RESEARCH ARTICLE Effects of initial fertilizer treatment on the 10‐year growth of mixed woodland on compacted surface‐coal‐mine spoils, S. Wales Martin John Haigh 1 | Heather Reed 7 | Margaret D'Aucourt 7 | Alison Flege 2 | Mike Cullis 3 | Simon Davis 4 | Frances Farrugia 7 | Svetla Gentcheva‐Kostadinova 5 | Elena Zheleva 5 | Elizabeth Hatton 7 | Keith Plamping 7 | Susan Powell 7 | Willemina Panhuis 7 | Benedict Sansom 6 | Sharon Sawyer 7 | Gill Wilding 7 | Pat Woodruffe 7 1 Department of Social Sciences, Oxford Brookes University, Oxford, UK 2 University of Cincinnati, Cincinnati, Ohio 3 Swansea Metropolitan Campus, University of Wales Trinity St David, Swansea, UK 4 Department of Earth Science & Engineering, Imperial College London, London, UK 5 Faculty of Forestry, University of Forestry, Sofia, Bulgaria 6 Arctium Ltd, Haywards Heath, UK 7 Cradlefornature.org, Witney, UK Correspondence Martin John Haigh, Oxford Brookes University, Department of Social Sciences, Oxford OX3 0BP, UK. Email: mhaigh@brookes.ac.uk Abstract The degradation of land formerly reclaimed after surface‐coal‐mining (opencast) is a widespread problem in upland Wales (UK). This community‐based project aims to sup- port the voluntary sector in land reclamation by investigating the means of reversing land degradation. It explores ways of encouraging trees to ameliorate the severely compacted, infertile, mine‐soils typical of former opencast sites. This study evaluates the benefits of a single initial application of 2‐year slow release fertilizer (SRF), both with and without additional supplements, through a 10‐year controlled experiment in a mixed planting of common Alder (Alnus glutinosa (L.) Gaertn), Oak (Quercus petraea (Matt.) Liebl., Quercus robur L. and hybrids) supplemented with Scots Pine (Pinus sylvestris, L.); Silver Birch (Betula pendula, Roth); Goat Willow (Salix caprea, L.) and Rowan (Sorbus aucuparia, L.). After 10 years, SRF treatment resulted in a small, marginally signif- icant, decrease in survival (85% vs. 83%) across all species, except Oak, but SRF‐treated trees were significantly larger than those given no‐SRF at planting (421 cm vs. 368 cm). By contrast, in Year 5 data, only SRF‐treated Alders are marginally significantly larger, whereas in Years 1–3 across all six species, significantly more records show greater mean growth in trees with no‐SRF than those given SRF at planting. Probably, this delayed response to SRF treatment resulted from the slow development of the larger soil ecosystem. Treatment with additional supplements (double SRF, remineralization agent and superphosphate) tended to have negative impacts on growth but double SRF and to a lesser degree remineralization had a positive effect on survival. KEYWORDS citizen science, common Alder, community forestry, goat willow, oak, Rowan, Scots Pine, Silver Birch, slow release fertilizer, surface‐mine (opencast) coal‐land reclamation 1 | INTRODUCTION This study explores the effect of an initial treatment of slow release fertilizer (SRF) on the 10‐year performance of trees planted as 2‐year whips on degraded land that was, formerly, reclaimed after the open- cast (i.e., surface‐mining) of coal. It is intended as a contribution to the work of voluntary community groups, who play a small but increasing role in land reclamation (McGowan, 2017). This voluntary action is Received: 22 April 2018 Revised: 16 July 2018 Accepted: 22 July 2018 DOI: 10.1002/ldr.3111 3456 © 2018 John Wiley & Sons, Ltd. Land Degrad Dev. 2018;29:3456–3468. wileyonlinelibrary.com/journal/ldr