(a) history and spread of pteridium
Pteridium is an ancient plant with records of Pteridium-like fossils in Oligocene deposits (Hungary) and Miocene deposits in England (Long & Fenton 1938) and Oregon (Graham 1963). There are single site records for Pteridium spores from the Ludhamian (Tiglian, the earliest interglacial) and Cromerian interglacials and more substantial records from all the substages of the Hoxnian (Holsteinian), accompanied at Gort in substage II by leaves with dichotomously branched veins, an incurved membrane and a lower surface covered in long multicellular hairs. Pteridium spores have been recorded in the three substages of the Ipswichian (Eemian), the last interglacial. Records in the late Weichselian (the Last Glacial) are sparse with spores recorded in scattered localities in southern and western Europe (Huntley & Birks 1983). In zone IV (Pre-Boreal, c. 9000 bp) Pteridium has been recorded at low frequency in Skye, the Caingorms, Tyrone and Hampshire. At Crane's Moor (Hampshire) spore frequencies in the following zone reached 5–10% of local tree pollen. The Flandrian (Holocene/Post glacial) expansion of site records did not occur until zone VI (Boreal, c. 8500 bp). At this point Pteridium was widespread throughout Spain, western France and the British Isles, with particularly high concentrations in the Skye region of north-west Scotland (Huntley & Birks 1983), and it almost reached its northern limit, at least in the British Isles. Spore frequency remained low throughout zones VI and VIIa (late Mesolithic) with Pteridium presumably confined mainly to the forest ground layer and natural clearances and margins, although with very high values in some western localities (Huntley & Birks 1983) suggesting open conditions, or only very thin forest cover. In zones VIIb and VIII, from the beginning of the Neolithic onwards (Godwin 1981), frequency increased greatly due to forest clearance. It is not surprising that the detailed analysis through prehistoric tree clearances regularly shows Pteridium making a quick response to forest opening (Turner 1964, 1965; Godw. Hist.; Rymer 1976). By 1000 bp the spore record is considerably reduced, especially in northern Scotland, reflecting climatic cooling and reduced spore production (Huntley & Birks 1983).
In undisturbed communities (similar to pre-Neolithic communities), Pteridium probably had a subordinate status in all communities except in open woodland, where the shade was moderate and the soil suitable. This implies that even when soil and climate are suitable for Pteridium, the natural woody vegetation excluded Pteridium by competition (McVean 1958). The basis for this deduction is partly the rarity or absence of Pteridium in vegetation cores from islands in West Highland freshwater lochs in comparison with the nearest similar vegetation on the mainland (McVean 1958). He drew the conclusion that the unmanaged vegetation (analogue for the Mesolithic) is unfavourable for Pteridium establishment from spores, rhizome spread or sporophyte survival, except in natural gaps. Where there were large open areas available on the mainland, there were opportunities for establishment, and both dispersal and vegetative spread. Thus, in the climax vegetation, Pteridium may be a subordinate component of the community or, where dominance occurs, this is in small patches. However, as yet there is no really convincing proof of this hypothesis.
During the Neolithic period and into the Bronze Age (VIIb, c. 4000 bp) there was an increase in the occurrence of Pteridium, associated with records of scrub development, vegetation clearance and charcoal use. By the Romano-British Iron age, Pteridium had expanded, and macrofossil evidence suggests that by this time it was being used for bedding (Turner 1965; Smith 1970; Page 1982; Brown 1999). This increase in Pteridium is therefore correlated with human activity, directly by felling, cutting, burning, cultivation and abandonment of land, and indirectly through grazing by domestic stock and changing the ‘balance’ between carnivores and small herbivores, including the later-introduced rabbit. Pteridium was important after clearance from 1600 bc. Later there is an indication of a reduction in Pteridium as if some measure of partial control was taking place (Walker 1966). Intense clearance began around 1300 ad (Moore & Chater 1969). This general explanation for the rise in Pteridium in the northern hemisphere has also been confirmed for P. esculentum after the arrival of Maori settlers in New Zealand at c. 800 bp (McGlone 2001; McGlone et al. 2005). More recent increases in Pteridium have been ascribed to land-use change. In County Mayo, Ireland, expansion occurred after a period of woodland clearance in the late 18th century, cropping with oats and potatoes peaking in the mid-1800s, followed by a decline and a change to marginal pasturing with subsequent Pteridium increase (Little & Collins 1995).
Current observations, archaeology and documentary records and the palynological record of the British flora and vegetation collectively show Pteridium as a ‘camp-follower of man’; it expanded as a result of the removal of factors limiting it, or the creation of opportunities for expansion. Man learned to use Pteridium for a range of purposes and its harvest must have at least restricted its spread and at most reduced its cover and intensity. However, as man has stopped using Pteridium as a resource in recent times, it has become regarded as a weed. When the pollen records of a range of unbiased samples were compared, Pakeman et al. (2000) concluded that the current abundance of Pteridium was less than, or at worst, equivalent to maximum historical records. Indeed, recent surveys suggest a slight deline in abundance (Pakeman et al. 1995, 2000).
(b) uses of pteridium
Pteridium has been used in a variety of ways by many cultures, and this has varied in time (Rymer 1976). The rhizomes have been used as either food or as a source of bread in aboriginal Australian, British, French, Japanese, Lapp, Roman and Siberian cultures (Rymer 1976; Veitch 1990). In Japan, the young croziers are still eaten after boiling (which has been shown to reduce the levels of toxins; Hirono et al. 1972, 1973) and bundles are sold in shops in spring. As a starchy substance, the rhizomes have been used for the preparation of glues and the brewing of beer. The rhizomes contain about 46% starch: they froth with water and are used as soap in country districts of France. Pteridium has also been used to produce strong yellow dye, and on the Isle of Man it was boiled with linen to bleach it. The fronds have also been used for packing fruit in baskets and for protection in gardens against the winter frost.
