Rötzer, T. Seifert, T. Pretzsch, H. (2009): Modelling above and below ground carbon dynamics in a mixed beech and spruce stand influenced by climate. Eur J Forest Res (2009) 128: 171-182

Abstract:

Tree growth and carbon dynamics are important issues especially in the context of climate change. However, we essentially lack knowledge about the effects on carbon dynamics especially in mixed stands. Thus, the objective of this study was to test the effects of climatic changes on the above and below ground carbon dynamics of a mixed stand of Norway spruce (Picea abies [L.] Karst.) and European beech (Fagus sylvatica L.) by means of scenario simulations. To account for the typical tree interactions in a mixed-species stand a spatial explicit tree growth model based on eco-physiological processes was applied. Three different climate scenarios considering altered precipitation, temperature, and radiation were calculated for an unthinned and a thinned stand. The results showed significant changes of above and belowground biomass over time, especially when temperature and radiation were increased additionally to decreased precipitation. The reduction in biomass increments of Norway spruce were more attenuated above than below ground. In contrast, the results for beech were the opposite: The belowground increments were reduced more. These results suggest a shift in the species contribution to above and belowground biomass under dryer and warmer conditions. Distinct effects were also found when thinned and unthinned stands were compared. A reduced stand density changed the proportions of above and below ground carbon allocation. As a main reason for the changed growth reactions the water balance of trees was identified which lead to changed biomass allocation pattern.

Pretzsch, H. (2009): Re-evaluation of allometry. State-of-the-art and perspective regarding individuals and stands of woody plants. Progress in Botany, Vol. 71., 2009 in press

Abstract:

Allometry in its broader sense is concerned with the size of organisms and its consequences for their shape and functioning. Since the postulation of the allometric equation in the 1930s, allometry in a narrow sense refers to analysis and modelling of logarithmic transformed bivariate size data by linear regression techniques.

This review first points out that allometric research built up a valuable set of hypotheses and biometrical methods for analysing size of organisms and its consequences for their shape and functioning. Then, a summary of the knowledge about allometry of woody plants and populations will unmask the search for overarching general allometric exponents of shape and form development largely as a hunt for a phantom. Tree size development and self-thinning processes in forest stands give evidence that allometric exponents certainly lie in a narrow corridor but are species specific and superimposed by site conditions, mechanical disturbances, competition and other types of stress. The discussion states that as long as allometry searches for universal constants to a certain extent it stills our innate desire to reduce complexity and generalise. However, time is ready to focus on and understand the differences between the species, sites etc. in order to contribute to a better system understanding. It is concluded that allometry has to draw attention both to the internal size-driven allometric partitioning process and to the external factors which determine optimal biomass allocation. And at best, allometric research should analyse both factors in order to understand and integrate them. A systematic analysis, ordering and causal explanation of allometric exponents, which reflects an individuals’ tricks and traits of optimising fitness, may provide an important link between plant genetics, physiology, plant biology and population biology. In contrast, application of inaccurate and imprecise general scaling rules can cause considerable flaws in modelling, prognosis and ecosystem management. 

Wipfler, Ph. Seifert, T. Biber, P. Pretzsch, H. (2009): Intra-annual growth response of adult Norway spruce (Picea abies L.) and European beech (Fagus sylvatica L.) to an experimentally enhanced, free-air ozone regime. Eur J Forest Res (2009) 128: 135-144

Abstract:

Several findings indicate an impact of ozone on stem diameter growth leaving the question unanswered, if and how the intra-annual growth pattern is changed. In this study the hypotheses are tested, that (1) ozone will alter the absolute growth and (2) alter and shift the period of growth activity within a year. Our data originates from the free air ozone fumigation experiment ‘Kranzberger Forst’ in a mixed stand of Norway spruce and common beech near Freising/Germany. Annual and intra-annual growth reactions of a sample of five adult beech and five spruce trees, exposed to double ambient ozone were examined and compared to the same number of untreated reference trees. Diameter increments were measured with plastic diameter girth bands and high-resolution, automatically logging micro-dendrometers, mounted at breast height (1.3 m). We used the increment data from the growth periods 2000 to 2005. The high-resolution micro-dendrometer data were examined by fitting a Weibull function to the standardized annual growth profiles to obtain curve parameters for statistical tests. We estimated the parameters ‘T’ which represents the point of time, when 63% of the annual diameter increment is performed and the parameter ‘m’, the Weibull module, which was used as an indicator for the span of time needed to complete the annual growth. The statistical significance of these curve parameters, together with the absolute diameter increment, was tested by use of mixed regression models. The analysis of the growth curve parameters revealed a significantly altered intra-annual growth pattern of both species induced by ozone. Spruce under ozone showed reduced absolute annual diameter increment and a preponed growth activity compared to untreated trees. Beech’s absolute diameter increment was not affected under ozone, but its growth activity was delayed. For both species, ozone fumigation did not alter the individual length of the annual growing season. These results are discussed with respect to drought, tree ring anatomy and tree allometry. The study shows that ozone is able to change growth behaviour of trees even if increment losses are not obvious.

