August 2, 2010

Plant Productivity on the Rise in China (and Birds Love It!)

Filed under: Adaptation, Animals, Plants

We like birds and always have a special place in our essay series for good news about their future. A recent article in Acta Oecologica deals with bird diversity in China and the news could not be better, particularly given the results from three other recent studies from China that find that find that plant productivity—a primary determinent of species richness of China’s birds—is on the rise, quite probabily a result of rising atmospheric carbon dioxide levels.

A team of four scientists from Illinois and two institutions in China developed “a comprehensive dataset of bird species richness in China, based on the literature.” Qian et al. state “We searched all relevant literature sources, including books, theses, journal articles, survey reports of nature reserves, and other technical reports. Our searches turned up 417 localities in China. Most of these localities are protected areas (including nature reserves, national parks, and scenic sites).” They used multivariate statistical techniques to link their species richness data to a variety of environmental variables. One of the variables was the widely-used satellite-based normalized difference vegetation index (NDVI) which in the authors’ words “is widely recognized as a measure of plant productivity and as a major determinant of breeding bird richness.” Qian found that “Of all environmental variables examined, normalized difference vegetation index, a measure of plant productivity, is the best variable to explain the variance in breeding bird richness”. They note that many others have found similar relationships between bird diversity and NDVI at a variety of spatial scales.

This raises an interesting question about what’s been happening to NDVI in China, and to our pleasant surprise, three recent articles bring great news for the birds. The first article was prepared by five scientists with Peking University and the University of Iowa, and it involves trends in NDVI for temperate grasslands in China. Piao et al.’s (2006) figure below (Figure 1) summarizes what they found for most of northern China over their 1982 to 1999 study period – the NDVI is going up at a highly statistically significant rate, precipitation has not changed, temperature has risen, and the overall soil moisture rate is unchanged. They note that “Average NDVI of the study area increased at rates of 0.5%/yr for the growing season (April–October), 0.61%/yr for spring (April and May), 0.49%/yr for summer (June–August), and 0.6%/yr for autumn (September and October) over the study period.” In trying to explain the rise in NDVI, Piao et al. state “atmospheric CO2 fertilization effect, increased nutrient deposition, and human activity such as grazing management, land abandonment due to migration into urban areas may also partly account for the observed NDVI changes. Elevated atmospheric CO2 concentration will lead to increase in water use efficiency through decrease in stomatal conductance, and thereby promote vegetation growth particularly in water stressed ecosystems” (emphasis added). We get the message – the grasslands of China are doing great and we are sure the birds are thankful for their ever-increasing bounty!

Figure 1. Interannual changes in (a) area-weighted growing season normalized difference vegetation index (NDVI), (b) growing season precipitation (mm), (c) growing season mean temperature (ºC), and (d) Thornthwaite’s
moisture index (Im) over the period 1982–1999 for temperate grasslands in China (from Piao et al., 2006)

Some of the same scientists in the previous article prepared another manuscript on the grasslands of China, this time focusing on trends in the total biomass of the grassland areas. You probably guessed already what they found? The Piao et al.’s (2007) graphic below (Figure 2) shows a near monotonic increase in biomass over their 1982 to 1999 time period. They state with regard to biomass carbon (C) “Biomass C stocks averaged 145.4 Tg C for the study period for a total area of 334.1 × 104 km2, and have increased by 17.7 Tg C (1 Tg = 1012 g) from 136.3 Tg C in the early 1980s (average of 1982–1984) to 154.0 Tg C in the late 1990s (average of 1997–1999), with an annual increase of 0.7%.” Once again, the birds must be thrilled with the extra biomass!

Figure 2. Interannual variations in aboveground biomass C for China’s grassland over the period of 1982–1999 (from Piao et al., 2007).

Our critics might argue that many birds live in forests, not grasslands. Go to Forest Ecology and Management and you will find more great news from many of these same scientists. Tan et al. used the satellite-based NDVI data to estimate carbon stocks in the forests of China, and they report that over the period 1982 to 1999 “The forest biomass C stock has increased by 7% with an annual rate of 0.0082 Pg C” (a Pg C is a billion tons of carbon). They state “The forest biomass C pool has increased by 0.0082 Pg C/year over the last two decades, but, the mechanisms of this increasing still remain uncertain. Increasing atmospheric CO2 concentration, nitrogen and phosphorus deposition, climate changes, and regrowth of forests and afforestation might be the possible mechanisms of this increase” (emphasis added).

With climate change, an exploding economy, and world-renowned pollution levels in cities, we might have thought forests and grasslands in China, and the birds that depend on the forests and grasslands would be in trouble trying to cope with so many anthropogenic influences. But when we looked into the scientific literature on these subjects, we find the grasslands and forests are thriving—at least partly in response to elevated atmospheric carbon dioxide, and we suspect the birds of China couldn’t be happier with the situation.


Piao, S., J. Fang, L. Zhou, K. Tan, and S. Tao. 2007. Changes in biomass carbon stocks in China’s grasslands between 1982 and 1999. Global Biogeochemical Cycles, 21, GB2002, doi:10.1029/2005GB002634.

Piao, S., A. Mohammata, J. Fang, Q. Caia, and J. Feng. 2006. NDVI-based increase in growth of temperate grasslands and its responses to climate changes in China. Global Environmental Change, 16, 340–348.

Qian, H., S. Wang, Y. Li, and X. Wang. 2009. Breeding bird diversity in relation to environmental gradients in China. Acta Oecologica, 35, 819-823.

Tan, K., S. Piao, C. Peng, J. Fang. 2007. Satellite-based estimation of biomass carbon stocks for northeast China’s forests between 1982 and 1999. Forest Ecology and Management, 240, 114–121

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