Formation of carbon–carbon composite using wood as a precursor

Abstract

The use of wood as structure-giving material may be an effective approach to reduce some barriers for producing high temperature ceramic especially carbon composites. The objective of this study was to develop a simple process for producing carbon–carbon (C–C) composite through porous template result from pyrolysing of wood. Walnut, known to be relatively permeable, was being heat treated under controlled atmosphere. The carbon-template formed was infiltrated with coal tar pitch. Morphological characterization of the resulting composite was carried out by scanning electron microscopy morphology and physical properties of sample were evaluated with determination of bulk density and open porosity. In addition mechanical properties of products were analysed with three-point bending test and Vickers micro hardness. Results showed that bulk density had an uprising trend with increasing the number of densification cycles and subsequently open porosity decreased. Moreover, from mechanical property's point of view, results had a good compatibility with increase in the densification cycles.     

Trophic consequences of postfire logging in a wolf–ungulate system

Controversy surrounds postfire logging, often because of negative effects on snag-dependent wildlife species. Few studies, however, have examined effects on early-seral species that may benefit from postfire logging, nor effects on trophic relationships. We studied the effects of postfire logging on trophic dynamics between wolves (Canis lupus), three ungulate species and ungulate forage biomass during the first 3 years in a large burn in the Canadian Rockies, Alberta, Canada. We examined plant biomass and ungulate responses to two treatments (post- and prefire logging) compared to a burned but unlogged area (control). We evaluated resource selection for the three treatments by elk (Cervus elaphus) using radiotelemetry and for deer (Odocoileus spp.), moose (Alces alces), and, secondarily, elk using pellet counts. Elk resource selection was modeled as a function of the trade-off between wolf predation risk and herbaceous forage biomass to test for trophic impacts of postfire treatments. Postfire logging had transient effects on total herbaceous biomass; while forb biomass was reduced, increases in graminoid biomass more than compensated by the third year. Prefire logging areas were dominated by a few species, but had generally higher forage biomass by the third year. Ungulates avoided postfire and prefire logged areas despite greater herbaceous biomass. Only when we considered elk resource selection as a function of both forage and wolf predation risk was the extent to which trophic interactions affected by postfire logging revealed. Wolves selected proximity to roads and the higher forage biomass associated with postfire logging in open logged areas. This translated to the highest predation risk for elk in postfire logged areas. Thus, ungulates avoided postfire logged areas because of human alteration of top-down predation risk despite enhancements to bottom-up forage biomass. Managers should consider trophic consequences of postfire logging on the interactions among species when gauging logging effects on terrestrial ecosystems. Making use of existing roads, minimizing the construction of new roads, and managing road removal following postfire logging will help mitigate the negative effects of postfire logging on terrestrial ecosystems.     

Gap evapotranspiration and drainage fluxes in a managed and a virgin dinaric silver fir–beech forest in Slovenia: a modelling study

The monthly water balance in gaps in a managed Dinaric silver fir–beech forest and a virgin forest remnant located in SE Slovenia was modelled using a capacity water balance model for two growing seasons. Two gaps of different size (ca. 0.07 and 0.15 ha) were selected in each forest and plots for soil moisture monitoring were established in each gap (2–4) and in the surrounding forest (2–3). We report on the modelled actual evapotranspiration (AET) and potential evapotranspiration (PET) and drainage fluxes (DF) from the rooting zone at the plots. Precipitation over the 2001 growing season (May–October) was considerably drier than average and that for 2002 growing season was wetter than average. Modelled AET for the 2001 growing season varied between 88% and 96% of PET for the managed forest plots and between 90% and 100% for the virgin forest plots. The values for the gap plots varied between 87% and 100% at the managed forest site and between 92% and 96% for the gaps in the virgin forest site. Monthly AET values declined to 57–59% of PET at plots in the centre of the gaps in the managed forest site and to 63–74% in the gaps in the virgin forest site (July), indicating that the highest drought stress occurs in gap centres. For 2002 growing season, AET for all plots was 100% of PET. Modelled DF values in 2001 were 13–35% of rainfall for plots in the gap centres and 12–16% for plots in the forest at the managed forest site. On an average, gap DF values were 20% (154 mm) higher than the forest plot values. DF values in 2002 were similar for all plots at the managed forest site, 31–33% of rainfall. At the virgin forest site, 2001 growing season, DF values varied between 12% and 30% of rainfall at the forest plots and between 12% and 32% at the gap plots. In 2002, DF values for all plots in the virgin forest site varied between 24% and 38% of growing season rainfall. The varying development of vegetation and forest in the gaps of the virgin forest remnant resulted in more variable evapotranspiration and DF during the drought year 2001, with values not as clearly related to distance from the gap centre as in the managed forest site.     

