Treebeard's Stumper Answer
It's officially spring! It's time to get outside and enjoy the wildflowers that are starting to appear. The best wildflower fields are in the back country on Figueroa Mountain and beyond, far from human disturbance. But it's convenient that many wildflowers are abundant right along the roads. Introduced weeds are common, but there are also many natives like poppies and lupines that thrive along our highways despite traffic and mowing and scraping. Wildlife follows. What environmental factors make the roadsides attractive for wildflowers and wildlife?
Arroyo Lupine (Lupinus succulentus) is a California native wildflower that is often abundant along local roads and highways, like this colony along rural Happy Canyon Road in the Santa Ynez Valley behind Santa Barbara. I shouldn't overstate my claim. Introduced weeds dominate along many roads and highways, but some natives hold their own. Introduced or native, these plants do well along our roads. And it's not just plants that favor roadsides. I regularly see once-endangered White-tailed Kites and other raptors as I drive to and from school. What environmental factors make the roadsides different for weeds, wildflowers, and wildlife?
Our roadsides are a disturbed habitat that is attractive for weeds and some native wildflowers that are adapted to follow fire and flood. Roads collect rainwater and let the sunlight in, like a jungle river. Road cuts create seeps and rocky exposures that some native plants prefer. Caltrans tends our scenic roads, and the cattle are on the other side of the fence. Roads are also avenues for invasive weeds that can take over the wildlands. It's nice to see lupines and poppies along the highway, but you'll find a lot more natural diversity in a remote place like Figueroa Mountain. Take a drive, but then go for a hike!
Roadsides are no doubt the most visible habitat for daily commuters like me, but Roadside Ecology is a still a complicated topic. It's important not to over-simplify. Here are a few of the environmental factors that make roadsides different. The effects are both positive and negative, with the kind of complexity that makes this an interesting subject.
- Modern roads are crowned. The road surface is curved to run water to the sides. Think about how much rainwater runs off your roof during a storm to appreciate how much water this directs to the sides of the road.
- Most road cuts go across the grain of the rock layers that make up the mountains, This can drain a small aquifer and dry up natural springs. I pass several "wet spots" along my drive to school along Highway 154 every day. There's a small pond by our old cabin on Kinevan Ranch that always goes dry in the summer. Dick Smith and Frank Van Shack have a photo in their book California's Backcountry (McNalley Loften, 1962) that shows the same pond with perennial cattails that are no longer there. I reckon it changed when the new highway was dug in over San Marcos Pass. On my drive to school, I pass Hot Springs Canyon at the upper end of Lake Cachuma. I believe the hot springs have been dry since the water tunnel was drilled through the mountains to connect Lake Cachuma with Goleta. Roads (and tunnels) have a big impact for wildlife in this dry country by lowering water tables.
- There are many exposed natural rock outcrops in our mountains, but they are mostly solid sandstone. Road cuts are fresh cuts where plants can get a hold, and they sometimes include extra water. It's a good place to look for rock-loving natives like Bush Poppy (Dendromecon rigida), Prickley Phlox (Leptodactylon californicum), and several kinds of Goldenbush (Hazardia squarrosa, Ericameria cuneata and E. arborescens).
- Roads let the sunlight into areas of dense chaparral and forest, and a whole different flora responds. You can see the same effect along tropical jungle rivers and west coast rivers like the North Umpqua in Oregon. The vegetation looks impenetrable from the river, but the old growth beyond the bank is quite open. In our native chaparral, it's just the opposite. It looks open from the road, but good luck crawing through it! Only a few interesting herbs like the root-parasites Indian Warrior (Pedicularis densiflora) and Chaparral Broomrape (Orobanche bulbosa) can grow under solid chaparral. (And the only way to find them is to crawl!)
- Some plants are adapted for disturbed habitats. This includes many weeds, but also some natives that are adapted to follow fire and flood and landslides and other natural disturbances. This includes some native shrubs like Elderberry (Sambucus mexicana) and Coyote Bush (Baccharis pilularis) that do especially well along roads. But I've never seen a Fire Poppy (Papaver californicum) along the highway!
- There are nitrogen compounds in car exhaust. Roads collect oil and worn away rubber from tires. We learn to be careful driving after the first fall roads since the roads are slippery with accumulated oil. Do these substances act as fertilizer?
- Here in temperate central California, there's no need to salt roads in winter to melt ice. (Though it does happen occasionally; see my Big Chill (01Feb02) stumper.) But in cold parts of the country, highway salt must make a difference. I reckon it's not good for native plants, but it must attract animals.
- Roads are avenues for plant migrations. Over the past 30 years, I've been watching new invaders like Asphodel (Asphodelus fistulosus), Moth Mullein (Verbascum blattaria), Spanish Broom (Spartium junceum), and French Broom (Genista monspessulana slowly spread along Highway 154 and sometimes into the woods. Roads are a consistent habitat, and maybe the wind from passing cars can help spread seeds and pollen.
- Roadsides are public, and beyond the fences are ranches, farms, and houses. Roadsides may be the only place where wildflowers can grow, or the only public place we can see them. Lester Hunt emailed this report from Wisconsin:In the upper midwest, railroad right-of-ways are great sources of prairie plants. I've collected any number of specimens of horsetail and spiderwort for my garden at the Great Northern tracks that cross my street. I think a main reason for the two phenomena is just the property-status of the land, together with its function. In both cases the land belongs to someone (the government in the one case, the railroad in the other) who, given the function to which they have dedicated this piece of ground, has no motive to disturb it further. In the case of the railroads, it is often more than a century since the land was dug up. Now if that ground had belonged to a farmer.... I hear that some of the best wildlife areas on earth are military gunnery ranges, but I've never ventured into one to check it out.
