Vegetation recording

Field work was carried out in two periods, September 1-16, 2020 and August 2-20, 2021. In the first period, sampling quadrats in treatment plots were put in the periphery of the established circular monitoring plots (see Supplementary materials, Appendix 1) and subjected to point-intercept vegetation recording, after which the above-ground biomass was cut as close to the soil surface as possible, immediately sorted into fractions  by plant species (with standing litter as a separate fraction) and dried at 55 ˚C until constant weight. The resulting data were used to create calibration models per species or functional groups for the prediction of plant species above-ground biomass from non-destructive point-intercept counts. In the second time period, sampling quadrats were located within the circular monitoring plots and surveyed using the same point-intercept method as in the first round. The resulting records were 1) used as-is, 2) subjected to prediction of species' biomass using the regression models of the first round.
In order to select grassland blocks, all monitoring blocks were initially surveyed in order to establish the dominant vegetation type. Out of the initially established 22 blocks, one was discontinued, four were located in closed-canopy forest, four were almost entirely covered by dense scrub and four had scrub-grassland mosaics with too high scrub cover for the point-intercept method to be practically applicable in all treatment plots, leaving nine blocks with mostly grassland vegetation (Fig. 1). Due to time constraints, only six of the nine blocks were included in first round of field work and were thus included in the construction of calibration models (i.e. block numbers 60, 62 and 70 were not sampled). Similarly, mown plots were not sampled, as they were in the process of being mown while the vegetation surveys were carried out. Including newly mown plots would have compromised the reliability of calibration models. In the second year, the field work took place one month earlier, allowing point-intercept recordings in the annually mown plots.
The total sample size for the two periods of fieldwork were therefore; 6 blocks × 4 treatment plots = 24 quadrats in the first period and 9 blocks × 5 treatment plots = 45 quadrats in the second period.