Showing papers in "Annals of Forest Science in 2013"

Hydraulic failure and repair are not routine in trees

Abstract: Trees can pull tons of water up to 100 m above ground, whereas even the best engineered suction pumps can manage only 10 m at most. Beyond this height, the pull of gravity exceeds atmospheric pressure. The pressure at the top of the water column then becomes negative, and pumps drain by a process of vaporization called cavitation. So how do plants, particularly tall trees, cope with cavitation? Do they have an astonishingly high resistance to this process or are they routinely exposed to cavitation events and possess remarkable repair capacities? These questions were first asked when the mechanism of sap ascent in trees was discovered in the late nineteenth century (Brown2013),but were not answereduntil reliable methods for measuring cavitation were introduced a century later. Early studies of plant hydraulics suggested that cavitation occurred only in conditions of severe drought (Fig.1a).However, manystudies carried out inthe last decade

Drought sensitivity of Norway spruce is higher than that of silver fir along an altitudinal gradient in southwestern Germany

Abstract: Context For Central Europe, climate projections foresee an increase in temperature combined with decreasing summer precipitation, resulting in drier conditions during the growing season. This might negatively affect forest growth, especially at sites that are already water-limited, i.e., at low elevation. At higher altitudes trees might profit from increasing temperatures.

Responses of labile soil organic carbon and enzyme activity in mineral soils to forest conversion in the subtropics

Abstract: & Aims Globally, extensive areas of native forest have been almost replaced by plantations to meet the demands for timber, fuel material and other forest products. This study aimed to evaluate the effects of forest conversion on labile soil organic C (SOC), soil respiration, and enzyme activity, and to quantify their relationship in subtropical forest ecosystems. & Methods Surface mineral soil (0–20 cm) was collected from a Cunninghamia lanceolata Hook. plantation, Pinus massoniana Lamb. plantation, Michelia macclurei Dandy plantation, and an undisturbed native broadleaf forest. Soil microbial biomass C, dissolved organic C, permanganateoxidizable C, basal respiration, and six enzyme activities were investigated. & Results Soil microbial biomass C was higher by 45.9 % in native broadleaf forest than that in M. macclurei Dandy plantation. The ratio of soil microbial biomass C to total SOC was 27.6 % higher in the M. macclurei Dandy plantation than in the native broadleaf forest. The soil respiration increased by 25.2 %a nd 21.7 %a fter conversion from native broadleaf forest to P. massoniana Lamb. and M. macclurei Dandy plantations respectively. The effects of forest conversion on the soil enzyme activities differed among the tree species. Soil microbial biomass C had higher correlation with soil respiration than with the other SOC fractions. Moreover, soil microbial biomass C was positively correlated with urease and negatively correlated with cellulase activity. Soil respiration had higher correlation with soil microbial biomass C, dissolved organic C and permanganate-oxidizable C. & Conclusion Forest conversion affected the soil microbial biomass C, soil respiration, invertase, cellulase, urease, catalase, acid phosphatase, and polyphenol oxidase activities, but their response depended on tree species. Soil respiration was mainly controlled by labile SOC, not by total SOC.

Growth response to climate and drought change along an aridity gradient in the southernmost Pinus nigra relict forests

Abstract: & Context Tree populations at the rear edge of species distribution are sensitive to climate stress and drought. However, growth responses of these tree populations to those stressors may vary along climatic gradients. & Aims To analyze growth responses to climate and drought using dendrochronology in rear-edge Pinus nigra populations located along an aridity gradient. & Methods Tree-ring width chronologies were built for the twentieth century and related to monthly climatic variables, a drought index (Standardized Precipitation–Evapotranspiration Index), and two atmospheric circulation patterns (North Atlantic and Western Mediterranean Oscillations). & Results Growth was enhanced by wet and cold previous autumns and warm late winters before tree-ring formation. The influence of the previous year conditions on growth increased during the past century. Growth was significantly related to North Atlantic and Western Mediterranean Oscillations in two out of five sites. The strongest responses of growth to the drought index were observed in the most xeric sites. & Conclusion Dry conditions before tree-ring formation constrain growth in rear-edge P. nigra populations. The comparisons of climate-growth responses along aridity gradients allow characterizing the sensitivity of relict stands to climate warming.

