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The Loess Plateau in China constitutes an area short of soil nitrogen and organic carbon due to local land degradation induced by various factors (i.e. long term changes of land use, climate conditions, and soil properties). The present study aimed to examine the effects of species and land management by afforestation on tree N acquisition capacity and soil N and C availability in degraded soils of the Loess Plateau area. We quantified root N uptake of inorganic and organic N sources as well as soil N and C availability, both at the tree species (i.e. Robinia pseudoacacia L., Juglans regia L. and Pinus tabulaeformis Carr.) and the land management (i.e. arable vs. monoculture vs. mixed afforested stands) levels. Our results indicated that afforestation improved soil N and organic C availabilities compared to abandoned arable land ( p < 0.05). In particular, the presence of N 2 -fixing R. pseudoacacia enhanced root N concentrations (ca. 3.0 times) and soil NO 3 - (ca. 5.4 times), soil total N (ca. 1.9 times) and organic C (ca. 3.4 times) availabilities, but decreased soil NH 4 + (ca. −33%), microbial biomass carbon (ca. −74%) and nitrogen (ca. −54%) in the mixed stand compared to J. regia monoculture. Under the experimental conditions applied, the afforested trees preferred organic over inorganic N compounds as well as NO 3 − over NH 4 + ; J. regia in monoculture had a highest root amino acids N uptake capacities (i.e. 76.6 ± 7.7 nmol N (g fw) − 1 h −1 for glutamine, 90.3 ± 8.9 nmol N (g fw) − 1 h −1 for arginine) compared to other tree species whereas such high uptake capacities were largely repressed in the mixed stand with R. pseudoacacia . Thus, in the Loess Plateau area, the inter-planting system of J. regia with N 2 -fixing R. pseudoacacia could improve the total soil N and organic C pools as well as plant N cycling compared to traditional arable land use and J. regia monoculture system. This study shows that inter-planting R. pseudoacacia with economic fruit trees can be considered a successful strategy for soil regeneration by afforestation in future land management projects. [ABSTRACT FROM AUTHOR]

Some essential features of forest hydrologic cycles are based on observations of the soil water balance. However, measurements of soil water dynamics in subtropical forests have mostly been restricted to the upper 100 cm of soil. The relative shallow depth in soil water measurement would bias the understanding how and to what extent soil water contributes to evapotranspiration. We investigated and compared the soil water dynamics down to 200 cm depth over 7 years in four subtropical plantations, including one mixed stand type ( Cunninghamia lanceolata mixed with Schima superba ) and three pure stand types ( C. lanceolata , Pinus elliottii , and Pinus massoniana ). We also examined the variations in fine root distribution and tree basal area increment across stand types. We showed that, in contrast to the P. elliottii and P. massoniana stands, the C. lanceolata stand type extracted deep soil water when the top soil was still wet, depleted soil water over a longer season, but consumed less total soil water during the dry season. Our results revealed that the mixed stand type depleted more soil water during the dry season than the pure C. lanceolata stand type. In addition to the species-specific traits of water consumption, the different soil water depletion between stand types seems to be also accounted for by the different slope aspect and rock fragment content. During the entire dry season, the four stand types mainly relied on the soil water in the 100–200 cm soil depth where fine root density was considerably low, however, the inter-annual variation in stem growth depended on the soil water depletion from 0 to 50 cm soil layer. We conclude from these results that deep soil water is likely to make a significant contribution to drought avoidance over the dry period, but the available of shallow soil water to the fine roots during dry season may determine how well trees grow. This study highlights the important to consider the deep soil water extraction when explain the ecosystem evapotranspiration variations. [ABSTRACT FROM AUTHOR]

