Diverging shrub and tree growth from the Polar to the Mediterranean biomes across the European continent

Abstract

Climate warming is expected to enhance productivity and growth of woody plants, particularly in temperature-limited environments at the northernmost or uppermost limits of their distribution. However, this warming is spatially uneven and temporally variable, and the rise in temperatures differently affects biomes and growth forms. Here, applying a dendroecological approach with generalized additive mixed models, we analysed how the growth of shrubby junipers and coexisting trees (larch and pine species) responds to rising temperatures along a 5000-km latitudinal range including sites from the Polar, Alpine to the Mediterranean biomes. We hypothesize that, being more coupled to ground microclimate, junipers will be less influenced by atmospheric conditions and will less respond to the post-1950 climate warming than coexisting standing trees. Unexpectedly, shrub and tree growth forms revealed divergent growth trends in all the three biomes, with juniper performing better than trees at Mediterranean than at Polar and Alpine sites. The post-1980s decline of tree growth in Mediterranean sites might be induced by drought stress amplified by climate warming and did not affect junipers. We conclude that different but coexisting long-living growth forms can respond differently to the same climate factor and that, even in temperature-limited area, other drivers like the duration of snow cover might locally play a fundamental role on woody plants growth across Europe.

Woody plant encroachment intensifies under climate change across tundra and savanna biomes

“…Woody encroachment has been reported from ecosystems around the world, including the tundra and the savanna. Several studies have analysed woody growth at different scales, including reviews of shrub expansion globally (Eldridge et al, 2011;Naito & Cairns, 2011), biomespecific analyses (Martin et al, 2017;Myers-Smith et al, 2011;Stevens et al, 2017), and continent-wide studies across biomes (Knapp et al, 2008;Pellizzari et al, 2017). However, woody encroachment rates and timings have not been explicitly compared between open biomes limited by climate extremes, nor have the specific influences of climatic factors been assessed.…”

Climate Warming Alters Age-Dependent Growth Sensitivity to Temperature in Eurasian Alpine Treelines

“…At each site, we selected trees at least 30 years old growing in the same site and located at least 5 m apart from each other across a rectangular area of 4200 m 2 [7,18,41]. Two age groups were established based on previous analyses and considering old (age > 75 years) and young (age ≤ 50 years) trees.…”

“…Climate warming is spatially heterogeneous, with the highest rates of temperature increase observed in peripheral Eurasian regions such as the Polar Urals (larch treelines) and the Mediterranean Basin (mainly pine treelines) [17,18]. Temperature thresholds have been proposed to explain abrupt changes in radial growth across these different treeline types dominated by diverse conifer species [19,20].…”

“…There is a research gap on how tree age affects climate-growth relationships in multi-aged treeline populations where old and young trees differently respond to climate, and this different response may affect future treeline shifts [7]. The radial growth of treeline species is mainly limited by low air and soil temperatures during the growing season [18,[23][24][25]. However, rising temperatures may selectively affect trees as a function of their ages, promoting the dominance of the most responsive age classes [12].…”

“…in the Spanish Pyrenees and the Siberian Larch (Larix sibirica Ledeb.) in the Russian Polar Urals (see [18] for more details of both sites). Our specific objectives are:…”