Under-damaged reed beds are harming small wetland birds

Wetlands are a paradise for a birdwatcher. The reed beds reaching into the lake can provide a haven for many different bird species. Changes in agriculture mean that many natural wetlands have been drained, leading to government agencies and charities conserving some as essential habitats for birds. But protecting these areas can have consequences. Research by Erwin Nemeth and Michael Dvorak in the Journal of Ornithology shows that to provide the birds with a variety of habitats, it is now time to damage some reed beds.

Nemeth and Dvorak examine the growth and decline of common reed, Phragmites australis, a plant found in wetlands across Europe. The plant dominates the reed belt around Lake Neusiedl on the Austria – Hungary border, forming the largest contiguous reed bed in Europe, outside of the Danube Delta. At the lake, you can find over three hundred bird species, the reeds offering nesting sites for many small birds such as Eurasian Reed Warblers, Acrocephalus scirpaceus, Little Crakes, Zapornia parva, and Water Rails, Rallus aquaticus.

One of the attractions for the many species of birds is that while Phragmites australis is one species, it varies as it ages, so the one reed provides a variety of nesting sites. Great Reed Warblers and Reed Buntings seek out the younger reeds, so they may be found in areas where the reeds have recently been cut back. Little Crakes, in contrast, prefer areas older than fourteen years. Water Rails are like Goldilocks, liking reed beds that are neither too young nor too old.

Yet as the reed beds get older, they start to degrade with broken stems and, eventually, matted stems. The mats are a significant problem, say Nemeth and Dvorak in their article: “Our models demonstrate that all species—not only species adapted to younger reed areas—are negatively affected by highly degraded reed stands. One of the most conspicuous variables in our analysis was found to be matted reed, which in our models showed a significant negative effect in four out of seven species. The reason for its negative influence is obvious: matted reed forms layers up to 1 m high, through which only few young reed stems are able to grow. Here Acrocephalus warblers have no dense reed stands to which to attach their nests, and rails moving along the ground are confronted with an impenetrable thicket.”

The ornithologists note that in these highly degraded areas, even Little Crakes suffer. And there’s a lot of matted reed. Nemeth and Dvorak state the oldest reed occupies around 46% of their study area. They add: “Since reed outside our study site is mainly within a National Park without reed harvesting, we would expect even more matted reed; but exact data are missing and maybe reed is less affected at other locations. Nevertheless, even if we cautiously estimate that half of the reed bed of Lake Neusiedl is formed by matted reed, we expect a massive negative influence on the abundance of small reed birds.”

In order to provide reeds at various ages of growth, some form of control is necessary. Nemeth and Dvorak point to work by Eric Hazelton and colleagues published in AoB PLANTS on Phragmites australis management in the United States. Following this, Nemeth and Dvorak argue that cutting and burning can reduce the build-up of biomass. They accept that cutting the reeds reduces insect and bird abundance for that year but point to research showing it increases biodiversity the following years. Cutting different areas in a rota would prevent any one year from being an ecopocalypse for the lake. On paper, it’s a good plan, but it’s probably not sustainable say the authors, as the climate warms.

Reed cutting is often done in the winter when ice covers the lake making the reeds accessible. If the lake doesn’t freeze over, then only the landward reeds are accessible. These can be harvested by machinery, but this damages the reed beds more than manual harvesting. For this reason, Nemeth and Dvorak put forward another alternative.

“Burning of degraded reed areas could be a promising and less destructive alternative. Until the 1990s, burning of reed was common practice to facilitate the growth of young reed for harvesting, but it was then banned to avoid air pollution. At the moment, it appears to be the only feasible way to reduce litter accumulation, and we thus recommend a cautious and controlled reintroduction of fire management at Lake Neusiedl for ecological reasons.”

Making this change would improve the bird habitat almost immediately. But as well as clearing old reeds, the biologists have a plan to promote new reed growth. Another suggestion they make is to let the water level of the lake fall.

Despite covering over three hundred square kilometres, none of it is deeper than 1.8 metres, and on average, it’s only a metre, or three feet, deep. Letting the water level drop further would help promote new growth of the reeds. However, such a fall would conflict with plans for tourism. The future of Lake Neusiedl and the birds that live around it will depend on a balance of human interventions for conservation and tourism.

ORIGINAL RESEARCH

Nemeth, E. and Dvorak, M. (2022) “Reed die-back and conservation of small reed birds at Lake Neusiedl, Austria,” Journal of Ornithology. https://doi.org/10.1007/s10336-022-01961-w
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