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  • Article  (173)
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  • Article  (173)
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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, 15 September 2013, Vol.304, pp.233-242
    Description: Interactions between plant species can be dynamic, changing spatially and temporally with variability in climatic, soil and stand conditions. We examined how inter- and intra-specific interactions between Mill. and (L.) Karst. varied with climate, site quality and stand density in the Black Forest of south-western Germany, using spatially explicit neighbourhood indices. The mixing response, a measure of complementarity, was quantified as the increase in growth of individual trees in a mixed-species neighbourhood compared to a mono-specific neighbourhood. Both species benefited from growing in mixed-species neighbourhoods, but this complementarity effect (−60% to 〉200%) depended on climatic conditions, site quality and stand density. Complementarity increased for with increasing mean maximum temperatures in August, those for increased with mean minimum temperatures in May and site quality, and in each case the magnitude of the effect was amplified with increasing stand density. Complementarity is often considered to become more important in less productive ecosystems, but this study showed that for the given pair of species, complementarity effects can increase as growing conditions improve. A simple model is proposed that describes how relationships between productivity and complementarity change depending on the resources limiting productivity.
    Keywords: Competition Index ; Competitive Reduction ; Individual Tree Model ; Plant–Plant Interactions ; Forestry ; Biology
    ISSN: 0378-1127
    E-ISSN: 1872-7042
    Source: ScienceDirect Journals (Elsevier)
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  • 3
    Language: English
    In: Forest Ecology and Management, 15 May 2017, Vol.392, pp.1-12
    Description: Due to their expected higher resilience following disturbances and adaptive potential to new climatic conditions, interest in uneven-aged mixed forests has increased in recent years. It is, however, unclear how to best quantify their site-specific growth potential, particularly at a time when there is a pressing need to consider the effects of a changing climate on tree and forest growth. Here, we address these topics using growth models for Norway spruce ( (L.) Karst.) and Silver fir ( Mill.), based on long-term observations from uneven-aged mixed forests in southwestern Germany. We used a linear mixed-effects framework for modeling basal area increment of individual trees. We accounted for site quality using a phytocentric index based on the past growth of dominant trees (growth index) and three classes of geocentric environmental descriptors: physiographic, edaphic and climatic (temperature means and precipitation sums aggregated over 5, 15 or 30 years). For a subset of the data where it was possible to determine site index, growth index proved to be better predictor of tree increment than site index. When considering the entire dataset, climate variables had the single largest positive impact on model fit, yet cross-validation results suggested that no improvement in predictive ability occurred unless physiographic variables were also added. Higher levels of spring and growing season precipitation stimulated growth for Norway spruce and Silver fir, respectively. Temperature-growth relationships were predominantly positive for Silver fir and negative for Norway spruce. Aggregating climate variables over progressively longer time spans clearly reduced model fit for Norway spruce, yet a similar pattern was not apparent for Silver fir. Our results indicate that without rigorous testing, tried-and-trusted decision tools developed for even-aged, single-species stands cannot be transferred to uneven-aged mixed forests. Precipitation- and temperature-based variables provide dynamic proxies which may allow us to better grasp the complexity of climate-growth relationships. This understanding is essential for reducing the uncertainty around predictions of climate change impacts on forest ecosystems.
    Keywords: Basal Area Increment ; Climate Change ; Climate-Sensitive Modeling ; Site Quality ; Uneven-Aged Forests ; Forestry ; Biology
    ISSN: 0378-1127
    E-ISSN: 1872-7042
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  • 4
    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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  • 5
    Language: English
    In: Forest Ecology and Management, 15 April 2018, Vol.414, pp.15-27
    Description: More frequent and intensive droughts are projected to affect the vitality of major European tree species. Therefore, it is important to search for alternative, more drought-tolerant species to ensure ecological stability, biodiversity, and productivity of forests in future. Based on their relative abundance at very dry and warm sites, the otherwise rare and little-known, minor broadleaved species like , , , and are thought to be drought-tolerant. However, there is so far only limited scientific evidence to support that notion. Here we quantified the effect of extreme droughts (1947, 1976, and 2003) on radial growth of mature trees of the minor broadleaves in relation to the common companion species and in southwest Germany. Based on tree-ring analyses with a commensurate sample size for such rare species, the ability to resist and recover from drought, as well as the medium-term resilience of mature trees was studied. Likewise, the sensitivity of the species to temperature and precipitation was assessed. Radial growth was positively related to spring and summer precipitation for all species, whereas high summer temperatures led to decreased growth rates for , , and . Whereas appeared to be resistant and resilient in relation to drought, and were also resilient but less resistant to drought stress. A synoptic ranking of the drought tolerance of all tree species suggests that the minor broadleaved tree species are not more drought-tolerant than , except for . We conclude that cultivation of these minor species as well as should be expanded on xerix sites, where reaches its growth limits.
    Keywords: Sorbus ; Acer ; Drought Tolerance ; Resistance ; Resilience ; Climate Sensitivity ; Dendroecology ; Forestry ; Biology
    ISSN: 0378-1127
    E-ISSN: 1872-7042
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  • 6
    Language: English
    In: Forest Ecology and Management, 01 January 2015, Vol.335, pp.87-98
    Description: The production of defect-free, high quality stem wood may be promoted through pruning of branches in hardwood species, yet this practice may also lead to wood defects, such as stem discoloration. Here, models to predict stem discoloration and the time of branch occlusion were developed for L. (sycamore maple) and L. (common ash) based on a pruning experiment in southwest Germany. The dataset consisted of 449 completely occluded branches originating from 115 destructively sampled sycamore maple and common ash trees that had been pruned either in late winter or summer, or had not been pruned and underwent natural branch shedding instead. We analyzed these data with linear and generalized linear mixed-effects models to predict (1) the time until branch occlusion, (2) the length of branch discolorations and (3) the occurrence of discolorations in the stem wood. For all treatments, the time until complete branch occlusion was negatively related to stem radial increment during branch occlusion and positively related to the branch diameter in case of green pruning or the length of the dead branch portion in case of natural branch shedding. The extent of branch discoloration was positively correlated with branch diameter (green pruning) or the dead branch length (natural shedding), which was itself correlated to branch diameter. The probability of stem discoloration after pruning increased with branch diameter and showed large interspecific differences, with a much higher risk for common ash. Thresholds for decay risk based on pruned branch diameters are reported for each species. In both branch and stem discoloration models, there was no evidence of significant effects related to the time of pruning. When analyzing a subset of the original data containing only branches with diameters up to 30 mm, we found that green pruning significantly reduced the duration of branch occlusion. The extent of branch discoloration was positively related to branch diameter and occlusion time and was not affected by pruning treatment or species. Our results indicate that pruning reduces the duration of branch occlusion and, hence, has the potential to increase the proportion of defect-free wood. Furthermore, the duration of branch occlusion after artificial pruning should be minimized in order to reduce the risk of discoloration and decay. Therefore, green pruning should start early in the life of a tree when its branches are still thin and be applied only to vigorous trees that can occlude the wounds rapidly.
    Keywords: Green Pruning ; Natural Branch Shedding ; Wood Quality ; Branch Occlusion ; Wood Discoloration ; Noble Hardwoods ; Forestry ; Biology
    ISSN: 0378-1127
    E-ISSN: 1872-7042
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  • 7
    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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  • 8
    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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  • 9
    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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  • 10
    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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