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

?Context

Tree species differ largely in their capability to produce characteristic shade leaves with effective morphological and physiological acclimation to low light.

?Aims

By 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.

?Methods

Leaf morphology, foliar N content, photosynthetic capacity (V _cmax, J _max and A _max) and leaf dark respiration (R _d) were measured in the canopies of 26 adult trees of Fraxinus, Acer, Carpinus, Tilia and Fagus species.

?Results

Six traits (the sun/shade leaf differentiation in specific leaf area, leaf size, A _max per leaf area or per mass, photosynthetic N use efficiency and R _d) 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.

?Conclusions

Our 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.     

From Framework to Forest Activities: A Comparative Analysis of Different Ownership Types in Two Adjacent Regions

The paper examines the interactions between the demands of society, the restrictions due to recreational and protective functions of forests and the intensity and kind of forest management in the various ownership classes in Switzerland (CH) and Baden–Württemberg (BW) in south–west Germany. A survey was carried out among owners of communal forests, private forest landholders owning more than 200 ha of forest land and small-scale forest enterprises with up to 200 ha of forest land. The survey adopted a two-dimensional approach, using regions and comparable ownership classes in order to identify basic differences and underlying key drivers. It became obvious that there are relevant distinctions between the two countries. The paper highlights the present use of forests, the restrictions perceived by their owners, and the underlying management strategies in terms of structure of the forests, tree species composition and thinning activities. In BW the financial function is the dominant motivation for the majority of the private owners. The communities emphasize both timber and non-timber functions of their forests. Except for the protection function (avalanches, rockslides) the utilisation and importance of the forest in CH is lower than in BW. Profitability of forests continues to be a key-driver of intensity of forest management activities, but there is less influence on the choice of basic silvicultural strategies. The results of this comparative survey are placed in the context of a forest policy framework and the medium-term financial situation in the two countries.

Environmental control of daily stem growth patterns in five temperate broad-leaved tree species

Tree ring analysis investigates growth processes at time horizons of several weeks to millennia, but lacks the detail of short-term fluctuation in cambial activity. This study used electronic high-precision dendrometry for analyzing the environmental factors controlling stem diameter variation and radial growth in daily resolution in five co-existing temperate broad-leaved tree species (genera Fraxinus, Acer, Carpinus, Tilia and Fagus) with different growth and survival strategies. Daily stem radius change (SRC(d)) was primarily influenced by the atmospheric demand for water vapor (expressed either as vapor pressure deficit (D) or relative air humidity (RH)) while rainfall, soil matrix potential, temperature and radiation were only secondary factors. SRC(d) increased linearly with increasing RH and decreasing D in all species. The positive effect of a low atmospheric water vapor demand on SRC(d) was largest in June during the period of maximal radial growth rate and persisted when observation windows of 7 or 21 days instead of 1 day were used. We found a high synchronicity in the day-to-day growth rate fluctuation among the species with increment peaks corresponding to air humidity maxima, even though the mean daily radial growth rate differed fivefold among the species. The five -species also differed in the positive slope of the growth/RH relationship with the steepest increase found in Fraxinus and the?lowest in Fagus. We explain the strong positive effect of high RH and low D on radial stem increment by lowered transpiration which reduces negative pressure in the conducting system and increases turgor in the stem cambium cells, thereby favoring cell division and expansion. The results suggest that mechanistic models of tree growth need to consider the atmospheric water status in addition to the known controlling environmental factors: temperature, soil moisture and precipitation. The results further have implications for sensitivity analyses of tree growth to climatic changes.     

Root architecture might account for contrasting establishment success of <Emphasis Type="Italic">Pseudotsuga menziesii</Emphasis> var. <Emphasis Type="Italic">menziesii</Emphasis> and <Emphasis Type="Italic">Pinus sylvestris</Emphasis> in Central Europe under dry conditions

Key message

Pinus sylvestris seedlings quickly expand their roots to deeper soil layers while Pseudotsuga menziesii concentrates its root system in the topsoil, thereby running the risk of desiccation during long dry spells, as indicated by lower survival after simulated summer drought.

Context

Pseudotsuga menziesii (Douglas-fir) is regarded as a promising species to maintain the productivity of Central European lowland forests given the projected increase of long dry spells.

Aims

Will the species be able to regenerate from seed and spread outside plantations in a drier temperate Europe?

Methods

We measured the relative growth rate, biomass allocation, root architecture, and phenotypic plasticity of Pseudotsuga menziesii seedlings sown in a common garden and grown under current precipitation and prolonged drought, respectively. The species’ competitive ability with respect to Pinus sylvestris L., the most drought-tolerant native conifer in Central Europe, was assessed during three growing seasons.

Results

Pinus sylvestris seedlings had higher relative growth rates than did Pseudotsuga menziesii seedlings, first in terms of aboveground biomass and later in terms of shoot height. This resulted in heavier and taller seedlings after three growing seasons under both moist and dry conditions. Shorter vertical roots corresponded with lower survival of Pseudotsuga menziesii seedlings under dry conditions.

Conclusion

Fast root proliferation allows Pinus sylvestris seedlings to reach deeper water pools that are less rapidly depleted during transient drought. By contrast, the shallow root system might put Pseudotsuga menziesii seedlings at the risk of desiccation during prolonged dry spells.

