Comment on "Drought-induced reduction in global terrestrial net primary production from 2000 through 2009"

Zhao and Running (Reports, 20 August 2010, p. 940) reported a reduction in global terrestrial net primary production (NPP) from 2000 through 2009. We argue that the small trends, regional patterns, and interannual variations that they describe are artifacts of their NPP model. Satellite observations of vegetation activity show no statistically significant changes in more than 85% of the vegetated lands south of 70°N during the same 2000 to 2009 period.     

Organic aerosol growth mechanisms and their climate-forcing implications

Surface- and volume-limited chemical reactions on and in atmospheric aerosol particles cause growth while changing organic composition by 13 to 24% per day. Many of these particles contain carbonaceous components from mineral dust and combustion emissions in Africa, Asia, and North America and reveal reaction rates that are three times slower than those typically used in climate models. These slower rates for converting from volatile or hydrophobic to condensed and hygroscopic organic compounds increase carbonaceous particle burdens in climate models by 70%, producing organic aerosol climate forcings of as much as -0.8 watt per square meter cooling and +0.3 watt per square meter warming.     

A procedural approach for studying the radiation regime of infinite and truncated foliage spaces. Part II. Experimental results and discussion

A procedural approach for estimating the realisations of the penetration function was presented as a series of executable, (semi)independent and interfaceable abstractions in an earlier paper. In the present paper, the approach is validated against the turbid medium model for case of both parallel and nonparallel beam radiation extinction in an infinite stand. The predictions of the approach are in good agreement within a cumulative relative error of 4% in the case of parallel beam radiation extinction. The predictions regarding the probability of penumbra compared with the more comprehensive theory of Denholm (1981a, b) are satisfactory in foliage spaces at low values of foliage area index. Finally, to illustrate the flexibility of the approach, the statistical characteristics of the beam radiation regime in a truncated foliage space are investigated, where besides mean values of the penetration function higher order moments like the variance, the autocorrelation coefficient and the sample spectrum in space and time continuum are computed.     

A procedural approach for studying the radiation regime of infinite and truncated foliage spaces. Part I. Theoretical considerations

A procedural approach for studying the solar radiation regime of infinite and truncated foliage spaces is proposed here as an alternative to the turbid medium approach. Essentially, the procedural approach involves abstracting a real world event, i.e. transfer of radiation in an ‘obstruction medium’. The mapping of this objective and concrete event to an abstract and orderly manipulation (mathematical, logical, …) of ‘object representations’ is the content of the solution. The solution is designed as executable, (semi)independent and interfaceable abstractions which can be implemented on a computer and executed in conjunction with a digitalised foliage space. The procedural approach is capable of predicting the light extinction process in both time and space continuum, either by treating the sun as a point or a disc source of direct radiation, for infinite and truncated foliage spaces with either dense or sparse filling of obstruction elements.     

Climatic control of the high-latitude vegetation greening trend and Pinatubo effect

A biogeochemical model of vegetation using observed climate data predicts the high northern latitude greening trend over the past two decades observed by satellites and a marked setback in this trend after the Mount Pinatubo volcano eruption in 1991. The observed trend toward earlier spring budburst and increased maximum leaf area is produced by the model as a consequence of biogeochemical vegetation responses mainly to changes in temperature. The post-Pinatubo decline in vegetation in 1992-1993 is apparent as the effect of temporary cooling caused by the eruption. High-latitude CO(2) uptake during these years is predicted as a consequence of the differential response of heterotrophic respiration and net primary production.     

Climate-driven increases in global terrestrial net primary production from 1982 to 1999

Recent climatic changes have enhanced plant growth in northern mid-latitudes and high latitudes. However, a comprehensive analysis of the impact of global climatic changes on vegetation productivity has not before been expressed in the context of variable limiting factors to plant growth. We present a global investigation of vegetation responses to climatic changes by analyzing 18 years (1982 to 1999) of both climatic data and satellite observations of vegetation activity. Our results indicate that global changes in climate have eased several critical climatic constraints to plant growth, such that net primary production increased 6% (3.4 petagrams of carbon over 18 years) globally. The largest increase was in tropical ecosystems. Amazon rain forests accounted for 42% of the global increase in net primary production, owing mainly to decreased cloud cover and the resulting increase in solar radiation.     

Imaging of humic substance macromolecular structures in water and soils

Humic substances (HSs) are the natural organic polyelectrolytes formed from the biochemical weathering of plant and animal remains. Their macromolecular structure and chemistry determine their role in biogeochemical processes. In situ spectromicroscopic evidence showed that the HS macromolecular structures (size and shape) vary as a function of HS origin (soil versus fluvial), solution chemistry, and the associated mineralogy. The HSs do not simply form coils in acidic or strong electrolyte solutions and elongated structures in dilute alkaline solutions. The macromolecular structural changes of HSs are likely to modify contaminant solubility, biotransformation, and the carbon cycle in soils and sediments.     

A mathematical comment on the formulae for the aggregation index and the shape index

Ina recent paper [Landscape Ecol. 15: 591–601 (2000)] He et al. describedanaggregation index AI _i to measure pixelaggregation within a single class i. We show that thecommonly used shape index SI _i is related to theproposed aggregation metric as SI _i =(A _i) +AI _i(1 –(A _i)), with(A _i) dependent on class areaA _i only. Moreover, it is shown that thenormalized shape index, SI _i ^*,equals (1 – AI _i). We conclude thatAI _i does not provide any information notprovided by SI _i, orSI _i ^*.This revised version was published online in May 2005 with corrections to the Cover Date.