The effects of conservation management of reed beds. I. The invertebrates

Published source details Ditlhogo M.K.M., James R., Laurence B.R. & Sutherland W.J. (1992) The effects of conservation management of reed beds. I. The invertebrates. Journal of Applied Ecology, 29, 265-276.
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Summary

Phragmites australis reed beds are valuable wildlife habitats and in the UK support some national rare fauna and flora. For conservation purposes reed beds may be managed by cutting, and in some areas reed is still harvested for thatching. Burning may also be used to arrest succession in reed beds, with periodic flooding also used as a management tool. Several studies done in dry habitats indicate that burning reduces populations of invertebrates, particularly molluscs. Because of this most conservation organisations do not use fire in reed bed management. However, as reed beds are usually wet because of periodic flooding, effects of fire on invertebrates might be different compared to that in dry habitats.

A replicated experiment was undertaken in plots in a stand of reed which were cut, burnt or left unmanaged. Invertebrate communities were sampled to assess any impact of management, and if any, how long the effects lasted.

Study site: The study was undertaken between April 1988 and May 1989 at Hundred Acre Marsh, Hickling Broad National Nature Reserve (National Grid ref: TG 434211), Norfolk, England.

Experimental design and treatments: A replicated experiment was undertaken in and area of 150 x 120 m, divided into 15, 30 x 40 m plots in a stand of reed. Strips around 2m wide were cut around each. Treatments applied were:

i) cut – late March 1988 reeds cut and removed;

ii) burnt - late March 1988 reeds burnt against the wind (the burn was considered typical for reed beds);

iii) left unmanaged.

Treatments were undertaken by the Broads Authority and the Norfolk Naturalists' Trust (now Norfolk Wildlife Trust) warden who were experienced in reed bed management. Following traditional practice, the reed bed was flooded in April 1988 and in April 1989. On 23 May 1989 water depth was measured at random points (16/plot), digging into the substrate to the water level as necessary if no standing water was present.

Invertebrate sampling: Invertebrates in the soil were sampled by heat extraction and hand-sorting (April, August and October 1988, and April 1989), and those above ground by water traps (May, July and October 1988 and May 1989), dissection of reed stems (June 1988) and in situ counting e.g. of insect larvae and galls (November 1988).

Only a few families showed differences between treatments, and this number declined with time after treatment. After 1 year, no soil invertebrates and only a few families of above-ground invertebrates showed any significant treatment effects. Most treatment effects were between the unmanaged control and both cut and burnt plots. A significant difference between cut and burnt treatments was recorded for only one family, with numbers lower in the cut plots. Many soil invertebrates were more abundant in drier parts of the reed bed, this trend was not apparent for above-ground invertebrates.

Soil/litter invertebrates The results suggest that few soil/litter invertebrates were affected adversely by burning compared to cutting. Scatopsidae (dipteran flies) appeared to have benefited from burning, and Hydrobius spp. water beetles from both cutting and burning. The abundance of Chironomidae (non-biting midges), Thripidae (thrips) and Corixidae (water bugs) appeared to have been reduced by cutting and burning, but a year after treatment the soil/litter taxa recorded showed no significant effects. Slugs, snails and earthworms were most numerous in burnt samples suggesting that burning was not a factor in determining there abundance.

Above-ground invertebrates: Several above-ground invertebrate families were adversely affected by management but effects decreased with time and were generally similar for both cutting and burning. Syrphidae, Dolichopodidae, Chironomidae and Tipulidae (crane-flies) were reduced in numbers, whilst Scatopsidae, Ephydridae (shore flies), Nitulidae (pollen beetles), Curculionidae (weevils), Aphididae (aphids) and Araneae (spiders).

Conclusions: From this short term study, the authors suggest that management by cutting or burning does not have a major influence on the invertebrate community; total number of invertebrates, species-richness, species diversity and evenness showed no relationship with treatment. Their general conclusion is that careful burning of reed beds is no worse than cutting, but that burning at the wrong time of year, or burning of dry reed beds are likely to cause damage.

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