Tree regeneration and future dynamics of the laurel forest on Tenerife,Canary Islands

Abstract. We studied two sites in the laurel forest of Tenerife to predict future changes in canopy composition. We used two projection methods: Horn's ‘Markovian Projection’, which utilizes information on juveniles in the vicinity of canopy trees, and a 'Stand Projection’, which ignores such information. We performed these projections both including and excluding a-sexual regeneration. Although all of our projections predict a change in species composition, inclusion of a-sexual reproduction decreased the magnitude of successional change. The persistence of Prunus lusitanica and Ilex canariensis appears to be highly dependent on a-sexual regeneration. Both the Markov- and stand projections predict a slight convergence in species composition between the two sites when only sexual regeneration is considered, and also a higher dominance of the shade-tolerant species Laurus azorica. When a-sexual regeneration is also considered, some divergence is shown, with less projected change in the stand projection than in the Markov projection. In spite of some differences between the models, general patterns such as an increase of shade-tolerant species (Laurus azorica and Prunus lusitanica) and a decrease of shade-intolerant species (Erica arborea, Erica scoparia and Myrica faya) are consistent.     

Guiding the Selection of Processing Additives for Increasing the Efficiency of Bulk Heterojunction Polymeric Solar Cells

In bulk heterojunction (BHJ) polymeric organic solar cells (OSCs), the use of processing additives in the material formulation has emerged as a promising, cost‐effective, and widely applicable method for optimizing the phase separation between the donor (D) and acceptor (A) materials, thus increasing their efficiency. So far, however, there has been no systematic approach for identifying suitable processing additives for a given D:A system. A method based on the Hansen solubility parameters (HSPs) is proposed for guiding the selection of processing additives for a given D:A combination. The method is applied to the archetypical poly(3‐hexylthiophene) (P3HT) and [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM) system. The HSPs of these materials are determined and used to define a set of numerical criteria that need to be satisfied by a processing additive in order for it to be effective in realizing a higher efficiency OSC. Applying the selection criteria results in the identification of three novel processing additives. OSCs made of these formulations demonstrate an increase in their short‐circuit current density (J_SC) and power conversion efficiency (PCE). These results demonstrate the efficiency of these novel processing additives and show that the HSPs represent a useful tool to determine and explore new types of processing additives for BHJ‐OSCs.     

MODELING STABILIZING SELECTION: EXPANDING THE ORNSTEIN-UHLENBECK MODEL OF ADAPTIVE EVOLUTION

Comparative methods used to study patterns of evolutionary change in a continuous trait on a phylogeny range from Brownian motion processes to models where the trait is assumed to evolve according to an Ornstein-Uhlenbeck (OU) process. Although these models have proved useful in a variety of contexts, they still do not cover all the scenarios biologists want to examine. For models based on the OU process, model complexity is restricted in current implementations by assuming that the rate of stochastic motion and the strength of selection do not vary among selective regimes. Here, we expand the OU model of adaptive evolution to include models that variously relax the assumption of a constant rate and strength of selection. In its most general form, the methods described here can assign each selective regime a separate trait optimum, a rate of stochastic motion parameter, and a parameter for the strength of selection. We use simulations to show that our models can detect meaningful differences in the evolutionary process, especially with larger sample sizes. We also illustrate our method using an empirical example of genome size evolution within a large flowering plant clade.     

Stand and neighbourhood parameters as determinants of plant species richness in a managed forest

Abstract. Patterns of species richness in a managed forest were related to ecological factors at two spatial scales. Local variables within a plot (5 m × 5 m) included 13 soil classes and nine stand classes. Neighbourhood variables were defined within a 25 m radius from the focal plot and were measured using a Neighbourhood Diversity Index (NDI - total diversity of different stand classes) and nine Neighbourhood Scores (NS - relative dominance of a given stand class). 224 species were registered in the survey of which 138 were true forest species. Local parameters (stand and soil class) were weak predictors of total and forest species richness. High total and forest species richness were significantly related to high values of NDI (i.e. heterogeneous neighbourhoods). Regression trees showed that total species richness was best predicted by the amount of roadside habitat in the neighbourhood and NDI. Forest species richness was positively related to NDI and negatively related to the amount of coniferous stands in the neighbourhood.     

