Xylogenesis in black spruce: does soil temperature matter?

In boreal ecosystems, an increase in soil temperature can stimulate plant growth. However, cambium phenology in trees was better explained by air than soil temperature, which suggested that soil temperature is not the main limiting factor affecting xylogenesis. Since soil temperature and snowmelt are correlated to air temperature, the question whether soil temperature directly limits xylogenesis in the stem will remain unresolved without experiments disentangling air and soil temperatures. This study investigated the effects of an increase of 4 °C in soil temperature and a consequent 1-week earlier snowmelt on growth of black spruce [Picea mariana (Mill.) BSP] in the boreal forest of Quebec, Canada. The soil of two natural stands at different altitudes was warmed up with heating cables during 2008-2010 and cambial phenology and xylem production were monitored weekly from April to October. The results showed no significant effect of the treatment on the phenological phases of cell enlargement and wall thickening and lignification. The number of cells produced in the xylem also did not differ between control and heated trees. These findings allowed the hypothesis of a direct influence of soil temperature on stem growth to be rejected and supported the evidence that, in the short term, air temperature is the main limiting factor for xylogenesis in trees of these environments.     

Responses of the seedlings of five dominant tree species in Changbai Mountain to soil water stress

Soil water stress was studied on the potted seedlings of five dominant tree species (Pinus koraienes Sieb.et Zucc.,Fraxinus mandshurica Rupr., Juglans mandshurica Maxim, Tilia amurensis Rupr. and Quercus mongolica Fisch.ex Turcz) from the broadleaved/Korean pine forest in Changbai Mountain. Leaf growth, water transpiration and photosynthesis were compared for each species under three soil moisture conditions: 85%-100% (high water, CK), 65%-85% (Medium water, MW) and 45%-65% (low water, LW) of 37.4% water-holding capacity in field. The results showed that the characteristic of typical drought-resistance of the leaves is significantly developed. The net photosynthetic rate and water use efficiency of Fraxinus mandshurica were higher in MW than those in CK. But for the other four species, the net photosynthetic rate and water use efficiency in CK were lower than those in MW and LW. The transpiration rate responding to soil moistures varied from species to soecies.     

Do position and species identity of neighbours matter in 8–15-year-old post harvest mesic stands in the boreal mixedwood?

Neighbourhood competition indices (NCI), where position and species identity of neighbours are known, have been used to investigate growth and competitive interactions among adult trees. In this study, we used NCI in 8–15-year-old stands following clear-cutting in a boreal mixedwood forest of eastern Canada to improve our understanding of early successional forest dynamics. Trees of increasing diameter from the center (≥1 cm) to the edge (≥5 cm) were mapped in twenty-five circular 450 m² plots. Target trees (DBH ≥ 1 cm) were sampled in plot center to determine their annual radial stem growth. For each species, we compared a set of growth models using either a spatially explicit NCI or a non-spatial competition index. Both types of indices estimated a species-specific competition coefficient for each pair of competitor–target species. NCI were selected as the best competition model for all target species although differences in variance explained relative to the non-spatial index were small. This likely indicates that competition occurs at the local level but that the high density and the relative uniformity of these young stands creates similar neighbourhoods for most trees in a given stand. The effective neighbourhood radius for competitors varied among species and was smaller for shade tolerant species. Intraspecific neighbours were the strongest competitors for most species. Aspen (Populus tremuloides) was a weak competitor for all species as opposed to balsam fir (Abies balsamea) which was a strong competitor in all cases. These results are in contradiction with some widely used forest policies in North America (e.g. free-to-grow standards) that consider broadleaf species, such as aspen, as the strongest competitors. For these early successional forests, the decision regarding the use of spatial or non-spatial competition indices should rest on the intended use. For even-age management, spatial indices might not justify their use in high-density stands but they are needed for the simulation of novel harvest techniques creating complex stand structure.     

How does organic matter affect the physical and mechanical properties of forest soil?

