Lower Crown Branches Research Articles

Spatiotemporal distribution of the hemlock woolly adelgid predator Laricobius nigrinus after release in eastern hemlock forests

Post‐release distributions of Laricobius nigrinus, a biological control predator of hemlock woolly adelgid Adelges tsugae Annand, were evaluated at eight hemlock forests in the eastern U.S.A. Vertical dispersal of F1 and F2L. nigrinus were assessed from within three crown strata (<7, 7–15 and >15 m) at four release sites. Horizontal distributions of L. nigrinus within the forest surrounding central release areas were observed in two separate studies, which included (i) release and monitor to capture parent and F1 movement by sampling the immature life stages of the offspring, and (ii) assessment of F3 to F6 generations where beetles were previously determined to be established. Laricobius nigrinus, released on lower crown branches, oviposited within the upper crown stratum and were slow to disperse from release trees. Monitoring L. nigrinus only from the lower crown would likely underestimate its presence because 86% of the F2 generation were detected above 15 m. By the fifth generation, the frequency distributions of larvae increased at increasing distance from release areas; larvae were recovered at a maximum distance of approximately 400 m and the spread rate was approximately 39 m/year. Slow dispersal of L. nigrinus and uninterrupted recovery of six generations in the presence of fluctuating prey density support its continued release as part of the A. tsugae biological control programme. These data contribute toward improved release strategies and monitoring for this biological control agent.

Distribution of vessel size, vessel density and xylem conducting efficiency within a crown of silver birch (Betula pendula)

Spatial patterns in vessel diameter, vessel density and xylem conducting efficiency within a crown were examined in closed-canopy trees of silver birch (Betula pendula). The variation in anatomical and hydraulic characteristics of branches was considered from three perspectives: vertically within a crown (lower, middle and upper crown), radially along main branches (proximal, middle and distal part), and with respect to branch orders (first-, second- and third-order branches). Hydraulically weighted mean diameter of vessels (D h) and theoretical specific conductivity of the xylem (k t) exhibited no vertical trend within the tree crown, whereas leaf-specific conductivity of the xylem (LSCt) decreased acropetally. Variation in LSCt was governed by sapwood area to leaf area ratio (Huber value) rather than by changes in xylem anatomy. The acropetal increase in soil-to-leaf conductance (G T) within the birch canopy is attributable to longer path length within the lower-crown branches and higher hydraulic resistance of the shade leaves. D h, k t and LSCt decreased, while vessel density (VD) and relative area of vessel lumina (VA) increased distally along main branches. A strong negative relationship between vessel diameter and VD implies a trade-off between hydraulic efficiency and mechanical stability of xylem. D h and VD combined explained 85.4% of the total variation of k t in the regression model applied to the whole data set. Xylem in fast-growing branches (primary branches) had greater area of vessel lumina per unit cross-sectional area of sapwood, resulting in a positive relationship between branch radial growth rate and k t. D h, k t and LSCt decreased, whereas VD increased with increasing branch order. This pattern promotes the hydraulic dominance of primary branches over the secondary branches and their dominance over tertiary branches. In this way crown architecture contributes to preferential water flow along the main axes, potentially providing better water supply for the branch apical bud and foliage located in the outer, better-insolated part of the crown.

Spatial variation in sapwood area to leaf area ratio and specific leaf area within a crown of silver birch

Spatial variation in sapwood area to leaf area ratio (Huber value, HV) and specific leaf area (SLA) was examined in branches of closed-canopy trees of silver birch (Betula pendula Roth). HV increased basipetally within a crown and decreased with increasing branch order, but exhibited no significant radial trend along a primary branch. HV was primarily determined by branch position in a crown and branch diameter at the sampling point, being independent of the size of the tree and branch. Greater HV in the lower-crown branches is considered a means to mitigate differences in hydraulic transport capacity between the branches located in different canopy layers. Beside branch position and sampling location on a branch, SLA depended significantly on several other variables characterising tree and branch size. SLA increased basipetally within a crown and along a primary branch, but exhibited no significant trend with branch orders. Because height caused leaf area (AL) to diminish more rapidly than leaf dry weight, AL primarily determined the vertical variation in SLA.

Effects of branch position on water relations and gas exchange of European larch trees in an alpine community

Water relations and gas exchange were studied in the crowns of small European larch (Larix decidua Mill.) trees with respect to branch position. The upper-crown branches showed significantly higher branch sap flux rate (Fla) and branch conductance (gb) compared to the lower crown (P<0.001). Values of leaf conductance (gl), transpiration rate (E) and net photosynthesis (A), averaged for different ranges of atmospheric vapour pressure deficit (VPD), were also higher in the upper crown position. We suppose that the up to 2.6-fold smaller soil-to-leaf hydraulic conductance observed in the lower branches (P<0.001, compared to upper branches) could contribute to the decreased values of Fla, gb, gl, and E in the lower crown position. Variation in tracheid lumen diameter with respect to crown position (P<0.001) supported the hypothesis that branches growing at the crown base are hydraulically more constrained than branches located at the top of the tree. Leaf area to sapwood area ratio (Ala/Asa) exhibited 1.4 times smaller values in lower crown (P<0.01), however, this could not compensate the effect of decreased hydraulic conductivity of the lower-crown branches.

