Dr. M D’Amico*

Dr. M Freppaz*

Prof. E Zanini*

*Università di Torino,

DISAFA, NatRisk

Vegetation and parent material influence on

pedogenic rates in the Western Italian Alps

Introduction

On the Alps (precipitation: 800-1500 mm/y), on sialic materials under subalpine

coniferous forest/ericaceae:

- Podzols are “climax” soils, they develop in more than 600-3000 years (e.g., Egli

et al. 2006, Dümig et al. 2011), the podzolization process is not observed in LIA

glacier forefields.

- climax vegetation in more than 200 years; on LIA moraines Alnus viridis, Salix

ssp, low cover by conifers and Ericaceae.

In more humid climates (Alaska, New Zealand, precipitation: 2000-10000mm):

- Podzols form in 200 years, E horizons in 90 years (with coniferous forest).

Climate is the reason for different rates.

Glacier retreat since the end of the Little Ice Age (ca. 1350-1850 AD):

- large surfaces attacked by pedogenesis and colonized by vegetation.

But...

Introduction In Aosta Valley (NW Italian Alps), E horizons are visible on 90 – 150 years old

moraines (Lys1, Verra Grande2 (Monte Rosa) and Miage (Mont Blanc)).

Study area: 2 forefields in the Monte Rosa Massif, but with different vegetation,

parent materials.

Lys forefield, gneiss

Subalpine chronosequences (grazed

grassland / forest)

Glacier tongue (dead ice, 2010):

2400 m; 1821 moraine: 2100 m.

Present-day timberline: ca. 2300 m

a.s.l.

Very stable surfaces, protected by

lateral moraines from external

inputs of “older” materials.

No river

erosion

C1-C2 horizons

Initial weathering in C1,

few roots

Depth pH Corg cm %

C1 0-8 6.6 0.04 C2 8-47+ 6.8 0

ca. 1880 SG7grazed grassland

Thin litter (OH), composed by

Graminaceae

Brown and structured Bw

Haplic Cambisol (Dystric)

ca. 1880 S6: larch-rhododendron

forest

Thick litter (OL-OF-OH)

E horizon, weak platy structure

BC horizon, weak Fe-Al illuviation

Haplic Regosol (Dystric)

Pre-LIA, subalpine forest 1821 moraine

E horizons only below larch-

rhododendron forest

patches, also in 90 years

old soils

Cambisols under herbaceous

vegetation below and

above timberline, in 150-

260 years

forest

grassland

Chronofunctions for spodicity

requirements:

IS(B)/IS(E) = 0.676*age0.185

Ca. 350 years necessary

IS=0.5Feo+Alo=0.045+0.003*age0.8

ca. 530 years are needed

forest

forest

TOC concentration in surface decrease in

forest soil after a strong initial increase,

faster increase in subsurface, compared to

grassland soils;

Significant differences (p<0.1)

C/N ratio and pH values significantly different

Verra Grande forefield, serpentinite

Western lateral moraines

(serpentinite 100%)

Basal till chronosequence

(serpentinite 100%)

Eastern lateral moraines

(serpentinite 95%)

0 point: unstable slopes West moraine East moraine

0 point: unstable slopes West moraine East moraine

Weak Corg accumulation in

surface CA horizon (roots)

11 species, total cover = 40%

No endemics

0 point: unstable slopes West moraine

No signs of pedogenesis

Only 6 species, with total cover <

1%

1 serpentine endemic (Cardamine

plumieri)

1860 moraines West arch

1860 moraines Basal till

1860 moraines East arch

1860 moraines West arch East arch Basal till

1821 moraines Western arch

1821 moraines Basal till

1821 moraines Eastern arch

Only 40 years???

Desappearence of all pioneer and

basophilous species;

Complete colonization by

acidophilous subalpine open

forest vegetation

1821 moraines?? West arch East arch Basal till

Thick litter (9 cm, OL-OF-OH)

E-B(s?)-C (podzolization!)

Only 40 years??? Accumulation and subsurface

redistribution of Corg;

E and Bs horizons formation;

Fe/Al/Ni cheluviation;

On serpentinite????

Depth pH Corg C/N Feo Ca/Mg Ni cm % % mg/kg

OH 2-3 6.3 24.1 25.1 A 3-10 6.4 1 20.0 0.17 0.4 13.3

AC 10-18 7.1 0.2 11.5 0.11 0.3 5.2 C 18-23 7.1 0.1 0.08 0.6 1.9

Depth pH Corg C/N Feo Ca/Mg Ni cm % % mg/kg

OH 5-9 5.8 21.1 19.5 E 9-13 6.1 1.2 16.7 0.38 0.3 39.8

B(s) 13-24 6.6 1.5 17.1 0.69 0.4 51.8 C 24-55 7.1 0.3 0.42 0.3 10.1

Climax soils East moraines West moraines

Dystric Regosol Haplic Podzol

Corg:

“rich” serpentine soils

pure serpentine

Gneiss forest soils

Gneiss grassland

Nutrient cycling

N tot:

“rich” serpentine soils

pure serpentine

Gneiss forest soils

Gneiss grassland

Available P/total P:

“rich” serpentine soils

pure serpentine

Gneiss forest soils

Gneiss grassland

Nutrient cycling

P tot:

“rich” serpentine soils

pure serpentine

Gneiss forest soils

Gneiss grassland

Nutrient cycling

Extremely different initial points:

Low “primary” nutrients

Low primary productivity

Low organic matter accumulation

Low acidification

Different pedogenic pathways (otherwise similar)

Conclusions

Parent material differences create different “starting points”, which create

different nutrient cycling which have impacts on the ecosystem development,

for a long time.

Many soil properties, including nutrient cycling, diverge after the colonization by

subalpine coniferous-ericaceous vegetation.

Quicker onset of podzolization in Valle d’Aosta can be caused by early

colonization by subalpine forest species

This can be caused by higher grazing intensity preventing Alnus and Salix ssp

colonization? Or to an extreme surface stability?

Thank you!