1. When tree-species mixtures are more productive than monocultures, higher light absorption is often suggested as a cause. However, few studies have quantified this effect and even fewer have ...examined which light-related interactions are most important, such as the effects of species interactions on tree allometric relationships and crown architecture, differences in vertical or horizontal canopy structure, phenology of deciduous species or the mixing effects on tree size and stand density. 2. In this study, measurements of tree sizes and stand structures were combined with a detailed tree-level light model (Maestra) to examine the contribution of each light-related interaction on tree- and stand-level light absorption at 21 sites, each of which contained a triplet of plots including a mixture and monocultures of Fagus syivatica and Pinus sylvestris (63 plots). These sites were distributed across the current distribution of these species within Europe. 3. Averaged across all sites, the light absorption of mixtures was 14% higher than the mean of the monocultures. At the whole community level, this positive effect of mixing on light absorption increased as canopy volume or site productivity increased, but was unrelated to climate. At the species population or individual tree levels, the mixing effect on light absorption resulted from light-related interactions involving vertical canopy structure, stand density, the presence of a deciduous species (F. syivatica), as well as the effects of mixing on tree size and allometric relationships between diameter and height, crown diameter and crown length. 4. The mixing effects on light absorption were only correlated with the mixing effects on growth for P. sylvestris, suggesting that the mixing effects on this species were driven by the light-related interactions, whereas mixing effects on F. syivatica or whole community growth were probably driven by non-light-related interactions. 5. Synthesis. The overall positive effect of mixing on light absorption was the result of a range of light-related interactions. However, the relative importance of these interactions varied between sites and is likely to vary between other species combinations and as stands develop.
•Biodiversity assessment based on forest inventory data.•Scale-overarching characterization of tree compositional and forest structural indices.•Track indices over time to monitor temporal ...behaviour.•Practice-oriented result aggregation.
Currently the paradigm of sustainable forest management is extended to a broad range of ecological, economic, and social forest functions and services. In particular, biodiversity becomes a more and more important issue in the forest planning processes. However, its quantification, monitoring and assessment still remain complex and difficult although data from regional or national forest inventories might contribute valuable information for quantifying biodiversity. Here, we demonstrate how such data can be tapped and aggregated to different spatial and temporal scales for deriving indicators to support biodiversity assessment and monitoring. By focusing on tree species and structural related indices, our method allows the evaluation of spatial and temporal variation of diversity indicators by using inventory data. We present a practice-oriented approach on how to integrate such indicators into forest planning processes and thereby extend the paradigm of sustainability of forest management. We exemplify our approach by inventory data from the Bavarian State Forest Enterprise to show how inventory data can be utilised to (i) assess biodiversity aspects from stand to landscape scales and (ii) integrate such information into forest management at different spatial and temporal scales. Finally, we discuss how this information extracted from forest inventories may contribute to a more generalised assessment, monitoring and planning of biodiversity in managed forest ecosystems.
Synthetic Aperture Radar Tomography (TomoSAR) allows the reconstruction of the 3D reflectivity of natural volume scatterers such as forests, thus providing an opportunity to infer structure ...information in 3D. In this paper, the potential of TomoSAR data at L-band to monitor temporal variations of forest structure is addressed using simulated and experimental datasets. First, 3D reflectivity profiles were extracted by means of TomoSAR reconstruction based on a Compressive Sensing (CS) approach. Next, two complementary indices for the description of horizontal and vertical forest structure were defined and estimated by means of the distribution of local maxima of the reconstructed reflectivity profiles. To assess the sensitivity and consistency of the proposed methodology, variations of these indices for different types of forest changes in simulated as well as in real scenarios were analyzed and assessed against different sources of reference data: airborne Lidar measurements, high resolution optical images, and forest inventory data. The forest structure maps obtained indicated the potential to distinguish between different forest stages and the identification of different types of forest structure changes induced by logging, natural disturbance, or forest management.
Frequency of drought years is expected to increase through climate warming. Mixed stands have often shown to be more productive than monospecific stands in terms of yield and of resistance against ...windthrows and bark beetle attacks. Mixture of beech and spruce is of particular interest. However, little is known about its growth reaction to drought. Therefore, we investigated the drought reaction of beech and spruce in mixed vs. monospecific stands along an ecological gradient. In particular, we sought evidence for mixture-related resilience on the individual tree level. Therefore, we quantified the response of tree ring width to drought. Moreover, we attempted to explain the relevance of individual tree response on the stand level by quantifying the stand level loss of volume growth after drought. At the individual tree level, beech was found to be more resilient and resistant in pure vs. mixed stands. Spruce, in contrast, was favored by mixture, and this was especially evident on drier sites. Along the gradient, growth losses at stand level increased in both mixed and pure stands in 2015, with growth gains on the drier sites observed in the same drought year, in accordance with the Stress Gradient Hypothesis. However, the stand level difference of growth loss between mixed and pure stands was not statistically significant. Mitigating mixture effects on the level of the individual tree thus did not become evident on the level of the whole stand.