Determining the physical and mechanical properties of soil and its behavior for engineering projects is essential for road construction operations. One of the most important principles in forest road construction, which is usually neglected, is to avoid mixing organic matter with road materials during excavation and embankment construction. The current study aimed to assess the influence of organic matter on the physical properties and mechanical behaviors of forest soil and to analyze the relation between the amount of organic matter and the behavior of forest soil as road material. A typical soil sample from the study area was collected beside a newly constructed roadbed. The soil was mixed with different percentages of organic matter(control treatment, 5, 10, and 15% by mass) and different tests including Atterberg limits, standard compaction, and California bearing ratio(CBR) tests were conducted on these different soil mixtures. The results showed that soil plasticity increased linearly with increasing organic matter.Increasing the organic matter from 0%(control) to 15%resulted in an increase of 11.64% of the plastic limit and 15.22% of the liquid limit after drying at 110 ℃. Also,increasing the organic matter content reduced the soil maximum dry density and increased the optimum moisture content. Increasing the organic matter from 0 to 15% resulted in an increase of 11.0% of the optimum moisture content and a decrease of 0.29 g/cm~3 of the maximum dry density. Organic matter decreased the CBR, which is used as the index of road strength. Adding 15% organic matter to the soil resulted in a decrease of the CBR from 15.72 to 4.75%. There was a significant difference between the two drying temperatures(60 and 110 ℃) for the same organic matter mixtures with lower water content values after drying at 60 ℃. The results revealed the adverse influence of organic matter on soil engineering properties and showed the importance of organic matter removal before excavation and fill construction.     

Enhancement of Seed Germination in Trema orientalis (L.) Blume—Potential Plant Species in Revegetation of Mine Wastelands

Natural forest succession takes a long time to accumulate sufficient nutrients to support plant growth and enhance soil microbial activity. Human intervention in selecting native pioneer plant species is therefore required to accelerate sustainable restoration. Trema orientalis (L.) Blume, a fast growing pioneer plant species, has the ability to grow in nutrient deficient soils and proves to have reclamation potential in mine wastelands. However, its use has been limited due to low germination percentages and nonsynchronous seed germination. In the present study we tested the effect of sulphuric acid (H₂SO₄), hydrochloric acid (HCl), gibberellic acid (GA₃), and potassium nitrate (KNO₃) in varying concentrations and time durations on germination percentages and seed germination synchrony. We found that all treatments had a significant effect in predicting seed germination probabilities. Logistic regression analysis revealed that treatment solution and concentration had a significant effect on seed germination. Treatment with concentrated H₂SO₄ for 15 min increased germination up to 92% within 20 days with the least imbibition time (8 days) and highest Seedling Vigor Index (491). The scanning electron microscope images of seeds treated with H₂SO₄ showed complete dissolution of the honeycomb-like network of deposits on the seed coat surface removing the physical barrier and enhancing germination.     

Is elevation of carbon dioxide concentration beneficial to seedling photosynthesis in the understory of tropical rain forests?

Cuttings of the southeast Asian tropical rain forest tree species, Pongamia pinnata (L.) Pierre were raised in growth chambers providing a photosynthetic photon flux density (PPFD) of 60 micromol m(-2) s(-1) with either a low or a high red:far-red light ratio (LR and HR, repectively). The chambers were supplied with air containing CO(2) at a concentration of either 400 (LR4 and HR4, respectively) or 800 micromol mol(-1) (HR8 and LR8, respectively). After 4 months, leaf morphology and photosynthetic characteristics were determined. Relative to HR4, the LR4 treatment increased leaf area and total chlorophyll concentration (Chl) by 24 and 25%, respectively, but reduced leaf mass per unit area (LMA) by 19%. Elevated [CO(2)] significantly increased leaf area and LMA but did not affect Chl of LR or HR plants. Leaf nitrogen concentration was unaffected by the red:far-red light ratio but decreased significantly in seedlings in the elevated [CO(2)] treatment. Photosynthesis measured in situ under the growth conditions of ambient light and [CO(2)] (A(amb)) was 30% lower on an area basis and 14% lower on a mass basis in LR4 plants than in HR4 plants. Elevated [CO(2)] reduced the activity of ribulose-1,5-bisphosphate carboxylase/oxygenase and thus decreased light-saturated photosynthetic rate in both HR and LR plants. Elevated [CO(2)] increased mean leaf area and decreased respiration rates in both LR and HR plants. The LR8 plants had significantly higher A(amb) than LR4 plants, but similar A(amb) to HR8 plants.     

