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  • Forests
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  • 1
    Language: English
    In: Plant and Soil, 2010, Vol.333(1), pp.93-103
    Description: Assessment of belowground interactions in mixed forests has been largely constrained by the ability to distinguish fine roots of different species. Here, we explored near infrared reflectance spectroscopy (NIRS) to predict the proportion of woody fine roots in mixed samples and analyzed whether the prediction quality of NIRS models is related to the complexity of the fine-root mixture. For model calibration and validation purposes, 11 series of artificial mixed species samples containing known amounts of fine roots of up to four temperate tree species and non-woody plants were prepared. Three types of models with different calibration/validation approaches were developed and tested against external independent data for additional validation. With these models the proportion of each species in root mixtures was predicted accurately with low standard error of prediction (RMSECV/RMSEP 〈6.5%) and high coefficient of determination (r 2  〉 0.93) for all fine-root mixtures. In addition, NIRS models also provided satisfactory estimates for samples with low (〈15%) or no content of particular components. The predictive power of the NIRS models did not decrease substantially with increasing complexity of the root samples. The approach presented here is a promising alternative to hand sorting of fine roots, which may be influenced substantially by operator variation, and it will facilitate investigating belowground interactions between woody species.
    Keywords: Fine roots ; Belowground diversity ; Near-infrared reflectance spectroscopy (NIRS) ; NIRS model ; Species proportions
    ISSN: 0032-079X
    E-ISSN: 1573-5036
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  • 2
    Language: English
    In: Forest Ecology and Management, 2012, Vol.265, pp.191-200
    Description: ► The tree species richness were experimentally controlled and sufficiently replicated. ► Overall soil exploitation was not significantly affected by species richness. ► Belowground competition is size-asymmetric. ► Belowground competition from other species did not affect fine-root morphology. ► Dominant species benefits more from species admixing. Belowground interactions in diverse plant communities may be decisive for the performance of individual species and community stability. Here we assessed the effect of tree species richness on belowground fine-root morphology and belowground competition between four different species in a 6-year-old field biodiversity experiment to test the hypotheses: (i) overall fine-root exploitation (total fine-root length and surface area) increases with tree species richness; (ii) belowground interspecific competition is size-symmetric. Overall fine-root length and surface area in the centre of neighbourhoods of four saplings were initially low (1.03 km m and 2.00 m m ), but reached 3.13 km m and 6.50 m m , respectively, across all species combinations after two growing seasons in the ingrowth cores. However, no significant differences were found among the different tree species richness levels. The saplings of different tree species grew in proportion to their initial sizes with respect to aboveground basal area increments. For belowground fine-root growth in mixed neighbourhoods, however, and had higher fine-root growth rates in ingrowth cores than in monocultures, whereas the reverse was true for and . After two years of root ingrowth, the competitive ability indexes ( = 0.07, = 0.08, = −0.19, = −0.18) revealed that belowground competition in this sapling stand was size-asymmetric and that conifers showed a higher competitive ability, when fine-root growth was related to aboveground standing basal area. Nutrient enrichment in ingrowth cores did not affect proliferation rates and morphology of fine roots significantly. Fine-root morphologies of different species were remarkably different, but within each species the morphology was not significantly influenced by tree species richness of neighbourhoods. Our results show that belowground competition may occur earlier than aboveground in mixed forest stands and fine-root growth of dominant species benefitted more from mixing with other species than that of inferior species.
    Keywords: Fine Root Morphology ; Tree Species Richness ; Niche Complementarity ; Morphological Plasticity ; Size-Asymmetric Competition ; Forestry ; Biology
    ISSN: 0378-1127
    E-ISSN: 1872-7042
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  • 3
    Language: English
    In: Forest Ecology and Management, 15 November 2016, Vol.380, pp.261-273
    Description: Increasing frequency of extremely dry and hot summers in some regions emphasise the need for silvicultural approaches to increase the drought tolerance of existing forests in the short term, before long-term adaptation through species changes may be possible. The aim of this meta-analysis was to assess the potential of thinning for improving tree performance during and after drought. We used results from 23 experiments that employed different thinning intensities including an unthinned control and focused on the response variables: radial growth, carbon- and oxygen-isotopes in tree-rings and pre-dawn leaf-water potential. We found that thinning effects on the growth response to drought differed between broadleaves and conifers, although these findings are based on few studies only in broadleaved forests. Thinning helped to mitigate growth reductions during drought in broadleaves, most likely via increases of soil water availability. In contrast, in conifers, comparable drought-related growth reductions and increases of water-use efficiency were observed in all treatments but thinning improved the post-drought recovery and resilience of radial growth. Results of meta-regression analysis indicate that benefits of both moderate and heavy thinning for growth performance following drought (recovery and resilience) decrease with time since the last intervention. Further, growth resistance during drought became smaller with stand age while the rate of growth recovery following drought increased over time irrespective of treatment. Heavy but not moderate thinning helped to avoid an age-related decline in medium-term growth resilience to drought. For both closed and very open stands, growth performance during drought improved with increasing site aridity but for the same stands growth recovery and resilience following drought was reduced with increasing site aridity. This synthesis of experiments from a wide geographical range has demonstrated that thinning, in particular heavy thinning, is a suitable approach to improve the growth response of remaining trees to drought in both conifers and broadleaves but the underlying processes differ and need to be considered.