A Systematic Approach to Solvent Selection Based on Cohesive Energy Densities in a Molecular Bulk Heterojunction System

The solubilities of 3,6‐bis(5‐(benzofuran‐2‐yl)thiophen‐2‐yl)‐2,5‐bis(2‐ethylhexyl)pyrrolo[3,4‐c]pyrrole‐1,4‐dione ( DPP(TBFu)₂ ) and [6,6]‐phenyl‐C₇₁‐butyric acid methyl ester ( PC₇₁BM ) in a series of solvents are measured, and this data is used to calculate the Hansen solubility parameters of the two materials. The dispersion, polar, and H‐bonding parameters of DPP(TBFu)₂ and PC₇₁BM were found to be (19.3, 4.8, 6.3) and (20.2, 5.4, 4.5) MPa^1/2, respectively, with an error of ± 0.8 MPa^1/2. Based on the solubility properties of the two materials, three new solvents (thiophene, trichloroethylene and carbon disulfide) were utilized for the DPP(TBFu)₂ : PC₇₁BM system which, after device optimization, led to power conversion efficiencies up to 4.3%.     

Predictability of plant and fungal species richness of old‐growth boreal forest islands

Abstract. The fragmentation and deterioration of old‐growth forest habitat by modern forestry have become a major threat to species diversity in Fennoscandia. In order to develop a conservation strategy for the remaining diversity it is essential to identify the existing diversity and to develop appropriate conservation and monitoring programs. For these purposes indicators of conservation value for administrative prioritization are required. This study examines the predictability of plant and fungal species richness on two spatial scales on 46 isolated old‐growth forest islands (0.17 ‐ 12 ha) in a forest‐wetland mosaic. We explore (1) to what extent area, isolation and stand structure variables can explain the variation in species richness and (2) if richness patterns of individual species groups correlate. Isolation showed no relation to species richness. Area explained 50 ‐ 70% of the variation in total species richness and was positively related to the density of crustose lichens and Red‐list species in island interiors. Stand structure variables explained 28 ‐ 66% of the residual variation in total species richness after controlling for island size, and 15 ‐ 73% of the variation in density of species in island interiors. The highest predictability of species richness was found among substrate‐specific fungi and Red‐list species. Different stand structure variables were found to explain richness in the different species groups, and only among a few species groups species richness correlated. Thus, species richness of one single species group is unlikely to be a good indicator for total biodiversity. The results show that measurements of stand size and stand structure variables may be a strong complementary tool, and sometimes a substitute to extensive species inventories when one aims to estimate and monitor plant and fungal species diversity in old‐growth Picea abies forests.     

Restoration of a species‐rich fen‐meadow after abandonment: response of 64 plant species to management

Abstract. Eleven years of abandonment of a species‐rich fen‐meadow under undisturbed environmental conditions resulted in transformation into areas with tall herb‐, sedge‐ and rush‐dominated communities and areas with Alnus thicket. Species cover was measured in permanent plots in both community types and succession was monitored during 14 yr of restoration following reintroduction of management. The annual increase in accumulated species number followed a log‐log‐time linear regression during 10 yr of grazing management. The expected number of years taken before this annual rate was equal to annual extinction, i.e. a stable situation according to species density, was up to six. The response of 64 species to management was evaluated through paired statistical tests of changes in cover and frequency over time. In total, 55 species could each be allocated to one unique response model (monotone or non‐monotone, concave models) independently of the importance value used (cover or frequency) and type of management (grazing following felling or mowing and mowing without grazing). Species which increased in response to grazing had the most persistent seed banks and CR‐strategies, while species decreasing in response to grazing had less persistent seed banks and CS‐strategies. Some of the species which increased due to grazing followed a model with a local maximum in cover and frequency. The results are discussed in relation to management of species with high cover value during restoration succession.     