Quantification of tree species diversity in forest stands—model BIODIVERSS

This paper presents a method for complex evaluation and quantification of tree-layer species diversity in forest ecosystems—model BIODIVERSS. The model was constructed for the assessment of species diversity on a small-scale (forest-stand) level, but may be applied with advantage to regional and large-scale inventories. The probability of correct classification of species diversity degree is relatively high; e.g. with a sampling intensity of only 1.5%, the correctness of the classification by the model is already 90%. Model BIODIVERSS is a simple and practical tool. It can be used directly during fieldwork, since for its application only a pocket calculator is needed.     

Effect of the seeds provenance and treatment on the germination rate and plants growth of four forest trees species of C?te d'Ivoire

The rapid rate of deforestation in Cote d'Ivoire has led to loss of plant species diversity and also threatens some commercial tree species with extinction.Some reforestation and afforestation has been completed.However,for some species,the numbers of surviving transplants has declined.Hence,it is necessary to develop properly adapted and resilient genotypes that can effectively support the programs of forest restoration.In this context we evaluated the effects of the provenances of seeds and of various treatments on the germination rates and on plant growth of four commercial trees species(Pycnanthus angolensis,Terminalia superba,Mansonia altissima and Pterygota macrocarpa).We analyzed these parameters for seeds of three provenances(Daloa,Akoupe and Daoukro) of four species and for thirty plants aged 6 months per provenance.Time to begin germination and time to reach maximum germination were similar among species,and were not influenced by either treatment or provenance.Untreated seeds and those soaked for 24 and 48 h in water at room temperature yielded the highest germination rates,irrespective of species or provenance.The one exception was P.angolensis, for which no germination was recorded.Within species,some provenances produced higher germination percentages than did others.No clear relationship was computed between the germination rate and the morphometric characteristics of the seeds which varied significantly between provenances.Plant growth and morphological variability also depended greatly on provenance.Genetic factors might be implicated,therefore provenance trials should be undertaken and evaluated.Furthermore,molecular analysis should be undertaken to confirm the implications of genetic factors and allow for genetic selection.     

Review on studies of Eupatorium adenophorum——an important invasive species in China

Eupatorium adenophorum Spreng. was introduced in Yunnan Province of China around 1940. Since then it has been spreading rapidly, particularly in the southern and southwestern parts of China and caused serious economic loss. The biological research and integrated control on E. adenophorum were carried out from 1980‘s in Yunnan Province. Together with other 15 invasive external species, the weed has been listed in the White Paper by The State Environmental Protection Administration of China. This paper briefly reviews thestudies on natural distribution, biological character, ecological character, chemical component, hazard, potential application and the control of E. adenophorum. The research direction for this invasive external species in future was also discussed.     

Are small-scale overstory gaps effective in promoting the development of regenerating oaks (Quercus ithaburensis) in the forest understory?

