Warming Effects on Pinus sylvestris in the Cold–Dry Siberian Forest–Steppe: Positive or Negative Balance of Trade?

Tatiana Shestakova,Matthias Saurer,Jordi Voltas,Alexander Kirdyanov,Rolf Siegwolf

doi:10.3390/f8120490

Abstract

Understanding climate change impacts on drought-prone forests is a critical issue. We investigated ring-width and stable isotopes (Δ13C and δ18O) in two Pinus sylvestris stands of the cold–dry Siberian forest–steppe growing under contrasting climatic trends over the last 75 years. Despite regional warming, there was increasing precipitation during the growing period at the southern site (MIN) but increasing water deficit (WD) at the northern site (BER). Intrinsic water use efficiency (WUEi) increased similarly (ca. 22%) in response to warming and rising atmospheric CO2. However, the steady increase in WUEi was accompanied by divergent growth patterns since 1980: increasing basal area increment (BAI) in MIN (slope = 0.102 cm2 year−2) and decreasing BAI in BER (slope = −0.129 cm2 year−2). This suggests that increased precipitation, mediated by CO2 effects, promoted growth in MIN, whereas intensified drought stress led to decreased carbon gain and productivity in BER. When compared to warm–dry stands of eastern Spain, the WUEi dependence on WD was three-fold greater in Siberia. Conversely, BAI was more affected by the relative impact of water stress within each region. These results indicate contrasting future trajectories of P. sylvestris forests, which challenge forecasting growth and carbon sequestration in cold–dry areas.

Highlights

Scots pine (Pinus sylvestris L.) is the world’s most widespread conifer as it can be found throughoutEurasia from the western Mediterranean to the Russian Far East
The region belongs to the forest–steppe belt which is bounded by the Siberian taiga in the north and the Mongolian grassland steppe in the south (Figure 1a)
Drier growing seasons became marginally more frequent after 1980 in but colder site (BER) according to MJJA SPEI4 (Wilcoxon rank test, p = 0.08), suggesting an intensifying impact of warming-induced drought stress which was especially noticeable at the turn of this century (Figure 3e)

Summary

Introduction

Scots pine (Pinus sylvestris L.) is the world’s most widespread conifer as it can be found throughoutEurasia from the western Mediterranean to the Russian Far East. There is growing evidence that some cold-constrained sites may be progressively affected by drought stress under warmer conditions due to exacerbated soil moisture deficit linked to decreased precipitation or increased evapotranspirative demand during the vegetative period [18,19,20] Such opposing influences of low temperatures and drought on growth dynamics bring much uncertainty about species vigor and productivity across the whole distribution range [2,16] and, in cold–dry environments [21]. Other dry environments typical of warmer regions such as the Mediterranean, where Scots pine is found at high altitudes, are subjected to winter cold and summer droughts [22] In this regard, the comparison of the simultaneous effects of low temperatures and drought on Scots pine performance near its trailing edge at cold (i.e., Siberian forest–steppe) and at warm environments (i.e., Mediterranean mountains) is of special interest to forecast climate change impacts on conifer forests

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