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The aim of this study was to denote biochemical soil activity in pure Scots pine, Norway spruce, silver fir, European larch, European beech and oak stands as well as in mixed fir-pine, beech-pine and fir-beech forests growing on a fertile fresh mixed deciduous site. The field work was carried out in the following Forest Districts: Nowe Ramuki (Mazursko-Podlaska forest region), Płońsk, Jabłonna, Brzeziny Siedlce, Grójec (Mazowiecko-Podlaska forest region) and Skarżysko, Ostrowiec and Marcule (Małopolska forest region). In 2015–2017, sample plots were assigned and chemical as well as soil enzyme activity measurements were made in each forest stand. Samples were taken from the organic (O) and humus (A) layers and for both the acidity (in 1M KCl), content of nitrogen, carbon, sum of exchangeable alkaline cations and hydrolytic acidity were determined. The investigation of soil enzymes included the measurements of urease, asparginase, acid phosphatase and dehydrogenase activity. Coniferous trees, especially fir, spruce or larch, and mixed fir-beech and pine-beech stands were observed to have a very positive influence on the biochemical soil properties. The highest activity of dehydrogenase was observed in soils of spruce and mixed fir-beech stands, whereas it was lower in soils of beech and pine stands, and the lowest in oak stands. Oak stands were furthermore characterized by the lowest soil acidity, lowest concentration of alkaline cations, the lowest nitrogen and carbon content as well as the smallest C/N ratio. In overall, soil enzyme activity showed a significant correlation with chemical soil parameters.

Hydraulic redistribution (HR) of water from wet- to dry-soil zones is suggested as an important process in the resilience of forest ecosystems to drought stress in semiarid and tropical climates. Scenarios of future climate change predict an increase of severe drought conditions in temperate climate regions. This implies the need for adaptations of locally managed forest systems, such as European beech (Fagus sylvatica L.) monocultures, for instance, through the admixing of deep-rooting silver fir (Abies alba Mill.). We designed a stable-isotope-based split-root experiment under controlled conditions to test whether silver fir seedlings could perform HR and therefore reduce drought stress in neighboring beech seedlings. Our results showed that HR by silver fir does occur, but with a delayed onset of three weeks after isotopic labelling with 2H2O (&delta, 2H &asymp, +6000&permil, ), and at low rates. On average, 0.2% of added &sup2, H excess could be recovered via HR. Fir roots released water under dry-soil conditions that caused some European beech seedlings to permanently wilt. On the basis of these results, we concluded that HR by silver fir does occur, but the potential for mitigating drought stress in beech is limited. Admixing silver fir into beech stands as a climate change adaptation strategy needs to be assessed in field studies with sufficient monitoring time.

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 (ETA); (ii) the soil water budget method (ETS) and (iii) modeling of stand ET (ETM). 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, ETA 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©; ETM) 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).

In Abies alba Mill. stands and mixed stands of A. alba and Picea abies L. (H. Karst), microsites neighbouring the trunks of adult trees were more conducive to A. alba regeneration. Although at the stand level, the effect of Fagus sylvatica L. was positive; the local effect of the adult F. sylvatica neighbourhood was insignificant. Hence, forming mixed stands with a fine-grained mosaic of admixed species might better facilitate natural regeneration of A. alba than monospecific stands. The establishment of natural regeneration in Abies alba Mill. stands is a slow, spatially heterogeneous and stochastic process. Recent studies based on inventory data indicate that A. alba more readily regenerates in mixed stands than in monospecific stands. The objective was to examine how this positive association evidenced at the stand level operates on the scale of microsites with contrasting local species composition and stand density. In 8 monospecific and 22 mixed stands with Fagus sylvatica L. or Picea abies L. (H. Karst), microsites with a contrasting density of A. alba seedlings were selected and compared in terms of local species composition, stand density, canopy characteristics and topsoil properties. In A. alba stands, seedling density was positively associated with the proximity of adult trees. In mixed stands of A. alba and P. abies, adult trees of both species exerted a positive effect on A. alba regeneration, but the P. abies neighbourhood influenced regeneration occurrence more strongly than the A. abies neighbourhood. In mixtures with F. sylvatica, however, the effect of local stand density and local species composition was not evidenced at all. Although at the stand level, P. abies and F. sylvatica exert a positive effect on A. alba regeneration, on the microsite scale, their influences differ. In stands with a dominance of A. alba, the hampered seedling establishment in gaps may be considered an inhibitive effect that facilitates the emergence of other species.

