Diachronic analysis of individual-tree mortality in a Norway spruce stand in the eastern Italian Alps

? Understanding tree mortality processes across time requires long term studies. Spatiotemporal patterns of mortality in a 200 years-old mono-layered Norway spruce stand were evaluated to determine what factors affected individual-tree mortality.

? We performed an analysis on two surveys (1993 and 2005) in a 1-ha permanent plot in the Paneveggio forest (Eastern Italian Alps). Tree diameter and age distribution between surveys were compared. We examined spatial patterns of living and dead trees before 1993, in 1993 and in 2005 using univariate and bivariate Ripley’s K(d) function, and a kernel estimator of local crowding. A logistic model was used to assess the effects of diameter, age, recent growth and competitive pressure on tree mortality.

? Spatial pattern analysis indicated mortality was associated to tree neighbourhood (neighbour effect at 2–5 m). An increment of regularization of tree spatial pattern occurred due to density-dependent mortality. Logistic regression showed tree diameter and recent growth were determinant on mortality risk during the monitoring period.

? Even if the stand is relatively aged, mortality dynamics are those typical of stem exclusion stage. Mortality was related to competitive dynamics, and small suppressed trees with slow growth rate had higher probability to die.

     

High resolution temporal variation in wood properties in irrigated and nonirrigated Eucalyptus globulus

? Environmental determinants of wood properties variation were examined in Eucalyptus globulus, a globally important hardwood plantation species, in southern Tasmania, Australia.

? Radial variation in wood properties, measured with the SilviScan system, were re-scaled from distance to time abscissa using stem radial growth data measured with dendrometers. With this re-scaled data it was possible to evaluate how water availability and temperature affected wood density, microfibril angle (MFA) and fibre and vessel transverse dimensions in irrigated and non-irrigated trees.

? Wood density, fibre radial diameter and MFA were sensitive to water availability. Wood density increased and fibre radial diameter decreased in response to reduced water availability. When high water availability was maintained, wood density was negatively correlated with temperature. Together, temperature and soil matric potential explained about 60% of temporal variation in wood density variation. In contrast MFA was not related to temperature but decreased with increasing water stress. Slower growing trees also had lower MFA than faster growing trees. Slower growing trees had a larger number of vessels per unit area of wood than faster growing trees within this even aged stand. However, vessel radius to the 4th power was significantly higher in faster growing trees than in slower growing trees.

? Overall, E. globulus wood properties were sensitive to temporal changes in environmental conditions (particularly water availability) and associated growth rates. The data provided support for the hypothesis that growth rates are hydraulically mediated.

     

Diminished vessel diameter as a possible factor in the decline of European ash (Fraxinus excelsior L.)

? The aim of this work was to examine the anatomy and functioning of secondary xylem in stems in relation to the decline of European ash (Fraxinus excelsior L.).

? We tested the hypothesis that declining trees show changes in the structure of wood, which result in impaired water transport.

? Anatomical analyses were carried out on wood samples (comprising all annual rings formed during the 30 years life of the analysed trees) collected at breast height from the main stem of healthy, weakened and dead ash trees. The width of annual wood increments, the diameter and density of earlywood vessels were measured and the theoretical hydraulic conductivity index through the secondary xylem calculated by application of Hagen-Poisseuille’s formula.

? Anatomical characteristics changed both with the age of trees and in response to unfavorable factors. The largest vessels were observed in healthy trees, which implied that they had the highest hydraulic conductivity index, whereas trees considered to be in decline produce smaller vessels and hence had reduced conductivity.

     

A comparison of mortality rates between top height trees and average site trees

? Although comparisons between methods of selecting trees for site index estimates are well documented in the literature, little is known on mortality rates of different canopy tree cohorts used for that purpose.

? This study was initiated to test the hypothesis that the mortality rates of top height trees are lower than those of codominants only or a combination of codominant and dominant trees. To test this hypothesis, we used records from a network of permanent sample plots in Québec and studied the fate of different cohorts of site trees for five different species.

? Our results did not show clear evidence of lower mortality rates for top height trees. Instead we found that depending on the species, top height trees have lower (Populus tremuloides, Pinus banksiana), higher (Picea mariana, Abies balsamea) or equal mortality rates (Betula papyrifera) than codominant trees or codominant and dominant trees combined.

? These results suggest a tendency for shade intolerant species to maintain lower top height tree mortality rates over time when compared to shade tolerant species. In the latter case, it is also shown that spruce budworm epidemics (Choristoneura fumiferana) did not change the pattern of mortality rates of site trees of A. balsamea.

