Determining the mechanical properties of hazel forks by testing their component parts

The ability to accurately predict the load-bearing capacity of tree forks would improve tree surveying and tree surgery techniques and assist with the biomechanical modelling of a tree’s structure. In this study, the bending strength of forks of hazel (Corylus avellana L.) was investigated by assessing the mechanical contributions from three component parts of each fork. Intact forks and ones in which either central or peripheral xylem lying under the branch bark ridge at the apex of the forks had been removed were subjected to tensile tests. The bending strength of these forks was compared with that of the arising branches by carrying out a three-point bending test on the smaller arising branches of the intact specimens. All forks failed in tension, splitting between the arising branches. By removing the centrally placed xylem, constituting approximately a fifth of the width of the fracture surface, the forks’ bending strength was reduced by around 32 %, while removing the outer four-fifths reduced the forks’ bending strength by 49 %. Intact forks had around 74 % of the maximum bending strength of the smaller arising branch. It is concluded that the tensile strength of the centrally placed xylem at the apex of a tree fork is a critical strengthening component. This helps to explain the weakness of forks with included bark, which lack this component. This study concludes that tree forks should not by default be considered flaws in a tree’s structure.     

Redistribution of water via layering branches between connected parent and daughter trees in Norway spruce clonal groups

Key message

We measured sap flow and shoot water potentials in clonally connected parent and daughter trees. We found bidirectional flow patterns in branches mediating the connection between parent and daughter trees.

Abstract

Layering is an important mode of vegetative reproduction at treeline, in which clonal daughter trees are formed by the rooting of lower (“layering”) branches of the parent tree. These branches mediate the connection between parent (PT) and daughter tree (DT). Here, we measured quantity and direction of sap flow in layering branches as well as PT and DT, and measured shoot water potentials in the crowns of a connected PT and DT. We found bidirectional sap flow pattern in layering branches, with the bidirectionality of the flow resulting from water potential dynamics of the parent and daughter trees varying diurnally. We found that 4.3 % of the total water transpired by the DT was supplied by the PT root system, with up to 25 % of the instantaneous daughter tree sap flow coming from the parent tree. In contrast, water provided by the daughter’s root system to the parent tree comprised only a negligible amount, less than 1 % of the parent’s entire sap flow. Additionally, after experimental excavation of part of the DT roots, layering branch flow towards the DT increased, while flows in the opposite direction almost vanished. This study showed that aboveground clonal connections can facilitate a new type of hydraulic redistribution where water is transported bidirectionally through branches. This transfer of water and nutrients is vital especially in the first years of the daughter tree but supplies considerable amounts of water even several years after the establishment of a new clonal tree.

     

Tree-ring wood anatomy and stable isotopes show structural and functional adjustments in olive trees under different water availability

Background and Aims

Olive tree (Olea europaea L.) is a drought-tolerant tree species cultivated in Mediterranean-type environments. Although it is tolerant to drought, dry conditions decrease its productivity. A thorough analysis of the hydraulic architecture and wood anatomical plasticity, as well as of their physiological significance, is needed to understand how olive trees will adapt to the predicted increase in frequency and severity of drought in the Mediterranean region.

Methods

Dendrochronological, stable isotopic (δ¹³C, δ¹⁸O) and wood anatomical analyses were applied to understand how different water availability can affect wood stem structure and function, in rainfed and irrigated at 100 % of crop evapotranspiration (ETc) olive trees in an experimental orchard close to Benevento (Italy) from 1992 to 2009.

Results

Dendrochronological data indicate that cross-dating and synchronization of ring-width time series in olive tree is possible. After the start of irrigation, significantly more negative δ¹³C and lower δ¹⁸O values were recorded in irrigated trees indicating higher stomatal conductance and transpiration rates. Increased water balance induced the formation of a higher number of vessels with higher diameter.

Conclusions

Water balance variations affected wood anatomy and isotopic composition. Anatomical analyses detected structural and functional adjustments in rainfed trees that produced more vessels with lower diameter to prevent cavitation. Isotopic analyses confirmed that irrigated trees continuously showed enhanced transpiration rates.     

