Several years ago, scientists noticed that recent herbarium specimens had been collected earlier in the season than specimens from decades past. Since most plants are collected when they are in flower, that meant they were flowering earlier. The easy explanation was that they were responding to the warmer temperatures caused by climate change. The trouble with that, says Larry Hufford, is that it didn’t happen with every species.
He searched the Herbarium’s database for the first date of collection for several plants common in eastern Washington, and found that the habitat a species lives in may be a factor in whether the plant is now blooming earlier than it did 100 years ago. Those in open areas, where the soil warms up sooner, are flowering as much as 2 months earlier. Those in sheltered woodland areas haven’t changed their flowering time.
But habitat was not the only factor affecting whether a species has changed its flowering time. The plant’s own life history pattern affects how the plant copes, or doesn’t cope, with environmental change. Hufford says many plants develop large underground storage structures to hold nutrients and moisture through the long dry season. That’s especially true in grasslands such as the Palouse. Such plants also make their flower and leaf buds underground, one or two years before the season when they will emerge.
“Those that are sitting underground may be especially responsive to what’s happening at ground level–to the onset of warmth and moisture,” says Hufford. Since their buds are already made and ready to go, they can respond right away when the soil warms up in spring, whether that occurs at the same time it did in years past, or weeks earlier.
With other plants, flowering is triggered by day length. It’s not affected by temperature (other than a hard freeze). Those species could be especially vulnerable to a warming environment, says Hufford. If their reliance on day length prevents them from blooming earlier, their flowers could end up getting fried by heat and drought, or they may appear too late for the insects that should pollinate them, because the insects will have been active earlier. A daylight-responsive species might fare OK if it can disperse its seeds to cooler habitats (farther north or at higher altitude), but many species don’t have that ability.
What that may mean, says Hufford, is that some species of plants are not going to cope well with climate change.
“We anticipate that some things will adapt and survive; others will migrate and survive; and those that can’t migrate or can’t evolve are going to go extinct,” he says.