The role of summer precipitation and summer temperature in establishment and growth of dwarf shrub Betula nana in northeast Siberian tundra

Table 1 Pearson’s correlation coefficient for relationships between annual ring-width index (RWI) of Betula nana and local climate variables (summer temperature (June–August), early summer temperature (June 16–July 20), precipitation (cumulative, June–August), mean snow depths (previous year’s October–May) and growing days and standardized precipitation evapotranspiration index (SPEI) in summer) over the years 1962–2011 (n = 50 years), the years with warm summers (early summer temperature above median (9.58 °C), n = 25) and the years with cool summers (early summer temperature below median, n = 25)

Climate variable	1962–2011
	All years		Warm summers		Cool summers
	(n = 50 years)		(n = 25 years)		(n = 25 years)
	Coeff.	p value	Coeff.	p value	Coeff.	p value
Temperature variables (°C)
Length of growing season	−0.289*	<0.046	0.249	0.253	0.302	0.142
Start date of growing season	−0.099	<0.493	0.177	0.396	−0.062	0.770
Summer temperature	−0.496**	<0.001	0.052	0.813	0.296	0.150
Early summer temperature	−0.727**	<0.001	0.468*	0.018	0.524**	0.007
Previous year’s summer temperature	−0.084	<0.568	0.013	0.950	−0.001	0.998
Previous year’s early summer temperature	−0.042	<0.772	0.339	0.098	−0.163	0.436
Precipitation variables (mm)
Summer precipitation	−0.136	0.348	0.530**	0.006	−0.190	0.363
Previous year’s summer precipitation	−0.139	0.336	0.451*	0.024	−0.124	0.554
Mean snow depth (cm)	−0.084	0.560	0.042	0.840	−0.243	0.242
SPEI
SPEI June–August	−0.107	0.458	0.408*	0.043	−0.091	0.664
Prev. SPEI June–August	−0.286*	0.044	0.445*	0.026	−0.097	0.643
SPEI previous year’s June–August	−0.208	0.146	0.507*	0.010	−0.151	0.471

The coefficients with * and ** represent a significant correlation between the RWI and the climatic variable (p < 0.05; p < 0.01)