European Forests Also Need Control Burns

…but are not getting them. European forests have grown up in thick stands of saplings, just like most American forests. In North America, the Natives kept the forest undergrowth cleared away, which benefited agriculture and hunting, by the controlled use of fire, as I explain in chapter 2 of my recent book Forgotten Landscapes. When European diseases and conquest killed off ninety percent of Native populations in America, the forests shifted from bountiful productivity to being “a forest of sticks” choked by undergrowth.  Native fires were an essential part of what a “natural” forest should be like in North America.

It appears to me that the same is true in Europe. It is likely that the tribal peoples of Europe, before (and after?) Roman conquest, burned their forests just as Native Americans did theirs. The forest preserves we see in America, and in Europe, today are not “natural” but have resulted from fire suppression in recent centuries. This would be true even of the last “virgin forest” in Europe,  Białowieża in Poland.

I explored one of the last fragments of pre-industrial Rhineland forest in France earlier this summer. It is (what passes in Europe for) an extensive forest southeast of Strasbourg. I hiked around on just a portion of its extensive system of trails. Beech trees (Fagus sylvatica) dominated the canopy and its seedlings were abundant on the forest floor. Maples (Acer pseudoplatanus) dominated the forest floor and had some canopy trees, along with two species of linden (Tilia cordata and T. platyphyllos). There were a lot of shrubs, especially the field maple (Acer campestre), dogwood (Cornus mas), hazelnut (Corylus avellana), and hawthorn (Crataegus monogyna).

This forest had been undisturbed for a long time—the beeches were large and tall. But it was not that long ago, perhaps a century and a half, when the forest had been cut down. In a desperate but successful attempt to control the resulting soil erosion, the French government planted conifers (in the lowlands, Norway spruce, and on the hillsides Douglas fir from America) which persist in a few places, remnants of once successful forestry but now ceding their dominance to hardwoods.

It was a peaceful and wonderful place to hike. But it was not natural. In my book I wrote about Native inhabitants being an essential part of the “natural” landscape in America. And it appears that the same is true in Europe. I suspect this is a general pattern. Sam Goldwyn is said to have quipped that wilderness is “where the hand of man has never set foot.” But I think this may not be true not only in America but anywhere else. Humans have always been, ever since we mastered fire, an important factor in the operation of entire landscapes all over the world.

The only alternative to small, frequent fires is large, perhaps equally frequent fires. This is what is happening in America, where the lack of control burns has allowed huge forest fires to get started especially in the west. But the same is true where I now live in France. With increasing frequency, the forests of southern France burn in the hot, dry summers. With global climate change, the forests where I now live in northern France will also burn more frequently. The problem will take care of itself, though not in a way we would like.

The Ecology of Disaster and Renewal

Nobody likes disaster. I strongly dislike even the smallest inconvenience. But they happen, and they have happened throughout the evolutionary history of life. And all organisms have inherited adaptations to cope with many of them, to a certain extent.

One such disaster (or, in ecological parlance, a disturbance) is fire. To all of us who watched Bambi, a forest fire is a disaster. But even in the Bambi movie, the dead forest had green grass growing after the fire. Disturbance is followed by renewal. This renewal occurs in stages (in ecological parlance, succession). There is no way to prevent all fires. Biomass burns. But most organisms have ways of dealing with fire—perhaps not as individuals, but at least as populations. Even alders, which grow out in the water, have to deal with it, because the flames can spread from the adjacent forest and burn their crowns.

A fire burned a large area of Cross Timbers forest near the Blue River in Johnson County, Oklahoma, in the summer of 2011. Despite its severe beauty, the fire was pretty grim for the plants and animals that experienced it.

There were burned turtle skeletons everywhere.

Yes, even the alders out in the middle of the river burned. But the next spring, in 2012, there was a luxurious growth of wildflowers and grasses, making use of the flush of nutrients released by the ashes of the fire. Many of the trees resprouted from the ground. By the summer of 2013, the growth was so exuberant that I could not even walk through it when doing field work with a visiting scholar from France.

But not all of the wildflowers, at least in 2012, were the same species that one normally finds in the spring. Two species in particular grew abundantly after the fire, but are rare the rest of the time. One is the mustard Selenia aurea.

The other is a member of the Hydrophyllaceae family, Phacelia strictiflora.

This wildflower is a relative of Phacelia grandiflora, which grows abundantly after chaparral fires in California. Now here is where it gets strange. It is no surprise that grasses and wildflowers grow abundantly after fires. What is strange is that a few species, such as Phacelia strictiflora, seldom grow except after large fires. That is, there is something about the fire that makes the seeds germinate. The flowers do not grow just because the ashes have released nutrients or because there is more sunlight as a result of the trees being burned. Many plant species that live in habitats with a fire cycle (such as the chaparral) require exposure to smoke chemicals in order to germinate. Phacelia grandiflora is one of them.

Oklahoma does not have any habitats with fire cycles. It therefore came as a surprise to us that the germination of the Oklahoma wildflower Phacelia strictiflora is greatly enhanced by exposure to smoke chemicals. The results of our research have just been published in the 2013 volume of the Oklahoma Native Plant Record. We demonstrated that very few Phacelia strictiflora seeds germinated—whether scarified or not; whether in light or in dark—unless exposed to a water suspension of smoke chemicals.

It was a fun experiment to do. How does one produce a smoke suspension, without having access to a budget for scientific equipment? You have probably already guessed the answer. Remember, this is Oklahoma. My student, Sonya Ross, who conducted the experiments, had access to a hookah pipe. We burned oak wood in the bowl and drew the smoke through the water. Usually hookah aficionados want the smoke, but we wanted the water, which after a few hours had turned amber and had a smoke scent.

This allowed me to produce a particularly interesting Darwin video. This was a low-budget experiment, but it yielded important results. This may be the first report of a plant species from a habitat that does not have a fire cycle but whose germination is so strongly enhanced by smoke. Many seeds germinate more upon exposure to smoke, but not this much.

There are a lot of interesting experiments just waiting to be done and which do not require a lot of equipment or a budget. Please check out the article. And I have to say, good work, Sonya.

Oh, and by the way, oak smoke is not very enjoyable, even after it has been through a hookah pipe.

Evotour, Part Six. Fire and Renewal in the California Mountains

Cuyamaca Rancho State Park in California used to have meadows surrounded by pines and black oaks. The pines and oaks extended partway up Stonewall Peak. But in 2003, a fire burned the entire area except some places around the meadow. Today, that meadow is the only place you can find pines and black oaks.

However, the chaparral shrubs have grown back profusely. I am accustomed to dry chaparral that consists mostly of dead sticks, but this chaparral was filled with fresh green stems, flowers, and fruits. Along with the profuse regrowth of manzanita, ceanothus, scrub oaks, and holly-leaved cherry, there were perennial wildflowers in full bloom: penstemon and yerba santa. The shrubs had grown over three meters tall and state park personnel, the few that remain after budget cuts, have to keep trimming them away from the trail. A few of the black oaks have resprouted, and a few pine seedlings have been replanted.

This is a theme I have presented before, but I enjoy being reminded of it when I see it again in the natural world. Ecological disturbances, such as fires, are disasters for the organisms killed by them, but act as a source of renewal for the ecosystem as a whole. Dead grass and wood are transformed into fertilizer that feeds the vigorous growth of new plants, either resprouts or seedlings. The chaparral in Cuyamaca, and the tallgrass prairie of the Midwest, depend on a fire cycle.

I do not doubt that my hike at Cuyamaca would have been prettier if the pines and black oaks had been intact, but I would not have seen the way organisms capitalize on natural disturbances as an opportunity for renewal.