Condensed from an article published on NASA’s Earth Observatory Website Posted on February 7, 2008
|Photo å©2007 John Kimbler|
If we had the time and knew how to listen, Nature could tell us thousands of stories about how climate change is affecting life on Earth. From every forest, every wetland, every ocean come more stories than there are scientists to listen. Several years ago, NASA oceanographer and amateur beekeeper Wayne Esaias realized he was overhearing one of those stories. The talk of climate change was coming from his bees.
The 25-year NASA veteran has made a career studying patterns of plant growth in the world’s oceans and how they relate to climate and ecosystem change, first from ships, then from aircraft, and finally from satellites. But for the past year, he’s been preoccupied with his bee hives, which started as a family project around 1990 when his son was in the Boy Scouts. According to his honeybees, big changes are underway in Maryland forests. The most important event in the life of flowering plants and their pollinators, flowering itself, is happening much earlier in the year than it used to.
The discovery has driven Esaias to completely remodel his ocean-centric career. He is now trying to rally financial support and scientific enthusiasm for the development of a national network of beekeepers whose hive observations can give scientists direct evidence of how climate change is affecting flowering plants and their pollinators. The information could refine predictions of the productivity of agricultural and natural ecosystems, help predict the spread of invasive species, and provide a tangible, missing link between satellite-based indicators of seasonal patterns of vegetation and the real world.
The Story of Honeybees
Europeans imported the honeybee along with most of our food crops when they came to America more than 400 years ago. When it comes to America’s agricultural productivity, it’s almost impossible to overestimate how dependent we have become on honeybees. Agriculture depends on managed honeybees not only because some crops, such as the 700,000 acres of almonds in California, can only be pollinated by honeybees, but also because our industrial-scale system of crop production hinges on huge numbers of pollinators being available in a very limited window of time, sometimes as short as a few days.
“When you grow a large crop for agriculture, you might have hundreds acres of, say, cucumbers all being managed to bloom at the same time, to be harvested at the same time, for efficiency,” Esaias explains. That kind of uniformity isn’t natural for native bees and other pollinators, which need a diverse and season-long food supply. “The only way for growers to ensure pollination is to have somebody bring in a colony of bees, 1 to 2 colonies per acre, and put them out in the field,” says Esaias.
|Bee hives set out in a cherry orchard to pollinate blossoms.|
A few stints pollinating cucumbers over the course of a summer, however, isn’t enough to support a hive. From spring until fall, worker bees forage from dawn until twilight over a radius of up to about 5 kilometers from the hive, bringing back pollen and nectar from plants that are blooming. They turn the nectar into honey, which feeds the colony in the winter or when nectar and pollen are scarce. As the bees stockpile honey, the hive weight goes up. In Maryland, the primary nectar source for honeybees is flowering trees, namely tulip poplar, black locust, basswood, and holly.
“During the peak of the nectar flow, a good, strong colony can gain 10 to 20 pounds in one day,” he says. “In Maryland, that goes on for a few weeks in late spring, and then, suddenly, it’s over.” For the remainder of the year, the weight of the hive dwindles as bees sustain themselves on the honey and pollen they have stockpiled during their three-to-four-week feeding frenzy. It was through this annual yo-yoing of weight gain and loss that Esaias’ bees began to tell him their story of climate change.
The family had “adopted” three hives around 1990 as part of his son’s participation in the Boy Scouts. When they went to pick up the hives from the assistant scout master, who was moving out of state, he also gave them a large rectangular scale, like the one a veterinarian would use for weighing your pet. Esaias came to realize that the scale was invaluable for keeping tabs on the health of the colony.
“Based on the weight of the hive you can tell if you need to give them supplemental food, when the nectar is coming in the area, when to add supers [stackable chambers added to the top of the hive where the bees store extra honey], and when to harvest the honey,” he explains.
|Wayne Esaias, a NASA scientist, records the weight of
his beehives. Once a hobby, his beekeeping has
developed into a scientific pursuit. Esaias believes that a
beehive’s seasonal cycle of weight gain and loss is a
sensitive indicator of the impact of climate change on
flowering plants. (Photo courtesy Elaine Esaias)
“Nearly every night in the spring and summer someone would go out weigh the hives,” he said. “And I guess just because I am a scientist, I started writing these things down. Even after my kids graduated and went off to school, I still kept the records. One day, I just decided to plot it all up [on a graph], just out of curiosity. And what I saw was that although you do see a lot of variability from year to year due to climate events, there was a very noticeable long-term trend, with flowering and nectar flows getting earlier and earlier in the year.”
