Needle Lifespan Research Articles

Изменчивость морфоструктурных показателей разных возрастных поколений в популяциях сосны (Pinus sylvestris L.) в условиях постоянного избыточного увлажнения почв северной тайги Архангельской области

The data is presented for studying the variability of morphostructural parameters of different age (g1 and g2) pine populations under conditions of constant excessive soil moisture of the northern taiga of the Arkhangelsk region. The frequency of occurrence distribution of the age and morphostructural parameters (size of the trunk and crown, self-pruning, length of coarse bark, size and number of side shoots, length and life span of needles) of trees is shown. It has been established that pine trees with smaller trunk and crown sizes, worse self-pruning are more common. Greater height and diameter of the trunk, length and diameter of the crown, better self-pruning, a greater length of the coarse bark is observed in the older generation (g2). This is due to the older age of the trees. It has been established that the relationship between the height of the trunk and the age of the trees is higher in the samples of young generative trees. It was revealed that the young generation (g1) has a significantly greater length and mass of cones, the length, width and height of the apophysis of seed scales compared to the older generation (g2).

The results of the introduction of twisted pine (Pinus contorta) in Bolshoy Solovetsky Island

Abstract In the central part of the Bolshoy Solovetsky Island, in the same type of growing conditions, two plots were created in 1988: the first consisted of twisted pine (Pinus contorta Loud. var. latifolia S. Wats) crops and the second one was of Scots pine (Pinus sylvestris L.). The aim of the study was to establish the morphological parameters of the twisted pine and its growth in the conditions of the Bolshoy Solovetsky Island in comparison with the native species P. sylvestris L. Also, we aimed to identify the features of P. contorta var. latifolia and determine the possibility and necessity of further introduction of the species. The preservation of the twisted pine and scots pine cultures was determined. Accounting trees were selected (62 and 31 trees, respectively), in which morphometric indicators were measured. Wood samples (cores) were taken from them with an age drill to measure radial growth. The radial increment was measured using the MBS-9 microscope and the Lintab device. To measure the increase in height, six medium-sized model trees were cut down. According to the taxation indicators, the two types differed slightly and the differences were most often unreliable. The average height of the twisted pine trees was significantly higher compared to that of Scots pine. The thickness of the bark varied; on average, at the age of 18, it was 1.35 ± 0.038 mm for twisted pine and 1.86 ± 0.095 for Scots pine, that is, the native pine bark was 38% thicker. Typical for twisted pine were a significant number of pathologies noted in 22% of the studied trees. Twisted pine was distinguished by a stronger development of the assimilation apparatus: the number of branches of the first order, the number of branches in the whorl, the life span of needles. An increase in radius (the width of the annual ring) was observed at 14–15 years, and then with age, the value decreased in twisted pine and remained at a consistently high level in Scots pine. The width of the late zone of the annual ring was 12% in Scots pine and 14% in twisted pine; but at a young age, the late wood in twisted pine was very small. The increase in height of the twisted pine was on average less than that of Scots pine. The dependence of the trunk volume on the diameter was almost identical in both species.

Seasonal water availability drives trait variation in isolated Basin and Range Pinus ponderosa

