Climate and population origin shape pine tree height-diameter allometry

Tree height-diameter allometry, the link between tree height and trunk diameter, reflects the evolutionary response of a particular species’ allocation patterns to above and belowground resources. As a result, it differs among and within species due to both local adaptation and phenotypic plasticity. These phenotypic variations in tree height-diameter allometry determine tree productivity, resistance and resilience to climate variation and, ultimately, the success of plant material used in restoration projects. We tested the effect of climate change and population origin on the phenotypic variation of tree allometry in four pine species at an early stage of development (ca. 11 years old) based upon data originated from multi-site provenance tests and planted along a wide climatic range in south-western Europe. For a representative sample of populations from each species, we used already-developed species-specific height-diameter allometric models to assess changes in allometry between present and future climatic conditions. We found that Pinus halepensis and Pinus pinaster were the most plastic species, while Pinus sylvestris and Pinus nigra showed negligible plastic responses. In addition, our models stressed that pine tree height-diameter allometry will change and phenotypic variation could increase, except in P. sylvestris, under future environmental conditions. For some of the species, this might allow the selection of phenotypes better suited to novel climatic conditions. These foreseeable changes in tree height-diameter allometry (among and within-species) could entail eco-evolutionary effects on the early forest plantation dynamics. Therefore, restoration and reforestation plans should consider these effects, as they may interfere with production and/or environmental goals.     

Can bioplastic or woodchip groundcover replace herbicides or plastic mulching for valuable broadleaf plantations in Mediterranean areas?

Weed control is fundamental in plantations of valuable broadleaved species. The most common weeding techniques are repeatedly applied herbicides and removable plastic mulching, both raising environmental concerns. We studied the performance of these techniques on a hybrid walnut plantation, compared with three biodegradable mulch alternatives: a prototype bioplastic film, a layer of composted woodchips and a layer of ramial chips. The durability and effect of the treatments on tree performance (survival, growth, physiological traits) and soil features (moisture and temperature) were evaluated over 4 years. Herbicide yielded the best results, while all the mulching treatments provided better results than controls for nearly all the variables. The performance of plastic and bioplastic films was similar, suggesting that the latter could replace plastic mulching. The performance of the two chip mulches was similar and slightly below that of the films, probably because of the excessive thickness of the former (13–14 cm). In summary, biodegradable mulches showed high effectiveness in controlling weeds and so could offer an alternative to herbicide application and plastic mulching when these are contra-indicated technically (accessibility, repeatability), economically (labour cost), legally or environmentally.     

Resilience of European larch (<Emphasis Type="Italic">Larix decidua</Emphasis> Mill.) forests to wildfires in the western Alps

European larch is a dominant species in the subalpine belt of the western Alps. Despite recent increases in wildfire activity in this region, fire ecology of European larch is poorly understood compared to other larch species around the world. This study aims to assess whether European larch forests are resilient to fires, and to find out the factors that drive such resilience. We assessed the recovery of larch forests along a gradient of fire severity (low, moderate, high) based on the abundance and dominance of post-fire larch regeneration. We established 200 plots distributed among burned larch forests in nine wildfires that occurred between 1973 and 2007 in the western Alps. We included variables regarding topography, climate, fire severity, fire legacies, ground cover, grazing intensity, and time since fire. To evaluate potential drivers of larch recruitment, we applied generalized linear mixed models (GLMM) and random forests (RF). Larch regeneration was much more abundant and dominant in the moderate- and high-severity fire classes than in the low-severity class. More than half of the plots in the moderate- and high-severity classes were classified as resilient, i.e., post-fire larch regeneration was enough to recover a larch stand. GLMM and RF produced complementary results: fire severity and legacies, such as snags, canopy cover and distance to seed source, were crucial factors explaining post-fire larch recruitment. This study shows that fire has a positive effect on larch regeneration, and we conclude that European larch forests are highly resilient to mixed-severity fires in the western Alps.     

Effects of drought and rewatering on growth and transpiration in European beech seedlings late in the growing season

Drought stress is one of the most important environmental factors affecting plant growth and survival. To date, most studies aim at understanding of post-stress physiological and anatomical adaptation to drought stress; however only few studies focus on plant recovery. In the present study, transpiration, shoot water potential, and anatomical and morphological measurements were performed on 4-year-old European beech seedlings with fully developed leaves. The seedlings were exposed to three levels of soil water potential (well-watered, moderate drought stress and severe drought stress) and followed by rewatering under greenhouse conditions. Reduced transpiration rates were observed in the stressed seedlings as a response to drought stress, whereas anatomical and morphological variables remained unchanged. Three days after rewatering, transpiration rates in both moderately and severely stressed seedlings recovered to the levels of those of well-watered seedlings. Drought stress promoted leaf budding, resulting in higher shoot dry mass of stressed seedlings. Our findings indicate that anatomical and morphological adaptations of European beech seedlings to drought stress are visibly limited during late-season growth stages. These results will help us to further understand factors involved in drought adaptation potential of European beech seedlings faced with expected climate-related environmental changes. To complete our findings, further experiments on plant recovery from drought stress should be focused on different periods of growing season.     

