Jacques Ranger

Input-output nutrient budgets as a diagnostic tool for sustainable forest management

Abstract Maintaining, and if possible increasing, soil fertility is a major goal for sustainable forest management, because it determines to a large extent the sites capacity for wood production. As, generally, forest soils are poor, and the demand for wood is still increasing, the boundary of resilience of each ecosystem must be known. Several cases must be identified: the case of natural or native species forests, either planted or not, which are extensively managed and the case of intensively managed plantations. In this paper, input–output budgets are calculated according to temporal and spatial scales. The measurement of the main inputs and outputs is discussed. When all the fluxes entering and leaving the selected compartment are measured, the budget provides a realistic picture of the direction of change in soil fertility. In other cases, the validity of the budget has to be considered according to the proposed hypothesis. A balanced budget means that the element considered is not depleted from the soil. This does not mean that no changes occur in the ecosystem. A positive budget means that the element considered is accumulating in the system, which is not always favorable. A negative budget means the element considered is depleted in the system, but it has to be related to the available soil reserves and to the rate of flux into available pool to be a real index of risk for the ecosystem. Information from several case studies shows the interest of these budgets because (i) they are able to characterize depletion before the direct analysis of the system would be able to indicate it, and (ii) they give useful quantitative data for recommendations applicable to forest management. These budgets have the disadvantage of being labor-intensive and expensive. They are also site-specific and give little direct information for identifying the mechanisms of nutrient tranformations within the ecosystem. The relationships between forest production and nutrient availability are not sufficiently known to be able to quantify the variation in production when nutrient depletion is observed. On account of the difficulty in calculating such a budget, the most efficient strategy could be the following: (i) calculate budgets in a representative network of sites; (ii) relate the individual budgets to more easily available parameters; and (iii) propose more simple indicators for managers. Land classification and the potential impact of forest management is required for giving appropriate recommendations to managers.

Metatranscriptomics reveals the diversity of genes expressed by eukaryotes in forest soils.

Eukaryotic organisms play essential roles in the biology and fertility of soils. For example the micro and mesofauna contribute to the fragmentation and homogenization of plant organic matter, while its hydrolysis is primarily performed by the fungi. To get a global picture of the activities carried out by soil eukaryotes we sequenced 2×10,000 cDNAs synthesized from polyadenylated mRNA directly extracted from soils sampled in beech (Fagus sylvatica) and spruce (Picea abies) forests. Taxonomic affiliation of both cDNAs and 18S rRNA sequences showed a dominance of sequences from fungi (up to 60%) and metazoans while protists represented less than 12% of the 18S rRNA sequences. Sixty percent of cDNA sequences from beech forest soil and 52% from spruce forest soil had no homologs in the GenBank/EMBL/DDJB protein database. A Gene Ontology term was attributed to 39% and 31.5% of the spruce and beech soil sequences respectively. Altogether 2076 sequences were putative homologs to different enzyme classes participating to 129 KEGG pathways among which several were implicated in the utilisation of soil nutrients such as nitrogen (ammonium, amino acids, oligopeptides), sugars, phosphates and sulfate. Specific annotation of plant cell wall degrading enzymes identified enzymes active on major polymers (cellulose, hemicelluloses, pectin, lignin) and glycoside hydrolases represented 0.5% (beech soil)–0.8% (spruce soil) of the cDNAs. Other sequences coding enzymes active on organic matter (extracellular proteases, lipases, a phytase, P450 monooxygenases) were identified, thus underlining the biotechnological potential of eukaryotic metatranscriptomes. The phylogenetic affiliation of 12 full-length carbohydrate active enzymes showed that most of them were distantly related to sequences from known fungi. For example, a putative GH45 endocellulase was closely associated to molluscan sequences, while a GH7 cellobiohydrolase was closest to crustacean sequences, thus suggesting a potentially significant contribution of non-fungal eukaryotes in the actual hydrolysis of soil organic matter.

