More People Means More Plants: Human Activity Encourages Plant Growth

Could more people mean more plants? That's a good question. Scientists decided to take a look at satellite data in order to see how the footprint of human activity might impact patterns of plant growth.

In order to get a broad overview of how human activity could be affecting plant growth, the researchers used data from NOAA's Advanced Very High Resolution Radiometers (AVHRR), onboard a series of polar-orbiting satellites. They also used NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) instruments on the Terra and Aqua satellites. These produce a vegetation index that allowed researchers to track changes in plant growth over large areas.

In all, the researchers examined 30 years of global vegetation greenness data. They found that the magnitude of changes over the study period was different depending on the size of the nearby population. For example, near areas defined as dense settlement, the vegetation index increased by 4.3 percent. That's less than near villages, where the index increased by almost 6 percent.

"Earth's land surface has been changed across very broad scales," said Thomas Mueller, one of the researchers, in a news release. "Human intervention has increased plant growth over large scales where intensification of agriculture has occurred."

In other words, it looks as if a human footprint has caused to plant productivity to increase. More specifically, human-caused factors such as land use, nitrogen fertilization and irrigation accounted for much of the growth changes seen since 1981. The findings reveal that humans have a drastic impact on the landscape and actually encourage plant growth.

"We now know that in addition to warmer climate at higher northern latitudes, human land use at lower latitudes also has a detectable global footprint on Earth's vegetation growth," said Compton Tucker, co-author of the new study.

The findings are published in the journal Remote Sensing.