California island native plants recovery

This video from the USA says about itself:

18 July 2007

On this segment of “Wonders of the West” we visit Santa Cruz Island and see some humpback whales along the way.

From the University of California – Santa Cruz in the USA:

Native vegetation makes a comeback on Santa Cruz Island

Sep 17, 2014 by Kathleen Wong

On islands, imported plants and animals can spell ecological disaster. The Aleutians, the Galápagos, the Falklands, Hawaii, and countless other archipelagoes have seen species such as rats, goats, brown tree snakes, and exotic grasses delivered by human visitors. Many of the newcomers have flourished to the point of driving unique island species extinct.

People are now trying to reverse the damage of these ill-advised translocations. Step one is obvious: eradicate the invaders. Step two, however, isn’t so clear. Experts argue over whether expensive, time-consuming, and labor-intensive restoration is necessary, or if simply removing non-natives is enough.

Now a study set in California’s Channel Islands indicates eradication alone can jumpstart recovery. Led by two UC Santa Cruz undergraduates, the research shows native shrubs reclaiming the island on their own nearly three decades after removal of sheep and other grazers. The study is published in the journal Restoration Ecology.

“Taking out those sheep triggered a large change in the vegetation; it was going from grassland back to coyote brush or California sage, to a more diverse community,” said Nissa Kreidler, one of the study’s student authors.

“People spend millions of dollars on restoring island ecosystems. So it’s a huge finding that passive recovery can be sufficient and under certain circumstances, active restoration is sometimes not necessary,” said Roxanne Beltran, the paper’s lead author.

Intensive supercourse

The paper grew out of an assignment in the Conservation and Ecology in Practice “supercourse” both students took in spring 2012. Taught primarily by UCSC professors Don Croll (ecology and evolutionary biology) and Erika Zavaleta (environmental studies), and UCSC Natural Reserve System Director Gage Dayton, the class spends the entire quarter learning techniques for ecological and conservation research while visiting the protected wildlands of the UC Natural Reserve System. Students read previous research pertaining to local ecology and management, then design and conduct their own short-term field studies.

On Santa Cruz Island Reserve, humans have had a major impact on land conditions. The first sheep arrived 150 years ago, to be joined by cattle, horses, and feral pigs. These large herbivores completely denuded some areas, and transformed others into non-native grassland.

The effort to eradicate sheep, cattle, and horses from the island began in 1981 and was largely complete by 1999; feral pigs were eliminated by 2007. Then the land was left alone. At nearly 100 square miles in size, Santa Cruz Island is far too large to actively replant native vegetation.

Initially, removing grazers caused unforeseen consequences. Ten years on, non-native grasses had taken over a larger share of the island. Dirk Van Vuren, now an ecology professor at UC Davis, documented that initial shift in the late 1980s and again in the 1990s. He compared the plants on either side of a sheep exclusion fence using photos and vegetation transects.

While deciding on a class project for the island, Beltran said, “we looked at his old black-and-white photos and saw herbivores had caused more damage than we could see currently. We decided to see exactly how much the island had recovered passively.”

Native vegetation makes a comeback on Santa Cruz Island

Promising results

The results were so promising that Beltran and Kreidler decided to develop them into a publishable paper. …

Back in Santa Cruz, the students compared photos shot from the same island vantage points in the early 1980s, late 1990s, and 2012. They found large areas once occupied by grasses replaced by woody shrubs, a shift that nearly doubles the amount of carbon stored on the island. Places grazed down to bare soil were being recolonized by plants, reducing soil erosion.

The vegetation transects told a similar story. The land area covered by grasses dropped by half, with native coastal sage scrub making equivalent gains. Aerial surveys and vegetation maps of the island from The Nature Conservancy, which manages the land, provided additional evidence of these changes.

“Thirty years after eradication, we’ve shown there is enough resilience for the vegetation to restore itself,” said Croll, a coauthor on the paper. “The findings help set expectations on how long recovery can take. Funders want immediate results. But sometimes it’s worthwhile to take the time to wait rather than incur the huge expense of active restoration.”