How do management techniques affect carbon stock in intensive hardwood plantations? M.L. López-Díaz a,⇑ , R. Benítez b , G. Moreno a a Forestry Research Group, University of Extremadura, Spain b Department of Mathematics, University of Extremadura, Spain article info Article history: Received 12 September 2016 Accepted 29 November 2016 Keywords: Walnut Silvopastoral systems Legumes Soil organic matter Fine root biomass Tree biomass increment Mineral fertilisation abstract Recent studies in temperate regions have shown that agroforestry systems, especially silvopastoral sys- tems, have greater carbon (C) sequestration potential than monocropping systems or pastures, or even forest plantations. In Europe, there is growing interest in establishing high quality wood plantations with intensive management comprising irrigation, fertilisation and chemical weed control to reduce rotation length. However, these operations can have major environmental impacts similar to the effects of inten- sive agriculture, such as impoverishment of soil C. The aim of this study is to identify optimum manage- ment practices for intensive systems of quality wood production to optimise soil C stock and plantation productivity. An experiment was conducted in Extremadura, mid-west Spain, from 2011 to 2014, in a 13- year-old hybrid walnut (Juglans major  regia mj 209xra) plantation with a density of 333 trees ha 1 . Two essays were established: one with three techniques to control competition from herbaceous strata beneath trees – mowing, ploughing and sheep grazing (1 sheep ha 1 ) – and the other to test implemen- tation of legumes (mixture of Trifolium michelanium and Ornithopus compressus complemented by the same quantities of phosphorous and potassium as mineral treatment) as an alternative to traditional mineral fertilisation (40 kg N ha 1 , 40 kg P 2 O 5 ha 1 and 50 kg K 2 O ha 1 ). The C stock estimate was based on soil organic carbon (SOC) and aboveground (tree trunks and branches) and belowground biomass (tree and pasture roots). Most of the C stock was contained in SOC, at 50% in the uppermost soil layer (0– 25 cm), followed by aboveground biomass. The response of SOC in each treatment was higher than the other parameters analysed, suggesting that SOC is a more sensitive pool to management techniques. Grazing as control of herbaceous vegetation and legume implementation as nitrogen supply are suitable techniques for optimising soil C stocks and also achieve adequate tree growth in the longer term. Ó 2016 Elsevier B.V. All rights reserved. 1. Introduction The importance of C sequestration in the land use scenario lies in its potential as a climate change mitigation strategy (Nair, 2012; IPCC, 2014). The Climate Change 2007 Synthesis Report (IPCC, 2014) proposed several management strategies in the agricultural sector to mitigate CO 2 concentrations in the atmosphere, including cropland and grazing land management and restoration of organic soils. The most cost-effective mitigation options in forestry are afforestation, sustainable forest management and deforestation reduction, although their relative importance differs greatly across regions. Europe has a shortage of quality wood, resulting in a growing interest in the establishment of hardwood plantations. In Spain, hardwood species are commonly harvested after long rotations of up to 50 or 60 years, although intensive management including irrigation, fertilisation and chemical weed control can reduce rota- tion length by half (to 20–25 years) (Rigueiro-Rodríguez et al., 2009). However, these operations can have major environmental impacts similar to intensive agriculture, such as impoverishment of soil C (Babcock et al., 2003). Sustainable forest management must be applied using multicriteria objectives that optimise both increasing biomass and C sequestration (Lal, 2005; Bravo et al., 2008). Management systems that maintain a continuous canopy cover and mimic regular natural forest disturbance are likely to achieve the best combination of high wood yield and C storage (Lal, 2005; Jandl et al., 2007). Recent studies in temperate regions have shown that agro- forestry systems, especially silvopastoral systems (integrated http://dx.doi.org/10.1016/j.foreco.2016.11.048 0378-1127/Ó 2016 Elsevier B.V. All rights reserved. ⇑ Corresponding author at: Avda. Virgen del Puerto n° 2, Plasencia, Cáceres 10600, Spain. E-mail address: lurdesld@unex.es (M.L. López-Díaz). Forest Ecology and Management 389 (2017) 228–239 Contents lists available at ScienceDirect Forest Ecology and Management journal homepage: www.elsevier.com/locate/foreco