Fire burning through grass and vineyards has been a feature of the latest fire season in northern CA. Given how dry and hot the climate is, only dirt is a sure thing. However with high enough winds, embers can carry long distances and cross fire breaks. For example in 2017, the Tubbs fire crossed highway 101. But I still agree that living close to trees is worse.

Grass burns, yes, but quickly and generally not in conflagrations. Trees are often (though not always, and increasingly less so) largely untouched by grass fire. Back-burning is highly effective on grassfire.

Scrub burns ferociously, far more violently than one might expect, thanks to the volatile oils. For much of Southern California, this is a poorly-manageable threat.

An entrenched crown fire is a true fury, not to be trifled with. The main fire can burn in a location for hours (rather than minutes), and individual trees or roots for days, even months.

The heat from even a modest forest fire is ferocious. I found myself a 1/2--1/4 mile or so from a relatively small burn (an acre or so), and could feel the radiant heat from inside a car.

A hillside on fire, or a fire-front overtaking a position, is like a blast furnace, with temps over 1,500°F. Plus choking, blinding smoke, poisonous fumes, low oxygen, and flying and falling flaming debris.

A 1km deforested buffer might help, along with building codes.

Last year, many of the houses that burned down in Malibu were miles from the nearest wildfires. It turns out that burning embers can travel miles in the right wind conditions.

And pasture land is the worst type of buffer, since dry grass burns easily, and quite hot. NorCal, for example, has lots of pasture land, especially in wine country, and that is one of the reasons that Santa Rosa and Napa have been hit with major fires every year for the past 3 years.

There are existing ways to protect a town from burning down, largely related to building designs and materials. The problem is that these all cost money, and the type of people that live in these high-risk mountain towns generally don't have the money to incorporate those features into their buildings.

I suggest you actually look at some satellite footage of Santa Rosa, Napa, and Malibu. California has plenty of ranches, but their not acting as a buffer around those areas. Also, being within a few miles of forest is really close in wildfire terms. When people think of wildfire buffers they point to things like roads and firebreaks, but that’s only useful when people are actively fighting fires. You want tens of miles not feet between structures and wildfires.