     

Improving models of forest nutrient export with equations that predict the nutrient concentration of tree compartments

? The objective of this study was to explore the distribution of major nutrients (N, P, K, Ca and Mg) in the aboveground compartments of an intensively managed tree species (Pinus pinaster Ait.). A total of 53 trees were cut down in even-aged stands respectively 8, 16, 26, 32 and 40 years old. The nutrient concentrations of the aboveground compartments were analysed.

? Nutrient concentrations of foliage did not vary with any of the variables used, except needle age. Nutrient concentrations of living branches, stem bark, stem sapwood, stem heartwood, stemwood and stem decreased with increasing branch diameter, bark thickness, sapwood thickness and heartwood thickness, respectively. Beyond a certain value of the predictive variable (stem diameter ≈ 15 cm; branch diameter ≈ 2.5 cm), the concentration of all the nutrients stabilised.

? A 50 year-old pine stand was used to obtain a validation dataset for nitrogen concentration. For this nutrient, the regression relationships gave satisfactory estimates for most compartments (mean error = 12–25%) and particularly for the stem.

? A procedure is proposed to estimate the nutrient exports associated with harvests of Pinus pinaster biomass.

     

Which factors most influence heartwood distribution and radial growth in plantation teak?

? To investigate the effect of climate on radial growth in young plantation grown teak (Tectona grandis L.), growth ring width was measured in 105 trees and correlated to precipitation and temperature data.

? The social status of trees within the stand was also determined and cross-sectional area (CSA) for the trunk correlated to the proportion of heartwood (HW) within the tree. HW develops asymmetrically in leaning stems of some conifer species, but it is not known if this phenomenon also occurs in broadleaf species. Therefore, we measured HW proportion in leaning and straight stems, along with the number of growth rings in the HW.

? Annual ring width depended strongly on mean monthly temperature during the rainy season and the most significant relationships were found corresponding to the months of June and July. With regard to the weaker relationship between precipitation and radial growth, correlations were highest during the period of bud-break at the beginning of the rainy season.

? The very high stand density affected radial growth, particularly in suppressed trees, which responded little to thinning operations. HW formation was greatest in dominant trees, and was highly regressed with stem CSA.

? Therefore, rapid growth of young stands should be encouraged by reducing stand density. Asymmetric HW formation occurred in both leaning and straight trees, and was significantly greater along the upper sides of leaning stems. It is probable that this eccentric HW formation is linked to mechanical loading on the tree.

     

Genetic parameters for grain angle in 28-year-old Norway spruce progeny trials and their parent seed orchard

? Sawn wood which acquires twist during drying is a substantial problem for the sawmill industry and is to a large extent caused by spiralled grain in the tree.

? In this study, the feasibility of using spiral grain angles as a selection trait in Norway spruce (Picea abies (L.) Karst) tree breeding and the extent of grain angle and its breeding values were investigated. Grain angles under bark and diameter were measured at breast height in three 28-year-old Norway spruce progeny trials and in their parent seed orchard.

? The mean grain angle value was 1.76° in the progeny trials and 1.84° in the seed orchard. Estimated genetic standard deviations for grain angle were almost 1°. Progeny trial heritabilities (H ² > 0.3) were larger than the seed orchard heritability (H ² = 0.24). Genotype by environment interaction among the progeny trials was negligible for grain angle. Progeny trial grain angles exhibited genetic correlation with seed orchard grain angles in the range 0.66 to 0.84.

? Thus, mature wood grain angles are also under considerable genetic control, raising the opportunity to reduce the occurence of left-grained trees, which are prone to producing twisted wood.

     

Modelling site quality and individual-tree growth in pure and mixed Pinus brutia stands in north-east Greece

? Simulation tools, based on individual tree growth and mortality models can produce the most detailed predictions of forest stand development under different management schedules. These models allow the manager to predict the development of any type of stand (even- and uneven-aged, and pure and mixed stands).

? Different model approaches and predictors are required for pure even-aged or mixed uneven-aged forest stands. This study developed and compared two sets of models which enable tree-level simulation of the development of pure and mixed stands of Pinus brutia in north-east Greece. The first set of models for even-aged forestry consists of site index models, diameter growth models, tree height models, and mortality models. The second set, which is for uneven-aged forestry, uses a past growth index instead of a site index.

? The simulations and overall fitting statistics suggest that the two types of models provide realistic and accurate predictions of forest stand development and allow one to simulate the development of complex Pinus brutia stand structures in Dadia National Park forests.

? The advantages of the two approaches are discussed and it is suggested that the growth index is an effective predictor of site quality and the set of models which used such variable as predictor performed in a similar way as the models using site index, which require more information and a given stand structure (even-aged).

