Vertical root distribution and biomass allocation along proglacial chronosequences in Central Switzerland

Figures & data

Table 1. Study site characteristics with terrain ages of the moraines, elevation, slope exposition, slope, bedrock, vegetation cover, species richness, and vegetation type of Stein Glacier (Susten Pass) and Griess Glacier (Klausen Pass) forelands

Moraine	Terrain age (years)	Elevation (m.a.s.l.)	Slope exposition (°)	Slope (%)	Bedrock	Soil type	Vegetation cover (%)	Species richness (n)	Vegetation type
Stein Glacier (Susten Pass, Central Switzerland)
30 a	30	1,990	ENE	40	Gneiss	Hyperskeletic Leptosol	49	23	Pioneer vegetation
160 a	160	1,990	ENE	31	Gneiss	Hyperskeletic Leptosol	98	43	Initial grassland and Salix shrubberies
3 ka	3,000	1,890	SW	25	Gneiss	Skeletic cambisol	94	33	Carex sempervirens grassland
10 ka	10,000	1,880	N	22	Gneiss	Entic Podzol	100	29	Rhododendron ferrugineum shrubberies and Nardus grassland
Griess Glacier (Klausen Pass, Central Switzerland)
80 a	80	2,200	WNW	27	Limestone	Hyperskeletic Leptosol	21	31	Pioneer vegetation
160 a	160	2,030	NE	31	Limestone	Hyperskeletic Leptosol	48	32	Scree vegetation
4.9 ka	4,900	2,010	N	37	Limestone	Calacaric Skeletic Cambisol	98	19	Carex ferruginea grassland
13.5 ka	13,500	2,000	NW	44	Limestone	Calacaric Skeletic Cambisol	100	11	Rhododendron hirsutum shrubberies and Carex ferruginea grassland

Figure 1. Location of (A) the Griess Glacier foreland (46°50′ N, 8°49′ E) and (B), (C) the lower and upper parts of the Stein Glacier foreland (47°43′ N, 8°25′ E). The terrain age of the moraines is given in years (a) and thousands of years (ka). Inset in (A) Switzerland with locations of both study sites. Satellite images: Google Maps, 2020, https://google.de/maps/place/Schweiz/@46.6192509,7.4679619.

Table 2. List of traits investigated in the present study

Root trait	Unit	Description
FRMD	g cm^−3	Dry weight of fine roots (diameter <1 mm) per unit soil volume
FRLD	cm cm^−3	Root length of fine roots (diameter <1 mm) per unit soil volume
SRL	cm g^−1	Root length per unit dry weight of fine roots
RTD	g cm^−3	Dry weight per root volume of fine roots
β		Measure for shallow and deep rooting, respectively: $Y=1-{\beta }^d$
BGB	kg m^−2	Belowground biomass
AGB	kg m^−2	Aboveground biomass
R:S ratio	%	Root-to-shoot ratio

Figure 2. Vertical distributions of mean FRMD, FRLD, SRL, and RTD per soil depth increment across the moraines of (a), (c), (e), (g) Stein Glacier and (b), (d), (f), (h) Griess Glacier forelands. Error bars show the standard error of the mean. The terrain age of the moraines is given in years (a) and thousands of years (ka).

Figure 3. Effect sizes of FRMD, FRLD, SRL, and RTD of (a), (c), (e), (g) Stein Glacier and (b), (d), (f), (h) Griess Glacier forelands. Effect sizes indicate the rate of change of the root traits per 100 years of terrain age. The response variables are on a log scale.

