Wood Density and Ring Width in Quercus rotundifolia Trees in Southern Portugal

Quercus rotundifolia Lam., known as holm oak or evergreen oak, occurs naturally in the western Mediterranean region, mainly as part of the agroforestry or agrosilvopastoral systems in Portugal (“montado”) and Spain (“dehesa”), and is economically important for acorn production. Less attention has been given to Q. rotundifolia wood, and its density variability is not known, namely related to tree growth. The wood density of 20 Q. rotundifolia trees was measured along the radial direction by X-ray densitometry and the factors responsible for ring width and wood density variation within and between trees were investigated at two sites located within the main species region in southern Portugal. Ring width was significantly different between sites, with an average of 1.81 mm and 1.55 mm. Wood density was very high and averaged between 888 kg/m3 and 914 kg/m3 but not significantly different between sites. Ring width and wood density showed a positive and significant correlation at both sites. Cambial age was the main source of variation for ring width and wood density, while between-tree effects accounted for a considerable proportion of wood density variation. The results are an important contribution for the species valorisation aiming at high-value wood products, also adding knowledge on the species growth of interest for tree selection and sustainable management.

Tracheid dimensions of Norway spruce in uneven-aged stands

Tracheid length and width patterns from pith to bark at a height of 0.6 m in uneven-aged Norway spruce (<i>Picea abies</i> L. (H.) Karst) trees were addressed. The identification of the main factors and a comparison with even-aged stands were also pursued. 96 trees were sampled from experimental stands in Southern Finland. The material encompassed the variation in tracheid properties from early years to silvicultural maturity, i.e. from corewood to outerwood up to a cambial age of 111 years. Data from 39 Norway spruce trees from even-aged stands we utilized for comparison. Models fitted to the data indicated that annual ring widths did not influence mean tracheid dimensions but the latewood proportion showed a significant influence on tracheid dimensions. Tracheids in uneven-aged stands were slightly wider and longer at the base of the stem with a similar tree diameter, cambial age, and annual ring number.

Tree-ring climate response of Jeffrey pine in the Cascade Creek Watershed, Northern California

Understanding the forest response to ongoing climate change is crucial in forest management strategies under anticipated climate adversity. To understand the retrospective growth dynamics of Jeffrey pine (Pinus jeffreyi Grev. &amp; Balf.), tree-ring chronology from the subalpine forest in the Lake Tahoe Basin, California was correlated with air temperature, precipitation, and Palmar Drought Severity Index (PDSI). The years 1757, 1782, 1886, 1859, 1876, 1920, 1929–30, 1977, 1988–89, 2001–02, 2008, and 2014 were some of the years with noticeable low growth. There was robust growth in 1747–49, 1792, 1828, 1866–68, 1913, 1969, 1984, 1998, and 2011. Ring width index (RWI) and basal area increment showed a recent growth increase. Climate-growth response analysis revealed the growth-inhibiting influence of the hot and dry summer. More pronouncedly, warm and wet winter was found to be conducive to tree growth in the following year. A significant growth correlation with the previous year climate (stronger with PDSI) and its absence in current spring may be suggestive of potential growth stimulation by predicted warmer and longer growing season in the future. However, since the RWI chronology consisted mostly of mature trees and because the old cambial age tends to have signal divergence, further studies incorporating younger trees and cohabitant species would provide deeper insights into the growth-climate response.

Modeling specific gravity and diameter inside bark of western hemlock and Sitka spruce growing in southeast Alaska

Western hemlock and Sitka spruce are two commercially important species in Alaska with harvests beginning to focus on naturally regenerated young-growth. We developed within-tree models of ring specific gravity (SG) and diameter inside bark (DIB) for young-growth western hemlock and Sitka spruce. Eight even-aged stands (age < 75 years) in southeast Alaska were felled and disks collected from multiple height levels; 128 trees and 451 disks were collected for western hemlock, and 217 trees and 952 disks were collected for Sitka spruce. Radial strips were prepared and scanned using X-ray densitometry. We fitted non-linear mixed-effects models to the data, with cambial age, height within tree, and dominance class used as explanatory variables. The R2 values (fixed effects only) for the SG models were 0.48 and 0.42 for western hemlock and Sitka spruce, respectively. The corresponding fit indices for the DIB models were 0.86 and 0.85 percent for western hemlock and Sitka spruce, respectively. Tree maps depicting the within tree variation in SG showed more variability in Sitka spruce than in western hemlock. The wood and growth properties of young-growth trees in Alaska will continue to become more important as the U.S. Forest Service transitions away from harvesting old-growth trees.

Radial variation studies on wood properties of Populus deltoides parents and their hybrids

The radial variation and the genetic variation of wood properties between the parents and offspring of Populus deltoides were studied in this work. The chemical composition, density, and anatomical characteristics of Populus deltoides cl. ‘Danhong’ and its offspring exhibited the phenomenon of transgressive segregation. The chemical compositions of the parents and offspring were decreased in several attributes (benzene alcohol extract, hemicelluloses, lignin) with the increase of the cambial age. Moreover, the fibre length, fibre width, ratio of fibre length to width, and wall thickness to lumen ratio of parents and offspring were increased with cambial age. In addition, the densities of parents and offspring were increased with the increase of cambial age. There were significant differences in wood properties among Populus deltoides and its hybrids. These results indicated that Populus deltoides cl. ‘Danhong’ could be considered as pulp material and Populus deltoides cl. ‘Nanyang’ as building material. According to the radial variation rule of each material character, the rotation cutting period can be selected as years 7 or 8.

