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Meeting greenhouse gas (GHG) emissions reductions targets outlined in Scotland’s Climate Change Plan[1] (CCPu) will require significant change for all sectors, including land use. Woodland creation and tree planting targets are embedded in the CCPu to contribute to GHG reduction targets. Agroforestry is defined as the combination of trees and agriculture on the same plot of land, with tree density varying dependent on agricultural land type, tree species and objective. There has been growing interest in agroforestry systems as an opportunity to integrate land management objectives and contribute to meeting tree planting targets and generate GHG reductions and removals. However, currently only 3.3% of the utilised agricultural area in the UK is managed as agroforestry (den Herder et al., 2015). Carbon schemes, such as the Woodland Carbon Code (WCC) could offer a potential route to provide financial support for agroforestry and incentivise its creation. This report examines existing evidence to assess the GHG potential of different forms of agroforestry suitable in Scotland, building on the recent Perks et al. (2018) and examines the potential economic viability of adopting such agroforestry practices.

Drought, as a significant risk to Scottish forests, is likely to be exacerbated by the changing climate. In light of increased drought events in recent years, we were asked to review the available evidence, and report on current drought-related research activities relevant to the forestry sector in Scotland. This report summarises the current state of research, describes ongoing projects and identifies knowledge gaps and potential research directions. Considerations around the policy and practice implications are made taking into account the available information. Drought, as a significant risk to Scottish forests, is likely to be exacerbated by the changing climate. In light of increased drought events in recent years, we were asked to review the available evidence, and report on current drought-related research activities relevant to the forestry sector in Scotland. This report summarises the current state of research, describes ongoing projects and identifies knowledge gaps and potential research directions. Considerations around the policy and practice implications are made taking into account the available information.

The effect of clear-fell harvesting on soil greenhouse gas (GHG) fluxes of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) was assessed in a Sitka spruce forest growing on a peaty gley organo-mineral soil in northern England. Fluxes from the soil and litter layer were measured monthly by the closed chamber method and gas chromatography over 4 years in two mature stands, with one area harvested after the first year. Concurrent measurements of soil temperature and moisture helped to elucidate reasons for the changes in fluxes. In the 3 years after felling, there was a significant increase in the soil temperature, particularly between June and November (3 to 5 ∘C higher), and in soil moisture, which was 62 % higher in the felled area, and these had pronounced effects on the GHG balance in addition to the removal of the trees and their carbon input to the soil. Annual soil CO2 effluxes reduced to almost a third in the first year after felling (a drop from 24.0 to 8.9 t CO2 ha−1 yr−1) and half in the second and third year (mean 11.8 t CO2 ha−1 yr−1) compared to before felling, while those from the unfelled area were little changed. Annual effluxes of N2O more than doubled in the first two years (from 1.0 to 2.3 and 2.5 t CO2e ha−1 yr−1, respectively), although by the third year they were only 20 % higher (1.2 t CO2e ha−1 yr−1). CH4 fluxes changed from a small net uptake of −0.03 t CO2e ha−1 yr−1 before felling to a small efflux increasing over the 3 years to 0.34 t CO2e ha−1 yr−1, presumably because of the wetter soil after felling. Soil CO2 effluxes dominated the annual net GHG emission when the three gases were compared using their global warming potential (GWP), but N2O contributed up to 20 % of this. This study showed fluxes of CO2, CH4, and N2O responded differently to clear-felling due to the significant changes in soil biotic and abiotic factors and showed large variations between years. This demonstrates the need for multi-year measurements of all GHGs to enable a robust estimate of the effect of the clear-fell phase on the GHG balance of managed forests. This is one of very few multi-year monitoring studies to assess the effect of clear-fell harvesting on soil GHG fluxes.

This paper evaluates the suitability of the ECOSSE model to estimate soil greenhouse gas fluxes from short rotation coppice willow (SRC-Willow), short rotation forestry (SRF-Scots Pine) and Miscanthus after land-use change from conventional systems (grassland and arable). We simulate heterotrophic respiration (Rh), nitrous oxide (N2O) and methane (CH4) fluxes at four paired sites in the UK, and compare them to estimates of Rh derived from the ecosystem respiration estimated from eddy covariance (EC) and Rh estimated from chamber (IRGA) measurements, as well as direct measurements of N2O and CH4 fluxes.Significant association between modelled and EC-derived Rh was found under Miscanthus, with correlation coefficient (r) ranging between 0.54 and 0.70. Association between IRGA-derived Rh and modelled outputs was statistically significant at the Aberystwyth site (r = 0.64) but not significant at the Lincolnshire site (r = 0.29). At all SRC-Willow sites, significant association was found between modelled and measurement-derived Rh (0.44 ? r ? 0.77); significant error was found only for the EC-derived Rh at the Lincolnshire site. Significant association and no significant error were also found for SRF-Scots Pine and perennial grass. For the arable fields, the modelled CO2 correlated well just with the IRGA-derived Rh at one site (r = 0.75). No bias in the model was found at any site, regardless of the measurement type used for the model evaluation.Across all land-uses, fluxes of CH4 and N2O were shown to represent a small proportion of the total greenhouse gas balance; these fluxes have been modelled adequately on a monthly time-step. This study provides confidence in using ECOSSE for predicting the impacts of future land-use on greenhouse gas balance, at site level as well as at national level.

