The Salem simulator version 2.0: a tool for predicting the productivity of pure and mixed forest stands and simulating management operations

A growing body of research suggests mixed-species stands are generally more productive than pure stands as well as less sensitive to disturbances. However, these effects of mixture depend on species assemblages and environmental conditions. Here, we present the Salem simulator, a tool that can help forest managers assess the potential benefit of shifting from pure to mixed stands from a productivity perspective. Salem predicts the dynamics of pure and mixed even-aged stands and makes it possible to simulate management operations. Its purpose is to be a decision support tool for forest managers and stakeholders as well as for policy makers. It is also designed to conduct virtual experiments and help answer research questions. In Salem, we parameterised the growth in pure stand of 12 common tree species of Europe and we assessed the effect of mixture on species growth for 24 species pairs (made up of the 12 species mentioned above). Thus, Salem makes it possible to compare the productivity of 36 different pure and mixed stands depending on environmental conditions and user-defined management strategies. Salem is essentially based on the analysis of National Forest Inventory data. A major outcome of this analysis is that we found species mixture most often increases species growth, in particular at the poorest sites. Independently from the simulator, foresters and researchers can also consider using the species-specific models that constitute Salem: the growth models including or excluding mixture effect, the bark models, the diameter distribution models, the circumference-height relationship models, as well as the volume equations for the 12 parameterised species. Salem runs on Windows, Linux, or Mac. Its user-friendly graphical user interface makes it easy to use for non-modellers. Finally, it is distributed under a LGPL license and is therefore free and open source.

Tree Growth Response to Low-Intensity Prescribed Burning in Pinus nigra Stands: Effects of Burn Season and Fire Severity

The study of the short-term post-burn tree growth in a mixed stand of Pinus nigra and Pinus pinaster and in a pure stand of P. nigra in the Cuenca Mountains (Spain) will enable us to determine the disturbance of prescribed burning conducted in two seasons. Dendrochronological methods and mixed modelling were used to investigate whether tree growth responses are influenced by stand and tree characteristics, fire season and fire severity variables. The findings revealed that prescribed burning scarcely affected tree growth. The type of stand (mixed or pure) was not critical for tree growth. The individual tree characteristics were significant factors in all the scenarios studied. The inclusion of some fire severity variables for the first time in tree growth models showed that the maximum scorch height determined a main part of the variability of tree growth. The time during which the temperature was above 60 °C in the cambium region and temperature was above 300 °C in the bark surface were only significant factors after spring burnings. The litterfall one year after the prescribed burning was not a significant factor in any of the models. Overall, the findings confirm the characteristic resistance of P. nigra to surface fires and favor the potential application of prescribed burning programs for this species in the Mediterranean Basin.

The Salem simulator version 2.0: a tool for predicting the productivity of pure and mixed stands and simulating management operations

A growing body of research suggests mixed-species stands are generally more productive than pure stands. However, this effect of mixture depends on species assemblages and environmental conditions and forest managers often lack tools to assess the potential benefit of shifting from pure to mixed stands. Here we present Salem, a simulator filling this gap. Salem predicts the dynamics of pure and mixed even-aged stands and makes it possible to simulate management operations. Its purpose is to be a decision support tool for forest managers and stakeholders as well as for policy makers. It is also designed to conduct virtual experiments and help answer research questions. In Salem, we parameterised the growth in pure stand of 12 common tree species of Europe and we assessed the effect of mixture on species growth for 24 species pairs (made up of the 12 species mentioned above). Thus, Salem makes it possible to compare the productivity of 36 different pure and mixed stands depending on environmental conditions and user-defined management strategies. Salem is essentially based on the analysis of National Forest Inventory data. A major outcome of this analysis is that we found species mixture most often increases species growth, in particular at the poorest sites. Independently from the simulator, foresters and researchers can also consider using the species-specific models that constitute Salem: the growth models including or excluding mixture effect, the bark models, the diameter distribution models, the circumference-height relationship models, as well as the volume equations for the 12 parameterised species. Salem runs on Windows, Linux, or Mac. Its user-friendly graphical user interface makes it easy to use for non-modellers. Finally, it is distributed under a LGPL license and is therefore free and open source.

Estimation of Carbon Pools in the Biomass and Soil of Mangrove Forests in Sirik Azini Creek, Hormozgan Province (Iran)

Despite the increasing interest on mangroves due to their recognition as one of the most carbon rich ecosystem, arid mangroves are still poorly investigated. We aimed to improve the knowledge on biomass and soil carbon sequestration for an arid mangrove forest located at the Azini creek, Sirik, Hormozgan Province (Iran). Three different regions were considered based on the composition of the principal species growing in the study area: 1) Avicennia marina, 2) mixed forest of A. marina and Rhizophora mucronata, and 3) R. mucronata. Biomass carbon storage, considering both aboveground (AGB) and belowground biomass (BGB), was significantly different between the cover areas. Significantly higher values of soil organic carbon stock were found in the sites under Rhizophora spp. than in the site with pure stand of Avicennia spp. . Overall, the mean forest biomass (TFB) was 305 Mg ha-1 and the highest proportion of organic carbon (62 %) was found to be stored in the soil, while the lowest was located in the root biomass (BGB; 10%). The AGB accounted for about 28% of the C stored in the studied site, with significant differences between the three vegetation areas. Our results on carbon storage can be used by local policy to promote conservation actions in arid mangrove forests, which also represent an important climatic threshold of mangrove worldwide distribution.

Annual dynamics of Zymoseptoria tritici populations in wheat cultivar mixtures: a compromise between the efficiency and durability of a recently broken-down resistance gene?

