The morphology of bracken (Pteridium aquilinum (L.) Kuhn) in the North York Moors - a comparison of the mature stand and the interface with heather (Calluna vulgaris (L.) Hull) 2. The rhizome.

摘要

The morphology of bracken rhizome is described from within a mature bracken stand, and at advancing and stationary stand margins where bracken-heather interfaces occur in the North York Moors National Park, UK. Stationary margins, i.e. those where bracken was not encroaching into heather at a significant rate, often had morphological characteristics intermediate to those of a mature stand and an advancing margin. In the mature stand, rhizome biomass was dominated by carbohydrate-storing long shootswhich comprised 63% of the total fresh weight, whilst the majority of rhizome buds (89% of all active and 86% of all dormant buds) were found on frond-bearing short shoots. At the margins of a bracken stand the proportion of rhizome composed of long shoots was even greater, and that of short shoots small relative to that in the mature stand. More transitional shoots were also found at the stand margins. Hence, close to the margin a greater proportion of fronds was found on transitional rhizome than isthe case in more mature parts of the stand. The majority of buds on all types of rhizome were in a dormant state. The proportion of buds which were active was, however, greater on long and transitional shoots than on short shoots. Hence, a larger proportion of buds were active close to the margin where the rhizome was composed less of short shoots than was the case further into a mature stand. The differences in the morphology of bracken in a mature stand and at the stand margins which are identified here support the idea of controlling bracken at stand margins in preference to the spraying of large areas of dense, mature bracken. Morphological differences include an increased proportion of active buds, greater frequency of fronds per unit rhizome biomass and reduced biomass reserves. Improved conditions for the re-invasion and re-establishment of alternative vegetation are also available at stand margins in comparison with the centre of a dense bracken stand.