首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 781 毫秒
1.
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   

2.
Since individual tree leaf area is an important measure for productivity as well as for site occupancy, it is of high interest in many studies about forest growth. The exact determination of leaf area is nearly impossible. Thus, a common way to get information about leaf area is to use substitutes. These substitutes are often variables which are collected in a destructive way which is not feasible for long term studies. Therefore, this study aimed at testing the applicability of using substitutes for leaf area which could be collected in a non-destructive way, namely crown surface area and crown projection area. In 8 stands of Norway spruce (Picea abies L. Karst.), divided into three age classes and two thinning treatments, a total of 156 trees were felled in order to test the relationship between leaf area and crown surface area and crown projection area, respectively. Individual tree leaf area of the felled sample trees was estimated by 3P-branch sampling with an accuracy of ±10%. Crown projection area and crown surface area were compared with other, more commonly used, but destructive predictors of leaf area, namely sapwood area at different heights on the bole. Our investigations confirmed findings of several studies that sapwood area is the most precise measure for leaf area because of the high correlation between sapwood area and the leaf area. But behind sapwood area at crown base and sapwood area at three tenth of the tree height the predictive ability of crown surface area was ranked third and even better than that of sapwood area at breast height (R2 = 0.656 compared with 0.600). Within the stands leaf area is proportional to crown surface area. Using the pooled data of all stands a mixed model approach showed that additionally to crown surface area dominant height and diameter at breast height (dbh) improved the leaf area estimates. Thus, taking dominant height and dbh into account, crown surface area can be recommended for estimating the leaf area of individual trees. The resulting model was in line with many other findings on the leaf area and leaf mass relationships with crown size. From the additional influence of dominant height and dbh in the leaf area model we conclude that the used crown model could be improved by estimating the position of the maximum crown width and the crown width at the base of the crown depending on these two variables.  相似文献   

3.
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   


4.
Crown architecture and growth allocation were studied in saplings of eastern white pine (Pinus strobus L.), a species classified as intermediate in shade tolerance. A comparison was made of 15 understory saplings and 15 open-grown saplings that were selected to have comparable heights (mean of 211 cm, range of 180-250 cm). Mean ages of understory and open-grown trees were 25 and 8 years, respectively. Understory trees had a lower degree of apical control, shorter crown length, and more horizontal branch angle, resulting in a broader crown shape than that of open-grown trees. Total leaf area was greater in open-grown saplings than in understory saplings, but the ratio of whole-crown silhouette (projected) leaf area to total leaf area was significantly greater in understory pine (0.154) than in open-grown pine (0.128), indicating that the crown and shoot structure of understory trees exposed a greater percentage of leaf area to direct overhead light. Current-year production of understory white pine was significantly less than that of open-grown white pine, but a higher percentage of current-year production was allocated to foliage in shoots of understory saplings. These modifications in crown structure and allocation between open-grown and understory white pine saplings are similar to those reported for more shade-tolerant fir (Abies) and spruce (Picea) species, but the modifications were generally smaller in white pine. As a result, white pine did not develop the flat-topped "umbrella" crown structure observed in understory fir and spruce, which approaches the idealized monolayer form that maximizes light interception. The overall change to a broader crown shape in understory white pine was qualitatively similar, but much more limited than the changes that occurred in fir and spruce. This may prevent white pine from persisting in understory shade as long as fir and spruce saplings.  相似文献   

5.
Induced (traumatic) resin in white spruce (Picea glauca (Moench) Voss) leaders resistant or susceptible to the white pine weevil (Pissodes strobi Peck) was analyzed for volatile terpenes and diterpene resin acids after simulated white pine weevil damage. Leaders from 331 trees were wounded just below the apical bud with a 1-mm diameter drill, coinciding with the natural time of weevil oviposition in the spring. Leaders were removed in the fall, and the bark and xylem from the upper and lower regions of the leader extracted and analyzed by gas chromatography. Unwounded trees had low amounts of resin in xylem compared with bark. In response to wounding, volatile terpenes and diterpene resin acids increased in the upper xylem (area of wounding), with resistant trees showing a greater increase than susceptible trees. Wounding caused monoterpenes in particular to decrease in the lower region of the leader (away from the drilled area) in greater amounts in susceptible trees than in resistant trees. In response to wounding, the proportion of monoterpene to resin acid increased in the upper and lower xylem of resistant trees, and slightly increased in the upper xylem of susceptible trees. Monoterpene-enriched resin is more fluid than constitutive resin, and probably flows more readily into oviposition cavities and larval mines, where it may kill immature weevils. Loss of resin components in the lower xylem suggested catabolism and transport of these materials to the site of wounding; however, energetic and regulatory data are necessary to confirm this hypothesis. This study provides a basis for measuring the ability of a tree to undergo traumatic resinosis that could be used to screen for resistance to white pine weevil.  相似文献   

