The autecology of sweet brier (Rosa rubiginosa L.)

Sweet brier is of particular interest in New Zealand, because it occurs widely as an unwanted plant in extensively grazed tussock grasslands of the eastern South Island. Since the control of the rabbit it has rapidly encroached on thousands of acres of pastoral land, causing much of it to become derelict, and forcing large tracts of land out of production. In the past, control measures have been many and varied, with usually disappointing results. The difficulty and high cost of eradicating sweet brier in these areas have- stimulated a desire for further research on this aggressive plant. The aim of the present investigation has been twofold; to produce an outline of the autecology of sweet brier; and to provide more detailed information about certain problems, especially those concerned with establishment and survival of seedlings. Many sweet brier populations throughout New Zealand were visited and much observational data was recorded. Detailed field work was confined to the Waimakariri catchment, North Canterbury, though other South Island populations were given close attention (figure 0.1). The detailed experimental work was carried out at Lincoln College. The seasonal activity of the species in the field was studied, and measurements were made on the growth of different plant organs in different habitats, and the reproductive capacity of populations. The survival of seed and seedlings was also followed. Some environmental factors were measured, but these were not sufficiently comprehensive to establish quantitatively the differences between any two sites, or to establish a statistical correlation between plant performance and environmental factors. Certain aspects were selected for experimentation, largely to help resolve ecological problems, and not to yield information of a basic physiological nature. The scope of experiments was limited to some extent by the difficulties involved in raising adequate stocks of seedlings at convenient times. One series of experiments tested the effects of temperature and daylength on the seasonal activity of buds, extension growth of shoots, and cambial activity. A further series studied the effects of different light climates, and different levels of soil water and aeration, exposure, and soil fertility. A large, greenhouse experiment was designed to test the effects of competition between sweet brier, grass, and clover seedlings. The general history and taxonomic status of sweet brier are discussed in Chapter 1, and the identity of the species in New Zealand is reviewed in Chapter 2. In Chapter 3, the distribution and ecology of the species is discussed to elucidate some of the major factors which apparently limit its occurrence in this country. Then follows a description of the principal plant communities and the types of habitat within which sweet brier is found. The remainder of this dissertation attempts to develop a logical sequence, beginning with a detailed discussion in Chapter 4 of the structure, life history, and seasonal behaviour of the species as determined by its genetic constitution. Chapter 5 examines the effects of some environmental factors on seedling growth, and Chapter 6 discusses the mature plant in its, natural environment. Chapter 7 is in part a synthesis; it reviews some of the more important biotic effects on seedling establishment, and attempts to relate the conclusions drawn in preceding chapters. Some of the reasons for the extraordinary success of sweet brier in New Zealand are outlined in Chapter 8.