     

Variation in the pith parameter of Gmelina arborea trees from fast growth plantations in Costa Rica

? The pith represents the central part of the cross-section of a tree trunk and it is composed of primary parenchyma tissue. And its eccentricity is associated with the presence of reaction wood, which affects trunk straightness, and diminishes the quality of the logs and products.

? Gmelina arborea trees (8 to 14 years old) from fast growth plantations in Costa Rica were sampled with the purpose of determining diameter, eccentricity and pith percentage as well as pith distance from the real centre of the cross section. These pith parameters were also evaluated in relation to management intensity (intensive, moderate and unmanaged), climate (dry and wet tropical) and tree height.

? Pith diameter varies from 0.15 to 1.10 cm and is located at 6 cm, at its maximum, around the real centre of the cross section. Percentage eccentricity might reach values of up to 26.5% and this parenchyma tissue represents between 1 and 5% of the total tree diameter.

? The level of management had a significant effect on the eccentricity and percentage of the pith, while the climate significantly affected the pith percentage and the distance of pith from the real centre of the cross section. Tree height affected significantly all the parameters evaluated.

     

Variations in water use by a mature mangrove of Avicennia germinans, French Guiana

? In the tropical intertidal zones, little is known on water uptake by mangroves. Transpiration rates are generally measured at leaf level, but few studies exist on water use at tree or stand levels.

? The objective of this study was to measure sap flow in trees of different sizes to appreciate the range of variation in water use that may exist in a site dominated by 80% mature Avicennia germinans.

? The results showed that from the dry to the wet season the mean water use increased from 3.2 to 5.3 dm³ d^?1 in small trees (DBH ～ 13 cm), from 11.5 to 30.8 dm³ d^?1 in medium trees (～24 cm) and from 40.8 to 64.1 dm³ d^?1 in large ones (～45 cm).

? Sapwood remained active up to a depth of 8 cm with radial variations within the stem. Weak correlations were obtained with VPD and net radiation.

? This study confirmed that transpiration was larger under low levels of salinity. Water use at stand level (～1900 living stems ha^?1) was estimated to be in the range of 5.8 to 11.8 m³ ha?1 d^?1 according to the season.

     

Towards standardised crown condition assessment in poplar plantations

? This work aims at developing new tools for rapid assessment of forest health indicators in poplar plantations.

? Crown transparency and discoloration were visually evaluated in all trees of four 15 m-radius sub-plots in 32 poplar clonal plantations, which were chosen according to a factorial scheme with three factors: tree age, site quality and understorey vegetation management. A subset of trees was assessed using digital photos processed with a semi-automatic image analysis system (the CROCO software) in order to compare visual and digital crown transparency estimates.

? Poplar crown conditions were better in young stands and rich sites. Harrowing understorey vegetation improved tree health in poor sites. Samples of 20 trees per stand provided the same information about crown transparency and discoloration as 60 trees. Calibration curves of digital crown transparency estimates were successfully fitted against visual crown transparency estimates. The same effects of stand age and site quality could be detected with digital crown transparency as response variable.

? The use of digital photos processed with CROCO in ca. twenty trees per stand is therefore recommended to accurately and objectively monitor crown condition in clonal poplar plantations.

     

Extending sapwood — Leaf area relationships from stems to roots in Coast Douglas-fir

? Studies of allometric relationships between leaf area and the cross-sectional area (CSA) of sapwood in the stem have shed light on the structural and functional relationships between water-conducting and photosynthetic tissues.

? The purpose of this study was to test whether sapwood-leaf area relationships could be extended from stems to roots in coast Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco). Twelve trees were felled, their stumps were excavated, and the CSA of sapwood and heartwood were estimated for individual roots, entire root systems, and stem section.

? Root sapwood CSA was greater than sapwood CSA throughout the stem, and the ratio of leaf area to sapwood CSA (A _l :A _s ) was accordingly lower for root sapwood. The relationship between sapwood CSA and leaf area was more variable in roots and at groundline compared to crown base. Root A _l :A _s decreased with relative tree height (tree height/mean stand height).

? The strong allometric relationship between leaf area and the CSA of sapwood in the stem generally holds when extended to roots. The greater CSA of sapwood in roots versus stems may reflect differences in their roles in supporting the tree.

     

Physical properties of wood in thinned Scots pines (Pinus sylvestris L.) from plantations in northern Spain

? The physical properties of wood and the associated variations within and between trees were evaluated by analysing 770 small specimens of clear wood from 11 Pinus sylvestris L. trees thinned from 3 plantations.

