|Ogilvy, T. (2004). Regeneration Ecology of Broadleaf Trees in Caledonian Forest. Unpublished PhD Thesis, The University of Edinburgh School of GeoSciences.
Regeneration Ecology of Broadleaf Trees in Caledonian Forest
School of Geosciences
University of Edinburgh
This thesis quantifies aspects of shade tolerance in tree seedlings of species native to the Caledonian pinewood ecosystem of Glen Affric (Highland Region, Inverness-shire). Growth, allocation and morphological responses of 15 species to irradiance under simulated forest canopy light were investigated in a nursery-based shade house experiment. The same responses of four of the 15 species (Ilex aquifolium, Alnus glutinosa, Sorbus aucuparia and Betula pubescens) to different developmental stages of Pinus sylvestris woodland were investigated in the field. The spatial and temporal growth responses of naturally regenerating S. aucuparia seedlings to shade and gap microhabitats were also studied. Data from the shade house experiment enabled further detailed exploration of the relationship between relative growth rates (RGR) and irradiance and potential cross-overs of ranks of growth in high and low light conditions.
The main findings were: i) species displayed typical responses to shade such as decreases in RGR and net assimilation rate (NAR), increases in specific leaf area (SLA) and leaf area ratio (LAR) and reduction in the root:shoot ratio; ii) despite similar responses to shade, species specific differences were clearly reflected in significant species-light interactions or species-stand interactions for all growth variables; iii) variation in RGR in low light could be explained by LAR and variation in high light explained by NAR in the nursery, but this pattern was not so clear in the field; iv) most species maximised growth rates at intermediate light levels rather than in full daylight conditions; v) Ellenberg's original light indicator values underestimate the light demand of some species in the nursery but conform well to responses in the field; vi) natural regenerating Sorbus aucuparia seedlings persist under the shade of old-growth P. sylvestris canopy up to 14 years; vii) responses of both planted and natural regenerated S. aucuparia seedlings reflect intermediate shade tolerant behaviour; viii) there was no clear evidence of an inhibitory effect of the abundance of Calluna vulgaris on seedling growth but low levels in shade were associated with a high abundance of S. aucuparia seedlings and successful growth and performance of I. aquifolium seedlings.
Recommendations for restoration or rehabilitation within the Glen Affric Caledonian pinewood include growing A. glutinosa, especially in the wet open woodland patches, to improve soil conditions and retard further degradation. B. pubescens and S. aucuparia are best planted on the edges of well-drained old growth stands and I. aquifolium under more shade (15% PAR) protected from extensive C. vulgaris cover and frost.