This potential 50 per cent drop in three years - which comes despite promises to increase woodland cover and tree planting in the UK - has "angered" growers who now face the "alarming prospect of dumping trees which they have been growing to fulfil predicted grant orders which have not materialised", the HTA added.
It said: "UK tree growers constantly face an uncertain market and threats from potentially devastating new pests and diseases such as Xylella fastidiosa, which could prove more devastating than the Chalara fraxinea outbreak of 2012."
The HTA Tree and Hedging Group discussed the issue last week.
The HTA said: "The industry has tried to convince Defra and its agencies of the need to develop a secure and stable market for UK-grown trees and to ensure plenty of lead time for public procurement projects. Despite repeated attempts to explain to civil servants the lead time for tree growing, the simple message that it takes time and commitment to grow trees does not seem to be getting through. Without a secure pipeline, the industry cannot supply UK trees in a sustainable way, and we will therefore import more and more trees.
"Based on interaction with landowners and other customers, the trade believes that new technological ‘improvements’ in woodland and tree planting grant administration by Defra and its agencies are to blame. If the cumbersome and complex grant system is not improved immediately, the knock on affect will be less seed sowing and planting for next year which will threaten the survival of UK growers.
HTA chief executive Carol Paris said: ‘No grower wants to destroy unwanted stock, and it angers us that all our efforts to convince government to take a simple, common sense approach to tree planting grants are falling on deaf ears. As an industry we are doing everything we can to grow trees in the UK, for the benefit of the family-run businesses and to protect the UK countryside, but we cannot grow trees commercially when the market is so unstable. We need a system which is fit for purpose and does not create this breakdown in the supply chain."
The market for UK tree growing for amenity and landscape woodland planting is estimated at £300 million.