Needle Loss Research Articles

Aufschlüsselung statistischer Beziehungen zwischen dem Nadelverlust von Fichten und anderen Informationen dreier Forstmonitoring-Programme Nordrhein-Westfalens | Itemisation of statistical relationships between needle loss in spruce and other information from three forest monitoring programmes in North-Rhine Westphalia

The paper is an introduction to the statistical model of Classification and Regression Trees (CART) to evaluate forest monitoring data in Germany. The advantages of this method as opposed to cluster methods are identified and illustrated on the example of spruce stands in North-Rhine Westphalia. The results confirm that age, altitude above sea level, chest-high diameter measurements and humus type are closely related to the degree of needle occurrence in spruce,and they reveal a positive correlation between Si-levels and loss of needles.

One-hundred-year foliage comparison of Pinus ponderosa and Pinus sylvestris under dry growing conditions in Brandenburg, Germany

The dynamics of six different needle parameters of Pinus sylvestris L. and Pinus ponderosa Dougl. ex P. & C. Laws. were examined retrospectively for a 112-year-old mixed stand in Brandenburg, Germany, using the needle trace method. Similarities were found in needle production, needle loss and needle density. However, needle age, needle retention and total number of needles revealed significant differences between the tree species, with higher values for P. ponderosa. Pinus ponderosa yielded approximately twice as much mean whole-crown needle dry mass as P. sylvestris. Furthermore, different branching systems could be detected between the species, with both pines following “Corner's rule”. The results suggest that under identical growing conditions, P. ponderosa exhibits more efficient water use and can therefore maintain a bigger crown (as the basis for increased growth) than P. sylvestris.

A Spatial Model for the Needle Losses of Pine-Trees in the Forests of Baden-Württemberg: An Application of Bayesian Structured Additive Regression

Summary The data that are analysed are from a monitoring survey which was carried out in 1994 in the forests of Baden-Württemberg, a federal state in the south-western region of Germany. The survey is part of a large monitoring scheme that has been carried out since the 1980s at different spatial and temporal resolutions to observe the increase in forest damage. One indicator for tree vitality is tree defoliation, which is mainly caused by intrinsic factors, age and stand conditions, but also by biotic (e.g. insects) and abiotic stresses (e.g. industrial emissions). In the survey, needle loss of pine-trees and many potential covariates are recorded at about 580 grid points of a 4 km × 4 km grid. The aim is to identify a set of predictors for needle loss and to investigate the relationships between the needle loss and the predictors. The response variable needle loss is recorded as a percentage in 5% steps estimated by eye using binoculars and categorized into healthy trees (10% or less), intermediate trees (10–25%) and damaged trees (25% or more). We use a Bayesian cumulative threshold model with non-linear functions of continuous variables and a random effect for spatial heterogeneity. For both the non-linear functions and the spatial random effect we use Bayesian versions of P-splines as priors. Our method is novel in that it deals with several non-standard data requirements: the ordinal response variable (the categorized version of needle loss), non-linear effects of covariates, spatial heterogeneity and prediction with missing covariates. The model is a special case of models with a geoadditive or more generally structured additive predictor. Inference can be based on Markov chain Monte Carlo techniques or mixed model technology.

Effectiveness of I–V watering devices in maintaining postharvest freshness and quality of cut Christmas trees

Experiments were carried out with cut Douglas-fir ( Pseudotsuga menziezii (Mirb.) Franco) and Leyland cypress [x Cupressocyparis leylandii (A.B. Jacks. & Dallim.)] Christmas trees to evaluate postharvest water uptake, moisture status, needle loss, and tree quality when water was supplied to displayed trees either by an I–V device or a traditional method of placing the base in water. In both experiments, trees consumed about 4× as much water with the traditional method. Based on measurements of twig moisture content, xylem pressure potential ( Ψ), needle loss, and total water consumption, tree freshness and quality was adequately maintained by the traditional method, but not the I–V device.