Effects of soil chemistry on tropical forest biomass and productivity at different elevations in the equatorial Andes

The dependence of aboveground biomass and productivity of tropical forests on soil fertility is not fully understood, since previous studies yielded contrasting results. Here, we quantify aboveground biomass (AGB) and stem wood production, and examine the impact of soil chemistry on these parameters in mature tropical forest stands of the equatorial Andes in Ecuador. In 80 plots of 0.04 ha at four elevation levels (500, 1,000, 1,500 and 2,000 m a.s.l., total sample area = 3.2 ha), we measured ten important soil chemical parameters, inventoried all trees ≥10 cm dbh and monitored stem diameter growth with dendrometer tapes in 32 plots. Top canopy height and stem density significantly decreased from 500 to 2,000 m, while tree basal area increased and AGB remained invariant (344 ± 17 Mg DM ha^?1, mean ± SE) with elevation. Wood specific gravity (WSG) showed a significant, but small, decrease. Stem wood production decreased from 4.5 to 3.2 Mg DM ha^?1 year^?1 along the transect, indicating a higher biomass turnover at lower elevations. The only soil variable that covaried with AGB was exchangeable K in the topsoil. WSG increased with decreases in N mineralisation rate, soil pH and extractable Ca and P concentrations. Structural equation modelling (SEM) revealed that nitrogen availability acts on stem wood production only indirectly through a negative relation between N mineralisation rate and WSG, and a positive effect of a lowered WSG on stem growth. The SEM analysis showed neither direct nor indirect effects of resin-extractable P on wood production, but a negative P influence on AGB. We conclude that nitrogen availability significantly influences productivity in these Andean forests, but both N and P are affecting wood production mainly indirectly through alterations in WSG and stem density; the growth-promoting effect of N is apparently larger than that of P.     

Wood grain patterns at branch junctions: modeling and implications

We apply a recent model of wood grain pattern formation to the junction between two tree branches. In model simulations, the export of indole-3-acetic acid (IAA) from a branch into the junction is necessary to maintain the continuity between the grain pattern of the branch and the grain of the subjacent stem. Increased IAA export corresponds to a larger effect on the overall grain pattern. Conversely, if IAA export stops, the grain pattern diverts around the branch. These results do not depend on specific values for the model parameters and appear to be quite general. Since long-range water transport is largely parallel to the wood grain, greater IAA export from a branch is expected to give improved access to the water resources of the tree. IAA export thus emerges as a likely regulator of branch vigor. In this way, the basipetal flux of IAA through a branch, and its morphological consequences at branch junctions, may play an important role in several aspects of tree form.     

Function of spiral grain in trees

Summary Through spiral grain, conduits for sap lead from each root to all branches. This uniform distribution of sap is indicated by the paths of vessels and tracheids, and has been proven experimentally by means of dyed sap injected into the base of stems or taken up by roots. Trees receiving water only from roots at one side of the root collar nevertheless stay green and continue growing. Spiral grain in bark distributes food from each branch to other flanks of the stem and to most roots. Experimental interruptions of the sap and food conduits caused the cambial zone to reorient new conduit cells in new directions, bypassing the interruption. In particular, spiral grooves cut into the stem surface caused spiral grain. The new cells reorient through division and growth. Although spiral grain is largely under genetic control, trees appear to have a spiral grain especially where needed for distribution of water when root spheres are dry at one side. Compared with straight-grained trees, spiral-grained stems and branches bend and twist more when exposed to strong wind, in this way offering less wind resistance and being less likely to break. Through the bending and twisting, snow slides down from branches rather than breaking them, but the main function of spiral grain is the uniform distribution of supplies from each root to all branches, and from each branch to many roots.     

Structural relationships between form factor,wood density,and biomass in African savanna woodlands

Key message

Variation in tree biomass among African savanna species of equal size is driven by a wide inter-specific variation in wood specific gravity.

