What Trump gets wrong about wildfires, by a fire scientist | Environment

You cannot possibly understand what it means to live with the risk of wildfire until you have to do so.

I’m a fire scientist and have spent most of my adult life in the flammable south-west. At the start of the fire season, you pack up the things in your house you cannot replace and stage them so they are ready to be thrown into the car. You make a plan for your family and your pets. You identify escape routes and put together a bag with clothing and you spend the summer alert to smoke, radio reports and evacuation notices.

Unfortunately, Donald Trump is one of those who does not understand wildfire. In a tweet, Trump blamed “poor forest management” in California for the devastating conflagrations currently burning in the state, and he threatened to withhold federal aid as if in punishment for this negligence.

But that is not what’s going on. For one thing, a large portion of the area burning is not forest.

Trump probably has in mind how a century of putting out wildfires in the American west has caused forests to grow dense with trees, making large, hot fires more common than they once were. This is not the predominant cause, however, of the fires currently making the news. To comprehend what is currently taking place in California, you have to comprehend how it has historically burned – and the vast changes now occurring across the landscape.

Fire is an integral part of California ecosystems because it consumes dead vegetation, creates space for new plant growth, and helps limit the density of vegetation. It affects almost every vegetated part of the state, from the conifer forests of the Sierra Nevada mountains to the oak woodlands lower down and, in the valleys, the grasslands and chaparral.

The severity of these fires is moderated by rain and snowfall. California’s Mediterranean climate means that the state receives heavy precipitation for only a few short months in the winter, and this is all that the vegetation has to tide it over until the winter storms begin the next year. As the temperature increases in spring and summer and plants use up the water stored in the soil, the amount of water held in plants decreases, making them more flammable. Similar to fire wood, the drier it is, the easier it burns.

Climate change is causing warmer temperatures, which dry out vegetation more. It is also causing winter precipitation to fall over a shorter period and the length of the fire season is increasing. Vegetation in California is increasingly primed for fire.

So if these are not classic forest fires, as Trump suggested, what are they? Down south in the Woolsey fire, in the Malibu area, it is actually grass and shrubs that are burning. The native chaparral shrublands are dominated by shrub species that evolved with fires occurring every several decades to every century or so. Human activity has shortened the time between fires, however, which kills native chaparral species before they can produce seeds. These frequent fires also allow non-native grasses to invade. Unlike shrubs, such grasses are capable of burning nearly every year and still recovering. This mix of invasive grasses and chaparral is what is fueling the Woolsey fire.

Up north, in the Camp fire, it is grass, brush and timber. Here another wildfire factor comes into focus: human development patterns. We like to live in beautiful places and oftentimes this includes building our homes and communities among the flammable vegetation. Fire hazard is very high across large portions of the state where building in forests and shrublands is common. In these flammable environments, when a wildfire occurs and buildings begin to burn, vegetation can become irrelevant. This is due to the fact that buildings, once ignited, are an incredible source of heat that can spread fire to neighboring buildings.

Seeing as fire is an important natural process in many of California’s ecosystems, from grasslands to forests, it makes sense that in many of these ecosystems, the most effective tool for managing the risks to society from wildfire is more fire. Prescribed fires, which are planned fires lit by managers, are conducted during much more benign weather than the warm, dry and windy conditions that are driving the current flames. Prescribed fires help reduce the buildup of vegetation and break up the continuity of these fuels across the landscape. Extreme weather will continue to occur, but at least when vegetation is more variable, it acts as an impediment to fires spreading rapidly.

Earlier this year, Donald Trump tweeted that more “forest clearing” was needed to stop destructive forest fires. In fact, clearcutting is not going to solve the wildfire problem in forests either. Cutting trees won’t stop wildfires from occurring where there are no trees. We cannot cut our way out of this problem.

Matthew Hurteau is an associate professor in the department of biology at the University of New Mexico