Interest in management of native warm-season grasses for multiple uses is growing in southeastern USA. Forage quality response of early-succession mixed stands of big bluestem (BB, Andropogon gerardii), indiangrass (IG, Sorghastrum nutans), and little bluestem (SG, Schizachyrium scoparium) to harvest intervals (30-, 40-, 60-, 90 or 120-d) and durations (one or two years) were assessed in crop-field buffers. Over three years, phased harvestings were initiated in May, on sets of randomized plots, ≥90 cm apart, in five replications (blocks) to produce one-, two-, and three-year-old stands, by the third year. Whole-plot regrowths were machine-harvested after collecting species (IG and LB) sample tillers for leafiness estimates. Species-specific leaf area (SLA) and leaf-to-stem ratio (LSR) were greater for early-season harvests and shorter intervals. In a similar pattern, whole-plot crude protein concentrations were greatest for the 30-d (74 g·kg(-1) DM) and the least (40 g·kg(-1) DM) for the 120-d interval. Corresponding neutral detergent fiber (NDF) values were the lowest (620 g·kg(-1) DM) and highest (710 g·kg(-1) DM), respectively. In vitro dry matter and NDF digestibility were greater for early-season harvests at shorter intervals (63 and 720 g·kg(-1) DM). With strategic harvesting, similar stands may produce quality hay for beef cattle weight gain.

The paper presents results of monitoring of beech (Fagus sylvatica L.) vegetative phenophases within the period of years 2005-2010 as related to results of evaluation involving data collected since 1991. This phenological study was performed in a young mixed forest stand situated in the Drahanska vrchovina uplands in the altitude of 625 m.a.s.l. Beginnings and duration of individual phenophases differed in dependence on the course of weather conditions in individual years of study. The highest variability was observed in the stage of budbreak. The obtained results indicate that the onset of spring phenophases was dependent on temperatures existing already in early spring and to the end of winter period. The statistical analysis proved a high correlation existing between the onset of spring phenophases on the one hand and soil and air temperatures on the other. Temperature requirements as defined for the beginnings of individual phenophases were evaluated on the base of cumulative sums of temperatures higher than 0 °C. The obtained results indicate that, as compared with results of long-term monitoring, the period of the duration of spring phenophases had been gradually shortened. On the other side, however, the duration of autumn phenophases was extended and they ended in the late autumn. Repeated extensions of the growing season to the detriment of winter dormancy might show a negative effect on the health condition of forest stands.

This paper presents an evaluation of the onset and duration of phenological stages of the European larch (Larix decidua Mill.) growing in a mixed stand in Drahanská vrchovina highlands. It covers the period of 2007–2010 and refers to results obtained in the preceding study period of 1991–2006. In individual years of this study, beginnings and durations of individual phenological stages differed in dependence on climatic conditions. Temperature requirements of European larch regarding the onset of individual phenological stages were evaluated on the base of sums of air temperatures above 0° C and of effective air temperatures higher than +5° C. Obtained results indicate that the onset and duration of spring phenological stages are dependent on air and soil temperatures already in the early spring. As far as the European larch is concerned, the breaking of buds is dependent on temperatures of air and soil; the corresponding correlation coefficients were R2 = 0. 8684 (y = −3.788x + 97.165) and R2 = 0.7627 (y = −6.667x + 101.88), respectively. The obtained results indicate that recently the onset of spring phenological stages occurred earlier and earlier in the study area of Drahanská vrchovina highlands and that their course was also shorter and shorter. In spring months, higher temperatures influence the phenological stage of flushing at most while in the autumn individual phenological stages occur later and later so that the growing season is longer and longer. This finding was corroborated by results of long-term studies.

