Practical implications for forest management

Until it is possible to determine whether biotic or edaphic variation explains sufficient quantities of phenotypic variation in trees at a fine geographical scale (i.e. within the rather limited range of the native pinewoods), it will be difficult to determine whether seed sourcing guidelines ought to be modified to take these details into account (Ying and

Yanchuk, 2006). At broader scales, however, for instance when considering introducing new species or translocations over larger differences, biotic or edaphic variation may be of greater effect and certainly warrants further investigation (Bucharova, 2016). Nonetheless, the analysis of climatic covariates clearly showed that improvements can be made upon geographical boundaries with a climatic site matching tool, and one could be designed with relative simplicity, such as those in the USA (Howe et al., 2009) and Canada (McKenney et al., 1999). The main problem with a site matching tool, or ‘floating’ seed transfer zones (sensu Rehfeldt, 1983) would be that, in order to obtain the closest match between seed source and planting site, it would be necessary for seed to be available already in storage, or to arrange bespoke seed collection and sowing in time for plants to be raised and deployed at the planting site, something which is rarely possible in GB (Whittet et al., 2016a). The entire process would be more effective if results from trials found quantitative limits in

environmental distance over which seed can be transferred without risk of maladaptation. The general geographical pattern of variation in climatic and community compositional was a longitudinal one, matching with empirical results from provenance tests and short term seedling studies with Pinus sylvestris in Scotland (Salmela et al., 2011; 2013; Donnelly et al., 2016; Perry et al., 2016a,b). Although no fully comparative data are yet available to determine transfer limits, it seemed subjectively possible that the number of seed zones for Scots pine could be reduced to three. These three seed zones would include a hyper-oceanic group in the far west of Scotland, a central group of populations at higher altitudes in the central and northern Highlands and a third group containing populations in and around the Cairngorms national park.

The potential that temporal reproduction isolation between distant pine populations exists in some years seems plausible. Further research is required to elucidate the mechanisms of these phenological differences in reproduction, but it is worth noting that temporal isolation is just one of many possible barriers to gene flow. Parameterising more complex models of pollen flow with empirical data can only reduce expectations of effective dispersal. A further

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hypothesis is that warming temperatures, if not synchronised across the landscape could act to increase asynchrony in reproduction. Exchange of genetic variation among populations maintains high levels of diversity among populations, which is a crucial prerequisite for genetic adaptation (Savolainen et al., 2007; Kremer et al., 2012). Therefore, forest

management planning at landscape scales ought to endeavour to identify realistic pollen and seed dispersal routes and incorporate them into the design of connected forest habitat networks.

Use of the individual based models did not support or refute the use of predictive

provenancing. It was, however, an effective means by which to formalise several arguments regarding the approach. Firstly, that adaptation to characteristics other than climate, e.g. soils or biota will impose additional selection on translocated genotypes meaning that

establishment mortality could be more severe, especially if variation in two selectively important traits is genetically uncorrelated and arranged in different spatial patterns.

Secondly, that the effect of varying proportions of provenances within a seed lot has no more than an additive effect, influencing the genetic composition at the time of planting, but having no emergent effect on the rate of adaptation. Finally, in all sets of circumstances, adaptation change under directional selection does happen and this is necessarily fastest when there are opportunities for recruitment (Kramer et al., 2008; Kuparinen et al., 2010), supporting the idea of utilising disturbance based management by imposing periodic disturbances in new and existing stands (Harvey et al., 2002; Brang et al., 2014; Cavers and Cottrell, 2015). This could be achieved by conducting thinning, as part of a continuous cover approach, or under shelterwood systems (Whittet et al., 2016c). Predictive provenancing from a single population is discouraged as it was found to result in very low population sizes and often extinction. Composite provenancing (i.e. deliberate mixtures of seed from further south with local seed) were found to be more useful than admixture (random) provenancing in all cases and therefore, admixture provenancing is also discouraged. One conceptual problem with the approach is that, outwith a long term experimental context, it would be impossible to determine whether predictive provenancing is effective. As such,

implementing predictive provenancing is an act of faith, rather than evidence based decision making.

The nursery surveys identified that there are two main problems in the supply chain for native tree seed and plants. These were related firstly to availability of seed and secondly, to minimal consumer confidence caused by difficulties in the approval of grant schemes. The availability of seed for some native species can be problematic, especially where lead-in

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times are lacking (Russell and Evans, 2003). There are currently few long term seed stores in Great Britain and therefore much of the stored seed is held in few locations. Additional seed stores in multiple locations could reduce the vulnerability of this key stage in the plant supply chain. For species with recalcitrant seeds, long term seed storage is not at present a viable option and so establishment of regional seed orchards, designed to conserve genetic diversity and improve seed availability may be a more appropriate strategy for improving seed availability in the long term. For recalcitrant-seeded species with late maturity such as oaks, public investment or involvement in assisting organisations with existing expertise in seed collection and stratification could increase productivity in the short term. Oak seed may be especially difficult due to obtain due to strong interannual variability in seed production (mast seeding) (Silvertown, 1980; Koenig and Knops, 2000). Planning for woodland creation schemes involving oaks must recognise that it will not always be possible to obtain seed or plants at short notice and so raised awareness and clearer communication is required when planting schemes involving oak are being conceived and reviewed. Establishment of a national forum on seed availability would be helpful in this regard and could perhaps provide anecdotal predictions of forthcoming seed crops.

A clear practical recommendation emerging from the nursery surveys was that longer lead-in times for planting schemes are required so that nurseries have the ability to better predict demand, thereby reducing waste and reliance on imported planting stock. A review of grant approvals with recommendations for streamlining the process has recently been produced at the request of the Scottish Government (MacKinnon, 2016), and this seems to have bolstered ambitions in Scotland (Anon, 2016). However, the future of subsidy schemes elsewhere is deeply uncertain. The United Kingdom voted to leave the European Union shortly after chapter five (Whittet et al., 2016a), which discussed subsidy schemes and plant imports was accepted for publication. Implications for the subsidisation of woodland planting schemes, implementation of plant health directives as well as environmental policy in general have generated uncertainty within the sector and will be complex (Glynn, 2016; Winkel and Derks, 2016). Certain aspects of deregulation, if it proceeds, may represent opportunities for increased levels of planting (Glynn, 2016). However, deregulation, if it proceeds, is also likely to lead to reduced levels of protection for existing forests (Glynn, 2016) and will perhaps favour production of timber over less profitable native woodland management.

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