Sunday, July 6, 2008

Where aliens dominate, natives retreat

It won't be a surprise for anyone who has wandered under a canopy of eucalyptus or clambered through a patch of strawberry guava that you won't find many native plants there.

(Image: Young leaves of 'ōhi'a, one of the overstory trees that can mark a native forest.)

Researchers confirm that in a paper in the journal Forest Ecology and Management, entitled, “Limited native plant regeneration in novel, exotic-dominated forests on Hawai'i.”

Interestingly, they say that in some locales, natives do okay under an alien canopy.

But not in Hawai'i.

The authors are Joseph Mascaro and Kristen Becklund of the University of Wisconsin, at Milwaukee and Madison, respectively, and Stefan Schnitzer o the Institute for Pacific Islands Forestry of the U.S. Forest Service.

“Recent evidence from Puerto Rico suggests that exotic-dominated forests can provide suitable regeneration sites for native species and promote native species abundance, but this pattern has been little explored elsewhere,” they wrote in the article's abstract.

To test the concept in Hawai'i, they studied plants in 46 sites and found, essentially, that the opposite is true in these islands.

They found that small native trees were missing entirely from 28 sites and were rare in all the others.

“Natives were never the dominant understory species'; in fact, they accounted for less than 10 percent of understory basal area in all but six sites, and less than 4 percent on average,” they wrote.

Where they did find a few natives, it tended to be near native-dominated forests, and the plants tended to be remnants from before the invasion of aliens, rather than the “products of active recolonization by native species.”

It's bad news for Hawaiian wildlands, since it means that without human intervention, the outlook is grim for native forests under threat of invasion.

“Hawaii's exotic-dominated forests can emerge, via invasion, without human disturbance and native Hawaiian plants are largely unable to colonize them once they appear,” they write.

© 2008 Jan W. TenBruggencate