Abstract

Tree form and taper is a fundamental component of tree structure and has been used for over a century in forestry to estimate timber yields and in ecological theories of scaling laws. Here, we investigate variation in form factor in the context of biomass in African savannas. Biomass is a fundamental metric of vegetation state, yet in African savannas it remains unclear whether variation in form factor F (taper) or wood specific gravity (G) is a more dominant driver of biomass differences between tree species of equal stem diameter and height. Improving our knowledge of vertical mass distribution in savanna trees provides insight into differences in life strategies, such as tradeoffs between production, disturbance avoidance, and water storage. Here, we destructively harvested 782 stems in a savanna woodland near Kruger National Park, South Africa, and measured whole tree wet mass, wood specific gravity, water content, and form factor. We found that three of four dominant species can vary in mass by over twofold, yet inter-specific variation in taper was low and taper did not vary significantly between common species (P > 0.05) (species-mean form factors ranged from F = 0.57 to 0.77, where cone F =  $0.\bar{3}$ , quadratic paraboloid F = 0.5, cylinder F = 1.0). Comparison of a general biomass allometry model to species-specific models supported the conclusion that the large difference in biomass between species of the same size was explained almost entirely (R ² = 0.97) by including species-mean G with D and H in a general allometric equation, where F was constant. Our results suggest that inter-specific variation in wood density, not form factor, is the primary driver of biomass differences between species of the same size. We also determined that a simple analytical volume-filling model accurately relates wood specific gravity of these species to their water and gas content (R ² = 0.68). These results indicate which species use a wide spectrum of water storage strategies in savanna woodlands, adhering to a trade-off between the benefits of denser wood or increased water storage.     

Laurel forests in Tenerife, Canary Islands

The efficiency of the conductive system in about 40-year-old Laurus azorica trees growing in a laurel forest was evaluated by comparing main stems and leaves (petioles) on the basis of theoretical sap flow values (1) calculated from vessel anatomy (taking vessels as ideal capillaries), (2) derived from measured dye velocity and (3) data taken from direct sap flow measurements. It was found that actual sap flow rate per wood area increases in stems from the pith towards the cambium. The outermost part of the stem is the most important part of the tree for conducting water. Maximum actually measured transpiration (sap flow rate) for the stand was practically identical to the theoretical rate calculated based on petiole anatomy, but it was about 45 times lower than that calculated based on stem anatomy. This illustrates the safety features of stem wood, which due to its high vessel density, is capable of transporting all the water required even when only a small area of its vessels is working. In the petioles, xylem is more efficiently used, but almost all vessels must work in order to supply water to leaves and any disturbance may cause leaf loss.     

The accuracy of the thermal dissipation technique for estimating sap flow is affected by the radial distribution of conduit diameter and density

There are conflicting reports on the accuracy of the thermal dissipation probe (TDP, the Granier method) measurement using the original formula, which is widely used to estimate the transpiration of individual trees and forest stands. In this article, six woody species of three wood types were used to study a possible association between TDP measurement accuracy and wood anatomical characteristics, including the vessel diameter and density, as well as sapwood depth. We found that TDP technique with Granier’s original equation underestimated the sap flux density in six species to various degrees, dependent on conduit size and sap flux. Our calibration using two conifers with small diameters and a high density of tracheids was relatively consistent with Granier’s calibration; however, because there were larger diameters and lower densities of vessels in the two diffuse-porous species, the original calibration significantly underestimated sap flow. Two ring-porous species had the largest diameters and lowest densities of vessels. In particular, Robinia pseudoacacia possessed the shallowest sap wood depth, less than a probe length. Our calibration for the ring-porous species, especially R. pseudoacacia, deviated far from the original calibration, which mostly underestimated the sap flow. The degree of underestimation was well associated with sap wood depth and the radial diameter and density distribution of conduits. Our results demonstrated that a new calibration must be operated for each species together with the sapwood depth determination and more probes may be applied for one stem in the field to obtain the more accurate sap flux. In addition, we investigated the effects of different environmental temperature and perfusing fluid composition on the TDP-based sap flux measurement. We found that an environmental temperature reduction from 25 to 0 °C did not alter the values of the maximum temperature difference (ΔT_m) between a heated probe and a reference probe when there was no sap flow, verifying that ΔT_m measured at night can be used as a reference in daytime.     

Wood mechanics, allometry, and life-history variation in a tropical rain forest tree community

Wood density plays a central role in the life-history variation of trees, and has important consequences for mechanical properties of wood, stem and branches, and tree architecture. Wood density, modulus of rupture, modulus of elasticity, and safety factors for buckling and bending were determined for saplings of 30 Bolivian rain forest tree species, and related to two important life-history axes: juvenile light demand and maximum adult stature. Wood density was strongly positively related to wood strength and stiffness. Species safety factor for buckling was positively related to wood density and stiffness, but tree architecture (height : diameter ratio) was the strongest determinant of mechanical safety. Shade-tolerant species had dense and tough wood to enhance survival in the understorey, whereas pioneer species had low-density wood and low safety margins to enhance growth in gaps. Pioneer and shade-tolerant species showed opposite relationships between species traits and adult stature. Light demand and adult stature affect wood properties, tree architecture and plant performance in different ways, contributing to the coexistence of rain forest species.     