    Keywords: Stand Density ; Water Stress ; Radial Growth ; Stable Carbon and Oxygen Isotopes ; Water Potential ; Resilience ; Forestry ; Biology
    ISSN: 0378-1127
    E-ISSN: 1872-7042
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  • 4
    Language: English
    In: Forest Ecology and Management, 01 August 2015, Vol.349, pp.94-105
    Description: Improved knowledge concerning nutrient removals through harvesting in former coppice forests is crucial for the sustainable management of these forests. This is especially true if the resumption of coppicing is being considered to serve increasing fuel wood demands. In this study the nutrient contents of various tree compartments of sessile oak ( (Mattuschka) Liebl.) and hornbeam ( L.) from two sites differing in soil fertility were determined using allometric equations to calculate nutrient removal associated with different harvesting intensities. Stand level nutrient contents in tree compartments were comparable between both study sites. The results for exchangeable base cations, plant available P, and total N indicate that coppicing is not a priori an unsustainable forest management system. On sites with large soil nutrient pools, even whole trees may be harvested without substantial reductions in ecosystem nutrient pools. However, on sites with a low nutrient capital, current harvesting practices would result in relatively high rates of nutrient export. In these stands, harvesting intensity should be based on careful selection of the tree compartments removed, e.g. stem only, to conserve nutrients on site. This study describes the impact of simulated tree harvesting on soil nutrient pools in aged coppice forest for the first time. Based on our findings, general assumptions related to soil sustainability of coppicing are replaced by clear recommendations regarding silvicultural nutrient management. Considering the large areas of aged coppice forests in Europe this study provides a methodological template which is needed to enhance their sustainable management.
    Keywords: Aged Coppice ; Oak ; Hornbeam ; Nutrient Content ; Nutrient Export ; Harvesting Intensity ; Forestry ; Biology
    ISSN: 0378-1127
    E-ISSN: 1872-7042
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  • 5
    Language: English
    In: Forest Ecology and Management, 01 October 2015, Vol.353, pp.164-172
    Description: Absorption of photosynthetically active radiation (APAR) is fundamental for tree growth and is strongly influenced by crown architecture. The aim of this study was to quantify the intra- and inter-specific variability in crown architecture in monospecific and mixed-species subtropical Chinese forests. A total of 68 trees, including , , , and were destructively sampled and their crown architectures were quantified in terms of the vertical distribution of live branch diameter, individual branch leaf area, leaf area and leaf-area density. The vertical distributions were fitted by a two-parameter right truncated Weibull distribution. Inter-specific variability was assessed using ANCOVA and post hoc Tukey tests and intra-specific variability was assessed by fitting linear and linear mixed effect models. The peak in the vertical distribution of leaf area was highest for the least shade tolerant species, (relative depth into the crown of 0.5), intermediate for (0.55), (0.55) and (0.6) and lowest for (0.75). For all species, the vertical distribution of leaf area was influenced by tree size except for . For and , the distribution of leaf area or branch sizes shifted upwards as tree diameter increased, possibly to overtop neighbouring trees. In contrast, as stem diameter increased, the vertical distribution of mean branch diameter shifted downwards, indicating that larger trees invested a higher proportion of their crown growth into their lower crown when compared to smaller trees. The vertical distribution of leaf-area density varied between species but not within a given species. Crown architectures were not influenced by stand density (basal area) or the species composition of the plot. This intra-specific consistency is useful for modelling light in forests. This study shows that there is a significant inter-specific variability in the crown architectures of the co-occurring species in these subtropical forests. There is also significant intra-specific variability related to tree size and this relationship varies between species. This crown architectural variability and its effect on stand structure are likely to influence the light absorption of these stands.