Pine mistletoe (Viscum albumssp.austriacum) contributes to Scots pine (Pinus sylvestris) mortality in the Rhone valley of Switzerland

SummaryIn recent years unusual high mortality of Scots pine (Pinus sylvestris) has been observed in the Swiss Rhone Valley. The exact causes, however, are not known. At a 2‐ha monitoring plot, tree mortality and crown condition have been monitored since 1996. Between 1996 and 2004, 59% of the Scots pines died, most of them following the drought periods 1996–1998 and 2003–2004, while only 15% of the deciduous trees died. Crown transparency, needle discolouration, dead branch percentage, mistletoe (Viscum albumssp.austriacum) rating,Tomicussp. shoot feeding, male flowering effect, tree stem diameter, crown shading and social tree class assessed in 1998 were used in a logistic regression model to predict tree mortality. Crown transparency, mistletoe rating and percentage of dead branches were found significant in the model and the probability of tree mortality increased with increasing rankings of these parameters. Needle discolouration could be used to substitute ‘dead branch percentage’ as predictor. While crown transparency increased with mistletoe rating, for trees in the same transparency class, trees with medium and heavy mistletoe infection were two to four times more likely to die than trees with no or only low mistletoe infection. For the surviving trees we found that trees with mistletoes showed a significantly higher increase in transparency in the year following a drought than trees without, while in a drought year the opposite was true. At the beginning of the observations no significant differences in transparency had been found between the trees with and without mistletoe. However, by the end of the observation period trees with mistletoe had significantly higher crown transparency. We conclude that mistletoe infection can be considered as both a predisposing factor for tree death, by increasing needle loss following drought and a contributing factor by increasing water stress during drought.

THE ECOLOGY OF ENERGY AND NUTRIENT FLUXES IN HEMLOCK FORESTS INVADED BY HEMLOCK WOOLLY ADELGID

The hemlock woolly adelgid (HWA, Adelges tsugae Annand) is currently causing a severe decline in vitality and survival of eastern hemlock in North American forests. We analyzed the effects of light HWA infestation on vertical energy and nutrient fluxes from the canopy to the forest floor. Canopy throughfall, litter lysimeters, and laboratory litter microcosms were used to examine the effects of HWA-affected and unaffected throughfall on litter type, leachate, and litter chemistry. Early in the season adelgid infestation caused higher dissolved organic carbon (DOC; +24.6%), dissolved organic nitrogen (DON; +28.5%), and K (+39.3%) fluxes and lower inorganic nitrogen fluxes (-39.8%) in throughfall and in adjacent litter solutions collected beneath infested compared to uninfested trees. Needle litter collected beneath uninfested hemlock had significantly lower N concentrations compared to needles collected beneath infested trees, while no difference in N concentrations was found in birch litter. Bacteria were significantly more abundant on hemlock and birch litter beneath infested trees, while yeasts and filamentous fungi showed no consistent response to HWA throughfall. Litter microcosms showed that less DOC was leaching from birch than from hemlock needles when exposed to HWA throughfall. Overall, NH4-N and DON leachate concentrations were higher from birch than from hemlock litter. Thus, HWA-affected throughfall leads to qualitative and quantitative differences in nitrogen export from the litter layer. The N concentration of hemlock litter did not change with time, but the N concentration in birch litter increased significantly during the course of the experiment, especially when HWA-affected throughfall was applied. We suggest a nonlinear conceptual model for the temporal and vertical transition of energy and nutrient fluxes relative to progressing HWA infestation from a pure hemlock to a birch/maple-dominated forest. Progressive needle loss and changes in needle chemistry are likely to produce a humped-shaped DOC curve, while N fluxes initially decrease as infestation continues but rise eventually with hemlock decline and immigration of hardwood species. These findings suggest that it is necessary to understand the biology and specific physiological/trophic effects of exotic pests on their hosts and associated ecosystem processes in order to decipher the temporal dynamics, direction of change, and functional consequences.

