A summit is being held in Romania to assess 20 projects to safeguard the Carpathian region of eastern Europe.
By Alex Kirby
BBC News Online environment correspondent
The effects of poverty and the fallout from EU membership could jeopardise the wildlife and landscapes of the entire area, conservationists say.
Delegates to the Brasov meeting will come from eight countries, the European Commission, conservation groups, the World Bank and the United Nations.
The Carpathian Mountains harbour almost half of Europe's remaining wolves.
The summit will look especially at ways to protect the lower Danube wetlands.
The mountains stretch from Austria to Ukraine, and are home to 481 endemic plants (found nowhere else).
Apart from being the home to 45% of European wolves, the mountains also contain the continent's largest populations of brown bears, lynx, European bison and rare birds, including the globally threatened Imperial eagle.
WWF, the global environment campaign, says the region offers "one of the last opportunities for repopulating Europe with large carnivores" - in a continent where 40% of mammals face some threat of extinction.
Because they are so remote, the Carpathians were spared some of the worst excesses of Soviet-era agriculture, with some parts escaping the introduction of collective farming.
But rural unemployment and poverty are now on the rise, leading to urban migration, the abandonment of land, the break-up of small communities, and an increase in poaching.
A further threat is the introduction of the European Union's common agricultural policy and its intensive methods of farming when the new member states join the EU.
The conservationists want the current protected areas system extended; support for local sustainable economic activities, like small-scale farming and eco-tourism; and better forest management and reform of some EU policies.
WWF says: "The mountain region can be protected before the residents of the Carpathians - people, animals and plants - begin to feel like strangers in their own land and leave it for ever."
They are particularly concerned with the plight of the floodplains of the lower reaches of the Danube.
More than 80% of the Danube basin's wetlands and floodplains have been destroyed in the last century, largely through activities like land reclamation, dam building and river regulation.
Increased pollution has added to the pressure on species including the sturgeon, egret, Dalmatian pelican, and white-tailed eagle.
Romania, Bulgaria, Moldova and Ukraine have committed themselves to establishing a corridor of restored and protected wetlands along the river - the Lower Danube Green Corridor.
Covering about 900,000 hectares (2.2 million acres), it will be Europe's largest international project to save wetlands.
The Brasov meeting, on 24 and 25 November, is designed to give the initiative fresh impetus.