The paper focuses on assessing the growth and production of a mixed oak/hornbeam forest stand established by combined regeneration in 1940 to 1942. The stand is situated at an altitude of 460 m. Since 1961, it is left to its natural development. The 25-year-old stand was characterized as an individually mixed, both diameter- and height-differentiated pole-stage stand. The proportion of tree species was as follows: sessile oak 77 %, hornbeam 19 %, birch 1 %, lime 1 %, black poplar 1 %, wild cherry tree, wild service tree, and field maple. During 41 years of measurements, the proportion of oak slightly decreased to 76 %, on the other hand, the proportion of hornbeam increased to 22%. The initial growing stock of the 25-year-old stand, 75 m3.ha-1, increased to 323 m3.ha-1 at an age of 66 years in 2008. At present, current volume increment ranged between 6.3 m3.ha-1.year-1 and 11.6 m3.ha-1.year-1 during years 1967 and 1998. Since the age of 61, the growth of the stand has decreased and then even ceased due to increased mortality of oak.

During the 2007-2009 period in the experimental field of the Institute of Forage Crops a study was conducted with the purpose of investigating the effect of weeds and some methods for their control in seed production stands of sainfoin (Onobrychis viciifolia Scop.). The trial was carried out on a slightly leached chernozem on an area with a natural background of weed infestation. As a result of the study it was found: Establishment of very uniform and productive seed production stands of sainfoin required effective weed control concentrated mainly in the first year when the degree of weed infestation was the highest and reached to a number of 245 plants/m2 and the fresh weed biomass to 1311 g/m2. The chemical control method showed the highest efficacy had the highest efficiency when, in the year of stand establishment at the stage of second-fourth true leaf of sainfoin, the treatment was conducted with imazamox 40g/l (Pulsar 40) at the dose of 48 g a.i./ha or with the system of Bentazon 600 g/l (Basagran 600 SL) - 900 g a.i./ha - fluazifop-P-butyl g/l (Fusilad Forte) - 120 g a.i./ha. In the years of seed production in spring at the beginning of vegetation, the treatment was conducted with imazamox 40 g/l (Pulsar 40) at the dose of 20 g a.i./ha + adjuvant DESH at the dose of 1000 ml/ha. An alternative to the chemical method is to sow sainfoin under cover of spring barley achieving more complete use of the area in the first year, a weed suppressive and ecological effect, but some negative residual effect on the crop was also observed; The pure stands of sainfoin with chemical control of weeds had the highest seed productivity, exceeding the zero check by 24 to 28%, followed by the stands with spring barley as a cover crop with an increase of 12% and the mixed stands of sainfoin with crested wheatgrass had the lowest productivity.

The increasing severity and frequency of summer droughts at mid-latitudes in Europe may impact forest regeneration. We investigated whether the sympatric species Quercus robur L., Q. petraea (Matt.) Liebl., and their morphological intermediates respond differentially to water deficit. Acorns were sourced from a naturally mixed population. Half of the potted seedlings were subjected to two successive drought periods during the first growing season, each followed by a plentiful re-watering. The surviving drought-exposed seedlings subsisted independent of the taxon of the mother tree. The phenological responses were also taxon-independent. However, drought-exposed plants showed a retarded height growth in the year following the treatment which was taxon-dependent. Offspring from Q. robur and from trees with leaves resembling Q. robur leaves and infructescences resembling Q. petraea infructescences showed a stronger decrease in height growth compared to the offspring from Q. petraea and from trees with leaves resembling Q. petraea leaves and infructescences resembling Q. robur infructescences. Diameter growth in the year following the drought treatment showed a weak taxon-dependent response. Together, our results may suggest that the composition of oak species and their hybrids in natural oak forests could be altered upon prolonged periods of precipitation deficit. ispartof: Forests vol:8 issue:11 pages:407-423 status: published