Shade tolerance and the functional trait Ameztegui, Aitor; Paquette, Alain; Shipley, Bill ...
Functional ecology,
April 2017, Letnik:
31, Številka:
4
Journal Article
Recenzirano
Odprti dostop
Summary
Despite being instrumental in forest ecology, the definition and nature of shade tolerance are complex and not beyond controversy. Moreover, the role it plays in the trait–demography ...relationship remains unclear.
Here, we hypothesize that shade tolerance can be achieved by alternative combinations of traits depending on the species' functional group (evergreen vs. deciduous species) and that its ability to explain the array of traits involved in demography will also vary between these two groups.
We used dimension reduction to identify the main trait spectra for 48 tree species, including 23 evergreens and 25 deciduous – dispersed across 21 genera and 13 families. We assessed the relationship between functional traits, shade tolerance, and demographic performance at high and low light using structural equation modelling.
The dimensions found corresponded to the trait spectra previously observed in the literature and were significantly related to measures of demography. However, our results support the existence of a divergence between evergreen and deciduous species in the way shade tolerance relates to the demography of species along light gradients.
We show that shade tolerance can be attained through different combination of traits depending on the functional and geographical context, and thus, its utilization as a predictor of forest dynamics and species coexistence requires previous knowledge on the role it plays in the demographic performance of the species under study.
A lay summary is available for this article.
Lay Summary
Allometric relations that link forest above ground biomass to top forest (i.e., canopy) height are of particular significance in the context of lidar and interferometric synthetic aperture radar ...remote sensing, as both techniques allow accurate height measurements at ecologically relevant spatial scales. Besides the often unknown allometry itself, its spatial variation in heterogenous forest environments restricts the performance when using a single fixed height-to-biomass allometric relation. This paper addresses how forest structure information derived from interferometric TanDEM-X data can be used to locally adapt the height-to-biomass allometry in heterogeneous forests, and to improve biomass estimation performance. The analysis is carried out using TanDEM-X interferometric measurements in three tropical forest test sites in Gabon. A structure index expressing forest density is derived from the TanDEM-X data. Then, a continuous relationship between the structure index and the allometric level that defines the forest height-to-biomass allometry is reconstructed from the available lidar data, and used to vary the height-to-biomass relationship. Finally, the potential of the derived structure index to support an allometric relationship common to all sites is evaluated. The experimental results show the appropriateness of TanDEM-X data for characterizing structure and in this way improving the biomass estimation performance.
Wood production is one of the most important ecosystem service that forests provide to society. However, under changing climatic conditions, this appears to be subject to increasing uncertainties. In ...the present study we analyzed how long-term productivity of oak (Quercus petraea Matt. Liebl. and Quercus robur L.) stands has developed, how oak behaved on tree and stand level depending on the stand structure and which trade-offs can be observed. For the analyses, data from 147 long-term monospecific and mixed stands were investigated, which have been regularly recorded since 1898. Firstly, long-term stand productivity has increased up to 21% until 2020 as compared to 1960. This trend was observed for both, monospecific as well as mixed oak stands. Secondly, stand productivity was on average 19% higher in mixed compared to monospecific oak stands. This superiority can be explained by higher stand densities, a vigorous understory and the admixture of beech in particular. With increasing age, the observed positive effect of stand density was higher. Thirdly, individual oak productivity slowed down under interspecific competition, especially in young to mid-aged stands. In this context, the productivity of individual oaks depended strongly on their social position within the stand. Fourthly, in terms of growth partitioning larger trees contributed most in young oak stands, regardless of mixture. In order to preserve oak as a productive component of future mixed forests, the results suggest a silvicultural promotion of oak. Consistent management of dominant and vital oaks can achieve high productive trees while maintaining the positive characteristics of highly structured and mixed forests. A vigorous secondary stand can increase overall stand productivity at lower densities and allows silvicultural flexibility at the stand level. Creating vertical stand structure to reduce competition has only a limited positive effect on productivity of individual oaks that is highly related to its social status. Special attention should still be paid to beech as admixed tree species, which can continue to crowd oak even at higher stand ages.
