Long-term recovery of bracken (Pteridium aquilinum (L.) Kuhn) after asulam spraying

This paper investigates the effects of a single asulam application, sprayed from the air, on the rhizome biomass, bud density, fronds and carbohydrate reserves of bracken (Pteridium aquilinum (L.) Kuhn) using a time sequence approach. Regression models were used to investigate how these characteristics varied with time after spraying, and were used, where appropriate, to calculate the time taken for full recovery after treatment. Frond density and biomass recovered in approximately eight years, bud numbers in seven, but rhizome biomass and total carbohydrate reserves required 10 to 12 years to recover. The consequences of these results are compared with predictions from a computer model and discussed in relation to the best timing of re-treatment and the management needed for long term control.     

Recovery of Moorland Vegetation after Aerial Spraying of Bracken (Pteridium aquilinum (L.) Kuhn) with Asulam

Bracken (Pteridium aquilinum) is a major weed of seminatural vegetation in Great Britain, as in many other countries. As a consequence, large areas have been subject to control with the intention of restoring the former vegetation. The use of aerial spraying with asulam, a narrow spectrum, carbamate herbicide, has become a common method of control. However, its long‐term efficacy has not been assessed in terms of either controlling the bracken or in producing suitable restored habitats. This study undertook such an assessment by comparing the results of a 2002 survey of the sites subject to bracken control by aerial spraying of asulam with previous (1990/1991 and 1994) surveys of the same sites. This showed that a single application of asulam was effective in eradicating bracken (<1% cover remaining) on a third of sites. However, on 10% of the sites, the bracken had regenerated completely (cover >80%) and on the remainder it was still present in patches (>20% of quadrats), often at high density. More than half the sprayed sites had seen good recovery of moorland vegetation, the target of the restoration, because they were now classified as having upland heathland vegetation within the National Vegetation Classification. Considerable amounts of bracken control are grant aided as part of agri‐environment schemes. These schemes should be adapted to encourage good practice, namely, intensive follow‐up treatment by spraying any emerging fronds, and to encourage treatment of previously sprayed areas rather than spraying of new areas in order to protect previous investment of grant aid.     

Aspects of Morphogenesis in a Dorsiventral Fern, Pteridium aquilinum (L.) Kuhn: With one Plate and ten Figures in the Text

The formation of the horizontal dorsiventral rhizome of Pteridiumaquilinum from the erect radial axis of the young sporelingis described. The shoot apex and the inception of leaves andbuds at the apical meristem have been investigated, and theirinception is shown to be essentially similar in long and shortshoots, later differences being due to differing rates of growthand internodal elongation in the two types of shoot.     

The influence of position on genet growth: a simulation of a population of bracken (Pteridium aquilinum (L.) Kuhn) genets under grazing

In a spatially explicit simulation model of vegetation dynamics (VegeTate), I labelled the initial mass of Pteridium aquilinum in each of 225 cells as a single, unique genet or clone. The physical environment was homogeneous and all genets shared the same phenotype. The aim was to discover whether and how the success of each genet was affected by its initial position relative to other genets and a competing grass species. In a scenario in which grazing generated a grass-bracken mosaic with complex spatial dynamics, the amount of growth of each genet ranged widely, from frequent extinction to mass increase by over 300 times. The main factor in the impact of position on genet growth was shown to be a benefit from the initial presence or proximity of a large mass of P. aquilinum. This was because a high density of P. aquilinum reduced local grazing intensity, allowing plant mass to accumulate and shifting the balance of competition in favour of P. aquilinum. Thus variations between cells in initial mass of P. aquilinum were greatly amplified. The implications of this amplification of initial differences between sites for population genetics are briefly discussed. Qualitative features of the spatial distribution of genets at the end of simulations matched reported observations on patchily distributed field populations of P. aquilinum. These features included dominance of a large population by a small minority of genets, widespread mixtures of a dominant genet and one or more subordinate genets, and the presence of patches of P. aquilinum formed both by agglomeration from neighbouring foci and by spread of dominant genets. Under less intense grazing, which allowed little or no development of vegetation mosaics, genet growth varied relatively little and initial variations in relative mass between genets were little changed. Based on this study, I hypothesize that any processes that generate non-linear spatial dynamics will also generate complex genet dynamics.     

A ten year study of the incidence of spores of bracken, (Pteridium aquilinum (L.) Kuhn.) in an urban rooftop airstream in south east Scotland

Field studies of bracken during sporing haveindicated very high numbers of sporesreleased per cubic metre of air. Thecarcinogenic nature of bracken spores poses ahealth hazard to workers and visitors in areasof sporing strands.A retrospective study of bracken spores trappedon slides exposed during Augustand September over the ten year period, 1988–1997, on a rooftop site in Edinburgh,has added an urban dimension to the aerobiologyof bracken.Results have revealed, apart from 1989,consistently low counts. The spore samplerwas situated downwind approximately 1.6 km fromthe nearest sporing stand.A spore calendar, based on the ten years ofcumulative data, has been constructed.     

Tree seed rain and seed removal,but not the seed bank,impede forest recovery in bracken (Pteridium aquilinum (L.) Kuhn)‐dominated clearings in the African highlands

Considerable areas dominated by bracken Pteridium aquilinum (L.) Kuhn occur worldwide and are associated with arrested forest recovery. How forest recovery is impeded in these areas remains poorly understood, especially in the African highlands. The component processes that can lead to recruitment limitation—including low seed arrival, availability and persistence—are important determinants of plant communities and offer a potential explanation for bracken persistence. We investigated key processes that can contribute to recruitment limitation in bracken‐dominated clearings in the Bwindi Impenetrable National Park, Uganda. We examined if differences in seed rain (dispersal limitation), soil seed bank, or seed removal (seed viability and persistence) can, individually or in combination, explain the differences in tree regeneration found between bracken‐dominated areas and the neighboring forest. These processes were assessed along ten 50‐m transects crossing the forest–bracken boundary. When compared to the neighboring forest, bracken clearings had fewer seedlings (bracken 11,557 ± 5482 vs. forest 34,515 ± 6066 seedlings/ha), lower seed rain (949 ± 582 vs. 1605 ± 335 tree seeds m^?2 year^?1), comparable but sparse soil seed bank (304 ± 236 vs. 264 ± 99 viable tree seeds/m²), higher seed removal (70.1% ± 2.4% vs. 40.6% ± 2.4% over a 3‐day interval), and markedly higher rodent densities (25.7 ± 5.4 vs. 5.0 ± 1.6 rodents per 100 trapping sessions). Camera traps revealed that rodents were the dominant animals visiting the seeds in our seed removal study. Synthesis: Recruitment limitation contributes to both the slow recovery of forest in bracken‐dominated areas, and to the composition of the tree species that occur. Low seed arrival and low persistence of unburied seeds can both explain the reduced density of seedlings found in bracken versus neighboring forest. Seed removal, likely due to rodents, in particular appears sufficient to constrain forest recovery and impacts some species more severely than others.