Turning old foes into new allies – harnessing drainage canals for biodiversity conservation in desiccated novel ecosystems

Drainage canals are ubiquitous components of agricultural landscapes worldwide. Although canals have greatly contributed to biodiversity loss by desiccating wetlands, they have recently attracted conservation attention due to their potential to function as refugia for native wetland-dependent species in intensively managed landscapes. However, their conservation role in complex landscapes comprising a mosaic of agricultural and desiccated semi-natural habitats, on which canals still pose a heavy burden, is unknown. Improved understanding of drainage canals and related biodiversity in these landscapes could help unlock their potential and support synergistic land management for nature conservation and water management. We applied a multitaxon approach, including plants, butterflies, true bugs, spiders and birds, to (1) assess the conservation value of drainage canals in a heavily drained European lowland region, (2) to test landscape-level and local canal parameters for aiding prioritization among canal types, and (3) to propose a reconciliation-based management framework that suits the interest of all stakeholders. We found that drainage canals concentrate more species across most taxa than adjacent semi-natural habitats, owing to the micro-environmental heterogeneity and the comparatively low management intensity in the canals. The species-concentrating capacity is particularly high in canals that traverse semi-natural habitats, although agricultural canals also support remarkable species diversity. However, agricultural canals are important dispersal corridors for invasive plants, which may negatively affect native species. Canal size has little effect on biodiversity but habitat stress is an important determinant. The higher the stress (due to sandiness and salinity), the higher is the added value of canals to landscape-wide biodiversity. Synthesis and applications We provide evidence that drainage canals can harbour surprisingly high levels of biodiversity and should therefore be recognized as important novel ecosystems with high conservation value, even within semi-natural habitats. Canals have previously been considered detrimental to nature conservation due to their association with loss of wetlands. However, by reducing water loss with reversible obstructions, controlling invasive species and applying specific conservation measures, they may be turned into conservation allies without compromising long-term interests of water management and agricultural land use.


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Drainage canals are ubiquitous components of agricultural landscapes worldwide. 23 Although canals have greatly contributed to biodiversity loss by desiccating wetlands, they 24 have recently attracted conservation attention due to their potential to function as refugia for  Netherlands), and are therefore refuges for organisms with high water demand (Chester & 73 Robson, 2013; Harvolk et al., 2014). This paradoxical situation has led to the recognition that 74 conservation value may be assigned to canals in agricultural landscapes, and therefore canals 75 should be considered in conservation planning and agri-environmental schemes ( The study was carried out in the Danube-Tisza Interfluve, Central Hungary (Fig. 1). The

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In the second half of the 20th century, regional aridification was further increased by climate

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The total length of registered canals in the region is 4723 km (Fig. 1). Canals are infrequently 155 managed by dredging (usually less than once a decade), reed cutting and shrub clearing.

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Mowing once a year and/or extensive grazing are the main management types of adjacent 157 grasslands, but neither mowing nor grazing extends into the canals on a regular basis.

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Permanent water in the canals is nowadays rare; most contain water only in spring and after 159 heavy rainy periods.  substrates difficult. Therefore we standardized the species richness scores of canals to 217 substrate specific average reference species richness scores, which yielded species excesses 218 (or deficits, if negative), which we expressed as percentages. The use of species excesses was 219 also beneficial because we were interested in the added conservation value of canals within a 220 broader landscape. We used the following equation for the calculations: where E i is the substrate specific species excess of the ith sampling unit of a canal (one of 223 eight plots for alpha diversity or the total species count for gamma diversity), C i is the species 224 richness of this sampling unit, R j is the species richness of the jth sampling unit of any of the 225 reference transects belonging to the same substrate type as the canal, and n is the number of 226 such reference sampling units.

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Invasive plant species were either absent or very scarce in reference transects; therefore, we 228 did not standardize their abundance in the canals but used the raw scores in subsequent 229 analysis. For butterflies, true bugs and spiders, we applied the above method of 230 standardization but the reference averages we used were specific to both substrate and season.

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In birds, we used the raw species richness scores for the analysis. Invasive or noxious pest 232 species were not encountered among animal taxa; therefore, all species were retained for the 233 analysis. 234 We applied a linear modelling approach to evaluate the biotic response variables (species  Woody vegetation affected gamma diversity in a hump-shaped manner; the hump was located 273 at 141.7 m but the upper limit of its confidence interval was beyond the upper limit of 274 available woody abundance, rendering the prediction unreliable. The abundance of reed had 275 no effect on the variation of the data ( Fig. 2A, Table S1-3, Fig. S1A-B) 276 We had more moderate results for species excesses on the alpha level, as it was not affected 277 by canal size, substrate or the abundance of woody species and reed. However, agricultural 278 canals had lower species excesses than grassland canals, and the former remained below the 279 reference level (i.e. showed species deficit), while the latter slightly exceeded it. Mean values 280 of small and large canals and canals of different substrate types did not differ from the 281 reference levels (Fig. 2B, Table S1-3 and Fig. S1C-D).   Table S1-3 and Fig. S2A-B).
We collected a total of 246 true bug species (30,012 adult individuals) in the study, and 219 318 occurred in the canals, of which 82 were collected exclusively there. Species excesses were 319 affected only by matrix and season, with higher scores in agricultural canals than in grassland 320 ones, and higher scores in summer than in spring. Compared to the reference levels, the 321 statistics confirmed significant species excess in agricultural canals but not in grassland ones, 322 in large canals but not in small ones, and on sandy substrate but not on fen or saline 323 substrates. Species excess was highly positive in summer but significant difference was also 324 confirmed for autumn data (Fig. 3B, Table S1-3 and Fig. S2C-D). reed abundance (Fig. S2G-H, Fig. S3 and Table S1-3).  in agricultural production systems (Szinell et al., 1998). To make canals net positive 482 contributors to conservation, the draining effect should be minimized while maintaining the 483 canal profile with all the diverse microhabitats, flora and fauna. This can be achieved by introducing more sluices and semi-permanent obstructions, such as earthen plugs (see also 485 Tichanek & Tropek, 2015 recommended to suppress weedy species (Hill et al., 2016), but the canals in our study did not 501 seem to require this intervention, which would probably promote invasive species.

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Furthermore, we encourage the retention of moderate amounts of woody plants and reed as 503 they can increase the quality of canals as refuge sites for biodiversity. Implementation of 504 these proposed guidelines would constitute a cost-effective, viable alternative to presently 505 applied practices (Fig. 4), which can successfully reconcile nature conservation aims and 506 water management in agricultural landscapes.