Assessing the effects of early silvicultural management on long-term site productivity of fast-growing eucalypt plantations: the Brazilian experience

Eucalyptus is the dominant and most productive planted forest in Brazil, covering around 3.4 million ha for the production of charcoal, pulp, sawtimber, timber plates, wood foils, plywood and for building purposes. At the early establishment of the forest plantations, during the second half of the 1960s, the eucalypt yield was 10 m3 ha−1 y−1. Now, as a result of investments in research and technology, the average productivity is 38 m3 ha−1 y−1. The productivity restrictions are related to the following environmental factors, in order of importance: water deficits > nutrient deficiency > soil depth and strength. The clonal forests have been fundamental in sites with larger water and nutrient restrictions, where they out-perform those established from traditional seed-based planting stock. When the environmental limitations are small the productivities of plantations based on clones or seeds appear to be similar. In the long term there are risks to sustainability, because of the low fertility and low reserves of primary minerals in the soils, which are, commonly, loamy and clayey oxisols and ultisols. Usually, a decline of soil quality is caused by management that does not conserve soil and site resources, damages soil physical and chemical characteristics, and insufficient or unbalanced fertiliser management. The problem is more serious when fast-growing genotypes are planted, which have a high nutrient demand and uptake capacity, and therefore high nutrient output through harvesting. The need to mobilise less soil by providing more cover and protection, reduce the nutrient and organic matter losses, preserve crucial physical properties as permeability (root growth, infiltration and aeration), improve weed control and reduce costs has led to a progressive increase in the use of minimum cultivation practices during the last 20 years, which has been accepted as a good alternative to keep or increase site quality in the long term. In this paper we provide a synthesis and critical appraisal of the research results and practical implications of early silvicultural management on long-term site productivity of fast-growing eucalypt plantations arising from the Brazilian context.

Influences of evergreen gymnosperm and deciduous angiosperm tree species on the functioning of temperate and boreal forests

It has been recognized for a long time that the overstorey composition of a forest partly determines its biological and physical–chemical functioning. Here, we review evidence of the influence of evergreen gymnosperm (EG) tree species and deciduous angiosperm (DA) tree species on the water balance, physical–chemical soil properties and biogeochemical cycling of carbon and nutrients. We used scientific publications based on experimental designs where all species grew on the same parent material and initial soil, and were similar in stage of stand development, former land use and current management. We present the current state of the art, define knowledge gaps, and briefly discuss how selection of tree species can be used to mitigate pollution or enhance accumulation of stable organic carbon in the soil. The presence of EGs generally induces a lower rate of precipitation input into the soil than DAs, resulting in drier soil conditions and lower water discharge. Soil temperature is generally not different, or slightly lower, under an EG canopy compared to a DA canopy. Chemical properties, such as soil pH, can also be significantly modified by taxonomic groups of tree species. Biomass production is usually similar or lower in DA stands than in stands of EGs. Aboveground production of dead organic matter appears to be of the same order of magnitude between tree species groups growing on the same site. Some DAs induce more rapid decomposition of litter than EGs because of the chemical properties of their tissues, higher soil moisture and favourable conditions for earthworms. Forest floors consequently tend to be thicker in EG forests compared to DA forests. Many factors, such as litter lignin content, influence litter decomposition and it is difficult to identify specific litter‐quality parameters that distinguish litter decomposition rates of EGs from DAs. Although it has been suggested that DAs can result in higher accumulation of soil carbon stocks, evidence from field studies does not show any obvious trend. Further research is required to clarify if accumulation of carbon in soils (i.e. forest floor + mineral soil) is different between the two types of trees. Production of belowground dead organic matter appears to be of similar magnitude in DA and EG forests, and root decomposition rate lower under EGs than DAs. However there are some discrepancies and still are insufficient data about belowground pools and processes that require further research. Relatively larger amounts of nutrients enter the soil–plant biogeochemical cycle under the influence of EGs than DAs, but recycling of nutrients appears to be slightly enhanced by DAs. Understanding the mechanisms underlying forest ecosystem functioning is essential to predicting the consequences of the expected tree species migration under global change. This knowledge can also be used as a mitigation tool regarding carbon sequestration or management of surface waters because the type of tree species affects forest growth, carbon, water and nutrient cycling.

Influence of nitrogen and potassium fertilization on leaf lifespan and allocation of above-ground growth in Eucalyptus plantations