    Keywords: Intra-Specific Variability ; Inter-Specific Variability ; Crown Architecture ; Leaf-Area Density ; Forestry ; Biology
    ISSN: 0378-1127
    E-ISSN: 1872-7042
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  • 6
    Language: English
    In: Forest Ecology and Management, 01 March 2015, Vol.339, pp.57-70
    Description: The rapid re-establishment of forests following large disturbances is being seen as one option to increase the contribution of forests to climate change mitigation. The temporary inclusion of pioneer trees as nurse crops on disturbed sites can facilitate the establishment of target tree species and may additionally benefit productivity and soil fertility. In this study we compared productivity and nutrient cycling between stands of oak target species ( and ) that were established with and without widely spaced ssp. or ssp. nurse crops. Simulation results for a full rotation of oaks (180 years) indicated that both types of forests, with and without nurse crops, have a comparable total productivity. However, stands with nurse crops supplied 59–96 Mg ha harvestable biomass after 20 years, whereas the first harvest of biomass from stands without nurse crops would occur at least 30 years later. Nutrient element costs associated with the removal of ssp. wood were low compared to ssp. Also, nurse crop stands had up to 2.5 times larger pools of exchangeable base cations in top mineral soils (0–30 cm) compared to mono-specific oak stands. The high soil cation pools may have resulted from reduced leaching under nurse crops or the increased recycling of cations, also from deeper soil depth, via litter fall and fine-root turnover. Our results show that forest reestablishment with pioneer tree species may be a suitable tool for the rapid recovery of forest productivity and mitigation potential following disturbances while simultaneously helping to maintain or increase soil fertility.
    Keywords: Nurse Crops ; Populus Ssp ; Betula Ssp ; Biomass Production ; Nutrient Cycling ; Forest Restoration ; Forestry ; Biology
    ISSN: 0378-1127
    E-ISSN: 1872-7042
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  • 7
    In: Global Change Biology, December 2017, Vol.23(12), pp.5108-5119
    Description: Improving our understanding of the potential of forest adaptation is an urgent task in the light of predicted climate change. Long‐term alternatives for susceptible yet economically important tree species such as Norway spruce ( are required, if the frequency and intensity of summer droughts will continue to increase. Although Silver fir ( and Douglas fir have both been described as drought‐tolerant species, our understanding of their growth responses to drought extremes is still limited. Here, we use a dendroecological approach to assess the resistance, resilience, and recovery of these important central Europe to conifer species the exceptional droughts in 1976 and 2003. A total of 270 trees per species were sampled in 18 managed mixed‐species stands along an altitudinal gradient (400–1200 m a.s.l.) at the western slopes of the southern and central Black Forest in southwest Germany. While radial growth in all species responded similarly to the 1976 drought, Norway spruce was least resistant and resilient to the 2003 summer drought. Silver fir showed the overall highest resistance to drought, similarly to Douglas fir, which exhibited the widest growth rings. Silver fir trees from lower elevations were more drought prone than trees at higher elevations. Douglas fir and Norway spruce, however, revealed lower drought resilience at higher altitudes. Although the 1976 and 2003 drought extremes were quite different, Douglas fir maintained consistently the highest radial growth. Although our study did not examine population‐level responses, it clearly indicates that Silver fir and Douglas fir are generally more resistant and resilient to previous drought extremes and are therefore suitable alternatives to Norway spruce; Silver fir more so at higher altitudes. Cultivating these species instead of Norway spruce will contribute to maintaining a high level of productivity across many Central European mountain forests under future climate change. The two extreme droughts in 1976 and 2003 affected negatively the radial growth response of Norway spruce, Silver and Douglas fir in the Black forest at all elevations. The 1976 drought had a less pronounced effect than the 2003 summer drought; however, firs were noticeably more resistant and resilient to extreme drought than spruce. Spruce was the most affected species when comparing performances of drought indices, and Silver fir the least affected. Douglas fir showed consistently the highest growth rates.
    Keywords: Abies Alba ; Central Europe ; Climate Change ; Dendroecology ; Drought Tolerance ; Forest Management ; Picea Abies ; Pseudotsuga Menziesii
    ISSN: 1354-1013
    E-ISSN: 1365-2486
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  • 8
    Language: English
    In: Soil Biology and Biochemistry, 2010, Vol.42(8), pp.1347-1354
    Description: How the mixture of tree species modifies short-term decomposition has been well documented using litterbag studies. However, how litter of different tree species interact in the long-term is obscured by our inability to visually recognize the species identity of residual decomposition products in the two most decomposed layers of the forest floor (i.e. the Oe and Oa layers respectively). To overcome this problem, we used Near Infrared Reflectance Spectroscopy (NIRS) to determine indirectly the species composition of forest floor layers. For this purpose, controlled mixtures of increasing complexity comprising beech and spruce foliage materials at various stages of decomposition from sites differing in soil acid–base status were created. In addition to the controlled mixtures, natural mixtures of litterfall from mixed stands were used to develop prediction models. Following a calibration/validation procedure, the best regression models to predict the actual species proportion from spectral properties were selected for each tree species based on the highest coefficient of determination ( ) and the lowest root mean square error of prediction (RMSEP). For the validation, the (predictions versus true proportions) were 0.95 and 0.94 for both beech and spruce components in mixtures of materials at all stages of decomposition from the gradient of sites. The decreased only marginally by 0.04 when models were tested on independent samples of similar composition. The best models were used to predict the beech-spruce proportion in Oe and Oa layers of unknown composition. They provided in most cases plausible predictions when compared to the composition of the canopy above the sampling points. Thus, tedious and potentially erroneous hand sorting of forest floor layers may be replaced by the use of NIRS models to determine species composition, even at late stages of decomposition.
