Once on the path to recovery, the rare and iconic Haleakala silversword on Maui appears to be fighting for survival as rainfall declines and temperatures rise in its mountainous habitat, according to scientists.
"Silversword reproduction on Haleakala has sharply decreased since the mid-1990s, and small- to medium-size plants are often dying without flowering," said research biologist Lloyd Loope, who recently retired from the U.S. Geological Survey.
As global warming begins to change weather patterns, the Haleakala silversword and other plants could become rarer in the state, scientists warn.
In a report due for publication in the journal Global Change Biology, Loope and colleagues at the University of Hawaii and University of Arizona say rainfall has dramatically declined in the past 20 years and that air temperatures have increased significantly since the 1950s.
Loope said that while there are still many thousands of silverswords, fewer seedlings are establishing themselves.
"The future of the species appears grim," he said.
At home in Haleakala’s typically cold volcanic cinders, the silversword, or Argyroxiphium sandwicense, has long been a popular attraction for Maui’s 1 million to 2 million annual visitors. The silvery plant grows for 20 to 90 years, then sends up a flowering stalk, goes to seed and dies.
Loope started monitoring the Haleakala silverswords in 1982 with the objective of documenting their spectacular recovery from goat damage and vandalism.
But he said dry and warm weather is reversing the recovery.
From a low of about 4,000 plants in the 1920s and 1930s, the numbers grew to about 65,000 plants in 1991, thanks to federal protection as a threatened species, according to scientists.
But Loope’s study found silversword numbers declined to 28,492 in 2010 due to a more than 80 percent decrease in seedlings from the mid-1980s.
In the past 30 years, rainfall has been decreasing over many parts of Hawaii, said state climatologist Pao-Shin Chu.
Chu, a University of Hawaii professor of meteorology, said the observations are based on 110 years of rainfall records.
Tradewinds are becoming less frequent, as well.
There were 27 percent fewer tradewind days in 2009 compared with 1973, according to scientists. Less frequent trades reduce the opportunity for rainfall for the windward slopes of Hawaiian isles, including Hilo, one of the wettest spots in the country.
On the wettest side of Hawaii island, the usually majestic Rainbow Falls in Hilo has been going through a dry spell since November.
But the leeward areas will bear the brunt of a drier Hawaii, with more frequent and longer dry spells, scientists say.
This year, meteorologists say, the usual rainy season is so far a no-show over much of the state.