Interspecific competition impacts on the morphology and distribution of fine roots in European beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) Karst.)

Morphology and vertical distribution patterns of spruce and beech live fine roots (diameter ≤2 mm) were studied using a soil core method in three comparable mature stands in the Solling: (1) pure beech, (2) pure spruce and (3) mixed spruce–beech. This study was aimed at determining the effects of interspecific competition on fine root structure and spatial fine root distribution of both species. A vertical stratification of beech and spruce fine root systems was found in the mixed stand due to a shift in beech fine roots from upper to lower soil layers. Moreover, compared to pure beech, a significantly higher specific root length (SRL, P<0.05) and specific surface area (SSA, P<0.05) were found for beech admixed with spruce (pure beech/mixed beech SRL 16.1–23.4 m g⁻¹, SSA 286–367 cm² g⁻¹). Both indicate a flexible ‘foraging’ strategy of beech tending to increase soil exploitation and space sequestration efficiency in soil layers less occupied by competitors. Spruce, in contrast, followed a more conservative strategy keeping the shallow vertical rooting and the root morphology quite constant in both pure and mixed stands (pure spruce/mixed spruce SRL 9.6/7.7 m g⁻¹, P>0.10; SSA 225/212 cm² g⁻¹, P>0.10). Symmetric competition belowground between mixed beech and spruce was observed since live fine roots of both species were under-represented compared to pure stand. However, the higher space sequestration efficiency suggests a higher competitive ability of beech belowground.     

Effects of root trenching of overstorey Norway spruce (Piceaabies) on growth and biomass of underplanted beech (Fagussylvatica) and Douglas fir (Pseudotsugamenziesii) saplings

In Central Europe, the conversion of pure Norway spruce stands (Picea abies [L.] Karst.) into mixed stands with beech (Fagus silvatica L.) and other species like e.g. Douglas fir (Pseudotsuga menziesii [Mirb.] Franco) is accomplished mainly by underplanting of seedlings beneath the canopy of overstorey spruce trees after partial cutting treatments what means exposure to shade and below-ground root competition by the overstorey to the seedlings. Particularly about the second factor, our knowledge is limited. Therefore, we carried out a below-ground competition exclusion experiment by root trenching and investigated the effects on soil resources, growth, and biomass partitioning of underplanted beech and Douglas fir saplings under target diameter and strip cutting treatments. The exclusion of overstorey root competition by trenching increased the soil water potential in the second year that had a fairly dry growing season and led to significantly higher foliar concentrations of most nutrients, particularly in Douglas fir, indicating an amended nutrient supply. Both improvements were accompanied by an increase in length and diameter increment of the underplanted saplings, appearing in both species only after having surpassed a species-specific threshold light value (Douglas fir 16% of above canopy radiation, beech 22%). We also found significant interactions between trenching and light for specific fine root length and further biomass and morphological parameters. Judged by the much steeper increase in height and diameter growth with increasing light after release from below-ground competition, Douglas fir saplings appeared to be more sensitive to root competition than beech saplings what conforms to older findings for beech. According to our results, a strip cutting seems to be more appropriate than a target diameter cutting treatment to replace a pure spruce stand by a mixed stand with beech and Douglas fir.     

Compared effects of competition by grasses (Graminoids) and broom (Cytisus scoparius) on growth and functional traits of beech saplings (Fagus sylvatica)

? The effect of two weeds (grasses and broom, Cytisus scoparius) competition on the growth and functional traits of European beech saplings (Fagus sylvatica) was investigated in an experimental plantation in the French Massif central.

? We hypothesized that grasses would have a much more harmful effect than broom on beech growth through strong competition for soil water and nitrogen.

? A randomized block design was used with three separate blocks, each possessing three types of vegetation; grasses (mainly Agrostis capillaris, Holcus mollis and H. lanatus), broom, and bare soil as a control.

? Two years after plantation beech sapling growth was significantly greater in bare soil than with competition from grasses, and was intermediate on broom. Growth was positively correlated with beech leaf nitrogen content (N_m) and xylem water potential (Ψ_x). N and Ψ_x were dependent, with nitrogen uptake probably decreasing with increasing drought. There was no clear correlation between growth and light transmitted 10 cm below the apex of the saplings.