Observance–Influence Analysis: A Case Study in a Forest Recreation Area

Importance–performance (I-P) analysis is a common evaluative measure in forest recreation management. However, concerns with I-P analysis have been raised. In this study, the observance–influence (O-I) analysis technique modified from I-P analysis was adapted for analysing the observance of various use and resource impacts by on-site visitors, and the influence that these impact conditions have on forest recreation area visitor experiences. During the summer and autumn of 2000, 476 Worak-san Forest National Park visitors in Korea were surveyed. The O-I grid generated from the survey data indicated that managers are doing a good job. The grid revealed most impacts clustering in the low priority concern and no concern quadrants. Impacts shown to be of most concern related to utility poles and power lines, poor maintenance of buildings, dead and dying trees, and discourteous behaviour. The O-I grid analysis model has considerable utility for park managers in analysing visitors’ perceptions of park impacts.     

Soil carbon and tree litter dynamics in a red cedar–scotch pine shelterbelt

Carbon sequestration in the woody biomass of shelterbelts has been investigated but there have been no measurements of the C stocks in soil and tree litter under this agroforestry practice. The objective of this study was to quantify C stored in surface soil layers and tree litter within and adjacent to a 35-year-old shelterbelt in eastern Nebraska, USA. The 2-row shelterbelt was composed of eastern red cedar (Juniperus virginiana) and scotch pine (Pinus sylvestris). A sampling grid was established across a section of the shelterbelt on Tomek silt loam (fine, smectitic, mesic Pachic Argiudolls). Four soil cores were collected at each grid point, divided into 0–7.5 and 7.5–15 cm depth increments, and composited by depth. Soil samples were analyzed for total, organic, and inorganic C, total N, texture, pH, and nutrient content. Under the shelterbelt, all surface litter in a 0.5 × 0.5 m² area at each grid point was collected prior to soil sampling, dried, weighed, sorted, and analyzed for total C and N. Average soil organic carbon (SOC) in the 0–15 cm layer within the shelterbelt (3,994 g m⁻²) was significantly greater than in the cultivated fields (3,623 g m⁻²). The tree litter contained an additional ∼1,300 g C m⁻². Patterns of litter mass and soil pH and texture suggested increased organic inputs by tree litter and deposition of wind-blown sediment may be responsible for greater SOC beneath the shelterbelt. Further research is needed to identify the mechanism(s) responsible for the observed patterns of SOC within and adjacent to the shelterbelt and to quantify the C in biomass and deeper soil layers.

Soil quality in a pecan–kura clover alley cropping system in the Midwestern USA

Intercropping alleys in agroforestry provides an income source until the tree crop produces harvestable yields. However, cultivation of annual crops decreases soil organic matter and increases soil erosion potential, especially on sloping landscapes. Perennial crops maintain a continuous soil cover, increase water infiltration, reduce soil erosion, and improve overall soil quality. The objective of this on-farm study was to assess the effects of a perennial legume, kura clover (Trifolium ambiguum M. Bieb.), on soil quality in a recently established pecan (Carya illinoinensis Wangenh. C. Koch) orchard. The pecan-kura clover agroforestry practice was established on deep loess soils of the Missouri River hills landscape. These silt loams are on 2–20% slopes and can be highly erosive. Kura clover, introduced as the alley crop 5 years after pecan planting, was selected based on its perennial growth habit, nitrogen-fixing ability, winter hardiness, high forage quality, and soil conservation properties. Kura clover was seeded in 2001 and harvested for hay annually beginning 2003. Soil quality indicators of total organic C, total N, water-stable aggregates, and selected soil enzymes were determined on surface soil samples collected annually after kura clover establishment. Soil organic C and activities of soil enzymes increased compared with cultivated and grass pasture control soils by the eighth year of establishment. Water-stable aggregation improved by 50% and surface soil shear strength improved significantly (P < 0.05) in alleys compared with control sites. Results illustrate that kura clover as the alley-cropped component improved soil fertility and biological activity through increased organic matter and improved soil structure, and yielded high quality forage valuable for the cattle-feeding operation. Kura clover maintained or improved soil quality, reduced soil erosion potential, and benefited pecan growth by providing a source of soil nitrogen and improving soil structure for adequate water infiltration and aeration.     