6.
Sustained management of natural forest depends on their ability to regenerate. The pace at which older trees are replaced by younger ones is important in this respect. This study was conducted to assess the demographic details of natural regeneration dynamics of south Indian moist deciduous forests. The status of natural regeneration has been assessed in eight localities of varying levels of disturbance in Thrissur Forest Division of Kerala State of southwest India. Enumeration of trees and their regeneration were analyzed at three levels of organization; whole-stand, stratum, and species.The trees of the forest were grouped into upper, middle and lower vertical strata. Species richness was highest in the middle stratum. Upper stratum species were commercially important. The mean basal area for the Forest Division was 12.83 m2/ha. and average number of trees per hectare (>=20 cm dbh) was 150. Regeneration of the upper stratum species was higher at about 10% gap in the canopy.The growing stock of established seedlings and saplings (height > 100 cm and dbh <=10cm) was very low compared to unestablished seedlings (height <=100 cm). Owing to very low survival probability in the sapling stage (dbh >=1 cm to <=10 cm), a low numbers of poles (dbh >=10 cm to <=20 cm) in the upper stratum was observed. Presence of fire, grazing, browsing and over expoitation by humans are the major constraints of natural regeneration recognized in these forests.  相似文献   

7.
To evaluate the relationship of overstory residual trees to the growth of unmanaged young-to-mature understory Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) and western hemlock (Tsuga heterophylla (Raf.) Sarg.), the basal area and volume of 14 paired plots with and without residual trees were examined in the Willamette National Forest, Oregon. Residual trees were large survivors of the fires that initiated the understory between 55 and 121 yr ago. Understory stands were naturally regenerated and not managed in any way. High residual tree and understory densities were negatively associated with understory volume. The relation of density of residual trees to total understory and Douglas-fir basal areas and volumes was best described by a negative logarithmic function. The rate of decrease in total understory and Douglas-fir basal areas and volumes per individual residual tree became smaller with increasing residual-tree density. Predicted total understory volume reduction was 23% with five residual trees/ha and 47% with 50 residual trees/ha, averaging 4.6% and 0.9% per residual tree, respectively. After including the estimated volume growth of residual trees since initiation of the understory, stand volume was still 19% lower with five residual trees/ha and 41% lower with 50 residual trees/ha than in stands with no residual trees, averaging a reduction of 38% and 0.8% per residual tree, respectively. In mixed stands of Douglas fir and western hemlock, predicted Douglas-fir basal area and volume declined more rapidly than did total understory basal area and volume when residual-tree densities exceeded about 15 trees/ha. This difference was probably due to the relative shade-intolerance of Douglas fir. Predicted Douglas-fir volume reduction was 13% with five residual trees/ha and 75% with 50 residual trees/ha, averaging 2.6% and 1.5% per residual tree, respectively. The southern aspects had more than 150% the total understory basal area and volume and more than 200% the Douglas-fir volume and basal area of the northern aspects. Lower density and basal area of understory trees, particularly of dominant and codominant Douglas fir, were associated with increasing residual-tree densities. Given the same diameter at breast height (DBH), heights of Douglas fir were not related to residual trees. Regardless of understory age, understory volume was greatest in stands with the lowest understory densities. These results suggest that timber production in unthinned green-tree retention units may be reduced and may depend on the density of leave-trees. Thinning of understory trees is recommended to reduce growth loss from intraspecific competition.  相似文献   