? Beech leaf mass on an area basis (LMA) was correlated with the three resource variables (water, nitrogen and light) and with growth, confirming that LMA is a sensitive functional trait integrating the degree of stress experienced by the saplings.

? The results suggest that broom is less competitive than grasses and, if properly managed on a sufficiently well-watered site, can generate satisfactory conditions for beech establishment and growth.

     

Influence of light availability on growth, leaf morphology and plant architecture of beech ( Fagus sylvatica L.), maple ( Acer pseudoplatanus L.) and ash ( Fraxinus excelsior L.) saplings

In a field study, we measured saplings of beech, ash and maple growing in a fairly even-aged mixed-species thicket established by natural regeneration beneath a patchy shelterwood canopy with 3–60% of above canopy radiation reaching the saplings. Under low light conditions, maple and ash showed a slight lead in recent annual length increment compared with beech. With increasing light, ash and maple constantly gained superiority in length increment, whereas beech approached an asymptotic value above 35% light. A suite of architectural and leaf morphological attributes indicated a more pronounced ability of beech to adapt to shade than ash and maple. Beech displayed its leaves along the entire tree height (with a concentration in the middle crown), yielding a higher live crown ratio than ash and maple. It allocated biomass preferentially to radial growth which resulted in low height to diameter ratios, and expressed marked plagiotropic growth in shade indicating a horizontal light-foraging strategy. In addition, beech exhibited the highest specific leaf area, a greater total leaf area per unit tree height, a slightly greater leaf area index, and a greater plasticity to light in total leaf area. Ash and maple presented a “gap species” growth strategy, characterized by a marked and constant response in growth rates to increasing light and an inability to strongly reduce their growth rates in deep shade. In shade, they showed some plasticity in displaying most of their leaf area at the top of the crown to minimize self-shading and to enhance light interception. Through this, particularly, maple developed an “umbrella” like crown. These species-specific responses may be used for controlling the development of mixed-species regeneration in shelterwood systems.     

Facilitative and competitive effects of a N-fixing shrub on white fir saplings

In Sierra Nevada forests, shrubs are considered strong soil moisture competitors with regenerating trees, reducing seedling establishment, and slowing growth. Recent studies, however, suggest that in some circumstances shrubs can facilitate tree establishment and growth by modifying harsh microclimate conditions; increasing acquisition of water, carbon, and/or nutrients via shared mycorrhizal connections; or enhancing soil fertility, particularly under nitrogen-fixing shrubs such as Ceanothus spp. We examined the establishment dates and growth rates and patterns of white fir saplings growing in greenleaf manzanita, whitethorn ceanothus, and bare patches to examine whether establishment was correlated with past wet years, whether saplings growing in ceanothus had nitrogen-enriched foliage or faster growth rates than in the other two patches, and whether saplings in shrub patches experienced competition for light.Sapling establishment was not correlated with high precipitation or heavy snowpack years, suggesting shade-tolerant saplings do not need wet years to become established. Soils under ceanothus were nitrogen enriched, but white fir sapling foliage did not have higher nitrogen concentrations and saplings did not grow faster in ceanothus than in the other two patches. Because growth rates of saplings were comparable in all patch types examined despite significantly different edaphic and abiotic conditions, we inferred that the various competitive and facilitative interactions affecting tree growth are in net balance across the patch types examined. However, competition for light is important—a significant percentage of growth release events occurred after saplings emerged above their host shrubs. Where shrubs are present, shade-tolerant species (i.e., white fir) are favored over drought-tolerant (pine) species. Our results may help interpret changes in understory conditions that are contributing to mixed conifer's compositional shift toward more shade-tolerant species after a century of fire-suppression.     