Functional traits explain growth–mortality trade-offs in a mixed broadleaf-conifer forest in northeastern China

The trade-offs between tree growth and mortality are important indicators of the life-history strategies of species and have been demonstrated to be maintained by inherent fitness differences among species. There is a growing consensus that functional traits which inflect the ecological performances of individuals may be correlated with growth–mortality trade-offs within communities. In this study, the aforementioned trade-offs were detected and their relationships with the functional traits were examined, based on data collected in a typical temperate forested area in northeastern China. Principal components analyses were performed for growth–mortality trade-off relationships. The factor scores on the first principal component were used to represent the species’ positions at an axis of life-history variations among different species. Correlation and multiple regression analyses were performed for the purpose of detecting the relationships between functional traits and the growth–mortality trade-off. The results showed that there were significant trade-offs between the tree growth and mortality rates in the examined plot. Among the six functional traits which were considered, the H_max was found to have the strongest effects on the demographic rates and trade-offs. The observed negative effects on the tree growth and mortality rates suggested that the large species often grow more slowly and living longer, while species at small adult size grow fast but die easily. It was also observed that the specific leaf area and the leaf carbon content level were also very important to the growth and mortality trade-offs. The traits considered in this study explained 68% of interspecific variations in the species positions in the growth–mortality trade-off. In addition, wood density was found to show no effect on the trade-off. This was likely due to the fact that the density of the wood may influence the demographic rates more strongly during the early life stages of the trees. The results of discrimination analysis further confirmed the explanations abilities of the functional traits on the variations of life-history strategies among the species. Due to the fact that the relationships between the functional traits and the trade-offs were found to be relatively variable, it will be necessary to further consider other traits which are more closely and mechanistically linked to individual performances in future investigations, such as leaf life span, leaf tissue density, photosynthetic capacity, and dark respiration rates.

     

Patterns of tree growth in a single tree selection silver fir–European beech forest

The basal area and height growth of trees and saplings in silver fir–European beech single stem selection forest were studied with regard to their social status and crown parameters of size, coverage, shading and vitality. On 24 permanent research plots (20 m × 20 m each) all trees [diameter at breast height (dbh) ≥10 cm] and saplings (≥1.3 m tall and dbh <10 cm) were surveyed. Repeated measurements of dbh (N = 1,608) and height (N = 1,135) 10 years apart enabled the calculation of annual basal area increment (BAI) of trees and saplings, and annual height (HI) increment of saplings. To obtain the growth characteristics for individual trees and saplings, their social status and crown parameters were assessed by rank. In the multivariate general linear model for BAI, social status, crown size and crown coverage of individuals as the predictors, and dbh² as the covariate, explained 70% of total variability. Similarly, social status, crown size, crown coverage and crown shading had a significant impact on the HI of saplings, explaining 70% of total variability. Among the observed variables, social status determined according to the individual’s position in vertical stand structure was, in addition to dbh, the most important predictor for both BAI and HI. Significant differences were observed between the BAI and HI models for the main tree species (European beech and silver fir), indicating their different growth characteristics. The applied method could be used as a supplement to the more widely used approaches for studying basal area and height growth of individual trees in selection forest stands.     

Error propagation in stock-difference and gain–loss estimates of a forest biomass carbon balance

According to the United Nations International Panel on Climate Change good practice guidance, an annual forest biomass carbon balance (AFCB) can be estimated by either the stock-difference (SD) or the gain–loss (GL) method. An AFCB should be accompanied by an analysis and estimation of uncertainty (EU). EUs are to be practicable and supported by sound statistical methods. Sampling and model errors both contribute to an EU. As sample size increases, the sampling error decreases but not the error due to errors in model parameters. Uncertainty in GL AFCB estimates is dominated by model-parameter errors. This study details the delta technique for obtaining an EU with the SD and the GL method applicable to the carbon in aboveground forest biomass. We employ a Brownian bridge process to annualize the uncertainty in SD AFCBs. A blend of actual and simulated data from three successive inventories are used to demonstrate the application of the delta technique to SD- and GL-derived AFCBs during the years covered by the three inventories (SD) and rescaled national wood volume harvest statistics (GL). Examples are limited to carbon in live trees with a stem diameter of 7 cm or greater. We confirm that a large contribution to the uncertainty in an AFCB comes from models used to estimate biomass. Application of the delta technique to summary statistics can significantly underestimate uncertainty as some sources of uncertainty cannot be quantified from the available information. We discuss limitations and problems with the Monte Carlo technique for quantifying uncertainty in an AFCB.     