8.
We examined the vertical profiles of leaf characteristics within the crowns of two late-successional (Fagus crenata Blume and Fagus japonica Maxim.) and one early-successional tree species (Betula grossa Sieb. et Zucc.) in a Japanese forest. We also assessed the contributions of the leaves in each crown layer to whole-crown instantaneous carbon gain at midday. Carbon gain was estimated from the relationship between electron transport and photosynthetic rates. We hypothesized that more irradiance can penetrate into the middle of the crown if the upper crown layers have steep leaf inclination angles. We found that such a crown has a high whole-crown carbon gain, even if leaf traits do not change greatly with decreasing crown height. Leaf area indices (LAIs) of the two Fagus trees (5.26-5.52) were higher than the LAI of the B. grossa tree (4.50) and the leaves of the F. crenata tree were more concentrated in the top crown layers than were leaves of the other trees. Whole-crown carbon gain per unit ground area (micromol m(-2) ground s(-1)) at midday on fine days in summer was 16.3 for F. crenata, 11.0 for F. japonica, and 20.4 for B. grossa. In all study trees, leaf dry mass (LMA) and leaf nitrogen content (N) per unit area decreased with decreasing height in the crown, but leaf N per unit mass increased. Variations (plasticity) between the uppermost and lowermost crown layers in LMA, leaf N, the ratio of chlorophyll to N and the ratio of chlorophyll a to b were smaller for F. japonica and B. grossa than for F. crenata. The light extinction coefficients in the crowns were lower for the F. japonica and B. grossa trees than for the F. crenata tree. The leaf carbon isotope ratio (delta(13)C) was higher for F. japonica and B. grossa than for F. crenata, especially in the mid-crown. These results suggest that, in crowns with low leaf plasticity but steep leaf inclination angles, such as those of F. japonica and B. grossa trees, irradiance can penetrate into the middle of the crowns, thereby enhancing whole-crown carbon gain.  相似文献   

9.
Different methodological approaches from the field of spatial statistics, the index of cluster size (ICS) and quadrat methods such as the two-term and three-term local quadrat variance (TTLQV and 3TLQV) and the new local variance (NLV) were tested to find a simple spatial measure to classify mixed coniferous uneven-aged, even-aged and conversion stands in the central Black Forest area of Germany. Altogether six stands were analysed with regularly distributed sample plots of 0.25 ha (50×50 m), each subdivided into 25 quadrats of 10×10 m. In each of the quadrats, diameter at breast height (dbh) for trees of the overstory (dbh>7 cm) was assessed and classified into three diameter classes. Height measurements were used to develop specific stand height curves for each stand and to calculate the standing volume per tree and per quadrat. The even-aged stands showed a regular distribution of the standing volume, while the conversion and uneven-aged stands were more clustered. This was detected using ICS, which proved to be a simple but very efficient measure for stand structure. The ICS also showed a highly random distribution of small and medium trees and a regular distribution of large trees of the overstory in the uneven-aged stand. Large and medium trees of one even-aged stand were also regularly distributed while conversion stands showed a regular, random or slightly clustered distribution of these trees. The more uneven the ages in the stands were, the larger were the phases detected by the NLV. The findings of the ICS were generally supported by the TTLQV and 3TLQV. The more uneven the ages in a stand were, the less clustered were the trees of different sizes of the understory. Clustering also decreased with increasing height of understory trees. The patterns detected in the investigated stands were related to the effect of different management regimes. Implications for the management of conversions stands based on the findings of the study are given.  相似文献   

10.

Key message

The position of trees in the canopy impacts xylem structure and its inter-annual variation. After canopy release, the increase in the hydraulic conductivity of growth rings was driven by an increase in radial growth in large trees, and by both an increase in radial growth and changes in xylem structure in saplings.

Context

Forest canopies are frequently subjected to disturbances that allow understory trees to access the upper canopy. The effect of canopy release on xylem anatomy has been assessed in juvenile trees and saplings, while the potential acclimation of larger trees remains poorly documented.

Aims

We estimated the potential hydraulic conductivity of growth rings in large understory trees compared to overstory trees, and evaluated the responses to canopy release in large trees and in saplings.

Methods

We recorded radial growth, wood density, and vessel structure in beech trees according to their position within the canopy and their size. Xylem traits were followed during 6 years after canopy release for large trees, and during 2 years for saplings. Vessel diameter and frequency as well as ring area were used to compute the potential annual ring hydraulic conductivity.

Results

Large understory trees displayed lower radial growth increments and lower potential annual ring hydraulic conductivity than overstory trees. After canopy release, potential annual ring hydraulic conductivity increased in large trees, due exclusively to increased radial growth without any change in specific hydraulic conductivity. It increased in saplings due to both increased radial growth and increased specific conductivity.

