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The morphology, inclination, and spatial distribution of leaves in different parts of tree crowns are important determinants of the radiation, momentum, and gas exchange between the canopy and the atmosphere. However, it is not well known how these foliage-related traits vary among species differing in successional status. We measured leaf size, leaf mass area (LMA), leaf inclination (angle to the horizontal), leaf area density (LAD), total leaf area (leaf area index, LAI), and leaf area distribution across the crown in adult trees of five common, early to late-successional tree species (Betula pendula Roth, Quercus petraea (Matt.) Liebl., Carpinus betulus L., Tilia cordata Mill., and Fagus sylvatica L.) using different canopy access techniques and the harvest of foliated trees (29 trees in total). Leaf size increased continuously with crown depth in B. pendula and T. cordata but peaked at mid-crown in Q. petraea, C. betulus, and F. sylvatica to decrease toward the shade crown. By contrast, LMA and leaf angle decreased continuously with crown depth in all species, but the pattern of vertical change varied. The mid/late- and late-successional species had higher LAI, lower shade-leaf LMA, lower leaf angles (shade and sun crown), and higher LAD in the uppermost sun crown in comparison to early successional B. pendula. We assume that the most peripheral sun leaf layer is partly acting as a shield against excess radiation, with foliage properties depending on the structure of the shade crown. We conclude that the vertical change in leaf morphology, inclination, and spatial distribution in tree crowns is highly species specific, with partial dependence on the species’ position in succession. peerReviewed

The optical properties of leaves and canopies determine the availability of radiation for photosynthesis and the penetration of light through tree canopies. How leaf absorptance, reflectance and transmittance and radiation transmission through tree canopies change with forest succession is not well understood. We measured the leaf optical properties in the photosynthetically active radiation (PAR) range of five Central European early-, mid- and late-successional temperate broadleaf tree species and studied the minimum light demand of the lowermost shade leaves and of the species&rsquo, offspring. Leaf absorptance in the 350&ndash, 720 nm range varied between c. 70% and 77% in the crown of all five species with only a minor variation from the sun to the shade crown and between species. However, specific absorptance (absorptance normalized by mass per leaf area) increased about threefold from sun to shade leaves with decreasing leaf mass area (LMA) in the late-successional species (Carpinus betulus L., Tilia cordata Mill., Fagus sylvatica L.), while it was generally lower in the early- to mid-successional species (Betula pendula Roth, Quercus petraea (Matt.)Liebl.), where it changed only a little from sun to shade crown. Due to a significant increase in leaf area index, canopy PAR transmittance to the forest floor decreased from early- to late-successional species from ~15% to 1%&ndash, 3% of incident PAR, linked to a decrease in the minimum light demand of the lowermost shade leaves (from ~20 to 1%&ndash, 2%) and of the species&rsquo, saplings (from ~20 to 3%&ndash, 4%). The median light intensity on the forest floor under a closed canopy was in all species lower than the saplings&rsquo, minimum light demand. We conclude that the optical properties of the sun leaves are very similar among early-, mid- and late-successional tree species, while the shade leaves of these groups differ not only morphologically, but also in terms of the resource investment needed to achieve high PAR absorptance.

This paper deals with the issue of segmentation methods in hemispherical photography determining diffuse site factor (DIFFSF) and leaf inclination angle distribution in forest stands simultaneously. Field inclination angle distributions were sampled in pure stands of European beech, hornbeam, sessile oak and silver birch on sites where towers facilitated crown access. In the same stands leaf litter traps were placed from which LAI values were derived after autumn leaf fall. Analogue hemispherical photographs were taken in summer before leaf fall. We combined the ellipsoidal G-function and Markov–Poisson model to invert leaf inclination angle functions (LIDF). Field leaf inclination angle distributions were planophile for three species and plagiophile for birch. The planophile distributions were well represented by ellipsoidal as well as beta distribution while plagiophile distribution of birch was exclusively represented by beta distribution. When segmentation methods were varied, LIDF parameter predictions were more in correspondence with field values by using sub-pixel methods than by using binary methods. When integrating vignetting properties into the segmentation algorithm or when accounting for standard sky luminance distribution, the accuracy of LIDF predictions varied; it is assumed that this is due to variation in sky properties during photography. Thus, different segmentation techniques in hemispherical photography did not yield constancy in deriving different required variables, i.e. DIFFSF and LIDF. Rather, method of segmentation affects leaf inclination angle estimation.