Glutathione-prostaglandin A1 conjugate as substrate in the purification of prostaglandin 9-ketoreductase from rabbit kidney

Using GSH-PGA₁ as substrate for determination of enzyme activity a pI 4.8 form of rabbit kidney prostaglandin 9-keto-reductase has been purified 95 times to a specific activity of 1755 nmol/min per mg protein. The purification procedures involve ion-exchange chromatography, gel-filtration and affinity chromatography. The latter procedure comprises Blue Sepharose affinity chromatography, and GSH-PGA₁-Sepharose affinity chromatography.The purified enzyme preparation also showed a weak NADP⁺-dependent 15-hydroxyprostaglandin dehydrogenase activity, 20 nmol/min per mg protein with PGE₁ as substrate. K_m(PGE₁) for the dehydrogenase is 142.6 ± 45.1 μM (S.E., n=7).     

Present and past old‐growth forests of the Lake Tahoe Basin,Sierra Nevada,US

Abstract. We described 38 relictual old‐growth stands – with data on the mortality, regeneration, floristic richness, fuel load and disease incidence in our study area in the Tahoe Basin of California and Nevada. The stands are within the lower and upper montane zones (1900–2400 m a.s.l.) and they are rare, occupying < 2% of the land in the Basin's watershed. Correlation matrices and ANOVAs of forest types and conifer species with environmental gradients revealed significant relationships with elevation, distance east of the Sierran crest, slope aspect, annual precipitation, date of complete snow melt, litter depth and degree of soil profile development. Pathogens, parasites and wood‐boring insects were present on 23% of living trees; 16% of all trees were dead. We compared these stands to a reconstruction of pre‐contact Basin forests and to ecologically analogous old‐growth forests of Baja California that have never experienced fire suppression management. Currently, overstorey trees (> 180 yr old) in the Basin stands have ca. 33% cover, 54 m².ha^‐1 basal area and 107 individuals.ha^‐1, values very similar to reconstructions of pre‐contact Basin forests and to modern Baja California forests. Understorey trees (60–180 yr old), however, are several times more dense than historic levels and species composition is strongly dominated by A. concolor, regardless of the overstorey composition. The ratio of Pinus: Abies has increased – and the age structure of extant stands predicts that it will continue to increase – from approximately 1:1 in pre‐contact time to 1:7 within the next century. Disease incidence and mortality in Baja forests were lower. Although we quantitatively defined current Basin old‐growth forests – in terms of stand structure – we realize that our definition will differ from that of both past and future old‐growth forests unless management protocols are changed.     

Experimental and theoretical estimation of the Hansen solubility parameters of paramylon esters based on the degrees of substitution and chain lengths of their acyl groups

Paramylon is a natural hydrophilic polysaccharide produced in the pyrenoids of euglenoids, and esterification may render paramylon hydrophobic. Esterification imparts not only thermoplasticity, but also potential compatibilities with other polymer resins and fillers. However, the dependence of the compatibility on the structure of the polymer ester has not yet been systematically studied. To estimate the affinities between paramylon esters and hydrophobic organic solvents/resins, the dependences of their Hansen solubility parameters, which are association indices, on the degrees of substitution and chain lengths of the ester groups were investigated. Experimental and theoretical investigations were conducted using the dissolution and Fedors methods, respectively. Esterification decreased the solubility parameter from 49 (paramylon) to approximately 18 MPa^1/2 (paramylon esters), indicating that the potential affinities of paramylon esters for hydrophobic organic solvents/polymers increased. A multiple regression analysis was also performed to investigate the effects of acyl chain length and degree of substitution with acyl groups on the solubility parameter. The solubility parameters of the paramylon derivatives were continuously variable from hydrophilic to -phobic. Hence, esterification with various acyl groups may control the hydrophobicities of paramylon esters, enhancing their miscibilities with various hydrophobic organic solvents and resins.