Soil Chemical Analysis

Statistics for Spatial Data.

https://hal.archives-ouvertes.fr/hal-00457602/document

A global overview of drought and heat-induced tree mortality reveals emerging climate change risks for forests

This paper contrasts the natural and anthropogenic controls on the conversion of unreactive N2 to more reactive forms of nitrogen (Nr). A variety of data sets are used to construct global N budgets for 1860 and the early 1990s and to make projections for the global N budget in 2050. Regional N budgets for Asia, North America, and other major regions for the early 1990s, as well as the marine N budget, are presented to highlight the dominant fluxes of nitrogen in each region. Important findings are that human activities increasingly dominate the N budget at the global and at most regional scales, the terrestrial and open ocean N budgets are essentially dis- connected, and the fixed forms of N are accumulating in most environmental reservoirs. The largest uncertainties in our understanding of the N budget at most scales are the rates of natural biological nitrogen fixation, the amount of Nr storage in most environmental reservoirs, and the production rates of N2 by denitrification.

/pdf/nitrogen-cycles-past-present-and-future-1zdbw0976r.pdf

Nitrogen cycles: past, present, and future

Future climate warming is expected to enhance plant growth in temperate ecosystems and to increase carbon sequestration. But although severe regional heatwaves may become more frequent in a changing climate their impact on terrestrial carbon cycling is unclear. Here we report measurements of ecosystem carbon dioxide fluxes, remotely sensed radiation absorbed by plants, and country-level crop yields taken during the European heatwave in 2003.We use a terrestrial biosphere simulation model to assess continental-scale changes in primary productivity during 2003, and their consequences for the net carbon balance. We estimate a 30 per cent reduction in gross primary productivity over Europe, which resulted in a strong anomalous net source of carbon dioxide (0.5 Pg Cyr21) to the atmosphere and reversed the effect of four years of net ecosystem carbon sequestration. Our results suggest that productivity reduction in eastern and western Europe can be explained by rainfall deficit and extreme summer heat, respectively. We also find that ecosystem respiration decreased together with gross primary productivity, rather than accelerating with the temperature rise. Model results, corroborated by historical records of crop yields, suggest that such a reduction in Europe's primary productivity is unprecedented during the last century. An increase in future drought events could turn temperate ecosystems into carbon sources, contributing to positive carbon-climate feedbacks already anticipated in the tropics and at high latitudes.

Europe-wide reduction in primary productivity caused by the heat and drought in 2003

Coweeta is one of the oldest continuously operating laboratories of its type in the world. For the first time, a complete review and summary of more than 50 years study of the hydrological and ecological responses of baseline and managed Southern Appalachian hardwood forests at Coweeta is now supplied by this volume. The long-term research approach represents a continuum of theory, experimentation and application using watersheds as landscape units of investigation. Thus, the information encompasses a wide range of interpretations and interests. In addition to in-depth analyses of terrestrial and stream processes, the breadth of coverage includes historical perspectives and relevance of ecosystem science to management needs. In a broader sense, the Coweeta research effort is considered from a perspective of national and international forest hydrology and ecology programs.

Forest hydrology and ecology at Coweeta.

We evaluated the importance of dissolved organic matter as a vehicle for the movement of N and P from the canopy and the forest floor into the mineral soil of a deciduous forest. We also examined the origin and nature of dissolved organic matter from the forest floor to see whether it was simply soluble plant material or highly humified matter. The average annual output from the forest floor in the form of dissolved organic matter was 18, 28, and 14% of the input in solid litterfall for C, N, and P, respectively. In throughfall, about half of the dissolved N and P was organic. But, in solution percolating from the forest floor, 94% of the N and 64% of the P was organic. Leaching from the forest floor was not a source of inorganic N and P for the mineral soil. Instead, the forest floor was a sink for the removal of these inorganic nutrients delivered in throughfall. Microbial immobilization was the most likely explanation for much of the inorganic nutrient removal. In contrast, the forest floor was an abundant contributor of N and P to the mineral soil in the form of dissolved, and possibly particulate, organic matter. Much of the dissolved organic matter entering the A horizon originated from the upper (Oa and Oe horizon) forest floor, but it was modified in several respects compared to the original soluble material. The solution percolating from the forest floor over most of the year was much richer in nitrogen, contained a much larger proportion of hydrophilic acids, and contained a much smaller proportion of carbohydrate-rich hydrophilic neutrals, than did the original water- extractable material in autumn litter. However, the fresh autumn litter did contain a similar proportion of soluble hydrophobic acids that resembled dissolved humic substances in several respects. Most of the flux of nitrogen from the forest floor to the A horizon was carried by humic substances and highly colored hydrophilic acids.

Fluxes of Dissolved Organic Nutrients and Humic Substances in a Deciduous Forest

http://www.srs.fs.usda.gov/pubs/ja/ja_swank003.pdf

Long-term hydrologic and water quality responses following commercial clearcutting of mixed hardwoods on a southern Appalachian catchment

(1) Early forest regeneration in southern Appalachian hardwood forests is dominated by the woody nitrogen-fixing legume, black locust (Robinia pseudo-acacia). Although it grows most prevalently on clear-felled areas, abandoned pastures, or disturbed roadsides, it may have historically been an important colonizer of burned sites. Although it commonly reproduces from seed germination, sprouting from stumps and roots is its most prevalent means of regeneration. Early sprout growth is rapid, attaining heights up to 8 m in 3 years. (2) Except for stands on high-nutrient sites, growth decreases after 10-20 years. In less vigorous stands, stem mortality may be high due to attacks by the locust stem borer (Megacyllene robiniae). The high mortality of black locust is an early successional mechanism that releases cpdominant species such as Liriodendron tulipifera, and creates canopy gaps favourable for growth of longer-lived individuals. (3) Total biomass accretion in 4, 17 and 38-year-old black locust stands growing on fertile, mesic sites was 33, 174 and 399 t ha-', respectively, in comparison to 198 t ha-' for an older, uneven-aged mixed oak forest with a history of disturbance. (4) Biomass accumulation was the predominant fate of fixed N in all three stands, with an addition to total soil N apparent only in the 38-year-old stand. (5) Symbiotic N fixation by black locust apparently increased the concentration of NO3 in the soil. The source of elevated soil NO3 is hypothesized to be high fluxes of N from leaf and root litter mineralization and nitrification, and perhaps from canopy insect frass. (6) Total stand N increased at a net average annual rate of 48, 75 and 33 kg ha-' year-', respectively, for ages 4, 17 and 38. Nodule biomass was 8, 106 and 4 kg ha-' in the 4, 17 and 38-year-old stands, respectively. (7) These patterns of N accretion are similar to those reported for other woody nitrogen-fixing species on secondary successional sites. They indicate that peak N fixation occurred from early to intermediate stages of forest succession, and declined with later successional development.

The role of black locust (robinia pseudo- acacia) in forest succession

Action des porcs sauvages sur la faune superficielle, les elements nutritifs, la biomasse de la litiere forestiere et du sol

Wayne T. Swank

Papers

Forest hydrology and ecology at Coweeta.

Fluxes of Dissolved Organic Nutrients and Humic Substances in a Deciduous Forest

Long-term hydrologic and water quality responses following commercial clearcutting of mixed hardwoods on a southern Appalachian catchment

The role of black locust (robinia pseudo- acacia) in forest succession

Effects of wild pig rooting in a deciduous forest