? Within-tree variations in basic density or volumetric shrinkage increased with cambial age and decreased with increasing ring width. The effect of the height in the stem on wood properties was considered indirect and height was not included as an explanatory variable in the mixed models proposed to estimate basic density and volumetric shrinkage.

? The models had random components for the intercept parameter and explained 52.5% of the total variance in basic density and 56% of the total variance in volumetric shrinkage. Linear shrinkage in the direction of the grain was extremely variable.

? Between-tree variation and between-plot variation in the physical properties of wood were high, considering that all trees sampled were growing in similar sites and stands. It would then be desirable to predict physical properties of wood on living trees in order to use the quality of wood as a criterion for timber tree selection in thinnings.

     

Genetic correlations between pulpwood and solid-wood selection and objective traits in Eucalyptus globulus

? If selective breeding is to be successful, significant genetic variation must be present in the traits targeted for improvement (i.e. “objective traits”).

? This study aimed to quantify genetic variation in Eucalyptus globulus pulpwood and sawn-timber objective traits (rotation-age whole-tree volume, survival, whole-tree basic density, sawn-board Janka hardness and sawn-board internal checking) and estimate additive genetic correlations between these and inexpensively-assessed “selection traits”.

? Significant genetic variation was identified in all objective traits at the subrace and/or family within subrace level.

? Selection-age diameter at breast height (1.3 m, DBH) was strongly genetically correlated with rotation-age volume (0.78) and survival (0.82). Subrace and additive genetic correlations of selectionage Pilodyn penetration with rotation-age 12-×-12-mm-sample basic density (?0.70 and ?0.75 respectively) and whole-tree basic density (?0.83 and ?0.91 respectively) were also strong.

? No significant subrace or additive genetic correlation between wood-sample gross shrinkage and sawn-board internal checking was detected. However, subrace and additive genetic correlations of sawn-board Janka hardness with Pilodyn penetration (?0.75 and ?0.58 respectively) and sample gross shrinkage (?0.77 and ?0.73 respectively) were significantly different from zero.

? These findings suggest that genetic improvement of the examined objective traits is possible through selective breeding, although none of the assessed selection traits were strongly correlated with internal checking.

     

Diurnal, daily, seasonal and annual patterns of sap-flux-scaled transpiration from an Acacia mangium plantation in South China

? In this study of a 19-year-old Acacia mangium plantation with a basal area of 26.6 m² ha^?1 in subtropical South China, whole tree sap flow was measured continuously over a two-year period and the dependence of stand sap flow (Et) on environmental factors was investigated at diurnal (hourly), daily, seasonal and annual scales.

? Daytime hourly mean Et was linearly correlated to photosynthetically active radiation (Q) and vapor pressure deficit (D) in each season during the whole study period (R ² > 0.57, P < 0.001), whereas daily daytime mean Et was less tightly coupled to Q and D (R ² < 0.50).

? Pronounced hysteresis was observed between Et and Q as well as D and the extent of the hysteresis varied seasonally.

? Total annual stand transpiration was higher in the first year (244.5 mm) than in the second year (185.8 mm) although rainfall was lower in the first year (1 122.4 mm) than in the second year (1 342.5 mm), from which it can be concluded that annual stand transpiration did not simply increase with increased annual rainfall.

     

Epicormic sprout development in pruned coast redwood: pruning severity, genotype, and sprouting characteristics

? Young coast redwood (Sequoia sempervirens (D. Don.) Endl.) trees were pruned to various heights to examine the effect of pruning severity on epicormic sprouting. Seven separate stands were used with as many as six treatments per stand in coastal Humboldt County, California, USA.

? Epicormic sprout development was affected by pruning severity but primarily at the most severe pruning treatments that removed all but the branches in the top 15% of tree height. Less severe treatments produced sprouts but the number and size of these sprouts were comparable to unpruned trees.

? Natural clonal patterns were also used to explore patterns of sprouting between genotypes. Linear mixed-effects models were developed to predict sprouting frequency as a function of pruning severity while accounting for the nested data structure (i.e., stem sections sampled nested within genotypes within treatments within sites).

? Comparing variances attributed to each of these random effects indicated that at any level of pruning severity, differences in epicormic sprouting between genotypes and sites expressed soon after pruning had disappeared after six growing seasons. Epicormic branches were more common two years after pruning than six years indicating many branches were dying. Branches were more common in the middle of the pruned bole, possibly because of competition from basal sprouts and the expanding tree crown.

     

Climate-growth variability in Quercus ilex L. west Iberian open woodlands of different stand density

? We present the longest tree-ring chronology (141 y) of Quercus ilex L. (holm oak), and discuss the species climate-growth relationships and the influence of stand density on tree sensitivity to climate.

