The vegetation of New Zealand has undergone extreme changes during the period of European settlement, with not only forest clearance but a deliberate attempt to replace the native vegetation with species from Europe and later from other parts of the world. Garden escapes continue this process to the current day. Several European ferns that have been introduced to New Zealand gardens have subsequently escaped. At the time of writing D. filix-mas is the most obvious and probably the most abundant in the rural areas of Canterbury having been observed in a wide range of habitats from suburban to farm, to forests both plantation and montane and in shrublands. This thesis investigates some of the ecology of D. filix-mas and explores its potential as a weed detrimental to New Zealand’s indigenous ecosystems. An extensive literature review revealed that in the Northern Hemisphere D. filix-mas grows over a wide range of climates, vegetation types and soils. However the literature review did not clearly show the forest light conditions under which D. filix-mas grows nor could the Northern Hemisphere experience in deciduous woodlands and coniferous forests be directly carried over into New Zealand’s podocarps, evergreen hardwood and evergreen beech forests. An experiment was designed to investigate tolerance to shade and field data was collected at several sites across North Canterbury for subsequent investigation with ordination and standard statistical methods. Records from around New Zealand were collated and used to generate a map of potential extent using the Land Environments New Zealand dataset. Positive growth was achieved under all shade treatments including the heaviest at 96% shade. However the field data suggests that under some of the lowest light availability D. filix-mas does not grow. In the field D. filix-mas is found in diverse habitats with a preference for sheltered sites with more southerly than northerly aspects. Interpretation of the ordination output combined with knowledge of the sites suggests that D. filix-mas is mostly associated with degraded sites and sites of past disturbance. Regenerating kanuka is a reliable place in which to find D. filix-mas but relatively natural beech forest is not. D. filix-mas can potentially grow over much of the South Island particularly in drier areas and can be invasive following disturbance and when grazing is removed, making it a potential problem for indigenous forest restoration efforts.