The stereoselectivity of the reaction of furan (1) with maleic anhydride (2) and maleimide (3) was studied experimentally and theoretically. Although the two reactions are highly similar with regard to their preference for endo and exo steroisomers, notable differences were experimentally observed and explained on the basis of calculated reaction-free energies and transition-state barriers. The experimental values of rate constants (k(1+2endo) = (1.75 +/- 0.48) x 10(-5); mol(-1) l s(-1); k(1+2exo) = (3.10 +/- 0.55) x 10(-5); mol(-1) l s(-1); k(1+3endo) = (1.93 +/- 0.082) x 10(-5); mol(-1) l s(-1), k(1+3exo) = (1.38 +/- 0.055) x 10(-5); mol(-1) l s(-1) all at 300 K) and the observed reaction course clearly confirm that neither of these reactions are prototypical examples of Diels-Alder [4 + 2] cycloadditions, whose dominant preference is for endo isomers. However, only by comparing their energetics-calculated at the CCSD(T) level of theory-with the analogous reactions involving cyclopentadiene (8) as a diene can these observations be understood. The low thermodynamic stability of furan [4 + 2] adducts opens retro-Diels-Alder reaction channels and overrules the very small kinetic preference (calculated and measured here) of initial formation for endo stereoisomers. On a macroscopic scale "an irregular"-thermodynamically more stable-exo stereoisomer was consequently observed as a dominant species.

Trees with hollows are key features sustaining biodiversity in wooded landscapes. They host rich assemblages of often highly specialised organisms. Hollow trees, however, have become rare and localised in Europe. Many of the associated biota is thus declining or endangered. The challenge of its conservation, therefore, is to safeguard the presence of hollow trees in sufficient numbers. Populations of numerous species associated with tree hollows and dead wood are often found in habitats that were formed by formerly common traditional silvicultural practices such as coppicing, pollarding or pasture. Although it has been occasionally mentioned that such practices increase the formation of hollows and the availability of often sun-exposed dead wood, their effect has never been quantified. Our study examined the hollow incidence in pollard and non-pollard (unmanaged) willows and the effect of pollarding on incremental growth rate by tree ring analysis. The probability of hollow occurrence was substantially higher in pollard than in non-pollard trees. Young pollards, especially, form hollows much more often than non-pollards; for instance, in trees of 50 cm DBH, the probability of hollow ocurrence was ∼0.75 in pollards, but only ∼0.3 in non-pollards. No difference in growth rate was found. Pollarding thus leads to the rapid formation of tree hollows, a habitat usually associated with old trees. It is therefore potentially a very important tool in the restoration of saproxylic habitats and conservation of hollow-dependent fauna. If applied along e.g. roads and watercourses, pollarding could also be used to increase landscape connectivity for saproxylic organisms. In reserves where pollarding was formerly practiced, its restoration would be necessary to prevent loss of saproxylic biodiversity. Our results point to the importance of active management measures for maintaining availability, and spatial and temporal continuity of deadwood microhabitats.

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Aim Open woodlands are biologically highly diverse habitats, and veteran (i.e., old, senescent) trees are key structures supporting their biodiversity. Open canopy structure had been maintained by both natural‐ and human‐induced disturbances. In the past two centuries, suppression of such disturbances, together with forestry intensification, has turned most lowland woodlands into closed‐canopy forests. We investigated the effect of increased canopy closure on veteran trees and several threatened beetles associated with them. Location Floodplain woodlands along the lower Dyje and Morava rivers, Czech Republic. Methods We used an approach combining the study of aerial photographs with on‐ground survey of veteran trees and associated endangered beetles. The aerial images were used to obtain the information on historical (1938) and recent (2009) canopy closure in the area of 146 km2, where we mapped large oaks (d.b.h. >70 cm), hollow trees and three associated beetles including the hermit beetle (Osmoderma barnabita), the great capricorn beetle (Cerambyx cerdo) and the jewel beetle Eurythyrea quercus. Results The presence of large oaks, hollow trees and their associated beetle species are negatively related to recent high canopy closure, and the historical level of canopy closure matters, as in nowadays closed‐canopy stands, the beetles and veteran trees are more common in places that were rather open in 1938 than in the places with closed canopy already in 1938. Moreover, the health state of veteran trees highly depends on the canopy closure. Main conclusion The negative effect of canopy closure on veteran trees and their endangered inhabitants is several decades delayed and may thus often go undetected. In the forests, however, large and hollow trees and their associated biodiversity are relics of the past, more open conditions. The restoration of open woodlands is therefore vital for preventing their further decline. Conservation management planning needs to take this into account wherever, veteran trees and associated biota are concerned.

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Organisms associated with dead wood (i.e. saproxylic species) are threatened by intensified forest and agricultural management. For a majority of saproxylic beetles the detailed information on their habitat requirements is still lacking, thus hindering efficient conservation information. This also applies to the violet click beetle (Limoniscus violaceus), one of the umbrella species of European saproxylic beetle fauna. This specie needs basal tree hollows for its larval development. We studied habitat preferences of L. violaceus in basal tree hollows using emergence traps installed on 208 trees located in five sites in France. We used logistic regressions and recursive partitioning methods to understand the species–habitat relationships and to identify key environmental variables to predict the occurrence of L. violaceus. The probability of occurrence of L. violaceus in basal hollows increases with increased tree circumference at 30 cm above ground and with increased hollow decay stage. The analysis of threshold values shows that the occurrence of the beetle is relatively high in trees that have a circumference greater than 360 cm, uncertain for those between 235 and 360 cm, and improbable for circumferences lower than 235 cm. Similarly, the occurrence of L. violaceus was probable in advanced stages of hollow decomposition and improbable in early stages. Our results provide non‐specialists with helpful habitat features of an umbrella species which is hard to detect. This will increase the ability of conservation managers to identify sites that deserve protection and better monitor the habitat of many saproxylic species associated with basal hollow trees.

1. The wrinkled bark beetle Rhysodes sulcatus is an endangered saproxylic beetle listed in the European Habitats Directive and in the Bern Convention (Annex II). It is considered a relict of primeval forests and belongs among the most threatened saproxylic beetles in Europe.2. The purpose of this study was to identify the key habitat requirements of the species. The study was carried out at several locations within different forest types in mid elevation forests dominated by oak, beech and spruce and montane beech-fir forests in the Czech Republic, Slovakia and Croatia.3. Coarse woody debris was checked for the presence of the beetle, and parameters of each inspected dead wood unit and its surroundings were recorded, including diameter, length, humidity, insolation, decomposition level and rot type. Surrounding forest characteristics, such as canopy density, main tree species, undergrowth, the amount and quality of the dead wood were also recorded.4. The analysis shows that the presence of the beetle is affected mainly by the diameter of dead wood as well as its humidity, as R. sulcatus was almost exclusively found in large, moist and well rotten fallen logs with a diameter greater than 60 cm. These findings may provide useful guidelines for sustainable forest management, specifically emphasising the need to retain large fallen logs at sites inhabited by R. sulcatus populations.