- Roads divide habitats, but they also connect otherwise disconnected habitats. That's complicated!
- Roadsides support whole food chains. Plants along the road attract many animals, as does roadkill. This brings predators and scavengers. Every morning on my drive to school, I pass Osprey eating their morning trout on the power line poles along the road at Lake Cachuma. Most days I see a White-tailed Kite hovering in the air looking for breakfast rodents along the highway.
- Roadkill (aka "flattened fauna") are interesting because I don't think the numbers are representative of total species populations. Skunks stand and spray, oppossums play dead, porcupines show their quills, deer wait until the last minute and then sprint. These may be good strategies in nature, but they don't work against cars! One conservative estimate is that one million animals are killed every day on US highways. Reed Noss describes it like this in his The Ecological Effects of Roads:Roadkill is a classic death-trap phenomenon. Animals are attracted to roads for a variety of reasons, often to their demise. Snakes and other ectotherms go there to bask, some birds use roadside gravel to aid their digestion of seeds, mammals go to eat de-icing salts, deer and other browsing herbivores are attracted to the dense vegetation of roadside edge, rodents proliferate in the artificial grasslands of road verges, and many large mammals find roads to be efficient travelways. Songbirds come to dustbathe on dirt roads, where they are vulnerable to vehicles as well as predators. Vultures, Crows, Coyotes, Raccoons, and other scavengers seek out roadkills, often to become roadkills themselves.
- I drive California State Highway 154 to and from school everyday. This is an official California Scenic Highway and it receives some special care. I suspect most of the California Poppies (Eschscholzia californica) and Lupines (Lupinus succulentus) along the roads are actually planted by Caltrans. I never find Eschscholzia caespitosa along the road, though I think it is the more common "California Poppy" in the backcountry. Linda Smith sent this observation:But why did the lupines SUDDENLY appear on 154? They weren't there a few years ago... I've been a fan of lupines for years. They thrived in Texas and other places I've lived. When I moved here, I assumed SYV didn't have the right conditions... then suddenly they began to reappear.I admit I just can't remember what the roads were like 20 years ago. I also don't remember the poppies on Grass Mountain. I used to avoid showing the road in my photos so they would look more "natural". Now with my digital camera, I'm trying to document the flora just so I can record that kind of slow change.
- These are all ecological effects of roads. Note that I haven't mentioned litter. I think of Hayduke in Edward Abbey's The Monkey Wrench Gang measuring his road trips by six-packs, and tossing the empties out the window into the great American desert: "Why the &$#@ shouldn't I throw &$#@ing beer cans along the highways?" I don't like litter, but I appreciate that it's appearance, not ecology. In fact cans and bottles can provide habitat. Once I found a live crawdad in a beer bottle on the shore of Lake Cachuma. It had grown too big to get out, but crawdads are filter feeders so that wasn't a problem. The lake was going down, and he was stranded on the shore in his bottle. I still imagine that crawdad trying to roll his glass exo-skeleton back to the water. (Yep, I helped him.) I guess litter can be part of the ecology of roads. But I draw the line at plastic diapers, no matter how nutritious for scavengers!
I'm sure there are many more environmental effects of roads, but that's a good start. Here are some links for further research:
- John Stilgoe from Harvard and the National Humanities Center tells the fascinating history of Roads, Highways, and Ecosystems. We take our roads for granted, but we shouldn't. Roads effect the human ecosystem as well as nature, and not all the consequences are desirable.
- Reed Noss has an introduction on the The Ecological Effects of Roads. Follow the links at the end of the article for more eco-activist discussion. I have a 30 year old xerox of a monograph by Robert E. Frenkel about Ruderal Vegetation Along Some California Roadsides (University of California Publications in Geography, vol. 20, 1970). That word "ruderal" is from the Latin ruder- or rudus, meaning rubble. It describes plants growing where the natural vegetational cover has been disturbed by humans. This monograph is long out of print. There is some recent discussion on the Web by: Richard T. Foreman's Roadsides and Vegetation (abstract), Howard Youth's Wildlife in the Fast Lane, Les Line's Native Plants Along Back Roads and Highways, a piece from Australia on Species diversity and genetic diversity of invertebrates in an agricultural woodland/landscape, J. Baird Callicot and Gary K. Lore's Introducing A Roadside Land Ethic - Roadside Use of Native Plants, Evelyn Boswell's Roadside Life a Cruel One for Plants, and Lee Wessman's A lupine's last stand on Highway 50.
- Planting roadsides with natives may actually save money as well as promote beauty, but I worry about the consequences. Mitigation procedures for local land development require that native plants be grown from locally collected seed to preserve biodiversity. But I'm sure state highway departments like Caltrans don't do that. For example, I've collected Encelia farinosa along the train tracks at Hollister Ranch. I even took a specimen to the Santa Barbara Botanic Garden to confirm my identification. Apparently it was hydro-mulched along the railroad right-of-way, even though it's a desert plant completely isolated from our native Encelia californica. Caltrans has recently been hydro-mulching roadcuts along Highway 154, and it looks like lots of lupines and poppies. The Clyde Robin Seed Company advertises their Roadside Wildflower Seed Mix by calling it an "all-time favorite of landscape architects and highway engineers across the country." But look at the actual seeds. These are not all natives anywhere! As a naturalist, I'm most interested in the small differences between different populations of plants from canyon to canyon and valley to summit. Despite good intentions from Caltrans and groups like Californians for Alternatives to Toxics (CAT) and The Lady Bird Johnson Wildflower Center, I'm worried that roadside "restoration" planting will introduce alien pollen and simplify nature beyond repair.
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