Predicting average growth and size distributions of Douglas-fir saplings competing with sprout clumps of tanoak or Pacific madrone

The average growth and size distributions of Douglas-fir (Pseudotsuga menziesii) saplings in three plantations were studied for 7 years (1983–1989) after thinning of associated sprout clumps of tanoak (Lithocarpus densiflorus) or Pacific madrone (Arbutus menziesii); in some cases understory vegetation (shrubs and herbs) was experimentally suppressed. Biologically based nonlinear equations explained 66, 90, and 53% of the variation in the average annual increment of Douglas-fir height, diameter-squared, and cover, respectively. Equations for annual increment of cover of hardwood and understory vegetation explained only 10 to 12% of the variation, because these parameters exhibited a high degree of variability. Model simulations demonstrated that, for the same initial levels of cover, tanoak had faster rates of cover growth than madrone and also caused greater limitations in growth of Douglas-fir. Suppression of understory vegetation increased growth of Douglas-fir only when hardwood cover was absent. Weibull functions adequately described size distributions for Douglas-fir in 92% of the individual-tree data sets. Regression functions of hardwood cover and average Douglas-fir size explained 51, 93, and 24% of the variation in the Weibull A, B, and C parameters, respectively. Model simulations with predicted Weibull parameters demonstrated that hardwood competition caused a positive skewing in size distributions for height and stem diameter of Douglas-fir.     

Patterns of tree growth in a single tree selection silver fir–European beech forest

The basal area and height growth of trees and saplings in silver fir–European beech single stem selection forest were studied with regard to their social status and crown parameters of size, coverage, shading and vitality. On 24 permanent research plots (20 m × 20 m each) all trees [diameter at breast height (dbh) ≥10 cm] and saplings (≥1.3 m tall and dbh <10 cm) were surveyed. Repeated measurements of dbh (N = 1,608) and height (N = 1,135) 10 years apart enabled the calculation of annual basal area increment (BAI) of trees and saplings, and annual height (HI) increment of saplings. To obtain the growth characteristics for individual trees and saplings, their social status and crown parameters were assessed by rank. In the multivariate general linear model for BAI, social status, crown size and crown coverage of individuals as the predictors, and dbh² as the covariate, explained 70% of total variability. Similarly, social status, crown size, crown coverage and crown shading had a significant impact on the HI of saplings, explaining 70% of total variability. Among the observed variables, social status determined according to the individual’s position in vertical stand structure was, in addition to dbh, the most important predictor for both BAI and HI. Significant differences were observed between the BAI and HI models for the main tree species (European beech and silver fir), indicating their different growth characteristics. The applied method could be used as a supplement to the more widely used approaches for studying basal area and height growth of individual trees in selection forest stands.     

Stand density and growth of Norway spruce (<Emphasis Type="Italic">Picea abies</Emphasis> (L.) Karst.) and European beech (<Emphasis Type="Italic">Fagus sylvatica</Emphasis> L.): evidence from long-term experimental plots

On the basis of nine Norway spruce (Picea abies (L.) Karst.) and ten European beech (Fagus sylvatica L.) thinning experiments in Germany, for which both residual and removed stock had been registered first during 1870, I scrutinize how moderate and heavy thinning from below (B-, C-grade) affects the production of merchantable volume compared with light thinning (A-grade). In relation to A-grade, cumulative merchantable volume (CV) of B- and C-grade amounts in average to 103–107% in juvenile and to 97–102% in mature Norway spruce stands. The corresponding findings for European beech are 101–106% and 94–102%. CV of individual stands varies between 89% and 130% for Norway spruce and 73% and 155% for European beech (CV of A-grade = 100%). These findings are substantiated by the relation between stand density (SDI) and periodic annual increment (PAI). On the B- and C-grade plots of spruce and beech, respectively, SDI was reduced down to 41–91% and 31–83% of the A-grade. When SDI is reduced in young stands, PAI follows a unimodal curve. Norway spruce’s PAI culminates in 109% if SDI is reduced to 59%; European beech’s PAI culminates in 123% when density is reduced to 50%. Whereas Norway spruce’s growth reacts most positively on thinning under poor site conditions and with increment reduction on favourable sites, European beech behaves oppositely. With stand development the culmination point of the unimodal relation moves towards maximum density, so that in older stands PAI follows the increasing pattern, which is the left portion of a unimodal curve. A model is presented which apparently unifies contradictory patterns of stand density–growth reactions by integrating relative stand density, average tree size and site fertility effects, and makes the findings operable for forest management.     