Tree species resistant to drought stress are likely to be more successful under the moisture-limited conditions predicted with climate change, and variation in drought-resistant traits can influence a species’ sensitivity to change. Trait variation is often tied to the timing, amount, and type of precipitation a given forest stand is exposed to, and local topographic heterogeneity may exacerbate or mitigate soil moisture stress. Although drought resistance is well-studied in widespread tree species, knowledge is limited on trait variation in drought-resistant conifers with more narrow distributions or isolated populations.Pinus ponderosa is amongst the most widespread conifers in semi-arid forests of western North America, and var. scopulorum occurs in some of the most arid portions of the species’ range. In the Northern Basin and Range physiographic province of western North America, scopulorum is isolated to montane sky islands, making it a model system for testing the effects of climate and topography on trait variation in drought-resistant conifers. To investigate the relationship between interacting climatic and topographic conditions and drought-resistant traits, we sampled 55 stands across six ranges in Nevada and Utah to quantify trait variation in cone volume, wood density, latewood to earlywood ratio (LER), specific leaf area (SLA), and needle lifespan and asked how these traits vary across the regional climate gradient. We then used linear mixed models to explore whether seasonal climatic moisture deficit (CMD), monsoonality, aspect, elevation, or tree-level attributes are associated with trait variation.Traits varied widely both within and among ranges, with trait responses strongly linked to seasonal water availability. Cone volumes and SLA increased with increasing summer (July-Aug) CMD, while cone volume decreased with increasing winter (Nov-Jan) CMD. Winter moisture stress was also tied to wood formation, as wood densities increased under greater cold season (Oct-Feb) CMD. Needle lifespan and LER were not shaped by seasonal CMD but rather by the degree of monsoonality, indicating that drought-resistant conifers may be able to take advantage of late-summer precipitation. Contrary to our expectations, local topographic variation had no influence on trait variation in the stands sampled here, while elevation and tree diameters were significant for wood traits alone. These findings suggest that both seasonal moisture stress and the timing of precipitation influence drought-resistant conifer trait variation in semi-arid environments and highlight the potential for these conifers to withstand extreme fluctuations in seasonal water availability, which is predicted to become more common as the climate continues to change.

Foliage Biophysical Trait Prediction from Laboratory Spectra in Norway Spruce Is More Affected by Needle Age Than by Site Soil Conditions

Scaling leaf-level optical signals to the canopy level is essential for airborne and satellite-based forest monitoring. In evergreen trees, biophysical and optical traits may change as foliage ages. This study aims to evaluate the effect of age in Norway spruce needle on biophysical trait-prediction based on laboratory leaf-level spectra. Mature Norway spruce trees were sampled at forest stands in ten headwater catchments with different soil properties. Foliage biophysical traits (pigments, phenolics, lignin, cellulose, leaf mass per area, water, and nitrogen content) were assessed for three needle-age classes. Complementary samples for needle reflectance and transmittance were measured using an integrating sphere. Partial least square regression (PLSR) models were constructed for predicting needle biophysical traits from reflectance—separating needle age classes and assessing all age classes together. The ten study sites differed in soil properties rather than in needle biophysical traits. Optical properties consistently varied among age classes; however, variation related to the soil conditions was less pronounced. The predictive power of PLSR models was needle-age dependent for all studied traits. The following traits were predicted with moderate accuracy: needle pigments, phenolics, leaf mass per area and water content. PLSR models always performed better if all needle age classes were included (rather than individual age classes separately). This also applied to needle-age independent traits (water and lignin). Thus, we recommend including not only current but also older needle traits as a ground truth for evergreen conifers with long needle lifespan.

Environmental Assessment of Urban Areas using Plants of Different Taxa as Indicators

Aim. Study of existing phytoindication approaches in order to determine how they can be optimally integrated and applied to the environmental assessment of urban areas. Material and Methods . The investigation encompassed 30 evenly distributed trial sites in the city of Kislovodsk, Stavropolskaya Oblast, Russia. Lichen poleotolerance, the fluctuating asymmetry of the leaves of Betula pendula Roth., the lifespan of needles of Pinus sylvestris L., and the correlations between Trifolium repens L. phenotypes were used as key phytoindicators. Results. The morphometric parameters of lichens, Betula pendula Roth., Pinus sylvestris L., Trifolium repens L. growing in the urban environment were studied. A phytoindication parameter matrix was developed as a component of an integrated approach to the environmental assessment of urban areas. The most ecologically vulnerable areas of the city of Kislovodsk were identified, and ecological zoning of the territory was carried out. Conclusion. Phytoindication analysis using reliable and valid techniques can provide a basis for an integrated ecological assessment of urban areas. In order to obtain reliable results, plants from different taxa should be used. The study has shown that the use of plant indicators in urban areas can provide timely and regularly updatable information about environmental status to support sustainable development.

