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1.
We investigated current shoot properties in two contrasting vertical positions (leader crown; LC, and lower branch; LB) within the crowns of mature trees of two subalpine conifer species, Abies mariesii and A. veitchii. For both LCs and LBs, shoot length decreased with increasing branching order. However, shoot properties were different between LCs and LBs. Shoots in LCs had more needle biomass per unit of shoot length. Shoots in sunny conditions pack needles closer along the shoot and intercept incoming light more completely. This causes the shoots in the LCs to have more needles. In contrast, less needle packing per unit shoot length in LBs results in the avoidance of mutual shading among needles in order to intercept limited light more effectively. Because branch systems in lower layers tend to be more shaded, the quantity of irradiance received by the shoots in LBs is smaller. Thus, reduced needle amounts on the shoots in LBs reflect the needle arrangement acclimating to the lower light availability. This study suggests the importance of changes in the properties of individual shoot as a component of a branch system and accordingly a whole-crown system in mature canopy trees of A. mariesii and A. veitchii.  相似文献   

2.
Structural characteristics of Abies mariesii M.T. Mast. saplings growing in sun and shade in a snowy subalpine parkland in central Japan were assessed to infer how saplings acclimate to suppression by larger individuals in a conifer clump and to extremely snowy conditions. Sun and shade saplings produced structurally different current-year shoots, and allocated biomass to needles and stem differently. Compared with sun saplings, shoots of shade saplings had lower needle mass per unit shoot size, which indicates less dense needle packing and more effective use of the limited available light by avoiding mutual shading among needles. Biomass allocation within lateral branches also differed between sun and shade saplings. Compared with sun saplings, needle mass was a smaller proportion of total branch mass in shade saplings although shade saplings retained needles for longer, thereby compensating, in part, for their lower annual production of needles. Thus shade saplings incur a high mechanical cost to support their low-light acclimated, conspicuously flattened crowns in this snowy habitat. Suppressed saplings are an important component of the persistent conifer clumps in snowy subalpine parklands. The observed structural characteristics of A. mariesii saplings, which ensure high shade- and snow-tolerance, contribute to the dominance of the species in snowy subalpine regions in Honshu, Japan.  相似文献   

3.
Mori A  Takeda H 《Tree physiology》2004,24(6):661-670
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.  相似文献   

4.
The impacts of thinning, fertilization and crown position on seasonal growth of current-year shoots and foliage were studied in a 13-year-old loblolly pine (Pinus taeda L.) plantation in the sixth post-treatment year (1994). Length of new flushes, and their needle length, leaf area, and oven-dry weight were measured in the upper and lower crown from March through November. Total shoot length was the cumulative length of all flushes on a given shoot and total leaf area per shoot was the sum of leaf areas of the flushes.

By the end of June, first-flush foliage reached 70% of the November needle length (14.3 cm) and 65% of the final leaf area (15.0 cm2). Cumulative shoot length of first- and second-flush shoots achieved 95% of the annual length (30.3 cm), whereas total leaf area per shoot was 55% of the final value (75.3 dm2). Fertilization consistently stimulated fascicle needle length, dry weight, and leaf area in the upper crown. Mean leaf area of upper-crown shoots was increased by 64% six years after fertilization. A significant thinning effect was found to decrease mean leaf area per shoot in the crown. For most of the growing season, the thinned-fertilized trees produced substantially more leaf area per shoot throughout the crown than the thinned-nonfertilized trees. These thinned-fertilized trees also had greater needle length and dry weight, longer first flush shoots, and more leaf area per flush than trees in the thinned-nonfertilized plots. Needle length and leaf area of first flush shoots between April and July were linearly related to previous-month canopy air temperature (Ta). Total shoot length strongly depended on vertical light gradient (PPFD) within the canopy, whereas shoot leaf area was a function of both PPFD and Ta. Thus, trees produced larger and heavier fascicles, more and longer flush shoots, and more leaf area per shoot in the upper crown than the lower crown. We conclude that thinning, fertilization, and crown position regulate annual leaf area production of current-year shoots largely by affecting the expansion of first flush shoots and their foliage during the first half of the growing season.  相似文献   


