Harnessing drainage canals for biodiversity conservation

A new paper led by Csaba Tölgyesi from the University of Szeged, Hungary, shows that drainage canals can be harnessed for biodiversity conservation in desiccated, heavily transformed regions by reconciling the interests of opposing stakeholders.

Drainage and subsequent land cultivation have been a major threat to global wetland ecosystems for centuries. In Europe, most lowland fens have been drained; approximately 25% of the arable land of the United States is artificially drained, and immense wetlands have recently been drained in tropical Southeast Asia to clear land for agriculture. Ironically, in these transformed landscapes, drainage canals represent the last moist and relatively undisturbed environments for native species.

Canals are refuges for native species in drained agricultural areas

This recognition has prompted the inclusion of canals and ditches in agri-environmental schemes in some EU countries. However, many drained regions also include desiccated but still semi-natural habitats, mostly grasslands. For their conservation and the reconstruction of more moist conditions, nature conservation authorities often fill up long sections of canals, which are interconnected with agricultural canals. But is this drastic and cost-intensive intervention the right approach?

In an intensive sampling program, we assessed canal biodiversity (including plants, butterflies, true bugs, spiders and birds) in a heavily drained lowland landscape in Hungary, Central Europe. We tested the effects of landscape matrix (agricultural vs. grassland canals) and local canal parameters (substrate type) in driving biodiversity patterns and aimed to propose a reconciliation-based management framework that suits the interests of opposing stakeholders: Conservationists, who are interested in removing canals for restoration purposes, and water resource administration, which regularly clean and deepen the canals to avoid water levels that could threaten agricultural production.

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Canals and ditches can support rich flora amidst agricultural lands (left) and often represent the only overwintering site for arthropods and other soil-dwelling fauna (right). Photos: Csaba Tölgyesi.

Canals are rich in biodiversity both in agricultural and semi-natural habitats

We found that drainage canals and their banks concentrate more species across most taxa than semi-natural grasslands. If a canal directly traverses such a grassland, the richness of native species is especially high. Canals of agricultural areas also host high biodiversity. However, the canals are also corridors for non-native invasive species, which may negatively affect biodiversity.

The generally high biodiversity of canals is explained by their environmental micro-heterogeneity, which includes a moisture gradient along the banks and the occasional woody and reedy patches scattered in the mostly herbaceous vegetation. The highest added value to landscape-wide biodiversity is encountered in stressed environments, such as on saline and sandy substrates, likelybecause environmental gradients are steeper and competitive plant species within them cannot seize dominance.

Reconciliation between stakeholders

Our findings highlight that the environmental heterogeneity that canals introduce into the landscape is favourable even when cutting through semi-natural habitats, such as grasslands. Therefore, a compromise between the two major stakeholders (conservationists and water resource management) would fit the interests of biodiversity protection. Introducing semi-permanent obstructions along a canal instead of filling up long canal sections would reduce water loss but the microhabitats of the canals would survive

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Construction of a semi-permanent obstruction in a grassland ditch to retain water without wiping off canal microhabitats. Photo: Csaba Tölgyesi.

At the same time, conservationists may reallocate resources to control invasive species in formerly overlooked canals, especially in agricultural areas. Decreasing the intensity of canal management, such as leaving uncut reed and woody vegetation and avoiding the clearing of herbaceous vegetation, would ensure the long-term survival of native species. This reconciled management framework can be summarized as follows:

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Read the full paper Turning old foes into new allies–Harnessing drainage canals for biodiversity conservation in a desiccated European lowland region in Journal of Applied Ecology

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