We investigated whether timing and rate of growth are related to the life strategies and fitness of three conifer species. Intraannual dynamics of wood formation, shoot elongation and needle phenology were monitored over 3 years in five Norway spruces (Picea abies (L.) Karst.), five Scots pines ( Pinus sylvestris L.) and five silver firs ( Abies alba Mill.) grown intermixed. For the three species, the growing season (delimited by cambial activity onset and cessation) lasted about 4 months, while the whole process of wood formation lasted 5–6 months. Needle unfolding and shoot elongation followed the onset of cambial activity and lasted only one-third of the season. Pines exhibited an ‘extensive strategy’ of cambial activity, with long durations but low growth rates, while firs and spruces adopted an ‘intensive strategy’ with shorter durations but higher growth rates. We estimated that about 75% of the annual radial increment variability was attributable to the rate of cell production, and only 25% to its duration. Cambial activity rates culminated at the same time for the three species, whereas shoot elongation reached its maximal rate earlier in pines. Results show that species-specific life strategies are recognizable through func tional traits of intra-annual growth dynamics. The opposition between Scots pine extensive strategy and silver fir and Norway spruce intensive strategy supports the theory that pioneer species are greater resource expenders and develop riskier life strategies to capture resources, while shade-tolerant species utilize resources more efficiently and develop safer life strate gies. Despite different strategies, synchronicity of the maximal rates of cambial activity suggests a strong functional convergence between co-existing conifer species, resulting in head-on competition for resources.

International audience; Previous studies on competitive interactions among silver birch, Scots pine, and Siberian larch have not addressed the direct importance of the species identity of nearby competitors.* We examined the joint importance of competition and species identity, using subject trees with a high local abundance of a single dominant neighboring species. Interspecific neighbors influenced annual height increment, shoot length, and branch number per unit crown length, especially in Scots pine. Silver birch and Siberian larch were predominantly affected by the level of competition alone, as estimated with competition indices.* In Scots pine, the effects may have been a direct consequence of the species identity of neighbors or they may have acted as a substitute for the effect of some non-measured variable associated with species-specific characteristics. These functionally equivalent alternatives suggest that simple indices are not adequate measures of the neighbor effect for Scots pine.* A simple extrapolation of individual tree growth to the stand level suggested that Scots pine and silver birch may grow faster in mixed than in pure stands. Siberian larch showed negative growth responses to interspecific neighbors, but the effects may be counterbalanced at the stand level by a corresponding increase in pine or birch growth.

International audience; We investigate the influence of tree canopy composition on humus form variability and heterogeneity by comparing a pure beech stand and a mixed beech-hornbeam one (70% beech and 30% hornbeam). Macro-morphological humus form descriptors were recorded using a spatially explicit sample design at stand level. Leaf litter composition and light intensity accounting for stand management as well as bulk density for harvesting practices (soil compaction) were also recorded. A multiple correspondence analysis (MCA) and geostatistics were used to assess humus form variability and heterogeneity, as well as the spatial correlation between stand characteristics and humus forms. Humus form variability and activity were greater under the mixed stand than under the pure one. Geostatistics revealed that humus form patchiness was greater under the mixed stand than under the pure one and the improvement in decomposition processes seemed to be confined to spatial distribution of hornbeam litterfall. From a practical viewpoint, these results could provide ideas on the way of mixing tree species at stand level. We assume that with a given percentage of mull-forming tree species, a dispersed tree mixture provides a more extensive improvement than a clumped mixture.; Variabilité et hétérogénéité des formes d'humus à l'échelle du peuplement : comparaison entre peuplement pur de hêtre et forêt mélangée hêtre-charme. Nous avons étudié l'influence de la composition d'un peuplement sur la variabilité qualitative et l'hétérogénéité spatiale des formes d'humus en comparant un peuplement pur de hêtre et un peuplement mélangé (70 % hêtre - 30 % charme). Les caractéristiques macro-morphologiques des formes d'humus ainsi que la composition spécifique de la litière, l'éclairement relatif sous le peuplement et la densité apparente du sol ont été mesurées à l'aide d'un échantillonnage spatialement explicite. Une analyse des correspondances multiples (ACM) couplée à des géostatistiques a été utilisée pour caractériser la variabilité et l'hétérogénéité des formes d'humus ainsi que leur corrélation spatiale avec les caractéristiques de peuplement. La variabilité, l'hétérogénéité et l'activité des formes d'humus sont plus fortes sous peuplement mixte. Sous ce peuplement, l'amélioration de l'activité des formes d'humus est liée à la distribution spatiale des retombées de feuilles de charme. Ces résultats semblent indiquer que, pour un pourcentage donné d'une espèce ligneuse à litière améliorante, un mélange d'arbre par pied a un meilleur impact sur les formes d'humus qu'un mélange par bouquet.