? Similarly to Quercus suber L., the most influential climatic variables upon holm oak growth were late spring and early summer precipitation, which enhanced growth, and high temperatures in the previous August and current July, which negatively affected growth.

? High density stands responded to similar climatic factors as low density stands, but their response was generally weaker. Holm oak sensitivity to climate has increased in recent decades, which might be related to increasing temperatures in the region. Sensitivity was higher in low density stands. Additionally, the effect of summer stress on growth seems to have increased during the same period, similarly to other species in the Iberian Peninsula, suggesting that trees are more vulnerable to climatic changes.

? Stand density could buffer the response to climate by smoothing climatic extremes. Nevertheless, the effect of competition might reverse this positive effect at the individual tree level. Precautions should be taken before providing management guidelines regarding the effect of climate change and stand density on holm oak.

     

The potential of plantations of Terminalia superba Engl. & Diels for wood and biomass production (Mayombe Forest, Democratic Republic of Congo)

? In the 1940s–1950s, large limba (Terminalia superba Engl. & Diels) plantations were established in the Democratic Republic of Congo to reduce the pressure on the natural forests.

? The objective of this study was to evaluate the potential of these long-rotation plantations as production forests (timber) and carbon sinks.

? Five different plantations, between 50 and 58 years old, were sampled. Over a sample surface of more than 73 ha, the diameter above buttresses of 2 680 trees, bole height of 265 trees and tree height of 128 trees was measured.

? To estimate the commercial volume, a nonlinear power law regression was used (R ² = 0.95). A power law variance function was applied to counter heteroscedasticity of the residual plot. Estimates of commercial tree and stand volume at 50 to 58 y were 5.6 ± 4.1 m³ and 183.9 ± 135.0 m³ ha^?1. Stand volumes appear low but are explained by a large decrease in tree density. However, the mean volume increment of 3.2–3.7 m³ ha^?1 y^?1 corresponds well with teak plantations of a similar age. For limba, aboveground biomass and carbon estimates of this study (resp. 108.4 and 54.2 Mg ha^?1) differ significantly from those of existing aboveground biomass models (resp. 135.7–143.9 Mg ha^?1 biomass and 67.9–72.0 Mg ha^?1 C). All aboveground biomass and carbon estimates for T. superba stands were lower than for the estimates of young fast-growing plantations like Tectona grandis L. f., Eucalyptus spp. and Acacia spp. (≤ 30 y).

     

Effects of the lateral growth rate on wood quality of Gmelina arborea from 3.5-, 7- and 12-year-old plantations

? Awareness of the shortage of fossil resources leads to an increasing demand for woody biomass. We investigated the feasibility of using fast-growing Gmelina arborea wood for material production. Gmelina arborea wood samples were collected from trees of varying cambium ages in Indonesia, from 3.5-, 7- and 12-year-old plantations.

? The lateral growth rate and the cambium age did not significantly affect the longitudinal released strain of the growth stress, xylem density, or microfibril angle at the outermost surface of the secondary xylem at any sampling site. However, fiber length in the 3.5-year-old plantation tended to be shorter in smaller diameter trees, whereas in larger diameter trees it was almost the same as that in trees from the 7- and 12-year-old plantations. This suggests that smaller diameter trees in the 3.5-year-old plantation had not yet produced mature wood.

? Xylem qualities had already reached values appropriate for harvesting, except in the smaller diameter trees from the 3.5-year-old plantation. This indicates that the larger diameter trees had already matured, regardless of their cambium age. These results suggest that the next step is to develop silvicultural treatments to increase the lateral growth rate during the early growing stage, in order to produce as much mature wood as possible, as quickly as possible.

     

Variation in the natural termite resistance of teak (Tectona grandis Linn. fil.) wood as a function of tree age

? Tree age is one of the most important factors to affect the natural durability of wood.

? The purpose of this study was to determine the natural termite resistance of heartwood and sapwood of teak (Tectona grandis Linn. fil.) for trees aged 8, 30 and 51 years. Reticulitermes speratus Kolbe was employed as a test termite using a no-choice feeding method.

? The heartwood and sapwood of all of the trees tested exhibited antitermitic activity. Based on the mean mass loss due to termite activity, the sapwood and heartwood regions of 8-year-old trees are the most susceptible to termites while the heartwood regions of the 30-year-old trees showed termite resistance similar to the termite resistance of 51-year-old trees.

? The mass loss is moderately correlated with n-hexane extractive content, total extractive content, brightness and redness of the wood.