Environmental groups are calling on the White House to take more concrete steps to shield the nation’s most important forests — the vast majority of which are on federal lands, and most of which have no formal protection.  “It’s the large trees — the oldest trees in the forest — that are our best carbon reservoirs,” forest scientist Dominick DellaSala of advocacy group Wild Heritage told reporters on Tuesday.   About 35 percent of U.S. forestland is composed of these forests, principally on federal land, according to a study DellaSala co-authored in September, published in Frontiers.  Yet only a quarter of those most valuable forests are under explicit protection, the authors found — and if logged over the next decade, would result in a significant uptick in U.S. emissions.   …“We are grateful for Biden roadmap from yesterday about natural climate solutions, but need national rulemaking to codify protection,” DellaSalla said.