Improving winter leaf area index estimation in coniferous forests and its significance in estimating the land surface albedo

Winter leaf area index (LAI) of evergreen coniferous forests exerts strong control on the interception of snow, snowmelt and energy balance. Simulation of winter LAI and associated winter processes in land surface models is challenging. Retrieving winter LAI from remote sensing data is difficult due to cloud contamination, poor illumination, lower solar elevation and higher radiation reflection by snow background. Underestimated winter LAI in evergreen coniferous forests is one of the major issues limiting the application of current remote sensing LAI products. It has not been fully addressed in past studies in the literature. In this study, we used needle lifespan to correct winter LAI in a remote sensing product developed by the University of Toronto. For the validation purpose, the corrected winter LAI was then used to calculate land surface albedo at five FLUXNET coniferous forests in Canada. The RMSE and bias values for estimated albedo were 0.05 and 0.011, respectively, for all sites. The albedo map over coniferous forests across Canada produced with corrected winter LAI showed much better agreement with the GLASS (Global LAnd Surface Satellites) albedo product than the one produced with uncorrected winter LAI. The results revealed that the corrected winter LAI yielded much greater accuracy in simulating land surface albedo, making the new LAI product an improvement over the original one. Our study will help to increase the usability of remote sensing LAI products in land surface energy budget modeling.

Variability in needle lifespan and foliar biomass along a gradient of soil fertility in maritime pine plantations on acid soils rich in organic matter

The variability in needle lifespan, foliar biomass and leaf area index was studied in 31 Pinus pinaster Ait. plots in Galicia (NW Spain), established along a gradient of soil productivity in plantations of similar age (11–14years). The soils under study were acidic (pH 3.7–5.3) and very rich in organic matter (6.9–34.3%). All needles were classified according to age class, and presence/absence of needles was recorded to evaluate survival. Specific leaf area and needle biomass were calculated for each plot. The foliage nutrient concentrations were also measured and site index was calculated. The maximum needle age was 5years. Survival of needles older than 2years declined rapidly. Needle longevity was positively affected by site index and foliar nutrient concentrations, particularly of Mg and K. This suggests that maritime pine responds to low soil fertility by decreasing needle lifespan at local scales. Needle biomass and leaf area index were significantly higher in 1 and 2-year-old needles. Total needle biomass and LAI values were very variable (average values of 4.89tha−1 and 1.64m2m−2, standard deviation 3.1 and 1.1 and CV of 64% and 69%, respectively) and were positively related to site productivity and foliar nutrients. The average litterfall rate was estimated to be 0.31year−1. The mean growth efficiency (0.36kgm−2year−1) was also rather variable (CV=50%) and was positively related to foliar K and needle longevity. The relationships between all variables associated with high levels of pine productivity and the mean shrub height were always significant and negative, indicating a reduction in the risk of ground fire.

Biogeographic variation in evergreen conifer needle longevity and impacts on boreal forest carbon cycle projections.

Leaf life span is an important plant trait associated with interspecific variation in leaf, organismal, and ecosystem processes. We hypothesized that intraspecific variation in gymnosperm needle traits with latitude reflects both selection and acclimation for traits adaptive to the associated temperature and moisture gradient. This hypothesis was supported, because across 127 sites along a 2,160-km gradient in North America individuals of Picea glauca, Picea mariana, Pinus banksiana, and Abies balsamea had longer needle life span and lower tissue nitrogen concentration with decreasing mean annual temperature. Similar patterns were noted for Pinus sylvestris across a north-south gradient in Europe. These differences highlight needle longevity as an adaptive feature important to ecological success of boreal conifers across broad climatic ranges. Additionally, differences in leaf life span directly affect annual foliage turnover rate, which along with needle physiology partially regulates carbon cycling through effects on gross primary production and net canopy carbon export. However, most, if not all, global land surface models parameterize needle longevity of boreal evergreen forests as if it were a constant. We incorporated temperature-dependent needle longevity and %nitrogen, and biomass allocation, into a land surface model, Community Atmosphere Biosphere Land Exchange, to assess their impacts on carbon cycling processes. Incorporating realistic parameterization of these variables improved predictions of canopy leaf area index and gross primary production compared with observations from flux sites. Finally, increasingly low foliage turnover and biomass fraction toward the cold far north indicate that a surprisingly small fraction of new biomass is allocated to foliage under such conditions.

