The use of trophic status indicator as a tool to assess the potential of birch-afforested soils to provide ecosystem services

Abstract

This study aimed to assess the impact of afforestation of post-arable soils on changes in their potential to provide ecosystem services. An additional aim of the study was to assess the suitability of the Soil Trophic Index (Siedliskowy Indeks Glebowy – SIG in Polish), as an indicator of soil ecosystem services (SESs) regulation, which is a novelty in this type of research. SIG is a number calculated from basic soil properties: TOC and TN contents, the sum of exchangeable alkaline cations, hydrolytic acidity, contents of the Ø < 0.02 mm fraction, bulk density, and soil horizon thickness. It is a number representing the basic properties of a 100 cm × 100 cm × 150 cm soil pedon. The SIG value refers to five categories of soil trophic subtype variants: dystrophic, oligotrophic, mesotrophic, eutrophic, and optionally hypertrophic, which are used to assess the potential of soils to provide ecosystem services. A detailed study was conducted on post-arable sandy and loamy soils afforested with silver birch (Betula pendula Roth) located in two forest districts in central Poland. Each stand covered arable and post-arable plots afforested with silver birch, located on the same soil complex, comprising sandy and loamy soils. Stands were diversified in terms of stand age: 21, 29, 40, 61, and 66-year-old stands on sandy soils, and 15, 33, 41, 61, and 80-year-old stands on loamy soils. At each stand, two soil profiles representing an arable field and a forest were made (20 profiles total). Soil samples were collected from each soil horizon (61 disturbed and 183 undisturbed samples in total). The SIG components were determined under laboratory conditions using standard methods. Based on the obtained results, changes in the potential of post-arable soils to provide certain regulating ecosystem services through afforestation with silver birch were found. The SIG values highlighted diversity in the quality of similarly-textured soils, and thus diversity in their potential to provide the studied regulating SESs. The soils represented almost all trophic types, from dystrophic to eutrophic. Afforestation with silver birch resulted in decreased SIG values in half the cases (mainly in sandy soils), indicating the relatively negative effects of this tree species on the soil system, including lowering the soil’s potential to provide certain regulating ecosystem services. In addition, it was confirmed that the SIG can be used to identify similarities and differences in the potential of similarly-textured soils to provide certain regulating ESs.