Table 6. Estimates of treatment effects on plant sizes throughout the growing season, as well as peak size and number of thawing degree days needed to reach peak size.

Species	Treatment	Effect ± sd	t-value	p-value	df	Peak size	TDD peak
Alopecurus magellanicus	Intercept (Normal)	84.4±11.4				112.9	334.0
	Removed	14.1±13.3	1.06	0.291		104.5	322.4
	Shallow	15.2±10.4	1.45	0.148		137.2	345.2
	Medium	42.1±9.9	4.25	<0.001		168.4	362.8
	Deep	19.1±10.0	1.91	0.058	173	127.0	334.9
Bistorta vivipara	Intercept (Normal)	360.5±60.6				505.4	296.0
	Removed	23.8±73.0	0.33	0.745		489.1	280.2
	Shallow	11.3±63.7	0.18	0.859		471.6	271.9
	Medium	238.3±63.2	3.77	<0.001		793.1	297.6
	Deep	344.3±60.0	5.73	<0.001	295	705.1	370.1
Cassiope tetragona	Intercept (Normal)	2.32±0.29				3.41	419.6
	Removed	−1.37±0.39	−3.53	<0.001		1.34	466.7
	Shallow	−2.13±0.31	−6.78	<0.001		0.16	0.0
	Medium	−1.89±0.32	−5.93	<0.001		0.18	295.1
	Deep	−0.84±0.29	−2.91	0.004	177	1.47	494.9
Dryas octopetala	Intercept (Normal)	18.2±2.2				22.2	410.2
	Removed	5.1±2.0	2.51	0.013		31.3	570.0
	Shallow	−0.8±1.7	−0.45	0.653		21.3	399.0
	Medium	11.0±1.9	5.96	<0.001		38.5	542.0
	Deep	6.9±1.9	3.69	<0.001	288	33.9	497.6
Luzula arcuata	Intercept (Normal)	77.4±10.9				108.9	236.6
	Removed	20.5±8.7	2.35	0.020		122.0	240.1
	Shallow	−23.8±7.1	−3.37	<0.001		71.0	248.5
	Medium	−7.9±7.6	−1.05	0.297		127.7	287.1
	Deep	11.2±7.0	1.60	0.112	261	131.9	269.0
Pedicularis hirsuta	Intercept (Normal)	29.6±2.2				34.9	526.6
	Removed	−4.5±1.8	−2.46	0.016		22.0	413.3
	Shallow	−12.4±1.5	−8.02	<0.001		22.6	520.8
	Medium	−5.7±1.9	−3.04	0.003		31.3	428.8
	Deep	−0.4±2.2	−0.17	0.867	112	47.0	570.0
Salix polaris	Intercept (Normal)	12.1±0.7				15.2	281.3
	Removed	0.3±0.7	0.51	0.611		14.1	283.0
	Shallow	0.6±0.6	1.08	0.283		14.8	280.3
	Medium	−0.2±0.6	−0.40	0.693		13.9	329.4
	Deep	−1.3±0.6	−2.34	0.020	324	10.5	296.2
Stellaria crassipes	Intercept (Normal)	6.9±1.4				10.9	515.7
	Removed	3.1±1.9	1.60	0.112		11.5	570.0
	Shallow	4.4±1.9	2.36	0.020		5.7	489.9
	Medium	−3.4±1.7	−1.98	0.050		7.2	570.0
	Deep	−1.8±2.0	−0.89	0.373	148	10.0	570.0

Effect values other than the intercept (here: Normal treatment) are deviations from the latter. Given are standard deviation (sd), t- and p-value and degrees of freedom (df) of the model. Modeled maximal plant sizes and TDD (thawing degree days, i.e. positive air temperature sums in °C) to reach the maximum size are based on the model shown in Table 3, and are shown as values for each treatment, rather than deviation from the Normal treatment. Normal = unmanipulated snow cover; Removed = snow removal on 1. May; Shallow = naturally early snowmelt; Medium = intermediately increased snow; Deep = maximally increased snow. Measures for plant species: average sum of leaf lengths (in mm) for Alopecurus magellanicus, Dryas octopetala, Luzula arcuata, Salix polaris; average sum of leaf areas (in mm²) for Bistorta vivipara; average annual shoot increment (in mm) for Cassiope tetragona; average plant sizes (in mm) for Pedicularis hirsuta, Stellaria crassipes.