Disbudding treatments on pistachio trees cv. mateur: dry matter accumulation and distribution within fruiting and non-fruiting branches under dry climate

Key message

After applying disbudding treatments, removal of fifty percent of flower bud each year improves dry matter accumulation in fruiting and non-fruiting branches of pistachio trees, which could minimize alternate bearing.

Abstract

Dry matter accumulation and distribution within branches of pistachio trees were investigated during 2005-2008 to determine the effects of fruiting on shoot growth under rain-fed conditions in arid climate. Four treatments were applied: T ₀ normal alternation cycle, T ₁ trees disbudded for 1 year, T ₂ trees disbudded for two successive years, and T ₃ removal of 50 % of all floral buds for each year. Consecutive disbudded treatment (T ₂) allowed a higher growth potential of pistachio trees with reference to normal biennial cycle (T ₀). Individual current shoot of T ₂ accumulated 44 % as much dry matter cm^?1 as those of ‘On’ trees, which have the highest yield. Removal of 50 % of floral buds (T ₃) significantly increased the dry matter accumulation in fruiting branch to reach 57 g in postharvest compared to 42.6 g for the control T ₀. Trees disbudded for 2 years (T ₂) had increased dry matter accumulation in the non-fruiting branch from 3.3 to 16.3 g. Leaves, current shoot, 1-year-old wood and inflorescence buds represented, respectively, 87, 5.3, 5 and 2.7 % of the total dry matter of individual branch of T ₂. In fruiting branches, nuts consisted of 83–87 %, leaves 7–10 %, rachises 4 %, 1-year-old wood 1.6–2 % and current shoot 0.8–1.3 % of the total dry matter. One-year-old wood played a major role as sources and sinks for developing current year shoot, leaves, inflorescence buds and nuts. Removal of 50 % of flower bud (T ₃) improves the dry matter accumulation in fruiting and non-fruiting branches. Thus, under rain-fed conditions, annual pruning could be used to minimize alternate bearing of pistachio.     

华南地区常见树种导管特征与树干液流的关系

为探讨树木结构与功能的关系,对华南地区常见8种树木边材的导管特征进行观察,并利用Granier热扩散探针法测量干、湿季树干的液流密度,分析导管特征与树干液流的关系。结果表明,除红锥(Castanopsis hystrix)有两种导管外,大叶相思(Acacia auriculaeformis)、荷木(Schima superba)、火力楠(Michelia macclurei)、藜蒴(C.fissa)、马占相思(A.mangium)、柠檬桉(Eucalyptus citriodora)、尾巨桉(E.urophylla×E.grandis)的导管类型单一。导管特征在种间存在明显差异,且导管长度、密度和孔径之间存在明显相关性,它们与标准化的边材面积呈现显著相关。湿季液流最大值与导管特征无明显相关性,但整树最大蒸腾速率与导管特征呈显著相关;树木的日蒸腾量与导管特征也有明显相关性。因此,树木的液流速率并不受树干的导管影响;而树干的导管孔径与边材面积间的负相关权衡机制,可以降低树种间由于导管孔径差异引起的树干的水分输送速率的差异性。     

Comparison of sap flow, cavitation and water status of Quercus petraea and Quercus cerris trees with special reference to computer tomography

