<p class="MDPI13authornamesori1" style="margin-bottom: 12.0pt; mso-line-height-alt: 14.0pt;">Larch (<em>Larix sibirica</em> Ledeb.) and Poplar (<em>Populus laurifolia</em> Ledeb.) Are Moving into the Goby Desert

Trees in the ecotones are most sensitive to the changing climate. Here we analyzed growth and dynamics of larch and poplar trees in the unique refugia that border Mongolian desert in southern Siberia. We aimed to analyze (1) larch (Larix sibirica Ledeb.) and poplar (Populus laurifolia Ledeb.) radial growth dependence on climate variables, (2) tree migration into desert, and (3) gross primary production (GPP) of ground cover in refugia and in the adjacent desert. We used on-ground survey, dendroecological methods, and remote sensing analysis (satellite and Unmanned Aerial Vehicle, UAV). We found that the larch population in refugia consists of an old-growth cohort and a young cohort. The age of old-growth trees (A = 500+) indicates that refugia may have existed throughout the Holocene. The young cohort (A = 50+) has existed since the warming onset in the 1970th. The poplar population includes single old-growth specimens (A &gt; 200 y) and young trees (A = 50+ y). Growth of both larch and poplar species is controlled by air and soil droughts (indicated by SPEI and scPDSI indexes, respectively). Old-growth larch trees are less sensitive to available moisture compared with young larch and poplar. Summer winds impair larch growth. In the 21st century, populations increased by +46% and +36% (for larch and poplar, respectively. Both larch and poplar trees are slowly migrating into the adjacent desert. Unexpectedly, poplar trees spread ahead of the more drought-resistant larch into the desert (by 280 m vs 35 m for larch). Poplar, due to its higher seed production, is pioneer tree species that occupies new niches caused by the changing hydrology regime. We found that desert vegetation, which is composed of small bushes, is “greening” due to GPP increase. The increased population and growth of larch and poplar trees, together with their migration into the desert, contradict the predicted shrinkage of their range at its southern boundary. However, the predicted increase of moisture deficit may impair the acceleration of tree growth and its southward migration in the future. Nevertheless, current changes in climate are favorable for the growth of trees and shrubs at the northern boundary of the Great Gobi Desert.