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Forested areas are increasing across Europe, driven by both reforestation programs and farmland abandonment. While tree planting remains the standard reforestation strategy, there is increased interest in spontaneous regeneration as a cost-effective method with equal or potentially greater benefits. Furthermore, expanding areas of already established forests are left for passive rewilding to promote biodiversity conservation. Effective and objective methods are needed for monitoring and analyzing the development of forest structure under these management scenarios, with airborne laser scanning (lidar: light detection and ranging) being a promising methodology. Here, we assess the structural characteristics and development of unmanaged forests and 28- to 78-year old spontaneously regenerated forests on former agricultural land, relative to managed forests of similar age in Denmark, using 25 lidar-derived metrics in 10- and 30-m grid cells. We analyzed the lidar-derived cell values in a principal component analysis (PCA) and interpreted the axes ecologically, in conjunction with pairwise tests of median and variance of PCA-values for each forest. Spontaneously regenerated forest in general had increased structural heterogeneity compared to planted and managed forests. Furthermore, structural heterogeneity kept increasing in spontaneously regenerated forest across the maximal 78-year timespan investigated. Natural disturbances showed strong impacts on vegetation structure, leading to both structural homogeneity and heterogeneity. The results illustrate the utility of passive rewilding for generating structurally heterogeneous forested nature areas, and the utility of lidar surveys for monitoring and interpreting structural development of such forests.

The biorefinery technology aiming at protein extraction is rising and identification of suitable plant biomass input with valuable protein compounds for extraction is needed. Forage crops has been evaluated by the Cornell Net Carbohydrate and Protein System (CNCPS), and the result used as proxy of extractable protein in a biorefinery process. This serves as a helpful link between crop production and refinery output, however, the method has never been validated. Such validation is the main aim of this study. Five forage species: white clover, red clover, lucerne, perennial ryegrass and tall fescue were cut at four dates during spring and processed in a lab-scale refinery (screw press and subsequent green juice extraction). The pulp fraction and the precipitated protein concentrate were both CNCPS analyzed to follow the initial crude protein (CP) plant input into these two fractions.Total recovery in concentrate was highest for the legumes, which points to an advantage of these species in protein extraction setups. High recovery of B1 and B2 (50% or higher for the grasses) in the pulp demonstrated a large proportion of soluble protein ending up in the fibrous pulp and shed light on the reason behind high feed quality of the pulp fraction. In conclusion, the existing tentative assumption of extractable protein being equal to CNCPS fractions of B1 and B2 and partly B3 was shown to be too simplified. The presented findings can improve crop species screening in terms of expected extractable protein yield.

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Direct field emissions of nitrous oxide (N2O) may determine whether biodiesel from oilseed rape (Brassica napus L.) fulfills the EU requirement of at least 50% reduction of greenhouse gas emissions as compared to fossil diesel. However, only few studies have documented fertilizer N emission factors (EF) and mitigation options for N2O emissions from oilseed rape cropping systems. We conducted a field experiment with three N levels (0, 171, and 217 kg/ha), where the N fertilizer was applied as ammonium sulfate nitrate with or without the nitrification inhibitor 3,4‐dimethylpyrazole phosphate (DMPP). N2O fluxes were measured using static chambers technique and soil samples were analyzed for water and mineral N content during a monitoring period of 368 days. The DMPP treatments showed a significantly increased level of ammonium (NH4+) for up to 18 weeks after spring fertilization as compared to the treatments without DMPP. However, this difference did not result in a corresponding decrease in NO3- soil content, and no differences in cumulative N2O emissions were found between any fertilized treatments with or without DMPP (mean, 1.26 kg N2O‐N ha−1 year−1). More field experiments are needed to clarify whether DMPP‐coated mineral fertilizers could mitigate N2O emissions under different weather conditions, for example, under conditions where fertilization events concurred with rainfall events increasing water‐filled pore space to the assumed 60% threshold for denitrification. Emission factors for mineral N fertilizer were 0.28%–0.36% with a mean of 0.32% across the fertilized treatments. These data concur with recent European studies suggesting that the EF for mineral N fertilizers in oilseed rape cropping systems may typically be lower than the default IPCC value of 1%. Further studies are needed to consolidate an EF for oilseed rape under temperate conditions, which will be determining for the sustainability of Northern European oilseed rape cultivation for biodiesel.

BACKGROUND New protein sources with low environmental and climatic impact are needed. Perennial crops show advantages as compared to annual crops and the upcoming biorefinery technology can extract proteins from the perennial biomass for protein concentrate production. The search for best‐suited biomass crops needs to include harvest during the full growing season to support economic viability of biorefinery plants. Here we examined two grasses under increasing N fertilizer regime (175, 350 and 525 kg N ha−1) and three legumes, subject to a four‐cut strategy. The well‐defined Cornell Net Carbohydrate and Protein System (CNCPS) was used to estimate potential extractable protein. A key, previously presented in the literature, was applied in order to translate the CNCPS results into potential extracted protein concentrate. RESULTS Crude protein (CP) yield per hectare was highest in red clover in 2015 (2907 kg CP ha−1) and the fertilized (525 kg N ha−1) tall fescue in 2016 (2435 kg CP ha−1). When translating the numbers into potential extraction of protein concentrate, the red clover had the highest protein concentrate yield per hectare in 2015 (835 kg CP ha−1) and lucerne in 2016 (803 kg CP ha−1). CONCLUSION The results revealed that the entire season needs attention for optimization and not only the first cut, since both CP yields and quality peaks in different cuts across the five species and 2 years. Further knowledge of CP yield responses to field management and species mixtures are needed in order to advise farmers on the optimal crop for biorefining. © 2021 Society of Chemical Industry.