Stem injection techniques can be used to introduce 15N into trees to overcome a low variation in natural abundance and label biomass with a distinct 15N signature, but have tended to target small and young trees, of a variety of species, with little replication. We injected 98 atom% 15N ammonium nitrate (NH4NO3) solution into 13 mature, 9- to 13-m tall edge-profile Sitka spruce trees in order to produce a large quantity of labelled litter, examining the distribution of the isotope throughout the canopy after felling in terms of both total abundance of 15N and relative distribution of the isotope throughout individual trees. Using a simple mass balance of the canopy alone, based on observed total needle biomass and modelled branch biomass, all of the isotope injected was accounted for, evenly split between needles and branches, but with a high degree of variability both within individual trees, and among trees. Both 15N abundance and relative within-canopy distribution were biased towards the upper and middle crown in foliage. Recovery of the label in branches was much more variable than in needles, possibly due to differences in nitrogen allocation for both growth and storage, which differ seasonally between foliage and woody biomass.

Altres ajuts: This work was funded by the UK Natural Environment Research Council (NERC), grant NE/G00725 X/1 and Forestry Commission UK Stem injection techniques can be used to introduce 15 N into trees to overcome a low variation in natural abundance and label biomass with a distinct 15 N signature, but have tended to target small and young trees, of a variety of species, with little replication. We injected 98 atom% 15 N ammonium nitrate (NHNO) solution into 13 mature, 9- to 13-m tall edge-profile Sitka spruce trees in order to produce a large quantity of labelled litter, examining the distribution of the isotope throughout the canopy after felling in terms of both total abundance of 15 N and relative distribution of the isotope throughout individual trees. Using a simple mass balance of the canopy alone, based on observed total needle biomass and modelled branch biomass, all of the isotope injected was accounted for, evenly split between needles and branches, but with a high degree of variability both within individual trees, and among trees. Both 15 N abundance and relative within-canopy distribution were biased towards the upper and middle crown in foliage. Recovery of the label in branches was much more variable than in needles, possibly due to differences in nitrogen allocation for both growth and storage, which differ seasonally between foliage and woody biomass.

A trial of six cold-tolerant eucalypt species, planted in 1981 near Exeter, in south west England, was assessed in 2010 for height, diameter at breast height and survival. The predicted soil moisture deficit on the site is low and it is relatively warm (AT 1662.5) and sheltered (DAMS 126), although it experienced a succession of cold winters in the 6 years following planting.The growth of some E. delegatensis was very rapid; the productivity of the seedlot having best survival (48%) was38 m3 ha-1 yr-1 although this seedlot was collected from one mother tree and was unrepresentative of the broader population at that location. Of the closely-related species E. johnstonii and E.subcrenulata, seedlots recorded as E. johnstonii had poor average survival (26%) and growth (7 m3 ha-1 y-1), while E. subcrenulata seedlots from Mount Cattley, Tasmania exhibited both good average survival (68%) and growth (25 m3 ha-1 y-1), with progenies from individual mother trees performing substantially better. Based on the results of this assessment, selected sources of E. subcrenulata appears suitable for woody biomass production in sheltered sites in south west England.Of the closely related E. coccifera and E. nitida, the former showed better survival, at 18% against 5%. The poor performance of these species is surprising, as the latter species, which is less cold-tolerant, has grown and survived well elsewhere in south west England, and overall survival of both species at Exeter in 1995 was 60%. The good cold-tolerance andgrowth of certain seedlots from single mother trees within provenances suggests that much of the variation in performance of all species is genetically determined at family rather than provenance level. The larger surviving trees in the trial could provide germplasm for further trials, with the possibility of later conversion of parts of the Exeter trial to seed stands.