Variation in the morphological structure of the crown of Norway spruce in North Estonian alkalised soil

Characterisation of tree crown structure provides critical information to assess a variety of ecological conditions for multiple purposes and applications. The aim of investigation was to elucidate the influence of the alkaline soil on the formation of the crown of Norway spruce (Picea abies (L.) Karst.). The seven sample plots (0.05ha) with 75–90-year-old spruce stands of Oxalis–Myrtillus site type were selected at different distances from a cement plant influenced over 40years by alkaline dust pollution. The studies were conducted 13years after dust pollution had practically stopped. High pH values (6.1–7.8), large concentrations of dominant dust components (Ca, Mg, K) and a lower level of N and organic matter in the upper layers of soil within about 6km from the emission source compared to the unpolluted control area 30.4km from the source (pH 3.3) were found. Disbalance in mineral composition in needles and shoots was established, deficite in N and excess in Ca and K concentrations were brought about a great differentiation in growth and biomass formation between unpolluted and polluted trees. On the most polluted area the average height of trees and living crown, the length and dry mass of shoots and needles were lower, and average life span of needles were shorter than in unpolluted area, indicating an increased defoliation rate of the crown.

ENSO and PDO strongly influence Taiwan spruce height growth

To assess the influences of the El Niño-Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO) on the mean annual height growth of the Taiwan spruce (Picea morrisonicola), we constructed two height growth indices (HGI1 and HGI2) using an ensemble empirical mode decomposition approach based on stem analysis of 19 trees. The most significant periodicities for HGI1 and HGI2 were 4.5 and 15.5years, respectively. Both indices positively correlated with the mean annual height growth and reflected the influences of local thermal environment variability at various lag times, up to 3years prior to the shoot extension season. The lagged relationships were likely caused by a combination of the species’ two-year height growth process, the delayed responses of the local climate to sea surface temperature (SST) variation, and persistence due to needle lifespan. The correlations between HGI1 and a detrended SST field showed a spatial pattern similar to that of the ENSO. At lags of both 3 and 4years, the correlations between HGI2 and the SST field revealed a spatial pattern resembling that of PDO. When leading by 3 and 4years, respectively, the NINO4 and PDO indices positively associated with the mean annual height growth and together explained 37% of the variance; the marginal effect of the NINO4 index was twice as large as that of the PDO index. The results show that the height growth of Taiwan spruce responded to both ENSO and PDO in a positive manner. This study demonstrates that quasi-periodic climate variation on an interannual (ENSO) to interdecadal (PDO) time scale can significantly influence tree growth and should be taken into account when assessing the impact of climate changes on forest productivity, and the results of this study provide a basis for incorporating the influences of such quasi-periodic climate variations into future model-based assessments.

Morphological acclimation to understory environments in Abies amabilis, a shade- and snow-tolerant conifer species of the Cascade Mountains, Washington, USA

Light-related plasticity in a variety of crown morphology and within-tree characteristics was examined in sun and shade saplings of Abies amabilis Dougl. ex J. Forbes growing in two late-successional forests with different snow regimes in the Cascade Mountains of Washington, USA. Compared with sun saplings, shade saplings typically had broad flat crowns as a result of acclimation at several scales (needle, shoot, branch, crown and whole sapling). Shoots of shade saplings had a smaller needle mass per unit of stem length than shoots of sun saplings, a feature that enhances light-interception efficiency by reducing among-needle shading. The low annual rate of needle production by shade saplings was associated with a longer needle lifespan and slower needle turnover. Reduced needle production within a shoot was reflected at the branch level, with lateral branches of shade saplings having a smaller needle mass than branches of the same length of sun saplings. Reduced allocation to needles permits greater investment in branches and stems, which is necessary to support the horizontally expanding branch system characteristic of shade saplings. Mean branch age of shade saplings was significantly higher than that of sun saplings. Shade saplings had lower needle mass per unit of trunk biomass or total biomass, reflecting greater investment in the trunk as a support organ. Increased investment in support organs in shade was more evident in the snowier habitat. The observed morphological acclimation makes A. amabilis highly shade and snow-tolerant and thus able to dominate in many late-successional forests in snowy coastal mountain regions.

