DWARF BLUEBELLS (Mertensia fusiform)
TALL BLUEBELLS (Mertensia ciliata)
GETTING A LIVING
Dwarf bluebells (M. fusiformis) is among the earliest blooming wildflowers in the Rocky Mountain subalpine meadows near Crested Butte, Colorado, emerging and flowering just one or two weeks after snowmelt. A plant of this species possesses thick leaves covered with stiff hairs that give it a measure of protection against frosty nights. The plant typically reaches peak blooming in early June, meaning that it emerges in May, a sometimes chilly month when nighttime freezes are common. The special advantage of early-blooming is an absence of competition from very many other species for resources and pollinators, more moisture, and less shading by other vegetation. The danger of arriving early is damage to plant parts from night frosts and a scarcity of pollinating bumble bees whose own emergence and activity can be retarded by frosty nights. As emphasized in earlier posts, a warming climate induces early snowmelt and warmer early spring days, but leaves the timing of night frosts largely unchanged.
Dwarf bluebells (M. fusiformis) is among the earliest blooming wildflowers in the Rocky Mountain subalpine meadows near Crested Butte, Colorado, emerging and flowering just one or two weeks after snowmelt. A plant of this species possesses thick leaves covered with stiff hairs that give it a measure of protection against frosty nights. The plant typically reaches peak blooming in early June, meaning that it emerges in May, a sometimes chilly month when nighttime freezes are common. The special advantage of early-blooming is an absence of competition from very many other species for resources and pollinators, more moisture, and less shading by other vegetation. The danger of arriving early is damage to plant parts from night frosts and a scarcity of pollinating bumble bees whose own emergence and activity can be retarded by frosty nights. As emphasized in earlier posts, a warming climate induces early snowmelt and warmer early spring days, but leaves the timing of night frosts largely unchanged.
By the time M. fusiformis has gone to seed, it's late arriving tall bluebell (M. ciliata) cousin is in bloom, with its peak flowering occurring sometime in the first or second week of July. This species achieves a height of a meter or more with a single plant often covered with a lineup of multiple hanging flowers against a lush background of soft, hairless green leaves. It expands its coverage locally through clonal colonies created by networks of rhizomes, and favors wet meadows and stream-sides at subalpine and lower alpine elevations.
DEFENSE
A changing climate affects both dwarf M. Fusiformis and tall M. Ciliate, moving peak blooming forward in time for both species as the date of spring snowmelt advances. The early blooming M. Fusiformis defends itself against night frosts with preformed underground ice-resistant flower buds and thick, ice resistant, hairy leaves, and avoids substantial losses of flower populations in years of early snowmelt and increased exposure to freezing night temperatures. Simply put, this species is pre-adapted to freezing from early blooming's normal increased exposure to frost. Its later blooming relation, M. Ciliata, does, however, suffer lower flower populations in early snowmelt years, but frost is unlikely to be the cause because it blooms so late in the summer. The problem for this species is likely to be a shortage of moisture caused by a lengthening and intensifying of the usual summer drought between snowmelt in May and the arrival of the summer monsoon rains in July and August. The earlier the snowmelt, the longer the drought.
Plants adapt to early season environmental variability in the form of frost damage or shortage of pollinators by producing flowers that develop later or last longer if un-pollinated giving them a shot at delayed pollination. Some also develop a capacity for early self-pollination, but this is not the case for outcrossing M. Fusiformis. For early blooming M. Fusiformis, a late snow melt in 2008 led to a short but intense and productive flowering period. An early snow melt in 2007 caused a longer flowering season and more late opening flowers. The total number of flowers didn't differ between years but the flowering peak shifted forward in 2007 and early arriving flowers did get exposed to some frost damage. Extended longevity of unpollinated flowers and the production of numerous late season flowers may be giving this species some resilience against climatic warming and the damage of early snowmelt. Possibly because of plant damage from hard frosts, seed set was nonetheless lower in 2007 than 2008.
As already noted, climate change and early snow melt causes peak blooming to jump farther forward for M. Fusiform than it does for its later blooming taller relation, M. Ciliata. This growing gap could leave bumble bees in a lurch without a source of nectar and pollen in some localities, potentially diminishing their populations. This could in turn create a pollinator shortage for the late blooming M. Ciliata and eventually cause its population to decline. Fortunately, so far researchers don't find any evidence of an actual pollinator shortage. Whatever the cause, in early snowmelt years, the total number of flowers for late blooming M. Ciliata drops substantially, and some locations plant populations disappear completely where they have been observed in the past. The most likely culprit is a lengthened and intensified midsummer drought caused by earlier snow melts.
To sum up, so far the early-blooming M. Fusiformis has stood up to the challenge of climatic warming, probably because of its pre-adaptation to the night frost problem, but late-blooming M. Ciliata populations and reproduction appear to be suffering from midsummer moisture shortages occurring because of a warming climate.
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