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Plant of the Week: Fire ecology

California is on fire. Wildfires in the western states are nothing new, but this year seems to be an especially bad one. Fire is a destructive force, but it is a part of the ecosystem that shapes our natural world. There is little doubt the world is changing, and not withstanding man’s own hubris, we individually and collectively need to consider how we will respond. Ignoring the fact that change is coming is not the best way forward.

FIRE ON THE MAOUNTAIN — This Douglas fir has a thick, insulating bark that protects the sapwood from fire. (Image courtesy Gerald Klingaman.)

The 2020 fire season is slated to be the worst on record by a wide margin. Since 2000, wildfires have burned an average of just over 800,000 acres per year in California. As of now, three times that acreage has already burned in the state and September and October are usually the worst months for fires. Extended droughts, large stands of insect-killed trees and a months-longer fire season — all driven by climate change, overemphasis on fire suppression in forested areas as people build homes in and around forests and more people living or recreating in fire-prone areas are all cited for the increasing destruction caused by fires over the past decade.

In an average year, 90 percent of the 8,000 or so fires that occur each year in California are caused by people. This year, as citizens try to get a break from the Covid-19 lockdown blues, the trend will likely continue. With about 105 million acres in the state, this year more than five percent of the land area could burn.

Many of the California plants have incorporated fire as part of their natural life cycle. Redwoods, Douglas fir and ponderosa pines are fire resistant species that have developed thick, insulating bark that insulates the sapwood from the high heat of a ground fire. However, if the fire is so intense it spreads to the canopy, these resistant species can be killed.

Many scrub pines of the mountain west such as the lodgepole and digger pine depend on fire for seed release. The seeds are kept locked inside the bristly cones and protected for foraging animals until a fire comes along, melting the terpenes and releasing the seeds.

Some plants, with fireweed being the most notorious in this regard, require smoke for germination. Seeds of this western wildflower are known to lie dormant for 50 years, then suddenly burst into growth following a fire. A new class of growth hormones, the karrikins, are now known to be produced by burning vegetation. These compounds are deposited on the soil surface after a fire, leached into the soil/seed interface with the first rain and then somehow trigger germination and/or establishment of the seedlings.

Fire has had an impact on the Arkansas landscape, too. In the prairie sections of the Ozarks and in the Grand Prairie region of eastern Arkansas, historically the prairies have remained open and free of woody shrubs and trees because of frequent wildfires. The forested parts of the state were also influenced by frequent fires which kept undergrowth to a minimum and encouraged the growth of grasses. In pre-European settlement days, Indians would periodically burn the prairies and woodlands to help keep the land clear, thus providing better grazing (and hunting opportunities) for buffalo, elk and deer.

Two centuries ago this began to change as European settlers moved in, built fences and homes and did all they could to suppress wildfires. Today, many of our once open prairie land is now covered in forests while our once open, savannah like forests are tangles of undergrowth. Fire, though a bitter pill, is part of the evolutionary history of our landscape and will be a part of our future in this changing world.

For more information about horticulture or to see other Plant of the Week columns, visit Extension’s Website, www.uaex.uada.edu, or contact your county extension agent. The Cooperative Extension Service is part of the U of A Division of Agriculture.

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