Functional relationships between crown morphology and within-crown characteristics of understory saplings of three codominant conifers in a subalpine forest in central Japan.

Light-related plasticity of crown morphology and within-crown characteristics were investigated in understory sun and shade saplings of three codominant subalpine conifers, Abies mariesii M.T. Mast., Abies veitchii Lindl. and Picea jezoensis var. hondoensis (Mayr) Rehd. Compared with those of sun saplings, current-year shoots of shade saplings allocated less biomass to needles, resulting in less dense needle packing and hence less mutual needle shading. The proportion of lateral branch biomass in foliage was either similar in sun and shade saplings or greater in shade saplings, depending on the species, suggesting that, over the lifetime of a branch, greater needle longevity in shade compensates for reduced biomass investment in needles of current-year shoots of shade saplings. Saplings with slower-growing branches tended to have greater needle life spans, suggesting that plasticity of branch growth rate and plasticity of needle life span are interdependent. Both Abies species showed greater light-related plasticity of needle life span and branch growth than P. jezoensis. The greater shade tolerance of the Abies species derives from their broad flattened crowns with slow-growing branches. This type of crown development incurs substantial support costs, but the long needle life span of shade saplings of the Abies species compensates, at least in part, for their low annual investment in foliage, especially in the case of A. mariesii, which has a longer needle life span and slower-growing and stouter branches than A. veitchii. Compared with the Abies species, P. jezoensis had a less plastic crown morphology, and less variability of needle life span and branch growth in response to light, resulting in lower shade tolerance. However, compared with the flattened crown of Abies shade saplings, the conical crown of P. jezoensis saplings imposes a smaller support cost, making this species better adapted to rapid height growth than to survival in shade.

Effects of deicing salt on the vitality and health of two spruce species, Picea abies Karst., and Picea glehnii Masters planted along roadsides in northern Japan

In northern Japan, the growth of Picea abies Karst., and Picea glehnii Masters, which have been planted along the highways, is often suppressed due to several environmental stresses. To examine the adverse effects of deicing salt, the primary source of stress, we measured needle life span, photosynthetic capacity, and water potential and transpiration rate of the two spruce species at a site with damaged trees, near the roadside and a site with healthy trees, located far from the highway. Results from the analysis showed large amounts of sodium and chlorine in the soil and snow at the damaged site. These elements had accumulated in the needles of the spruce. Moreover, physiological traits of the spruce, at the damaged site were also affected. Therefore, we concluded that poor physiological traits might be attributed to an accumulation of deicing salt in the needles, resulting in the suppression of tree growth.

Phenological patterns of mature longleaf pine ( Pinus palustris Miller) under two different soil moisture regimes

Significant differences in above-ground net primary productivity (ANPP) have been identified along a soil moisture gradient in mature longleaf pine-wiregrass ecosystems [Can. J. For. Res. 29 (1999) 743]. To determine if differences in ANPP were apparent at the individual tree level, patterns of mature longleaf pine ( Pinus palustris Miller) shoot and needle phenology were characterized on xeric and wet/mesic sites in southwest Georgia. Towers provided access to the crowns of the mature trees. Needle abscission patterns were monitored over one growing season (1999); shoot and needle growth patterns were monitored over three growing seasons (1999–2001). Environmental variables, including soil moisture content, predawn needle water potential and gap fraction, as well as several crown structural characteristics, were also measured. Crowns at the two sites had similar average branch characteristics, with the exception of average branch angle, which was significantly greater at the wet/mesic site. The starting dates for shoot elongation and linear shoot growth were similar at the two sites during all 3 years; cessation of shoot growth occurred significantly earlier at the wet/mesic site in 1999. Duration of shoot elongation was longer at the xeric site; however, shoot growth rate was greater at the wet/mesic site. In contrast, during all 3 years, start of needle elongation and start of linear needle growth occurred significantly earlier at the wet/mesic site; cessation of needle growth occurred significantly earlier at the wet/mesic site in 2000. Duration of needle growth was similar at both sites, but needle growth rate was greater at the wet/mesic site in 2000 and 2001. No consistent differences in shoot and needle phenology with crown position were observed, except shoots were longer in the top crown third at the xeric site during 1999 and 2001. Average needle lifespan was determined to be 15 months. Mature longleaf pine exhibited a determinant pattern (one seasonal flush) of shoot and needle growth during the first two growing seasons, and an indeterminate pattern (multiple seasonal flushes) during the third growing season. Soil moisture content was not strongly correlated to patterns of needle abscission; however, predawn needle water potential explained 17% of the variation in early growing season needle demography.

