Wood anatomical traits highlight complex temperature influence on Pinus cembra L. at high elevation in the Eastern Alps

In the context of climate change, scientific community is raising attention on tree response to increasing temperature. In this sense, populations at the edge of their distributional area are crucial to understand the species climate sensitivity. Pinus cembra is of particular interest being a typical high-elevation taxon, spread with mostly scattered populations within its range. Despite its potential, this species is traditionally disregarded by dendrochronological studies because of its low tree-ring variability and climate sensitivity. In this study, we tested the potential of dendroanatomy of this species, analysing time series of xylem anatomical traits of nine trees at the species elevation limit. We measured the mean ring width (MRW) and cell number (CN) per ring. Besides, to improve the time resolution of climate/growth associations, we split each ring in ten sectors, on which we measured the mean lumen area (LA) and both radial and tangential cell-wall thickness (CWTRad and CWTTan). These parameters, assessed on 1.5 7106 tracheids, were correlated with monthly and fortnightly climatic data, obtained by the daily climate records over 89 years (1926-2014). The most important factors affecting xylem features were late-spring and summer temperatures. LA and CWT showed a stronger temperature response than MRW, starting from mid-May and early June, respectively. CWT evidenced the longest period of response to temperature, with a significant difference between CWTRad and CWTTan. Analysis of xylem anatomical traits at intra-ring level and the use of daily temperature records proved to be useful for high resolution and detailed climate/growth association inferences in Pinus cembra

Retrospective Analysis of Wood Anatomical Traits Reveals a Recent Extension in Tree Cambial Activity in Two High-Elevation Conifers

The study of xylogenesis or wood formation is a powerful, yet labor intensive monitoring approach to investigate intra-annual tree growth responses to environmental factors. However, it seldom covers more than a few growing seasons, so is in contrast to the much longer lifespan of woody plants and the time scale of many environmental processes. Here we applied a novel retrospective approach to test the long-term (1926–2012) consistency in the timing of onset and ending of cambial activity, and in the maximum cambial cell division rate in two conifer species, European larch and Norway spruce at high-elevation in the Alps. We correlated daily temperature with time series of cell number and lumen area partitioned into intra-annual sectors. For both species, we found a good correspondence (1–10 days offset) between the periods when anatomical traits had significant correlations with temperature in recent decades (1969–2012) and available xylogenesis data (1996–2005), previously collected at the same site. Yet, results for the 1926–1968 period indicate a later onset and earlier ending of the cambial activity by 6–30 days. Conversely, the peak in the correlation between annual cell number and temperature, which should correspond to the peak in secondary growth rate, was quite stable over time, with just a minor advance of 4–5 days in the recent decades. Our analyses on time series of wood anatomical traits proved useful to infer on past long-term changes in xylogenetic phases. Combined with intensive continuous monitoring, our approach will improve the understanding of tree responses to climate variability in both the short- and long-term context

Contrasting effects of environmental change factors on the radial growth of co-occurring European beech and fir trees across Europe

Under predicted climate change, silver fir (Abies alba) and European beech (Fagus sylvatica) are the most likely replacement species for the more heat- and drought-sensitive monocultures of Norway spruce (Picea abies) planted across large parts of continental Europe. Our current understanding of the climate-related adaptation potential of fir and beech mixtures is, however, limited. Here we compile and analyse 2855 tree-ring width (TRW) series from 17 mixed beech-fir forest sites in five European countries. Dendroecological techniques that combine various detrending methods with an application of documented environmental change trends reveal wide variation of radial growth between fir and beech across space and time. Coincidental with peak SO2 emissions, the growth of silver fir declined between 1950 and 1980 at most sites, whereas beech growth increased during this period. Correspondent to a significant warming trend from 1990–2010, average beech growth declined, but silver fir growth increased. Our observations of long-term growth trends support the replacement of spruce monocultures with multi-species mixtures that have demonstrated a higher tolerance of environmental changes

TP and OJP xylem anatomical chronologies

Turkey Point, Ontario, Canada Old Jack Pine, Saskatchewan, Canada 1970-201