In forest ecosystems, assessment of evapotranspiration fluxes (ET) and distinction of its components, i.e. tree transpiration (T), rainfall interception (I), and soil plus understory evapotranspiration (ETu), are a major issue. At the Vielsalm Terrestrial Observatory in Belgium (VTO, Integrated Carbon Observation System network, ICOS), covered by a mixed forest of broadleaved (mainly Fagus sylvatica L.) and coniferous species (mainly Pseudotsuga menziesii [Mirb.] Franco), the water vapor fluxes have been continuously measured by eddy covariance since 1996, without distinction of its components. Widely validated for CO2 fluxes, water vapor fluxes measured by eddy covariance still lack validation, particularly in mixed and/or heterogeneous stands. During 2010–2011, three other methods to assess ET were implemented, in order to inter-validate them and to disentangle species specific ET into its components. These methods were: (i) the analytical method which relies on measurement of each elementary flux, i.e. tree transpiration, interception loss and evapotranspiration of soil plus understory (ET A ); (ii) the soil water budget method (ET S ) and (iii) modeling of stand ET (ET M ). Our results showed that during dry foliage conditions, stand T + ETu estimated by the analytical method or model were in very good agreement with eddy covariance ET measurements. Interception loss measured was 14% and 30% of rainfall (P) for beech and Douglas-fir respectively, leading to 19% for the whole stand. Beech interception being quite low, ET A for the stand is probably slightly underestimated. Over 2010 and 2011, the mean seasonal value of ET was 1.9 mm d −1 , considering all the methods. The four methods gave close estimates, with maximum deviations from the mean being of 12%, and uncertainties, while remaining acceptable (maximum 26% with analytical method) overlap between methods. Regardless of methods, flux measurements during rainy conditions were more complex to characterize. A slight underestimation of ET by the eddy covariance method was observed at different time step, in comparison to the others implemented methods. On an annual scale, the forest water balance model estimates (BILJOU © ; ET M ) were similar in beech (68% of potential evapotranspiration, PET) and Douglas-fir sub-stands (72% of PET), despite their differences in phenology and water use patterns. Low differences were also observed between species in the water flux partitioning, with modeled ET composed of ca. 58%, 33% and 9% of T, I and ETu respectively on the annual timescale (2010–2011). [ABSTRACT FROM AUTHOR]

Both spatially explicit and spatially non-explicit individual tree crown width models were developed for Norway spruce ( Picea abies (L.) Karst.) and European beech ( Fagus sylvatica L.) using a large dataset from fully stem-mapped permanent research plots (PRPs) located in various parts of the Czech Republic. A number of tree and stand characteristics were evaluated for their potential contributions to the description of the crown width variations. In addition to diameter at breast height (DBH), other significant predictor variables identified for crown width models are dominant height (HDOM), height-diameter ratio (tree slenderness coefficient), height to crown base, DBH sum of all tree species per PRP and proportion of DBH sum for a species of the interest (spatially non-explicit competition measures), and Hegyi’s index (spatially explicit competition measure). Among various base functions evaluated, a simple power function was chosen to expand through the integration of tree and stand variables. The PRP-level random effects were also included using mixed effect modeling approach. Both spatially explicit and spatially non-explicit models and their mixed effect versions described large parts of the crown width variations [ R 2 adj = 0.76–0.78 (Norway spruce), 0.70–0.73 (European beech)] without significant residual trends. For both species, spatially explicit mixed effect model described larger part of the crown width variations than its spatially non-explicit mixed effect counterpart. The models showed that after DBH, height-diameter ratio for Norway spruce and HDOM for European beech showed the largest contribution to the models. The crown width increased with increasing dominant height, but decreased with increasing height-diameter ratio, height to crown base, and competition among the trees within a stand. For both species, spatially explicit competition exhibited significantly larger effect on crown width than spatially non-explicit ones. This suggests that spatially explicit models can be more appropriate for description of the individual tree growth dynamics than spatially non-explicit ones. However, because of a little difference between the fit statistics of spatially explicit and spatially non-explicit models, the later models can be applied for precise predictions of crown width as they do not require spatially explicit competition measures, which are computationally complex and difficult. [ABSTRACT FROM AUTHOR]

• Pre-commercial thinning strategies simultaneously promote the growth of Norway spruce and provide forage for ungulates. • There was higher amount of forage in stand with no PCT compared to PCT stands. • Pre-commercial thinning didn't influence on birch browsing. • Some version of PCT strategies can be implemented to increase the forage availability in forest landscape. Mixed stands of Norway spruce and birch have the potential to simultaneously produce timber and provide large ungulates with a significant amount of forage during the regeneration phase. While the growth and yield of such mixtures are well studied, little is known about potential trade-offs between timber and forage production and which management techniques are suitable for meeting both goals. In this study, four different pre-commercial thinning (PCT) strategies were used to study the trade-offs between production and available forage for free-ranging ungulates in a Norway spruce-birch mixture. The four PCT strategies were: 1) retaining 2000 birch stems ha−1 with 2000 Norway spruce ha−1, 2) removing all birches within a 0.75 m radius around Norway spruce stems, 3) removing all birches and other broadleaves, and 4) no PCT (control). Growth of Norway spruce was higher in the 2000 birch ha−1 and full removal treatments compared to the untreated control, but these two treatments did not differ from one another in volume production of Norway spruce. We found a negative effect of PCT on forage availability but no effect on ungulate browsing. Therefore, PCT strategies that provide both sufficient birch forage and maximize volume production of Norway spruce can be implemented. [ABSTRACT FROM AUTHOR]