Crown condition as a function of soil, site and tree characteristics

One of the aims of this work is to describe how the target variable “tree vitality” in terms of needle loss is affected by other explanatory variables. To describe such a relationship in a realistic way, we use generalized additive mixed models (GAMMs) which allow to take spatial correlation of the data into account and in addition allow the inclusion of explanatory variables as predictors with the possibility of having non-linear effects. The GAMMs are fitted in a Bayesian framework using Markov chain Monte Carlo techniques. Data are available for two years 1988 and 1994. We select a set of best explanatory variables from a large set of variables including tree-specific variables, such as species, age, nutrients in the needles and site-specific variables such as altitude, relief type, soil depth and content of different nutrients in the top soil. In the two models for 1988 and 1994, different sets of explanatory variables were selected as best predictors. In both models, the effects of explanatory variables allowed a plausible interpretation. For example, the site-specific variables such as relief and soil depth were significant predictors, since these factors determine how well water and nutrient supply is balanced at a specific site. The selected sets of explanatory variables differed between 1988 and 1994, giving an indication of a possible change in the main causes of forest deterioration between 1988 and 1994. From the set of nutrient variables measured in the soil and in the needles, in 1988 altitude a.s.l. and magnesium supply were among the explanatory variables, in 1994 a combination of Al in the soil and the N/K-ratio (in the needles) was selected in the model. In 1988 altitude a.s.l. was among the most important predictors in the model. This is in contrast to 1994 where altitude was not selected. This may have to do with the fact that in the early phase of forest health monitoring (1988) one of the main causes of forest deterioration was magnesium deficiency. Later on this may have changed to a combination of soil acidification and nitrogen eutrophication. Thus by using an adequate model such as the GAMM, sets of explanatory variables for needle loss may be identified. By fitting two GAMMs, with different sets of “best” predictors, at two time points 1988 and 1994, we can detect changes in these sets of “best” predictors over time. This allows us to use the monitoring data with the tree vitality indicator crown condition/needle loss as a tool for forest health management, which may involve decisions about concrete counter measures like e.g. forest liming.

Bud development types as a new macroscopic marker of Norway spruce decline and recovery processes along a mountainous pollution gradient

Summary A new macroscopic marker of decline and recovery processes in Norway spruce ( Picea abies ) based on proportions of bud development types was evaluated in 315 mature trees in two mountainous regions of the Czech Republic. This study was conducted in 1998 at 63 sites located in the Krusne hory Mts, which exhibited a wide range of damage corresponding to a gradient of increasing air pollution load (mainly SO 2 and NO x ) and the Sumava Mts, a relatively unpolluted area. Proportions of bud development types (regular buds, buds with growth potential and aborted buds) were found to refl ect the current intensity of primary shoot formation in crowns as well as a capability to replace needle loss by formation of secondary shoots via differentiation of buds with growth potential. Using cluster analysis, the trees were classifi ed according to the proportion of individual bud development types into one of three shoot growth categories: accelerated, stabilized or decreased shoot growth. Trees with accelerated shoot growth are characterized by intense production of assimilative organs and a small pool of viable buds with growth potential. Trees with stabilized shoot growth have high potential for crown recovery via activation of abundant buds with growth potential, and trees with decreased shoot growth have high rates of aborted buds, slow primary shoot formation and small pools of buds with growth potential. This new marker refl ects well the forest recovery observed in areas with recent decreases in pollution loads. The results indicate that traditional macroscopic markers such as crown defoliation are less sensitive to the current status of tree crowns when compared with the proportion of individual bud development types. The potential of this new marker for forestry practice and tree physiology is discussed.