Table 3. Mean vertical root distribution coefficient, β, and root fractions in the soil top 30 cm (RF_Top30cm) across the moraines of the study sites

Site	Moraine	βFRMD	RFTop30cm	βFRLD	RFTop30cm
Stein Glacier	30 a	0.974^a	70.15^a	0.961^a	54.61^a
Stein Glacier	160 a	0.942^a	80.63^a	0.947^a	83.22^a
Stein Glacier	3 ka	0.921^a	92.08^a	0.919^a	91.50^a
Stein Glacier	10 ka	0.936^a	87.38^a	0.933^a	86.09^a
Griess Glacier	80 a	0.961^a	67.46^b	0.963^a	69.71^b
Griess Glacier	160 a	0.956^a	72.53^b	0.958^a	73.68^ab
Griess Glacier	4.9 ka	0.818^b	99.50^a	0.838^b	99.76^a
Griess Glacier	13.5 ka	0.922^a	88.31^ab	0.931^a	91.34^ab

Notes. The model of Gale and Grigal (1987) was used to calculate β coefficients from FRMD and FRLD. A post hoc LSD test was conducted to compare root distribution measures among the moraines. The significance level was adjusted according to the Bonferroni method. Superscript letters indicate significant differences. The terrain age of the moraines is given in years (a) and thousands of years (ka).

Figure 4. Vertical distribution of (a), (b) root mass and (c), (d) root length across the moraines (see Table 1) of the (a), (c) Stein Glacier and (b), (d) Griess Glacier forelands. The vertical root distribution was fitted using the model proposed by Gale and Grigal (1987). The resulting β coefficients are shown in Table 4. The cumulative root fraction represents the percentage of roots from the soil surface to the depth considered relative to the total roots of the soil profile. Models are plotted showing the 95 percent confidence intervals.

Table 4. Mean BGB, AGB, and R:S ratio across the moraines of the study sites

Site	Moraine	BGB (kg m^−2)(<1 mm/1–2 mm/>2 mm)	AGB (kg m^−2)(grasses/forbs/shrubs)	R:S ratio
Stein Glacier	30 a	0.16 (82/11/16)	0.16 (14/23/63)	0.96
Stein Glacier	160 a	0.99 (48/14/38)	0.84 (6/11/84)	1.18
Stein Glacier	3 ka	0.96 (82/10/8)	0.41 (28/51/20)	2.32
Stein Glacier	10 ka	2.29 (40/10/49)	1.95 (5/5/91)	1.17
Griess Glacier	80 a	0.09 (55/21/24)	0.44 (2/19/80)	0.22
Griess Glacier	160 a	0.37 (82/7/31)	0.34 (14/35/51)	1.07
Griess Glacier	4.9 ka	1.21 (75/9/15)	0.48 (37/17/46)	2.50
Griess Glacier	13.5 ka	2.03 (71/6/23)	0.38 (37/22/62)	5.29

Notes. Percentage contributions of root diameter classes (<1 mm, 1–2 mm, >2 mm) and functional groups (grasses, forbs, shrubs) are given in parentheses. The terrain age of the moraines is given in years (a) and thousands of years (ka).

Figure 5. AGB, BGB, and R:S ratio across different moraines and the relationships between AGB and BGB of (a), (c), (e), (g) Stein Glacier and (b), (d), (f), (h) Griess Glacier forelands. A post hoc LSD test was conducted to compare biomass measures among the moraines. The significance level was adjusted according to the Bonferroni method. Superscript letters indicate significant differences.

Table 5. Pearson correlation coefficients of vertical root distribution coefficients and vegetation composition

	βRD	βRLD	BGB
Species richness	−0.3	−0.35	0.23
AGB	−0.01	0.02	0.61
Grass AGB	−0.65	−0.59	0.54
Forb AGB	0.02	0.04	0.05
Shrub AGB	0.06	0.08	0.55
Vegetation cover	−0.33	−0.33	0.38
Grass cover	−0.29	−0.35	0.32
Forb cover	−0.25	−0.25	0.13
Shrub cover	−0.16	−0.13	0.57

Note. Bold numbers indicate significant correlations (p < .05).

Gale, M., and D. F. Grigal. 1987. Vertical root distributions of northern tree species in relation to successional status. Canadian Journal of Forest Research 17 (8):829–34. doi:https://doi.org/10.1139/x87-131.

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