5.
Montane red spruce (Picea rubens Sarg.) in the northeastern United States has undergone a decline during the past two decades. One symptom associated with the decline syndrome is the episodic browning of first-year foliage in early spring. To examine the potential role of winter desiccation in this browning, the water relations of red spruce foliage in a subalpine forest on Mt. Moosilauke, New Hampshire, USA, were monitored from January to May, 1989. All sampled trees lost water during the winter and the first-year foliage on some trees turned brown in early spring. The relative water content of first-year shoots during the winter was a significant predictor of spring browning; red spruce trees that showed browning had desiccated faster and reached lower relative water contents. Damaged trees also had more closely packed needles and lower cuticular resistances to water loss. The first-year shoots had a significantly lower average relative water content than older shoots before and after browning. Cuticular resistance to water loss decreased with elevation. Sun-exposed shoots lost more water than shaded shoots because of solar heating of needles. Winter desiccation can occur before the decline-related spring browning of red spruce foliage.  相似文献   

6.
Total foliage dry mass and leaf area at the canopy hierarchical level of needle, shoot, branch and crown were measured in 48 trees harvested from a 14-year-old loblolly pine (Pinus taeda L.) plantation, six growing seasons after thinning and fertilization treatments.

In the unthinned treatment, upper crown needles were heavier and had more leaf area than lower crown needles. Branch- and crown-level leaf area of the thinned trees increased 91 and 109%, respectively, and whole-crown foliage biomass doubled. The increased crown leaf area was a result of more live branches and foliated shoots and larger branch sizes in the thinned treatment. Branch leaf area increased with increasing crown depth from the top to the mid-crown and decreased towards the base of the crown. Thinning stimulated foliage growth chiefly in the lower crown. At the same crown depth in the lower crown, branch leaf area was greater in the thinned treatment than in the unthinned treatment. Maximum leaf area per branch was located nearly 3–4 m below the top of the crown in the unthinned treatment and 4–5 m in the thinned treatment. Leaf area of the thinned-treatment trees increased 70% in the upper crown and 130% in the lower crown. Fertilization enhanced needle size and leaf area in the upper crown, but had no effect on leaf area and other variables at the shoot, branch and crown level. We conclude that the thinning-induced increase in light penetration within the canopy leads to increased branch size and crown leaf area. However, the branch and crown attributes have little response to fertilization and its interaction with thinning.  相似文献   


7.
Boyce RL  Saunders GP 《Tree physiology》2000,20(16):1077-1086
Water relations of Engelmann spruce (Picea engelmannii Parry) and subalpine fir (Abies lasiocarpa (Hook.) Nutt.) trees growing at an elevation of 3230 m on Mt. Evans, Colorado, USA, were studied during the winters of 1995-1996 and 1996-1997. During both winters, current-year and 1-year-old shoots were collected weekly and their relative water contents (RWC) determined. Measured meteorological parameters were used in a conifer winter water relations model, WINWAT, to simulate changes in shoot RWC of P. engelmannii and A. lasiocarpa during the winter. The model failed to predict shoot RWCs in 1996-1997 when calibrated with 1995-1996 data. The cold early summer of 1995 inhibited xylem formation, which appears to have caused lower rates of water recharge to the needles during the 1995-1996 winter than during the 1996-1997 winter. We conclude that summer climate strongly affects winter water relations in these subalpine species, and that changes in both summer and winter climate must be considered when predicting future ranges of these species.  相似文献   

8.
The research described in this paper was performed in the Niepolomice Forest (Southern Poland) in 2001 as part of the Forest Environmental Monitoring and Management System (FOREMMS; 5FP IST) project. The material for the present study consisted of the measurement results of the biomass of Scots pine shoots with needles and needles alone carried out on 113 felled sample trees. The purpose of this study was to construct empirical equations for estimating the foliage biomass of Scots pine from easy to measure parameters. To achieve this aim, the dependence of the foliage biomass of Scots pine on stem diameter, height, age, crown length, basal area increment of the trees was analyzed. Using the biometric characteristics such as: tree diameter at breast height (dbh), basal area increment, age, height, and crown length empirical equations for estimating the foliage biomass of Scots pine reasonably precisely have been established. The created empirical equation gives accurate foliage biomass estimates. The explained variability varies between 65 and 85%, it depends on the number of variables applied in the equation. The equations presented in this paper were created with a view to their possible use in ecological studies where biomass quantity may be used, for example, in modeling carbon circulation in the forest ecosystem. From the point of view of forestry practice, these equations may help to assess biomass production in Scots pine stands.  相似文献   

