Post by marchesarosa on Dec 16, 2009 13:59:25 GMT
Primary production is the production of organic compounds from atmospheric or aquatic carbon dioxide, principally through the process of photosynthesis, with chemosynthesis being much less important. All life on earth is directly or indirectly reliant on primary production. The organisms responsible for primary production are known as primary producers or autotrophs, and form the base of the food chain. In terrestrial ecoregions, these are mainly plants, while in aquatic ecoregions algae are primarily responsible. Primary production is distinguished as either net or gross, the former accounting for losses to processes such as cellular respiration, the latter not." wiki
Globally net primary productivity (NPP) has increased. As the IPCC’s WG II report (p. 106) says:
"Satellite-derived estimates of global net primary production from satellite data of vegetation indexes indicate a 6% increase from 1982 to 1999, with large increases in tropical ecosystems (Nemani et al., 2003) [Figure 1]. The study by Zhou et al. (2003), also using satellite data, confirm that the Northern Hemisphere vegetation activity has increased in magnitude by 12% in Eurasia and by 8% in NorthAmerica from 1981 to 1999."
Amazonia
In a synthesis of long term ecological monitoring data across old growth Amazonia, Phillips et al (2008) find that from approximately 1988 to 2000 not only that the biomass of these tropical forests increased but that they have become more dynamic, that is, they have more stems, faster recruitment, faster mortality, faster growth and more lianas. These increases have occurred across regions and environmental gradients and through time for the lowland Neotropics and Amazonia. They note that the simplest explanation for this suite of results is that improved resource availability has increased net primary productivity, in turn increasing growth rates, which can all be explained by a long-term increase in a limiting resource. They suggest that this no-longer-limiting resource might be CO2, although other factors (e.g., insolation or diffuse radiation) may also play a role.
Gloor et al. (2009), based on analysis of data from 135 forest plots in old growth Amazonia from 1971 to 2006 show that the observed increase in aboveground biomass is not due to an artifact of limited spatial and temporal monitoring. They conclude that biomass has increased over the past 30 years (p. 2427).
These findings are consistent with satellite data that indicate that the net primary productivity of the Amazon increased substantially from 1982–99, a period that experienced considerable global warming (see Figure 1).
Sahel
Satellite Imagery shows that parts of the Sahara and Sahel are greening up consistent with the trend recorded in Figure 1 (Owen 2009). The United Nations’ Africa Report (Figure 2) notes:
“Greening of the Sahel as observed from satellite images is now well established, confirming that trends in rainfall are the main but not the only driver of change in vegetation cover. For the period 1982-2003, the overall trend in monthly maximum Normalized Difference Vegetation Index (NDVI) is positive over a large portion of the Sahel region, reaching up to 50 per cent increase in parts of Mali, Mauritania and Chad, and confirming previous findings at a regional scale.” (United Nations 2008: 41). Figure 2: Source: United Nations (2008),
Australia
Similarly, an Australia-wide analysis of satellite data for 1981–2006 indicates that vegetation cover has increased average of 8% (Donohue et al. 2009).
