# Siberian Pine and Larch Response to Warming-Drying Climate in the Southern Boundary of Their Range
## 1 Introduction
A deciduous pattern and high water-use efficiency allow that species to grow in semi-desert conditions (up to 250 mm/year) [27]. Due to its resistance to harsh environments, larch is the dominant species within the Siberian permafrost zone, and it formed northern and alpine treelines. Since the warming onset (the 1970s), larch growth has increased, and densification of larch forests has been reported [24; 28]. In the most parts of the larch habitat, including high elevations, air and soil temperatures are namely limiting larch growth. Consequently, the current warming has stimulated larch growth [21]. Meanwhile, the warming-driven increase in aridity has facilitated seasonal water stress at the beginning of the growing season [21]. In addition, the warming-driven burning rate has led to the transformation of sparse southern larch forests into forest-steppe and steppe communities [22]. Unlike larch, Siberian pine is intolerant to low air humidity. This highly moisture-sensitive species primarily occupies areas with precipitation up to 1000+ mm/year, although it can successfully grow at lower precipitation levels (about 500 mm/year). Compared to larch, Siberian pine is a less cold-resistant species, and it can be found beyond the Arctic Circle and often forms (together with larch but behind larch) treelines in the mountains. Siberian pine rarely forms pure stands. Regularly, that species, together with fir (_Abies sibirica_ [PERSON]) and spruce (_Pica obovata_ Ledeb. ), forms mixed \"dark-needle coniferous\" forests, which are the second (after larch forests) largest forest formation in Siberia. In the warming and drying climate, Siberian pine, as well as fir, has experienced increasing mortality in the low elevations since the 1990s. That phenomenon is caused mainly by the synergy of water stress (inciting factor) and pest attacks (contributing factor) [8; 10; 29; 30]. Meanwhile, in the areas of sufficient precipitation, Siberian pine has shown increased growth and uphill migration [31]. Despite the contrasting ecological niches of Siberian pine and larch, both species can form mixed forests within the boundaries of their ranges, e.g., in the southern Siberian Mountains. Meanwhile, in the future, the spatial distribution of climate and growth rates of these species will experience significant changes. The first phases of those changes should be yet observable within the edges of both species' ranges. Therefore, we selected a study area within the southern part of Altai-Sayan Mountain Country, i.e., the Tannu-Ola Ridge (Figure 1). The Siberian pine forests that occupied the northern slope of that ridge are within the southern edge of that pine range. Larch forests on the southern slope sharply turn into Mongolian steppes to the south. For our studies, we selected three contrasting elevation belts, i.e., the treeline ecotone, the mixewood forest formed by larch and Siberian pine, and the forest-steppe ecotone. We hypothesize that distinct changing climate influences on the larch and Siberian pine growth will be visible (1) along the elevation gradient and (2) within the different elevation belts. In addition, we analyzed the temporal dynamics of birch (_Betula_ sp. ), a minor component of the forests, and shrubs (which occurred mostly within and beyond the treeline ecotone). Figure 1: (**a**) The study area location; (**b**) test plot locations: 1—treeline ecotone (elevation \(\sim\)2100 m), 2–5—mixed forest (\(\sim\)2000–1200 m), 6—forest-steppe ecotone (\(\sim\)1100 m). The Siberian pine- and larch-dominant stands are marked by red and yellow, respectively, and mixed stands are marked by green. We seek the answers to the following questions:  
1. What are the Siberian pine and larch radial growth dynamics within the treeline, mixewood forest, and forest-steppe ecotone? 2. How do larch and Siberian pine growth depend on the air temperature, moisture variables (precipitation, VPD, soil moisture), and wind speed along the elevation gradient? 3.