9.
Proe MF  Mead DJ  Byrne D 《Tree physiology》2000,20(10):653-661
Stem injection of (15)N-labeled ammonium sulfate was used to determine effects of pruning on canopy nitrogen dynamics in open-grown Pinus radiata D. Don in New Zealand. Trees were planted in July 1990 and the isotope introduced in December 1994. Tree crowns were divided into three zones: base section, from which branches of pruned trees were removed; mid section, between the pruned zone and the height of the trees at the start of the year in which they were pruned; and top section, which grew predominantly after the isotope was applied. Pruning removed 32% of the green crown length, representing 75% of foliage biomass. Needles were sampled from each region of the crown until July 1996. Branch growth was used to predict foliage biomass for each sampling occasion. Approximately 45% of the applied isotope was recovered from needles sampled in December 1994 (1 week after application and immediately before pruning), two-thirds of which occurred in needles in the base section. Thereafter, changes in isotope content of needles in the base section of unpruned trees largely reflected foliage biomass fluctuations and dilution of the isotope by continued uptake from the unlabeled soil nitrogen pool. Recovery of isotope in needles from the mid-crown section increased by 58 and 86% from December 1994 to July 1995 in control and pruned trees, respectively. Within this crown section, there was evidence of isotope translocation from old to new needles, with both isotope dilution and efflux observed in the needle cohorts that had been present at the time the isotope was applied. Therefore, isotope dynamics did not reflect the dynamics of the total nitrogen pool in the mid-crown section. By July 1996, a small proportion of the applied isotope was recovered from the new foliage formed in the top section of the crown. Within the top section, isotope dynamics closely matched total nitrogen fluxes. Pruning the lower crown did not affect nitrogen dynamics elsewhere in the crown for the following 18 months.  相似文献   

10.
Grassi G  Minotta G 《Tree physiology》2000,20(10):645-652
Norway spruce seedlings (Picea abies Karst.) were grown in low light for one year, under conditions of adequate and limiting nutrition, then transferred to high light. Three months after transfer we measured photosynthesis, leaf nitrogen concentration, leaf chlorophyll concentration and leaf mass per area (LMA) of current-year and 1-year-old shoots; silhouette area ratio (SAR, the ratio of shoot silhouette area to projected needle area) was also measured in current-year shoots. At the foliage level, the effects of light and nutrient treatments differed markedly. Light availability during foliage expansion primarily affected LMA and SAR (morphological acclimation at the needle and shoot level, respectively). By contrast, nutrient supply in high light affected photosynthetic capacity per unit of leaf tissue (physiological acclimation at the cellular level) but did not affect LMA and SAR. The capacity for shade-sun acclimation in foliage formed before transfer to high light differed greatly from that of foliage formed following the transfer. The morphological inflexibility of mature needles (measured by LMA) limited their shade-sun acclimation potential. In contrast, at high nutrient supply, shoots that developed just after the change in photosynthetic photon flux density largely acclimated, both morphologically and physiologically, to the new light environment. The acclimation response of both current- and 1-year-old shoots was prevented by nutrient limitation. Analysis of growth at the whole-plant level largely confirmed the conclusions drawn at the shoot level. We conclude that nutrient shortage subsequent to the opening of a canopy gap may strongly limit the acclimation response of Norway spruce seedlings. Successful acclimation was largely related to the plant's ability to produce sun foliage and adjust whole-plant biomass allocation rapidly.  相似文献   

11.
King DA 《Tree physiology》1991,9(3):369-381
Relationships between tree height and crown dimensions and trunk diameter were determined for shade-tolerant species of old-growth forests of western Oregon. The study included both understory and overstory species, deciduous and evergreen angiosperms and evergreen conifers. A comparison of adult understory species with sapling overstory species of similar height showed greater crown width and trunk diameter in the former, whether the comparison is made among conifers or deciduous trees. Conifer saplings had wider crowns than deciduous saplings, but the crown widths of the two groups converged with increase in tree height. Conifer saplings had thicker trunks than deciduous saplings of similar crown width, possibly because of selection for resistance to stem bending under snow loads. The results suggest that understory species have morphologies that increase light interception and persistence in the understory, whereas overstory species allocate their biomass for efficient height growth, thereby attaining the high-light environment of the canopy. The greater crown widths and the additional strength requirements imposed by snow loads on conifer saplings result in less height growth per biomass increment in conifer saplings than in deciduous saplings. However, the convergence in crown width of the two groups at heights greater than 20 m, and the proportionately smaller effect of snow loads on large trees, may result in older conifers equalling or surpassing deciduous trees in biomass allocation to height growth.  相似文献   