    Keywords: Forest Floor ; Mixed-Species Forests ; Beech ; Spruce ; NIRS ; Agriculture ; Chemistry
    ISSN: 0038-0717
    E-ISSN: 1879-3428
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  • 9
    In: Journal of Ecology, May 2017, Vol.105(3), pp.761-774
    Description: Promoting mixed‐species forests is an important strategy for adaptation and risk reduction in the face of global change. Concurrently, a main challenge in ecology is to quantify the effects of species diversity on ecosystem functioning. In forests, the effects of individual tree species on ecosystem functions depend largely on their dimensions, which are commonly predicted using allometric equations. However, little is known about how diversity influences allometry or how to incorporate this effect into allometric equations. Ignoring the effects of interspecific interactions on allometric relationships may result in severely biased predictions. This study examined the effects of tree‐species diversity, competition and tree social status on crown‐projection area (cpa), height (h) and live‐crown length (lcl) of trees using a European‐wide data set containing 17 target species and 12 939 trees. The cpa, h and lcl were predicted as functions of stem diameter at 1·3 m, tree‐species diversity, tree height relative to the stand mean height (rh) and a competition index (CI) that accounted for stand density and interspecific differences in competitive ability based on species‐specific wood density or shade tolerance. Averaged across species, diameter had the greatest effect on cpa and lcl, followed by the competition index, while rh had the greatest effect on lcl. Tree‐species diversity had the smallest effect on cpa, h and lcl. Interspecific variability in cpa, h or lcl responses to diversity, CI, or rh was sometimes related to wood density or shade tolerance. Synthesis. This study shows the strong influence of stand structure and species composition on allometric relationships. These influences can be quantified using measures of competition, tree‐species diversity and relative tree height so that general equations can be developed for a given species to be applied to a wide range of species compositions and stand structures. This new approach will greatly improve predictions of biomass and carbon stocks in structurally and compositionally diverse forests. Tree allometry is influenced by, and influences, many forest functions. However, little is known about how allometry of a given species varies with forest structure and tree‐species composition, or whether any interspecific differences in allometric responses relate to species traits. Using a European wide data set, this study shows how stand structural characteristics and tree‐species diversity can influence tree allometry.
    Keywords: Biodiversity ; Biomass Partitioning ; Complementarity ; Plant Allometry ; Plant–Plant Interactions ; Stand Structure ; Tree Height
    ISSN: 0022-0477
    E-ISSN: 1365-2745
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  • 10
    Language: English
    In: Oecologia, 2016, Vol.182(2), pp.319-333
    Description: Forest diversity-productivity relationships have been intensively investigated in recent decades. However, few studies have considered the interplay between species and structural diversity in driving productivity. We analyzed these factors using data from 52 permanent plots in southwestern Germany with more than 53,000 repeated tree measurements. We used basal area increment as a proxy for productivity and hypothesized that: (1) structural diversity would increase tree and stand productivity, (2) diversity-productivity relationships would be weaker for species diversity than for structural diversity, and (3) species diversity would also indirectly impact stand productivity via changes in size structure. We measured diversity using distance-independent indices. We fitted separate linear mixed-effects models for fir, spruce and beech at the tree level, whereas at the stand level we pooled all available data. We tested our third hypothesis using structural equation modeling. Structural and species diversity acted as direct and independent drivers of stand productivity, with structural diversity being a slightly better predictor. Structural diversity, but not species diversity, had a significant, albeit asymmetric, effect on tree productivity. The functioning of structurally diverse, mixed forests is influenced by both structural and species diversity. These sources of trait diversity contribute to increased vertical stratification and crown plasticity, which in turn diminish competitive interferences and lead to more densely packed canopies per unit area. Our research highlights the positive effects of species diversity and structural diversity on forest productivity and ecosystem dynamics.
    Keywords: Basal area increment ; Complementarity ; Ecosystem functioning ; Biodiversity ; Species diversity
    ISSN: 0029-8549
    E-ISSN: 1432-1939
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