The dataset comprises net primary productivity (NPP) measured as kilogrammes of dry above-ground vegetation per square metre per year. Sampling was conducted at six salt marsh sites at four spatial scales: 1 metre (m) (the minimal sampling unit) nested within a hierarchy of increasing scales of 1-10 m, 10-100 m and 100-1000 m. Three of the sites were in Morecambe Bay, North West England and three of the sites were in Essex, South East England. NPP measurements were based on vegetation re-growth after cutting in winter 2013 and harvesting in summer 2013. This data was collected as part of Coastal Biodiversity and Ecosystem Service Sustainability (CBESS). The project was funded with support from the Biodiversity and Ecosystem Service Sustainability (BESS) programme. BESS is a six-year programme (2011-2017) funded by the UK Natural Environment Research Council (NERC) and the Biotechnology and Biological Sciences Research Council (BBSRC) as part of the UK's Living with Environmental Change (LWEC) programme.