Needle life span, photosynthetic rate and nutrient concentration of Picea glehnii, P. jezoensis and P. abies planted on serpentine soil in northern Japan.

We investigated the adaptation of three spruce species (Picea glehnii Masters, P. jezoensis Carr. and P. abies Karst.) to growth in northern Japan on serpentine soils (characterized by high concentrations of heavy metals and Mg, a low Ca/Mg ratio and low fertility) and fertile brown forest soils. Among species, seedling survival on serpentine soil was highest in P. glehnii. Shoot growth of P. glehnii was similar whether grown on serpentine or brown forest soil, whereas shoot growth of the other species was significantly less on serpentine soil than on brown forest soil. On serpentine soil, needle life span of P. glehnii was at least 3 years longer than that of the other two species. Needle area per shoot of P. glehnii was significantly higher on serpentine soil than on brown forest soil up to a shoot age of 8 years. In all three species, light-saturated photosynthetic rate (Pmax) decreased with needle age independently of soil type. However, on serpentine soil, Pmax in P. glehnii was higher, particularly in older needles, than in the other species. Furthermore, on serpentine soil, needle concentrations of nitrogen and phosphorus were higher in P. glehnii than in the other species. We conclude that P. glehnii is better adapted to serpentine soil than P. jezoensis and P. abies at least in part because of its greater needle life span and higher needle nutrient concentrations.

A model of air-tree-soil system for ozone impact analysis

PGSM is a model of air-tree-soil system, that simulates plant growth subject to the combine influence of stress and stimulus factors from air and soil. The input parameters of tree, soil, and air allow the model to be adapted to any tree, planted at a specific location. Previously, the model was developed to simulate ponderosa pine ( Pinus ponderosa L) exposed to high ozone and drought stresses in Southern California. This paper evaluates the robustness of the model by applying it to loblolly pine ( Pinus taeda L.) in North Carolina. The model was first calibrated with the experimental data of loblolly pine seedlings. The simulated diameter, height, and biomass of canopy, roots and stem were comparable to measured values. The simulated photosynthetic rate was suppressed 15–30% by ozone approximately two times the concentration of ambient air. The measured suppression was 21–27%. After the calibration with seedling data, the model was extended to simulate the growth of mature trees in Duke Forest over a period of 55 years, under the estimated historic time series of meteorology and air quality. The simulated stem diameter and tree height were comparable to the observed. Hypothesis testing with the model suggested that the needle life span might be important to the sensitivity of a pine species to ozone damage.

On the specific pattern of long chain polyprenols in green needles of Pinus mugo Turra.

In green needles of Pinus mugo the most abundant polyprenols occur as a mixture of prenologues in which the dominant alcohol is built of 16 isoprene units. The characteristic spectrum of polyprenols (prenol-15, -16 and -17) was the same irrespective of the location of plant and of distinct morphological differences observed in the various selected forms of this species. The constant pattern of the polyprenols spectrum was preserved throughout the 2-year life span of needles, although the level of polyprenols was increased 2-3-fold. The polyprenol pattern in Pinaceae family differs from species to species, thus it may serve as chemotaxonomic criterion within this systematic group.

Acclimation to low irradiance in Picea abies: influences of past and present light climate on foliage structure and function.