Persisting bark beetle outbreak indicates the unsustainability of secondary Norway spruce forests: case study from Central Europe

Abstract: Secondary Norway spruce forests in the Western Beskids are among the most damaged forests in Europe Although spruce bark beetle (Ips typographus) has been recently causing large-scale damage to these forests, our understanding of I typographus dynamics in this environment is inadequate for evaluating forest sustainability This study aims to evaluate the patterns of damage caused by I typographus to spruce forests with compromised ecological stability Forest infestation by I typographus was inferred from sanitary felling data collected from 1998 to 2004 Stand and site data were obtained from forest management plans Spatial-dependence analysis, ordinary kriging and neural network-based regression modelling were used to investigate the patterns of infestation and the casual relationships in the studied ecosystem I typographus long-distance dispersal substantially decreased with outbreak culmination The spread of infestation was only weakly related to stand and site parameters Infestations spread isotropically at the stand and patch level but directionally at the regional scale The large-scale spread of infestation can be explained by the uniform age and species composition of the investigated forests and by the ability of populations to overwhelm suboptimal trees The observations presented here suggest that secondary spruce forests in Europe may be unsustainable due to unprecedented bark beetle outbreaks, which can be further amplified by changing climate

Models for predicting microfibril angle variation in Scots pine

Abstract: Context Microfibril angle (MFA) is one of the key determinants of solid timber performance due to its strong influence on the stiffness, strength, shrinkage properties and dimensional stability of wood.

Within- and between-stand variation in selected properties of Sitka spruce sawn timber in the UK: implications for segregation and grade recovery

Abstract: Information on wood properties variation is needed by forest growers and timber processors to best utilise the available forest resource and to guide future management. This study aims to quantify the variation in selected properties of Sitka spruce (Picea sitchensis (Bong.) Carr.) structural timber. Twelve harvest-age stands were selected, ten trees per site were felled and processed into 301 logs. Dynamic modulus of elasticity (MOEdyn) was measured on each tree and log using portable acoustic instruments. Logs were processed into structural timber and its MOE and bending strength was determined. Overall, the timber satisfied the MOE, bending strength and density requirements for the C16 strength class. Approximately 25 % of the total variation in timber mechanical properties was attributed to between-stand differences, with the remaining 75 % attributed to within-stand differences. A series of equations were developed to predict site, tree and log-level variation in timber properties. Knowledge of the site and stand factors that are associated with differences in timber properties can assist with segregation of the current resource. Portable acoustic tools can also be used to increase the stiffness of sawn timber by segregating out individual trees and logs that will yield low stiffness timber.

Shrub biomass estimation in the semiarid Chaco forest: a contribution to the quantification of an underrated carbon stock

Abstract: The quantification of biomass of woody plants is at the basis of calculations of forest biomass and carbon stocks. Although there are well-developed allometric models for trees, they do not apply well to shrubs, and shrub-specific allometric models are scarce. There is therefore a need for a standardized methodology to quantify biomass and carbon stocks in open forests and woodlands. To develop species-specific biomass estimation models for common shrubs, as well as a multispecies shrub model, for the subtropical semiarid Chaco forest of central Argentina. Eight shrub species (Acacia aroma, Acacia gilliesii, Aloysia gratissima, Capparis atamisquea, Celtis ehrenbergiana, Larrea divaricata, Mimozyganthus carinatus, and Moya spinosa) were selected, and, on average, 30 individuals per species were harvested. Their total individual dry biomass was related with morphometric variables using regression analysis. Crown area as well as crown-shaped variables proved to be the variables with the best performance for both species-specific and multispecies shrub models. These allometric variables are thus recommended for standardized shrub biomass assessments. By accounting for the shrub component of the vegetation, our models provide a way to improve the quantification of biomass and carbon in semiarid open forest and woodlands.

Investigating biochemical processes to assess deadwood decay of beech and silver fir in Mediterranean mountain forests

Abstract: Context We investigated the relationships between decay classes, morphological characteristics and chemical compounds in Abies alba Mill. and Fagus sylvatica L. stumps in two forest stands in the central Apennines (Italy). The analysis of deadwood decomposition is important in estimating carbon sequestration potential and carbon residence time in forest ecosystems. In addition, deadwood decomposition affects nutrient cycling and microhabitat distribution.

