Habitat Heterogeneity
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Increase heterogeneity of forest, scrub and open habitat
Data collection in progress
Iberian Highlands
Spain
Problem: Land abandonment has led to loss of extensive livestock grazing across large areas of the landscape. The absence of large herbivores brings with it the loss of key ecological processes such as grazing, browsing and trampling. This has led to a reduction in the heterogeneity of vegetation and an increase in susceptibility to fire.
Action: The project is reintroducing large herbivores, including Tauros, bison and horses, into the landscape. Natural grazing by these animals will increase the heterogeneity of habitats and the diversity of biophysical and ecological conditions. Natural grazing is expected to increase the area of grassland and create more open habitats like scattered scrubland and open forests, providing habitat for a range of species.
Indicator: The heterogeneity of vegetation cover and structure will be measured in areas where large herbivores are being released. An increase in heterogeneity, with more diversity of biophysical and ecological conditions, will indicate successful reinstatement of the ecosystem function performed by the reintroduced grazers.
Methods
Heterogeneity of habitats is being surveyed at Rewilding Spain’s natural grazing areas. Thirteen pairs of 10 x 10 m sampling plots have been established using a before-after control-impact (BACI) design. One plot in each pair is fenced with 1.8m high hunting mesh to prevent access by herbivores, while the other is unfenced to allow natural grazing. This design will allow Rewilding Spain to assess the effects of natural grazing separate from any environmental variables that may affect the vegetation over the course of the project timeframe. Paired plots were chosen to be as similar as possible in terms of microclimate and initial vegetation present.
Vegetation is surveyed twice a year, in late April to early May and early June. The first surveys were undertaken before large herbivores were introduced to the area, as a baseline. In each 10 x 10 plot, data such as soil type, and observations of general vegetation structure and impacts of herbivory are recorded, as well as the number, percentage cover, height and species of any trees and shrubs present. Photographs of each plot are taken (Fig. 1). Detailed vegetation assessments are made at four 1 x 1 m quadrats within each plot, with all species present recorded. Vegetation monitoring is planned to be carried out in the long term (> 20 years), with sampling repeated every 3-5 years at several of the natural grazing areas.
In addition, habitat heterogeneity will be monitored at the landscape scale using a before-after study design, leveraging satellite remote sensing to assess changes in vegetation structure in areas where herbivores have been introduced and natural grazing has been restored. This monitoring will involve the classification of medium-to-high-resolution satellite imagery (e.g., Sentinel-2, Planet) into broad vegetation categories, including bare ground, grasslands, shrubland, and tree cover. Image classification will be conducted using supervised or unsupervised machine learning techniques, with spectral indices (e.g., NDVI, EVI). This approach will enable the detection of shifts in vegetation cover and spatial heterogeneity resulting from grazing impacts in the medium-long term.
Results
Baseline data is currently being collected at the natural grazing area in Solanillos, where 34 Serrano horses and 13 tauros are currently present. This page will be updated once we have data to share.
Lessons learned
In year 1, it was decided to compare the resolution and cost-effectiveness of habitat survey methodologies based on images obtained from UAVs and high-resolution satellite images. The natural grazing site at Solanillos was analysed in the same way based on each data source. The results (Fig. 2) showed that using high resolution satellite images is a more cost-effective approach than drone mapping. Therefore, going forwards, Rewilding Spain will measure changes in the heterogeneity of the landscape using high resolution satellite images.
Figure 2: Comparison of habitat mapping of the natural grazing site at Solanillos using UAVs (drones) versus high-resolution satellite images.
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