Bracken Litter Research Articles

Acid deposition: Effects of sulphuric acid at pH 3 on chemical and biochemical properties of bracken litter

The effects of increased acid deposition on some biochemical and chemical properties of bracken litter overlying a podzolic soil contained in monolith lysimeters were investigated. Pairs of lysimeters each received 1500 mm yr −1 of “rain” consisting either of distilled water or pH 3.0 sulphuric acid applied evenly over a 5-yr period. The acid-treatment resulted in a marked acidification of the litter, associated with accelerated leaching of Ca 2+, Mg 2+, K + and Mn 2+. Acid treatment also increased the concentration of extractable Al 3+ in the litter. The biochemical changes observed in the litter as a consequence of acidification included decreases of 33% in ATP content and 54% in respiration rate. Significant reductions in the mineralization rates of urea, glucose and acetate, and in the activities of 4-nitrophenylphosphatase, β-N- acetyl- d-glucosaminidase , exo-1,4,β- d-xylosidase and peroxidase were also observed in the acid-treated litter. The acid-treated litter also contained slightly less total N, ammonium-N and total P, and slightly more residual hexose carbohydrate than the control litter. The effects observed were consistent with a decrease in microbial activity associated with litter acidification and were reflected in a small (5.5%) but significant ( P < 0.05) decrease in litter decomposition. Acid treatment decreased the ATP content of the mineral soil by about 13% in the 3 cm immediately beneath the litter, but below this depth no significant difference was observed.

Field trials in south-west Scotland

SynopsisSouth-west and west Scotland contains a large proportion of the bracken-infested hill pasture in that country and considerable effort has been expended over the past five decades on a scientific approach to bracken control. The trials of various, more or less successful, herbicides culminated in the current work based on the use of asulam or glyphosate which will control, but only in rare cases eradicate, bracken. Current work is aimed at improving the control effect by investigating and refining timing, rate and method of application, additives and mixtures. Particular emphasis is placed on techniques of improving the underlying sward, where present, and of investigating the factors influencing its growth. Experimental work has not shown any degree of allelopathy towards sown-in grass and clover seed growth, but depth of bracken litter is shown to be important. Doubt is expressed regarding the requirement for a total programme of bracken control and follow-up fertiliser treatment in all cases before grant aid is approved

Botanical implications of bracken control

In addition to bracken, Pteridium aquilinum, and other ferns, only a restricted range of species among the natural flora suffer severe damage if sprayed with asulam in late summer. Of the plants associated with bracken in relatively well-drained situations those affected most by the herbicide include the three Ulex species, Rumex acetosella, young plants of Calluna vulgaris, some Compositae and grasses of the genera Poa, Holcus and Agrostis (though not A. setacea). In damp and wet upland habitats, Cirsium palustre, Juncus effusus, Glyceria fluitans and a few other species are moderately susceptible to asulam but the majority of plants appear to be resistant or only slightly damaged. Areas from which bracken has largely been removed tend to be invaded by such species as Deschampsia flexuosa, Holcus mollis, Chamaenerion augustifolium, Digitalis purpurea and Urtica dioica. If grazing pressure is low the absence of competition enables woody species to regenerate from seed. Colonization and subsequent spread of the perennial plants is influenced by what was present as ground flora before the bracken was killed and by the depth of bracken litter. Asulam is considered to be a useful aid to the management of nature reserves where encroachment by bracken needs to be checked. Its most widespread use for bracken control is likely to be on upland farms to clear bracken from marginal land with the aim of increasing and improving pasture. Adjoining woodland and moorland habitats may suffer from resulting changes in land management. Moreover, indiscriminate aerial spraying of asulam over large areas may affect local populations of plants, notably ferns, in the more open areas not protected by a canopy of bracken.

The sheep headfly, Hydrotaea irritans (Fall.) (Diptera, Muscidae): larval habitat and immature stages

AbstractNumerous habitats were sampled for larvae of sheep headfly, Hydrotaea irritans (Fall.), in infested areas of Northumberland during the winters 1973–74 and 1974–75. Most of the larvae found came from near the surface of soil beneath pasture and long grass. The mean larval density in these sites was 1·93/m2; the greatest density in a single site was 3·87/m2 which compares well with unpublished estimates of adult fly density. Only two larvae were recovered from cow dung. One larva was found in bracken litter, and none in other types of litter, or in horse dung, peat, moss or rotten wood. Larvae were reared to the mid-third instar from eggs laid in the laboratory. Field-collected larvae fed readily on Musca and Calliphora larvae, and did not appear to diapause in December; their identity was confirmed by rearing them to the adult stage. The egg, second- and third-instar larvae, and puparium are described and figured. Descriptions are given of changes in the mouthparts during growth of the third-instar larva, and of the features by which field-collected larvae can be identified.

Allelopathic potential of western bracken

In laboratory studies, water-soluble extracts from senescent western bracken (Pteridium aquilinum [L.] Kuhn var.pubescens Underw.) fronds reduced germination of western thimbleberry (Rubus parviflorus Nutt.) and delayed germination of salmonberry (R. spectabilis Pursh.), but did not affect Douglas fir (Pseudotsuga menziesii [Mirb.] Franco). In greenhouse studies, unincorporated western bracken litter reduced emergence of all three species but did not influence root and shoot length or dry weight. However, bracken litter incorporated into the soil reduced both shoot length and dry weight of western thimbleberry seedlings. Allelopathic interactions may explain the relative absence of woody shrubs such as western thimbleberry and salmonberry from sites dominated by western bracken.