Storm damage of Douglas-fir unexpectedly high compared to Norway spruce

Abstract: Since storm damage has a large impact on forest management in Central Europe, we investigated the main storm risk factors for two important conifer species, Douglas-fir (Pseudotsuga menziesii [Mirbel] Franco) and Norway spruce (Picea abies [L.] Karst.). We compared general storm damage levels of Douglas-fir and Norway spruce, the latter being known to have high storm risk among European tree species. Generalized linear mixed models and boosted regression trees were applied to recorded storm damage of individual trees from long-term experimental plots in southwest Germany. This included two major winter storm events in 1990 and 1999. Over 40 candidate predictors were tested for their explanatory power for storm damage and summarized into predictor categories for further interpretation. The two most important categories associated with storm damage were timber removals and topographic or site information, explaining between 18 and 54 % of storm damage risk, respectively. Remarkably, general damage levels were not different between Douglas-fir and Norway spruce. Under current forest management approaches, Douglas-fir may be considered a species with high storm risk in Central Europe, comparable to that of Norway spruce.

Mast seeding in deciduous forests of the northern Apennines (Italy) and its influence on wild boar population dynamics

Abstract: Pulsed food resources may strongly affect the population dynamics of several consumer species, with consequences on the ecosystem. One of the most common pulsed resources is forest mast seeding. We analysed mast seeding in deciduous forests in a mountainous area of northern Apennines and its effect on population dynamics of wild boar (Sus scrofa L.). We performed a quantitative, 20-year analysis on annual seed production in Turkey oak (Quercus cerris L.), beech (Fagus sylvatica L.) and chestnut (Castanea sativa Mill.) forest stands using litter traps. The wild boar population density was estimated by means of drive censuses and hunting bag records. The role of other biotic (density of predators) and abiotic (climate) factors potentially affecting wild boar mortality was also investigated. Turkey oak and chestnut showed high levels of seed production, whereas lower levels were found in beech. The pulsed resources of chestnut and Turkey oak positively affected piglet density. Analyses also highlighted the influence of snow cover and wolves on wild boar population dynamics. Wild boar can be considered a pulse rate species, the management of which can be improved by annual monitoring of seed production.

Differential response to soil drought among co-occurring broad-leaved tree species growing in a 15- to 25-year-old mixed stand

Abstract: In the context of global environmental changes, better understanding of tree response to soil drought in young mixed species stands is needed to anticipate forest adaptation and management practices for the future. We investigated the functional response of five co-occurring broad-leaved tree species growing in a 15- to 25-year-old mixed stand in northeastern France during the 2006 summer drought. We measured functional traits related to water acquisition (phenology, rooting pattern and vulnerability of xylem to cavitation) and the ecophysiological response (sap flux density, leaf water potential) of these species to soil water shortage. Our study highlights contrasted drought response strategies among these species and a trade-off between leaf phenology, resistance of xylem to cavitation and root system depth. At this site, a deep root system seemed to be a key functional trait for the species to cope with drought. Quercus robur and Salix capreae can be characterised as drought-avoidance species as they possess a deep root system and therefore did not strongly experience soil drought. Despite deep rooting capacity, Betula pendula did not really avoid soil drought and strongly regulated transpiration during dry periods. Nevertheless, the earliness of budburst of this species contributes to high annual growth rate. In contrast, Carpinus betulus and Fagus sylvatica both displayed typical characteristics of drought-sensitive species.

Selection of mixed-effects parameters in a variable–exponent taper equation for birch trees in northwestern Spain

Abstract: Taper equations predict the variation in diameter along the stem, therefore characterizing stem form. Several recent studies have tested mixed models for developing taper equations. Mixed-effects modeling allow the interindividual variation to be explained by considering both fixed-effects parameters (common to the population) and random-effects parameters (specific to each individual). The objective of this study is to develop a mixed-effect variable exponent taper equation for birch trees in northwestern Spain by determining which fixed-effects parameters should be expanded with random-effects parameters. All possible combinations of linear expansions with random effects in one and in two of the fixed-effects model parameters were tested. Upper stem diameter measurements were used to estimate random-effects parameters by the use of an approximate Bayesian estimator, which calibrated stem profile curves for individual trees. Parameter estimates for more than half of the mixed models investigated were nonsignificant. A first order autoregressive error structure was used to completely remove the autocorrelation between residuals, as mixed-effects modeling were not sufficient for this purpose. The mixed model with the best fitting statistics did not provide the best calibration statistics for all upper stem diameter measurements. From a practical point of view, model calibration should be considered an essential criterion in mixed model selection.

