Does Photosynthetic Bark have a Role in the Production of Core vs. Outer Wood?

This paper hypothesizes a correlation in some species between the cambial age of transition from core (juvenile) to outer (mature) wood and the cambial age of transition from photosynthetic to non-photosynthetic bark. Secondly, this paper hypothesizes that the relationship is causal: a signal produced in relation to the photosynthetic bark affects wood development a few millimeters away. It is further hypothesized that the photosynthetic periderm is replaced by a non-photosynthetic one at light levels below its light compensation point. In T'suga heterophylla and Pseudotsuga menziesii var. menziesii, the cambial age at which the first periderm dies (the base of photosynthetic bark) ranges from 16 to 33 and 12 to 43 years, respectively, for four Oregon Coast Range populations. These values are in the same range as the cambial ages of transition from core to outer wood, as shown by literature values and data reported here on tracheid length in T. heterophylla. In both species, the cambial age at the base of the live crown is not coincident with, nor consistently higher or lower than, the height of the lowest photosynthetic bark. Data presented here are consistent with the photosynthetic bark hypothesis of formation of core wood, but manipulative studies are needed to further explore the relationship

Effect of Extraction on Wood Density of Western Hemlock (Tsuga Heterophylla (RAF.) SARG.)

Extractives can account for between 1 to 20% of the oven-dry weight of wood of various tree species and can influence wood density values appreciably. Removing these chemical deposits (extraction) in wood samples can help establish a consistent baseline for comparing wood densities where extractives are expected to differ between sample parameters. Although western hemlock is a very important timber species in the Pacific Northwest, laboratories that determine wood density may or may not remove extractives prior to density assessment. Wood density values were compared before and after extraction for 19 young-growth western hemlock samples. Extraction was performed using 95% ethyl alcohol-toluene solutions. Ring density values averaged 0.045 g/cm3 lower for extracted samples compared to unextracted samples across rings. Slightly higher amounts of extractives were found at rings near the pith; however, a general consistency in extractive content existed among samples and along the radial profile

Patterns of xylem variation within a tree and their hydraulic and mechanical consequences

Xylem is nonuniform in its structure and function throughout the plant stem. Xylem structure varies from pith to bark, from root to apical meristem, from stem to branch, at nodes vs internodes, and at junctions of branches, stems or roots compared to the internodal regions nearby. At smaller scales, anatomy varies systematically within one growth ring and it varies among the layers of the cell wall. Xylem properties vary by the plane in which they are examined, owing to cell shape, cell orientation, and the orientation of microfibrils in the cell walls. As concluded by Larson (1967, p. 145), "more variability in wood characteristics exists within a single tree than among [average values for] trees growing on the same site or between [average values for] trees growing on different sites." This structural heterogeneity results in spatial variation in hydraulic and mechanical performance of the xylem. Whereas wood technologists have long acknowledged the importance of wood variability (e.g., Northcott, 1957; Dadswell, 1958; Larson, 1962; Cown and McConchie, 1980; Beery et al., 1983; Megraw, 1986; Schniewind and Berndt, 1991), this heterogeneity often has been overlooked by botanists, who have tended to view stems a homogeneous organs ("biomass") with only a passive role in the biology of the plant. This chapter details the patterns of variation in xylem structure found within a wood plant, and emphasizes what is knpwn and what is not known about the functional consequences of this variation for shoot water movement and mechanics

Wood Density and Hydraulic Properties of Ponderosa Pine From the Willamette Valley VS. the Cascade Mountains