Shoot growth processes, assessed by bud development types, reflect Norway spruce vitality and sink prioritization

Crown defoliation, is a product of the tree crown status from the past several years of growth, which can be misleading if used as a stress indicator when assessing current Norway spruce vitality. To evaluate recovery processes in previously damaged trees a newly developed macroscopic indicator based on proportions of bud development types was investigated. In 1998 and 1999, 474 mature Norway spruce trees were sampled for macroscopic measurements, 293 trees for tree-ring increments and 40 trees for study of metabolic markers (concentration of chlorophylls, phenolic compounds and lignin). Study sites were located in the Czech Republic, in the Sumava Mts, a relatively unpolluted and undisturbed area, and in the Krusne hory Mts, which exhibited a whole range of tree damage corresponding to a gradient of increasing air pollution load. Three categories of trees were identified which reflect current levels of intensity of shoot formation and capacity to replace potential needle loss by activation of buds with growth potential: accelerated, stabilized and decreased shoot growth. Relative to sink prioritization, we concluded that the highest vitality occurred in trees with stabilized shoot growth and the lowest vitality in trees with accelerated shoot growth. In conifers, the amount of allocated assimilates to low priority carbon sinks (such as stem growth, production of protective chemical compounds and reproductive organs) depends on what is remaining from the shoot growth processes which are of the highest priority. Significant inverse relationships were found between the intensity of shoot growth, tree-ring increments, production of reproductive organs and concentration of phenolic compounds in the needles. The highest allocation of assimilates to crown recovery occurred in trees with crown defoliation of 50–69% indicating forest recovery was observed in the most heavily damaged areas impacted by air pollution in the past. The present criterion of bud development types has potential for forestry management applications as it is easily applied in the field and, in contrast with standard forestry measurement of crown defoliation, it reflects accurately tree recovery and decline processes under multiple stress impacts.

Fungal decomposition of Abies needle and Betula leaf litter

The effect of litter type and incubation temperature on the ability of fungi to decompose leaf litter of subalpine trees was examined by a pure-culture test. Mass loss of Abies needle and Betula leaf litter and utilization patterns of lignin and carbohydrates were investigated under two temperature conditions (20 C and 10 C) and compared for 29 species in basidiomycetes, ascomycetes and zygomycetes. The decomposing ability was generally higher in basidiomycetes than in ascomycetes and zygomycetes. Mass loss (% original mass) of litter was higher in Betula than in Abies and higher at 20 C than at 10 C. The 29 fungi were divided into lignocellulose decomposers, cellulose decomposers and sugar fungi based on their substrate utilization in Abies and Betula litter. Mass loss of lignin and carbohydrates by lignocellulose and cellulose decomposers was higher in Betula than in Abies. Mass loss of carbohydrates was higher at 20 C than at 10 C, but the temperature did not influence mass loss of lignin, indicating lignin decomposition by fungi was less sensitive to temperature than carbohydrate decomposition. Lignin/carbohydrate loss ratio (L/C) of Collybia spp. that caused selective delignification was lower at 20 C than at 10 C. These results indicate that the decomposability of litter, lignin and carbohydrate was different between Abies and Betula and that temperature affected not only the rate at which fungi decompose litter but also the ability of fungi to use lignin and carbohydrates.

Fungal decomposition of Abies needle and Betula leaf litter

The effect of litter type and incubation temperature on the ability of fungi to decompose leaf litter of subalpine trees was examined by a pure-culture test. Mass loss of Abies needle and Betula leaf litter and utilization patterns of lignin and carbohydrates were investigated under two temperature conditions (20 C and 10 C) and compared for 29 species in basidiomycetes, ascomycetes and zygomycetes. The decomposing ability was generally higher in basidiomycetes than in ascomycetes and zygomycetes. Mass loss (% original mass) of litter was higher in Betula than in Abies and higher at 20 C than at 10 C. The 29 fungi were divided into lignocellulose decomposers, cellulose decomposers and sugar fungi based on their substrate utilization in Abies and Betula litter. Mass loss of lignin and carbohydrates by lignocellulose and cellulose decomposers was higher in Betula than in Abies. Mass loss of carbohydrates was higher at 20 C than at 10 C, but the temperature did not influence mass loss of lignin, indicating lignin decomposition by fungi was less sensitive to temperature than carbohydrate decomposition. Lignin/ carbohydrate loss ratio (L/C) of Collybia spp. that caused selective delignification was lower at 20 C than at 10 C. These results indicate that the decomposability of litter, lignin and carbohydrate was different between Abies and Betula and that temperature affected not only the rate at which fungi decompose litter but also the ability of fungi to use lignin and carbohydrates.