Background: Most current approaches in forest science and practice require information about structure and growth of individual trees rather than- or in addition to- sum and mean values of growth and ...yield at forest stand level as provided by classic experimental designs. By inventing the wheel design, Nelder provided the possibility to turn to the individual tree as basic information unit. Such trials provide valuable insights into the dependency of growth on stand density at particular sites.Methods: Here, we present an extension of the original design and evaluation by Nelder.(i) We established Nelder wheels along an environmental gradient through Europe in atlantic climate in Belgium and Germany, Mediterranean climate in Italy, continental climate in Hungary as well as on high land climate in Mexico. Such disjunct Nelder wheels along an environmental gradient can be regarded and analysed as a two-factor design with the factors of site condition and stand density.(ii) We present an advanced statistical approach to evaluate density dependent growth dynamics of trees planted in form of the Nelder design, which considers spatio-temporal autocorrelation.(iii)We prove the usefulness of the methods in improving ecological theory concerning density related productivity,trade-offs between facilitation and competition, and allometric relations between size variables.Results: First evaluations based on remeasured Nelder wheels in oak(Quercus robur L.) show a size growth differentiation during the first observation period. In particular, height growth is accelerated under higher competition indicating facilitation effects. We detect furthermore a high variability in allometric relations.Conclusions: The proposed design, methods, and results are discussed regarding their impact on forest practice,model building, and ecological theory. We conclude that the extended Nelder approach is highly efficient in providing currently lacking individual tree level information.
•Summer temperature shows a mainly positive effect on the tree heights of oak.•Decreasing water supply seems to eclipse positive effect of summer temperature.•Stand density and vertical structure ...modify height growth in a mainly positive manner.•Climate sensitivity of oaks height growth seems to be lower in mixtures.
Sessile oak (Quercus petraea (Matt.) Liebl.) and pedunculate oak (Quercus robur L.) play an important role in increasing the resistance of central European forests to severe droughts. But outside their real niche the competitiveness of both oak species can be low in mixed-species stands. This paper examines the height growth of oaks depending on environmental conditions and inter-specific competition. Height growth of trees was analysed using data from forest inventories covering monospecific and mixed-species stands within the German federal state of Bavaria. By means of regression analyses of 23,607 height measurements, we found that site conditions and stand structure have strong effects on the height growth of oak. Summer temperature, water balance in the vegetation period and base saturation were the main explanatory site variables. The first positive effect of summer temperature had no influence at warmer sites with mean summer temperatures above 16.4 °C, while the effect of water balance was positively linear. In addition, stand density modified the height growth of oak in a mainly positive manner. Vertical structure also had a positive effect, which was found for most species compositions, except monospecific stands and oak-hornbeam mixture. In most mixtures, oaks height growth seemed to be less climate-sensitive compared to monocultures. A currently warmer and drier climate seemed to favour the height growth superiority of European beech, whereas it decreased the superiority of Scots pine. The results indicated that even if the climate changes as predicted, the growth of oak will depend upon silvicultural promotion. Our findings can be used to improve regional guidelines for oak silviculture with special regard to climate-sensitive height growth. For example, a regionally delayed introduction of admixed species can reduce silvicultural treatments by ensuring oak vitality in mixed forests at the same time.
•Remote sensing proven a key approach for diversity estimates.•CHM LiDAR shown to be a key instrument for estimating tree species diversity.•Height Variation Hypothesis developed to assess tree ...species diversity.•Height Heterogeneity shown to be related to tree species diversity.
An indirect method for estimating biodiversity from Earth observations is the Spectral Variation Hypothesis (SVH). SVH states that the higher the spatial variability of the spectral response of an optical remotely sensed image, the higher the number of available ecological niches and hence, the higher the diversity of tree species in the considered area. Here for the first time we apply the concept of the SVH to Light Detection and Ranging (LiDAR) data to understand the relationship between the height heterogeneity (HH) of a forest and its tree species diversity, a concept we have named the ‘Height Variation Hypothesis’ (HVH). We tested HVH in two different European forest types: a coniferous mountain forest in the eastern Italian Alps and a mixed temperate forest in southern Germany. We used the heterogeneity index Rao’s Q to estimate HH using a Canopy Height Model (CHM) at different resolutions derived from LiDAR data, and linear regression models and relation analysis to assess the relationships between HH and three species diversity indices derived from in situ collected data: Shannon’s H, Simpson’s S and species richness. The relationships were calculated for all plots in both study areas, and separately for plots with a defined Canopy Closure (CC > 70%, CC > 80%, CC > 90%) to understand the effect of forest density on the relationship between HH and tree species diversity. Our results showed that HH is related to the tree species diversity of the forest ecosystems reaching (in the case of Shannon’s H) values of R2 = 0.63 for the coniferous mountain forest and R2 = 0.56 for the mixed temperate forest, particularly when calculated with a CHM resolution of 2.5 m. The associations also increased with increasing canopy closure suggesting that HVH is scale and forest density dependent. Our results also underlined that the abundance-based diversity measures are more highly correlated with HH than with species richness. Finally, our findings suggest that the HVH is a valuable tool for assessing tree species diversity in forest ecosystems, and could also be useful for overall biodiversity estimates.
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