YARROW (Achillea Millefolium)
GETTING A LIVING
Wherever one goes in the montane and subalpine Rockies, Yarrow (Achillea) seems to be there. It likes slightly disturbed soils in both meadows and forests and doesn't mind a fairly dry landscape. This is a widely distributed species that occurs from sea level up to 12,000 feet elevation.
DEFENSE
Given its status as a “weedy” species, a warming climate will likely do little harm to this plant given its capacity to flourish in dry meadows right along side such prairie species as big leaf sage. Its been introduced in Australia and New Zealand where it has become an aggressive weedy invasive. Achillea contains inflammation fighting flavonoids and has been used historically as a folk remedy around the world. The adaptive value of flavonoids could be as a defense against fungal pathogens.
REPRODUCTION
Achillea is a member of the sunflower family with from four to eight ray flowers. It’s flower heads are small, perhaps a centimeter across and the flowers themselves are miniscule. Yarrow is self-compatible, meaning that a flower can become fertile using its own pollen, maximizing its reproductive ability where pollinators are scarce and there is a potential for quick, opportunistic spreading into disturbed soils. A wide range of insect species can pollinate this plant and are attracted by a nectar reward, increasing further its likelihood of reproductive success. Its ubiquity is further assisted by an ability to expand and propagate through spreading rhizomes.
BIG SAGEBRUSH (Artemisia tridentata)
GETTING A LIVING
Big Sagebrush (Artemisia) flourishes in the semi-arid habitats of the Great Basin and Rocky Mountains receiving from 20 to 40 cm (6-16 inches) of rain annually. Artemisia is especially abundant in the central Rockies around Gunnison, Colorado where it provides winter habitat to the threatened Gunnison Sage Grouse. In this area, the plant reaches its highest elevations in the drier subalpine meadows above Crested Butte.The plant's big advantage in dry habitats is its 1-4 meter taproot reaching down into the damper soils unavailable to many other high-mountain meadow plants. Artemisia reproduces by way of both seedlings and shoots charging up from rhizomes that give it the ability to easily spread from existing plants out over the landscape. Artemisia is threatened throughout much its range by the invasive, fire-prone cheatgrass that displaces it through periodic burns, and from being uprooted for grazing and other kinds of land development. Nonetheless, the plant is poised to expand its range at the expense of showy mountain wildflowers in the Crested Butte area if recent research findings stand the test of time. Pollen deposits over the past 10,000 years reveal a hint of what can happen to montane meadows in the mountain west under a warmer climate. Pollen records show that as the tree-line moved upward historically during periods of climatic warming, Artemisia pollen becomes more abundant. In short, as climate warmed in the distant past, Artemisia flourished.
Does this mean that a warmer climate today will cause Artemisia to outcompete and displace showy forbs (i.e. wildflowers) common currently in high-mountain meadows? We will only know this for sure in a future warmer world, but biologists can tell us what that future might be like by simulating climatic warming in a montane meadow by using overhead infrared heating lamps on test plots and comparing plant growth for different species with untouched adjacent control plots. This is exactly what scientists at the Rocky Mountain Biological Lab in Gothic, Colorado having been doing now for two decades on a meadow containing more than 100 plant species, the vast majority of which are those wildflowers that absorb the attention of so many of us who visit the area for the enjoyment of high mountain beauty. On this meadow, researchers have carefully kept track of soil temperatures, moisture, and other measures over the full period of time for both test and control plots, and they have measured above ground biomass for shrubs and forbs to measure responses to artificial heating. The meadow includes a dry upland portion as well as a slope between and a wet lowland segment. In the relatively dry areas of the site, Artemisia has expanded its biomass at the expense of forms in the warmed plots in comparison to controls, while in the wet areas shrubby cinquefoil (Pentaphylloides floribunda) did the same thing. In the warmed plots, sagebrush also expanded its seedling establishment. These results together infer that showy wildflowers will likely be displaced by better-adapted shrubs in a warmer world. Instead of diverse meadows in the Crested Butte wildflower wonderland, we will see instead an expanded sage scrubland.
