•Long-lasting individual tree growth contradicts textbook knowledge.•Mass growth culminates mostly far beyond rotation age.•Spacing, thinning, or fertilization do not cause earlier growth ...decrease.•Environmental changes may strongly increase level and peristence of growth.
The course of tree growth, especially the level and persistence until advanced age, indicates the competitivenes and fitness of trees and determines stand structure and dynamics. The velocity of size growth and aging affects many other plants and animals living at and from trees. Thus forestry and many ecosystem functions and services are depending on the course of tree growth.
First, novel empirical findings of particular persisting tree growth in various parts of the world were presented and motivated this review. The revealed increasing, mostly positive, deviations of observed from theoretically expected tree growth directed this review to be based on literature and own long-term experiments, stem analyses, and increment cores from temperate forests. Second, the common growth theory and respective growth equations were revisited; they later were used for analyzing observed courses of dominant trees' mass growth and productivity. Third, tree developments over size and age were analyzed as affected by tree species, site conditions, thinning, and fertilization and enviromental changes. Stem analyses and increment core analyses of Norway spruce (Picea abies (L.) Karst.) representing the growth from 1560 to 1882 indicated a persistence of volume growth beyond age of 300 years even in this historic period of comparatively steady environmental conditions. The mass growth of 735 dominant trees revealed mean culmination ages between 211 and 480 years with the ranking sessile oak (Quercus petraea (Matt.) Liebl.) > European beech (Fagus sylvatica L.) > Norway spruce > Scots pine (Pinus sylvestris L.). Trees on sites with high site index grew quicker, peaked, and decreased earlier in annual growth, whereas trees on poor sites culminated later in terms of age. The courses of annual growth in dependence on tree mass ran more synchronous on different sites. They differed much more in the level than in the rhythm. A total of 910 Scots pines on combined thinned and fertilized compared with control plots revealed for both groups a continous increase of growth until high ages and no preponed size-related growth decrease of the treated trees.
For analyzing any modification of the course of growth by environmental changes I used a dataset of 591 cored European beeches and for corroboration 580 permanantly surveyed tree from long-term experiments of the four above mentiond main tree species in Europe. On top of their long-lasting growth all species together showed a strong acceleration of annual growth. Their growth acceleration was obviously caused by environmental changes and the highest in 1850 to 1900. It lessend in the last 50 years, and did not trigger any preponed age- or size related decrease. Finally, I discussed the consequences of the amazingly high and long-lasting tree growth for forest ecology, management and future research.
Many recent studies have shown that the structure, density, and productivity of mixed-species stands can differ from the weighted mean of monospecific stands of the respective species. The tree and ...stand properties emerging by inter-specific neighborhood should be considered in models for understanding and practical management. A promising approach for this is a more realistic representation of the individual tree allometry in models and management concepts, as tree allometry determines many structural and functional aspects at the tree and stand level. Therefore, this paper is focused on the crown allometry in mixed and mono-specific stands. Firstly, we review species-specific differences in the crown allometry in monospecific stands. Secondly, we show how species-specific differences and complementarities in crown allometry can emerge in mixed-species stands. Thirdly, the consequences of allometric complementarity for the canopy packing density will be analyzed. Fourthly, we trace the crown allometry from the tree level to the stand density and show the relevance for the self-thinning in mixed versus monospecific stands. Fifth, the consequence of the findings for modeling and regulating tree and stand growth will be discussed. The review deals mainly with widespread even-aged, mono-layered stands, but the main results apply for more heterogeneous stands analogously.
Forest ecosystems have been exposed to climate change for more than 100 years, whereas the consequences on forest growth remain elusive. Based on the oldest existing experimental forest plots in ...Central Europe, we show that, currently, the dominant tree species Norway spruce and European beech exhibit significantly faster tree growth (+32 to 77%), stand volume growth (+10 to 30%) and standing stock accumulation (+6 to 7%) than in 1960. Stands still follow similar general allometric rules, but proceed more rapidly through usual trajectories. As forest stands develop faster, tree numbers are currently 17-20% lower than in past same-aged stands. Self-thinning lines remain constant, while growth rates increase indicating the stock of resources have not changed, while growth velocity and turnover have altered. Statistical analyses of the experimental plots, and application of an ecophysiological model, suggest that mainly the rise in temperature and extended growing seasons contribute to increased growth acceleration, particularly on fertile sites.
Left: In canopies of un-thinned or just moderately thinned mixed species stands (95% and 75% line, respectively) the sum of the crown cross section area mostly exceeds pure stands (100% reference ...line) due to multiple crown overlaps. Right: Mixing species with varying morphological traits can cause a selection effect (a–c) but beyond this may trigger a morphological plasticity which can lead to denser canopy space filling, completer light capture, and productivity gains of mixed versus pure stands (d–f). Display omitted
•Canopy space filling can increase with species number.•Complementary crown shapes may increase canopy space filling.•Mixing can modify allometry and inner space filling of tree crowns.•Denser canopy space filling can increase light interception.•Denser canopies may increase stand productivity and resilience.
