Summary• Limited information on likely supply and spatial yield of bioenergy crops exists for the UK. Here, productivities are reported of poplar (Populus spp.) and willow (Salix spp.) grown as short-rotation coppice (SRC), using data from a large 49-site yield trial network.• A partial least-squares regression technique was used to upscale actual field trial observations across England and Wales. Spatial productivity was then assessed under different land-use scenarios.• Mean modelled yields ranged between 4.9 and 10.7 oven-dry tonnes (odt) ha -1 yr -1 . Yields were generally higher in willow than in poplar, reflecting the susceptibility of older poplar genotypes to rust and their tendency for single stem dominance. Replacing 10% of arable land, 20% of improved grassland and 100% of set-aside grassland in England and Wales with the three most productive genotypes would yield 13 Modt of biomass annually (supplying 7% of UK electricity production or 48% of UK combined heat and power (CHP) production).• Results show existing SRC genotypes have the immediate potential to be an important component of a mixed portfolio of renewables and that, in future, as new and improved genotypes become available, higher yields could extend this potential further.

Accurate estimation of the greenhouse gas (GHG) mitigation potential of bioenergy crops requires the integration of a significant component of spatially varying information. In particular, crop yield and soil carbon (C) stocks are variables which are generally soil type and climate dependent. Since gaseous emissions from soil C depend on current C stocks, which in turn are related to previous land management it is important to consider both previous and proposed future land use in any C accounting assessment. We have conducted a spatially explicit study for England and Wales, coupling empirical yield maps with the RothC soil C turnover model to simulate soil C dynamics. We estimate soil C changes under proposed planting of four bioenergy crops, Miscanthus (Miscanthus  giganteus), short rotation coppice (SRC) poplar (Populus trichocarpa Torr. & Gray  P. trichocarpa, var. Trichobel), winter wheat, and oilseed rape. This is then related to the former land use -arable, pasture, or forest/seminatural, and the outputs are then assessed in the context of a life cycle analysis (LCA) for each crop. By offsetting emissions from management under the previous land use, and considering fossil fuel C displaced, the GHG balance is estimated for each of the 12 land use change transitions associated with replacing arable, grassland, or forest/seminatural land, with each of the four bioenergy crops. Miscanthus and SRC are likely to have a mostly beneficial impact in reducing GHG emissions, while oilseed rape and winter wheat have either a net GHG cost, or only a marginal benefit. Previous land use is important and can make the difference between the bioenergy crop being beneficial or worse than the existing land use in terms of GHG balance.

ABSTRACT:This paper presents a method for reconstructing automatically the quantitative structure model of every tree in a forest plot from terrestrial laser scanner data. A new feature is the automatic extraction of individual trees from the point cloud. The method is tested with a 30-m diameter English oak plot and a 80-m diameter Australian eucalyptus plot. For the oak plot the total biomass was overestimated by about 17 %, when compared to allometry (N = 15), and the modelling time was about 100 min with a laptop. For the eucalyptus plot the total biomass was overestimated by about 8.5 %, when compared to a destructive reference (N = 27), and the modelling time was about 160 min. The method provides accurate and fast tree modelling abilities for, e.g., biomass estimation and ground truth data for airborne measurements at a massive ground scale.

Xylem vulnerability to cavitation is a promising criterion for identifying trees with high drought tolerance, but traditional techniques for measuring cavitation resistance are unsuitable for screening large numbers of genotypes. We tested the potential of the new Cavitron technique for high throughput screening of cavitation resistance in five poplar (Populus spp.) and four willow (Salix spp.) clones. The Cavitron technique enabled the screening of three to four clones per day with sufficient accuracy to reveal significant differences between clones. Because intraspecific screening may be better carried out through the identification of correlated and more easily measured traits, we attempted to identify accessible parameters that correlate to cavitation resistance. Variability in vulnerability to cavitation across clones was poorly correlated with anatomical traits such as vessel diameter, vessel wall strength, wood density and fiber wall thickness; however, a striking correlation was established between cavitation resistance and aboveground biomass production, indicating a possible trade-off between xylem safety and growth potential.