Conclusion

Tree size impacted xylem structure and resulted in plasticity of the potential hydraulic conductivity of the annual tree ring following canopy release.
  相似文献   

11.
Recent studies have shown that stomata respond to changes in hydraulic conductance of the flow path from soil to leaf. In open-grown tall trees, branches of different heights may have different hydraulic conductances because of differences in path length and growth. We determined if leaf gas exchange, branch sap flux, leaf specific hydraulic conductance, foliar carbon isotope composition (delta13C) and ratios of leaf area to sapwood area within branches were dependent on branch height (10 and 25 m) within the crowns of four open-grown ponderosa pine (Pinus ponderosa Laws.) trees. We found no difference in leaf gas exchange or leaf specific hydraulic conductance from soil to leaf between the upper and lower canopy of our study trees. Branch sap flux per unit leaf area and per unit sapwood area did not differ between the 10- and 25-m canopy positions; however, branch sap flux per unit sapwood area at the 25-m position had consistently lower values. Branches at the 25-m canopy position had lower leaf to sapwood area ratios (0.17 m2 cm-2) compared with branches at the 10-m position (0.27 m2 cm-2) (P = 0.03). Leaf specific conductance of branches in the upper crown did not differ from that in the lower crown. Other studies at our site indicate lower hydraulic conductance, sap flux, whole-tree canopy conductance and photosynthesis in old trees compared with young trees. This study suggests that height alone may not explain these differences.  相似文献   

12.
Some saplings and shrubs growing in the understory of temperate deciduous forests extend their periods of leaf display beyond that of the overstory, resulting in periods when understory radiation, and hence productivity, are not limited by the overstory canopy. To assess the importance of the duration of leaf display on the productivity of understory and overstory trees of deciduous forests in the north eastern United States, we applied the simulation model, BIOME-BGC with climate data for Hubbard Brook Experimental Forest, New Hampshire, USA and mean ecophysiological data for species of deciduous, temperate forests. Extension of the overstory leaf display period increased overstory leaf area index (LAI) by only 3 to 4% and productivity by only 2 to 4%. In contrast, extending the growing season of the understory relative to the overstory by one week in both spring and fall, increased understory LAI by 35% and productivity by 32%. A 2-week extension of the growing period in both spring and fall increased understory LAI by 53% and productivity by 55%.  相似文献   

13.
Understory individuals were found to form patches in a 100-year-old deciduous broad-leaved forest. The closed forest canopy was uniform, and so the light conditions at various locations across the forest floor differed little after the leaf flush of the overstory. To explain the distribution pattern in the understory, a hypothesis was proposed: in spring, the forest floor is divided into patches according to the timing of leaf flush of the overstory individuals, and the light conditions are more favorable for understory plants under the crowns of trees with later-flushing leaves. In the plot, three groups of early, intermediate, and late, were recognized in the overstory concerning the timing of leaf flush. As for the start of leaf flush, a difference of 31.6 days was recognized among tree species, and for the end of leaf flush, a difference of 40.3 days. In the spring of 1998, the relative photosynthetic-photon-flux density under an intensively studiedCastanea crenata tree (late-flushing species) usually showed higher values than that under a similarly studiedAcer mono tree (early-flushing species). Analysis of the spatial-distribution pattern using Morisita’s1δ index revealed that the understory community had an aggregated distribution. In the overstory, the late- and the intermediate-flushing-species groups showed aggregated distributions, while the early-flushing-species group showed random distribution. Spatial correlation between the understory and the overstory was analyzed by using Morisita’sRδ index. The distribution of whole understory community spatially co-occurred with that of the late-flushing-species group of the overstory. In contrast, the understory community was less developed below the members of the early-flushing-species group of the overstory. We consider that the data presented here support our hypothesis, and we suggest that the growth and survival of understory individuals were promoted in the places receiving light for long periods in spring.  相似文献   

14.
We used gas exchange techniques to estimate maximum rate of carboxylation (V(cmax)), a measure of photosynthetic capacity, in the understory and upper crown of a closed deciduous forest over two seasons. There was extensive variability in photosynthetic capacity as a result of vertical canopy position, species type, leaf age and drought. Photosynthetic capacity was greater in oaks than in maples and greater in the overstory than in the understory. Parameter V(cmax) was maximal early in the season but declined slowly throughout most of the summer, and then more rapidly during senescence. There was also an apparent decline during drought in some trees. Variability in V(cmax) as a result of species or vertical canopy gradients was described well by changes in leaf nitrogen per unit area (N(a)). However, temporal changes in V(cmax) were often poorly correlated with leaf nitrogen, especially in spring and summer and during drought. This poor correlation may be the result of a seasonally dependent fractional allocation of leaf nitrogen to Rubisco; however, we could not discount Rubisco inactivation, patchy stomatal closure or changes in mesophyll resistance. Consequently, when a single annual regression equation of V(cmax) versus N(a) was used for this site, there were substantial errors in the temporal patterns in V(cmax) that will inevitably result in modeling errors.  相似文献   

