Genetic resources of native tree species and their deployment under climate change

Abstract

Current and emerging threats to trees and forest ecosystems require a re-evaluation of the way forest genetic resources are managed. Governments in the United Kingdom and elsewhere are committed to the restoration, expansion and creation of new woodlands. Tree populations are often adaptively differentiated from one another, so a key question underpinning the success of planting schemes is the choice of seed origin. A long held understanding is that locally sourced seeds will have the best opportunity to tolerate conditions of the planting site (local provenancing). However, the rate at which the environment is changing introduces a great deal of uncertainty into decision making and there is concern that climate change is proceeding at rates faster than those with which locally adapted trees would be able to cope. As such, there are suggestions that seed collected from areas already experiencing the anticipated future conditions will improve the adaptability of forests (predictive provenancing). This thesis investigated outstanding questions relating to the merits of the local provenancing and predictive provenancing approaches, and the practical implementation of seed sourcing policy in British forestry. The validity of existing seed zone boundaries used under local provenancing was analysed for ancient semi-natural Scots pine Pinus sylvestris L. forests of Scotland. Vegetation description and analyses of climatic covariates revealed that the existing series of seed zones used to guide selection of planting stock for restoration do not necessarily environmentally match seed sources to planting sites under current conditions. Additional disparity is introduced when edaphic variation (or proxies for this) is considered. To determine whether future adaptation under local provenancing may be restricted by limited pollen flow among populations of native Scots pine in Scotland, the timing of pollen production in five populations was estimated by repeatedly measuring strobilus development on a series of twenty trees over three consecutive springs. Differences in the mean predicted date of pollen production were found, with populations in the warmer west shedding pollen earliest each year, although the timing and differences in timing among populations varied from year to year, with shedding taking place earliest in the warmest of the three years and latest in the coolest year. A theoretical multi-patch, ecological genetic individual-based model (IBM) was developed to investigate the utility of different seed sourcing strategies (local versus non local provenance) and their capacity to help populations adapt to directional climate change. As well as being adapted to climate, which varied in a clinal pattern, individuals also had to be well adapted to the habitat conditions of the planting site in order to survive hard selection at the seedling stage. The model showed that population size of a new planting was reduced when planting stock adapted to the future conditions but not to current conditions was deployed. The differences were most severe when selection acted simultaneously on both the climate-related and the habitat-related phenotype. Finally, a series of in-depth qualitative surveys conducted with members of the domestic forest nursery and seed supply sector in Great Britain found that there are many difficulties associated with seed sourcing and the supply of trees. These problems arise due to a very limited ability to predict demand at the time of seed sowing, and lead to waste when demand is overestimated and importation of planting stock when demand is underestimated. Confidence and competitiveness in the domestic sector could be greatly improved by updating seed sourcing guidelines and by simplifying certain aspects of the process by which forest planting projects are funded.