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  • 11
    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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  • 12
    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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  • 13
    Language: English
    In: Soil biology & biochemistry, 2010, Vol.42, 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 (R2) and the lowest root mean square error of prediction (RMSEP). For the validation, the R2 (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 R2 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. ; Includes references ; p. 1347-1354.
    Keywords: Forest Soils ; Biodegradation ; Soil Ph ; Prediction ; Calibration ; Forest Trees ; Botanical Composition ; Leaves ; Simulation Models ; Forest Litter ; Soil Horizons ; Organic Horizons ; Overstory ; Near-Infrared Reflectance Spectroscopy ; Model Validation ; Picea Abies ; Temperate Forests ; Accuracy ; Regression Analysis
    ISSN: 0038-0717
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
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  • 14
    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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  • 15
    In: Journal of Ecology, January 2013, Vol.101(1), pp.220-230
    Description: Partitioning of tree mortality into different modes of death allows the tracing and mechanistic modelling of individual key processes of forest dynamics each varying depending on site, species and individual risk factors. This, in turn, may improve long‐term predictions of the development of old‐growth forests. Six different individual tree mortality modes (uprooted and snapped (both with or without rot as a predisposing factor), standing dead and crushed by other trees) were analysed, and statistical models were derived for three tree species (European beech Fagus sylvatica, hornbeam Carpinus betulus and common ash Fraxinus excelsior) based on a repeated inventory of more than 13 000 trees in a 28 ha near‐natural deciduous forest in Central Germany. The frequently described U‐shaped curve of size‐dependent mortality was observed in beech and hornbeam (but not ash) and could be explained by the joint operation of processes related to the six distinct mortality modes. The results for beech, the most abundant species, suggest that each mortality mode is prevalent in different life‐history stages: small trees died mostly standing or being crushed, medium‐sized trees had the highest chance of survival, and very large trees experienced increased rates of mortality, mainly by uprooting or snapping. Reduced growth as a predictor also played a role but only for standing dead, all other mortality modes showed no relationship to tree growth. Synthesis. Tree mortality can be partitioned into distinct processes, and species tend to differ in their susceptibility to one or more of them. This forms a fundamental basis for the understanding of forest dynamics in natural forests, and any mechanistic modelling of mortality in vegetation models could be improved by correctly addressing and formulating the various mortality processes. Modelled annual mortality logits and probabilities over d.b.h. (cm) for beech. Median estimates and 95% credible interval. Tree mortality can be partitioned into different processes related to six distinct mortality modes, jointly explaining the emergent ‐shaped curve of size‐dependent mortality. This forms a fundamental basis for the understanding of forest dynamics in natural forests and may improve mechanistic modelling thereof.
    Keywords: Beech ; Demographic Trait ; Growth Estimation ; Growth‐Related Mortality ; Longevity ; Mortality Mode ; Mortality Model ; Plant Population And Community Dynamics ; Size‐Related Mortality
    ISSN: 0022-0477
    E-ISSN: 1365-2745
    Source: John Wiley & Sons, Inc.
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  • 16
    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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  • 17
    Language: English
    In: Oecologia, 2012, Vol.169(4), pp.1105-1115
    Description: The phenomenon of overyielding in species-diverse plant communities is mainly attributed to complementary resource use. Vertical niche differentiation belowground might be one potential mechanism for such complementarity. However, most studies that have analysed the diversity/productivity relationship and belowground niche differentiation have done so for fully occupied sites, not very young tree communities that are in the process of occupying belowground space. Here we used a 5–6 year old forest diversity experiment to analyse how fine-root (〈2 mm) production in ingrowth cores (0–30 cm) was influenced by tree species identity, as well as the species diversity and richness of tree neighbourhoods. Fine-root production during the first growing season after the installation of ingrowth cores increased slightly with tree species diversity, and four-species combinations produced on average 94.8% more fine-root biomass than monocultures. During the second growing season, fine-root mortality increased with tree species diversity, indicating an increased fine-root turnover in species-rich communities. The initial overyielding was attributable to the response to mixing by the dominant species, Pseudotsuga menziesii and Picea abies , which produced more fine roots in mixtures than could be expected from monocultures. In species-rich neighbourhoods, P. abies allocated more fine roots to the upper soil layer (0–15 cm), whereas P. menziesii produced more fine roots in the deeper layer (15–30 cm) than in species-poor neighbourhoods. Our results indicate that, although there may be no lasting overyielding in the fine-root production of species-diverse tree communities, increasing species diversity can lead to substantial changes in the production, vertical distribution, and turnover of fine roots of individual species.
    Keywords: Species diversity ; Species richness ; Fine roots ; Overyielding ; Vertical niche differentiation ; BIOTREE
    ISSN: 0029-8549
    E-ISSN: 1432-1939
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  • 18
    In: Ecological Applications, October 2016, Vol.26(7), pp.2190-2205
    Description: Droughts and their negative effects on forest ecosystems are projected to increase under climate change for many regions. It has been suggested that intensive thinning could reduce drought impacts on established forests in the short‐term. Most previous studies on the effect of thinning on drought impacts, however, have been confined to single forest sites. It is therefore still unclear how general and persisting the benefits of thinning are. This study assesses the potential of thinning to increase drought tolerance of the wide spread Scots pine () in Central Europe. We hypothesized (1) that increasing thinning intensity benefits the maintenance of radial growth of crop trees during drought (resistance) and its recovery following drought, (2) that those benefits to growth decrease with time elapsed since the last thinning and with stand age, and (3) that they may depend on drought severity as well as water limitations in pre‐ and post‐drought periods. To test these hypotheses, we assessed the effects of thinning regime, stand age, and drought severity on radial growth of 129 Scots pine trees during and after drought events in four long‐term thinning experiments in Germany. We found that thinning improved the recovery of radial growth following drought and to a lesser extent the growth resistance during a drought event. Growth recovery following drought was highest after the first thinning intervention and in recently and heavily thinned stands. With time since the last thinning, however, this effect decreased and could even become negative when compared to unthinned stands. Further, thinning helped to avoid an age‐related decline in growth resistance (and recovery) following drought. The recovery following drought, but not the resistance during drought, was related to water limitations in the drought period. This is the first study that analyzed drought‐related radial growth in trees of one species across several stands of different age. The interaction between thinning intensity and time since the last thinning underline the importance to distinguish between short‐ and long‐term effects of thinning. According to our analysis, only thinning regimes, with relatively heavy and frequent thinning interventions would increase drought tolerance in pine stands.