Reciprocal and advanced generation hybrids between Corymbia citriodora and C. torelliana: forestry breeding and the risk of gene flow

Abstract: Corymbia F1 hybrids have high potential for plantation forestry; however, little is known of their reproductive biology and potential for genetic pollution of native Corymbia populations. This study aims to quantify the influence of reproductive isolating barriers on the success of novel reciprocal and advanced generation Corymbia hybrids. Two maternal taxa, Corymbia citriodora subsp. citriodora and Corymbia torelliana, were pollinated using five paternal taxa, C. citriodora subsp. citriodora, C. torelliana, one C. torelliana x C. citriodora subsp. citriodora hybrid and two C. torelliana x C. citriodora subsp. variegata hybrids. Pollen tube, embryo and seed development were assessed. Reciprocal hybridisation between C. citriodora subsp. citriodora and C. torelliana was successful. Advanced generation hybrids were also created when C. citriodora subsp. citriodora or C. torelliana females were backcrossed with F1 hybrid taxa. Prezygotic reproductive isolation was identified via reduced pollen tube numbers in the style and reduced numbers of ovules penetrated by pollen tubes. Reproductive isolation was weakest within the C. citriodora subsp. citriodora maternal taxon, with two hybrid backcrosses producing equivalent capsule and seed yields to the intraspecific cross. High hybridising potential was identified between all Corymbia species and F1 taxa studied. This provides opportunities for advanced generation hybrid breeding, allowing desirable traits to be amplified. It also indicates risks of gene flow between plantation and native Corymbia populations.

Diversity of ophiostomatoid fungi associated with the large pine weevil, Hylobius abietis, and infested Scots pine seedlings in Poland

Abstract: Bark beetles are known to be associated with fungi, especially the ophiostomatoid fungi. However, very little is known about role of pine weevils, e.g., Hylobius abietis, as a vector of these fungi in Europe. The aims of our study were to demonstrate the effectiveness of H. abietis as a vector of ophiostomatoid fungi in Poland and to identify these fungi in Scots pine seedlings damaged by weevil maturation feeding. Insects and damaged Scots pine seedlings were collected from 21 reforestation sites in Poland. The fungi were identified based on morphology, DNA sequence comparisons for two gene regions (ITS, β-tubulin) and phylogenetic analyses. Sixteen of the ophiostomatoid species were isolated and identified. In all insect populations, Leptographium procerum was the most commonly isolated fungus (84 %). Ophiostoma quercus was also found at a relatively high frequency (16 %). Other ophiostomatoid fungi were found only rarely. Among these rarer fungi, four species, Leptographium lundbergii, Ophiostoma floccosum, Ophiostoma piliferum and Sporothrix inflata, were isolated above 3 %. L. procerum was isolated most frequently and was found in 88 % of the damaged seedlings. S. inflata was isolated from 26 %, while O. quercus occurred in 10 % of the seedlings. This study confirmed that L. procerum and O. quercus were common associates of H. abietis, while others species were found inconsistently and in low numbers, indicating causal associations. H. abietis also acted as an effective vector transmitting ophiostomatoid species, especially L. procerum and S. inflata, to Scots pine seedlings.

Spatially explicit competition in a mixed planting of Araucaria cunninghamii and Flindersia brayleyana

Abstract: A 20-year-old Nelder wheel planted with hoop pine (Araucaria cunninghamii Aiton ex D.Don) and Queensland maple (Flindersia brayleyana F.Muell.) in 18 spokes and 8 rings represents nominal point densities of 3,580, 2,150, 1,140, 595, 305, 158, 82, and 42 stems/ha and offers an opportunity to examine competition and spatial interaction between these two species. This study aimed to evaluate the intraspecific and interspecific competition between two contrasting tree species and to determine the distance over which competition can be observed. Competition was estimated using Hegyi’s index, implemented using the Simile visual modeling environment, and calibrated using nonlinear least squares with PEST. Interactions were detected between pairs of stems closer than D ij < 40(d i + d j ) where D is distance (in centimeters) and d is stem diameter (in centimeters diameter at breast height). F. brayleyana trees surrounded by A. cunninghamii trees experience negligible competition, whereas A. cunninghamii surrounded by F. brayleyana trees suffer strong competition. Forty times diameter offers a useful guide to the extent of competition in even-aged stands planted with these species. Competition can be observed empirically when pairs of trees are closer than 40 times the sum of their diameters, but the intensity of the competition may vary considerably with species.