Highlights: [•] We study tree-ring responses to climate of Abies alba in western European mountains. [•] We compare responses of pure stands to those of three different mixtures. [•] Climatic drivers are temperature at high elevation and drought at low altitude. [•] Mixture reduces A. alba sensitivity to summer drought. [•] Mixture effects depend on local climatic conditions. [ABSTRACT FROM AUTHOR]

Abstract: The effect of tree species mixture on stand volume yield and on tree-species-specific diameter and height growth rates were analysed in managed mixed stands of Scots pine (Pinus sylvestris L.) and silver birch (Betula pendula Ehrn.). Data were obtained from 14 repeatedly measured stands located in Southern Finland on mineral soil sites with varying admixture of Scots pine and silver birch. Statistical analysis was carried out for studying the effect of species mixture on the development of stand characteristics. For the analysis, the plots were categorised into three groups (plot types) according to the species dominance. In order to analyse species-specific growth rates, individual-tree mixed linear growth models for tree diameter and height growth were developed for both tree species. The results clearly show that the yield of the managed mid-rotation, mixed stands was greater for stands dominated by Scots pine than for stands dominated by birch, and the stand volume increment decreased with an increasing proportion of silver birch. Analysis of diameter and height growth by tree species revealed that the main reason for this pattern is the negative impact of birch competition on the growth of pine trees. The increase in diameter of pine was clearly hampered if the proportion of birch was high. An abundance of birch also slightly decreased the growth in height of Scots pine, although the effect was less than on diameter growth. Species mixture did not affect the diameter growth of birch but did have a significant effect on height development. Height growth of birch was considerably greater in pine-dominated stands than in birch-dominated stands. In pine-dominated mixed stands, the height growth of birch was quite close to that of dominant pine trees, and birches can endure in competition with pines for light. The results apply for even-aged and single-storey managed stands, where stocking density and structure are controlled with pre-commercial and commercial thinnings. The results are not applicable to unmanaged mixed stands undergoing self-thinning. This study provides new information on mixed stands from a silvicultural perspective, which can be applied in decisions involving the management of mixed stands. [Copyright &y& Elsevier]

Abstract: This modeling study used recent observations at a temperate broad-leaved forest in Central Germany to calculate water balances of a Fagus sylvatica monoculture and mixed stands of F. sylvatica, Tilia spp., Acer spp., Carpinus betulus, Fraxinus excelsior and Quercus robur. To simulate soil water flow the modeling framework Expert-N was applied which combines models that describe the physiological and hydrological processes of the plant-soil system including models of evapotranspiration (Penman–Monteith equation), interception (revised Gash model) and soil water flow (Richards equation). Measurements of rainfall partitioning, volumetric soil water content, evapotranspiration and tree transpiration provided reliable data for the parameterization and the calibration of the model for three stands of different diversity levels. They allowed to include species specific physiological (transpiration rates, response to dry soil water conditions) and structural (leaf area dynamics) characteristics. During the 3-year long observation period 2005–2007 the mean yearly precipitation was 652mm, the simulated mean yearly interception loss of the three observed forest stands was between 219 and 272mm, the transpiration accounted for 197–225mm, the forest floor evaporation for 96–104mm, the drainage for 16–60mm and the runoff for 13–50mm. The calculations of the water balance were sensitive to the species composition of the forest and showed differences of rainfall interception and root water uptake between the stands. The applied stand-level model was able to simulate the water dynamics of the monospecific and mixed forest stands. It was shown that differences in drought tolerance of tree species can have a strong impact on the simulated soil water extraction during periods when available soil water is low. [ABSTRACT FROM AUTHOR]