“Once I saw this trend, I wondered, well, how does what I see in my back yard compare with what other people have seen in this area? I found basically two datasets for comparison: one from 1922-23 in what is now downtown Chevy Chase, when it used to be a USDA agricultural research center; another study with hive weights was done by a researcher at the University of Maryland.”
To compare his data to older records, he had to adjust for the difference in elevation; his home near Clarksville is in Maryland’s Piedmont, while the other locations were down on the coastal plain. “But once I adjusted for these regional differences based on elevation,” he said, “you see this dramatic advance in peak flowering time of almost a month.”
|Hive weight is an important indicator of hive health.
(Photo courtesy Wayne Esaias.)
Esaias scoured scientific books and papers for observations that could corroborate the story his bees were telling about how flowering times were changing in Maryland. He discovered that for several decades, Smithsonian botanist Stan Shetler had been keeping tracks of flowering dates for trees in and around Washington, D.C., based on calls from city residents that their backyard trees, including tulip poplar and black locust, two of the most important nectar producers in the state, were in bloom. Those records showed an advance in flowering (earlier blooming) beginning as far back as 1970.
“My hive records don’t go back that far. They start in 1992,” says Esaias. “But what’s interesting is that when I project the trend I see in my data back in time, it seems like the changes in my area could have started in the mid-1980s, which is about 15 years later than the changes began in D.C. I wondered, why is that?”
Esaias thinks that urbanization is mostly responsible for the changes in flowering. Urbanization would also explain why flowering seems to have been affected earlier in D.C. than in his “backyard.” Urbanization creates a heat island, an area where surface temperatures are much higher than surrounding rural areas. Pavement, less soil moisture, air pollution, and heat generated by energy use conspire to raise the city temperatures as much as 10 degrees Fahrenheit (6 degrees Celsius) over surrounding areas. As cities get bigger, the urban heat island expands, too. As temperatures rise, spring comes earlier. Earlier leaf emergence and flowering have been observed in numerous cities across the world.
“I am farther out from the city, and it took 15 years for the urban heat island effect to get here,” he concludes. Between urbanization and global warming from greenhouse gases, temperatures will continue to rise in coming years; the acceleration in flowering times that Esaias’ honeybees have documented so far may not be the end of the changes.
Will Plants and Pollinators Get Out of Sync?
According to Esaias, the changes aren’t just dramatic, they’re also kind of scary. The fertility of most flowering plants, including nearly all fruits and vegetables, depends on animal-mediated pollination. As the pollinators move from flower to flower for nectar–a high-energy, sugary enticement, the plants dust them with pollen, which the animals transfer from flower to flower.
“Flowering plants and pollinators co-evolved. Pollination is the key event for a plant and for the pollinators in the year. Some species of pollinators have co-evolved with one species of plant, and the two species time their cycles to coincide, for example, insects maturing from larva to adult precisely when nectar flows begin,” says Esaias.
|Individual grains of pumpkin pollen hitch a ride on a
honeybee. As bees move from flower to flower, they
carry pollen with them, fertilizing nearby plants. This
relationship between plants and pollinators may be
affected by climate change.
(Photo å©2007 John Kimbler)
The concern is that in thousands upon thousands of cases, we don’t really know what environmental and genetic cues plants and pollinators use to manage this synchrony. According to ecologist David Inouye of the University of Maryland, some plant-pollinator pairs in a particular area likely do respond to the same environmental cues, and it’s reasonable to expect they will react similarly to climate change. But other pairs use different cues, the pollinator emerging in response to air temperature, for example, while the plant flowers in response to snow melt. Migratory pollinators, like hummingbirds, seem to be particularly at risk, since climate change will almost certainly affect different latitudes differently. There is no guarantee that the thousands of plant-pollinator interactions that sustain the productivity of our crops and natural ecosystems won’t be disrupted by climate change.
As an example of how environmental cues for the timing of significant life cycle events might become uncoupled, Esaias points out that you don’t have to look any further than his bees. “What limits the growth of my honeybees in the spring are those coldest of the cold nights, because what is happening in their colony is that they are in a cluster, and they have to keep the queen and the larvae at 93 degrees. They do that by eating lots of honey, and tensing their muscles, and generating heat.”
