In recent decades laurophylloid vegetation has started to colonise forests of southern Switzerland and northern Italy. The increased colonisation since about 1950 is due to increased winter temperatures and urbanisation. With respect to the changes in the vegetation cover, the question arises as to whether or to which extent they influence soil organic matter quality and chemistry. In southern Switzerland, the common forest vegetation at sites bc. 1000 m a.s.l. consists predominantly of chestnut species (Castanea sativa) that have been introduced approx. 2000–3000 years ago. An older vegetation type, however, would be a Quercetum– Betuletum forest that can still occasionally be found in the area Locarno/Ascona/Cannobio. We studied the short-term influence of the laurophylloid vegetation and also the long-term influence of chestnut on soil characteristics including total organic carbon and nitrogen, pH, CEC, soil lightness and chemical fractions of soil organic matter. The characterisation of the functional groups of fulvic and humic acids was performed using IR-spectroscopy.
In general, short-term differences in the C/N ratio and also in the quality and quantity of fulvic and humic acids seem to be likely between laurophyllous and chestnut stands. In general, lower C/N ratios and fulvic and humic acid contents were measured in soils under laurophyllous species. The laurophylloid vegetation gave rise to higher percentages of proteic amides, aliphatic CH₂ and CH₃ and lower C=O amide groups in the fulvic acids. A trend towards a lower humification degree was measurable for the sites with laurophylloid vegetation where organic matter seems to be less resistant to biodegradation. A significant effect of the laurophylloid vegetation on the org. C concentration was, however, not detectable. Chestnut very probably influenced soil organic matter in the long-term by producing lower total C and N contents, by a decrease in soil darkness, a lower amount of humic acids and a decreased CEC as compared to the older Quercetum–Betuletum vegetation. The differences in humus chemistry between chestnut and Quercetum–Betuletum stands were, however, small because the quality of the litter source seems to be similar.
The colonisation of laurophyllous species is an obvious indication of human impact and of fast and accelerating climate change that after a few decades already led to a remarkable influence on soil and humus chemistry.