Influence of climatic conditions on growth rings of Salix uva-ursi Pursh from the southeastern shore of Hudson Bay, Subarctic Canada

Figures & data

Figure 1. Location of the study area: (A) (1) the meteorological station in Kuujjuarapik (black square) and the other meteorological stations (black dots): (2) Kuujjuaq (Quebec), (3) Inukjuak (Quebec), (4) Fort George (Quebec), and (5) Moosonee (Ontario). (B) Detailed location of the sampling sites (red circles)

Figure 2. Average (A) monthly climate variations, (B) monthly extreme air temperatures, (C) monthly number of days with rain or snow, and (D) snow cover depth for the Kuujjuarapik meteorological station (12.2 m a.s.l., Quebec, Canada). Tmax abs = the highest monthly averaged daily maximum air temperatures; Tmax avg = average of Tmax; Tmin avg = average of Tmin; Tmin abs = the lowest monthly averaged minimum daily air temperatures. Averages calculated from years with complete monthly data between 1925 and 2017 as shown in Figure 6.

Figure 3. Photographs of (A) lichen–spruce woodlands with Picea glauca [Moench] Voss and shrub vegetation on rocky outcrops and (B) bearberry willow growing on exposed granitic rock cracks

Figure 4. Selected features of bearberry willow wood anatomy, important from a dendrochronology point of view: well-defined semi-ring porous growth rings with (A) regular and (B) variable widths, (C) wedging and locally absent growth rings, and (D) reaction wood with gelatinous cells

Figure 5. Example of the bearberry willow serial sectioning technique. Positions of sampling microtome sections within individual plant and corresponding growth ring width curves

Table 1. Definitions of thermal and precipitation indices

Number	Symbol	Unit	Description
Thermal indices
1	Tavg	°C	Average air temperature calculated for given period (month or year in this study) from daily average air temperature
2	TmaxH	°C	Absolute maximum air temperature—the highest measured daily maximum air temperature for the given period
3	SCTmax5	°C	Positive degree days from days with Tmax > 5°C. Degree days calculated as the sum of degrees Celsius above the threshold
4	SCTmax10	°C	Positive degree days from days with Tmax >10°C
5	SCTmax15	°C	Positive degree days from days with Tmax >15°C
6	TminL	°C	Absolute minimum air temperature—the lowest measured daily minimum air temperature for the given period
7	SCTmin−5	°C	Negative degree days* from days with Tmin <−5°C
8	SCTmin−10	°C	Negative degree days* from days with Tmin <−10°C
9	SCTmin−15	°C	Negative degree days* from days with Tmin <−15°C
10	Aabs	°C	Absolute amplitude of air temperature—difference between the highest TmaxH and the lowest TminL
Precipitation indices
11	PToT	mm	Precipitation total
12	RToT	mm	Rain total
13	RNoD 0.1	Number of days	Number of days with rain total ≥0.1 mm
14	RNoD 1	Number of days	Number of days with rain total ≥1 mm
15	RNoD 5	Number of days	Number of days with rain total ≥5 mm
16	RNoD 10	Number of days	Number of days with rain total ≥10 mm
17	RDToT	mm × day^−1	Average daily precipitation total. Simple index of daily precipitation intensity.
18	SToT	mm	Snow total
19	SNoD 0.1	Number of days	Number of days with snowfall ≥0.1 mm
20	S%inP	%	Contribution of snow fall total into precipitation total
21	PNoD 0	Number of days	Number of days with precipitation total = 0 mm
22	DSC	cm	Depth of snow cover

Table 2. Correlation coefficients between monthly air temperatures at Kuujjuarapik and corresponding air temperatures at neighboring stations. The monthly air temperatures from these stations were used to reduce the gaps in the Kuujjuarapik series. h - altitude m a.s.l

