Quiet fears hang over Russia’s newest border with a NATO nation.

ALONG THE FINNISH-RUSSIA BORDER — On a recent afternoon, an attack from Russian military bases a few miles from here seemed a distant prospect.

That’s not only because, as NATO’s newest member, Finland now enjoys the guaranteed protection of 30 nations, including the United States — a development that President Biden will celebrate during a visit to Helsinki this week.

It’s also because most of the Russians once stationed in the area went to fight in Ukraine, and many if not most of them, Finnish officials say, are dead. It may be years before Russia poses a conventional military threat from across the verdant forest of pine, spruce and birch.

But there were some Russians to be seen on a sunny June day at the Vaalimaa border crossing, about midway between Helsinki and St. Petersburg. A trickle came and went, many in expensive cars: an Audi Q7, a black BMW with two sleek bikes mounted on a rack. These Russians were likely dual passport holders, possibly headed to other European countries that they can reach only by land because of flight restrictions following Russia’s invasion of Ukraine last year.

For anyone trying to cross the border illicitly, border guard foot patrols roam the woods. But their trail-sniffing dogs encounter few Russians trying to sneak into Finland. Perhaps the biggest concern on this afternoon was a black bear seen prowling the area.

The peaceful scene belied the fear among many Finns that despite Russia’s weakened state, this transit point, and their country, could one day become a Russian target. That anxiety prompted Finland to seek membership in the North Atlantic Treaty Organization last year, a process completed in April when Finland became its 31st member in what Mr. Biden calls a strategic blow for President Vladimir V. Putin of Russia.

That move infused a long, placid relationship between Moscow and Helsinki with sharp new tensions.