Concurrent measurements of sap velocity (heat pulse) and ultrasound acoustic emission were performed on the trunks of mature Turkey oak (Quercus cerris) and sessile oak (Quercus petraea) trees. Plant water status was assessed by measuring leaf water potential, leaf conductance and transpiration. Wood density was estimated non-destructively on the trunk section of the plants by mobile computer tomography, which measures the attenuation of a collimated beam of radiation traversing the trunk in several directions, as the device rotates around the tree. Absorption is proportional to the density of the wood. As wood density is strictly correlated to water content, this non-invasive method allows the water content in the trunk section to be evaluated as well as mapped. Leaf water potential declined each morning until a minimum was reached at midday and recovered in the afternoon, lagging behind changes in transpiration rate. Good correspondence was found between the patterns of sap velocity and cavitation rate. A close correlation was demonstrated between wood density, water content and sap velocity. Sap now was always higher in Turkey oak than in sessile oak. Trunk signatures by computer tomography appeared to differentiate the two oak species, with the Turkey oak stem clearly more hydrated than the sessile oak; water storage reservoirs could play an important role in tree survival during extended periods of low soil water availability and in the relative distribution of tree species, especially in the context of global climate change. Late-wood conducting elements of oak species seem to play a significant role in water transport. The mobile computer tomograph was confirmed as a peerless tool for investigating stem water relations. Diurnal variations in the measured parameters under natural drought conditions and the differences between the two oak species are discussed.     

Spatial variations in non-structural carbohydrates in stems of twelve temperate tree species

The radial, axial and inter-specific variations in concentrations and contents of non-structural carbohydrates (NSC) in stems were investigated for 12 Chinese temperate tree species. These species had contrasting leaf phenology (evergreen and deciduous) and wood types (non-, ring- and diffuse-porous wood). For each species, we sampled bark (periderm and phloem), outer wood (light-colored) and inner wood (dark-colored) at four heights along the stem (stump, breast height, crown base and mid-crown). Concentrations of total NSC (TNC, sum of sugars and starch), sugars and starch were much higher in bark than those in wood. On average, contents of sugars and starch accounted for 48 and 52 % of the TNC, respectively, and contents of TNC in bark, outer wood, and inner wood accounted for 34, 38, and 28 % of the stem total, respectively. Bark was the major pool of sugars in the stem (accounting for 50 % of the stem total on average), while outer wood was the major pool of starch (41 %). The concentration of sugars varied axially for all the conifers but did not for the broadleaved species. Mean concentrations of TNC, sugars and starch in stem varied by more than twofold among the species. However, there were no significant differences in these values for the species groups with different leaf phenology or wood types. Ignoring the radial, axial and inter-specific variations in NSC in stem would introduce large bias in estimating NSC storage at tree or ecosystem levels.     

Architecture of Iberian canopy tree species in relation to wood density,shade tolerance and climate

Tree architecture has important consequences for tree performance as it determines resource capture, mechanical stability and dominance over competitors. We analyzed architectural relationships between stem and crown dimensions for 13 dominant Iberian canopy tree species belonging to the Pinaceae (six Pinus species) and Fagaceae (six Quercus species and Fagus sylvatica) and related these architectural traits to wood density, shade tolerance and climatic factors. Fagaceae had, compared with Pinaceae, denser wood, saplings with wider crowns and adults with larger maximal crown size but smaller maximal height. In combination, these traits enhance light acquisition and persistence in shaded environments; thus, contributing to their shade tolerance. Pinaceae species, in contrast, had low-density wood, allocate more resources to the formation of the central trunk rather than to branches and attained taller maximal heights, allowing them to grow rapidly in height and compete for light following disturbances; thus, contributing to their high light requirements. Wood density had a strong relationship with tree architecture, with dense-wooded species having smaller maximum height and wider crowns, probably because of cheaper expansion costs for producing biomechanically stable branches. Species from arid environments had shorter stems and shallower crowns for a given stem diameter, probably to reduce hydraulic path length and assure water transport. Wood density is an important correlate of variation in tree architecture between species and the two dominant families, with potentially large implications for their resource foraging strategies and successional dynamics.     

Source-driven remobilizations of nutrients within stem wood in Eucalyptus grandis plantations

Nutrient remobilizations in tree ligneous components have been little studied in tropical forests. A complete randomized block design was installed in Brazilian eucalypt plantations to quantify the remobilizations of phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sodium (Na) within stem wood. Three treatments were studied: control with neither K nor Na addition (C), 3 kmol ha^?1 K applied (+K), and 3 kmol ha^?1 Na applied (+Na). Biomass and nutrient contents were measured in the stem wood of eight trees destructively sampled at 1, 2, 3 and 4 years after planting in each treatment and annual rings were localized on discs of wood sampled every 3 m in half of the trees. Chemical analyses and wood density measurements were performed individually for each ring per level and per tree sampled. Nutrient remobilizations in annual rings were calculated through mass balance between two successive ages. Our results show that nutrient remobilizations within stem wood were mainly source-driven. Potassium and Na additions largely increased their concentration in the outer rings as well as the amounts remobilized in the first 2 years after the wood formation. The amount of Na remobilized in annual rings was 15 % higher in +Na than in +K the fourth year after planting despite a 34 % higher production of stem wood in +K leading to a much higher nutrient sink. A partial substitution of K by Na in the remobilizations within stem wood might contribute to enhancing Eucalyptus grandis growth in K-depleted soils.     

