Visitors to the Cedar Tree Neck sanctuary might see a brilliant blue starflower, a state-listed box turtle, or a chestnut-sided warbler. If they are very lucky, they could spot a rhinoceros beetle, which is rarely still found on the mainland and with its characteristic horns can lift objects up to 850 times its own weight, making it one of the strongest animals on the planet.

These are only a few of the more than 100 species that Sheriff's Meadow Foundation is hoping to identify next weekend when it hosts a full-day biological inventory at its hallmark preserve on the north shore in West Tisbury. People of all ages and ecological experience are invited to join with Island naturalists on Saturday, June 16, to see how many different plant and animals species they can find on the Cedar Tree Neck property.

The event, similar to those held by other environmental organizations across the country, has a dual purpose. The observations help scientists establish up-to-date lists of found species, but perhaps more importantly, the exercise also allows members of the general public to develop an interest and appreciation for their natural ecosystems.

"We have all the incredible species out here, and yet there are so many people that have been on the Vineyard a long time and probably haven't ever seen a wild geranium or scarlet tanager, which is one of the most beautiful birds in the world," said Sheriff's Meadow Foundation executive director Richard Johnson.

"Most people know Cedar Tree Neck as a beautiful preserve and a wonderful place to walk, which it is. But we also want them to see the immense amount of biological activity and diversity all around them," he added. "Who knows? It's possible we might find something on Saturday that hasn't been seen in a while."

The inventory events also help raise awareness about the grave and growing threats to the biodiversity of the planet. Leading ecologists estimate that if development continues at its current pace, the world will lose between 30 and 70 per cent of its species by the end of the century.

Such a widespread loss would be the largest mass extinction since the end of the Cretaceous Period, some 65 million years ago. But unlike the previous five mass extinction events - which are understood to have been sparked by ice ages, asteroids or volcanic events - this sixth extinction will be almost purely man-made, through habitat destruction and global warming.

The forecast has many ecologists understandably concerned.

"I believe we have an ethical obligation to all the other species that are out there," Mr. Johnson said. "Regardless of whether you believe a creator put them there, or that they evolved over millions of years, I think it's important that we try to coexist with them. Aside from their intrinsic value, they also provide us with clean air, clean water, and a host of other services, not to mention their aesthetic beauty."

For a variety of reasons, the Vineyard remains a relative hot spot of biodiversity. Island ecology, geologic formations and conservation measures have made the Vineyard a safe haven to roughly 70 state-listed rare species, including a number of plants and insects that have all but disappeared from the mainland.

"I can't say enough about how important this place is," said Timothy Simmons, a restoration ecologist with the state Natural Heritage and Endangered Species Program. "When I started working out here in the 1980s, we were blowing people away across the country with the stuff we were still finding out here."

But Mr. Simmons added that species are being lost both statewide and on the Island at a rate that cannot be determined. No one has seen the regal fritillary butterfly on the Vineyard since he spotted it at Quenames a number of years ago.

"I'm afraid we saw the last one," Mr. Simmons said, "and we didn't realize it at the time."

Meanwhile, other efforts are underway to protect the remaining biodiversity on the Island. Sheriff's Meadow Foundation is now working with the Polly Hill Arboretum and The Nature Conservancy on a multi-year project to identify and map all the rare plants that have been found on the Vineyard. They will then contribute their findings to the Martha's Vineyard Commission and other land use organizations to prioritize the protection of certain areas that are of particular importance.

With its sea-blown woodlands, rocky cliffs, sandy beaches, streams and freshwater ponds, Cedar Tree Neck was set aside long ago as one of those special places. Assembled from a series of gifts and purchases - including land donated by Henry Beetle Hough, the late Gazette editor and co-founder of the Sheriff's Meadow Foundation - the entire preserve now totals more than 450 acres of contiguous protected land.

Mr. Johnson said that some old-growth trees in the interior of the lot appear never to have been cut. "The more you learn about the property, the more fascinating it becomes," he said.

Rare moths, dragonflies and butterflies have all been spotted at the sanctuary in the past. There are also between eight and 10 different varieties of ferns, as well as wild sarsaparilla and jack-in-the-pulpit.

Mr. Johnson said he hopes next week to find the worm-eating warbler, a tiny bird that does not nest anywhere else on the Vineyard. And he said they may get lucky and catch an early imperial moth, which was once abundant throughout New England but is now found only on the Island.

The event will begin at 7 a.m. next Saturday in the Cedar Tree Neck parking lot off Obed Daggett Road, and will continue on until 5 p.m. People can come and ago at their leisure throughout the day, and children are encouraged to participate.

"It would be very helpful to have some young curious explorers out there. They're the ones with the instincts to find the snakes and turtles and such," Mr. Johnson said.

He also believes it is important to get kids involved in their natural surroundings.

"Obviously, we protect what we love and we only love what we know. So if we want people to care about it, they need to know about it first," he said. "By getting all these people walking together in the woods, we can all learn as we go along."