Leaf retention time increases with decreasing irradiance, providing an effective way of amortizing the costs of foliage construction over time. To elucidate the physiological mechanisms underlying this dependence, I studied needle life span, morphology, and concentrations of carbon, nitrogen and nonstructural carbohydrates along a gradient of relative irradiance in understory trees of Picea abies (L.) Karst. Maximum needle life span was greater in shaded trees than in sun-exposed trees. However, irrespective of irradiance, needles with maximum longevity were situated in the middle rather than the bottom of the canopy, suggesting that needle life span is determined by the irradiance to which needles are exposed during their primary growth. Morphology and chemistry of current-year needles were adapted to prevailing light conditions. Current-year needles exposed to high irradiances had greater packing of foliar biomass per unit area than shaded needles, whereas shaded needles maximized foliar area to capture more light. Nitrogen concentrations were higher in shaded needles than in sun-exposed needles. This nitrogen distribution pattern was related to the high nitrogen cost of light interception and was assumed to improve light absorptance per needle mass of shaded needles. In contrast, in both 1- and 2-year-old needles, morphology was independent of prevailing light conditions; however, needle nitrogen concentrations were adjusted toward more effective light interception in 2-year-old foliage but not in 1-year-old foliage, indicating that acclimation of sun-adapted needles to shading takes more than one year. At the same time, needle aging was accompanied by accumulation of nonstructural carbohydrates (NSC), and increasing concentrations of needle carbon, suggesting a shift in the balance between photosynthesis and photosynthate export. The accumulation of NSC and carbon resulted in a dilution of the concentrations of other needle chemicals and explained the decline in needle nitrogen concentrations with increasing age. Thus, although morphological inadequacy to low light availabilities may partly be compensated for by modifications in needle chemistry, age-related changes in needle stoichiometric composition progressively lessen the potential for acclimation to low irradiance. A conceptual model, advanced to explain how environmental factors and age-related changes in the activities of needle xylem and phloem transport affect needle longevity, predicted that adaptation of needle morphology to irradiance during the primary growth period largely determines the fate of needles during subsequent tree growth and development.

Spruce Budworm Defoliation and Growth Loss in Young Balsam Fir: Spacing Effects on Needlefall in Protected Trees

Abstract Age-dependent Weibull models were used to describe precise measurements of needlefall from a pair of protected plots of young, unspaced, balsam fir (Abies balsamea [L.] Mill.). These models showed that the age-specific rates of needlefall tended to increase with needle age throughout the observed crown. Where crown level effects were evident, needle lifespans were shorter in the lower crown than in the upper crown. The influence of crown level in the unspaced plots, however, was too inconsistent to be useful as a general predictor of needlefall rates. Comparing the results with previous work on spaced sample plots showed that spacing affected many aspects of needlefall. The mean needle lifespan of 5.3 yr (SE = 0.17) on the spaced sample plots was significantly greater than the 4.7 yr (SE = 0.22) estimated for the unspaced plots. These differences were most extreme in the lower crown. Spacing also influenced the earliest phase of needlefall. For needles under 2 yr, the mean age-specific rates of fall were negligible in the spaced plots, but were about 6%/yr in the unspaced plots. Thereafter, annual increases in the age-specific rates of needlefall were similar in the spaced and unspaced plots. Spacing also affected the pattern of year-to-year variation in needlefall. There was evidence of statistically significant trends in mean needle lifespans over time in the spaced plots, but not in the unspaced plots. For. Sci. 42(3):282-289.

Modelling the effects of needle mortality rate and needle area distribution on dry matter production of Douglas fir.

A physiological simulation model was used to analyse the effects of increased needle mortality rate and changes in needle area distribution (LAI) on primary production of a Douglas fir (Pseudotsuga menziesii) stand. Needle life-span, which may decrease as a result of air pollution and soil acidification, is an important aspect of forest decline. Results show that simulation models can be used to study the possible consequences of these phenomena in forest stands. The model quantified the relationship between total LAI and stand growth (taking into account different light distributions within the canopy that result from needle area distribution and clustering of needles). The effect of an increase in needle mortality rate was strongly dependent on initial LAI: at low initial LAI, productivity will decrease as a result of an increase in needle mortality and decreased light interception; at high initial LAI, light interception does not necessarily decrease significantly when needle mortality increases, but productivity may even increase because of decreased maintenance respiration. These effects are discussed, and compared with other species, such as Scots pine (Pinus sylvestris) which has a relatively low LAI. The authors recommend using more quantitative techniques in forest decline inventories (e.g. estimating LAI from light interception measurements) in order to account for these LAI differences. (Abstract retrieved from CAB Abstracts by CABI’s permission)