In a 2005 report titled 'Forests on the Edge,' the U.S. Forest Service said three river systems in Maine were among 15 watersheds in the country that would see the greatest increases in housing density through 2030.

Now, a case study of five southern and central Maine watersheds offers more evidence that forestland south of Interstate 95 will face escalating development pressure in the next 25 years.

'Recent trends and projections indicate that residential development in south-central and southwest Maine will continue to increase in the coming decades,' wrote Eric M. White, a research economist for the U.S. Forest Service and author of the case study.

Why should anyone care? Forests provide clean water, homes for wildlife and valuable resources for the state's economy. Development pressure threatens the rural character of the state and reduces the opportunities for outdoor recreation.

Timber production is also likely to be affected, with consequences far beyond the local sawmill. Housing development often results in smaller lot sizes, which can make timber harvesting more difficult and costly. At the same time, rising property values and higher taxes provide greater incentives to develop.

'If residential development continues to expand in the case-study watersheds, these market factors will make the retention of land in forest use increasingly difficult,' wrote White.

The overwhelming majority of forestland in southern Maine is held by small landowners, not by forest-products companies. Although it is not discussed in White's report, the average age of those owners is increasing. About 40 percent are older than 65, according to Tom Doak, executive director of the Small Woodland Owners Association of Maine. Two-thirds are older than 55.

That means two-thirds of the small forested parcels in southern and central Maine are virtually certain to change hands in the next two or three decades.

It's the 'Perfect Storm' for southern Maine: Sharply rising demand for smaller lots will occur at the same time as forestland is passing to a new generation of owners. 'This is a huge issue,' said Kevin Doran, natural resources educator for the Maine Forest Service.

How did the storm develop? The 2005 report and recent case study provide clues.

While Maine's population grew 4 percent in the 1990s, the number of housing units jumped 11 percent. With about 100,000 vacation homes, or 16 percent of its housing stock, Maine has the highest percentage of seasonal dwellings in the nation. The number increased by about 15 percent in the 1990s, and shows no sign of abating.

The number of people who live in each housing unit also fell during the last decade, from 2.09 in 1990 to 1.96 in 2000. Nationally, there are about 2.43 people per housing unit. With a steady increase in population and a decline in household size, the number of housing units must increase.

Where is the residential development likely to occur? The biggest change is expected in the Lower Penobscot watershed. By 2030, housing density is expected to increase on 310,200 forested acres -- the greatest change among the 1,026 watersheds nationwide that were considered in the 2005 report.

Also making the Top 15 list for rapid growth were the Lower Androscoggin, where residential development will occur on 213,800 acres, and the Lower Kennebec, 210,000 acres.

Rounding out the five watersheds considered in the recent case study were the St. George-Sheepscot, where increased housing density is expected on 131,000 now-forested acres, and the Presumpscot, 84,800 acres.

'Based on the spatial distribution of forest ownership [in the five watersheds], it appears that much of the projected development will occur on forests owned by individual and family forest landowners ...' wrote White.

Growth is uneven across the region, with some towns losing a small number of housing units and others (notably in the Lower Penobscot) showing increases of more than 40 percent.

Maine is not alone in facing the issue of rapid residential development. The original 2005 report noted 'some 44.2 million acres (over 11 percent) of private forests -- particularly in the East, where most private forests occur -- are likely to see dramatic increases in housing development in the next three decades, with consequent impacts on ecological, economic and social services.'

But the 2005 U.S. Forest Service report and more recent case study suggest Maine faces perhaps the greatest challenge in the nation as it attempts to balance residential growth and forest conservation.

Longtime Maine journalist Andrew Kekacs writes for Forests for Maine's Future, a collaboration of the Un i versity of Maine Center for Research on Sustainable Forests, the Maine Department of Conservation, the Maine TREE Foundation and the Small Woodland Owners Association of Maine. For more information about forest issues in Maine, visit forestsformainesfuture.org.