    Keywords: Basal Area Increment ; Drought ; Pinus Sylvestris L. ; Radial Growth ; Recovery ; Resistance ; Scots Pine ; Stand Density ; Water Stress
    ISSN: 1051-0761
    E-ISSN: 1939-5582
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  • 19
    Language: English
    In: Forest Ecology and Management, 15 December 2018, Vol.430, pp.105-116
    Description: The timely establishment of natural regeneration of the preferred species after the death or removal of mature trees is essential in continuous-cover forestry. In the context of the gradual shift from even-aged and monospecific to uneven-aged and/or mixed forest stands, the limited availability of statistical models to predict seedling establishment, survival, and growth has increasingly become a bottleneck for forest management planning and, ultimately, a potential limitation to a wider adoption of alternative silvicultural approaches. We investigated the development of top height and density of natural regeneration in 19 uneven-structured, mixed silver fir ( Mill.) and Norway spruce ( (L.) H. Karst.) stands in southwestern Germany using long-term observations (35 years) from permanent plots. We used linear mixed-effects models to analyze the influence of overstory and understory-related variables on regeneration of fir and spruce. The height of the five tallest juvenile trees per regeneration subplot and species increased significantly with diminishing canopy cover and increasing structural diversity of the overstory. However, competition exerted by tall juveniles substantially impacted the development of smaller neighbors, which were less able to profit from favorable overstory conditions. These results indicate that canopy cover and structural diversity need to be taken into account when modeling height development of juvenile trees in irregular stands. Importantly, these results also demonstrate the potential of silvicultural interventions to shorten the time period when terminal shoots are vulnerable to browsing. Densities of juvenile trees displayed a unimodal relationship with the mean height of the regeneration. Fir and spruce densities culminated at a mean height of approx. 50 cm and decreased rapidly afterwards. This pattern indicates an early onset of competition within the regeneration layer. For both species, juvenile densities were unrelated to overstory structural diversity, yet they showed positive relationships with overstory density and site productivity. Overall, fir juveniles developed faster in height than spruce juveniles. Even rather rapid group-shelterwood cutting regimes with complete canopy removal within two decades still favored fir regeneration. In addition, a high proportion of fir in the regeneration cohort had a stronger negative effect on spruce juvenile density than vice versa. Since spruce is less shade-tolerant than fir, it is likely that fir will dominate the future stand composition. Overall, our models provide the basis to predict natural regeneration dynamics in structurally complex stands dominated by fir and spruce and to further evaluate alternative treatment scenarios.
    Keywords: Regeneration Height ; Regeneration Density ; Residual Overstory ; Structural Diversity ; Uneven-Aged Silviculture ; Norway Spruce ; Silver Fir ; Forestry ; Biology
    ISSN: 0378-1127
    E-ISSN: 1872-7042
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  • 20
    Language: English
    In: Forest Ecology and Management, 15 August 2018, Vol.422, pp.323-337
    Description: Mixed-species forests can have higher productivity, in terms of wood volume, than monospecific forests. In addition, higher tree species richness has been found to positively correlate with multiple ecosystem services and functions. Surprisingly, stem quality as one of the most important factors regarding the economic value of forests has rarely been formally studied in diverse forests. This paper aims at investigating how tree species richness influences stem quality and which factors may drive quality development in these stands. Stem quality, understood here essentially as the suitability of a particular stem for particular end-uses, is influenced by a tree's ability to capture sufficient resources for growth and is influenced by neighbouring trees, e.g. through shading and physical crown interactions. We collected data on crown size, stem form and tree health for over 12,000 trees in 209 study plots in six European regions (Finland, Germany, Poland, Romania, Italy and Spain) within naturally diverse forests to assess the impact of tree species richness on these characteristics. Results showed that quality variability between regions, stands and individual trees was high across species. At the stand level, there was a slight tendency towards lower stem quality with increasing diversity. However, individual trees of high quality were present at all diversity levels and for all target species. Tree species richness could not be confirmed as a primary influence on stem quality at the stand level. Rather, stand and individual tree properties such as structural composition, competition, tree size and crown characteristics were identified as the main factors for stem quality development, even in mixed stands. Many of the factors identified in this study can be directly or indirectly influenced by forest management strategies tailored to produce high-quality timber in mixed-species forests. Our findings suggest that diverse stands are not inferior regarding stem quality, while at the same time being able to provide various other ecosystem services
    Keywords: Timber Quality ; Biodiversity ; Tree Species Richness ; Ecosystem Services ; Fundiveurope ; Forestry ; Biology
    ISSN: 0378-1127
    E-ISSN: 1872-7042
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