Belowground competition from overstory trees influences Douglas-fir sapling morphology in thinned stands

We evaluated effects of belowground competition on morphology of naturally established coast Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco) saplings in 60- to 80-year-old thinned Douglas-fir stands in southwestern Washington. We separately quantified belowground competition from overstory and understory sources using trenching and understory removal. In this light-limited environment of 26 ± 16% (std. dev.) full sunlight, 2-year exclusion of tree root competition by trenching increased sapling stem biomass by 18%, total aboveground biomass by 21%, number of interwhorl buds by 68%, total foliar biomass by 33%, and foliar biomass on branch components over 4 years old by 143%. Belowground competition did not influence shoot:root ratio or foliar efficiency (i.e., stem growth per unit foliage biomass). Sapling needle size, specific leaf area, and internodal distance also were not affected by belowground competition; these variables were apparently a function of the low-light environment. The principal source of belowground competition was roots of overstory trees; effects of belowground competition from understory vegetation were minor. Thus, under a partial overstory, morphology of Douglas-fir regeneration was influenced by both belowground and aboveground competition from overstory trees. In this environment, understory vegetation control would not likely influence belowground competition to an extent that would affect sapling morphology.     

Short-term effects of selection and clear cutting on the shrub and herb layer vegetation during the conversion of even-aged Norway spruce stands into mixed stands

The conversion of even-aged Norway spruce (Picea abies (L.) H. Karst.) stands into more site adapted mixed stands is the main silvicultural goal in Germany and many other European countries. The conversion will primarily be achieved with the help of selection cutting, removing single target diameter trees and creating small gaps. At sites highly susceptible to windthrow, however, small scale clear cutting (up to 1 ha) might be an appropriate alternative. Both selection and clear cutting will affect the understorey vegetation, an important component of forest biodiversity and ecosystem functioning. Thus, with the help of a BACI-experiment (before–after/control–impact), the short-term effects of selection and small scale clear cutting on the herb and shrub layer vegetation were studied at two sites in the Solling Hills (Lower Saxony, Germany). Both treatments led to an increase in herb and shrub layer species numbers, due to persistent and invading (mainly pioneer tree species and indicators of disturbance) species and to a shift in plant traits. Most responsible for the changes in vegetation was a higher light availability, and to a lesser degree soil disturbance. The number of annuals and ruderals, however, increased only immediately after clear cutting, whereas on selection cutting plots the numbers remained high. Gaining in number and coverage were competitive perennials (Epilobium angustifolium, Juncus effusus, Rubus idaeus) especially on the clear cuttings, fulfilling a nutrient retention function. The competitives did not deter tree species from regenerating in the clear cut plots, whereas on selection cutting plots the large expansion of R. idaeus appeared to be hindering tree colonisation. Suffering under clear cut conditions were predominantly shade-tolerant, closed-forest species, but no loss of these species could be detected. This indicates the potential for a fast recovery of these forest species, as soon as, pioneer trees expand.     

Tree regeneration and plant species diversity responses to vegetation control following a major windthrow in mixed broadleaved stands

By increasing resource availability, canopy opening enhances tree recruitment as well as the development of neighbouring vegetation. The proliferation of early successional and highly competitive vegetation may have dramatic consequences on seedling establishment. However, differences in competitive abilities have been shown among the plant growth forms commonly encountered in forests. We may thus expect that vegetation management leading to control of different plant growth forms would have different consequences on tree seedling growth and development. To test this hypothesis, we analysed the effects of an intensity gradient of four vegetation control treatments (untreated, coppice control, coppice and non-tree plant control, and coppice, non-tree and pioneer (tree) plant control) on plant species richness and natural tree regeneration in three post-storm sites. Higher plant species richness and a better natural tree regeneration were observed in the more intensive treatments that significantly improved the balance of the relative abundance of tree species. Suppressing the more competitive vegetation, mainly Rubus fruticosus and graminoids, led to the recruitment and growth of tree species sensitive to competition and good tree species diversity. Practical recommendations in terms of vegetation control relative to tree regeneration and plant species richness are given.     