Sap flow-based quantitative indication of progression of Dutch elm disease after inoculation with Ophiostoma novo-ulmi

Key message

The rate of progression of Dutch elm disease can be continuously and quantitatively estimated from sap flow measurements.

Abstract

Response of sap flow to inoculation with Ophiostoma novo-ulmi, a causal agent which causes vascular mycosis called Dutch elm disease, was studied in a field experiment comprised of 4-year-old wych elm trees (Ulmus glabra). Sap flow was measured on inoculated trees using the trunk heat balance method with external heating (EMS 62, Czech Republic) throughout the experiment. The first detectable symptoms of reduction in sap flow occurred 6 days after inoculation and all inoculated trees died within 16 days. Our experiment confirmed the ability of O. novo-ulmi to quickly kill young elm trees. The disease progressed faster than in previous experiments utilizing O. ulmi. To the best of our knowledge, this is the first experiment using sap flow measurements on trees inoculated by O. novo-ulmi. The trunk heat balance sap flow method is an effective non-invasive tool for continuous quantitative monitoring of the progression of vascular tree diseases, and show increased potential for field and greenhouse studies on changes in xylem hydraulic conductivity in a wide range of broadleaved and coniferous tree species.     

Effect of forest thinning and wood quality on the short-term wood decomposition rate in a <Emphasis Type="Italic">Pinus tabuliformis</Emphasis> plantation

The effects of forest thinning and wood quality on wood decomposition in the mineral soil were investigated in a Chinese pine (Pinus tabuliformis Carriére) plantation in northern China by measuring mass loss and changes in wood properties (carbohydrates, lignin and nitrogen (N) concentrations) in wood stakes of two tree species—loblolly pine (Pinus taeda L.) and trembling aspen (Populus tremuloides Michx.). Stakes were inserted to a 20 cm soil depth in stands with three thinning levels (low, moderate, and heavy) and an unharvested control and removed after 1 year. There were significant differences in stake mass loss among the treatments. The species effect on the stake mass loss was marginally significant. Wood N content of both species increased during decomposition in all thinning treatments, and was only correlated with aspen mass loss. Wood properties of stakes placed in each stand before insertion (t?=?0) were similar, except for pine lignin concentration and aspen lignin: N ratio, but neither had any effect on thinning treatment results. Lignin concentration increased and carbohydrate concentration decreased in both aspen and pine wood stakes during decomposition across all thinning treatments, which suggests that brown-rot fungi are dominant wood-decomposers on our study site. We conclude that thinning has a significant influence on the wood decomposition in the mineral soil of this Chinese pine plantation.     

Cleavage of model replication forks by fission yeast Mus81-Eme1 and budding yeast Mus81-Mms4

The blockage of replication forks can result in the disassembly of the replicative apparatus and reversal of the fork to form a DNA junction that must be processed in order for replication to restart and sister chromatids to segregate at mitosis. Fission yeast Mus81-Eme1 and budding yeast Mus81-Mms4 are endonucleases that have been implicated in the processing of aberrant DNA junctions formed at stalled replication forks. Here we have investigated the activity of purified Mus81-Eme1 and Mus81-Mms4 on substrates that resemble DNA junctions that are expected to form when a replication fork reverses. Both enzymes cleave Holliday junctions and substrates that resemble normal replication forks poorly or not at all. However, forks where the equivalents of either both the leading and lagging strands or just the lagging strand are juxtaposed at the junction point, or where either the leading or lagging strand has been unwound to produce a fork with a single-stranded tail, are cleaved well. Cleavage sites map predominantly between 3 and 6 bp 5' of the junction point. For most substrates the leading strand template is cleaved. The sole exception is a fork with a 5' single-stranded tail, which is cleaved in the lagging strand template.