Abstract: A number of different research approaches have been used to investigate the influence of tree species on the particular ecological parameters in mixed forest stands. While it is widely recognized that trees have species-specific effects on particular resources like radiation, water and nutrients more interacting effects of mixtures are assumed to exist. In this paper we examine the spatial variation of humus mass in a mixed stand and discuss the influence of specific spatial factors on humus mass variation. Our study site is located in the Solling area, an intermediate mountain range in the south of Lower Saxony in Germany. It is located in a 130–140-year-old European beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L). Karst.) mixed stand. To better understand processes which determine amount of humus mass variation within mixed stands of European beech and Norway spruce we measured humus mass of the OF and ecological factors at sample points (litter fall of beech and spruce, radiation, and precipitation beneath the forest canopy). We used a structural equation model (SEM) to analyse data for the effect of species-specific litter input, radiation and throughfall on humus mass variation. Additional to classical regression approaches SEM enables us to consider latent, non-observed, factors or variables. In this paper we present a special SEM, a so-called linear structural relationship (LISREL) model, showing how self-formulated latent variables like “decomposition environment” and “decomposition inhibition” affect the humus mass of the OF layer. Latent structures are of great importance in order to understand and analyse processes determining humus mass variation. In our model, “latent variables” are identified, which explain the contribution of measured variables to improvement or deterioration of humus decomposition, and hence more or less accumulation of organic material in the surface humus layers, in our case the OF layer. Spruce needle input impedes humus dynamics, while beech leaf litter input and higher throughfall amounts show supporting effects. These model results are in agreement with formerly reported findings, but yield further an interval-scaled combined measure which is better founded and more comprehensive than earlier descriptive approaches to the single ecological factors involved. Besides of the ecological interpretation of the results we succeed in determining a valid structural equation model taking into account all relevant ecological factors of humus decomposition. [Copyright &y& Elsevier]

Abstract: To clarify the utility of spectral vegetation indices (VIs) for estimating light conversion efficiency (ɛ) in Japanese coniferous forests, we investigated the relationships between six VIs (NDVI, EVI, SAVI, PRI, CI, and CCI) and ɛ in two mature monospecific forests of deciduous conifer (Japanese larch) and evergreen conifer (Japanese cypress) and one young mixed stand of deciduous conifer with evergreen undergrowth (hybrid larch and dwarf bamboo). In each forest canopy, we measured seasonal variations in CO2 flux, radiation environment, and visible–near-infrared spectral reflectance during 1 or 2 growing seasons. We calculated ɛ as gross primary production (GPP) divided by the difference between incoming and reflected photosynthetically active radiation (PAR). VIs and ɛ under clear skies were averaged between 11:00 and 13:00 JST and their relationships were analyzed. In the larch forest, all calculated VIs were positively correlated with ɛ, and the highest correlation was that with CCI. Because of effects of extreme reduction in PRI in autumn with needle yellowing, the correlation of ɛ and PRI was relatively small in this forest. In the cypress forest, on the other hand, no significant correlation was found except with PRI and CCI. The highest correlation in this forest was that with PRI, suggesting that the leaf biomass-related VIs based on near-infrared reflectance are not sufficient for estimating ɛ of evergreen forest. In the mixed forest, with relatively sparse vegetation cover, all VIs were significantly correlated with ɛ, but the best correlation was that with SAVI, possibly owing to the reduction in the effect of the reflectance from background soil. Correlation analysis of the pooled data from all forests showed the highest correlation between ɛ and PRI. These results indicate that PRI is an effective VI in the remote estimation of ɛ in both deciduous and evergreen forests, although there are some sensitivity differences between vegetation types. [Copyright &y& Elsevier]

Abstract: The development of different stand structures, including Norway spruce (Picea abies (L.) Karst.) and silver birch (Betula pendula Roth), were simulated from the time of precommercial thinning until the dominant height of spruce reached 13m. The aim was to find a combination of Norway spruce and silver birch that ensured a satisfactory development of spruce combined with a long-term admixture with birch. Empirical models were used to create initial stands and to estimate the growth of the individual trees. The initial number of stems was 2500ha−1 and the proportion of birch was 0, 20, 40 and 60%. The initial average height of Norway spruce was set to 3m and for birch the height was varied between 1–6m. Conditions describing a medium fertility in southern Sweden was used in the simulations. In mixtures with the greatest initial birch height, the total volume after 15 years was similar to or greater than in a monoculture of Norway spruce with 2500 stems ha−1. The total volume was greater in mixtures compare to Norway spruce monocultures of the same density as the spruce component in the mixtures. The volume of Norway spruce decreased with increasing initial birch height if the average height of birch exceeded 2m. The status of competitive birches at the time of first commercial thinning was identified by investigating variables describing vital birches in a survey study. Given the conditions used in this study, it was concluded that leaving birch with an average height slightly greater (0.5–1m) than that of spruce after precommercial thinning will result in a large number of competitive birches at first commercial thinning. It was also indicated that the dimensions of the Norway spruce will be similar to a monoculture of Norway spruce with 2500stemsha−1. When the initial average height of birch exceeded 4m the increase in the number of competitive birches leveled off due to intra-species competition. [Copyright &y& Elsevier]

