Restoration of pastures under tree canopy: effects of the undergrowth clearing and grazing in the maintenance of herbaceous species diversity and production

In a context of global change, the mountains of southern Europe have suffered in recent decades processes of land abandonment, leading to the loss of cultural mosaic landscapes, with negative effects on ecological and economic sustainability of agroecosystems. In the framework of the MIDMACC Project (LIFE18 CCA/ES/001099), landscape management measures to adapt marginal areas of Spanish mid-mountain to the impacts of global change have been tested. In this regard, experiences of forest management measures (thinning and undergrowth scrub clearing) followed by grazing with native cattle breeds have been conducted in two reforested areas in “La Garcipollera” valley (Huesca, Spain) to create and maintain herbaceous pastures under tree canopy (one area with Pinus nigra and the other with Populus x canadensis). The effects of forest management and grazing on the floristic composition and production of the herbaceous pasture were analysed in both areas separately. For this purpose, three replicates per each of three typologies of monitoring plots with a surface of 400 m² were established: i) control plots (without neither forest management nor livestock), ii) managed plots without livestock and iii) managed plots with livestock (2 cows per plot for 48 hours and twice a year). Vegetation surveys were conducted every spring from 2020 in the pine area and 2021 in the poplar area to 2023. In those, the coverage of the bare soil and every plant species growing within four 1m² subplots per plot were recorded. Additionally, in order to estimate dry biomass (production of the pasture) for the initial and final stage of the experiment, at each plot we collected the plants growing within four 0,5m² subplots adjacent to the previous. Our results indicated that, after three years of experimentation, forest management decreased the bare soil cover, increased the cover, richness and biomass of herbaceous species and reduced the cover and richness of woody species compared to the control plots. This trend was common for both the pine and poplar areas. In the case of grazing effects, we found that the entry of livestock in the plots in the managed pine areas increased the bare soil cover and herbaceous plants cover and richness but reduced the biomass production and the woody species cover (thus controlling scrub encroachment). Regarding plots in the managed poplar areas, grazing affects differently from pine areas since no significant effects on herbaceous nor woody species cover and richness were found compared to control plots (shorter study period). Nevertheless, a positive effect of grazing was found since bare soil cover was reduced and herbaceous biomass production was increased compared to the plots with no livestock entry. Although in the mid-term (three/two years after the measures) the whole expected effects of grazing are not yet evident, the improvement of the herbaceous species and the control of scrub encroachment by cattle are apparent.

Acknowledgements: This research was supported by the LIFE MIDMACC (LIFE18 CCA/ES/001099), funded by the EC.