Relationship between tree morphology and growth stress in mature European beech stands

Abstract: In European Beech (Fagus sylvatica L.) large growth stresses lead to severe log end splitting that devaluate beech timber. Our study aimed at detecting relationships between growth stress and some morphology parameters in trees. Growth stress indicators were recorded for 440 mature trees in nine stands from five European countries, together with morphology parameters. Most trees displayed an uneven distribution of growth stress around the trunk. Moreover, growth stress intensity varied largely between individual trees. Geometry of the trunk was a poor predictor of growth stress intensity. Crown asymmetry resulted in a larger stress dissymmetry within trees. Trunk inclination was not correlated to max tension stress, contrary to what is usually found in younger trees. In the case of small inclination, growth stress was close to expected from biomechanics of restoring verticality. Trees exhibiting a larger inclination probably evolved a different mechanical solution: a rather large crown, lower tree slenderness and a sufficient asymmetry in growth stress as to prevent a higher inclination due to growth. A large slenderness is the best accurate predictor of a large growth stress, although variations in the ratio height/diameter at breast height explained only 10 % of the variability of growth stress. A large crown surface was the best predictor of a low level of growth stress. A large spacing between trees seems a good solution to lower the risk of growth stress in mature beech.

Modelling the effects of climate change and timber harvest on the forests of central Nova Scotia, Canada

Abstract: Understanding the range of possible climate change impacts on forests and the interactions between them is vital to sustainable forest management. We examine whether the combined influence of climate change and timber harvest will affect tree species distribution and productivity beyond predictions based on climate alone. We used the landscape disturbance model LANDIS-II to simulate two climate and two harvest scenarios in 14,000 ha of managed watersheds. The elevated temperature led to a decline in the abundance of boreal species and a substantial increase in some temperate and pioneer species. Importantly, the interaction of climate change and timber harvest yielded changes in the distribution of some species that would not be expected based on climate alone. Conversely, some late-successional species exhibited resistance to climate-driven changes in their distribution. Climate change caused an increase in forest productivity when harvest was simulated, but a decrease in no-harvest scenarios. A time lag in forest response was likely responsible for this decrease in the absence of widespread mortality. The finding that disturbance may drive the range expansion of early-successional broadleaved species and cause a decline of red spruce has implications for forest community associations, as well as for forest management where conifers are favoured for pulp production.

Methods for the very early selection of Pinus radiata D. Don. for solid wood products

Abstract: There has been an increasing interest in very early selection of radiata pine to reduce the breeding cycle for solid wood products. For such selection, new approaches are required to assess wood quality in wood from very young stems. Nursery seedlings of clones of radiata pine were grown in leant condition using two leaning strategies for 18–20 months. Opposite wood and compression wood were isolated from the leaning stems and tested for dynamic modulus of elasticity, density, longitudinal shrinkage, volumetric shrinkage and compression wood area using new methods evolved for testing small size samples quickly and reliably. The methods were tested for their efficiency in differentiating clones by their wood properties. Leaning of stems provided distinct opposite and compression wood for testing. Automated image analysis method used for compression wood area assessment was found to be a quick and effective method for processing large number of samples from young stems. Compression wood was characterised by high basic density, high longitudinal shrinkage and low volumetric shrinkage than that of opposite wood. Acoustic velocity in opposite wood had a strong negative association with longitudinal shrinkage. The study signifies the importance of preventing mixing of opposite wood with compression wood while assessing wood quality in young stems thus making leaning a critical strategy. The comparison of wood properties of opposite wood revealed significant differences between clones. Opposite wood of the clone with the lowest dynamic modulus of elasticity exhibited the highest longitudinal shrinkage. Significant differences in measurable wood properties between clones suggest the prospects of early selection for solid wood products.

