https://www.clw.csiro.au/aclep/documents/McBratney%20et%20al.%202003.pdf

On digital soil mapping

Contents

 Summary

I Introduction
II Variability of N : P ratios in response to nutrient  supply
III Critical N : P ratios as indicators of nutrient  limitation
IV Interspecific variation in N : P ratios
V Vegetation properties in relation to N : P ratios
VI Implications of N : P ratios for human impacts  on ecosystems
VII Conclusions

 Acknowledgements


 References



Summary
Nitrogen (N) and phosphorus (P) availability limit plant growth in most terrestrial ecosystems. This review examines how variation in the relative availability of N and P, as reflected by N : P ratios of plant biomass, influences vegetation composition and functioning. Plastic responses of plants to N and P supply cause up to 50-fold variation in biomass N : P ratios, associated with differences in root allocation, nutrient uptake, biomass turnover and reproductive output. Optimal N : P ratios – those of plants whose growth is equally limited by N and P – depend on species, growth rate, plant age and plant parts. At vegetation level, N : P ratios 20 often (not always) correspond to N- and P-limited biomass production, as shown by short-term fertilization experiments; however long-term effects of fertilization or effects on individual species can be different. N : P ratios are on average higher in graminoids than in forbs, and in stress-tolerant species compared with ruderals; they correlate negatively with the maximal relative growth rates of species and with their N-indicator values. At vegetation level, N : P ratios often correlate negatively with biomass production; high N : P ratios promote graminoids and stress tolerators relative to other species, whereas relationships with species richness are not consistent. N : P ratios are influenced by global change, increased atmospheric N deposition, and conservation managment.

https://nph.onlinelibrary.wiley.com/doi/epdf/10.1111/j.1469-8137.2004.01192.x

N : P ratios in terrestrial plants: variation and functional significance

Terrestrial net primary production (NPP) quantifies the amount of atmospheric carbon fixed by plants and accumulated as biomass. Previous studies have shown that climate constraints were relaxing with increasing temperature and solar radiation, allowing an upward trend in NPP from 1982 through 1999. The past decade (2000 to 2009) has been the warmest since instrumental measurements began, which could imply continued increases in NPP; however, our estimates suggest a reduction in the global NPP of 0.55 petagrams of carbon. Large-scale droughts have reduced regional NPP, and a drying trend in the Southern Hemisphere has decreased NPP in that area, counteracting the increased NPP over the Northern Hemisphere. A continued decline in NPP would not only weaken the terrestrial carbon sink, but it would also intensify future competition between food demand and proposed biofuel production.

Drought-Induced Reduction in Global Terrestrial Net Primary Production from 2000 Through 2009

La secheresse exceptionnelle de 2003 a ete l'occasion de faire le point de nos connaissances sur les mecanismes ecophysiologiques permettant aux arbres de traverser un tel evenement climatique extreme. L'analyse a ete conduite a l'echelle de l'arbre et du peuplement, tandis que l'intensite de la secheresse a ete quantifiee a l'aide d'un calcul de bilan hydrique sur neuf sites forestiers europeens contrastes du reseau CARBOEUROPE. Le role du couvert dans les echanges avec l'atmosphere est rappele puis integre dans l'analyse des reductions de bilan d'eau et de carbone en 2003 dus a la regulation stomatique. Les caracteristiques du complexe sol-racine, important a la fois pour l'acces a la ressource et a l'efficience de son absorption, constituent un des premiers traits d'adaptation a la secheresse. La reponse et les adaptations des especes ont surtout ete analysees en termes de diversite inter-specifique de fonctionnement hydraulique et du couplage entre proprietes hydrauliques et regulation stomatique. Enfin, nous discutons l'hypothese selon la quelle les dysfonctionnements hydrauliques ou les deficits de mise en reserve sont impliques dans les reactions differees de croissance, de developpement, d'induction de deperissement. Par exemple, des mesures de reserves glucidiques dans les troncs de chenes menees en fin d'ete 2003 ont permis de predire l'etat des couronnes des arbres au printemps 2004. Les faibles taux d'amidon etaient associes a une forte mortalite de branches et de jeunes pousses.

/pdf/temperate-forest-trees-and-stands-under-severe-drought-a-2nxodt1dqz.pdf

Temperate forest trees and stands under severe drought: a review of ecophysiological responses, adaptation processes and long-term consequences

Humans have fundamentally altered global patterns of biodiversity and ecosystem processes. Surprisingly, existing systems for representing these global patterns, including biome classifications, either ignore humans altogether or simplify human influence into, at most, four categories. Here, we present the first characterization of terrestrial biomes based on global patterns of sustained, direct human interaction with ecosystems. Eighteen “anthropogenic biomes” were identified through empirical analysis of global population, land use, and land cover. More than 75% of Earth's ice-free land showed evidence of alteration as a result of human residence and land use, with less than a quarter remaining as wildlands, supporting just 11% of terrestrial net primary production. Anthropogenic biomes offer a new way forward by acknowledging human influence on global ecosystems and moving us toward models and investigations of the terrestrial biosphere that integrate human and ecological systems.

https://esajournals.onlinelibrary.wiley.com/doi/epdf/10.1890/070062

Putting people in the map: anthropogenic biomes of the world

In western Europe, forest area has been expanding rapidly since the 19th century, mainly on former agricultural land. Previous studies show that plant diversity differs between these recent forests and ancient forests that were already forested at the time of first national cadastral surveys, around 1800. Here, we investigated the duration of such agricultural aftereffects. In northeastern France, large areas were deforested during the Roman occupation and thereafter abandoned to forest. In one such forest that was farmed during the period AD 50-250, we show that species richness and plant communities vary according to the intensity of former agriculture. These variations are linked to long- term changes of chemical and structural soil properties. Hence, we suggest that such effects of past agricultural land use on forest biodiversity may be irreversible on an historical time scale.

