Biospheric Sciences Branch Seminar

V. N. Sukachev Institute of Forest, Krasnoyarsk, Russia
(Altai-Sayan Mountain System, Siberia) Speaker: Prof. Viatcheslav (Slava) Kharuk Abstract: Tree response to climate trends is most likely observable in zones where temperature limits tree growth. Our satellite-based and on-ground studies showed that trees in the forest-tundra ecotone of Sayan-Altai Mountains system, Siberia, are strongly responded to warming during the past three decades. There was an increase in forest stand crown closure, regeneration propagation into the alpine tundra, and transformation of prostrate Siberian pine, fir and larch into arboreal forms. Measurements of tree radial and apical growth increments showed strong positive trends since the mid 1980s, which are strongly correlates with summer temperatures. During this time period sparse stands transformed into closed stands, with existing closed stands increasing in area at a rate of ~ 1 %/yr, and advancing their upper border by ~ 1.0 m/yr. Regeneration of Siberian pine and larch has appeared mainly during the last two decades. Their numbers depend on growing season temperatures, and, which is notable, winter temperatures. A temperature increase of 1?º allows regeneration to occupy areas ~150 m higher in elevation. Regeneration is propagating into the alpine tundra at a rate of 3-5 m/yr. Regeneration and arboreal forms now occur at elevations of 30 to 200 m higher in comparison with the former tree line. Siberian pine response to warming is greater in comparison with larch, both in radial growth increments and regeneration amount. Improving climate provides competitive advantages to Siberian pine: its presence in the alpine forest-tundra ecotone is increasing, as well as in areas typically dominated by larch, where it has been found to be forming a secondary canopy layer. A comparative analysis showed that the described tree response to climate warming is characteristic for the boreal Eurasian mountain forest-tundra ecotone.