Spatial pattern of trees influences species productivity in a mature oak–pine mixed forest

Spatial pattern has a key role in the interactions between species in plant communities. These interactions influence ecological processes involved in the species dynamics: growth, regeneration and mortality. In this study, we investigated the effect of spatial pattern on productivity in mature mixed forests of sessile oak and Scots pine. We simulated tree locations with point process models and tree growth with spatially explicit individual growth models. The point process models and growth models were fitted with field data from the same stands. We compared species productivity obtained in two types of mixture: a patchy mixture and an intimate mixture. Our results show that the productivity of both species is higher in an intimate mixture than in a patchy mixture. Productivity difference between the two types of mixture was 11.3 % for pine and 14.7 % for oak. Both species were favored in the intimate mixture because, for both, intraspecific competition was more severe than interspecific competition. Our results clearly support favoring intimate mixtures in mature oak–pine stands to optimize tree species productivity; oak is the species that benefits the most from this type of management. Our work also shows that models and simulations can provide interesting results for complex forests with mixtures, results that would be difficult to obtain through experimentation.     

Stand dynamics in a logged and silviculturally treated Costa Rican rain forest, 1988–1996

The lowland rain forests of Central America are poorly known from the standpoint of management for timber production. We studied the stand dynamics of a logged Costa Rican rain forest under three different regimes of post-logging silvicultural treatment. The site was located on low hills with Ultisols in Holdridge's Tropical Wet Forest life zone. The Pentaclethra macroloba-dominated forest had been high graded before planned management began. Management of the 540 × 540 m (29.2 ha) experimental area began with a timber harvest in the whole area during 1989–1990, 4 trees ha⁻¹ being cut overall for 10.1 m³ ha⁻¹. The experimental plots were 180 × 180 m (3.24 ha), comprising a 100 × 100 m (1.0 ha) central permanent sample plot (PSP) with a 40-m wide buffer strip. Two types of post-harvest silvicultural treatment: liberation/refinement (in 1991) and shelterwood (in 1992) were applied under a complete randomized block design with three replicates, using logged but untreated plots as controls. PSP data reported are for the 1988–1996 period for individuals with ≥10 cm DBH. The most marked changes in forest structure were caused by silvicultural treatment, basal area under the liberation/refinement treatment being reduced to ca. 65% of its probable mature forest value. Recruitment exceeded mortality in the years following intervention under all three treatments, but forest structural recovery was slowest under the liberation/refinement treatment. Post-intervention mortality rates appeared higher under the liberation/refinement treatment than under the control or shelterwood treatments, though differences were not statistically significant. In relation to tree attributes, mortality rates increased with decreasing DBH increment, crown illumination and quality of crown form. Commercial DBH increments were higher under the liberation/refinement treatment than in control plots during the 1993–1996 period. On the basis of its response to intervention during the first seven years of management, the forest appears resilient and productive; trends over time in mortality rates under the most intense silvicultural regime require close attention however. Pentaclethra-dominated forests are important components of the productive forest resources of Costa Rica and Nicaragua and, given current deforestation rates in areas such as southern Nicaragua, it is now urgent that the existing biophysical knowledge of these forests be applied to forest conservation and management.     

Selection of mixed-effects parameters in a variable–exponent taper equation for birch trees in northwestern Spain

Context

Taper equations predict the variation in diameter along the stem, therefore characterizing stem form. Several recent studies have tested mixed models for developing taper equations. Mixed-effects modeling allow the interindividual variation to be explained by considering both fixed-effects parameters (common to the population) and random-effects parameters (specific to each individual).

Aims

The objective of this study is to develop a mixed-effect variable exponent taper equation for birch trees in northwestern Spain by determining which fixed-effects parameters should be expanded with random-effects parameters.

Methods

All possible combinations of linear expansions with random effects in one and in two of the fixed-effects model parameters were tested. Upper stem diameter measurements were used to estimate random-effects parameters by the use of an approximate Bayesian estimator, which calibrated stem profile curves for individual trees.

Results

Parameter estimates for more than half of the mixed models investigated were nonsignificant. A first order autoregressive error structure was used to completely remove the autocorrelation between residuals, as mixed-effects modeling were not sufficient for this purpose.

Conclusion

The mixed model with the best fitting statistics did not provide the best calibration statistics for all upper stem diameter measurements. From a practical point of view, model calibration should be considered an essential criterion in mixed model selection.     

