Temperature sensitivity and recruitment dynamics of Siberian larch (Larix sibirica) and Siberian spruce (Picea obovata) in northern Mongolia’s boreal forest

This study sought to clarify the recruitment dynamics and growth of Siberian larch (Larix sibirica) and Siberian spruce (Picea obovata) in relation to changing temperatures in northern Mongolia. These tree species are the primary forest species found in the closed-canopy boreal forest of north-central Mongolia. Mongolia’s boreal forests exist along the southern terminus of the Siberian boreal system in both pure and mixed species stands. I collected tree cores and cross-sections as well as site and tree stature parameters from 118 forest plots in the Darhad valley of north-central Mongolia. Principle components analysis of 130 L. sibirica tree ring series informed the construction of two composite chronologies for this species. A chronology for P. obovata was developed using 24 tree ring series. Correlation analysis between tree ring indices and temperature data showed two distinct growth signals: a positive response to growing season temperatures was exhibited by one L. sibirica chronology and a negative response to spring temperatures was exhibited by a second L. sibirica chronology. The P. obovata chronology exhibited strong negative correlations with mean monthly and mean maximum monthly growing season temperatures. Multiple analyses of variance (MANOVA) indicated that tree stature (dbh, height) and site parameters (latitude, longitude, slope, aspect, elevation) did not significantly predict growth response or species. Forest recruitment events appear episodic for both species. Synchronous establishment of saplings, based on approximate root collar age, suggests an initial floristic model for mixed composition stands likely due to supra-annual variations of fire, land-use and climate. Forest management activities in the region should consider the diverging growth response to temperature shown here by prioritizing protection forests and the various ecosystem services provided by forests in arid ecosystems. In addition, promoting selection harvests over clear-felling would maximize future alternatives under conditions of rapidly changing climate. Care should be taken in new forest management planning activities until adequate information exists on the likely trajectory of this system due to climate-induced forest change.

► Cohort analysis of forest plots sampled in northern Mongolia indicate all-aged stands.
► Recruitment events appear to be episodic and synchronized by fire and climate.
► Tree ring analysis of larch reveals diverging intraspecies response to temperature.
► Analysis of spruce shows that warming temperatures result in negative growth response.
► Inter and intraspecies divergence will challenge forest managers in a warming climate.