Building HS2 could lead to some plant species becoming endangered while emission savings from the high-speed rail scheme are likely to be "relatively small at best", according to a report by MPs.
Better safeguards needed to be implemented if harmful environmental impacts of HS2 were to be minimised, the report from the House of Commons Environmental Audit Committee said today.
The MPs said that Parliament, in its capacity as the planning authority for the high-speed rail project, should ensure that everything possible was done to minimise damage to ancient woodlands and Sites of Special Scientific Interest.
Where loss was genuinely unavoidable, compensation should be applied to the fullest extent possible.
The committee also said that consideration should be given to reducing the maximum 225mph speed of the HS2 trains until electricity generation had been sufficiently carbonised.
Launching the report, the committee's chairman Joan Walley said: "So far the consultation process on HS2 has not fully addressed the many environmental concerns we have.
"The Government needs to show real commitment to dealing with the impact that HS2 will have on our countryside and wildlife.
"Ancient woodlands and other hard-to-replace sites of natural value should not be subordinated to crude economic calculations of cost and benefit. "
She went on: "It is imperative that an infrastructure project on such a large scale implements proper environmental safeguards and ensures that impacts are minimised.
"This means adopting stringent, enforceable standards and setting aside adequate funding.
"That won't happen if HS2 Ltd can avoid implementing safeguards if they consider them to be 'impracticable' or 'unreasonable'.
"There needs to be a separate ring-fenced budget for these safeguards and for compensation, separate from the rest of the HS2 budget, to prevent the environment being squeezed if HS2 costs grow."
The report said that "some species may become endangered" and there could be "significant environmental harm to wildlife and ecosystems" if there was any delay in new biodiversity offset sites being established to provide compensation for land taken by the HS2 route.
The report said: "There is some debate about whether HS2 will deliver a reduction in emissions by taking travellers off the roads and planes. But, at best, the savings are likely to be relatively small."
The report also said while t he aim of HS2 to produce " no net biodiversity loss" was a challenging one, the Government should seek to produce biodiversity gains.
The committee said that only 60% of the route has so far been surveyed and f urther data-gathering, particularly on protected species not included in the current HS2 environmental statement, should be carried out as soon as possible.
Ms Walley said: "Ancient woodland should be treated with particular care.
"HS2 will damage some woodlands, and where that happens compensation measures should be much higher than the level indicated in the calculation that HS2 Ltd will use."