Interactions between an above‐ground plant parasite and below‐ground ectomycorrhizal fungal communities on pinyon pine

1 Recent research has demonstrated important linkages between above- and below-ground components of terrestrial ecosystems, but the relationships between aerial parasitic plants, such as dwarf mistletoes, and below-ground organisms, such as mycorrhizal fungi, have not been examined in detail. 2 We examined the relationship between dwarf mistletoe infection, host vigour and the ectomycorrhizal colonization and fungal community composition of pinyon pine (Pinus edulis) using a combination of field observations and glasshouse studies. 3 High levels of dwarf mistletoe infection were not associated with increased mortality or needle loss of infected pinyons, but infected trees had lower shoot growth. 4 Ectomycorrhizal colonization was positively associated with dwarf mistletoe infection severity at two sites in two years. In addition, the ectomycorrhizal fungal community structure of trees with low, intermediate and high levels of dwarf mistletoe were significantly different, primarily due to a shift in the dominance of ascomycete fungi. 5 These higher levels of ectomycorrhizal colonization were associated with increased fungal inoculum under the crowns of pinyons heavily infected with dwarf mistletoe. In addition, 33% more pinyon seedlings were found in the understories of mistletoe-infected trees than uninfected trees. 6 These findings point to complex multi-trophic interactions between the above-ground and below-ground communities of pinyon pine, and suggest that a detailed understanding of host-parasite relationships may require study of other symbionts associated with the host.

Loss of a Sewing Needle in the Tongue During Attempted Tongue Piercing: Report of a Case

ated with the halo vest: A review of 245 cases. J Neurosurg 65:762, 1986 16. Kameyama O, Ogawa K, Suga T, et al: Asymptomatic brain abscess as a complication of halo orthosis: Report of a case and review of the literature. J Orthop Sci 4:39, 1999 17. Nottmier EW, Bondurant CP: Delayed onset generalized tonicclonic seizures as a complication of a halo orthosis. J Neurosurg 92:233, 2000 18. Rosenblum D, Ehrilich V: Brain abscess and psychosis as a complication of a halo orthosis. Arch Phys Med Rehab 76:865, 1995

Seasonal development of Scots pine under climatic warming: effects on photosynthetic production

In boreal conditions under climatic warming, photosynthesis will start earlier in the spring than it does in the present climate. As a first approximation this phenomenon would increase the annual photosynthetic production of boreal conifers, as they can use the high amounts of incoming solar radiation prevailing during spring to a greater extent than in the present climate. However, the recovery of photosynthesis is accompanied by a simultaneous dehardening of the needles. Thus, climatic warming may also cause a premature dehardening of the needles during spring. This may result in needle losses caused by frost damage; so climatic warming may also decrease the annual photosynthetic production of boreal conifers. Using computer simulations with ecophysiological models, these counteracting effects of climatic warming on photosynthetic production were studied in Scots pine (Pinus sylvestris L.) trees growing in southern Finland. The results show that because of our insufficient understanding of the environmental regulation of frost hardiness, it is not possible to conclude which one of the two potential effects will dominate under climatic warming. This finding calls for further empirical development and testing of the frost hardiness models.