12.
Norway spruce trees in the subalpine forests of the European Alps are frequently attacked by the needle rust Chrysomyxa rhododendri. The obligate parasite undergoes a complex life cycle with a host shift between rhododendrons (Rhododendron sp.) and Norway spruce [Picea abies (L.) Karsten] and causes a yellowing and defoliation of the current-year needles in summer. Infected trees show several anatomical, morphological and physiological modifications, including a decrease in pigment content and net photosynthesis of infected needles, lower biomass production and reduced radial and height growth. The consequences are diminished timber yield and cripple growth. Because of repeated heavy infections in recent years, forest managers report increasing difficulties in both natural regeneration and afforestation at high elevation sites, where rhododendrons occur. This review gives a summary of the present knowledge about the effects of C. rhododendri infections on Norway spruce, including so far unpublished findings and with particular attention to the phenomena of resistant trees. Implications for subalpine forests and counter strategies are discussed.  相似文献   

13.
Dwarf mistletoes (Arceuthobium species) are arboreal, hemiparasitic plants of conifers that can change the structure and function of the tree crown. Hemlock dwarf mistletoe (Arceuthobium tsugense subsp. tsugense) principally parasitizes western hemlock (Tsuga heterophylla) and effects 10.8% of all western hemlock trees in Oregon, USA. In this study, we climbed 16 western hemlock trees (age 97–321 years, height 33–54.7 m) across a gradient of infection (0%–100% of branches infected) and measured occurrence of all dwarf mistletoe infections, dwarf mistletoe caused deformities, foliage, branch and crown metrics, and sapwood area. We then modelled over 25 different response variables using linear and generalized linear models with three metrics of severity as explanatory variables: total infection incidence, proportion of all live branches infected, and proportion of all live, infected branches with 33 per cent or more foliage distal to infection. A strong effect of dwarf mistletoe intensification was the reduction of branch foliage and an increase in the proportional amount of foliage distal to infections, with severely infected trees having the majority of foliage distal to infections. Increasing severity led to an apparent crown compaction as crown volumes decreased and became increasingly comprised of deformities. Sapwood area was unrelated to infection severity. Branch length and diameters were unrelated to increasing infection severity despite severely infected branches supporting 1–70 infections. The most severely infected tree had 3,615 individual plants in the crown. Our results suggested that shifts in crown structure and branch deformation, foliage amount, and foliage distal to infection, reflected a likely reduction of capacity for tree growth that coincided with a hypothesized increase in resource demand by dwarf mistletoe plants as infection severity intensified.  相似文献   

14.
Chrysomyxa rhododendri (DC.) De Bary is a needle rust with a host shift between Rhododendron sp. and Norway spruce (Picea abies (L.) Karst.), penetrating only the new developing flushes of the conifer. Because little is known about its effects on trees, we investigated several parameters related to photosynthesis in artificially infected 3-year-old Norway spruce seedlings. The potential efficiency of photosystem II (PSII; derived from chlorophyll fluorescence measurements) was reduced in infected current-year needles as soon as disease symptoms were visible, about three weeks after inoculation. Two weeks later, photosynthetic O(2) evolution (P(max)) of infected needles was less than 20% of control needles, whereas respiratory O(2) uptake (R(D)) was about three times higher than that of control needles. Nonstructural carbohydrate concentrations were about 60% of control values in all parts of the shoots of infected trees. Photosynthetic inhibition was associated with marked decreases in chlorophyll concentration and chlorophyll a/b ratio but only a small reduction in carotenoid concentration. In infected trees, P(max) of noninfected 1-year-old and 2-year-old needles was 50 and 80% higher than in the corresponding age class of needles of control trees. Estimation of potential daily net dry mass production, based on P(max), R(D), specific leaf area, carbon content and needle biomass, indicated that seedlings infected once were able to produce 60%, and those infected twice only 25%, of the dry mass of controls. We conclude that afforestation and regeneration of Norway spruce is seriously impaired in regions where seedlings are frequently attacked by Chrysomyxa.  相似文献   