Station	Kuujjuaq (Quebec)	Inukjuak (Quebec)	Fort George (Quebec)	Moosonee (Ontario)
Period	1947–2017	1925–1993	1925–1969	1925–2017
Location	58°10′ N, 68°42′ E h = 40	58°47′ N, 78°08′ E h = 24	58°10′ N, 68°42′ E h = 40	58°10′ N, 68°42′ E h = 40
January	0.788	0.877	0.943	0.819
February	0.773	0.885	0.930	0.863
March	0.877	0.940	0.973	0.909
April	0.820	0.894	0.961	0.820
May	0.704	0.776	0.841	0.748
June	0.792	0.784	0.537	0.672
July	0.538	0.672	0.769	0.587
August	0.703	0.744	0.858	0.763
September	0.778	0.855	0.801	0.829
October	0.841	0.881	0.929	0.869
November	0.809	0.857	0.948	0.858
December	0.823	0.858	0.941	0.876

Figure 6. Temporal coverage of climatic data for the Kuujjuarapik station. Lines represent years with complete monthly data calculated according to the rules adopted in this article. S = snow, R = rain, P = precipitation, SC = snow cover, T_max = maximum air temperature, T_min = minimum air temperature, T_avg = average air temperature

Figure 7. Time series plot of the bearberry willow (A) ring width and (B) index chronologies for the eastern shore of Hudson Bay covering the last 105 years. Red line indicates eleven-year moving average. Gray shading represents changing sample sizes between years. Note the decline in growth in recent decades

Table 3. Meteorological conditions accompanying the formation of negative dendrochronological years

Year	Description of meteorological conditions
1926	The second coldest year in the entire meteorological series (dev −6.8°C); very low temperature in May (−22.8°C); the highest amplitude in May in the whole series (47°C)
1945	145 mm of precipitation from January to March
1980	The lowest maximum temperature in February in the entire meteorological series (−11.2°C); long duration of snow cover (June 9—last day of snow cover^a); occurrence of six freeze–thawing cycles in late spring (June)/early autumn (September)^b
1989	The coldest March in the entire meteorological series (dev −5.4°C); long duration of snow cover (May 29—last day of snow cover^a); occurrence of six freeze–thawing cycles in late spring (June)/early autumn (September)^b
1997	The coldest March in the entire meteorological series (dev −5.4°C)

Note: dev = deviation from the average monthly or annual temperature over the entire instrumental period (1925–2017).

^aThe average last day of snow cover in Kuujjuarapik is May 24.

^bThe average number of freeze–thawing cycles in late spring (June)/early autumn (September) in Kuujjuarapik is two.

Figure 8. Single-month and strongest seasonal correlations of the bearberry willow chronology. T_avg = average air temperature; P_ToT = precipitation total, T_max = maximum air temperature, T_min = minimum air temperature, T_maxH = absolute maximum air temperature, T_minL = absolute minimum air temperature. Statistically significant values are marked by colored bars (p(a) < .05, n = 35, 1957–1992)

Figure 9. Results of climate–growth response analyses comparing the bearberry willow chronology and various (A) thermal, (B), (C) precipitation, and (D) snow indices calculated based on daily data from the Kuujjuarapik meteorological station. Gray shading indicates statistically insignificant values (p(a) > .05, n = 35, 1957–1992)

Table 4. Trends in selected precipitation indices and mean temperature impacting (significantly correlated) the radial growth of bearberry willow for the period 1957–2014

Period	June	July	January–December
Missing	2 years	2 years	10 years
RNoD0.1	+0.3	0	+12.5*
RNoD1	0	0	+9.5*
RNoD10	0	0	+2.4*
Tmean	0.47*	0.42*	0.38*

Note: Statistical significance of trends tested with Mann-Kendall method and trend magnitudes calculated with related Sen’s slope. missing = number of missing years.

*p < .001.

Figure 10. Comparisons of variability of bearberry willow growth rings indices with (A) annual mean temperature and (B) number of days with rain >0.1 mm