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CONTRIBUTIONS TO THE ECOLOGY OF BRACKEN ( PTERIDIUM AQUILINUM )
Author(s) -
WATT A. S.
Publication year - 1971
Publication title -
new phytologist
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.742
H-Index - 244
eISSN - 1469-8137
pISSN - 0028-646X
DOI - 10.1111/j.1469-8137.1971.tb02598.x
Subject(s) - bracken , frond , rhizome , biology , population , shoot , frost (temperature) , botany , pteridium aquilinum , litter , microsite , horticulture , ecology , geography , fern , seedling , demography , sociology , meteorology
S ummary The phenomena of change from the marginal belt to the hinterland on the acid sandy podsol of area E are regarded as symptoms of senescence (increase in age of the frond population and in patchiness: reduction in height and number of fronds, in size of plant and its rate of growth). They are considered in relation to causes, primary and secondary. The primary cause is the plant's reaction on itself: in the invading marginal plant increasing competition until the maximum number is reached (at 30–40 ft; 9–12 m) and reaction on the root and rhizome system through the amount and kind of litter. Once started a chain of reactions is set up in which frost and drought are important but secondary causes. Litter (s.l.) acts in two ways with opposing effects on the welfare of bracken but with no hard and fast line between them and the effect varying with the conditions. Litter (s.s. = the L layer) when abundant, as in the mid‐region of the marginal belt, means protection from winter frost and drought and by delaying emergence of the fronds reduces liability to spring frost and in its F and H forms induces a concentration of roots in them, a rise in the general level of the shoot system and greater vulnerability of the growing points to frost and drought. With age of the population the F and H layers increase relatively to the L (s.s.). Data on the vigour and vertical distribution of the rhizome system from an area (Blaxhall Heath) vacated by bracken and from the live bracken marginal to it show a similar robust but dead system in both, which in the latter has a younger, superficial, attenuated system, consisting mostly of intermediate and short shoots above it and lying almost wholly in the F layer. Details show that the process of degeneration has not only been checked but recently reversed. Response to fluctuations in weather show that the hinterland plant is not inherently weak, but its attainment of a size and vigour similar to that of the marginal plant depends on conditions enabling it to reach that status and to maintain it on the continued provision of open conditions with little competition. The interpretation of degeneration (regression) advanced here does not invoke the presence of a pathogen. The results are considered briefly in relation to the status of bracken in a man‐controlled environment.