The Nature Conservancy, which was sent reeling last month after a series of Washington Post articles exposed embarrassing problems and questionable practices within the organization, has announced a number of policy reforms decided upon in a board meeting last week. TNC, the world’s wealthiest environmental group, will stop drilling for oil on land it controls, making loans to staff members, and selling undeveloped land to trustees for use as home sites. The Post articles revealed, among other things, that TNC had drilled for natural gas on the last native breeding ground of an endangered bird and had given its president, Steven McCormick, a $1.5 million low-interest home loan. In the wake of the articles, two senators called for taking a close look at TNC’s finances. The group hopes the new changes will head off further scrutiny and criticism. “This sounds like a big step in the right direction,” said Peter Dobkin Hall of Harvard’s Hauser Center for Nonprofit Organizations