Pretzsch, H. Mette, T. (2008): Linking stand level self-thinning allometry to the tree-level leaf biomass allometry. Trees 22: 611–622

Abstract:

Long-term experimental plots of Norway spruce and European beech are investigated for a link between stand-level self-thinning and tree-level leaf biomass allometry. Self-thinning refers to the finding of Reineke (1933), who postulated for unthinned forest stands that w with β = −1.605; i.e. an increase of mean (quadratic) diameter d q by 1% results in a decrease of tree number N by 1.605%. On the individual tree level, leaf biomass (w L) can be related allometrically to the tree diameter d: L = adα. If we assume that (a) the stands have reached the ceiling leaf area, (b) the specific leaf area (leaf area/leaf weight) is constant, and (c) differences resulting from the use of mean quadratic diameter or individual tree diameter are negligible, then the decrease in the stands’ leaf biomass due to the trees lost in self-thinning must be compensated by an equivalent increase in the remaining trees’ leaf biomass. This means, the absolute slope of the individual trees’ leaf biomass allometry α and the self-thinning allometry β would be equal and just have the opposite sign: α = −β. The analysis of the two long-term plots reveals that α is stronger than β, both for spruce (β = −1.744, α = 1.840) and especially for beech (β = −1.791, α = 2.181). The cause is traced back to a changing average specific leaf area during stand development [assumption (b) is wrong]. The results do not only bridge a gap between tree and stand allometry, but also emphasize an important effect for the understanding and modelling of the resource allocations in trees and forests.



Seifert, T. (2007): Simulating the extent of decay caused by Heterobasidion annosum s. l. in stems of Norway spruce. Forest Ecology and Management 248: 95-106

Abstract:

Heterobasidion annosum (FR.) BREF. sensu lato causes severe economic damage in stands of Norway spruce (Picea abies [L.] Karst). The primary damage is the deterioration of timber by decay. Secondary damage can be attributed to higher risks of windthrow and stem breakage, growth reduction of infected trees as well as higher machining and handling costs for decayed stems during grading and processing. Regardless of the importance of this pathogen there are very few software tools which support management decisions in red rot affected forests and none of them are parameterised with data from Central Europe. The present study aimed to develop a model which is able to spatially predict the extent and degree of decay in the stem as well as its effects on the growth of Norway spruce. This involves the integration of several sub-models into a tree growth simulator: (i) diameter of decay, (ii) height of decay, (iii) form of decay, (iv) degree of decay, and (v) feedback of the pathogen on tree growth. The model is parameterised mainly from published data of other authors. The input for the time of infection of a tree is delivered from a separate model. A grading algorithm is used to evaluate the impact of different scenarios on the revenue of infected stands in typical stands of Norway spruce in Germany. This integrated system of growth and red rot simulation is able to support management decisions on various levels and documents that if red rot is not taken into consideration in the affected stands, clear misinterpretations and thus inaccuracies will arise in the economic results from tree growth simulators. The need for further research was identified especially in model validation and the tree-pathogen interaction.



Pretzsch, H (2006b): Species-specific allometric scaling under self-thinning: evidence from long-term plots in forest stands. Oecologica (2006) 146: 572-583.

Abstract:

Experimental plots covering a 120 years’ observation period in unthinned, even-aged pure stands of common beech (Fagus sylvatica), Norway spruce (Picea abies), Scots pine (Pinus sylvestris), and common oak (Quercus Petraea) are used to scrutinize Reineke’s (1933) empirically derived stand density rule ( , N = tree number per unit area, = mean stem diameter), Yoda’s (1963) self-thinning law based on Euclidian geometry ( = mean biomass per tree), and basic assumptions of West, Brown and Enquist’s (1997, 1999) fractal scaling rules ( w = biomass per tree, d = stem diameter). RMA and OLS regression provides observed allometric exponents, which are tested against the exponents, expected by the considered rules. Hope for a consistent scaling law fades away, as observed exponents significantly correspond with the considered rules only in a minority of cases: (1) exponent r of varies around Reineke’s constant −1.605, but is significantly different from r=−2, supposed by Euclidian or fractal scaling, (2) Exponent c of the self-thinning line roams roughly about the Euclidian scaling constant −3/2, (3) Exponent a of tends to follow fractal scaling 8/3. The unique dataset’s evaluation displays that (4) scaling exponents and their oscillation are species-specific, (5) Euclidian scaling of one relation and fractal scaling of another are coupled, depending on species. Ecological implications of the results in respect to self-tolerance (common oak > Norway spruce > Scots pine > common beech) and efficiency of space occupation (common beech > Scots pine > Norway spruce > common oak) are stressed and severe consequences for assessing, regulating and scheduling stand density are discussed.