Irreversible impact of past land use on forest soils and biodiversity

1 Afforestation has been widespread in western Europe over the past 200 years. In France, nearly half of the current forested area has previously been used for agricultural purposes. 2 The impact of previous land use on vegetation (physiognomy, species richness and Ellenberg's indicator value) and soil (carbon, nitrogen, phosphorus contents and pH) in the Vosges mountains (north-eastern France) was studied. Previous land uses were classified into four categories (old forest, pasture, cropland, garden) based on historical records. The potential bio-indicative value of &5N as a marker of these previous land uses was also tested. 3 Previous croplands and gardens displayed a higher species richness than old forests (24, 27 and 16 species per plot, respectively), higher Ellenberg's indicator values for nitrogen, humidity and pH and higher vegetation cover. Vegetation of previous pastures was very similar to old forest. 4 Soils under previous agricultural lands displayed a higher phosphorus content, higher pH values and lower C/N ratios than old forests. &5N was the lowest, at any depth, in old forests. 5 These differences could be interpreted as consequences of the fertility transfer which occurred from pastures to croplands or gardens, through the spread of animal manures on tilled areas. The persistence of such landscape differentiation, even a century later, should be taken into account in forest management.

https://www.jstor.org/stable/pdfplus/2960507.pdf

Influence of past land use on the vegetation and soils of present day forest in the vosges mountains, france

Combined archaeological and ecological investigations in a large ancient oak forest in Central France have revealed a dense network of ancient human settlements dating from the Roman period. We demonstrate a strong correlation between present-day forest plant diversity patterns and the location of Roman farm buildings. Plant species richness strongly increases toward the center of the settlements, and the frequency of neutrophilous and nitrogen-demanding species is higher. This pattern is paralleled by an increase in soil pH, available P, and δ15N, indicating the long-term impact of former agricultural practices on forest biogeochemical cycles. These extensive observations in a forested region on acid soils complement and confirm previous results from a single Roman settlement on limestone. Ancient Roman agricultural systems are increasingly being identified in contemporary French forests; the broad extent and long-lasting effects of previous cultivation shown in this study require that land-use history be considered as a primary control over biodiversity variations in many forest landscapes, even after millennia of abandonment.

Present forest biodiversity patterns in france related to former roman agriculture

Conifer needles are an important link in the cycling of Total Mercury (THg) and Methylmercury (MeHg) in the boreal ecosystem due to the high THg and MeHg concentrations in litterfall Translocation within the tree of Hg from soils to the crown canopy has been assumed to be a minor source of the Hg in litterfall This paper, however, is the first to present direct observations of THg/MeHg transport from the soil via xylem sap Xylem sap concentrations of THg and MeHg were measured in sap drained from different levels along the boles of freshly cut 100 year old Norway spruce (Picea abies) and Scots pine (Pinus sylvestris) The trees came from a mixed stand growing on podzolized till soils at the Svartberget Forest Research Station in N Sweden Soil solution concentrations of THg and MeHg at different levels in the soil profile were measured for comparison Concentrations of THg in xylem sap ranged from 10–15 ng L-1 in both the Scots pine and Norway spruce Concentrations of MeHg varied from 003 ng L-1to 016 ng L-1, with higher values in Scots pine than Norway spruce If these concentrations are representative of the transport from soils to needles in xylem sap at this site, then only 3% of the MeHg in litterfall (012 mg ha-1 yr-1) and 11% of the THg (26 mg ha-1 yr-1) can originate via this pathway The upward transport via xylem sap is larger relative to the open field inputs (84% of THg and 17% of MeHg) Comparison of soil solution and xylem sap THg/MeHg suggested some degree of THg exclusion during water uptake in Scots pine and Norway spruce, but MeHg exclusion only in Norway spruce

Xylem sap as a pathway for total mercury and methylmercury transport from soils to tree canopy in the boreal forest

Influence of acid atmospheric inputs on surface water chemistry and mineral fluxes in a declining spruce stand within a small granitic catchment (Vosges Massif, France).

Etienne Dambrine

Papers

Irreversible impact of past land use on forest soils and biodiversity

Influence of past land use on the vegetation and soils of present day forest in the vosges mountains, france

Present forest biodiversity patterns in france related to former roman agriculture

Xylem sap as a pathway for total mercury and methylmercury transport from soils to tree canopy in the boreal forest

Influence of acid atmospheric inputs on surface water chemistry and mineral fluxes in a declining spruce stand within a small granitic catchment (Vosges Massif, France).