Eucalyptus grandis (W. Hill ex Maiden) leaf traits and tree growth were studied over 3 years after the establishment of two adjacent complete randomized block designs in southern Brazil. In a nitrogen (N) input experiment, a treatment with the application of 120 kg N ha(-1) was compared to a control treatment without N addition, and in a potassium (K) input experiment a control treatment without K addition was compared to a treatment with the application of 116 kg K ha(-1). Young leaves were tagged 9 months after planting to estimate the effect of N and K fertilizations on leaf lifespan. Leaf mass, specific leaf area and nutrient concentrations were measured on a composite sample per plot every 28 days until the last tagged leaf fell. Successive inventories, destructive sampling of trees and leaf litter fall collection made it possible to assess the effect of N and K fertilization on the dynamics of biomass accumulation in above-ground tree components. Whilst the effects of N fertilization on tree growth only occurred in the first 24 months after planting, K fertilization increased the above-ground net primary production from 4478 to 8737 g m(-2) over the first 36 months after planting. The average lifespan of tagged leaves was not modified by N addition but it increased from 111 to 149 days with K fertilization. The peak of leaf production occurred in the second year after planting (about 800 g m(-2) year(-1)) and was not significantly modified (P < 0.05) by N and K fertilizations. By contrast, K addition significantly increased the maximum leaf standing biomass from 292 to 528 g m(-2), mainly as a consequence of the increase in leaf lifespan. Potassium fertilization increased the stand biomass mainly through the enhancement in leaf area index (LAI) since growth efficiency (defined as the ratio between woody biomass production and LAI) was not significantly modified. A better understanding of the physiological processes governing the leaf lifespan is necessary to improve process-based models currently used in Eucalyptus plantations.

Impact of forest tree species on feldspar weathering rates

Abstract An in situ experimental approach was used to test the impact of several forest tree species on weathering of a plagioclase used as a test-mineral. Tree species were Norway spruce, Scots pine, sessil oak, pedunculated oak and European beech. The experiment was carried out by putting a fixed mass of test-mineral into the soil under different tree species stands located in the same conditions. Test-minerals were inserted into soils at various depths (0, 5, 15, 40 cm) and then maintained over two periods (3 and 9 years). At the end of their incubation period, test-minerals were collected, weighed and analysed. Mass losses of test-minerals were highest for bags inserted under litters (0-cm depth). At 0- and 5-cm depth, dissolution rates significantly decreased over the 9 years of the experiment. There was a significant positive linear relation between specific surface area of test-minerals and their mass losses. Test-mineral evolution in mass and specific surface area was strongly dependent on environmental conditions, mostly soil pH and soil type. Test-minerals which were inserted into soil layers of low acidity (pH >4.5) had very low mass losses and specific surface area increments. Coniferous species promoted mass losses more significantly than broadleaved species did. Tree species provoked more or less mass losses through modifications in the acidity of the soil.

The dynamics of biomass and nutrient accumulation in a Douglas-fir (Pseudotsuga menziesii Franco) stand studied using a chronosequence approach

Abstract Douglas-fir is presently one of the dominant species used in France for afforestation. It was widely introduced without knowing exactly its effects on soils and superficial waters. The aim of this research was to obtain quantitative data on the biogeochemical functioning of a Douglas-fir ecosystem, and to provide relevant information to forest managers. The results presented here concern nutrient accumulation on a stand according to its stage of development. A chronosequence of stands was used to rapidly obtain information on ecosystem dynamics in particular because it is possible to assimilate stands of different ages to the different stage of development of a single stand. The present results make it possible to evaluate with sufficient accuracy nutrient losses at crop harvest. Several scenarios could be drawn using various rotation lengths and harvesting intensities. These results could be introduced in management models. Nevertheless, a direct relationship between nutrient losses and the immediate or delayed decrease of forest productivity is not easy to predict. It depends more on soil nutrient dynamics than on the present available nutrient pool. Comparison between the two main species used in forestry showed that the nutrient efficiency of Douglas-fir for biomass production was at least the same as for Norway spruce. This important conclusion needs to be confirmed by other measurements.

Potential contribution of the seed bank in coniferous plantations to the restoration of native deciduous forest vegetation

In this study, we compared the soil seed bank and current vegetation under coniferous plantations and adjacent native deciduous forests. The objective was to assess how much of the initial plant diversity is retained in such plantations, and the potential to restore this initial plant community from seed bank in case of reversion to broadleave stands. Four stands growing side by side and with different dominant species were selected at two locations (site of Haye: Quercus petraea, Pseudotsuga menziesii, Pinus sylvestris and Picea abies; site of La Petite-Pierre: Quercus petraea, Fagus sylvatica, Pinus sylvestris and Picea abies). In each stand, ground vegetation was surveyed and soil seed bank was sampled. Composition of ground flora and seed bank of stands were quite different: only 11 to 30 % of the species were in both the ground flora and the seed bank. Composition of the seed bank was mainly influenced by site location and sylvicultural practices such as the type of afforestation or the tree cover. Species richness of seed banks and vegetation were higher in the site of Haye than in the site of La Petite-Pierre. Seedling density strongly decreased with stand age. Whereas between 65 and 86 % of species found in the ground vegetation of native deciduous stand were also present in the understory or the seed bank of mature coniferous stands, this was only about 50 % in young coniferous stands. Species of deciduous stands which were absent from coniferous stands were typical of old forests. In contrast, species mainly found in the coniferous stands were often ruderal. In the studied areas, it would be possible to restore up to 86 % of the native deciduous forest vegetation, but some plant species typical of ancient forests may have disappeared during the coniferous stage.

