An American beech tree grows in Judy Wagner's backyard. For the past 18 years the retired health policy analyst has watched as the tree grew. First it became taller than the privacy fence and now it measures about 40 feet tall, standing over her townhome in Bethesda, Md.

It's a tree she knows well and for three years she has put that knowledge to use. Every few days Wagner completes a short online survey, cataloguing the amount of leaves and buds she sees on the tree. Her answers are recorded in a national database.

"It's a very low-energy, low-effort kind of activity," Wagner says. "And yet it makes me watch that tree."

As humble as it appears, Wagner is making a contribution to scientific research.

She and thousands of other so-called citizen scientists share observations in nature with Nature's Notebook, the digital centerpiece of the USA National Phenology Network. Relying on both professional and amateur data from across the country, the network studies and analyzes the life-cycle events of plants and animals.

Recording when trees bloom, birds nest and species migrate is important in the analysis of where and how our climate is changing. And it's difficult to do alone.

"There [are] only so many scientists out there," says Jake Weltzin, an ecologist with the U.S. Geological Survey and the executive director of the USA National Phenology Network.

"By engaging the public, or people who have not historically participated in science … they can actually contribute information on a much broader spatial scale and for a much longer time period than scientists could by themselves."

Scientific observation isn't always the result of billion-dollar satellites or research labs. It can happen in a backyard.

From the field to the lab and back again

Citizen science is nothing new. For a long time, the field of science stretched well beyond the walls of ivory towers.

Thomas Jefferson, among other notable 18th-century figures, made important contributions to science while earning his place in history for other reasons. In the 19th and 20th centuries, as the field grew increasingly complex, professional science was born.

Since then, groups like the Audubon Society have looked for ways to engage the public in scientific inquiry. For more than 100 years, the conservation group has collected data from cold-braving, bird-watching volunteers during its annual Christmas Bird Count -- originally developed as a less-lethal alternative to the tradition of hunting birds at Christmas.

In the digital age, citizen science takes on a new realm of possibilities.

"We can share information almost in real time," Weltzin says. "We can tweet our findings, we can accumulate information, we can aggregate it, we can analyze it [and] we can share it with other nations."

The immediacy and accessibility of social media and smartphone apps has a flattening effect on science, Weltzin says, making the scientific process relevant once again to the armchair enthusiast.

"To participate in a meaningful scientific activity like tracking phenology, you don't need a Ph.D. anymore," Weltzin says.

Going further afield

If such a thing as extreme citizen science exists, its champion is Adventurers and Scientists for Conservation.

Founded in 2011, the organization serves as a matchmaker and training agency, connecting scientists looking for data in hard-to-reach places with thrill-seeking explorers willing to go to great lengths to get it.

It's the brainchild of Gregg Treinish who came to a realization after hiking the Appalachian Trail and the length of the Andes Mountains.

"I had a profound desire to be doing more with my time outside," Treinish says.

The interest in benefiting science is one shared by many in the adventurer community he says, and is appreciated by researchers who may not have the funds or the wherewithal to, say, climb Mount Everest.

"If a scientist [needs] data, they can come to us and we'll find them athletes who are willing to go wherever they need it," Treinish says. "If you're an adventurer and you come to us, we can then plug you into somebody who needs research."

One doesn't even need to climb a mountain to marry outdoorsmanship with an inquisitive mind.

Earlier this month the group debuted the Road Kill Survey for Road Bikers. With a few taps on their smartphones, cyclists can report sightings of live and dead animals along highways. The data are shared with researchers at the University of California, Davis Road Ecology Center, who look at the effects of transportation systems on landscapes and communities.

Armed with slick, data-driven Web sites, citizen scientists can even plumb the depths of the universe.

Planethunters.org, a project of Zooniverse.org, lets user sift through images collected by NASA's Kepler spacecraft to look for evidence of planets that might otherwise be overlooked by computer analysis.

"The human brain is particularly good at discerning patterns or aberrations and experiments have shown that when many people work together, the collective wisdom of the crowds can be better than an expert," the project's Web site states.

Strength in numbers

The distributed approach calls to mind crowdsourcing -- a 21st-century buzzword used to describe large numbers of people working collaboratively to solve a problem.

But some in the citizen science community shy from the label, saying their projects tend to be more formalized and often involve the gathering of new information, not just the cataloging of existing information.

"These projects are all pretty structured," says Bruce V. Lewenstein, a professor of science communication at Cornell University, who studies public understanding of science. "In order for them to be generating data that's producing reliable knowledge about the natural world … you better have people following the protocol."

The resulting data, Lewenstein says, are surprisingly accurate. Participants are self-aware of the fact that they are amateurs and therefore put more effort in following instructions closely, Lewenstein says.

Even if they do get something wrong, the sheer quantity of data associated with citizen science projects lets researchers more easily spot and correct aberrations.

Some projects send professional scientists to independently verify the contributions of amateur scientists. The professionals are often pleased with what they find, Lewenstein says.

"It looks like the amateurs are getting better data than the professionals, or at least as good as the professionals," he says.

iNature

With noses perpetually buried in phones and tablets, some say there's little time for an authentic engagement with the natural world. Perhaps we suffer from a "nature-deficit disorder," as proposed in the 2005 book, "Last Child in the Woods," by Richard Louv.

But Weltzin is more optimistic. As executive director of the USA National Phenology Network, he sees firsthand the illuminating effects of technology.

He envisions a "network of people who are learning about science, learning about climate change, learning about the natural world because they're actually engaging with it, using the technology as an interface."

In other words, screens are a distraction but they are also a gateway to engagement.

If backyard phenologist Judy Wagner is any indication, Weltzin might be onto something.

"It gets you more connected to the issues both in an advocacy sense and in understanding research," Wagner says. "I think it's just the greatest as a concept."

Besides, it gives her a reason to pay attention to the American beech in her backyard, a species of trees she claims as her favorite. They are, in her words, the most stately and beautiful of all trees.