The Willamette Valley (WV) race of ponderosa pine (Pinus ponderosa) is being widely planted for timber in the Willamette Valley, western Oregon, because it grows in habitats that are either too wet or too dry for Douglas-fir (Pseudotsuga menziesii). Compared to the eastern Cascade Mountains (CM), the WV has 3 to 5 times the annual precipitation and warmer temperatures year around. This study characterized the wood quality of the WV race (4 sites) and the CM (4 sites), and also compared the behavior of their wood for water transport for the living trees (1 site in the WV and 1 site in the CM). The average tree ages at the sites ranged from 30 to 83 years at breast height. Between rings 27 and 31, compared to the CM, the WV had denser wood (0.48 vs. 0.40 g/cm3), denser earlywood (0.41 vs. 0.36 g/cm3), and denser latewood (0.62 vs. 0.50 g/cm3), with no significant differences in mean latewood proportion (about 0.35) or mean growth ring width (about 2.5 mm). The pith-to-bark trend in density differed between regions. In the WV, total wood density, earlywood density, and latewood density increased with growth ring from the pith. In the CM, total wood density and latewood density decreased slightly with growth ring width, and earlywood density remained unchanged. An additional sample of younger trees (23 years at breast height) from a genetic trial in the WV in which the seed source was the CM, had low density wood in the first few rings (like the CM trees) but had a steady increase in wood density with growth ring number (like the WV trees). Specific conductivity (ks) of trunk wood was lower in the WV, consistent with its higher wood density and suggestive that the WV race is more drought-adapted than the CM populations. There was no decline in ks from outer to inner sapwood in the WV trees, but a large decline in the CM trees. In water transport experiments, at an applied air pressure of 3.0 MPa, the WV and CM trees had lost 19% and 32% of their ks, respectively, again suggesting that the WV trees are slightly more drought-adapted than are the CM trees. At the other applied air pressures tested (0.5, 2.0. 4.0, and 5.0 MPa), there were no significant differences in loss of conductivity between the two sites. Trunk wood from breast height had a 50% loss of ks at 3.3-3.6 MPa. The loss of relative water content (100% - RWC) was about the same in both sites, except at 4.0 MPa, in which the CM trees had a larger loss of RWC than the WV trees. More work is needed on physiology to better understand the wood density/water transport relations. Ponderosa pine may be more interesting to study than other species because the earlywood, which transports most of the water, shows substantial density differences between geographic regions

Tropolone Content of Increment Cores as an Indicator of Decay Resistance in Western Redcedar

The high decay resistance of western redeedar (Thuja plicata Donn) is due to the presence of toxic extractives, called tropolones, in the heartwood. Therefore, tropolone content may be used as an indicator of decay resistance. With increment core-sized samples of western redcedar heartwood, we used gas chromatography to measure tropolone content and soil block tests to assess decay resistance. Results showed that decay resistance was extremely variable at low tropolone levels, but was uniformly high at tropolone levels of 0.25% or greater. Analyzing tropolone content of western redeedar increment cores is a useful way to assess decay resistance of standing trees

Heartwood Formation and Natural Durability—A Review

This paper reviews recent literature on the formation of heartwood and on the components that affect natural durability. It includes discussion about the function of heartwood in living trees, factors influencing the natural durability of heartwood, the process of heartwood formation, and variations in heartwood quantity and quality. Heartwood formation is a regular occurrence in tree stems, and heartwood may have many different properties from sapwood, including natural decay resistance. A greater understanding of the heartwood formation process could allow control of heartwood production. Recent research involving enzymatic analyses have provided valuable insight into the biochemical processes involved in heartwood formation. Further study of the role natural durability plays in living trees would help to bring together many of the disparate strands of research relating to heartwood

Compression wood has little impact on the water relations of Douglas-fir (Pseudotsuga menziesii) seedlings despite a large effect on shoot hydraulic properties

• Compression wood has been shown to reduce stem permeability, but it is not known to what extent it affects leaf‐level processes. Here, we report whole‐plant hydraulic properties of Douglas‐fir (Pseudotsuga menziesii) seedlings induced to form varying amounts of compression wood. • Seedlings were grown under three bending treatments to assess the impact of compression wood on hydraulic properties, including stomatal conductance (gs), above‐ground shoot conductance (Kl(abg)), and both specific and leaf area‐specific conductivity (ks and kl, respectively). • Kl(abg) was significantly lower (50% reduction) in severely bent seedlings than in controls. Similarly, both ks and kl of the main axis were significantly reduced (by 52% and 46%, respectively) in severely bent seedlings relative to controls. Seedlings in the moderate bending treatments had ks and kl that were intermediate between controls and severe bending. • Despite clear differences in above‐ground shoot hydraulic properties, severely bent seedlings maintained the same water potentials as controls and had similar diurnal patterns of gs. This suggests that when the entire soil–plant–atmosphere continuum is considered, even a severe reduction in stem ks caused by compression wood has little impact on leaf‐level processes.Keywords: biomechanic, stomatal conductance, reaction wood, tradeoff, hydraulic architecture, hydraulic conductivityKeywords: biomechanic, stomatal conductance, reaction wood, tradeoff, hydraulic architecture, hydraulic conductivit

Do gymnosperm needles pull water through the xylem produced in the same year as the needle?