Forest production model for upland black spruce stands—Optimal site occupancy levels for maximizing net production

The objective of this study was to develop a forest production model for determining optimal density management regimes for upland black spruce ( Picea mariana (Mill.) B.S.P.) stands based on the maximization of net production. This objective was attained via the development of an allometrically extended stand density management diagram (SDMD), which was used to describe the mass dynamics of biotic and abiotic tree components by initial density regime, site quality and fine root turnover rate. Specifically, periderm, stem, branch, foliage and abiotic crown masses were estimated employing multivariate allometric regression functions based on data derived from 125 destructively sampled trees. Below-ground mass estimates were obtained using generalized allometric relationships derived from the literature. Abiotic masses included three basic components: (1) allometrically estimated retained woody debris consisting of abiotic crown structures that remained attached to the main stem; (2) fine woody debris arising from needle loss, root turnover, and abscission of modular components; (3) coarse woody debris arising from trees which incurred mortality through self-thinning. The algorithmic version of the model (1) simultaneously calculates periodic annual net production estimates (Mg/ha/year) by 10-year intervals over 100-year rotation lengths for eight initial density conditions, (2) given (1), determines the occupancy level for which net production is maximized for each stage of development (decade interval), and (3) given (2), determines the optimal size–density trajectory within the context of a SDMD. Additionally, results derived from multiple model simulations employing a range of initial densities (1500, 1650,…, 16,350 stems/ha), site indices (9, 10,…, 15 m) and fine root turnover rates (0.2, 0.3,…,0.8 proportion/year), indicated that black spruce productivity was maximized when site occupancies were maintained slightly below the zone of imminent competition mortality. Instructions for acquiring an executable version of the model through the Internet are also included.

Variation in Postharvest Quality among Nordmann Fir Provenances

Needle retention is an important trait when selecting for high quality Christmas trees. Nordmann fir [Abies nordmanniana (Stev.) Spach.] is generally considered to have good needle retention, but recent research has shown that when cut trees are allowed to dry, significant needle loss problems can develop. This has the potential to limit the use of this species in situations where trees are harvested early, shipped long distances, sold in warm weather markets and displayed for extended periods of time. A set of 39 provenances where tested to identify provenance differences in needle retention. Branches where collected in two consecutive years in October in 1999 and 2000 and November 2000. Small branch samples where cut and displayed indoors under controlled conditions and allowed to dry. Strong provenance differences in needle loss were seen for all three test dates. No significant interactions were seen among the October collections, but significant rank changes occurred from October to November. Predicted (BLUP) provenance mean values ranged between 11% and 27% for needle loss when branches where allowed to dry, averaging all three tests. Despite only one test location, the study clearly indicates that it should be possible to select for provenances with generally better needle retention characteristics.

Defoliation and growth loss in young Sitka spruce following repeated attack by the green spruce aphid, Elatobium abietinum (Walker)

Green spruce aphid, Elatobium abietinum (Walker), is a serious defoliator of Sitka spruce ( Picea sitchensis (Bong.) Carr.). In a field experiment in Hafren Forest, mid-Wales, different population densities of E. abietinum were created amongst plots of P91 Sitka spruce by applying insecticides and artificially infesting trees with aphids. Trees subjected to high aphid populations (HP treatment) lost 51, 29 and 15% of their older needles because of infestation in 1994, 1997 and 1999, respectively, whereas trees with low aphid populations (LP treatments) suffered only 15% defoliation in 1999. Aphid numbers, defoliation rates and tree growth were monitored from 1993 to 2000, to determine: (1) relationships between defoliation and aphid density, (2) the impact of repeated infestations on spruce growth, and (3) whether previous defoliation influenced subsequent infestation and damage. Defoliation rate showed an asymptotic relationship with E. abietinum density in each year, and was higher relative to aphid density for older age-classes of shoots. Relationships obtained in 1997 and 1999 confirmed previous observations that low E. abietinum densities cause relatively high rates of needle loss. Repeated defoliation in the HP treatment reduced height and volume growth by 8 and 6%, respectively, by the end of the experiment. Reductions in volume increment were related to changes in total needle DW per tree. In 1999, all trees in the experiment were colonised by E. abietinum because of a natural increase in aphid populations, but significantly fewer aphids were recorded on the previously defoliated trees in the HP treatment ( P = 0.007). However, despite lower aphid densities, defoliation rates were similar and growth losses were higher in the HP treatment, suggesting that the differences in aphid density were primarily a reflection of changes in general tree vigour, rather than a result of induced changes in host quality.