Influence of cambial age and climate on ring width and wood density in Pinus radiata families

Abstract: The correlation between tree ring width and density and short-term climate fluctuations may be a useful tool for predicting response of wood formation process to long-term climate change. This study examined these correlations for different radiata pine genotypes and aimed at detecting potential genotype by climate interactions. Four data sets comprising ring width and density of half- and full-sib radiata pine families were used. Correlations with climate variables were examined, after the extraction of the effect of cambial age. Cambial age explained the highest proportion of the ring to ring variation in all variables. Calendar year and year by family interaction explained a smaller but significant proportion of the variation. Rainfall had a positive correlation with ring width and, depending on test site, either a negative or positive correlation with ring density. Correlations between temperature during growing season and ring density were generally negative. Climate variables that influence ring width and wood density can be identified from ring profiles, after removing the cambial age effect. Families can be selected that consistently show desirable response to climate features expected to become prevalent as a result of climate change.

Thinning increases cone production of stone pine (Pinus pinea L.) stands in the Northern Plateau (Spain)

Abstract: & Context Edible stone pine (Pinus pinea L.) nut is a forest product which provides the highest incomes to the owners of stone pine forests. & Aim The objective of this work is to evaluate the effect of first thinning on growth and cone production in an artificially regenerated stand in order to determine optimum intensity. & Methods A thinning trial was installed in 2004 to compare two thinning regimes (heavy and moderate) and a control treatment. From 2004 to 2012, six inventories of forest attributes were carried out, and the cone crop was harvested annually.Weevaluatedtheeffectofthinningsongrowthusing repeated measures analysis of variance with a mixed model approach. With regards to cone production, we first estimated the probability of finding cones in a tree by applying a generalized mixed model and then estimated cone production by using a mixed model, including climatic variables. & Results We found that thinning had a positive influence on tree diameter increment. Thinning increased the probability of finding cones and cone production. However, significant differences between heavy and moderate thinnings were not found. & Conclusion We recommend early silvicultural treatments in stone pine stands to favor the development of trees and larger edible pine nut production.

Growth response of Scots pine with different crown transparency status to drought release

Abstract: One short-term adjustment of trees to drought is the reduction of photosynthetic tissues via leaf shedding. But in conifers, it usually takes several years to fully restore needle mass and assimilation capacity. This study aims to evaluate whether leaf shedding sustainably damages conifers or if these trees still have the ability to recover from drought with respect to their foliage and wood formation. An irrigation experiment was established in a mature dry forest to test the growth reactions of Scots pine (Pinus sylvestris L.) differing in crown transparency (low, medium, high) to a drought release by irrigation in comparison with equivalent control trees growing under naturally dry conditions on the same site. Drought and high crown transparency had a combined negative effect on radial tree growth: Control trees with medium to high crown transparencies showed a substantially shorter growth period and a long-lasting growth depression in response to the severe summer drought in 2003. However, all trees benefited from irrigation, irrespective of their crown status, and immediately increased growth in response to irrigation. The progressed drought-induced defoliation seemed to be a weakening factor for trees suffering from drought, but this can be reversed if the water supply is improved.

Veneer grades, recoveries, and values from 5-year-old eucalypt clones

Abstract: Processing young, small eucalypt logs into veneer is a burgeoning industry across southern China. However, plantations supplying these logs were mostly established for pulpwood; little information is available on variation and selection among commercial eucalypt clones/varieties in regards to suitability for veneer production. Tree growth and log form were assessed on 11 eucalypt clones from a 5-year-old trial in southern China. Logs from these were rotary peeled for veneer; recovery percentages plus a range of quality and value traits were assessed on the outturn. Tree volumes, green veneer recovery ratios (%), veneer quality grades, log value, and value m−3 varied significantly among both clones and log positions up the stem. The clone with the best veneer recovery ratio (50.5 %) provided nearly twice that of the poorest clone (28.4 %). Average veneer value log−1 by clone ranged from RMB 6.7 (US$1) up to RMB 15.1 (US$2) and average value m−3 by clone ranged from 589 RMB m−3 (US$88) up to 925 RMB m−3 (US$139). Overall, sweep was the key factor influencing veneer recovery ratio and value. Knots, especially dead knots, holes and splitting were major factors influencing veneer quality grade. Middle and upper logs had significantly higher veneer recoveries, grades, and values m−3 than the lower logs. Excellent potential exists for selecting among eucalypt clones, and even among log positions within trees, for optimizing veneer production.