DEFENSE
Artemisia is a visually satisfying silver-gray evergreen shrub with small three-lobed leaves and a pungent, wonderful, addictive odor emanating from its inner complements of terpenoid compounds. Pick a few leaves and squish them in your hand and breath in; you will love it! Artemisia is pictured here with Wyoming Paintbrush, an attractive but threatening root parasite that sucks up nutrients. Artemisia nonetheless overcomes this threat and is a highly successful prairie plant that does well in an arid environment. One reason for its success is its capacity to engage in chemical warfare. That wonderful “sage” smell that smashed Artemisia gives off comes from those very terpenoids that give the plant a special advantage in competing with seedlings and young plants from other species. The terpenoids inhibit the growth of seedlings and lowers the respiration rate of juvenile plants giving Artemisia a huge advantage in its competitive struggle for spatial dominance. These same chemicals also ward off some of the plant's herbivorous predators.
REPRODUCTION
In the world of wildflowers, pollinators typically do the work of getting pollen from one plant to another. For Artemisia, this work is done by the wind. Wind pollination is common among trees but less so for shrubs. The advantage is that the plant has no worries about a shortage of pollinators; the wind will invariably blow. A wind pollination strategy could be an advantage in droughty landscapes where a long dry spells periodically depress pollinator populations. Drought could thus be to the benefit of Artemisia relative to wildflowers. In a world of climate warming, Artemisia looks to have a bright future in high elevation Rocky Mountain habitats. This is a faint repayment for the stunning losses of sagebrush habitat to chaining, burning, and herbicide spraying to make room for cattle forage in the western great plains. Millions of acres of sage brush habitat have been taken over by agriculture, roads, urbanization, energy development, exotic plants, and woodlands to the detriment of threatened species such as the sage grouse. Millions more acres are threatened by cheat grass invasion. The upward extension of Artemisia into meadow habitat will be a minor compensation for past harms, and is probably not worth the habitat loss that will result for mountain wildflowers and their dependent herbivores and pollinators.
Fleabane (Erigeron) spreads itself widely through the high mountain landscape all the way from lower elevation sagebrush prairies up to the highest subalpine meadows splashing shades of purple and lavender all over the place. In spreading it is helped along by rhizomes in its root structure. The contrast of its orange disk flowers with its lavender rays can't help but get the attention of any wildflower lover, especially a photographer. Erigeron flourishes alongside sagebrush in dry, rocky prairies the lower elevations, but it also does well in high-elevation wet or dry meadows alongside a variety other showy wildflowers.
DEFENSE
Erigeron survives the challenges of summer drought pretty effectively once it comes into bloom and for this reason could be up to the challenge of climate warming. The problem is, its one vulnerability against which it lacks a defense, and that is climate change-induced increased exposure to night freezes that kill its flower buds. Early snowmelt results in Erigeron emerging ahead of schedule and facing increased exposure to freezing temperatures at night. Even though climate warming raises daytime temperatures and moves average Rocky Mountain snowmelt dates forward in time, the timing of below freezing night temperatures remains essentially unchanged. Since the 1970s, the average snowmelt date per decade has advanced by about 4 days. With snow melt dates advancing rapidly in the Rocky Mountains and the initial emergence of Erigeron following suit, more and more plants get exposed to night frost that damages the plant’s flower parts and leaves and frequently killing flower buds. In some years with early snowmelt in the Rocky Mountain Biological Lab survey plots, most or all flower buds are killed by frost. The abundance of Erigeron flowers on these plots between 1975 and 2006 has diminished as the snowmelt date moved forward in time.
REPRODUCTION
A key pollinator for Erigeron is a butterfly, Mormon fritillary (Speyeria mormonia). This same pollinator in turn depends heavily on Erigeron for nectar and successful reproduction. In years when Erigeron populations are low because of exposure to night freezing, Speyeria populations suffer and can’t lay as many healthy eggs as otherwise and populations of the next generation in the following year are reduced. Not only do night freezes harm Erigeron and Speyeria reproduction, such freezes also damage Speyeria larvae and pupae reduces their chances for survival to adulthood. A reduction in Speyeria populations may have its own cascading negative effects on other species it normally visits such as orange sneezeweed (Dugaldia hoopsii), curly golden weed (Pyrrocoma crocus), and showy goldeneye (Heliomeris multiflora). These three wildflower species will see their populations suffer reductions in pollination by Speyeria.
ASPEN SUNFLOWER (Hellianthella quinquenervis)
GETTING A LIVING
Aspen sunflower (Hellianthella) resides in high elevation montane and subalpine meadows and open woodlands. It is one of those big, showy, yellow spring and early summer wildflower that stands out and advertises to the world, and especially to pollinators, "here I am." Hellianthella ironically means "little sunflower," but these guys are by no means little, reaching as much as 1-2 meters in height and sporting always east-facing, single flower heads that reach 10cm in diameter. Their mostly basil leaves have five veins running through them if you need some security about having the plant correctly identified.
