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News Article

Imports vs production in UK tree nurseries

Understanding the impact of demand variability on forest pest introduction to the UK

Nurseries are engaged in a constant balancing act whereby each plant grown requires a planned investment of time and resources but consumer demand can vary at much shorter notice, leaving growers with a misalignment between demand and supply. Tree nurseries are even more vulnerable to these market effects as saplings require years of growth before being sold. Nurseries are therefore constantly re-evaluating whether their stock will match consumer demand and in situations where it falls short, they will supplement with foreign grown specimens.

These imported horticultural specimens have been identified as one of the main in-routes for forest pests reaching UK soils; the introduction of ash dieback in 2012 was traced to a nursery in Southern England which had imported plant material from the Netherlands. Almost 300 plant pathogens have made their way to British shores in the last 50 years, with the majority being native to mainland Europe. Whilst relatively few of these introductions have affected the forestry sector, they have been extremely wide reaching and damaging in their effects. Dutch elm disease led to a vast reduction in the number of UK elms and more recently, ash dieback has taken its toll. Better understanding of the socioeconomic conditions which contribute to nurseries importing material can therefore help the UK to better protect against forest pests.

In order to understand how the risks of importing an exotic pest or pathogen are increased or decreased by nursery behaviour in response to consumer demand, researchers at Rothamstead Research and the University of Cambridge built a model designed to compare different cost/demand scenarios. The authors used three settings for tree production cost i.e. where local production was 25%, 50% or 75% of the cost of importing a tree from Europe. This was then related this to three different models of demand variability where demand fluctuated from a set baseline by different magnitudes. Mean demand was taken as 1000 trees with fluctuations ranging from 0-500.

The results revealed that when it is considerably cheaper to grow a tree within the nursery than import it, changes in demand will have little effect on the level of imports and therefore risk of introducing a pest. This risk increases, however, when the cost ratio starts to decrease and importing becomes more economically viable in the face of fluctuating demand. The larger fluctuations mean producers are unable to predict demand effectively so reduce output in order to minimise losses from unsold trees. This means they are then inevitably unable to deal upswings in demand, forcing them to import the shortfall.

“Our results suggest that a balanced management of demand variability and costs can significantly reduce the risk of importing an exotic forest pest or disease,” Vasthi Alonso-Chavez, lead author

Solutions to the issues raised by this modelling including higher import taxes to dissuade nurseries from outsourcing, and increasing the length of grant schemes to allow for more accurate production.


To read the original press release or the published paper, follow the links below:


  • Alonso Chavez, V., Gilligan, C.A. and van den Bosch, F., 2018. Variability in commercial demand for tree saplings affects the probability of introducing exotic forest diseases. Journal of Applied Ecology.DOI: 10.1111/1365-2664.13242


To find over 120 similar papers use the search string below in the Forest Science Database:

("forest pests" OR "introduced species") AND ("planting stock" OR "imports") AND (“economic”)

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