When it gets warm enough outside for them to maintain a temperature of 93 degrees, they start laying eggs around the edges of the cluster, and the cluster begins to expand. As long as the workers can keep the brood temperatures at 93 degrees, the eggs will grow into adult bees in about 3 weeks. But if a single cold, cold night in March intervenes, says Esaias, then eggs at the edges that the workers can’t keep warm will die. The cluster shrinks, and the colony must begin again.
|Broods of honeybee larvae depend on warm
temperatures to survive. An early-spring cold
snap can kill the developing workers at the outer
edges of the cluster at the heart of the hive. This
setback slows the hive’s preparations for the
honey-production season. If plants are not
affected in the same way, the bees may become
out of sync with their primary food source.
(Photo å©2005 Max Westby)
“Trees, on the other hand, may not feel those cold temperatures in the same way because their roots are well insulated,” Esaias suggests. The sun-warmed ground is slower to chill than the air, so trees may not be feeling the cold snaps in the same way that the bee colony does. Thus, flowering may occur before the bee colony has built up enough workers to take advantage of it, which means the hive will struggle to stockpile enough honey to sustain them through the next winter.
“I am not saying they are definitely different,” Esaias stresses, “I am just saying there are good reasons to think that their response to climate change would not be identical. The truth is we don’t know what the relationships are between weather and climate, pollinators, and plants for thousands of species.”
Since crops alone can’t sustain the pollen and nectar requirements of honeybee colonies, the potential for honeybees and other pollinators to become out of sync with their most important natural food sources is something that concerns Esaias. A national network of scale-equipped honeybee hives, Esaias believes, would reveal when flowering occurs now and help us better predict how plants and pollinators in both natural and agricultural ecosystems will, or won’t, adapt to climate change in the future.
Perhaps the best part of the whole idea, according to Esaias, is that the 1-to-5-kilometer-radius area in which a hive’s worker bees forage is the same spatial scale that many ecological and climate models use to predict ecosystems’ responses to climate change. It also matches the spatial scale of satellite images of vegetation collected by NASA’s Terra and Aqua satellites. This similarity of scale means that all these ways of studying ecosystems could be integrated into a more sophisticated picture of how plant and animal communities will respond to climate change than any one method alone could provide.
“In my mind, the data from a network of hive scales would be an essential addition to ecosystem models,” Esaias concludes. “If we want to relate models and satellite data to something as tangible as food for people and wildlife, if we want to be able to predict where the thousands of species that occupy ecosystems today will survive in the future, we need to monitor when that plant-pollinator interaction is occurring.”
“The best part,” Esaias says excitedly, “is that the observers we need are already out there! The bees are already collecting these data for us.” About half of the approximately 6 million honeybee colonies in the United States are kept by individual or family-scale beekeepers. Esaias’ vision is to develop a how-to guide, an automatic data recorder, and the computer and networking resources at Goddard Space Flight Center that would be needed to collect and preserve the data. Ideally, a hive data recorder would be hooked up to the Internet so that volunteers’ hive weights could appear on a Website hosted at Goddard. His goal is to get the cost per kit below $200 and then to get NASA funding to outfit a network of volunteers, HoneybeeNet, and analyze their data. He’s been working with local bee clubs in Maryland to prototype the idea, rounding up some 20 volunteers who already have or are willing to purchase their own scales.
In the meantime, he and several colleagues at NASA, the Department of Agriculture, and several U.S. universities submitted a proposal to NASA to integrate satellite, hive data, and the results from ecological models into an early-detection system operated by the U.S. Geological Survey that monitors the spread of invasive species. By using satellite data on landscape and vegetation type along with honeybee hive data, they hope to improve predictions of the spread of the African honeybee, an aggressive and unpredictable species of bee that is colonizing the southern United States. In addition, satellite and ecological model information on vegetation could help scientists pin down the cause or causes of “colony collapse disorder,” which wiped out 30 to 90 percent of many beekeepers’ colonies in the 2006-07 winter.
He feels a sense of urgency about getting the HoneybeeNet going now. “All I can say right now is that much of what is in the [scientific] literature about the dates of the Maryland nectar flow is wrong; it’s obsolete data. We are headed into an era of global change across the country, and we don’t even know where we are starting from! How are we possibly going to predict change? If we don’t get on board quick, we’re gonna miss the boat.”
|(Photo å©2007 Bob Shaw)|
Abu-Asab, M. S., Peterson, P. M. Shetler, S. G. and Orli, S. S. (2001). Earlier plant flowering in spring as a response to global warming in the Washington, DC, area. Biodiversity and Conservation 10:597-612. doi:10.1023/A:1016667125469
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