Green treasures: Investigating the biodiversity potential of equine yards through the presence and quality of landscape features in the Netherlands

large, or too small, and therefore did not qualify as a LF, they were considered as not contribut- ing towards biodiversity and were thus not included in any further analyses involving LFs. A number of features not listed in the EU’s proposed FLFC, were included in the current survey. Where these features functions could be argued to resemble commonly classified LFs, they were considered as such, e.g. solitary, monumental and pollard trees were considered iso- lated trees and the function of permanent woodpiles and cluttered corners may be considered similar to rock piles. Additionally, features including monocultural and herbaceous grassland, birdhouses, bat boxes, insect hotels and proven nesting sites are not considered in the EU FLFC. However, they can have potential utility in contributing towards biodiversity [36–38]. Therefore, it would be beneficial to investigate their presence on farms to help gauge potential importance and determine whether further investigation on these types of landscape feature is warranted. Data analysis Once the survey was closed, all responses were downloaded and transferred to IBM SPSS for Social Scientists 28.0. There were a total of 1149 responses to the survey, with 529 completions. Only these responses were considered for further analysis. Descriptive statistics were conducted to describe the characteristics of the yards, outlining type of yard, i.e. ownership, yard size, number of horses, soil type, number of LFs and size of LFs. Descriptive statistics were also calculated for all LFs, whereby the geometric mean, median

and mode was calculated for all LFs that could be measured. Percentage Property Coverage (PPC) with LFs was calculated using the following formula: PPC ¼ TPA TLFC ð1Þ Total property area (TPA) was defined as the total area of the equestrian yard and total landscape feature coverage (TLFC) was composed of the sum of the surface of the two-dimen- sional (length x width) woody, grassy, wet and stony features as indicated in Table 1 with an * (i.e. all woody elements, excluding vertical LFs of solitary, monumental and pollard tree; all grassy features excluding monocultural and herbal grassland, all wet features, and all stony fea- tures). Data were visually inspected for unrealistic outliers (e.g. 100 hedgerows at a property of Table 2. The proposed EU Functional Landscape Feature Classes cross-referenced to the LF types commonly recognized in policy documents and their geometric specifications according to Czu´cz, Baruth, Terres, et al. [10], and the concurrent classification of current survey items. EU Functional LF (FFLF) class Examples for commonly recognized subtypes according to Czu´cz, Baruth, Terres, et al. [10] The proposed functional landscape feature classes with geometric specifications Classification of current survey items Woody features Isolated trees, Tree lines and avenues, hedges, woody strips, trees in group, field coppices and riparian woody vegetation width > = 1 m AND (width < = 20 m OR area < = 0.5 ha) Isolated trees (e.g. solitary, monumental and pollard trees), tree lanes (i.e. avenues), tree rows (i.e. lines), fruit orchards,

wild hedges, trimmed hedges, woody strip, forage wall, permanent woodpile Grassy features Grassy strips, field margins, embankments, buffer strips, grassed ’thalweg’ width > = 1 m AND (width < = 20 m OR area < = 0.5 ha) Flowering strips, embankment, buffer strip Wet features Inland channels of fresh water, standing small water bodies such as natural or man-made ponds, ditches. width > = 1 m AND (width < = 20 m OR area < = 0.5 ha) Pond Stony features Dry stone walls, terrace elements, rock outcrops, natural or artificial stacks of stone. (width OR height) > = 1m AND (width < = 20 m OR area < = 0.5 ha) Cluttered corner https://doi.org/10.1371/journal.pone.0301168.t002 PLOS ONE Biodiversity potential of equine yards through landscape features PLOS ONE | https://doi.org/10.1371/journal.pone.0301168 April 11, 2024 5 / 16