     

Canopy vs. understory: Does tree diversity affect bee and wasp communities and their natural enemies across forest strata?

Bees and wasps provide important ecosystem services such as pollination and biocontrol in crop-dominated landscapes, but surprisingly little information is available on hymenopteran communities in temperate forest ecosystems. Species richness and abundance of bees and wasps can be hypothesised to increase with plant diversity, structural complexity, and availability of food and nesting resources. By experimentally exposing standardised nesting sites, we examined abundance and species richness of cavity-nesting bees (pollinators), wasps (predators) and their associated parasitoids across a tree diversity gradient in a temperate deciduous forest habitat. In addition, spatial distribution of individuals and species across forest strata (canopy vs. understory) was tested. Abundance and species richness was high for predatory wasps, but generally low for pollinators. Species-rich forest stands supported increased abundance, but not species richness, of pollinators and predatory wasps, and also increased abundance and species richness of natural enemies. In addition, the forests showed a distinct spatial stratification in that abundance of bees, wasps and parasitoids as well as parasitism rates were higher in the canopy than understory. We conclude that particularly the canopy in temperate forest stands can serve as an important habitat for predatory wasp species and natural enemies, but not bee pollinators. Enhanced tree diversity was related to increased hymenopteran abundance, which is likely to be linked to an increase in nesting and food resources in mixed forest stands.     

Lichen diversity in temperate montane forests is influenced by forest structure more than climate

Although the effect of forest management on lichens in temperate forests has been widely examined, little is known about the influence of management-related factors on their biodiversity relative to factors that cannot be altered by management. Here we determined whether forest structure or climate determines lichen diversity in the Bavarian Forest National Park in southeastern Germany, taking spatial variables into account. We investigated 517 single tree stems along 4 transects in 113 pre-stratified plots (8 m in diameter) in this montane forest. We grouped environmental variables into three sets: climate (macroclimate, non-manageable), forest structure (manageable), and space. The explanatory powers of these sets of variables for lichen diversity were compared using variance partitioning for the lichen community, species density, and threatened species density. The relationships of single characteristics of forest structure with lichen species diversity were analyzed using generalized linear models (GLM). Lichen diversity was better explained by stand structures than by climate. Spatial effects influenced the number of species per plot. Among the structural features, the availability of dead wood and sycamore maple as well as forest continuity were most important for the enhancement of lichen diversity. Open canopy structures affected the total diversity positively. Although the availability of large trees was not an influential factor in the GLM at the plot level, high diversity levels were generally associated with large stem diameters at the level of single stems. We provide recommendations for sustainable forest-management practices that aim at specifically enhancing lichen diversity in temperate areas experiencing low levels of air pollution.     

Productivity of temperate broad-leaved forest stands differing in tree species diversity

? Understanding the effects of tree species diversity on biomass and production of forests is fundamental for carbon sequestration strategies, particularly in the perspective of the current climate change. However, the diversity-productivity relationship in old-growth forests is not well understood.

? We quantified biomass and above-ground production in nine forest stands with increasing tree species diversity from monocultures of beech to stands consisting of up to five deciduous tree species (Fagus sylvatica, Fraxinus excelsior, Tilia spp., Carpinus betulus, Acer spp.) to examine (a) if mixed stands are more productive than monospecific stands, (b) how tree species differ in the productivity of stem wood, leaves and fruits, and (c) if beech productivity increases with tree diversity due to lower intraspecific competition and complementary resource use.

? Total above-ground biomass and wood production decreased with increasing tree species diversity. In Fagus and Fraxinus, the basal area-related wood productivity exceeded those of the co-occurring tree species, while Tilia had the highest leaf productivity. Fagus trees showed no elevated production per basal area in the mixed stands.

? We found no evidence of complementary resource use associated with biomass production. We conclude that above-ground productivity of old-growth temperate deciduous forests depend more on tree species-specific traits than on tree diversity itself.

     

Agroforestry systems recover tree carbon stock faster than natural succession in Eastern Amazon,Brazil

Agroforestry Systems - The potential of agroforestry systems (AFS) for atmospheric carbon sequestration in degraded tropical lands is of key interest for climate change and rural development...     

An inventory of Guadua (Guadua angustifolia) bamboo in the Coffee Region of Colombia

Management of renewable natural resources and the corresponding policy formulation should be founded on reliable data and information. This refers both to information on the resource itself and to information on the market situation. In this paper, we present methodology and major results of an inventory of the Guadua resources, in a study area of about 1 million ha within the Coffee Region of Colombia. This inventory produced for the first time sample-based statistical estimations of the Guadua area and growing stock. In the study area, land cover of Guadua patches was estimated to be 3.9% or about 40,000 ha (minimum patch area 0.3 ha). This is higher than figures published earlier. Estimation for mean number of standing culms (including shoots and dry culms) per hectare was 6,940 with a mean diameter at breast height of 10.8 cm, apparent commercial volume of 654 m3/ha, commercial wood volume of 304 m3/ha, oven-dry biomass of 311 ton/ha, and total carbon stock of 156 ton/ha. While the low-intensity sampling approach worked well and may serve as an example for similar studies, we identified a number of issues for further research, particularly in what refers to as the basic mensurational models for Guadua volume and biomass estimation from inventories.