15.
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   


16.
In the 1970s, public opposition to clearcut harvesting in hardwood forests of the eastern United States led forest managers and scientists to consider alternative practices that retain a low-density overstory forest cover. From 1979 to 1984, a form of clearcut-with-reserves harvesting was applied in 80-year-old Appalachian mixed-hardwoods to create four experimental stands with two-aged structures. The residual stand basal area averaged 5.3 m2/ha, comprising an average of 36 reserve trees/ha. The reserve trees were evenly distributed throughout the stand, initially with considerable space between their crowns, thus providing the sunlight and seedbed conditions needed to recruit desirable shade-intolerant reproduction after harvest. This study examined the response of the 100-year-old reserve trees and the development of the 20-year-old natural reproduction located in their immediate vicinity.Diameter at breast height (Dbh), height, and relative position were recorded for all reproduction ≥2.5 cm within transects adjacent to northern red oak (Quercus rubra L.) and yellow-poplar (Liriodendron tulipifera L.) reserve trees. Each transect was divided into five zones, which represented positions relative to the reserve tree crown edge, and basal area was computed for each of three shade tolerance classes within each zone. A repeated measures ANOVA was used to compare basal area of reproduction by tolerance classes and zone. In general, basal area of reproduction, particularly that of shade-intolerant species, increased with distance from the reserve tree. Regression analyses also indicated that dbh and height of reproduction was positively related to distance from the reserve trees. Although height growth of reserve trees was similar for both species, northern red oak exhibited significantly greater dbh and crown radial growth than yellow-poplar.The results indicated that reserve trees influence the growth rate and species composition of reproduction in their immediate vicinity. Basal area of reproduction increased from 10.1 to 17.7 m2/ha with increasing distance from the reserve trees. Basal area of intolerant species more than doubled along the same gradient. Basal area of reproduction in the two-age stands was 30–40% less than that observed in even-aged stands on similar growing sites, but the reduction was offset by growth of the reserve trees. The surface area covered by the reserve tree crowns increased approximately 88% for northern red oak and 44% for yellow-poplar. Since the sphere of influence of reserve trees increases over time, forest managers must consider their long-term impact on reproduction when prescribing clearcut-with-reserves harvests and other practices that involve retaining trees for many years.  相似文献   

17.
Mountain pine beetle, Dendroctonus ponderosae Hopkins can cause extensive tree mortality in ponderosa pine, Pinus ponderosa Dougl. ex Laws., forests in the Black Hills of South Dakota and Wyoming. Most studies that have examined stand susceptibility to mountain pine beetle have been conducted in even-aged stands. Land managers increasingly practice uneven-aged management. We established 84 clusters of four plots, one where bark beetle-caused mortality was present and three uninfested plots. For all plot trees we recorded species, tree diameter, and crown position and for ponderosa pine whether they were killed or infested by mountain pine beetle. Elevation, slope, and aspect were also recorded. We used classification trees to model the likelihood of bark beetle attack based on plot and site variables. The probability of individual tree attack within the infested plots was estimated using logistic regression. Basal area of ponderosa pine in trees ≥25.4 cm in diameter at breast height (dbh) and ponderosa pine stand density index were correlated with mountain pine beetle attack. Regression trees and linear regression indicated that the amount of observed tree mortality was associated with initial ponderosa pine basal area and ponderosa pine stand density index. Infested stands had higher total and ponderosa pine basal area, total and ponderosa pine stand density index, and ponderosa pine basal area in trees ≥25.4 cm dbh. The probability of individual tree attack within infested plots was positively correlated with tree diameter with ponderosa pine stand density index modifying the relationship. A tree of a given size was more likely to be attacked in a denser stand. We conclude that stands with higher ponderosa pine basal area in trees >25.4 cm and ponderosa pine stand density index are correlated with an increased likelihood of mountain pine beetle bark beetle attack. Information form this study will help forest managers in the identification of uneven-aged stands with a higher likelihood of bark beetle attack and expected levels of tree mortality.  相似文献   