15.
Photosynthesis of tree seedlings is generally enhanced during short-term exposure to elevated atmospheric CO2 partial pressure, but longer-term studies often indicate some degree of photosynthetic adjustment. We present physiological and biochemical evidence to explain observed long-term photosynthetic responses to elevated CO2 partial pressure as influenced by needle age and canopy position. We grew Pinus radiata D. Don. trees in open-top chambers for 5 years in sandy soil at ambient (36 Pa) and elevated (65 Pa) CO2 partial pressures. The trees were well watered and exposed to natural light and ambient temperature. In the fourth year of CO2 exposure (fall 1997), when foliage growth had ceased for the year, photosynthetic down-regulation was observed in 1-year-old needles, but not in current-year needles, suggesting a reduction in carbohydrate sink strength as a result of increasing needle age (Turnbull et al. 1998). In 5-year-old trees (spring 1997), when foliage expansion was occurring, photosynthetic down-regulation was not observed, reflecting significantly large sinks for carbohydrates throughout the tree. Net photosynthesis was stimulated by 79% in trees growing in elevated CO2 partial pressure, but there was no significant effect on photosynthetic capacity or Rubisco activity and concentration. Current-year needles were more responsive to elevated CO2 partial pressure than 1-year-old needles, exhibiting larger relative increases in net photosynthesis to elevated CO2 partial pressure (98 versus 64%). Lower canopy and upper canopy leaves exhibited similar relative responses to growth in elevated CO2 partial pressure. However, needles in the upper canopy exhibited higher net photosynthesis, photosynthetic capacity, and Rubisco activity and concentration than needles in the lower canopy. Given that the ratio of mature to juvenile foliage mass in the canopy will increase as trees mature, we suggest that trees may become less responsive to elevated CO2 partial pressure with increasing age. We conclude that tree response to elevated CO2 partial pressure is based primarily on sink strength and not on the duration of exposure.  相似文献   

16.
The needles of pine trees are indicative of the overall health of the tree, and their length is affected by many factors. This study describes the effect of high levels of pathogen infection on lengths of both needles and shoots. Dothistroma septosporum is an important foliar pathogen of pines causing necrosis and premature defoliation with successive years of high infection leading to growth reduction and in extreme cases tree death. Corsican pine trees with all foliage infected by D. septosporum had needles of primary, secondary and tertiary shoots reduced by 31.8%, 44.0% and 64.2%, respectively, compared to non‐infected trees. Needle lengths were reduced both in the upper and lower portions of the canopy, with a greater reduction lower in the canopy. Trees with high levels of infection had shorter shoots in the upper canopy with fewer, shorter needles on these shoots compared to trees with low levels of infection. The results demonstrate the substantial negative effect on needle and shoot lengths of trees with high levels of D. septosporum infection, comparable to factors such as water and nutrient availability known to have a strong influence on these parameters. The reductions in length reduce the photosynthetic capacity of the tree and compound the immediate reductions caused by necrosis and premature defoliation. These effects on needle and shoot lengths contribute to the reductions in volume growth of affected trees and, moreover, are longer lasting than the immediate effects of necrosis and premature defoliation.  相似文献   

17.
Kolari KK  Sarjala T 《Tree physiology》1995,15(11):747-752
From March to October, acid phosphatase activity and phosphorus (P) concentration were measured in four needle age classes of the upper and lower crowns of fertilized and unfertilized Scots pine (Pinus sylvestris L.) trees. Negative correlations between acid phosphatase activity and P concentration were observed in current-year needles and in needles in the upper part of the crown, whereas there was a positive correlation between enzyme activity and P concentration in older needles and in needles in the lower part of the crown. In May and October, needles of all ages showed increased acid phosphatase activity. The most sensitive response of acid phosphatase activity to phosphate supply and phosphorus status of the whole tree was seen in current-year needles on the first whorl where a 300% increase in acid phosphatase activity was observed in response to a decrease in foliar P concentration of 1.7-1.8 mg P g(DW) (-1).  相似文献   