Characterization and comparison of the wood anatomical traits of plantation grown Quercus acutissima and Quercus variabilis

Oaks are important tree species, providing essential biomaterial for the wood industry. We characterize and compare wood anatomical traits of plantation grown Quercus acutissima Carruth. and Q. variabilis Blume to provide more detailed information to understand xylem radial growth, structure, and function, as well as differences between sapwood and heartwood, to provide data relevant for tree breeding and value-added wood utilization of oak plantations in China. In this study, radial strips were collected at breast height from the main trunk of the two species. Latewood percentage and growth ring width were investigated by X-ray densitometry and a Tree Ring Analysis System, respectively. Vessel and fibre lumen diameter, vessel and fibre wall thickness, vessel density, fibre wall thickness/diameter ratio, tissue proportions, and pit membrane thickness in between vasicentric tracheids were observed with light microscopy and electron microscopy and quantified. There were significant differences in a few wood anatomical traits between the two species: vessel wall thickness and vessel lumen diameter were higher in Q. acutissima than in Q. variabilis, while higher axial parenchyma proportion in sapwood was found in Q. variabilis than in Q. acutissima. More abundant tyloses were found in heartwood than in sapwood of both species. Our work showed the intraspecific and interspecific variation of the two species. Most differences between sapwood and heartwood must be attributed to differences in cambial age during their formation.

Cambial-age related correlations of stable isotopes and tree-ring widths in wood samples of tree-line conifers

A recent analysis of stable isotopes of the Alpine Holocene Tree-Ring Dataset, consisting of samples from 192 larch and cembran pine trees, revealed that δD and δ18O exhibit no trends in adult trees, but evidence trends in the juvenile period of the first 100 years of cambial age. In this work we applied the Spearman statistical analysis on different cambial age classes to verify if these changes were correlated with tree-ring width values, that are known to show age trends. The results prove a significant correlation between tree-ring-width (TRW) and both hydrogen and oxygen stable isotopes before 100 year of cambial age, but not afterwards, in both larch and cembran pine. A trend in the correlation values was also found between the two water isotopes, while no trend was found in correlations involving δ13C. We hypothesized the δD and δ18O values reflect the higher xylogenesis activity of the juvenile period, that is associated with reduced atom exchanges of photosynthates with xylem water. The result indicates that the climate response of δD and δ18O may differ in the juvenile and mature period of tree life at treeline.

Alpine Holocene tree-ring dataset: age-related trends in the stable isotopes of cellulose show species-specific patterns

Stable isotopes in tree-ring cellulose are important tools for climatic reconstructions even though their interpretation could be challenging due to nonclimate signals, primarily those related to tree aging. Previous studies on the presence of tree-age-related trends during juvenile as well as adult growth phases in δD, δ18O, and δ13C time series yielded variable results that are not coherent among different plant species. We analyzed possible trends in the extracted cellulose of tree rings of 85 larch trees and 119 cembran pine trees, i.e., in samples of one deciduous and one evergreen conifer species collected at the tree line in the Alps, covering nearly the whole Holocene. The age trend analyses of all tree-ring variables were conducted on the basis of mean curves established by averaging the cambial-age-aligned tree series. For cambial ages over 100 years, our results prove the absence of any age-related effect in the δD, δ18O, and δ13C time series for both the evergreen and the deciduous conifer species, with the only exception being larch δD. However, for lower cambial ages, we found trends that differ for each isotope and species; i.e., mean δ13C values in larch do not vary with aging and can be used without detrending, whereas those in cembran pine show a juvenile effect, and the data should be detrended. Mean δ18O values present two distinct aging phases for both species, complicating detrending. Similarly, mean δD values in larch change in the first 50 years, whereas cembran pine changes between 50 and 100 years. Values for these two periods of cambial age for δD and δ18O should be used with caution for climatic reconstructions, ideally complemented by additional information regarding mechanisms for these trends.

Sperry’s packing rule affects the spatial proximity but not clustering of xylem conduits: the case of Fagus sylvatica L.

Sperry’s packing rule predicts the optimum packing of xylem conduits in woody plants, where the frequency of xylem conduits varies approximately inversely with the square of the conduit radius. However, it is well established that such anatomical disposition does not remain fixed but is subject to a suite of adaptations induced by physiological constraints driven by both ontogenetic development and environmental characteristics. Here we challenge the hypothesis that increasing frequency of xylem conduits, concomitant with the decrease in their lumen area along the xylem pathway, would affect the spatial distribution of vessels inside tree-rings and their aggregation. To this end, we measured the vessels’ anatomical characteristics inside each tree-ring along with a complete radial series taken at different stem heights of Fagus sylvatica L. trees. Point pattern analysis indicated a significant effect of the distance from the tree base and a weak effect of cambial age on the nearest neighbour distance among xylem vessels, suggesting that vessels were closer to each other near the apex, and became progressively more distant toward the base. The spatial pattern of xylem vessels violated the assumption of complete spatial randomness, vessel spatial arrangement followed a uniform distribution at different distances from the tree base. Although there was an increase in the intensity and proximity among vessels, we demonstrated that no patterns of aggregation between vessels were found in sampled F. sylvatica trees. Rather, point pattern profiles clearly highlighted a lack of aggregation of vessels in the face of a regular spatial distribution in the annual growth rings along the stems.