Fire, grazing enhance our grasslands

pgeweather@pge.comOctober 20, 2012 

Robert Wilson of San Luis Obispo took note of three pictures of early San Luis Obispo on display at Miner’s Hardware on Santa Barbara Street that showed the mountains around San Luis Obispo covered with dry grass with only a few patches of brush. Today, these mountains are nearly covered with chaparral and sagebrush. He wondered if this is because of changes in the climate or the American Indian custom of burning off the brush regularly in years past.

To begin with, our Mediterranean climate with its prolonged dry spells tends to support the development of grasslands. Another reason San Luis Obispo County is well-suited for grasslands is the abundant outcroppings of serpentine, the state rock of California.

Serpentine has a distinctive greenish-gray color, and soils derived from serpentine tend to support grasslands and discourage  trees. In fact, plants that grow in these soils are often stunted because the low levels of calcium and high levels of magnesium. Consequently, the historic abundance of grasslands allowed cattle ranching in San Luis Obispo County to thrive.

Except for alternating periods of drought and high rainfall that can create havoc with local agriculture, yearly average rainfall has trended slightly upward since 1870, when rain records were first recorded at Cal Poly, the home of climatology in San Luis Obispo. 

According to sky visibility records at San Luis Obispo County Regional Airport, the number of foggy or overcast days seems to be slightly trending upward, but these visibility records don’t go back far enough to draw any adequate conclusions.

The main reason for the increased amount of chaparral and sagebrush on these mountains is the lack of grazing and fire. Extensive studies have repeatedly shown that fire and grazing increases species richness and diversity.

PG&E biologist Sally Krenn told me, “Historically, grazing animals, including great herds of elk and deer, have been a vital part of the state’s grassland ecology for thousands of years. Managed grazing, when it’s done well, actually enhances the organic matter in the soil, improving its ability to store carbon, and it improves the water and mineral cycles and allows the whole ecosystem to function in a way that’s healthier.”

Beginning in 1992, Bob and Terri Blanchard implemented a managed grazing program on the Pecho Ranch, which they lease from PG&E. The Pecho Ranch is along the rugged coast between Diablo Canyon nuclear power plant to the south and Montaña de Oro State Park to the north. The ranch is about 3,500 acres, with steep mountains and flat, narrow coastal plains.

The Pecho Ranch is divided into 25 pastures. The Blanchards allow the entire herd to graze a pasture for several days, creating a brief period of intense impact on the rangeland vegetation. After each grazing period, the pasture is rested for months. According to Bob Blanchard, “The point is to mimic the beneficial effects of the migratory herds.”

Those who have hiked the Point Buchon trail that weaves through this beautiful ranch will tell you the Blanchards’ program has been a stunning success. In contrast, the treasured and neighboring state park, which has areas that have not been grazed or burned for quite some time, lacks the ecological health and biodiversity of the Pecho Ranch.

There is ample evidence that Native Americans greatly changed the character of the San Luis Obispo County landscape with fire. Henry Lewis, an award-winning author, educator and historian, concluded that American Indians used fire to burn vegetation for at least 70 reasons. The major reasons were for hunting, crop management, improving growth yield and controlling pests. The use of fire by Native Americans tended to replace forested land with grassland.

These vegetation burns lasted after the Spanish missions were established. However, early settlers in California, who failed to understand the benefits of vegetation burns, demanded the governor put a stop to them.

Anthropologists and botanists say that frequent burning by Native Americans sustained a parklike landscape with grass and scattered oak trees. Today, chaparral and sagebrush have invaded these areas because grazing and burning have diminished. Without these burns, fuel levels have increased to dangerous proportions in many parts of the county.

Krenn went on to tell me that, “Thick, dense sagebrush and chaparral plant communities, although it provides habitat for some species, prevents the establishment of native grasslands. Ideally you want to see a mosaic of plant communities that will allow increased diversity of plant and animal species.

Without the use of fire or animal impact, grasslands can become overgrown with brush, such as coyote brush and black sage.”

Today’s forecast
A weak cold front produced mostly gloomy and much cooler weather along the beaches and coastal valleys Saturday. San Luis Obispo only reached the mid-60s.

This cold front will produce a steeper pressure gradient as it passes to the south. Strong to gale-force (25- to 38-mph) northwesterly winds will produce partly cloudy to mostly clear skies later this morning through this afternoon.

Today’s high temperatures will range from the 70s in the North County and the 60s in the coastal valleys and along the beaches.

A 1,005-millibar low- pressure system will move toward California from the Pacific. The associated cold front will produce increasing clouds and southerly winds Monday. This cold front is forecast to pass over the Central Coast on Monday evening, with rain and fresh to strong (19- to 31-mph) southerly winds. Rain will turn to scattered showers Tuesday morning. Total rainfall amounts from this system should range between 0.10 and 0.40 of an inch. Snow levels will range between 5,000 and 5,500 feet Monday, then lowering slightly Tuesday.

Another but weaker cold front is expected to pass the Central Coast on Wednesday, with gentle to moderate (8- to 18-mph) southerly winds and a few scattered rain showers.

High pressure will build over the Great Basin on Thursday into Saturday and will produce gusty northeasterly (offshore) winds, clear and dry skies and warmer temperatures.

Today’s surf report
Strong to gale-force (25- to 38-mph) northwesterly winds will generate a 5- to 7-foot northwesterly (320-degree deep-water) sea and swell (with a 5- to 12-second period) today, decreasing to 3 to 5 feet (with a 7- to 11-second period) by Monday morning.

Increasing southerly winds will generate 3- to 5- foot southerly (195-degree shallow-water) seas Monday afternoon through early Tuesday morning. A 3- to 5-foot west-northwesterly (290-degree deep-water) sea and swell (with a 7- to 11-second period) is forecast along the coast Tuesday afternoon through Friday.

An intense low-pressure system is forecast to develop near the international dateline Wednesday. A long period west-northwesterly swell from the storm is forecast to arrive along the coast Oct. 28-29.

Arriving from the Southern Hemisphere:

A 1- to 2-foot Southern Hemisphere (220-degree deep-water) swell (with a 17- to 19-second period) will arrive along the coast  Wednesday into Thursday.

Seawater temperatures
Seawater temperatures will range between 55 and 58 degrees through Friday.

•  •  •

The Diablo Canyon nuclear power plant provides pedestrian hiking opportunities on specific coastal portions of its property. Through its land stewardship program, PG&E has preserved these areas, providing examples of the Central Coast in its natural, open space context. To learn more and make reservations, log into http://pge.modwest.com/pgereservations/trails home.php

John Lindsey’s column is special to The Tribune. He is a media relations representative for PG&E and longtime local meteorologist. If you have a question, send him an email at pgeweather@pge.com.

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