Diversity of ectomycorrhizal fungus assemblages on nursery grown European beech seedlings

Abstract: An important feature of forest nursery management is the production of first-rate planting stock, which is closely connected with an adequate development of ectomycorrhizas on seedling roots. The aim of this study was to provide a detailed assessment of the ectomycorrhizal (ECM) fungal diversity of European beech grown in bare-root forest nursery conditions. Morphological and molecular analyzes were used to identify ECM fungi, quantify fungal richness, and record differences in the relative abundance of individual taxa. Twenty-seven different mycorrhizal fungal taxa were found in four tested nurseries. Of these 27, only 6 were present in more than one nursery. Taxa richness in individual nurseries ranged from 6 to 13, indicating that ECM colonization potential is nursery-dependent. The most frequent taxa were: Tuber sp. 1, Cadophora sp., Cenococcum geophilum agg., Hebeloma sacchariolens, and Laccaria tortilis. According to the analysis of similarity, ECM fungal communities were significantly different between nurseries (R = 0.7741; p < 0.0001). Beech seedlings grown in bare-root nurseries are colonized by a highly diverse suite of ECM fungi; thus, artificial inoculation of seedlings is generally not necessary in nursery practice.

Inter- and intra-annual variations in canopy fine litterfall and carbon and nitrogen inputs to the forest floor in two European coniferous forests

Abstract: The amount and chemistry of litterfall have been known to strongly vary among the years with important implications for ecosystem nutrient cycles, but there are few quantitative data describing such variations. We studied the climatic implications on the variation in litterfall and its C and N input to soil in two distinct European coniferous forests. Year-to-year variations in canopy litterfall were measured in a Scots pine stand (Hyytiala, Finland) over 13 years, and a Douglas fir stand (Speulderbos, The Netherlands) over 3 years. Important inter-annual variations in litterfall were observed in Scots pine. Litterfall was mainly driven by leaf senescence; however, premature needle fall was observed in high wind speed and early frost events. The seasonal variation in litterfall was characterized by a maximum in September in Scots pine, and by a biphasic variation pattern in Douglas fir, in May and November. Lower seasonal variations and lower annual average in litterfall N content were observed in Scots pine. Significant inter- and intra-annual variations in litterfall and chemistry and between the sites were demonstrated; and it depended on year-to-year differences in climate and extreme weather events.

Low light acclimation in five temperate broad-leaved tree species of different successional status: the significance of a shade canopy

Abstract: Tree species differ largely in their capability to produce characteristic shade leaves with effective morphological and physiological acclimation to low light. By examining the sun/shade leaf differentiation in leaf morphology, foliar nitrogen and photosynthetic capacity in five temperate tree species of different successional status, we aimed at identifying those leaf traits that determine the development of a typical shade crown with low light-acclimated leaves. Leaf morphology, foliar N content, photosynthetic capacity (V cmax, J max and A max) and leaf dark respiration (R d) were measured in the canopies of 26 adult trees of Fraxinus, Acer, Carpinus, Tilia and Fagus species. Six traits (the sun/shade leaf differentiation in specific leaf area, leaf size, A max per leaf area or per mass, photosynthetic N use efficiency and R d) were found to characterise best the degree of low light acclimation in shade leaves. All five species exhibited certain modifications in leaf morphology and/or physiology in response to low light; Fagus sylvatica showed the highest and Fraxinus excelsior the lowest shade leaf acclimation. Our results indicate that the five early/mid- to late-successional species have developed species-specific low light acclimation strategies in their shade crowns which differ in terms of the relative importance of leaf morphological and physiological acclimation.

