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Title: Succession and homeostasis in heath vegetation
Author: Legg, Colin J.
ISNI:       0000 0001 3607 7518
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 1978
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The development of an Arctostaphyleto-Callunetum community following fire was studied in stands up to 40 years old on the Muir of Dinnet, Aberdeenshire, Five phases in the development of 'the vegetation were recognized and designated the initial, pioneer, building, mature, and degenerate phases. Plant species were classified according to the time in the succession at which they were most abundant,. The major classes were: a) species abundant in the initial phase but absent or rare in later phases; b) species which occurred throughout the succession though sometimes not fully developed in the initial phase; c) species occurring only in the nature and degenerate phases, The behaviour of each species was found to be related to its morphology and habitat requirements. The diversity of the community decreased from the initial to the mature phase, reflecting the build-up in dominance of Calluna and Hypnum cupressiforme in the shrub and ground strata respectively. An increase in species evenness and diversity occurred in the degenerate phase where the Calluna had become degenerate , and the. dominance was shared by Erica cinerea, Arctostaphylos uva-ursi, Pleurozium schreberi and Hylocomium splendens to form a mosaic in the vegetation Each of the species studied showed a different strategy of production of underground perennating organs, or of seed production, distribution and dormancy which enabled it to survive a fire or re-establish itself in the community, 6. Seeds of several native heathland and non-heathland species were introduced into stands of heath vegetation of different ages since burning, and also into stands disturbed by removing successive strata of the vegetation. Germination and survival were monitored over two growing seasons, 7. Seed germination and establishment in closed vegetation was very low: the maximum survival observed over two growing seasons was 3.4% of total Sarothamnus scoparius seeds planted in pioneer-phase plots. Establishment from seed is therefore of little significance in the post-fire succession except during the first few years following the fire, or when considered over a much longer time period as in succession to woodland, 8. The germination and establishment of each species introduced to the vegetation showed a unique response to communities of different ages, and to disturbed communities, 9. The soil surface structure and layer of lichens in the pioneer-phase vegetation, and the mat of mosses in the mature-phase vegetation were as significant in producing a micro-habitat unsuitable for the germination of seeds as 'the shrub layer. The shrub canopy may, under certain circumstances, protect young seedlings from grazing and extreme drought, 10, The succession was recognized as passing through two phases; first, the establishment of plants from seed or from surviving stem, bases, and the vegetative spread to fill the space available thus forming a mosaic, each patch dominated by . one Cor more) species; and second, the competitive interaction between neighbouring patches and the local replacement of one dominant by another, 11, A model was constructed of vegetation change as a Markovian process of plant-by-plant replacement, Each patch in the vegetation was recognized as being in one of 15 possible ''states" defined by the dominant species, A transition probability matrix for the 15 states was obtained from field observations and applied in a matrix model to predict the pattern of vegetation development, 12, It was found that the transition probabilities for states containing Calluna as dominant or co-dominant changed as a function of the age of the plant. This factor was incorporated as a step function in the model, a different transition matrix being used for patches in which the dominance of Calluna had been maintained for a certain number of generations of the model. This model gave good agreement with the observed proportions of dominants at different stages of the succession, 13, The model quantifies the results of interaction between each species and its neighbours and illustrates the uniqueness of the response of each species and the complexity of the system, 14, The overall picture of post. fire succession helps to explainthe co-existence of many species in a dynamic, yet stable system through the complementary life-strategies of plants, In a successional community the plant niches are separated in time as well as in space and habitat requirements.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available