Clearance work for HS2 has been completed over the past week on ancient woodland, despite objections and concerns raised by the Woodland Trust.
The charity fears felling trees at this time of year could increase damage to eco-systems and claims HS2 Ltd pledged work would not start before 1 October.
Most trees in Little Lyntus and Fulfen woods, Staffordshire, are now felled.
HS2 said it had informed the charity and it intended to "translocate" the woods to a nearby site.
Translocation involves moving coppice stools and trees from the ancient site to "a receptor site", HS2 said, adding this would be carried out in the autumn.
However, Luci Ryan, from the Woodland Trust, said the work should be undertaken later in the year for "the best chance of success".
"[HS2] has carried out these works at the wrong time of year, not only earlier than they should but also earlier than they said they would, which will only serve to increase the damage they have done and the risk that the translocation will fail," she said.
"To think they can replicate complex, centuries-old eco-systems is simply wrong."
HS2 insists it informed the charity of the works on the woodlands near Lichfield and said it is "one of the most environmentally responsible infrastructure projects ever delivered in the UK".
"Around 80,000 trees have already been planted," a spokesperson said.
HS2's phase one ecology lead Kat Stanhope said: "Our aim is for HS2 to be the most sustainable railway in the world, and it will make a major contribution to helping Britain fight climate change and reach its net zero carbon targets by 2050.
"But even before HS2 starts operating, there are countless environmental projects and innovations occurring up and down the route to protect, preserve and enhance Britain's precious natural environment."
Both Little Lyntus and Fulfen woods are privately-owned and contain ancient coppiced trees.
Almost all of Little Lyntus has been cut down (1.4ha of 1.43ha) and nearly half of Fulfen Wood. (0.4ha of 1ha).
It comes after the felling of the 300-year-old Hunningham Oak near Leamington Spa last week, which was cut down to make way for a service road.
A last-minute plea has also been made to save a 250-year-old pear tree in nearby Cubbington, voted England's tree of the year in 2015, which is also set to be felled for HS2.
HS2 Ltd estimates that a total of 29.4ha of woodland across 32 ancient woodlands will be affected by phase one of the line.