Effects of tightening speed on torque coefficient in lag screw timber joints with steel side plates

To investigate the effects of tightening speed on the torque coefficient in lag screw timber joints with steel side plates, tightening tests were conducted on main timber members made from Cryptomeria japonica, Chamaecyparis obtusa and Pseudotsuga menziesii, under four tightening speed conditions (1, 4, 10, and 20 rpm). Major stick-slip behavior was observed in C. obtusa based on the relationship of tightening angle with clamp force, tightening torque, and thread torque at tightening speeds of 1 and 4 rpm. In addition, tightening speed’s effects on the torque coefficient (K) varied depending on the wood species of the main member. In P. menziesii, K was not affected by the tightening speed: the ratio of torque expended on tightening was 25% on average, and the ratio of torque expended on bearing surface friction was higher than the ratio of torque expended on thread friction.     

Temperature dependences of the dynamic viscoelastic properties of wood and acetylated wood swollen by water or organic liquids

In this study, to summarize the changes of thermal-softening behaviors of wood and acetylated wood due to differences in the kinds of swelling liquids, the following measurements were conducted. Untreated and acetylated wood samples were swollen by various liquids and the temperature dependences of the dynamic viscoelastic properties were measured after the heating and cooling histories were unified among the samples. The results obtained are as follows. Untreated samples swollen by high-polarity liquid had lower peak temperature of tanδ, however acetylated samples had higher peak temperature of tanδ than those of untreated wood. On the other hand, untreated wood samples swollen by low-polarity liquid had higher peak temperature of tanδ, however acetylated samples had lower peak temperature of tanδ than those of untreated wood. The amount of swelling is determined by interaction between wood and liquid due to proton-accepting power and molar volumes of liquid and so on, therefore the peak temperature of tanδ and degree of reduction in dynamic elastic modulus (E´) with increasing temperature were corresponded to the amount of swelling.     

Influence of pretreated wood dowel with CuCl<Subscript>2</Subscript> on temperature distribution of wood dowel rotation welding

This study examined the temperature distribution during rotation welding process using birch (Betula spp.) wood dowel and Chinese larch (Larix gmelinii) substrates. Wood dowels were divided into two categories including an untreated group and a group pretreated with cupric chloride. The mechanics test results indicated that the pullout resistance of the pretreated group with welded time 3 s showed the best performance. As a fitting analyses result, both the untreated group and pretreated group showed a significant nonlinear relationship among temperature, welded depth and welded time. In the untreated group case, a linear regression relationship was found between the highest temperature of the welding interface and the depth. However, two-stage fitting was used to fit the regression for the pretreated group. Compared with the untreated group, thermogravimetric (TG) analysis of the pretreated group welding interface presented two pyrolytic peaks, and it illustrated that the pretreatment promoted the depolymerization and pyrolysis of wood constituents.     

Experimental study on the fire performance of straight-line dovetail joints

To study the fire performance of the common dovetail joint in Chinese ancient architecture, we performed fire exposure and fire resistance tests of straight-line dovetail joints. The fire exposure test shows that the contact part of the dovetail joint was hardly charred because the gap between them is small. In the reference test, the displacement linearly varies with the load when the dovetail joint is fully pressed together. In the fire test, fire retardant coating can improve the fire resistance of the specimen, and its fire protection effect is remarkable. With the increase in load, the fire resistance of specimens obviously decreases. The effect of a tiny 2–4 mm gap between the tenon and the mortise on heat transfer is notably limited. The load level does not significantly affect the speed of temperature increase.     

Pore structure and the properties of electric double layer capacitor electrode of bamboo-derived activated carbon prepared by superheated steam

Bamboo-derived activated carbon prepared by superheated steam (BAC) exhibited performance for utilization as an electric double layer capacitor (EDLC) electrode. Pore structure and EDLC performances were investigated by comparison with phenol resin-derived activated carbon (MSP-20), which is commercially available and often used for the purpose. The nitrogen adsorption isotherm showed that BAC had a large BET-specific surface area of 1268 g/m² with a developed pore structure, especially of the mesopore, in comparison with MSP-20. It is considered that inherent ash in bamboo promoted activation, in addition to physical activation by superheated steam. Capacitance per electrode volume (C_V) was 52 F/cm³ with BAC. Because the density of BAC is high (0.78 g/cm³) compared with that of MSP-20 (0.58 g/cm³), sufficient C_V for usage was obtained, although the capacitance per electrode mass (C_M) at 5 mA/cm² itself of BAC (67 F/g) was lower than that of MSP-20 (126 F/g). With IR drop, the resistance value of BAC (9.7 Ω) was lower than that of MSP-20 (10.5 Ω). Especially, the diffusion resistance of BAC disclosed to be smaller than that of MSP-20. These results indicated that BAC produced by steam activation is a promising material with a pore structure suitable for ion transfer in EDLC.