18.
This study presents empirical data on regeneration and growth of understory trees and constructs simple models for predicting these characteristics at various stand structure and post-thinning standing volume levels. The field experiment was established on a grass/herb mineral soil site in central Finland. Regeneration and understory tree growth data were collected from 24 Norway spruce (Picea abies L.)-dominated mixed substands. Seedlings with heights from 5 to 130 cm were measured in 1996 and 2007. In addition, the annual height growth of Norway spruce seedlings was measured in 2007. The spatial pattern of the substands varied from clustered to regular with a decreasing standing volume. Stand complexity was uniform across the range of standing volume. In the 2007 survey, the amount of Norway spruce regeneration increased from approximately 400 to 5,000 seedlings ha−1 when the post-thinning standing volume level was reduced from 230 to 90 m3 ha−1, respectively. Nearly no seedlings were found when the standing volume was over 300 m3 ha−1. The annual diameter increment in Norway spruce understory (dbh < 5 cm) trees decreased, on the average, from 2.3 to 0.3 mm with an increase in the standing volume level from 90 to 340 m3 ha−1, respectively; their height growth showed also a decreasing trend when the standing volume increased. The results indicated that a post-thinning standing volume lower than 150 m3 ha−1 with a regular overstory spatial structure provides a suitable environment for regeneration and growth of Norway spruce understory trees in the studied forest type.  相似文献   

19.
Specific leaf area (SLA) and leaf area index (LAI) were estimated using site-specific allometric equations for a boreal black spruce (Picea mariana (Mill.) BSP) fire chronosequence in northern Manitoba, Canada. Stands ranged from 3 to 131 years in age and had soils that were categorized as well or poorly drained. The goals of the study were to: (i) measure SLA for the dominant tree and understory species of boreal black spruce-dominated stands, and examine the effect of various biophysical conditions on SLA; and (ii) examine leaf area dynamics of both understory and overstory for well- and poorly drained stands in the chronosequence. Overall, average SLA values for black spruce (n = 215), jack pine (Pinus banksiana Lamb., n = 72) and trembling aspen (Populus tremuloides Michx., n = 27) were 5.82 +/- 1.91, 5.76 +/- 1.91 and 17.42 +/- 2.21 m2 x kg-1, respectively. Foliage age, stand age, vertical position in the canopy and soil drainage had significant effects on SLA. Black spruce dominated overstory LAI in the older stands. Well-drained stands had significantly higher overstory LAI (P < 0.001), but lower understory LAI (P = 0.022), than poorly drained stands. Overstory LAI was negligible in the recent (3-12 years old) burn sites and highest in the 70-year-old burn site (6.8 and 3.0 in the well- and poorly drained stands, respectively), declining significantly (by 30-50%) from this peak in the oldest stands. Understory leaf area represented a significant portion (> 40%) of total leaf area in all stands except the oldest.  相似文献   

20.
We investigated how richness and composition of vascular plant species in the understory of a mixed hardwood forest stand varied with respect to the abundance and composition of the overstory. The stand is in central Spain and represents the southernmost range of distribution of several tree and herbaceous species in Europe. Understory species were identified in 46 quadrats (0.25 m2) where variables litter depth and light availability were measured. In addition, we estimated tree density, basal area, and percent basal area by tree species within 6-m-radius areas around each plot. Species richness and composition were studied using path analysis and scale-dependent geostatistical methods, respectively. We found that the relative abundance of certain trees species in the overstory was more important than total overstory abundance in explaining understory species richness. Richness decreased as soil litter depth increased, and soil litter increased as the relative proportion of Fagus sylvatica in the overstory increased, which accounted for a negative, indirect effect of Fagus sylvatica on richness. Regarding understory species composition, we found that some species distributed preferentially below certain tree species. For example, Melica uniflora was most frequent below Fagus sylvatica and Quercus petraea while the increasing proportion of Q. pyrenaica in the overstory favored the presence of Cruciata glabra, Arenaria montana, Prunus avium, Conopodium bourgaei, Holcus mollis, Stellaria media and Galium aparine in the understory. Overall, these results emphasize the importance of individual tree species in controlling the assemblage and richness of understory species in mixed stands. We conclude that soil litter accumulation is one way through which overstory composition shapes the understory community.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号