RENO - Until now, it's been a no-brainer. The hottest, driest summer months were considered the worst time to set a fire to help thin overstocked forests around Lake Tahoe.
In addition to concerns about a fire growing out of control, the summer tourist season swells Tahoe's population to five times the year-round numbers. A smoky haze isn't what the Chamber of Commerce sells in those postcards of the aqua, alpine lake.
But now comes a new take from the latest blue-ribbon scientific panel to assess the entire Tahoe watershed, the contributors to the lake's alarming loss of clarity and the steps that should be taken to improve the health of the forest surround it:
Seasonal wind patterns appear to make summer the best time for prescribed burning. Scientists say the burning program must be accelerated to rid the forests of dead and insect-infested trees.
''Controlled burning over the last several years has taken place in the autumn. They've decided to do the management when you don't get the tourists upset,'' said Dennis Murphy, a biology professor at the University of Nevada, Reno, who was team leader of the latest watershed assessment.
''It turns out that the best time to burn so as to avoid tourists is not the best time to do burning in terms of health standards and the efficiency of the burns,'' he said.
Fall air is more stagnant. It takes a smaller burn with less smoke to reach the level of violating California's air quality standards, Murphy said.
In the summer, when fires traditionally burned before settlement of the basin, fires ''produced a lot of smoke through the evening that sticks around until late morning, but then it is blown outside the basin,'' he said.
So does he think the burning season will change?
''That is a public policy dispute,'' Murphy said.
''We scrupulously avoided telling policy makers what it is they should do. We gave them the information they need to make those hard decisions,'' he said.
The scientific team says the prehistoric Tahoe basin was a smokier, but healthier ecosystem.
The relatively good, smoke-free air found during the summer at Lake Tahoe these days is an artificial phenomenon caused by years of fire suppression, said Tom Cahill and Steve Cliff, two researchers at the University of California, Davis.
''The recent conditions are an aberration, achieved by putting out naturally occurring fires,'' Cahill said.
''Every square foot of forest of the basin used to burn every 30 years,'' he said.
But tourists don't like smoke.
''And neither do the people who live here. It is going to have to be a balancing act,'' said Pam Drum, spokeswoman for the Tahoe Regional Planning Agency.
''The tourism folks are going to want some assurances. We haven't really had any of those conversations yet,'' she said.
Forest Service officials are reviewing the latest findings.
The agency set fire to about 1,000 acres around the lake last year and plans a similar effort this year. Agency officials are already sensitive to complaints about smoke.
''Trying to find the right balance is a real challenge for us,'' said Linda Massey, a spokeswoman for the Forest Service's Lake Tahoe Basin Management Unit at South Lake Tahoe, Calif.
''It is a very fine line we walk - between some moisture and not too much moisture, some wind and not too much wind,'' she said.
In November, some residents on Lake Tahoe's north shore had to leave their homes when wind deviated from the forecast and a prescribed burn choked the area with smoke.
''The smoke just hung there. We got huge complaints. If you have to leave your home and go to a motel, you are not a happy camper,'' she said.
Steve Teshara, executive director of the Lake Tahoe Gaming Alliance representing casinos and other tourism interests, understands why burning might be better done in the summer.
''But I can tell you, it does have an impact on tourism. It impacts the beauty of the area,'' Teshara said.
''If we are going to be persuaded that some modest burning should be done in the summer, they are going to have to do a better job of campaigning to tell people why,'' he said.
''And they will have to try it at a scale that doesn't mar what otherwise would have been someone's wonderful Tahoe experience if they hadn't been choked by smoke,'' he said.
Massey said most Tahoe residents ''understand there are certain trade-offs.
''If you are going to live in the forest, especially an unhealthy forest like this, you have to do whatever is necessary to restore the health,'' she said.
''But if you're coming from Southern California for the weekend to get out of the smog and they end up in the smoke, they think their vacation has been ruined and our name as an agency is 'mud.'''