Light-dependent development of two competitive species (Rubus idaeus, Cytisus scoparius) colonizing gaps in temperate forest

Forest regeneration can be inhibited by competition for environmental resources (water, nutrients, light) between tree seedlings and some competitive species that are generally light-demanding species developing in gaps. The study’s aim was to quantify the development of two competitive species (Rubus idaeus and Cytisus scoparius) present in the chaîne des Puys, France, relatively to light in gaps inside Picea abies stands. On 29 transects linking the stand to the gap centre (223 points), light intensity was measured (0–80% of relative light) and floristic measurements (cover and height of the different species) were done. Development of both competitive species is positively connected to light, with a bell-shaped curve with a maximum of 40–50% for R. idaeus and a quite constant increase to 80% (maximum of light recorded in the experimentation) for C. scoparius. These results are discussed relatively to understorey vegetation management in order to favour forest regeneration.     

Die Verbreitung von Mäusen in verschiedenen Waldgebieten Bayerns

Nearly 5.000 small mammals were captured in 75.000 trapnights in 9 different woord areas of Bavaria in the years 1972–80. The investigations were performed in following habitats: Closed forests of beech and oak, coniferous and mixed forests and cultivations with a rich vegetation of shrubs, forbs or grasses. 14 species were found in this region and their preferences for different habitats and areas are described. The most frequent and widespread species was the bank vole (Clethrionomys glareolus) which was dominating in mixed forests and in cultivations with a very heterogenous vegetation consisting mainly of shrubs. The occurrence of the dormouse (Muscardinus avellanarius), the harvest mouse (Micromys minutus) and the northern birch mouse (Sicista betulina) was very rare and restricted to certain regions and habitats.     

Effects of acidic fog and ozone on the growth and physiological functions of Fagus crenata saplings

The effects of simulated acid fog (SAF) and ozone (O₃) stress on the growth and physiology of beech (Fagus crenata) saplings were investigated. Three-year-old beech saplings were exposed to SAFs of pH 3 and pH 5 (control) during May 2007 to July 2008. In each SAF treatment group, half of the saplings were exposed to 60 ppb of O₃ during September 2007 to July 2008. In comparison to the control saplings, those from the pH 3 treatment had lower total plant biomasses, epicuticular wax amounts, Ca²⁺ concentrations in their leaves, and lower starch concentrations in their leaves and roots. The effect of O₃ was significant only for the starch concentration in the roots, but the O₃ exposure also negatively affected the growth and physiology of beech saplings. Results show that acid fog exerts various severe effects, and that both chronic acid fog and O₃ exposure suppressed the physiological functions of beech saplings.     

Secondary Succession Following Catastrophic Windthrow in a Boreal Forest in Hokkaido,Japan

Abstract

In 1954, Picea-Abiesforests of central Hokkaido were leveled by a windstorm caused by a typhoon. Successional dynamics following disturbance on several forest habitats were monitored over a thirty-four year period. Differences in site conditions, such as soil, topography, and forest floor vegetation, influenced the direction of succession, but some patterns prevailing in this area were discernible. In the early stage of succession (up to year 10), all sites were immediately occupied by Rubus idaeusvar. aculeatissi-muswhich was an inconspicuous component of the stands before disturbance. Plants which dominated the understory of stands before disturbance mostly disappeared during secondary succession except for Sasa senanensis.Residual conifers also survived except for those at a moss-floor site. Betulaspp. and Salixspp. invaded within 6-8 years. At year 10-18, R. idaeussuddenly decreased in canopy cover, while S. senanensisreplaced R. idaeusas the dominant component. Trees, both residuals and invaders, were successful in growing over the shrub layer during this period and species diversity reached a peak. These observations suggest that the timing of tree establishment occurs during the transition from R. idaeuscommunity to S. senanensiscommunity in the shrub-layer, as a deterministic process founded in the life history traits of species.     