Climate change impacts resulting from fossil fuel combustion and concerns about the diversity of energy supply are driving interest to find low-carbon energy alternatives. As a result bioenergy is receiving widespread scientific, political and media attention for its potential role in both supplying energy and mitigating greenhouse (GHG) emissions. It is estimated that the bioenergy contribution to EU 2020 renewable energy targets could require up to 17-21 million hectares of additional land in Europe (Don et al., 2012). There are increasing concerns that some transitions into bioenergy may not be as sustainable as first thought when GHG emissions from the crop growth and management cycle are factored into any GHG life cycle assessment (LCA). Bioenergy is complex and encapsulates a wide range of crops, varying from food crop based biofuels to dedicated second generation perennial energy crops and forestry products. The decision on the choice of crop for energy production significantly influences the GHG mitigation potential. It is recognised that GHG savings or losses are in part a function of the original land-use that has undergone change and the management intensity for the energy crop. There is therefore an urgent need to better quantify both crop and site-specific effects associated with the production of conventional and dedicated energy crops on the GHG balance. Currently, there is scarcity of GHG balance data with respect to second generation crops meaning that process based models and LCAs of GHG balances are weakly underpinned. Therefore, robust, models based on real data are urgently required. In the UK we have recently embarked on a detailed program of work to address this challenge by combining a large number of field studies with state-of-the-art process models. Through six detailed experiments, we are calculating the annual GHG balances of land use transitions into energy crops across the UK. Further, we are quantifying the total soil carbon gain or loss after land use change at 100 fieldsites which encapsulate a range of UK climates and soil types. Our overall objective is to use our measured data to parameterise and validate the models that we will use to predict the implications of bioenergy crop deployment in the UK up to 2050. The resultant output will be a meta-model which will help facilitate decision making on the sustainable development of bioenergy in the UK, with potential deployment in other temperate climates around the world. Here we report on the outcome of the first of three years of work. This work is based on the Ecosystem Land Use Modelling & Soil Carbon GHG Flux Trial (ELUM) project, which was commissioned and funded by the Energy Technologies Institute (ETI). Don et al. (2012) Land-use change to bioenergy production in Europe: implications for the greenhouse gas balance and soil carbon. GCB Bioenergy 4, 372-379.

Three trials of snow gums {Eucalyptus pauciflora) and other cold-tolerant eucalypts, planted in 1985, were assessed for height, diameter at breast height and survival. The trial sites were in southern England but differed in their climate, particularly maritime influence, summer moisture deficit, and in their altitude and soils. Patchy survival and windthrow within the trials posed constraints on the identification of trees of different locations (origins) that performed better. There were, however, some origins that showed good growth and survival across two or three trials. E. pauciflora ssp debeuzevillei from Mount Gininl (Australia) showed superior growth and survival at Thetford (East Anglia) and Torridge (Devon), while E. pauciflora ssp niphophila from Mount Bogong (also Australia) exhibited high survival across all three trials. If biomass production is the objective, many of the origins are too slow growing and faster growing species are available, including other eucalypts. The Mount Ginini origin of E. pauciflora ssp debeuzevillei was estimated to produce 7 m³ ha¯¹ y¯¹ at Thetford and 10 m³ ha¯¹ y¯¹ at Torridge at 26 years old, while Sitka spruce is estimated to yield 13m³ ha¯¹ y¯¹ on a similar rotation. A eucalypt species other than snow gum that showed some promise was f.perriniana, origin 'Smiggin Hole' (New South Wales, Australia) which yielded a mean annual increment of 25m³ ha¯¹ y¯¹ over 24 years at Chiddingfold (Sussex). However, survival was poor at Thetford and so it may be suited to only the warmest of sites (above accumulated temperature (AT5) of 1900).

Eucalypts have been planted successfully in Great Britain and Ireland since the mid nineteenth century. While most of the seven hundred species of eucalypts are not suited to the relative cold of the climate of the British Isles, trials in Britain and Ireland have shown that certain species and subspecies can grow successfully. Further, some eucalypts are the fastest growing trees in the British Isles with mean annual increments of between 25 m3/ha/year and 38 m3/ha/year being reported. Rapid development of a wood biomass energy sector has encouraged a reassessment of the potential of eucalypts grown on short rotations as a source of energy. This article describes the history of eucalypts in the British Isles and their potential.

International audience; This study aimed to evaluate the effects of repeated aerial nitrogen (N) and sulphur (S) misting over tree canopies of a Sitka spruce plantation in Scotland. We combined δ13C and δ18O in tree rings to evaluate the changes in CO2 assimilation (A) and stomatal conductance (gs) and to assess their contribution to variations in the intrinsic water-use efficiency (WUEi). Measurements of δ15N enabled shifts in the ecosystem N cycling following misting to be assessed. We found that: i) N applications, with or without S, increased the ratio between A and gs in favour of A, thus supporting a fertiliser effect of added N. ii) After the treatments have ceased, the trees quickly adjusted to the reductions of N deposition, but not to the reduction in S deposition, which had a negative effect on WUEi by reducing A. This indicates that the beneficial role of N deposition may be negated in forests that previously received a high load of acid rain. iii) δ15N in tree rings seems to reflect the N dynamics caused by canopy retention, with the fingerprint also present in the litter, after the experiment stopped. iv) Both our results (obtained using canopy N applications) and a collection of published data (obtained using soil applications) showed that generally WUEi increased in response to an increase of N applications, with the magnitude of the changes related to soil conditions and the availability of other nutrients. The opposite directions of shifts in δ15N in tree rings suggest that both the quantity of the applied N and its quality, mediated by processes occurring during canopy N retention, are important determinants of the interactions between N and C cycles, which occur in forests. Stable isotopes are useful probes to understand these processes and to put in the results of short-term experiments into context.