JOINT BASE LEWIS-McCHORD — An un-developed stretch of native prairie in south Puget Sound offers one of the few habitats in the world where a 2-inch butterfly thrives. It is also the main artillery impact range for Joint Base Lewis-McChord.The Army’s Stryker combat brigade and other troops regularly practice military maneuvers and live-fire training on acres of scenic, open grassland where a small population of Taylor’s checkerspot butterfly feed on nectar of native blooms, mate and lay eggs.The butterfly’s listing as a federal endangered species in the fall “has the potential to cause major restrictions on training,” said Jeffrey Foster, an ecologist at the military installation.That has the Army working to boost the numbers of butterflies, once found at more than 70 sites in Puget Sound, Oregon and British Columbia but are now reduced to 14 sites. The effort mirrors others by the Army at installations around the country. At JBLM, 44 miles south of Seattle, the program is helping not only the Taylor’s checkerspot, but the streaked horned lark and Mazama pocket gopher.In October, the U.S. Fish & Wildlife Service said the Taylor’s checkerspot was in danger of becoming extinct and designated nearly 2,000 acres in Clallam County, Puget Sound and Oregon’s Willamette Valley as critical habitat. The USFWS said it considered “military training under present conditions a threat to the short-term and long-term conservation of the Taylor’s checker-spot.” The eight-wheeled, armored Stryker vehicle and soldier foot traffic can crush larvae and damage plants on which the butter-flies rely.