranking of provenances with regard to suitability under conditions of increasing frequency and intensity of drought events was possible.
Patterns in drought response in a large tree-ring network
Zang C, Hartl-Maier C, Dittmar C, Rothe A, Menzel A (2013) Patterns of drought tolerance in major European temperate forest trees: climatic drivers and variability (prepared for resubmission to Global Change Biology)
Based on a new tree-ring network in Southern Germany and the alpine Austria, 1760 trees from 86 sites with the economically important species Picea abies, Abies alba and Fagus sylvatica, we analyzed the spatial differentiation in drought response due to bioclimatic gradients and species differences, a possible change in within-population growth variability triggered by drought events, and the interconnection of tree size, tree age, average growth rate and drought response. The results point at a generally large influence of bioclimate and species, with P. abies being generally more prone to drought induced growth declines across the whole bioclimatic gradient.
A software framework for bootstrapped response function analysis
In order to facilitate analyzing large data sets for general climate/growth relationships, we contributed a software framework for principal components regression of proxy and climate data (in the context of paleoclimatic calibration also known as response function analysis), that yields robust parameter estimates via bootstrapping. Examining the stationarity of climate/growth associations is of pivotal importance in the context of a possible divergence effect. Our framework lowers the barrier for applying moving calibrations over varying time intervals and window sizes to allow for thorough examination of these effects.
Additional to the publically available software package (Zang, 2012), an accompanying methods paper has been published in Dendrochronologia (Zang & Biondi, 2013).
Trends in inter-annual variability of multiple carbon proxies related to climate
Various data streams (crop yield data, NDVI satellite products, tree-ring data) are used to identify trends in inter-annual variability in the carbon cycle related to changes in climatic variability on the European level. The main result of this study that was carried out as a joint effort with several European scientists suggest that climatic extremes in combination with an increasing mean temperature lead to an increasing inter-annual variability in crop yield, especially in areas which already are largely affected by production insecurity due to climatic extremes. The manuscript is published as a discussion paper (Biogeosciences Discussions 10, 17511-17547, 2013, www.biogeosciences-discuss.net/10/17511/2013/)