Predicting the mortality of Pinus sylvestris attacked by Gremmeniella abietina and occurrence of Tomicus piniperda colonization

The fungus Gremmeniella abietina (Lagerb.) Morelet is widely distributed in the northern hemisphere and causes scleroderris canker in several coniferous species. In Sweden, large areas, mainly with 30- to 40-year-old Scots pine (Pinus sylvestris L.) forests, were attacked by the fungus in 2000. The main aim of this study was to investigate the relationship between tree crown transparency (CT) induced by G. abietina and P. sylvestris tree mortality. Furthermore, regeneration–colonization by Tomicus piniperda (L.) was monitored in the investigated stands. Thirty-five permanent sample plots were established in five P. sylvestris stands (38–46 years old) infected by G. abietina and located in the central part of Sweden. During the 2 years following the attack, the total tree mortality accounted for 380 trees·ha–1 and 6.2 m2·ha–1 on average in the five stands, corresponding to 35% of the trees and 27% of the basal area at the time of the attack. Galleries with broods of T. piniperda occurred in trees with a CT value higher than 97%. A model was derived for predicting the probability of P. sylvestris tree mortality. The mortality of individual trees was found to be related to CT, position of needle loss within the crown (CTPOS), and tree diameter at breast height. Furthermore, there was an interaction between CT and CTPOS and a tendency for CT and site to interact. For a P. sylvestris tree with a 0.16-m diameter at breast height and a CT value of 90% spread throughout the crown, the model indicated a mortality probability of 0.03. Above this CT value, the probability of mortality increased substantially. For coniferous species, irrespective of the cause of damage, a CT value of 90%–95% appears to be a critical range; any values greater than this indicate a high probability of mortality.

Defoliation by the common pine sawfly (Diprion pini) and subsequent growth reduction in Scots pine: a retrospective approach

The foliage status in the main stem of Scots pines (Pinus sylvestris) was studied retrospectively using the needle trace method (NTM) on a stand, seriously defoliated by the pine sawfly (Diprion pini) in the 1980s. Needle density increased abruptly in the seasons following the defoliation. The strongest reduction in annual needle production occurred one year later. As a consequence of lower needle production, the annual number of attached needles decreased three to five years after the defoliation. Needle retention and the average age of attached needles tended to increase after defoliation. In analyses of covariance with the NTM variables, needle density (logarithmic transformed values) and average age of attached needles, had the highest, significant, negative relationship with radial and height increments both in the period prior to the defoliation and in the time when the trees were suffering from defoliation. The relationships between height increment and the number of needles and needle loss were positive and significant. Also radial increment had a positive relationship with the number of needles but not with needle loss. Interestingly, an abrupt increase in the needle density gave a good indication of the effects of a sudden defoliation in pines.

Postharvest Characteristics of Canaan Fir and Fraser Fir Christmas Trees

Needle retention, xylem pressure potential and overall quality of canaan fir (Abies balsamea var. phanerolepis (L.) Mill.) and fraser fir (Abies fraseri (Pursh) Poir.) Christmas trees were evaluated over a 40-day display period. Cut trees were stored outdoors for 24, 48, or 96 hours, and half the trees had a 2.5-cm section trimmed from the basal portion of the stem, before placement in water at an indoor display room. Controls were placed in water immediately after harvest. Xylem pressure potentials and overall quality were similar for both species except for trees stored 96 hours. Untrimmed canaan fir dried to -2.4 MPa and was rated below average by the end of the display period compared to -1.3 MPa and a good quality rating for fraser fir. Needle retention and color characteristics were excellent across all treatments for fraser fir during the entire display period. Needle loss for canaan fir began relatively soon during display, generally increased across all treatments, and was highly variable. In addition, quality of some canaan fir trees decreased as needles turned brown, but did not shed during the display period. Tree water status alone did not completely account for loss of needles and quality in canaan fir; the need exists to identify seed sources with better postharvest characteristics.