In Scotland it is used as thatch for houses that could last for 20–30 years, cordage for securing heather, stacks and sheds and as fuel for domestic heating. Pteridium has also been employed routinely for animal bedding and, indeed, human bedding since Roman and Viking times. Pteridium has also been used for animal feed; Aitken (1888) reports cut Pteridium heaped into stacks like beehives, and when this material was fed to Highland cattle as silage, the cattle suffered no ill effects. When Pteridium is cut early a silage of reasonable quality can be produced, but it is not generally attractive to stock and its digestibility is low (Watson & Smith 1956). The dry matter was close to hay in starch equivalent, and when cut late it was little better in nutritional value than straw. In Wales the young green fronds were used as pig food, and dried fronds were chopped up with straw and hay and given to horses.
There are many examples of the use of Pteridium as a fertilizer. At Stonefield in 1779 the rent included ‘16 cartloads of pulled fern deliverable at the tenants’ expense to the mansion house in Fernoch for the buildings of the said lands of Fernoch’ (L. Rymer, pers. comm.). It is also used as manure by cutting, wetting and trampling down and then mixing with calcium-rich materials and soil (A.S.W.). Recently Pteridium has been tested as a mulch, green manure and as a source of potash in organic agriculture and potato production (Taylor & Thomson 1998; Donnelly 2003), and for compost in modern horticulture (Pitman 1995; Davies 2004). Dead fronds of ‘Pteridium aquilinum var. esculentum’ provided a useful mulch for Sinapsis alba (white mustard), Trifolium repens (white clover), Lolium perenne (perennial ryegrass), Eucalyptus fastigiata (brown barrel) but not Leptospermum polygalifolium (yellow tea tree) (Taylor & Thomson 1998).
Pteridium has also been used industrially: it has been processed into a board, similar to beaverboard, resembling Bakelite; and as basic ash, rich in potash, that was used for soap and glass-making. Pteridium was also used as faggots for fuel in baking ovens; it has been used to fire brick and lime kilns. For this use, fronds were cut at the end of June when the levels of potassium were at a maximum; it is half-dried, then burned slowly in a pit. It has also been assessed for its suitability as a crop to produce energy through combustion or the production of biogas (Lawson et al. 1986).
Pteridium has been used as a medicine. It has been utilized as an antihelminthic, but according to Langham (1579), there are at least 21 uses including ‘Burnings, Cattle galled, Festers, Gnats, Horsesicke, Kanker, Miltpaine, Mother suffocat, Nosebleeding, Purgation, Sinewes griefes, Skinne off, Sores, Wormes, Wounds, Makes women barren’. It has also been used as a cure for rickets, and as an aphrodisiac (Cameron 1900; Rymer 1976). The fronds have a characteristic smell and are repellent to insects, serving well for wrapping up fruits and vegetables. It is also a plant of fokelore; ‘fern seed’ apparently can confer the power of invisibility, and burning bracken it is reputed ‘doth draw downe the rain’ (Rymer 1976).
In the past, Pteridium was such an important resource that its harvesting was once a right, and an appreciated privilege, protected in some places through byelaws to prevent over-exploitation. Where this occurred the Pteridium harvesting was restricted to ensure that the frond harvest was taken at the end of the growing season, at a time (Stage 5, Fig. 4) after the carbohydrates and nutrients had been re-translocated to the rhizomes, and there was minimal impact on the frond production in the following year. Thus, at Lakenheath Warren Pteridium was not to be cut until after the 29th of August each year (Crompton & Sheail 1975). In this way there would be a minimal effect on future productivity and hence a sustainable crop was ensured. Thus, in the past, Pteridium was very useful to man though now under the modern economic regime it is a pest to be destroyed or reduced.
The classification of Pteridium as a weed is a relatively recent phenomenon. Its abundance and distribution are generally regarded as being relatively stable until the last 200 years when a combination of changing factors (land management practices) reduced control and allowed it to expand. Pteridium is not recorded as a weed until complaints about its spread were first noted in the early 19th century and its control was attempted by flooding with spring water (McTurk 1837; Murray 1837). Poel (1951) more recently tested this method in two small-scale studies; the first killed most fronds within 4 months, but there was no effect on the rhizomes or the adjacent Callunetum. The second compared two 1-m2 quadrats; irrigation reduced frond numbers from 50 m−2 to zero in less than 16 months; unfortunately, effects on rhizomes were not reported.
Since then, there have been increased generalizations that Pteridium was spreading, caused by, inter alia: a change from cattle to sheep grazing in Wales and the highlands, a change from heavy wether sheep to lighter ewes grazing in North Wales, muirburn, severe winters, acid rain, elevated nitrogen loads, and even myxomatosis which reduced the rabbit population. The change in grazing systems from heavier to lighter animals with a lower trampling effect and hence reduced damage to developing fronds reduced the limitation on Pteridium performance (Pakeman & Marrs 1992). There is also a possibility that Pteridium has been severely affected by occasional very hard winters (e.g. those in the 10th century and 1940, Watt 1940), and a reduced frequency of these has allowed Pteridium to expand.
In general terms, Pteridium has ceased to be a useful plant, and has become in Britain a weed to be checked or destroyed.