This research investigated the longevity of functional connections between leaf traces and stem xylem in 16 species of conifers to better understand the spatial use of sapwood for water transport. The first question was which ring(s) stained when a vacuum was applied to the distal end of the cut surface of a needle attached to a short stem segment. The vacuum was applied to either 1‐ or 2‐yr‐old foliage taken from 4–6‐yr‐old saplings. The 16 species were then categorized based on the growth ring that most consistently stained when the vacuum was applied to the 2‐yr‐old needles. There were three distinct stain patterns for the evergreen conifers and one pattern for the deciduous conifers. Three evergreen species could not be categorized. The second question used needle fall data to ask whether the leaf trace appeared to break because of age or stem diameter in 5‐yr‐old Pseudotsuga menziesii saplings. An apparent threshold stem diameter at which needles tended to be shed was more related to diameter than age. These xylem connection patterns could affect leaf cohort physiology and the spatial pattern of water flux in sapwood.Keywords: needle trace, leaf age, leaf trace, foliage retention, xylem anatomy, radial water transport, dye ascentKeywords: needle trace, leaf age, leaf trace, foliage retention, xylem anatomy, radial water transport, dye ascen

Genetic variation in basic density and modulus of elasticity of coastal Douglas-fir

Douglas-fir trees from 39 open-pollinated families at four test locations were assessed to estimate heritability of modulus of elasticity (MOE) and basic density. After trees were felled, sound velocity was measured on 4-m logs with the Director HM200. Disks were taken to estimate dry and green wood density; dynamic MOE was estimated as green density × (sound velocity)2. Heritability estimates of MOE (across-site h 2=0.55) were larger than those for total height (0.15) and diameter at breast height (DBH; 0.29), and similar to those for density (0.59). Negative genetic correlations were found for MOE with height (r A=−0.30) and DBH (r A=−0.51), and were similar to those found for density with height (r A=−0.52) and DBH (r A=−0.57). The partial correlations of height with MOE and density, while holding DBH constant, were positive, implying that the observed negative correlations between height and the wood properties were a function of the high positive correlation between height and DBH and the strong negative correlations between DBH and the wood properties. Taper [DBH/(height−1.4)] was found to be negatively associated with MOE. Selection for MOE may produce greater gains than selection for density because MOE had a larger coefficient of additive variation (9.6%) than density (5.1%). Conversely, selection for growth may have a more negative impact on MOE than density because of the greater genetic variation associated with MOE. Family mean correlations of the wood quality traits with stem form and crown health were mostly nonsignificant

Storage versus substrate limitation to bole respiratory potential in two coniferous tree species of contrasting sapwood width

Abstract Two coniferous tree species of contrasting sapwood width (Pinus ponderosa L., ponderosa pine and Pseudotsuga menziesii Mirb., Douglas-fir) were compared to determine whether bole respiratory potential was correlated with available storage space in ray parenchyma cells and/or respiratory substrate concentration of tissues (total nitrogen content, N; and total non-structural carbohydrate content, TNC). An increment corebased, laboratory method under controlled temperature was used to measure tissue-level respiration (termed respiratory potential) from multiple positions in mature boles (>100-years-old). The most significant tissue-level differences that occurred were that N and TNC were two to six times higher for inner bark than sapwood, TNC was about two times higher in ponderosa pine than Douglas-fir and there was significant seasonal variation in TNC. Ray cell abundance was not correlated with sapwood respiratory potential, whereas N and TNC often were, implying that respiratory potential tended to be more limited by substrate than storage space. When scaled from cores to whole boles (excluding branches), potential net CO 2 efflux correlated positively with live bole volume (inner bark plus sapwood), live bole ray volume, N mass, and TNC mass (adjusted R 2 > >0.4). This relationship did not differ between species for N mass, but did for live bole volume, live bole ray volume, and TNC mass. Therefore, N mass appeared to be a good predictor of bole respiratory potential. The differences in net CO 2 efflux between the species were largely explained by the species' relative amounts of whole-bole storage space or substrate mass. For example, ponderosa pine's inner bark was thinner than Douglas-fir's, which had the greater concentration of ray cells and TNC compared with the sapwood. This resulted in ponderosa pine boles having 30-60% less ray volume and 10-30% less TNC mass, and caused ponderosa pine net CO 2 efflux/ray volume and net CO 2 efflux/ TNC mass to be 20-50% higher than Douglas-fir. In addition, because inner bark respiratory potential was 2-25 times higher than that of sapwood, ponderosa pine's thinner inner bark and deeper sapwood (relative to Douglas-fir) caused its bole net CO 2 efflux/live bole volume to be 20-25% lower than that of similarlysized Douglas-fir trees