In the tropics, old-growth forests are converted to other land cover types at a high rate and young secondary forest may gain in importance. Information on associated changes in leaf gas exchange and other leaf traits can be valuable for modelling biogeochemical fluxes under altered land-use patterns. We studied in situ photosynthetic parameters and stomatal conductance for water vapour in eight abundant tree species of young secondary forest and eight tree species of natural old-growth forest in Central Sulawesi, Indonesia. In sun leaves, the average maximal stomatal conductance (g smax) in the secondary forest (SF) species was 2.1 times higher than in the old-growth forest (OGF) species. Species with a high g smax reduced g s sharply when vapour pressure deficit of the air increased, whereas species with a low g smax were much less sensitive to air humidity. For area-based photosynthetic capacity (A max-area), the SF species had a 2.3 times higher average than the OGF species. For both, g smax and A max-area the variation among species was higher in the OGF than in the SF. When all tree species (n=16) are considered, species means of specific leaf area (SLA), leaf N concentration and leaf P concentration were significantly correlated with g smax and A max-area. The strong correlation between A max-area and foliar P (r 2=0.8) is remarkable as the alluvial soils in the study region are rich in nutrients. If the eight OGF species are analysed separately, the only significant correlation was observed between SLA and mass-based A max; in the SF species strong correlations were found between leaf size and A max-area and g smax. These results show that the conversion of old-growth forest to young secondary forest in Sulawesi significantly alters tree leaf gas exchange characteristics and that chemical and structural leaf traits can be used for the prediction of these changes. The best correlations between leaf gas exchange parameters and leaf traits were obtained by different traits in the SF species, the OGF species and the entire pool of studied species.

In einem artenreichen Laubmischwald wurden Untersuchungen zur Kronendimension der koexistierenden Arten Esche (Es), Hainbuche (Hbu) und Winterlinde (WLi) (Baumalter 80–100 Jahre) durchgefuhrt. Ziel war es zu prufen (i) wie sich die untersuchten Baumarten hinsichtlich ihrer Kronenform unterscheiden, (ii) inwiefern die Kronenform von der Artzugehorigkeit der Nachbarn beeinflusst wird und (iii) ob sich aus der Analyse der Besetzung des Kronenraums Ruckschlusse auf die Konkurrenzstarke der Arten im Bestand ziehen lassen. Auf 17 target-neighbour-plots wurden sowohl die horizontale Kronenausdehnung (Kronenprojektionsflache) als auch die vertikale Kronendimension (Kronenlange, Hohe der maximalen Kronenausdehung) erfasst. Bei der Kronenablotung wurde zusatzlich zur expositionsorientierten Acht-Punkt-Projektion die Ausdehnung eines Baumes in Richtung des Stammes eines Nachbarbaums vermessen. Die Ergebnisse zeigen, dass die artspezifische Kronenform in diesem Bestand deutlich von der Artzugehorigkeit der Nachbarbaume beeinflusst wird. Esche und Hainbuche wiesen in artgleichen Kombinationen signifikant geringere Kronenausladungen auf als in Nachbarschaft zu einer anderen Baumart. Vor allem die Winterlinde wies mit beiden anderen Arten grose Uberlappungsbereiche im Kronenraum auf. In Nachbarschaft zur Esche nahm sie den Zwischenstammbereich fast ganzlich ein (96% des Stammabstands). In Nachbarschaft zur Hainbuche zeigte die Winterlinde dagegen eine (nicht signifikante) Verringerung der Kronenausdehnungen im Vergleich zu artgleichen Nachbarn. In den drei gemischten Paarkombinationen ergaben sich folgende Asymmetrien in der Kronenausdehnung: Hbu > WLi, Hbu > Es, WLi > Es. Die gefundenen stark asymmetrischen Muster in der horizontalen Kronenausdehnung haben zumindest in den letzten 40 Jahren nicht zum Ausschluss von Individuen einer Art im Bestand gefuhrt. Wir vermuten, dass die Wirkung asymmetrischer Konkurrenz durch vertikale Aufteilung des Kronenraums effektiv verringert wird und Koexistenz erleichtert.