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Global variation in total bark thickness (TBT) is traditionally attributed to fire. However, bark is multifunctional, as reflected by its inner living and outer dead regions, meaning that, in addition to fire protection, other factors probably contribute to TBT variation. To address how fire, climate, and plant size contribute to variation in TBT, inner bark thickness (IBT) and outer bark thickness (OBT), I sampled 640 species spanning all major angiosperm clades and 18 sites with contrasting precipitation, temperature, and fire regime. Stem size was by far the main driver of variation in thickness, with environment being less important. IBT was closely correlated with stem diameter, probably for metabolic reasons, and, controlling for size, was thicker in drier and hotter environments, even fire-free ones, probably reflecting its water and photosynthate storage role. OBT was less closely correlated with size, and was thicker in drier, seasonal sites experiencing frequent fires. IBT and OBT covaried loosely and both contributed to overall TBT variation. Thickness variation was higher within than across sites and was evolutionarily labile. Given high within-site diversity and the multiple selective factors acting on TBT, continued study of the different drivers of variation in bark thickness is crucial to understand bark ecology.

Bark thickness is ecologically crucial, affecting functions from fire protection to photosynthesis. Bark thickness scales predictably with stem diameter, but there is little consensus on whether this scaling is a passive consequence of growth or an important adaptive phenomenon requiring explanation. With a comparative study across 913 species, we test the expectation that, if bark thickness–stem diameter scaling is adaptive, it should be possible to find ecological situations in which scaling is predictably altered, in this case between species with different types and deployments of phloem. ‘Dicots’ with successive cambia and monocots, which have phloem-free bark, had predictably thinner inner (mostly living) bark than plants with single cambia. Lianas, which supply large leaf areas with limited stem area, had much thicker inner bark than self-supporting plants. Gymnosperms had thicker outer bark than angiosperms. Inner bark probably scales with plant metabolic demands, for example with leaf area. Outer bark scales with stem diameter less predictably, probably reflecting diverse adaptive factors; for example, it tends to be thicker in fire-prone species and very thin when bark photosynthesis is favored. Predictable bark thickness–stem diameter scaling across plants with different photosynthate translocation demands and modes strongly supports the idea that this relationship is functionally important and adaptively significant.

The utility of trees as bioindicators of atmospheric mercury (Hg) depends upon how accurately tree tissue concentrations reflect air-Hg concentrations at a given location and time. The relationship between air-Hg, and Hg concentration in tree tissues was investigated using potted Pinus nigra (Austrian pine) saplings 6 to 7 years in age moved from a tree farm in Oregon, USA, to three locations with different weather, two with different air total Hg (THg) concentrations, all with different predominant gaseous oxidized Hg chemistry, and one being impacted by the marine boundary layer. An aqueous Hg bromide root spike showed no significant effect on above ground tissue concentration. Over two growing seasons, needles, bark, and tree rings were sampled and analyzed for THg concentrations to compare with those collected when the trees originally arrived in Reno, NV (control) versus that measured in the new locations. Overall, foliar Hg concentrations increased significantly at all new locations relative to the control. Spring sample concentrations were lower than fall for foliage at two locations, indicating resorption of Hg along with nutrients. All trees had higher mean Hg concentrations in the outermost tree rings relative to the control, consistent with increased air total Hg concentrations and changing air chemistry. Higher concentrations were measured in the outer bark of trees where ambient GOM concentrations were highest. Higher inner bark concentrations were correlated with the more humid location where high methylmercury concentrations have been measured in fog. Results demonstrated that Pinus nigra tissues are effective biomonitors for air Hg exposures and that translocation from leaves to rings via the phloem is an important pathway for sequestration in plant tissue. We also show that plants are active assimilators of atmospheric Hg, and as such, local environmental conditions influence ring, bark, and foliage concentrations. The latter has important implications for understanding tissue Hg concentrations, and supports the use of tree ring Hg concentrations as archives.

The utilization of E. pellita bark as waste is still not widely carried out due to a lack of information about the chemical content. Therefore, the current study aimed to analyze the chemical content of the bark of E. pellita using pyrolysis-gas chromatography-mass spectrometry (PyGCMS). The results showed the total extractive content of E. pellita’s inner bark, outer bark, and mix-bark was 12.17%, 16.19%, and 14.85%, respectively. The holocellulose content of E. pellita mix-bark was 65.45%, while the inner bark and outer bark were 60.68% and 59.29%, respectively. The alpha-cellulose content of E. pellita bark was 57.97%, while the inner and outer barks were 56.43% and 54.14%; the lignin content of the clason mix-bark of E. pellita was 25.39%, and for the inner bark and outer bark were 28% and 26.72%, respectively. The results of pyGCMS showed that the extractives of the bark of E. pellita were catechol, 3-methyl-catechol, resorcinol, 3,5-Dimethoxy-4-hydroxytoluene, and (E)-3,3′-Dimethoxy-4,4′-dihydroxystilbene

• A technique for measuring in vitro respiration was investigated to understand why rates were higher than those reported in vivo and to elucidate trends within mature Pseudotsuga menziesii (Douglas-fir) trees. • Extracted increment cores were divided into 3-4 radial depths and a gas chromatograph was used to compare respiration rates radially and vertically within stems. • Respiration of inner bark was 2-3 times greater than sapwood, and 50-70% higher in outer than inner sapwood. Inner bark and outer sapwood released > 40% more CO2 at treetops than at bases. Trends were robust for CO2 production on a core dry-mass, volume, or total carbon basis. By contrast, CO2 production on a nitrogen basis showed almost no significant variation. • This in vitro technique provided an effective index for relative differences in respiration within tree stems. Discrepancies between in vitro and in vivo measurements might be related to the gaseous environment in stems. The estimated within-stem gradients in respiration were possibly determined by enzyme quantity and availability and could be useful in scaling to whole-trees.