DEFENSE
Some countries have historically hired mercenary armies to defend themselves against their enemies. In a certain sense, some plants do the same thing. Hellianthella does something very much like this to defend itself against egg-laying flies whose larvae prey on its seeds. Hellianthella produces nectar in its tiny flower bracts on its flower head that is continuously harvested by ants throughout the summer. In the process of collecting nectar, ants chase off flies that would otherwise lay their eggs. The ants get a living and Hellianthella gets its seeds protected and increases its potential for reproduction. Unfortunately, Hellianthella is not so well defended against night freezes.
Some countries have historically hired mercenary armies to defend themselves against their enemies. In a certain sense, some plants do the same thing. Hellianthella does something very much like this to defend itself against egg-laying flies whose larvae prey on its seeds. Hellianthella produces nectar in its tiny flower bracts on its flower head that is continuously harvested by ants throughout the summer. In the process of collecting nectar, ants chase off flies that would otherwise lay their eggs. The ants get a living and Hellianthella gets its seeds protected and increases its potential for reproduction. Unfortunately, Hellianthella is not so well defended against night freezes.
The single most important force driving biological timing at high elevations is the date of snowmelt. If snows melt earlier, plants will emerge and bloom earlier, gaining a longer season in which to grow and reproduce. The plus of a longer growing season can be more than trumped by a dangerous stress: increased exposure to night frost from early emergence due to a shift backward in the snowmelt date and stability in the nighttime freezing temperature profile. Hellianthella lacks defenses against frost. Because it emerges and develops typically after snowmelt, and snowmelt historically occurred mostly after the danger of nighttime freezes, such defenses were unnecessary. A warming climate can cause daytime temperatures to rise above freezing earlier in the spring but works more slowly on pushing back nighttime freezing temperature. Early snowmelt moves up the timing of first emergence for Hellianthella, exposing flowers to a greater danger of frost damage. Seventy-four percent of flower buds have been damaged by frost annually on survey plots near the Rocky Mountain Biological Laboratory in recent years. The resulting loss of flowers and the seeds they produce dampens recruitment to the plant's populations and diminishes food supplies for pollinators, herbivores, and seed predators.
REPRODUCTION
A "killing frost" reeks havoc on plant parts essential to survival and and reproduction. Older plant parts such as stems and mature leaves are better able to resist frost then newer leaves and buds. A plant's reproductive organs are usually the most frost sensitive of all. Flowers and ovaries in Colorado Rocky's wildflowers, such as the Hellianthella, frequently suffer damage from early season frosts even though leaves and stems survive. Below freezing, ice crystals can form within and between cells destroying cell walls and causing plant solutes to leak away. Frost damage can also become a pathway for infection by pathogens, and freezing in soils can cause soil heaving that can damage newly emergent plants.
A "killing frost" reeks havoc on plant parts essential to survival and and reproduction. Older plant parts such as stems and mature leaves are better able to resist frost then newer leaves and buds. A plant's reproductive organs are usually the most frost sensitive of all. Flowers and ovaries in Colorado Rocky's wildflowers, such as the Hellianthella, frequently suffer damage from early season frosts even though leaves and stems survive. Below freezing, ice crystals can form within and between cells destroying cell walls and causing plant solutes to leak away. Frost damage can also become a pathway for infection by pathogens, and freezing in soils can cause soil heaving that can damage newly emergent plants.
Over the long haul, the picture on frost and plant population health is murkier. An early spring killing frost in one year will reduce seedlings in the next but also put a dent in future seed predator populations who will lack a fruitful site to lay their eggs. With less predation in the next year, seed survival will increase and a boom in seedlings will occur in year two. Predator populations will take more time to recover than seedlings giving wildflower populations such as Hellianthella a window for population recovery. Here is a plus offered by climate change--starved pathogens. Species prone to frost exposure because of early blooming may well genetically adapt with an in-species variation in timing for emergence and blooming, and this could be the case for Hellianthella. If early spring killing frosts become the norm, those plants within the species genetically prone to a later emergence and blooming time will selectively become more predominant. This won't be a free lunch because increasing populations of late bloomers will be constrained by competition for space, resources, and pollinators with suites of other species already adapted for late blooming. Evolutionary adaptation may offer some wiggle room for dealing with climate change but how much is unclear.
