Thesis (Ph.D.)--Tufts University, 2003. / Adviser: Colin M. Orians. Submitted to the Dept. of Biology. Includes bibliographical references (leaves 181-200). Access restricted to members of the Tufts University community. Also available via the World Wide Web;

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During its life cycle the Calluna vulgaris L. plant passes through four phases related to its age and physiognomy. These are the pioneer, building, mature and degenerate phases. Within each phase, the Calluna plant provides possible habitats for invertebrates within the Calluna-derived litter, on the surface of this litter and in the canopy of the Calluna plant; many invertebrates are also found in the atmosphere above the plant canopy. The invertebrate fauna occurring within the litter includes mites, springtails, false scorpions, harvestmen, spiders, beetles, millipedes, Hemiptera, flies and Hymenoptera. The most numerous and frequently occurring of these are the mites, being almost equally divided into carnivores and those that feed on detritus. The size and diversity of the invertebrate population found within the litter is greatest under pioneer Calluna in heaths that have not been managed by burning, and greatest under degenerate in heaths that have been managed by burning. Otherwise it varies little as the Calluna passes through the different phases. The invertebrate fauna is greatest in numbers and highest in diversity on the surface of the litter. All those found within, the litter also occur in this habitat, often in greater numbers. The numbers and frequency of the beetles and millipedes are greater in this habitat than within the litter, although very few millipedes are found on the litter surface under managed heather. The carnivores and detritus feeders constitute the largest feeding classes. The diversity is greatest under degenerate unmanaged plants and building managed plants. Many more differences in the number of invertebrates are found between phases of managed than unmanaged heather. The invertebrate fauna found within the Calluna canopy includes harvestmen, spiders, springtails, thrips, leafhoppers, spittle bugs, beetles, flies, Hymenoptera and mites. The diversity of their populations in the unmanaged heather is greatest in the canopy of pioneer plants, while in the managed heath it is greatest in the degenerate plants. What few numerical differences are found involve larger numbers in the pioneer than other phases of heather. Many more differences are found between phases of managed than unmanaged heather. The invertebrate fauna found above the Calluna canopy consists mainly of Diptera and Hymenoptera, although spiders, leafhoppers, aphids and beetles are also found. The largest feeding class is the carnivores, animal parasites are found in greater numbers here than elsewhere. The size and diversity of the populations do not differ above different phases of Calluna, both managed and unmanaged, although that above managed heather is lower than that above unmanaged heather. Management by fencing and fertilizing reduces the number of invertebrate families present and has a variable effect on the diversity of the invertebrate populations.

The phasic, cyclical model of Calluna-dominated vegetation dynamics, proposed by A.S. Watt, is evaluated by investigation of the gap in the degenerate plant. Succession in the gap is analysed by Markov models and found to be non-Markovian, with a number of processes occurring simultaneously. Vegetation changes are better interpreted in terms of certain ecological attributes of the species concerned. The inter-relationships between three important moss species are investigated further. Regeneration of Calluna is very variable. Seedling establishment requires a safe site and sufficient moisture, and depends on wet summers. Vegetative layering occurs more frequently but varies between parent plants and substrate types. The presence of soil micro-organisms appears necessary for adequate adventitious root production. An outbreak of heather beetle was monitored and contrasted with outbreaks in the Netherlands. The population was reduced by a parasitoid which acted density independently. At these low densities, a mosaic of gaps is formed in the vegetation by spatial heterogeneity of heather beetle attacks. These gaps behave in a similar fashion to degenerate gaps, and most Calluna regeneration occurs by layering. The value and limitation of Watt's model is discussed, especially by reference to forest gap-dynamics theory.

The declining area of heathland in north-west Europe is causing widespread concern amongst conservationists. The aim of the experiments described in this thesis was to investigate methods of heath creation by establishing the dwarf shrub, <I>Calluna vulgaris</I> (L.) Hull, on the ex-arable land. Arable land, surplus to requirement and available through set-aside schemes, could be used to expand or join together small pockets of remnant heath. Field experiments were designed to test various methods of introducing <I>Calluna</I>, but, in all cases, it failed to persist and spread after introduction. The most promising method of introduction was to transplant young plants. The conditions at the field site, in arable production immediately prior to the experiments being set up, were such that <I>Calluna</I> was unable to establish dominance. High residual soil fertility combined with a large weed seed bank produced a dense cover of vegetation in which <I>Calluna</I> did not persist. Pot experiments were carried out to determine whether soil amendments might make the creation of heath more feasible on ex-arable sites. Most amendments reduced the dry matter production of the weed species tested compared to the control treatment (un-amended field soil). One treatment, elemental sulphur, significantly reduced the growth of a major weed species (<I>Trifolium repens</I>) at very low application rates, whilst <I>Calluna</I> grew well on the amended soil. Elemental sulphur lowers soil pH and therefore reduces the availability of most plant nutrients and increases the solubility of some metals. When tested in the field, high rates of sulphur significantly increased the survival of <I>Calluna</I> transplants. The author suggests that soil modification with an acidifying agent is the key to heath creation on agriculturally-improved soils. Vegetation management, such as the use of herbicides may also have a part to play, although once soil conditions are suitable this management would be reduced very much to a secondary role.

Upland plant communities are vulnerable to environmental change, especially if the component species have limited dispersal abilities and consist of fragmented populations. Oceanic-montane liverwort-rich heath is a rare upland vegetation type found in the oceanic areas of the British Isles and Norway. This thesis contributes both fundamental knowledge about the liverworts’ biology and an understanding of how this can be applied in conservation management, taking into account the compositional changes that have already occurred within liverwort heath. These issues were explored by i.) a re-survey of 50- and 20-year old liverwort heath plots, ii.) assessment of the genotypic diversity of one liverwort using microsatellite markers, iii.) ex-situ and in-situ experimental studies on growth and reproduction and, iv.) transplantation of one liverwort to unoccupied sites to assess habitatlimitation and the potential of translocation as a conservation management tool. The re-survey revealed that the liverwort heath has undergone compositional changes. Liverworts and dwarf shrubs decreased while graminoids increased. This was linked to grazing pressure, eutrophication and warmer and drier conditions. High genotypic diversity was demonstrated in a liverwort unknown to reproduce sexually in the British Isles (Anastrophyllum alpinum), suggesting that sexual reproduction must have occurred in the past. The data also indicated clonal growth at the local level, but no dispersal of vegetative fragments between populations. Thus, dispersal limitation is likely to have implications for the species under future environmental change. Ex situ and in situ cultivation of whole liverworts and fragments revealed that most of the species can grow from both fragments and whole shoots. Therefore, in the absence of sexual reproduction, the species can persist locally by growth and vegetative spread. Also, there is potential for ex situ conservation of these species, in situ enhancement of existing populations, and creation of new ones. Translocation of Herbertus hutchinsiae suggested that the species is dispersal limited. Transplants grew at all sites, exhibiting best growth within range. Therefore, translocation is a management option for this species to enhance or increase extant populations, to restore populations that have declined over the last half century and to reach future suitable climate space. These results have large implications for nature conservation management, to safeguard the unique liverwort heath.