Stefan Fleck

Review of ground-based methods to measure the distribution of biomass in forest canopies

Abstract• ContextEcological research and an effective forest management need accurate information on the structure of the forest canopy to understand the biochemical, physiological and biogeochemical processes within a forest.• Research questionThis paper reviews the currently available instruments for measuring the distribution of biomass within forest canopies. We compare the most well-established approaches and present the different measurable parameters. A special focus lies on the resolution of the obtained data.• ResultsIt was found that only 3D laser scanners offer data with the resolution required by ecologists, private landholders, the forest industry and the public to detect trends in tree growth patterns and canopy interactions in all three spatial dimensions. But data validation, data analysis and parameter extraction are still under development, and the price of the instrument is quite high.• ConclusionResearch should focus on the parameter extraction from terrestrial laser scanner data as this could allow the calculation of functional attributes for different sections of a canopy on a high spatial resolution. It could also help ecologists characterize the structure of forest stands in a quick and precise way.

Automated Detection of Branch Dimensions in Woody Skeletons of Fruit Tree Canopies

Modeling the 3D canopy structure of trees provides the structural mapping capability on which to assign distributed values of light-driven physiological processes in tree canopies. We evaluate the potential of automatically extracted skeletons from terrestrial lidar data as a basis for modeling canopy structure. The automatic and species independent evaluation method for lidar data of trees is based on the SKELTRE algorithm. The SKELTRE skeleton is a graphical representation of the branch hierarchy. The extraction of the branch hierarchy utilizes a graph splitting procedure to extract the branches from the skeleton. Analyzing the distance between the point cloud points and the skeleton is the key to the branch diameter. Frequency distributions of branch length and diameter were chosen to test the algorithm performance in comparison to manually measured data and resulted in a correlation of up to 0.78 for the branch length and up to 0.99 for the branch diameter.

Within-canopy variation in photosynthetic capacity, SLA and foliar N in temperate broad-leaved trees with contrasting shade tolerance

Key messageThe relative shade tolerance ofT. cordata,F. sylvatica, andC. betulusin mature stands is based on different species-specific carbon and nitrogen allocation patterns.AbstractThe leaf morphology and photosynthetic capacity of trees are remarkably plastic in response to intra-canopy light gradients. While most studies examined seedlings, it is not well understood how plasticity differs in mature trees among species with contrasting shade tolerance. We studied light-saturated net photosynthesis (Amax), maximum carboxylation rate (Vcmax), electron transport capacity (Jmax) and leaf dark respiration (Rd) along natural light gradients in the canopies of 26 adult trees of five broad-leaved tree species in a mixed temperate old-growth forest (Fraxinusexcelsior, Acer pseudoplatanus, Carpinusbetulus, Tiliacordata and Fagussylvatica), representing a sequence from moderately light-demanding to highly shade-tolerant species. We searched for species differences in the dependence of photosynthetic capacity on relative irradiance (RI), specific leaf area (SLA) and nitrogen per leaf area (Na). The three shade-tolerant species (C. betulus, T. cordata, F. sylvatica) differed from the two more light-demanding species by the formation of shade leaves with particularly high SLA but relatively low Na and consequently lower area-based Amax, and a generally higher leaf morphological and functional plasticity across the canopy. Sun leaf morphology and physiology were more similar among the two groups. The three shade-tolerant species differed in their shade acclimation strategies which are primarily determined by the species’ plasticity in SLA. Under low light, T.cordata and F.sylvatica increased SLA, mass-based foliar N and leaf size, while C.betulus increased solely SLA exhibiting only low intra-crown plasticity in leaf morphology and N allocation patterns. This study with mature trees adds to our understanding of tree species differences in shade acclimation strategies under the natural conditions of a mixed old-growth forest.

Low light acclimation in five temperate broad-leaved tree species of different successional status: the significance of a shade canopy

Abstract• ContextTree species differ largely in their capability to produce characteristic shade leaves with effective morphological and physiological acclimation to low light.• AimsBy examining the sun/shade leaf differentiation in leaf morphology, foliar nitrogen and photosynthetic capacity in five temperate tree species of different successional status, we aimed at identifying those leaf traits that determine the development of a typical shade crown with low light-acclimated leaves.• MethodsLeaf morphology, foliar N content, photosynthetic capacity (Vcmax, Jmax and Amax) and leaf dark respiration (Rd) were measured in the canopies of 26 adult trees of Fraxinus, Acer, Carpinus, Tilia and Fagus species.• ResultsSix traits (the sun/shade leaf differentiation in specific leaf area, leaf size, Amax per leaf area or per mass, photosynthetic N use efficiency and Rd) were found to characterise best the degree of low light acclimation in shade leaves. All five species exhibited certain modifications in leaf morphology and/or physiology in response to low light; Fagus sylvatica showed the highest and Fraxinus excelsior the lowest shade leaf acclimation.• ConclusionsOur results indicate that the five early/mid- to late-successional species have developed species-specific low light acclimation strategies in their shade crowns which differ in terms of the relative importance of leaf morphological and physiological acclimation.

Exceedance of critical loads and of critical limits impacts tree nutrition across Europe

Key messageExceedance of critical limits in soil solution samples was more frequent in intensively monitored forest plots across Europe with critical loads for acidity and eutrophication exceeded compared to other plots from the same network. Elevated inorganic nitrogen concentrations in soil solution tended to be related to less favourable nutritional status.ContextForests have been exposed to elevated atmospheric deposition of acidifying and eutrophying sulphur and nitrogen compounds for decades. Critical loads have been identified, below which damage due to acidification and eutrophication are not expected to occur.AimsWe explored the relationship between the exceedance of critical loads and inorganic nitrogen concentration, the base cation to aluminium ratio in soil solutions, as well as the nutritional status of trees.MethodsWe used recent data describing deposition, elemental concentrations in soil solution and foliage, as well as the level of damage to foliage recorded at forest plots of the ICP Forests intensive monitoring network across Europe.ResultsCritical loads for inorganic nitrogen deposition were exceeded on about a third to half of the forest plots. Elevated inorganic nitrogen concentrations in soil solution occurred more frequently among these plots. Indications of nutrient imbalances, such as low magnesium concentration in foliage or discolouration of needles and leaves, were seldom but appeared more frequently on plots where the critical limits for soil solution were exceeded.ConclusionThe findings support the hypothesis that elevated nitrogen and sulphur deposition can lead to imbalances in tree nutrition.

Chapter 17 - Meteorology

Meteorological variables affect composition, structure, growth, health, and dynamics of forest ecosystems. The measurement of meteorological data at forest monitoring plots is essential for the interpretation of climate change effects. Within an ecological monitoring network, standard meteorological variables such as precipitation, air temperature, relative humidity, solar radiation, wind velocity, and direction should be measured. These variables are essential for the calculation of total deposition of air pollutants, for the interpretation of biological processes or for the derivation of water budgets and percolation from the rooting zone. Additional variables of interest are soil temperature, stand precipitation, and soil moisture. The magnitude and changes in time of the meteorological variables can be assessed as explanatory factors for other observations made in forest ecological monitoring. A detailed description of different methods is given. As an example for an integrated analysis, the application of meteorological data in water budget modeling is described and results of a pilot study are shown.