Partitioning of applied <Superscript>15</Superscript>N fertilizer in a longleaf pine and native woody ornamental intercropping system

The cultivation of ornamentals to produce woody floral products—the fresh or dried stems that are used for decorative purposes—may be an attractive option for southeastern landowners looking to generate income from small landholdings. Since many shrubs native to the understory of the longleaf pine (Pinus palustris Mill.) ecosystem have market potential, one possibility is the intercropping of select species in the between-row spacing of young longleaf pine plantations. The objective of this study was to evaluate how interspecific competition affects the fate of ¹⁵N fertilizer when American beautyberry (Callicarpa americana L.), wax myrtle (Morella cerifera (L.) Small) and inkberry (Ilex glabra (L.) A.Gray) are intercropped with longleaf pine. Nitrogen derived from fertilizer (NDF), utilization of fertilizer N (UFN) and recovery of fertilizer N (RFN_soil) were compared between agroforestry and monoculture (treeless) treatments to assess the effects of competition. Results varied by species, with NDF being higher for C. americana foliage and lower for all M. cerifera tissues in the agroforestry treatment. No effect was observed for I. glabra. UFN was lower for all species in the agroforestry treatment. RFN_soil was higher in the agroforestry treatment for I. glabra, but no treatment effects were observed for C. americana or M. cerifera. Overall, while it is clear that interspecific competition was present in the agroforestry treatment, the inefficiency of fertilizer use suggests that nitrogen was not the most limiting resource. Management interventions, particularly those that address competition for water, will likely be critical to the success of this system.     

Does tree seedling growth and survival require weeding of Himalayan balsam (Impatiens glandulifera)?

The effect of Himalayan balsam (Impatiens glandulifera) on survival and growth of naturally regenerated silver birch (Betula pendula) and planted Norway spruce (Picea abies) and silver fir (Abies alba) seedlings was studied in a weeding experiment over 3 years. Three different treatments were applied: control, mowing, and hand weeding by pulling out the entire plant. There were no consistent treatment effects on height and diameter of the tree seedlings. The coverage of Rubus fruticosus had a negative impact on diameter increment of Norway spruce and silver fir. As opposed to growth, treatment effects on seedling survival could be found for planted Norway spruce and silver fir. However, it is very likely that these effects, namely higher seedling survival after mowing, have to be attributed to the control of bramble (Rubus fruticosus) rather than to that of Himalayan balsam. It is concluded that Himalayan balsam is not able to seriously affect the growth of already established seedlings.     

Impact of deer on temperate forest vegetation and woody debris as protection of forest regeneration against browsing

A 3-year field experiment with paired exclosure (fenced areas, excluding deer) and control plots (unfenced areas, free access to deer), with two treatments with and without woody debris, was carried out at two sites in a temperate forest in eastern France. The aim of the experiment was to assess the effect of browsing by roe deer (Capreolus capreolus) and red deer (Cervus elaphus) on the diversity and richness of plant species and to test the effectiveness of using woody debris to protect seedlings and saplings from deer browsing. In presence of deer, both plant species richness and diversity were reduced the first year of the study, but this negative impact of deer then disappeared after 3 years. Deer browsing mostly affected species composition of plant communities. We observed a decrease in the abundance of preferred species such as Carpinus betulus, Rubus fructicosus, Rubus idaeus, Anemone nemorosa and Epilobium angustifolium, and palatable species such as Acer spp., Carex spp., Festuca spp. and Mycelis muralis, whereas unpalatable species such as Lamium spp., or species particularly resilient to browsing such as grasses (Brachypodium spp. and Luzula spp.) increased in abundance. The use of woody debris as protection against browsing by deer did not limit damage to seedlings and saplings of the main commercially valuable species, Abies alba and Quercus spp. Instead of limiting deer impact, use of woody debris seemed to increase the negative effect of deer browsing on regeneration in control plots relatively to those without protection.