This study presents an individual tree diameter at breast height (dbh) growth model for mixed Pinus densiflora (Red pine) and Quercus variabilis (Oak) uneven-aged stands in central region of Korean peninsula. The different model components, including the effects of tree age, tree size, competition and growing site are evaluated for both Red pine and Oak. The aim is to understand and model the individual growth patterns of the two species. Based on sensitivity analysis of radial growth using a variety of combinations of independent variables, the conclusion could be reached that the size and aspect components have a positive effect on radial growth, while the other variables such as age, competition index, elevation, and slope have a negative influence. All model component effects, except the effect of elevation, are greater in pine than in Oak, indicating that Red pine is relatively less suppressed than Oak in the study area. Among the topographic variables, slope appears to be an important critical factor for Red pine. For Oak, elevation is the primary critical factor and other variables have no great effect. These interrelationships between radial growth and the age, size, competition, and site variables correspond quite well with ecological expectations and silvicultural experience of the two species in Korea. [Copyright &y& Elsevier]

Summary: Recent knowledge about root systems of trees mostly originates from studies in pure stands. But the root systems may change if more than one species is present. The fine root system (d &#60; 2 mm) of spruce was characterized for pure stands and for comparable mixed spruce/beech stands to a soil depth of 80 cm. This made it possible to estimate the effects of interspecific competition on stagnic cambisol and on dystric cambisol, respectively. An additional pure beech stand was studied on stagnic cambisol to evaluate the mixture effect also on the root system of beech. The total fine root biomass was greater in each mixed stand compared to the neighbouring pure stand. Fine roots of beech were over-represented in the rooting zone of the mixed stand, which indicates a competitive displacement of fine roots of spruce. In addition, spruce developed a more superficially distributed root system in the mixed compared to the pure stands. The low abundance of spruce roots in mixed stand and the limitation of spruce roots to the uppermost soil layers underlines the high competitive ability of beech in the rooting zone of the investigated mixed stands. Unser Wissen über das Wurzelsystem von Altbäumen stammt größtenteils aus Reinbeständen. Wurzelsysteme können aber je nach der Anwesenheit ein oder mehrerer Baumarten unterschiedlich entwickelt sein. In der vorliegenden Untersuchung wurde das Feinwurzelsystem (d &#60; 2 mm) der Fichte in Reinbeständen und in vergleichbaren Fichten-Buchen-Mischbeständen charakterisiert. So konnte der Einfluss von interspezifischer Konkurrenz auf das Wurzelsystem der Fichte abgeschätzt werden. Die Untersuchungen wurden auf Pseudogley und auf podsolierter Braunerde durchgeführt. Auf Pseudogley wurde ein zusätzlicher Buchenbestand bearbeitet, um den Effekt der Baumartenmischung auf die Buche beurteilen zu können. Die gesamte Feinwurzelbiomasse des Mischbestandes war auf beiden Standorten größer als die des jeweils benachbarten Reinbestandes. Buchenfeinwurzeln waren im Mischbestand überrepräsentiert, während Fichtenfeinwurzeln verdrängt wurden. Außerdem entwickelte die Fichte im Mischbestand ein flacheres Wurzelsystem als im Reinbestand. Die Ergebnisse unterstreichen die hohe Konkurrenzkraft der Buche im Wurzelraum der untersuchten Mischbestände. [Copyright &y& Elsevier]

A stand-based model for predicting basal-area mean diameter growth for Norway spruce (Picea abies (L.) Karst.) in young mixed stands of spruce and birch (Betula pendula Roth, B. pubescens Ehrh.) was developed and compared with two existing growth models developed for older stands. The main data were from experiments with four different pre-commercial thinning regimes. A multiplicative model with four independent variables was found suitable. The independent variables were total number of trees per hectare of all the species, site index, dominant height of spruce, and a measure of competition between birch and spruce, i.e. dominant height of spruce divided by the dominant height of birch multiplied by the proportion of spruce of total number of trees. The R2 value was 0.59 and the coefficient of variation was 12%. A test with an independent data set from the National Forest Inventory (NFI) indicated that the function developed in this study is suitable for young stands at medium to highly productive areas. Large deviations between observed and predicted growth for the two existing functions were revealed in highly productive stands. The tests based on data from the NFI also indicated that the existing function developed for spruce in older mixed stands is suitable for practical purposes for young stands. [Copyright &y& Elsevier]