Cultivar mixtures slow polycyclic epidemics but may also modify the evolution of pathogen populations by diversifying the selection pressures exerted by their plant hosts at field scale. We compared the dynamics of natural populations of the fungal pathogen Zymoseptoria tritici in pure stands and in three binary mixtures of wheat cultivars (one susceptible cultivar and one cultivar carrying the recently broken-down Stb16q gene) over two annual field epidemics. We combined analyses of population ‘size’ based on disease severity, and of population ‘composition’ based on assessments of changes in the frequency of virulence against Stb16q in seedling assays with more than 3000 strains. In the field, disease levels were lower in mixtures, with each cultivar providing the other with reciprocal protection. The three cultivar proportions in the mixtures (0.25, 0.5 and 0.75) modulated the decrease in (i) the size of the pathogen population relative to the two pure stands, (ii) the size of the virulent subpopulation, and (iii) the frequency of virulence relative to the pure stand of the cultivar carrying Stb16q. Our findings suggest that optimal proportions may differ slightly between the three indicators considered. We identified potential trade-offs that should be taken into account when deploying a resistance gene in cultivar mixtures: between the dual objectives ‘efficacy’ and ‘durability’, and between the ‘size’ and ‘frequency’ of the virulent subpopulation. Based on current knowledge, it remains unclear whether virulent subpopulation size or frequency has the largest influence on interepidemic virulence transmission.

Distribution of organic carbon and nutrients in soil aggregates under different Cunninghamia lanceolata stand types in southern Guangxi of China

Background: By microscopically characterizing soil organic carbon (Corg) and nutrients pertaining to different Cunninghamia lanceolata stands at aggregate scale. A theoretical foundation can be laid to more sustainably employ soil resources in Cunninghamia lanceolata plantations, thus improving soil health and fertility.Methods: Soil Corg, total nitrogen (Ntot), available phosphorus (Pava) and exchangeable cations (including calcium (Ca2+), magnesium (Mg2+), potassium (K+) and sodium (Na+)) received the analysis within aggregate fractions acquired from 0-10 cm and 10-20 cm depth in three different stands, mixed stand of Cunninghamia lanceolata and Michelia macclurei (stand A), Cunninghamia lanceolata and Mytilaria laosensis (stand B) and pure stand of Cunninghamia lanceolata (stand C), respectively. The soil aggregates were classified into macro-aggregates (>2 mm), meso-aggregates (2-0.25 mm) and micro-aggregates (<0.25 mm) fractions by one dry-sieving process.Results: The two mixed stands displayed a relationship with the higher stable characteristic pertaining to soil aggregates than the pure stand, especially stand A. Meanwhile, micro-aggregates acted as the main fractions that carried soil Corg, Ntot, and Pava, and both micro- and macro-aggregates referred to the main fractions that carried exchangeable cations. As for the soil nutrient stocks, only the exchangeable K+ cation stock of the pure stand dominated among the Corg and nutrients stocks, in addition, the rest of the other nutrients stocks of the mixed forests (stand A and B) took an advantage over the pure stand. Moreover, the Corg and nutrients stocks in stand A and B were reflected in the macro-aggregates, differently, those of stand C were mainly reflected in the micro-aggregates.Conclusions: Thus, selecting suitable broadleaf tree species mixed with Cunninghamia lanceolata can alleviate the problems of pure stand soil aggregate stability reduction and soil Corg and nutrient loss for promoting soil resources to be sustainably utilized and protecting the health and quality of soil in the hilly area in southern Guangxi, China.

Estimating the contribution of plant traits to light partitioning in simultaneous maize/soybean intercropping

Spatial configuration and plant phenotypic plasticity contribute to increased light capture in relay intercropping, but there is little information on whether these factors also increase light capture in simultaneous intercropping. We developed and validated a three-dimensional functional–structural plant model to simulate light capture in maize and soybean sole crops and intercrop scenarios, using species traits observed in sole crops and intercrops. The intercrop maize phenotype had 2% greater light capture than the sole crop phenotype in a pure stand. The soybean intercrop phenotype had 5–10% lower light capture than the sole crop phenotype in a pure stand. The intercrop configuration increased the light capture of maize by 29% and reduced the light capture of soybean by 42%, compared with the light capture expected from sole crops. However, intercrop configuration only marginally affected total light capture by the intercrop system (+1%). Testing of individual soybean plant traits revealed that plasticity in leaf dimensions was the main reason for differences in light capture by soybean in simulated sole crops and intercrops. The results of this study illustrate a major shift of light capture from shorter species (soybean) to the taller component (maize) in a simultaneous strip intercrop. Plastic plant traits modulate this overall effect, but only marginally.

Effects of a Plasma Water and Biostimulant on Lawn Functional Value

The research was conducted between 2014 and 2016 at the Agricultural Experimental Station of the University of Environmental and Life Sciences in Wrocław. In the experiment, Poa pratensis and Lolium perenne in pure stand and in mixtures were used as Factor A. Two substances that stimulate grass growth and development constituted Factor B. The first was a biostimulant produced from brown algae (Phaeophyceae), containing various essential chemical compounds including amino acids, vitamins, alginic acid, microelements, and other unexplored biologically active components. The other was water treated with low-pressure glow plasma (LPGP). The seeds were sown in well-mixed light, alluvial loamy sand soil. During three growing seasons, a 9-point scale was used to evaluate grass density, leaf fineness, susceptibility to disease, and lawn overwintering. The lawns were mown every 14 days at a height of 4 cm. The substances with a stimulating effect significantly affected lawn grass features, including turf density and overwintering. Additionally, the biostimulant and plasma water reduced the incidence of fungal diseases. Better transport of water in plants after its low-pressure glow plasma treatment may be due to the effect of its declustered structure, its higher oxygen concentration, and its better solubility of the biostimulant.