Action: Manage ditches
Key messagesRead our guidance on Key messages before continuing
- One controlled, before-and-after study in the UK found that managing ditches increased common toad numbers.
- One replicated, site comparison study in the Netherlands found that numbers of amphibian species and abundance was significantly higher in ditches managed under agri-environment schemes compared to those managed conventionally.
Intensification of agricultural and other land management can result in loss of ditch biodiversity through activities such as mowing, grazing and use of fertilizer and pesticides leading to water pollution. These can have significant effects on amphibian populations. Ditch management practices such the frequency, season and technique used to clean or dredge ditches have also been found to affect the presence of amphibians (Twisk et al. 2000). Management practices that maintain and increase species diversity should therefore be encouraged.
Twisk W., Noordervliet M.A.W. & ter Keurs W.J. (2000) Effects of ditch management on caddisfly, dragonfly and amphibian larvae in intensively farmed peat areas. Aquatic Ecology, 34, 397–411.
Supporting evidence from individual studies
A replicated, site comparison study of 42 managed ditches within pasture in the Western Peat District of the Netherlands (Maes, Musters & De Snoo 2008) found that amphibian diversity and abundance was significantly higher in agri-environment scheme compared to conventionally managed ditches. Adult green frog Rana esculenta numbers in conventional ditches declined with distance from reserves; this was not the case in agri-environment scheme ditches. Farmers managing ditches under agri-environment schemes are encouraged to reduce grazing/mowing intensity and reduce fertilizer inputs compared to conventional management, and not to deposit mowing cuttings or sediments from ditch cleaning on the ditch banks. Monitoring was undertaken along 18 agri-environment and 24 conventionally managed ditches in April–July 2008. Ditches were perpendicular to eight nature reserve borders and monitoring was just inside reserves and at four distances from reserve borders (0–700 m). Three methods were used during each sampling period: five minute counts, 20 dip net samples and two overnight funnel traps.
A controlled, before-and-after study in 1999–2012 of seven ditches in pasture in Suffolk, UK (Beebee 2012) found that common toad Bufo bufo numbers increased after restoring ditch management. Numbers of adults counted three to seven years after management (after 3–4 years toad maturation) were significantly higher than in the subsequent five years once management ceased (563 vs 245). The year after ditch clearance, large numbers of tadpoles were seen and toadlets increased from 10s–100s to 1,000s in one of the dredged ditches. In comparison, highly vegetated unmanaged ditches supported few or no tadpoles through to metamorphosis. Ditch management including dredging was undertaken in five of seven ditches in 1999. Monitoring was undertaken three times in March by eggs counts, torchlight surveys, netting ditches and counting breeding adults.