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Perennial ryegrass swards were grown in large containers on a soil and were exposed during two years to elevated (700 #L L -1) or ambient atmospheric CO2 concentration at outdoor temperature and to a 3 °C increase in air temperature in elevated CO2. The nitrogen nutrition of the grass sward was studied at two sub-optimal (160 and 530 kg N ha -I y -l ) and one non-limiting (1000 kg N ha -I y -l ) N fertilizer supplies. At cutting date, elevated CO2 reduced by 25 to 33%, on average, the leafN concentration per unit mass. Due to an increase in the leaf blade weight per unit area in elevated CO2, this decline did not translate for all cuts in a lower N concentration per unit leaf blade area. With the non-limiting N fertilizer supply, the leaf N concentration (% N) declined with the shoot dry-matter (DM) according to highly significant power models in ambient (% N = 4.9 DM -°38) and in elevated (% N = 5.3 DM -°'52) CO2. The difference between both regressions was significant and indicated a lower critical leaf N concentration in elevated than in ambient CO2 for high, but not for low values of shoot biomass. With the sub-optimal N fertilizer supplies, the nitrogen nutrition index of the grass sward, calculated as the ratio of the actual to the critical leaf N concentration, was significantly lowered in elevated CO2. This indicated a lower inorganic N availability for the grass plants in elevated CO2, which was also apparent from the significant declines in the annual nitrogen yield of the grass sward and in the nitrate leaching during winter. For most cuts, the harvested fraction of the plant dry-matter decreased in elevated CO2 due, on average, to a 45-52% increase in the root phytomass. In the same way, a smaller share of the plant total nitrogen was harvested by cutting, due, on average, to a 25-41% increase in the N content of roots. The annual means of the DM and N harvest indices were highly correlated to the annual means of the nitrogen nutrition index. Changes in the harvest index and in the nitrogen nutrition index between ambient and elevated CO2 were also positively correlated. The possible implication of changes in the soil nitrogen cycle and of a limitation in the shoot growth potential of the grass in elevated. CO2 is discussed.Abbreviations: 350-outdoor climate; 700 -outdoor climate +350/~L L -l [CO2]; 700+ -outdoor climate +350 #L L-I (CO2) and +3 °C; N --low N fertilizer supply; N + -high N fertilizer supply; N++-non-limiting N fertilizer supply; DM -dry-matter.

Process and empirical-based models that describe lignocellulosic biomass yield of the perennial energy grass Miscanthus (MiscanFor © ), short rotation coppice (SRC) trees and shrubs, poplar and willow (ForestGrowth-SRC) and a number of short rotation forest trees (ESC-CARBINE), were used to estimate the yield potential for current and future climates across Great Britain (GB Miscanthus and SRF poplar increased as the 'best feedstock' option. Except for a few localized examples, only SRF poplar had a higher yield than SRC or Miscanthus. These data suggest that in current and future climates, lignocellulosic biomass plantation species can be selected and optimized for best yield performance in different regions of GB. This modelling framework provides a valuable starting-point for which to test the performance of new genetic material, as this becomes available and parameterized for the models and socio-economic scenarios that may impact on the bioenergy industry.

Abstract. Quantifying soil organic carbon stocks (SOC) and their dynamics accurately is crucial for better predictions of climate change feedbacks within the atmosphere-vegetationsoil system. However, the components, environmental responses and controls of the soil CO 2 efflux (R s ) are still unclear and limited by field data availability. The objectives of this study were (1) to quantify the contribution of the various R s components, specifically its mycorrhizal component, (2) to determine their temporal variability, and (3) to establish their environmental responses and dependence on gross primary productivity (GPP). In a temperate deciduous oak forest in south east England hourly soil and ecosystem CO 2 fluxes over four years were measured using automated soil chambers and eddy covariance techniques. Mesh-bag and steel collar soil chamber treatments prevented root or both root and mycorrhizal hyphal in-growth, respectively, to allow separation of heterotrophic (R h ) and autotrophic (R a ) soil CO 2 fluxes and the R a components, roots (R r ) and mycorrhizal hyphae (R m ).Annual cumulative R s values were very similar between years (740 ± 43 g C m −2 yr −1 ) with an average flux of 2.0 ± 0.3 µmol CO 2 m −2 s −1 , but R s components varied. On average, annual R r , R m and R h fluxes contributed 38, 18 and 44 %, respectively, showing a large R a contribution (56 %) with a considerable R m component varying seasonally. Soil temperature largely explained the daily variation of R s (R 2 = 0.81), mostly because of strong responses by R h (R 2 = 0.65) and less so for R r (R 2 = 0.41) and R m (R 2 = 0.18). Time series analysis revealed strong daily periodicities for R s and R r , whilst R m was dominated by seasonal (∼150 days), and R h by annual periodicities. Wavelet coherence analysis revealed that R r and R m were related to short-term (daily) GPP changes, but for R m there was a strong relationship with GPP over much longer (weekly to monthly) periods and notably during periods of low R r . The need to include individual R s components in C flux models is discussed, in particular, the need to represent the linkage between GPP and R a components, in addition to temperature responses for each component. The potential consequences of these findings for understanding the limitations for long-term forest C sequestration are highlighted, as GPP via root-derived C including R m seems to function as a C "overflow tap", with implications on the turnover of SOC.