Distribution of coarse and fine roots of Theobroma cacao and shade tree Inga edulis in a cocoa plantation

Abstract: Cocoa (Theobroma cacao L) is often cultivated below legume shade trees, but root interactions between the species are not well known The first step in understanding these interactions is the description of spatial root system distribution of cocoa and shade trees We studied the root distributions of cocoa and Inga edulis Mart (inga) in an agroforestry plantation in the humid tropics of Costa Rica Fine roots were sampled by soil coring, and a fractal root architecture model parameterised with data from partial root excavations was used for determining coarse root distribution Fine root length in the 0–50 cm soil layer was 26,762 and 22,026 km ha−1 for cocoa and inga, respectively, with 24 % and 23 % of fine root length of cocoa and inga, respectively, in the 0–2 cm layer Horizontally, root distributions of the two species with cocoa at 3 × 3 m and inga at 9 × 9 m spacing overlapped strongly, while inga did not cover all points at 18 × 18 m spacing Both species seem to efficiently capture nutrients released from the litter layer on the soil surface, and nutrient leaching in shaded cocoa plantations is unlikely The proximity of root systems may facilitate N exchange between the N2-fixing inga and cocoa, but competition for other nutrients is likely

Assessing temporal variation of primary and ecosystem production in two Mediterranean forests using a modified 3-PG model

Abstract: & Context Forest ecosystem carbon uptake is heavily affected by increasing drought in the Mediterranean region. & Aims The objectivesofthisstudy weretoassessthe capacity of a modified 3-PG model to capture temporal variation in gross primary productivity (GPP), and ecosystem net carbon uptake (NEE) in two Mediterranean forest types. & Methods The model was upgraded from a monthly (3-PG) to a daily time step (3-PGday), and a soil water balance routine was included to better represent soil water availability. The model was evaluated against seasonal GPP and NEE dynamics from eddy covariance measurements. & Results Simulated and measured soil water content values were congruent throughout the study period for both forest types. 3-PGday effectively described the following: GPP and NEE seasonal patterns; the transition of forest ecosystems from carbon sink to carbon source; however, the model overestimated diurnal ecosystem respiration values and failed to predict ecosystem respiration peaks. & Conclusions The model served as a rather effective tool to represent seasonal variation in gross primary productivity, and ecosystem net carbon uptake under Mediterranean droughtprone conditions. However, its semi-empirical nature and the simplicity inherent in the original model formulation are obstaclespreventingthemodel workingwellfor short-termdaily predictions.

Plasticity of reproductive allocation of a woody species (Ulex europaeus) in response to variation in resource availability

Abstract: Context - While many woody perennials grow and reproduce in varying environments, their ability to modify their reproductive allocation under varying resource availability is unclear. Aims - This study aimed to demonstrate the occurrence of plasticity of reproductive allocation in a pioneer woody species (Ulex europaeus). Methods - We studied seed production in 144 plants under different irradiance and population densities. We measured their basal area, their whole shoot biomass and photosynthetic biomass, and their reproductive output (number of fruits per individual and number of seeds per fruit). Results - We found that newly produced photosynthetic biomass was influenced by environmental variation, which in turn determined plants' reproductive output. In addition, in low light conditions investment in reproduction was more reduced than investment in growth indicating plasticity of reproductive allocation. Conclusion - These results provide the first evidence for plasticity of reproductive allocation of a woody plant. It may lead to the ability of this pioneer species to survive and to continue to reproduce even at low rates in non-optimal shady habitats and to maintain a non-empty seed bank in forest systems with long unfavourable periods between two disturbances.

Effects of pre-commercial thinning on growth and reproduction in post-fire regeneration of Pinus halepensis Mill

Abstract: Excessive recruitment in post-fire regeneration of Pinus halepensis can require pre-commercial thinning. The 1994 Moratalla fire (Spain) and the thinning applied there since 2004 provided good conditions for testing pre-commercial thinning effectiveness. To analyse pre-commercial thinning effects on tree size, reproductive potential, stem biomass and annual growth in 15-year-old saplings. Twenty nine circular plots (5 m radius) were established based on (1) years since thinning and (2) aspect. Non-thinned plots were included as controls. Sapling variables were measured and pine cones were counted and classified according to maturity. Three saplings per plot were felled, five sample disks were extracted from each and tree rings were analysed with Windendro® software. Sapling size, annual growth and stem biomass were higher in thinned plots than in control plots 2–4 years after thinning. Annual growth declined five years after thinning. Cone counts were higher 2–5 years after thinning, depending on the cone type. Aspect influenced some variables. Thinning accelerated stand maturity but positive effects were indiscernible until 2–5 years later. Serotinous cones, which are fundamental to regeneration after fire, increased in number after 5 years. The effects of aspect were inconclusive due to interactions with years since thinning.