Mixed-species forest stands are well explored in their favourable ecological, economical, and socio-economical functions and services compared with pure stands, but still poorly understood in their structure and functioning. Canopy structure and tree morphology affect the environmental conditions within the stand, the tree growth, and by this most forest functions and services. Here, I review how canopy structure and crown morphology in mixed stands can differ from pure stands and how this depends on the selection of tree species and interactions between them. The focus is on the macrostructure of canopy and crowns derived from the trees’ positions, their convex crown hulls, and their space filling with branches.
In mixed canopies the sum of the crown projection area, but not the ground coverage by crowns, mostly exceeds pure stands due to multiple crown overlaps. The interspecific differences in crown shape and allometric scaling cause a ‘selection effect’ when complementary species are combined. In interspecific environment furthermore ‘true mixing effects’ like intraspecific shifts in size, shape, and inner space filling of crowns may occur. The much denser and more plastic canopy space filling in mixed stands may increase light interception, stand density, productivity, and growth resilience to disturbances. I discuss the relevance of interspecific interactions for forest management, model building, and theory development and draw perspectives of further research into stand canopy and crown structure.
Display omitted
•Crown shape (CS) and tree ring patterns (TRP) are significantly correlated.•Competition causes CS to be erratic, reduces CS and tree ring growth.•Competition reductions promote wider ...crowns and wider ring growth.•TRP can be predicted from CS with high accuracy.•To predict TRP from CS, simple models to advanced (e.g., machine learning) approaches are useful.
Tree crowns and growth rings are physiologically and functionally connected through supporting and resource sharing. Management interventions may strongly influence tree growth by altering this linkage. However, conventional approaches have limited ability to characterize crown shape precisely, thus hindering our understanding of the relationship between crown shape and tree ring patterns. We, thus, aimed to test three hypotheses: (HI) Crown shape (regularity vs. irregularity) and ring patterns (regularity or irregularity) are significantly correlated and (HII) vary across density gradients; if so, (HIII) internal ring patterns could be predicted from external crown shape metrics. We, therefore, employed terrestrial laser scan-based crown shape and coring-based tree ring width metrics for Norway spruce (Picea abies (L.) H. Karst.) trees covering a range of density gradients to assess temporal changes of crown shape and tree ring patterns. We found a significant and positive influence of crown shape quantifying metrics on ring patterns, indicating crown regularity or irregularity strongly reflects tree ring regularity or irregularity (p < 0.05). Crown shape and ring patterns always showed comparable patterns across density gradients (e.g., trees from lower-density stands produced transgressive crown and ring growth) and significantly varied across competition level. Trees grown in lower-density stands are more likely to produce upper-reaching crowns (maximum crown radius expansion shifted to the mid- to upper-crown) than trees grown in competitive conditions, which result in lower-reaching crowns (maximum crown radius shifted to the crown base) with reduced crown shape and ring pattern parameters. Crown irregularities increased as density decreased through competition reduction, resulting in more regular ring patterns (stable growth). Since both crown shape and ring patterns are simultaneously impacted by stand density or competition, the relationship between crown shape and ring patterns is competition-neutral. When viewed separately, both patterns had a strong relationship with the competition index. Finally, our comparative model predictions showed that approaches ranging from simple linear models to complex machine learning techniques (e.g., random forest, neural network, support vector machine, etc.) were effective in predicting ring patterns using external TLidar-crown shape, indicating a potential method to evaluate the crown shape and ring pattern link. The relationship between the crown and growth ring and their synchronous patterns across competition gradients suggests that internal growth can be assessed from the external appearances of trees and recommends further consideration in forest modeling.
Biodiversity along temperate forest succession Hilmers, Torben; Friess, Nicolas; Bässler, Claus ...
The Journal of applied ecology,
November 2018, Letnik:
55, Številka:
6
Journal Article
Recenzirano
Odprti dostop
1. The successional dynamics of forests—from canopy openings to regeneration, maturation, and decay—influence the amount and heterogeneity of resources available for forest-dwelling organisms. ...Conservation has largely focused only on selected stages of forest succession (e.g., late-seral stages). However, to develop comprehensive conservation strategies and to understand the impact of forest management on biodiversity, a quantitative understanding of how different trophic groups vary over the course of succession is needed. 2. We classified mixed mountain forests in Central Europe into nine successional stages using airborne LiDAR. We analysed α- and β-diversity of six trophic groups encompassing approximately 3,000 species from three kingdoms. We quantified the effect of successional stage on the number of species with and without controlling for species abundances and tested whether the data fit the more-individuals hypothesis or the habitat heterogeneity hypothesis. Furthermore, we analysed the similarity of assemblages along successional development. 3. The abundance of producers, first-order consumers, and saprotrophic species showed a U-shaped response to forest succession. The number of species of producer and consumer groups generally followed this U-shaped pattern. In contrast to our expectation, the number of saprotrophic species did not change along succession. When we controlled for the effect of abundance, the number of producer and saproxylic beetle species increased linearly with forest succession, whereas the U-shaped response of the number of consumer species persisted. The analysis of assemblages indicated a large contribution of succession-mediated β-diversity to regional γ-diversity. 4. Synthesis and applications. Depending on the species group, our data supported both the more-individuals hypothesis and the habitat heterogeneity hypothesis. Our results highlight the strong influence of forest succession on biodiversity and underline the importance of controlling for successional dynamics when assessing successional stages with highest diversity (early and late successional stages) are currently strongly underrepresented in the forests of Central Europe. We thus recommend that conservation strategies aim at a more balanced representation of all successional stages.
