Mike Swezy, MMWD natural resource specialist

The world would be a lonesome, barren place without trees. Actually, the world as we know it - in terms of climate - wouldn't exist without trees, which is why environmentalists have long sounded the alarm over deforestation.

All we have to do is look up to know that in Marin, deforestation is not our problem. The 25,000-plus acres that make up Mount Tamalpais are plump with trees, which generously soak up carbon dioxide and "exhale" oxygen, and all manner of lush plant life, including 73 species found nowhere else in Marin but on its slopes. As the largest landholder on Mount Tam, with more than 21,000 acres, Marin Municipal Water District has a big stake in how those slopes are maintained.

"It's a given that well-vegetated, stable watersheds yield the best water, and that's what we're about," says Mike Swezy, the district's natural resource specialist - an avowed "fern feeler" -- who oversees the work of nurturing and maintaining the county's urban forest so that we can, in turn, drink (and breathe) deeply.

"MMWD is built like a national park, with rangers; maintenance staff, who help protect habi-tats through restoration and erosion control; and fern feelers like me," says Swezy, who helped found the Marin Conservation Corps in the early '80s and worked at Lake Tahoe as an ecologist with the California State Parks before joining MMWD in 1995, when his position was created.

And while all the trees on Mount Tam are visually appealing, lovely to walk among, and doing their part for the climate, their abundance is not a good thing when it comes to fire danger, a threat that extends beyond the mountain to what sits in its shadow: our densely populated communities.

The Miwok Way

In modern times, 40,000 acres on Mount Tam burned in 1923 and 20,000 acres were lost in 1945. That there have been no fires of note since is worrisome. "The assumption," Swezy warns, "is that conditions exist for it to happen again."

Before Europeans arrived and began planting their favorite trees, most of Marin was open grassland intermixed with oak woodlands. On the mountain were regal coast redwoods and Douglas fir, the deep-red madrone, and sweet-scented California bay. Back then, overgrowth was handled by the Coast Miwok, who purposely set fires to maintain and rejuvenate the land.

"We think they probably used fire almost every year, and we have fire records that showed that fire burned through large areas on average every 10 years," says Swezy. Miwok reliance on fire is not just a matter of human record. Trees themselves record fire just as they record their growth: Charcoal from fire remains as burned tissue within a tree trunk's rings.

Loss and Gain

Thick forests and plentiful undergrowth are longstanding concerns for MMWD. A new one is sudden oak death syndrome, which since 1995 has swept through the county, "decimating our live oak and tan oak forests": 40 to 50 percent of the native oak populations in certain areas of the county are dying, says Swezy. One exception is our "magnificent" valley oak.

"We've lost large, beautiful specimens. Whole hillsides have been taken, along with every favorite tree" between his post at the Sky Oaks Ranger Station above Fairfax and Lake Lagunitas, says Swezy. But this tree-lover is undaunted.

Despite the disease, Swezy is all for planting native trees. Native trees can live hundreds of years longer than nonnatives because they are adapted to the environment - and that means what we plant today is a gift to future generations.

FOR MORE INFORMATION

Marin Municipal Water District: www.marinwater.org

Marin ReLeaf: www.marinreleaf.org

California Native Plant Society, Marin Chapter: www.marin.cc.ca.us/cnps

California Oak Mortality Task Forc: www.suddenoakdeath.org