18.
On calm, cold days in winter, sun-exposed needles of red spruce (Picea rubens Sarg.) may warm 10 to 20 degrees C above ambient air temperature, and undergo rapid (>/= 1 degrees C min(-1)) fluctuations in temperature as light breezes or passing clouds alter the energy balance of the foliage. It has been proposed that the resulting rapid freeze-thaw cycles (freezing stress) cause a type of winter injury in montane red spruce that is characterized by necrosis of sun-exposed foliage. In autumn and winter, we monitored rapid freezing stress response of needle sections from 10 montane red spruce trees by subjecting needles to rapid freezing over the temperature span typically recorded in the field. In autumn, experimental rapid freezing stress produced severe injury only at temperatures considerably lower than expected for that time of year. In winter, rapid freezing caused occasional, moderate injury in fully hardened foliage of trees susceptible to both slow and rapid freezing. Seasonal changes in sensitivity to rapid and slow freezing were correlated, suggesting that environmental factors that are known to affect sensitivity to slow freezing may also affect sensitivity to rapid freezing. Experimental manipulation of the start and end temperatures of rapid freezing stress events showed that moderate to severe needle injury can occur in susceptible trees at temperature spans slightly more extreme than those typically recorded in the field. The extent of injury was similar at different starting temperatures if rapid freezing occurred over the same temperature span. Year-old foliage was consistently less sensitive to rapid freezing stress than current-year foliage, but some year-old foliage was damaged when the rapid freezing stress regime caused severe injury in current-year foliage. We conclude that rapid freeze-thaw cycles can explain light to moderate injury of current-year foliage, but they do not explain the more severe and widespread pattern of foliar damage that has occurred intermittently over at least the last 18 years.  相似文献   

19.
Vitellaria paradoxa, known as Shea tree or karité, is one of the dominant trees of agroforestry parklands in Sahelian region with an immense commercial value. In this study, we examined infestation of fruit-bearing shoots and fruits on two sites in western Burkina Faso across different reproductive phenophases, crown heights and aspects. The number of infested and healthy shoots and fruits were counted on 60 reproductively active trees randomly selected from on-year shea trees in each site, using a metal frame (0.5 × 0.5 m) to mark a fixed area of the canopy for sampling. The shoot and fruit borer was identified as Salebria sp. (Lepidoptera:Pyralidae), which was not reported earlier. The proportion of infested trees and shoots varied significantly between sites and among reproductive phenophases (P < 0.0001). The site close to the natural forest had the highest infestation rate than distantly located site. Among reproductive phenophases, the proportions of infested trees and shoots were the highest during flowering and fruit set, respectively. Fruit infestation also varied significantly between sites, crown heights and aspects (P < 0.001). The site close to the natural forest and the crown with north-east aspect were heavily infested while the bottom part of the crown had the lowest infestation. As a whole, 49–80% of trees, 24–31% of shoots and 4–15% of fruits were found infested, depending on the site. These infestation levels combined with precocious flower and fruit abscissions would pose serious economic losses that justify a call for immediate pest control initiatives.  相似文献   

20.
The stand density of a forest affects the vertical distribution of foliage. Understanding the dynamics of this response is important for the study of crown structure and function, carbon-budget estimation, and forest management. We investigated the effect of tree density on the vertical distribution of foliage, branch, and stem growth, and ratio of biomass increment in aboveground tissues; by monitoring all first-order branches of five trees each from thinned and unthinned control stands of 10-year-old Chamaecyparis obtusa for four consecutive years. In the control stand, the foliage crown shifted upward with height growth but the foliage quantity of the whole crown did not increase. In addition, the vertical distribution of leaf mass shifted from lower-crown skewed to upper-crown skewed. In the thinned stand in contrast, the foliage quantity of individual crowns increased two-fold within 4 years, while the vertical distribution of leaf mass remained lower-crown skewed. The two stands had similar production rates, numbers of first-order branches per unit of tree height, and total lengths of first-order branches. However, the mortality rate of first-order branches and self-pruning within a first-order branch were significantly higher in the control stand than in the thinned stand, which resulted in a higher ratio of biomass increment in branch. Thinning induced a higher ratio of biomass increment in foliage and lower in branch. The increased foliage quantity and variation in ratio of biomass increment after thinning stimulated stem growth of residual trees. These results provide information that will be useful when considering thinning regimes and stand management.  相似文献   

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