We investigated the effect of small-scale overstory gaps on the ecophysiology and growth of Quercus ithaburensis saplings. The study aim was to characterize how changes in daily exposure to direct beam radiation affect photosynthetic performance in the short term and growth and biomass partitioning in the long term. Using individual net-houses, the following treatments were applied: (a) Unshaded (daily irradiance = 100 %), (b) shading net with no gap (Shade-daily irradiance = 6 %), (c) shading net with 1 h gap allowing direct beam radiation (11:00 am–12:00 pm, Shade+1-irradiance = 20 %), (d) shading net with 3 h gap (11:00 am–2:00 pm, Shade+3-irradiance = 44 %). The experiment was performed in an irrigated field. We measured growth, biomass allocation, leaf traits, daily courses of leaf gas exchange and water potential. Oak dry-weight increased while height to dry-weight ratio and specific leaf area decreased with increasing daily exposure to direct beam radiation. Leaf chlorophyll content was less affected. Higher net carbon assimilation rates (A), stomatal conductance (gs) and A/gs were associated with higher instantaneous photosynthetic photon flux density (PPFD) throughout the entire experimental PPFD range. However, during gap-hours, while exposed to saturating radiation levels of similar level (ca. 1,800 µmol photon m^?2 s^?1), A in the Shade+1 oaks was about half that of the Shade+3 oaks and nearly one-third that of the Unshaded oaks. Patterns of gs, intercellular CO₂ (Ci) and quantum efficiency of photosystem II pointed towards the possibility of a metabolic limitation. In conclusion, oaks benefited significantly from small scale overstory gaps though their capacity to utilize transient saturating radiation levels decreased with decreasing gap duration.     

Basal area growth rates of five major species in a Pinus–Cunninghamia forest in eastern China affected by asymmetric competition and spatial autocorrelation

We analyzed basal area (BA) growth using growth data obtained from permanent plots over 4 years for five major tree species in Anhui Province, eastern China. The studied species were dominant conifers (Pinus massoniana and Cunninghamia lanceolata) and co-dominant broad-leaved species (Castanopsis eyrei, Castanopsis sclerophylla, and Loropetalum chinense). A hierarchical Bayesian approach was used to estimate species-specific parameters and to quantify a spatially autocorrelated random effect. We selected a model that included only the following relevant predictor variables: initial size, asymmetric competition, spatially autocorrelated random effect, and random effect associated with plots. For all species analyzed, the model accounted for significant proportions of the variation (R ² = 70–98 %) in BA growth rates. The initial slope of the relationship between BA growth rate and the initial BA tended to be steeper for P. massoniana than for C. lanceolata. The BA growth rate increased from an initial low value and then leveled off, with a lower maximum BA growth rate for C. lanceolata than for P. massoniana. The BA growth rate of P. massoniana was significantly affected by asymmetric competition with neighbors. The results of our analyses were used to predict to what extent thinning neighboring trees at different intensities would reduce competition impacts on BA growth of P. massoniana and C. lanceolata. Our results also helped to clarify the ecological characteristics of the species analyzed, as well as the spatial distribution of unknown factors influencing tree growth.     

Decomposition of litter and soil organic matter—can we distinguish a mechanism for soil organic matter buildup?

This synthesis paper presents a model for estimating the buildup of soil organic matter in various types of coniferous forests. The knowledge used was obtained from a well‐studied forest with good Iitterfall data, decomposition information and validation measurements of the soil organic matter layer. By constructing a simple model for litterfall, and the information on maximum decomposition levels for litter, we could estimate the annual increase in soil organic matter and extend this to encompass stand age. The validation measurement and the estimated amount of soil organic matter differed by about 8 or 26% over a 120‐yr period, depending on the litterfall model. The estimated increased storage of soil organic matter as a consequence of climate change was found to be drastic. We thus found that the soil organic matter layer would grow about four times as fast as a result of the needle component only. This estimate was based on a comparison between latitudes with a difference of 17°.     

Effects of shrub?grass patterns on soil detachment and hydraulic parameters of slope in the Pisha sandstone area of Inner Mongolia,China

The characteristics of soil holding capacity for different shrub-grass patterns are important to research the mechanisms regulating vegetation on slopes. The ob...     

How does drought tolerance compare between two improved hybrids of balsam poplar and an unimproved native species?