Nutrient dynamics in a chronosequence of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) stands on the Beaujolais Mounts (France). 1: Qualitative approach

Nutrient fluxes were determined in a chronosequence of Douglas-fir stands in the Beaujolais Mounts (France). Annual and seasonal variations occurred during the 3 years of investigation; fluxes were generally highest in autumn-winter. Atmospheric inputs were among the mean values from a monitoring network of forest ecosystems in France. Nutrient outputs from the soil profile were higher than average and occurred mainly during vegetation dormancy. Mean input-output budgets were negative for N, S, K, Ca and Mg, characterising an imbalance of the site chemistry dynamics. The P budget was positive. Most of the nutrient output from the ecosystem occurred as losses in the drainage water. These losses were related to excess nitrification and consecutive cation mobilisation throughout the soil profile. Surface water, however, had a neutral pH and very low nitrate and aluminium contents, which may have been buffered by the subsoil. Budgets differed between stands and tended to be more negative in the youngest stand. Part of this behaviour was related to stand age and part to the former land use of plots. Theoretical budgets were calculated for forest rotation lengths of 20, 40 and 60 years; it was concluded that shorter rotations would increase nutrient losses. The trend of a decrease in budget deficits with stand age suggests that the effect of vegetation change will be reduced at the next rotation but the impact of stand development may remain. Predicted nutrient budgets for a second 60 year Douglas-fir rotation suggested that available Ca in the soil would be depleted and that this depletion would be even more drastic if whole tree harvesting were adopted. In conclusion, Douglas-fir stands introduced changes in soil function that may impoverish the soil if present trends remain the same over the next forest rotations. The maintenance of sustainability will require nutrient input by fertilisation.

Processes controlling silica concentration in leaching and capillary soil solutions of an acidic brown forest soil (Rhône, France)

Abstract Chemical analysis of leaching and capillary soil solutions collected at different soil depths was performed on a monthly basis for several years at the Vauxrenard site (Rhone, France). The seasonal variations in dissolved silica (Si) indicated considerable differences whether contained in leaching or capillary soil solutions. In capillary solutions, the maximum and minimum Si concentrations occurred in the summer and winter, respectively, while the opposite trend was observed with leaching soil solutions. In both solutions types, significant relationships may be obtained between Si concentration and soil temperature (T) and, to a lesser extent, H+ concentration. Evaporation or evapotranspiration had little effect on Si in capillary solutions, limited to the upper soil layers. An inverse relationship between Si and T found in leaching solutions indicated that weathering did not control Si concentration. In contrast, a positive relationship between Si and T found in capillary solutions was consistent with this process. This was reinforced by a significant relationship obtained between logSi and pH, which was consistent with surface-controlled and proton-promoted weathering. Calculated apparent activation energy and reaction order with respect to pH were both consistent with muscovite at the laboratory scale. It is suggested that Si concentration in leaching solutions was controlled mainly by diffusion of aqueous silica (essentially orthosilicic acid) from capillary solutions in relation to soil drainage. Thermodynamic calculations showed that the temperature-dependence of the solubility of Si-containing secondary phases did not significantly control Si concentration in both soil solution types. However, it was calculated that the reversible formation of some hypothetical siliceous phases (Si/A1>1) proceeded at relatively slow rates, thus limiting their impact on Si concentration. Kinetic calculations showed excellent results by correlating Si concentration in capillary solutions to specific weathering rate for primary soil silicates. In agreement with most of the statistical analysis, soil temperature appeared to be the main driving force for chemical weathering. Protons (H+) had a significant influence in the deeper soil horizons as well as in the seasons corresponding to lesser soil temperature variations. An important effect of organic ligands and particularly of low molecular weight compounds on weathering may explain larger Si concentration observed in the upper soil layers.