Control of bracken and restoration of heathland. II. Regeneration of the heathland community

Summary

In many areas of Britain, bracken Pteridum aquilinum although a native species, can be a highly invasive, especially on marginal land such as heath and moorland on acidic soils. The effectiveness of a range of bracken control and heathland restoration treatments (cutting, spraying with asulam and seed sowing) at a heather Calluna vulgaris heath and a grass heath in Breckland, eastern England, was assessed over 10 years. An earlier paper looked at the effects on bracken control itself (Lowday & Marrs 1992), whilst here regeneration of heathland communities following bracken control in the same experimental areas are summarised.

Study sites: The study was undertaken at Cavenham Heath (a Calluna heath – National Grid ref: TL 755725) and Weeting Heath (a grass heath, mainly sheep's fescue Festuca ovina - National Grid ref: TL 757885) in the Breckland region of Suffolk, eastern England.

Bracken control treatments: Six treatments were applied to bracken encroached areas on the two heathlands:

i) untreated controls;

ii) cutting once yearly in late July between 1978 to 1984 (cutting using a mechanised sythe, fronds left in situ);

iii) cutting twice yearly in mid-June and late July between 1978 and 1984;

iv) spraying with asulam (4.4 kg active ingredient applied in 400 l water/ha using a motorised backpack mistblower) in August 1978;

v) spraying with asulam twice in August 1978 and August 1979;

vi) Asulam applied in August 1978, cut once/year in late July from1979 to 1984.


Each treatment was undertaken with and without seeding (using seed from the local area):

Cavenham – 20,000 C.vulgaris seeds sown/m²;

Weeting – a seed mix of Yorkshire fog Holcus lanatus, fescue spp. mainly F.ovina bird's-foot trefoil Lotus corniculatus and common sorrel Rumex acetosella (5,000, 10,000, 600 and 4,400 seeds/m² respectively).


A randomised block design was used (four replicate blocks each with 12 treatments randomly allocated to 10 x 7 m plots with a central 6 x 3 m sampling area, each surrounded by a 1 m cut pathway).

After 6 years a further two treatments were added, with the bracken control treatments being either continued/reapplied or discontinued.

Vegetation assessment:
Weeting Heath - Vegetation was harvested within four 20 x 20 cm quadrats in three randomly selected 1 m² quadrats in each 6 x 3 m sampling zone in July 1979-83, 1986 and 1988. Vegetation was sorted by species, dried (80ºC fro 24 h) and weighed.

Cavenham Heath – the above procedure was followed in July 1979-84 and 1986. In 1986 it was apparent that due to great variability within plots due to increasing roe deer Capreolus capreolus and rabbit Oryctolagus cuniculus grazing , biomass measurements may have been confounded. Therefore in the 14, 1 m² quadrats around the perimeter of each sampling zone (to avoid trampling) plant species frequencies were recorded (May1986 and 1988).

At Weeting, 13 species (11 vascular plants, 2 bryophytes) were recorded during the 10 years, heath vegetation (excluding bracken) first appeared in 1981 when F.ovina, H.lanatus and R.acetosella were all found in treatment plots, with F.ovina and R.acetosella also occuring very sparsely in control (bracken) plots. L.corniculatus was the only sown species that failed to appear.

In most plots two species were dominant: F.ovina (sown) and wavy hair-grass Deschampsia flexuosa (colonizing naturally). F.ovina rapidly colonized the seeded plots, D.flexuosa appeared 5 years later. After 10 years D.flexuosa was co-dominant on many plots. The other vascular species recorded were: common bent Agrostis capillaris, mouse-ear chickweed Cerastium holosteoides, rosebay willow-herb Chamerion angustifolium, heath bedstraw Galium saxatile, ground ivy Glechoma hederacea, heath wood-rush Luzula multiflora, and stinging nettle Urtica dioica and oak Quercus robur (seedlings). C.angustifolium and a bryophyte crust was abundant in some plots, usually where bracken control had ceased, and both were present in untreated plots.

The summer appearance of restored plots after 10 years was a dense grassland with profuse flowering, in comparison to the adjacent tightly rabbit grazed heath. In 1989 (11 years after treatment) rabbits increased and began to graze the area.

At Cavenham, 13 vascular and three bryophyte species were recorded. Calluna (the only sown species) was found mainly on seeded plots, especially where bracken was cut. A.capillaris, broom fork-moss Dicranum scoparium and G.saxatile were most abundant on plots where the bracken was cut twice yearly. Other species appeared independent of treatment, reflecting low abundance and ubiquitous or clumped distributions. Two clonal species, sand sedge Carex arenaria and wood small-reed Calamagrostis epigejos invaded large patches.

Most of the species colonizing the restored areas had higher Ellenberg nitrogen-indicator values than the dominant heathland species, indicating that soil fertility at the two sites may be too high for successful heathland restoration.

Conclusions: At Weeting there was regeneration towards sheep’s fescue-wavy hair-grass grassland. Sheep’s fescue (one of the sown species) quickly dominated with hair-grass colonizing naturally after 5 years. At Cavenham Calluna establishment was promoted both by seeding and cutting control of bracken. Here establishment of most other plant species showed no response to heather seeding, implying that their establishment was not inhibited by heather establishment.


References
Lowday J.E. & Marrs R.H. (1992) Control of bracken and the restoration of heathland. 1. Control of bracken. Journal of Applied Ecology, 29, 195-203


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