Climate change impacts on stand structure and competitive interactions in a southern Swedish spruce–beech forest

It is believed that European beech (Fagus sylvatica L.) will increase its competitive ability at its northern range margin in Scandinavia due to climate change. In mixed old-growth forests of beech and Norway spruce (Picea abies (L.) Karst.) at Siggaboda nature reserve (southern Sweden), stand structure characteristics were sequentially recorded in the years 2004, 2005 and 2007 as well as growth in stem diameter using tree-coring analyses. Using these measurements, we studied the effects on stand dynamics of an extreme storm event (2005 “Gudrun” hurricane), drought and heat (mid-summer 2006, spring 2007) and subsequent bark beetle attacks on spruce (growing season 2007), overlaid with warming tendencies. The storm, which caused disastrous damage in many stands nearby, had comparatively little impact on the structure of the spruce–beech stand. All together, only 32 trees (19 spruces, 10 beeches, 3 other species) per hectare were thrown or broken mainly in the leeward direction (NE) or impacted by secondary damage by uprooted neighbour trees; this represents 7% of the total tree number and 11% of the growing stock. Diameter and height structure did not change significantly. However, the 2006 drought and the 2007 attack of biotic agents changed the stand structure and composition strongly due to the death of about 19% of the dominating older spruce trees that accounted for 35% of total stand volume. This resulted in a considerable increase in beech’s contribution to stem number (4% increase) and wood volume of the living stand (7% increase). A comparison of diameter growth of beech and spruce during the periods 1894–1949 and 1950–2005 showed a distinct decrease in growth superiority of spruce during the last 50 years. These results support the idea of a northward migration of European beech as a nemoral tree species in Sweden, due to a higher tolerance to the abiotic and biotic threats accompanying climate change and an increased competitive ability compared to boreal tree species Norway spruce.     

Commercial thinning that maintained species diversity of a mixed black spruce–jack pine stand enhanced productivity

Commercial thinning enables forest managers to meet timber production objectives. Thinning reduces tree density to alleviate competition for resources and favour growth of selected tree species. However, in doing so, thinning can homogenize the composition of mixed-species forests and raise biodiversity issues. There is increasing evidence that species richness can lead to higher productivity through a complementarity effect. Hence, thinning that would maintain species diversity of mixed-species forests could enhance stand productivity and help forest managers to reconcile timber production objectives and biodiversity issues. The objective of this study was to compare post-thinning stand production, experimentally over 10 years, in mixed and monospecific stands of black spruce (Picea mariana [Mill.] B.S.P.) and jack pine (Pinus banksiana Lamb.). The post-thinning stand production curve of the mixed stand converged toward that of the unthinned mixed stand while the production curves of the thinned and unthinned monospecific stands remained parallel. The convergent productivity of the mixed stand could be explained by a positive interaction between effects of thinning and niche complementarity. We propose that thinning that maintains species diversity of mixed stands could help forest managers who are implementing ecosystem management to reconcile timber production objectives with biodiversity issues.     

Evict or infect? Managing populations of the large pine weevil, Hylobius abietis, using a bottom–up and top–down approach

Hylobius abietis is the most important pest of replanted coniferous sites in Northern Europe, where feeding by adult weevils can result in up to 100% mortality of seedlings. Field trials were conducted with the aim of reducing H. abietis populations developing in Sitka spruce stumps by increasing pressure from natural enemies (top–down pressure), and reducing the quality of stumps for development (bottom–up pressure). Top–down pressure was applied through inundative treatment of stumps with entomopathogenic nematodes (Heterorhabditis downesi or Steinernema carpocapsae). Bottom–up pressure was applied by treating stumps with the wood colonising fungus Trichodermakoningii. Natural levels of parasitism of H. abietis by the parasitoid Bracon hylobii and the effect of applied agents on B. hylobii were also investigated. Heterorhabditis downesi parasitised more immature weevils than S. carpocapsae, and significantly reduced numbers of adults emerging from stumps compared to controls. Entomopathogenic nematodes did not significantly impact on populations of B. hylobii, and over three sites the effects of both agents were additive. Stumps modified by application of the fungus (bottom–up pressure) did not have fewer H. abietis developing in, or emerging from them; however, development of H. abietis was more advanced in these stumps, and the success of natural enemies was differentially affected. T.koningii facilitated B. hylobii while having the opposite effect on entomopathogenic nematodes, suggesting that it affected the outcome of competition between the nematodes and the parasitoid.     

Different xylogenesis responses to atmospheric water demand contribute to species coexistence in a mixed pine–oak forest

Seasonal patterns of wood formation(xylogenesis) remain understudied in mixed pine-oak forests despite their contribution to tree coexistence through temporal niche complementarity.Xylogenesis was assessed in three pine species(Pinus cembroides,Pinus leiophylla,Pinus engelmannii) and one oak(Quercus grisea) coexisting in a semi-arid Mexican forest.The main xylogenesis phases(production of cambium cells,radial enlargement,cell-wall thickening and maturation) were related to climate data consideri...