The charity says figures released by the Forestry Commission show that tree planting targets have been missed for the third year in a row.
In 2012 the Scottish Government had committed to creating 100,000 hectares of new woodland cover by 2022, but in the 2013/14 planting season just 8,300ha of woodland was planted — far short of the 10,000 hectares a year needed to achieve this.
The last time the required level of tree planting was reached was 2001.
Charles Dundas from the trust said: "Planting rates are governed by the availability of grants for woodland creation through Scotland's Rural Development Programme (SDRP). The reason that the Scotland is failing to hit a target of 10,000 hectares a year is that there is simply not enough money available."
A spokesman for Forestry Commission Scotland said around two-thirds of new planting (65%) in the UK took place in Scotland
A further 15,000ha was expected under the current SRDP in addition to in Forestry Commission woodland.