The different strategies of Pinus sylvestris and Larix sibirica to deal with summer drought in a northern Mongolian forest–steppe ecotone suggest a future superiority of pine in a warming climate

Abstract

Pinus sylvesteris L. is locally common at the lower forest line to the steppe in Mongolia’s taiga forests, which are otherwise dominated by Larix sibirica Ledeb. The factors responsible for the occurrence of pine patches in the forest–steppe ecotone are insufficiently studied. We analyzed the response of P. sylvestris to summer drought in the western Khentey Mountains, northern Mongolia, by measuring shoot water potentials and exemplary measurements of δ13C signatures, CO2–H2O gas exchange, chlorophyll fluorescence yield, and concentrations of nonstructural carbohydrates. Pine trees growing in the forest–steppe ecotone show conservative water consumption with a sensitive stomatal regulation and relatively constant shoot water potentials under dry conditions. This might be a selective advantage for P. sylvestris against increasing aridity driven by global warming, since the main competitor, L. sibirica, often suffers from drought stress even under the current climate in the study area.