The ecosystem carbon sink implications of mountain forest expansion into abandoned grazing land: The role of subsoil and climatic factors
Author(s)
Date Issued
2019
Type
article
Volume
672
Start Page
106
End Page
120
Journal
Abstract
Woody encroachment is a widespread phenomenon resulting from the abandonment ofmountain agricultural and
pastoral practices during the last century. As a result, forests have expanded, increasing biomass and necromass carbon
(C) pools.However, the impact on soil organic carbon (SOC) is less clear. Themain aimof this studywas to investigate
the effect of woody encroachment on SOC stocks and ecosystem C pools in six chronosequences located
along the Italian peninsula, three in the Alps and three in the Apennines. Five stages along the chronosequences
were identified in each site. Considering the topsoil (0–30 cm), subsoil (30 cm-bedrock) and whole soil profile,
the temporal trend in SOC stocks was similar in all sites, with an initial increment and subsequent decrement in
the intermediate phase. However, the final phase of the woody encroachment differed significantly between the
Alps (mainly conifers) and the Apennines (broadleaf forests) sites, with a much more pronounced increment in
the latter case. Compared to the previous pastures, after mature forest (N62 years old) establishment, SOC stocks
increased by: 2.1(mean) ± 18.1(sd) and 50.1 ± 25.2 Mg C·ha−1 in the topsoil, 7.3 ± 17.4 and 93.2 ±
29.7 Mg C·ha−1 in the subsoil, and 9.4 ± 24.4 and 143.3 ± 51.0 Mg C·ha−1 in the whole soil profile in Alps and
Apennines, respectively. Changes in SOC stocks increased with mean annual air temperature and averageminimum
winter temperature, and were negatively correlated with the sum of summer precipitation. At the same time, all other C pools (biomass and necromass) increased by 179.1±51.3 and 304.2±67.6Mg C·ha−1 in the Alps and the
Apennines sites, respectively. This study highlights the importance of considering both the subsoil, since deep soil
layers contributed 38% to the observed variations in carbon stocks after land use change, and the possible repercussions
for the carbon balance of large areas where forests are expanding, especially under pressing global warming
scenarios.