Bracken Regression on an East Suffolk Heath

BRACKEN REGRESSION ON AN EAST SUFFOLK HEATH R . GARRETT-JONES

AN apparent disorder causing decline and death of bracken (Pteridium aquilinum) has been reported recently from South Wales (Garrett-Jones, 1960, 1961), Yorkshire West Riding (Fidler, 1963, Watson et al., 1965) and North Riding (Parker and McCrae, 1965), and other Northern Counties (Barnett and Watson, 1968).

Prior to these reports, other workers (e.g., Braid, 1934, 1947) had noted isolated occurrences in Scotland and Northern England of apparent disease and death of bracken; but it seems evident that the later reports signify a phenomenon, although somewhat similar to some described by Braid, considerably more widespread than anything that had occurred previously. The cases hitherto reported have all been on upland sites and sometimes in situations which may be climatically marginal for the species, from exposure or nearness to its upper altitudinal limit; however, the condition does not appear to be commonly associated with the extreme Upper fringe of the bracken area, nor with the most exposed sites.

DĂźring the growing season of 1968, the writer noticed patches of degenerated bracken on Blaxhall Heath, East Suffolk, on both sides of the Snape to Tunstall road (grid reference 380564); these were showing a variety of symptoms corresponding well with those that had been seen on some of the other sites reported. The Heath at this place is bounded by Forestry Commission plantations, and consists largely of Callunetum with considerable stretches of Caricetum and several patches of Pteridietum. The most vigorous patches of Pteridium form a pure stand and carry fronds over 5 ft. in height; elsewhere the fern is smaller and intermingles with the other communities.

The abnormalities observed were as follows: 1. Patches, the largest extending to about 50 yards on the long axis, devoid of current frond growth and covered with old bracken litter, with little colonisation by other species. Several such patches were present within areas of growing bracken.

2. In the areas surrounding the bare patches, some prematurely yellowed and dead fronds were present. The dead fronds were very shrivelled, more so than in the case of the normal autumn die-back of fronds.

3. On some other bracken areas on the Heath, a high proportion of yellow fronds in October before the onset of general die-back.

4. In one area, a small-scale mosaic of vigorous fronds up to 4 feet in height with smaller, bright green and evidently lateemerged fronds, not yet fully expanded in October, intervening.

This is interpreted as a recovery phase.

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5. Some malformation of fronds, showing as lack of complete bilateral symmetry and failure of the lamina to expand fully, the ultimate divisions being cuneiform. The degree of distortion showed wide Variation between fronds. Affected fronds were appreciably more brittle than normal.

All these phenomena have been noted, though not always together, at other sites where bracken degeneration has been observed.

Watt (1954, 1956), working in Breckland, observed annual fluctuations in the advance and retreat of bracken, which he ascribed to Variation in climate and in the degree of protection of buds by the litter layer. None of his observations, however, appears to refer to extensive disappearance of areas of bracken, so suddenly as to leave the ground uncolonised for at least a season.

The climatic conditions which may be critical for bracken would appear to be: (a) winter freezing of the soil, which is not closely correlated with the duration of air frosts, but depends also upon aspect, soil type and the presence of any insulating layer of growing plants, plant remains or snow; (b) spring frosts which destroy emerged or emergent fronds; (c) possibly, drought conditions during the growing season; (d) waterlogging of the soil around the rhizomes. Although a broad change of British climate has occurred, with a marked increase in the frequency of severe winters, since 1939 (e.g., Lamb, 1965), no climatic aberrations that have been encountered during the past few years would seem to explain the degeneration at Blaxhall; recent winters have been mild and although 1968 rainfall was high, especially during the growing season, the sites concerned are on very free-draining sands not subject to waterlogging. The phenomenon seems to denote a pathogenic condition, as has been postulated in some of the other cases.

On the upland sites reported earlier, grazing animals, especially sheep, have been present. One of the phenomena, often the most obvious, associated with the bracken regression in most of the recent cases, has been grazing of the fronds by sheep. At first, it was supposed that this abnormal grazing was indeed the cause of death of the fern; later, it was found that its growth failed after a period of grazing quite insufficient to account for complete death of the rhizome system, normally hard to kill by defoliation. Nevertheless the grazing, trampling and dunging of the sheep, with the resultant break-down of the litter layer, is thought to have aggravated the supposed pathogenic effects. It is, therefore, of special interest that similar symptoms of regression are seen at Blaxhall, where no domestic grazing animals are present and where the litter has remained substantially undisturbed.

It would be interesting to determine whether the course of the phenomenon at Blaxhall is progressive and what will be the succes-

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sion of plant colonisation on bracken litter after failure of the fern, under the dry East Anglian conditions. It is hoped that some local observer may, as a result of this note, be able to follow it up.

Mapping the Vegetation of the Heath, if this has not already been done, would be useful.

Hull (1968), as a result of inspection of material from Ilkley Moor, suspects the presence in the bracken of a pathogenic mycoplasm; this has yet to be confirmed by electron microscopy. T h e method of transmission and the ränge of effects produced in the host plant by any such pathogen remain to be shown experimentally.

A cursory Observation of many of the East Anglian areas of bracken suggests some very widespread abnormality, and it may prove difficult to find completely normal plants for comparative purposes.

Summary Düring the 1968 season, abnormality and failure of growth of fronds of bracken was observed on Blaxhall Heath. Symptoms shown resembled those reported at other places, most of which have been on upland rough grazings.

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Braid, K. W . (1934). History of the bracken disease. Scot. J. Aeric.

17, 297-305.

Braid, K. W. (1947). Bracken control—artificial and natural.

Grassland Soc. 2, 181-9.

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Fidler, J. H . (1963). T h e role of sheep in the degeneration of bracken on Ilkley Moor. The Naturalist, April-June, 1963, 41-2.

Garrett-Jones, R. (1960). Grazing of bracken by sheep in South Wales.

Proc. 4th Brit. Weed Control Conf., 1958, 194-6.

Garrett-Jones, R. (1961). Bracken grazing by sheep. Agriculture 68, 510.

Hull, R. (1968). (John Innes Institute, Norwich) Private communication.

I.amb, H . H . (1965). I n : T h e biological significance of climatic change in Britain, Ed. Johnson and Smith. Academic Press, London.

Parker, W. H . and McCrae, C. T . (1965). Bracken poisoning of sheep in the North York Moors. Vet. Record 77, 861-6.

Watson, W. A., Barley, R. M., and Barnett, K. C. (1965). Bright blindness—a condition prevalent in Yorkshire hill sheep. Vet. Record 77, 1060-9.

Watts, A. S. (1954). Contributions to the ecology of bracken. VI Frost and the advance and retreat of bracken. New Phytol. 53, 117-30.

Watt, A. S. (1956). Contributions to the ecology of bracken. VII Bracken and litter. New Phytol. 55, 369-81.

R- Garrett-Jones,

49 Gledhow Wood Avenue, Leeds 8,

Yorkshire.