Hydraulic traits and tree-ring width in Larix sibirica Ledeb. as affected by summer drought and forest fragmentation in the Mongolian forest steppe

Abstract

Wood-anatomical traits determining the hydraulic architecture of Larix sibirica in the drought-limited Mongolian forest steppe at the southern fringe of the boreal forest respond to summer drought, but only weakly to variations in microclimate that depend on forest stand size. Siberian larch (L. sibirica Ledeb.) is limited by summer drought and shows increasing mortality rates in the Mongolian forest steppe. The climate sensitivity of stemwood formation increases with decreasing forest stand size. The trees’ hydraulic architecture is crucial for drought resistance and thus the capability to deal with climate warming. We studied whether hydraulic traits were influenced by temporal or forest size-dependent variations in water availability and were related to tree-ring width. Hydraulic traits (tracheid diameter, tracheid density, potential sapwood area-specific hydraulic conductivity) of earlywood were studied in stemwood series of 30 years (1985–2014) and were related to climate data. Tree-ring width was measured for the same period. Trees were selected in stands of four different size classes with increasing drought exposure with decreasing stand size. Tracheid diameters and hydraulic conductivity decreased with decreasing late summer precipitation of the previous year and were positively correlated with tree-ring width. Forest stand size had only weak effects on hydraulic traits, despite known effects on stemwood increment. Decreasing tracheid diameters and thus hydraulic conductivity are a drought acclimation of L. sibirica in the Mongolian forest steppe. These acclimations occur as a response to drought periods but are little site-dependent with respect to stand size.