Thinning the groves

The U.S. Forest Service’s plans for the 328,000-acre Giant Sequoia National Monument in the Southern Sierra have sparked a legal battle over the best way to restore its 34 sequoia groves, which contain the largest -- and some of the oldest -- trees in the world. Critics say the Forest Service’s policy of putting out wildfires has hurt sequoias by allowing a buildup of undergrowth that robs the trees of space and light and also thwarts the natural wildfire cycle they need to reproduce. The Forest Service says it must first thin the groves mechanically before it can reintroduce fire. But next door in Sequoia and Kings Canyon national parks, managers have relied almost entirely on deliberately set, controlled burns to thin sequoia groves since 1964. Here is a look at the issue.

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Giant Sequoias need fire

-- Fire is a requirement for giant sequoia seed germination.

-- Intense heat causes cones to release their millions of seeds.

-- Fire also produces mineral-rich soil for seed protection and germination.

-- Snow covering the ground waters the seeds when it melts in the spring.

-- Burned areas offer a better mix of sun and moisture that seedlings need.

Fire scars on sequoia trunks are evidence of the frequent wildfires before 1905. Sequoia bark is very thick and has tannins that protect it from disease and fire.

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Prescription for a burn

In Sequoia National Park, prescribed burns are five-year projects that build on each other like puzzle pieces. Weather conditions that disperse smoke away from populated areas are favored on the day of a burn. Moisture in plants is also monitored -- drier fuels burn cleaner and produce less smoke, but fires in dry growth may be harder to contain.

1. On a site with natural firebreaks, such as roads or a river, a down-wind backfire is set. This creates a “black line,” or burned area.

2. Small fires are set in succession with torches. They burn in the direction of the wind, toward the burned area. A firefighting crew keeps fires contained.

3. The small fires meet the burned area, completing the prescribed burn. Small trees, shrubs and decaying vegetation have been reduced by at least 50%, aiding sequoia growth.

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The controversy

-- The monument bars timber production, saying trees can be cut only “if clearly needed for ecological restoration and maintenance or public safety.” The Forest Service thinning plan nonetheless allows trees as large as 30 inches in diameter to be logged -- including century-old sequoias.

-- Responding to a lawsuit brought by conservation groups, a federal judge on Monday halted logging on more than 1,000 acres in the monument. The same judge stopped a similar logging project in the monument two months ago. The California attorney general has also filed a suit to stop logging.

-- The Forest Service says logging is necessary because growth in the groves is so dense that prescribed burns could get out of control and would add to San Joaquin Valley air pollution problems.

-- Critics say equipment could compact soil and damage groves, removing large trees would hurt the Pacific fisher, and logging would violate monument protections.

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How mechanical thinning works

-- Heavy equipment clears brush and cuts trees. Grinding machines can reduce a whole tree to wood chips in a few minutes.

-- Downed trees and other debris are transported out of the forest on skidders to flat-bed trucks. Debris is burned to reduce fire hazard.

Excavator machine is often used to thin in plantations and stands with small-diameter trees, such as young white firs.

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Pacific Fisher

Fisher habitat remains a contested issue in logging plans put forward by the Forest Service.

-- Nocturnal relative of the mink, otter and marten; weasel family.

-- Found in hollow trees or rotting logs in old-growth forests.

-- Fur trapping and logging shrank the range of fishers.

Sources: ESRI; TeleAtlas; U.S. Geological Survey; U.S. Forest Service; National Park Service, U.S. Department of the Interior: Fire and Fuels Management Plan; Florida Department of Forestry; Sequoia and Kings Canyon national parks website; Giant Sequoia National Monument -- Final Environmental Impact Statement.