Current individual tree growth models rarely consider the mode of tree competition, which can be size-asymmetric when growth is limited by light or size-symmetric when belowground resources are ...scarce. Even with the same competition index, growth reactions may vary considerably due to a prevailing resource limitation, as the dominant trees in a stand benefit disproportionately more on light-limited sites. To scrutinize and model the relationship between mode of competition and site conditions, 34 long-term experiments with 120 plots dating back to 1871 were used. The data cover the dominating tree species in central Europe along a broad range of ecological conditions. For Norway spruce (Picea abies (L.) Karst.), Scots pine (Pinus sylvestris L.), and sessile oak (Quercus petrea (Matt.) Liebl.), stronger light competition can be shown on fertile sites compared with sites with poorer conditions. Based on these findings, we constructed an enhanced version of a classic potential modifier growth model. Simulations for archetypical stands yield a transition from size-asymmetric to size-symmetric competition along the gradient from fertile to poor sites that is not covered by traditional models. It was concluded that by integrating the interaction between competition and site quality, individual tree models become more site sensitive, a prerequisite for their application under fluctuating environmental conditions.
How tree morphology develops in mixed-species stands is essential for understanding and modelling mixed-stand dynamics. However, research so far focused on the morphological variation between tree ...species and neglected the variation within a species depending on intra- and interspecific competition. Our study, in contrast, addresses crown properties of nine mature Norway spruces (Picea abies L. Karst.) of a pure stand and compares them with ten spruces growing in mixture with European beech (Fagus sylvatica L.). The same was done with 11 pure stand beeches and 12 beeches growing in mixture with spruce. Through application of a terrestrial laser scanner and a new skeletonization approach, we deal with both species’-specific morphological traits such as branch angle, branch length, branch bending, crown volume and space occupation of branches within the crown, some of which were hardly accessible so far. Special attention is paid to distinct differences between trees growing in mixed and pure stands: for spruce, our study reveals significantly longer branches and greater crown volumes in the mixed stand when compared to the pure stand. In case of European beech, individuals growing in mixture show flatter branch angles, more distinct ramification, greater crown volumes and a lower share of a single branch’s space occupation in the total crown volume. The results show that the presented methods yield detailed information on the morphological traits analyzed in this study and that interspecific competition on its own may have a significant impact on crown structures. Implications for production ecology and stand dynamics of mixed-species forests are discussed.
A more detailed understanding of the micro-climatic thermal benefits of different urban tree species and the retrospective species characteristics is necessary to guide management decisions. In this ...review, we focused specifically on empirical data collected at ground level for below-canopy surface temperature (ST) and transpiration cooling (AT), using a meta-analysis method. Tree canopy density was clearly identified as the most influential driver of different mechanisms of cooling benefits. Secondly, climate of the cities where the trees were grown showed significant impacts on cooling potentials: trees grown in Oceanic and Continental climates showed a higher cooling potential compared to trees grown in Mediterranean climate for AT and sub-tropical climate for ST. Thirdly, tree growth in size and ground surface cover showed significant impact. ST decreases almost linearly with the increase of canopy density; however, the rate is significantly lower over transpiring grass surfaces. Transpiration of trees planted over grass was ten times higher (4.15 g m−2 min−1) compared to a tree planted in paved cut-out pits (0.44 g m−2 min−1). Moreover, diffuse porous wood anatomy and trees originating from temperate and resource-rich forests showed better cooling potentials. Among the leaf traits, dark green leaves, < 0.15 mm of thickness showed higher AT and ST benefit. The review pointed out the lack of standardized study protocols in determining tree cooling benefits and empirical data, particularly at tropical and sub-tropical climate. Finally, the study suggested some recommendations for plantings that optimize the cooling benefits from urban greenspaces.
•Determinant variables about tree species cooling potential have been investigated.•Surface (ST), transpiration air-cooling (AT) and human comfort (TC) was reviewed.•Leaf area index showed a positive correlation with all three mechanisms of cooling.•Surface temperature reduction was more over asphalt than grass or building walls.•Darker, thin leaved species with diffuse porous wood anatomy provided better AT.
PDF