The probability of stem survival after fire is strongly influenced by energy allocation to bark because bark thickness affects heat transfer during fire. Greater relative investment in inner bark versus outer bark should also enhance survival because of greater moisture content of inner bark. We measured stem diameter, bark thickness, and habitat preference of five species typical of long-leaf pine savannas, and six species characteristic of adjacent wetlands (pocosins), and calculated relative bark thickness, the inner bark proportion, radial growth, and bark accumulation of each species. We hypothesized that savanna species have thicker bark and greater relative investment in inner bark than pocosin species, because fires occur more frequently in savannas than pocosins. As hypothesized, savanna species have relatively thicker bark than pocosin species. Relative bark thickness and the rate of bark accumulation were correlated with the mean location of a species along the pocosin-to-savanna gradient. However, the inner bark proportion did not differ between savanna and pocosin species. Our results indicate that relative bark thickness is likely the primary bark trait affecting fire-induced topkill and influencing the distribution of species along the pocosin-to-savanna gradient.

The chemical compositions of the dichloromethane extracts of inner and outer barks from six Pinus species ( P. elliotii , P. oocarpa , P. caribeae , P. merkusii , P. montezumae , and P. insularis ) grown in Indonesia were investigated by GC and GC–MS. Generally, the amounts of extractive contents were higher in the inner bark than in the outer bark except for P. merksuii . Fatty acids, monoterpenes, sesquiterpenes, resin acids, triterpenoids, and steroids were detected and quantified. Inner and outer barks differed not only in content of these compounds but also in their composition. Fatty acids and alcohols were the major classes of lipophilic compounds in the outer bark of P. caribeae , P. insularis , and P. montezumae . Steroids and triterpenoids were the dominant compounds identified in the inner bark of P. elliotii , P. insularis , and P. merkusii . Resin acids were the most abundant group in the inner bark of P. oocarpa whereas monoterpenes and sesquiterpenes were recorded in minor quantities in both bark layers of all species.

KEY MESSAGE : The collapse of some cell types and the simultaneous growth or expansion of others hinder the estimation of the contribution of individual tissues to the variation of bark dimension over time. Information on the spatio-temporal pattern of secondary changes occurring in older bark, as well as the activity of phellogen and the development of periderm is still relatively scarce. Anatomical and histometrical investigations were carried out on the bark of mature Quercus petraea growing in Ljubljana, Slovenia. The bark of the oaks was on average 19 mm thick, with the inner bark and the rhytidome accounting for 39 and 61 %, respectively. A high correlation was found between the widths of the rhytidome and of the entire bark, but a fairly weak one between inner bark and entire bark. The youngest phloem increment on average represented around 5 % of the inner bark and around 2.1 % of the entire bark. Growth-ring boundaries were not distinguishable in the collapsed phloem; however, counting the phloem increments was possible due to the presence of phloem fibres at the transition from early to late phloem. We also followed the spatial–temporal secondary changes in collapsed phloem tissue. Phloem increment development in Q. petraea showed that patterns of phloem formation at one location remained practically unchanged in different years. The relationship between processes occurring in different bark tissues is not linear. In addition to the high variability in bark, the collapse of some cell types and the simultaneous growth or expansion of others hinder the estimation of the contribution of individual tissues to the variation of bark dimension over time.

The contents of individual phenolic compounds in the inner bark of silver birch ( Betula pendula Roth) were analyzed by HPLC-DAD. Samples from 21 mature trees originating from three micropropagated parent trees were collected six times over a 1-year period. Significant seasonal variation in the quantities of ten compounds and four chromatographically unresolved compound pairs was found. A majority of the compounds also exhibited significant quantitative variation among birch clones. There were no qualitative differences associated with the season or among the clones. However, wounding of the bark induced the production of new types of bark phenolics: several ellagitannins were detected in the callus tissues of birch for the first time.

CONTEXT: Past human land use has received increasing attention as an important driver of ecosystem change also in seemingly natural landscapes. Quantification of historical land use is therefore critical for assessing the degree of human impact and requires integration of ecology, history and archaeology. OBJECTIVE: This study aims to assess and compare levels of resource use by different actors during 355 years across a large landscape of northern Sweden. METHOD: Data on resource use derived from case studies were extrapolated using demographic data to estimate harvested resources at the landscape scale. Here, we examined the use of the key-specie Scots pine by native Sami peoples and farmers and through commercial logging, and reconstructed historical forest conditions in order to interpret harvest levels and sustainability. RESULTS: We show that (1) the pre-industrial use of Scots pine resources in Pite Lappmark was sustainable from a landscape perspective, and (2) that the early commercial logging, in contrast, was not sustainable. Large and old Scots pine trees were logged at a very high rate, reaching up to 300 % of the annual ingrowth. CONCLUSION: We suggest that historical landscape studies should incorporate analysis at different spatial scales, as such an approach can mirror the overall use of resources. Only then can land use data be applied across larger spatial scales, function as reference values and be compared to those of other regions, time-periods and types of human impact.