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Araucaria forest expansion on grassland in the southern Brazilian highlands as revealed by 14C and δ 13C studies
Ist Teil von
Geoderma, 2008, Vol.145 (1), p.143-157
Ort / Verlag
Elsevier B.V
Erscheinungsjahr
2008
Link zum Volltext
Quelle
Alma/SFX Local Collection
Beschreibungen/Notizen
The vegetation of the southern Brazilian highlands in Rio Grande do Sul State is a mosaic of grassland (C
4) and deciduous forests (C
3) with the conifer
Araucaria angustifolia. It was uncertain, whether the grasslands represent relics of drier periods in the Holocene or if they are the result of deforestation in recent times. We analyzed plant tissues from gramineous and woody species, organic surface layers, as well as soil organic matter of 13 Andosols and Umbrisols in grassland, shrubland, pine plantations and
Araucaria forest for stable carbon isotope ratios (
δ
13C) and
14C activity. The soil organic matter was separated into a free particulate organic matter (fPOM) and a heavy, organo-mineral fraction by density fractionation. All grassland soils have consistently
δ
13C values of −
18.7 to −
14.3‰ typical for C
4 grasses. In
Araucaria forests and forest patches within grassland the
δ
13C values of both, the fPOM throughout the soil and the organic surface layers, are characteristic for the present below- and above-ground input from C
3 trees. The C
3- and C
4-derived SOC stocks reflect expansion of
Araucaria forest on grassland, which started after 1300 yr BP. The youngest forests are found at the forest border and in forest patches. Grassland soils lose their typically black colour from the top downwards after shrub encroachment or establishment of forest as indicated by increasing melanic indexes which are closely related to the
δ
13C values. The natural
13C depletion with depth in grassland soils counteracts the enrichment of
13C in the subsoils of present
Araucaria forest. The results clearly indicate that current grasslands represent relics at least from the early and mid Holocene period (6000–8000 yr BP) and are not the result of recent deforestation.