International audience; It is widely believed that distance-independent tree models fail to take into account the complexity of mixed stands due to the fact that spatial structure often has a greater impact on growth and dynamics in mixed stands than in pure stands. On the other hand, distance-dependent tree models are difficult to use because they require a map of the stand, which is not only very costly but also impracticable in a routine management context.* This paper reports the development of a model bridging distance-dependent and distance-independent tree models, and that is designed to simulate the growth of a mixed forest. The model used distributions of the number of neighbours to reconstruct tree neighbourhoods and compute the competition indices needed as inputs to the growth model. * Data were collected from a mixed forest of sessile oak and Scots pine in central France. The study showed that local competition indices explained a significant proportion of growth variability and that intraspecific competition was greater than interspecific competition. The model based on neighbourhood distributions gave consistent predictions compared to a distance-dependent model.* This type of model could be used instead of distance-dependent models in management contexts.; On considère généralement que les modèles arbre indépendant des distances ne permettent pas de rendre compte de la complexité des peuplements mélangés. En effet, la structure spatiale a souvent un rôle plus important sur la croissance et la dynamique dans ces peuplements que dans les peuplements purs. Les modèles arbre dépendant des distances sont quant à eux difficile à utiliser, car ils nécessitent une cartographie du peuplement qui est une information très coûteuse à obtenir et qui n'est pas disponible dans un cadre de gestion courante.* Cet article présente un modèle intermédiaire entre un modèle arbre indépendant des distances et un modèle arbre dépendant des distances. Ce modèle a été développé pour simuler la croissance de peuplements mélangés. Il utilise des distributions de nombre de voisins pour reconstruire le voisinage des arbres. Ces voisinages reconstruits permettent ensuite de calculer les indices de compétition nécessaires dans l'équation de croissance.* Les données ont été récoltées dans des peuplements mélangés de chêne sessile et de pin sylvestre dans le centre de la France. Ce travail montre que des indices de compétition locaux expliquent une part significative de la croissance individuelle et que la compétition intraspécifique est supérieure à la compétition interspécifique. Le modèle basé sur les distributions de voisinage donne des prédictions cohérentes par rapport au modèle arbre dépendant des distances.* Ce type de modèle pourrait être utilisé à la place des modèles arbre dépendant des distances dans des contextes de gestion.

We conducted dendroecological analyses in 80-year-long tree ring chronologies to detect neighborhood effects (competition intensity, species identity) on the δ13C signature of tree rings and radial stem increment of Fagus sylvatica trees growing either in monospecific or mixed patches of a temperate forest. We hypothesized that tree ring δ13C is a more sensitive indicator of neighborhood effects and the impact of climate variability on growth than is ring width. We found a closer correlation of summer precipitation to δ13C than to ring width. While the ring width showed a decline over the test period (1926–2005), the mean curve of δ13C increased until the mid of the 1970s, remained high until about 1990, and markedly decreased thereafter. Possible explanations related to ontogeny and environmental change (‘age effect’ due to canopy closure; elevated atmospheric SO2 concentrations in the 1960s–1980s) are discussed. Beech target trees surrounded by many allospecific trees had a significantly lower mean δ13C in the period 1926–1975 than beech with predominantly or exclusively conspecific neighborhood, possibly indicating a more favorable water supply of beech in diverse stands. Contrary to expectation, trees subject to more intense competition by neighboring trees (measured by Hegyi’s competition index) had lower δ13C values in their tree rings, which is thought to reflect denser canopies being linked to increased shading. We conclude that tree ring δ13C time series represent combined archives of climate variability, stand history and neighborhood effects on tree physiology and growth that may add valuable information to that obtained from conventional tree ring analysis. peerReviewed