Fragile, yes. Not necessarily unstable unless we humans mess it up.
The reason it's fragile has to do with the cold temperatures and difficult growing conditions, with a very short growing season each year. All organic matter grows - and decomposes - much, much more slowly than in warmer climates. It can take years for a tiny Arctic flower to mature: push its stalk above the ground, slowly develop leaves to protect itself against the cold, slowly slowly develop a flower and then seeds... things that can happen in a matter of weeks in the tropics.
So any environmental damage takes much longer to regenerate - whether it's tracks made by vehicles, bushes crushed, not to mention the danger of oil spills.
The animals and people who live (naturally) in these areas have long since found a balance with their surroundings. They take no more than is necessary, and use everything, carefully. They have adapted, as has the plant life..
Modern technologically-focused societies haven't understood this, and have been rushing in to take out the mineral resources, without paying attention to the fragile natural surroundings.