Detecting Nothofagus pumilio Growth Reductions Induced by Past Spring Frosts at the Northern Patagonian Andes.

Gabriel Sangüesa-Barreda,Ricardo Villalba,José Miguel Olano,Vicente Rozas,Duncan A. Christie

doi:10.3389/fpls.2019.01413

Abstract

Extreme climatic events, such as late frosts in spring during leaf flush, have considerable impacts on the radial growth of temperate broadleaf trees. Albeit, all broadleaved species are potentially vulnerable, damage depends on the particularities of the local climate, the species, and its phenology. The impact of late spring frosts has been widely investigated in the Northern Hemisphere, but the potential incidence in Southern Hemisphere tree species is still poorly known. Here, we reconstruct spring frost occurrence at 30 stands of the deciduous tree Nothofagus pumilio in its northern range of distribution in the Patagonian Andes. We identified tree ring-width reductions at stand level not associated with regional or local drought events, matching unusual minimum spring temperatures during leaf unfolding. Several spring frosts were identified along the northern distribution of N. pumilio, being more frequent in the more continental Argentinean forests. Spring frost in 1980 had the largest spatial extent. The spring frosts in 1980 and 1992 also induced damages in regional orchards. Spring frost damage was associated with (i) a period of unusually warm temperatures at the beginning of leaf unfolding, followed by (ii) freezing temperatures. This study helps expand our understanding of the climatic constraints that could determine the future growth and dynamics of Andean deciduous forests and the potential use of tree-rings as archives of extreme events of spring frosts in northern Patagonia.

Highlights

Disturbances, such as fires, insect outbreaks, or droughts, dictate the future dynamics of forest ecosystems around the world, and their occurrence and severity will increase with climate change (Seidl et al, 2017; Navarro et al, 2018)
Serm. et Bizarri a coexisting evergreen conifer that is unaffected by spring frost damage in the leaves, A. chilensis is sensitive to extreme minimum temperatures in the xylem at juvenile stages, when thin bark does not prevent frost damage (Payette et al, 2010; Arco Molina et al, 2016)
We considered the following five criteria: i) spring frosts induce significant local growth reductions in comparison with the mean regional tree-ring chronology, ii) frost damage is concurrent with anomalies in the absolute minimum temperatures during the leaf unfolding period, iii) the evergreen A. chilensis does not show significant growth reductions for these years, iv) during years with spring frost damage other important climatic variables that could explain the growth reductions do not show

Summary

Introduction

Disturbances, such as fires, insect outbreaks, or droughts, dictate the future dynamics of forest ecosystems around the world, and their occurrence and severity will increase with climate change (Seidl et al, 2017; Navarro et al, 2018). In temperate deciduous species, spring-frost episodes at the beginning of leaf unfolding damage new tissues through the formation of intracellular ice crystals in buds and new leaves, deviating carbon reserves to replace the damaged tissues (Inouye, 2000) and resulting in a shorter growing season in response to the retreat of the leaf-out (Gu et al, 2008) These events cause lower annual secondary growth (Dittmar et al, 2006; Príncipe et al, 2017) and impact negatively on reproduction and population dynamics (Inouye, 2000; Augspurger, 2011). Determining the frequency and severity of these extreme climate events is essential to assess their influence on deciduous forest functioning and dynamics and predict their interaction with a warmer climate (Augspurger, 2013)

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Results

Conclusion