Poplars are one of the woody plants that are very sensitive to water stress, which may reduce the productivity of fast-growing plantations. Poplars can exhibit several drought tolerance strategies that may impact productivity differently. Trees from two improved hybrids, Populus balsamifera?×?Populus trichocarpa Torr. & Gray (clone B?×?T) and P. balsamifera?×?Populus maximowiczii A. Henry (clone B?×?M), having P. balsamifera L. as a parent and trees from native and unimproved P. balsamifera were subjected to a 1-month drying cycle in a growth chamber and then rewatered. The unimproved and native B clone maintained higher stomatal conductance (g(s)) than the hybrids, and high photosynthetic activity and transpiration, even when soil water content was nearly zero. As a result, both instantaneous water use efficiency (WUE(i)) and leaf carbon isotope composition (δ(13)C) indicated that this clone was less affected by drought than both hybrids at maximal drought stress. However, this clone shed its leaves when the drought threshold was exceeded, which implied a greater loss of productivity. The B?×?M hybrid showed a relatively conservative response to water stress, with the greatest decrease in transpiring versus absorbing surface (total leaf area to root biomass ratio). This clone was also the only one to develop new leaves after rewatering, and its total biomass production was not significantly decreased by drought. Among the two hybrids, clone B?×?T was the most vigorous, with the greatest transpiration (E(i)) and net CO(2) assimilation (A) rates, allowing for high biomass production. However, it had a more risky strategy under drought conditions by keeping its stomata open and high E(i) rates under moderate drought, resulting in a lower recovery rate after rewatering. The opposite drought response strategies of the two hybrids were reflected by clone B?×?T having lower WUE(i) values than clone B?×?M at maximal drought, with a very low Ψ(min) value of -3.2 MPa, despite closed stomata and stopped photosynthetic activity. Positive linear relationships between A and g(s) for the three hybrids indicated strong stomatal control of photosynthesis. Moreover, the three poplar clones showed anisohydric behaviour for stomatal control and their use under long-term drought should be of interest, especially the B?×?M clone.     

Low rates of pollen contamination in a Scots pine seed orchard in Sweden: the exception or the norm?

We investigated mating structure and gene flow in a clonal seed orchard of Scots pine (Pinus sylvestris L.) over three consecutive pollination seasons (2010–2012) with nine nuclear microsatellite markers. The paternity of 1991 offspring from four maternal parents was assigned to 28 candidate fathers using an exclusion procedure and a likelihood-based method implemented in the program CERVUS. Relative reproductive success was highly variable among pollen parents but consistent across years and ranged from 0.1% to 18.3%. Consequently, the seed crops’ effective number of fathers was reduced to 52.9%, 48.8%, and 45.7% of the census in the three seasons, respectively. Self-fertilization fluctuated around the orchard's expected value of 5.1%, reaching 4.05%, 7.71%, and 6.61%, respectively. Pollen contamination was estimated to be 5.64%, 7.29%, and 4.89%, respectively, after correction for cryptic gene flow. CERVUS provided similar results as the exclusion method, but estimates greatly varied depending on the input parameters, mainly the proportion of fathers sampled. These results indicate the studied seed orchard is a well-functioning production population with only minor negative effects of self-fertilization and pollen contamination on the quality of seed crops. Genotyping issues associated with microsatellites as a potential source of false paternity assignment and exclusion are discussed.     

How does science-based policy advice matter in policy making? The RIU model as a framework for analyzing and explaining processes of scientific knowledge transfer

A “linear” scientific knowledge transfer from science (“truth”) to political practice (“power”) does not seem to be possible. Therefore an alternative understanding of scientific knowledge transfer is suggested: In the RIU-model, scientific knowledge is produced in the science system (Research), and science-based problem solutions are utilized within politics by political actors (Utilization). Between the two spheres there is no “automatic” connection that leads to a linear application of science in policy making. Rather, it highlights the important sphere of “integration”, a step that lies between science and utilization. Integration means the orientation of research toward political and practical problems with the aim to describe and solve them (Integration). By the example of a German case study (activities of the German federal environment agency in waste policy) it will be shown (1) what important integration measures are, and (2) how they lead to science-based policy advice that matters in policy making.     

Which factors influence the density of birch (Betula pendula Roth) seeds in soil seed banks in temperate woodlands?

European Journal of Forest Research - The natural regeneration of disturbed forest sites is becoming increasingly important due to climate change. Following disturbance events affecting large areas...