Physiological and foliar symptom response in the crowns of Prunus serotina, Fraxinus americana and Acer rubrum canopy trees to ambient ozone under forest conditions

The crowns of five canopy dominant black cherry ( Prunus serotina Ehrh.), five white ash ( Fraxinus americana L.), and six red maple ( Acer rubrum L.) trees on naturally differing environmental conditions were accessed with scaffold towers within a mixed hardwood forest stand in central Pennsylvania. Ambient ozone concentrations, meteorological parameters, leaf gas exchange and leaf water potential were measured at the sites during the growing seasons of 1998 and 1999. Visible ozone-induced foliar injury was assessed on leaves within the upper and lower crown branches of each tree. Ambient ozone exposures were sufficient to induce typical symptoms on cherry (0–5% total affected leaf area, LAA), whereas foliar injury was not observed on ash or maple. There was a positive correlation between increasing cumulative ozone uptake ( U) and increasing percent of LAA for cherry grown under drier site conditions. The lower crown leaves of cherry showed more severe foliar injury than the upper crown leaves. No significant differences in predawn leaf water potential ( ψ L) were detected for all three species indicating no differing soil moisture conditions across the sites. Significant variation in stomatal conductance for water vapor ( g wv) was found among species, soil moisture, time of day and sample date. When comparing cumulative ozone uptake and decreased photosynthetic activity ( P n), red maple was the only species to show higher gas exchange under mesic vs. drier soil conditions ( P < 0.05). The inconsistent differences in gas exchange response within the same crowns of ash and the uncoupling relationship between g wv and P n demonstrate the strong influence of heterogeneous environmental conditions within forest canopies.

The role of epicormic shoot production in maintaining foliage in old Pseudotsuga menziesii (Douglas-fir) trees II. Basal reiteration from older branch axes

Basal reiteration (epicormic shoot production from older branch axes) occurred continuously and repeatedly in branches of 450-year-old Pseudotsuga menziesii (Mirb.) Franco var. menziesii (coastal Douglas-fir) trees reproducing sections of branches comprising less than 100 to as many as 10 000 foliated shoots. Basal reiteration occurred mostly from primary and secondary branch axes but also occurred from higher-order axes if lower-order axes had died back. Basal reiteration occurred in distal sections of upper-crown branches, while it occurred in more proximal sections of middle- and lower-crown branches, indicating that basal reiteration works to distribute foliage more uniformly within branches that have reached maximum size. Basal reiteration occurred repeatedly producing two to six generations of reiterated axes within branches. Less than 22.5% of foliated shoots on branches were produced by sequential branching of the primary axis. Basal reiteration also maintained a constant rate of new shoot production within the branch. Growth-ring analysis showed that basal reiteration occurred over a wide range of axis ages (5–58 years). In conjunction with previous studies, we showed that adaptive reiteration of various architectural units by epicormic shoot production is an inherent process that maintains foliage in the crown of old P. menziesii trees.Key words: branch growth, branching pattern, crown maintenance, longevity.

Variation in specific needle area of old-growth Douglas-fir in relation to needle age, within-crown position and epicormic shoot production.

Variation in specific needle area (SNA; cm2 projected fresh needle area g-1 oven-dried needle weight) was investigated in relation to needle age, within-crown position and epicormic shoot production in 450-year-old Douglas-fir (Pseudotsuga menziesii Mirb. (Franco) var. menziesii) trees. Specific needle area decreased with increasing needle age. The magnitude and rate of change in SNA with needle age were greatest for lower-crown branches, and decreased toward the middle- and upper-crown branches. For all branches, there was no difference between regular and epicormic shoots in the relationship between SNA and needle age. Specific needle area decreased with increasing distance from branch base, and this relationship was significant for the majority of needle age classes of the upper- and middle-crown branches. In the lowercrown branches, SNA did not vary with distance from branch base for the majority of needle age classes. For all branches, there was no difference between regular and epicormic shoots in the relationship between SNA and distance from branch base for the majority of needle age classes. These results indicate that renewal of foliage by epicormic shoot production maintains needle quality. Branch SNA increased linearly with decreasing height in the crown at a mean rate of 0.951 +/- 0.110 cm2 g-1 per vertical meter. Total needle area of branches was estimated from total needle dry weight taking into account within-branch variation in SNA. Analyses of allometric relationships between branch size and foliage amount (needle area and needle dry weight) showed that branch length was a better predictor of foliage amount than branch diameter for old Douglas-fir trees. Total needle dry weight and needle area of the sample trees, estimated from branch length and branch height and taking into account vertical within-crown variation in branch SNA, ranged from 42.4 to 154.2 kg and from 246.2 to 816.0 m2 per tree, respectively.

Effects of simulated chronic defoliation in summer on growth and survival of blue gum (Eucalyptus globulus Labill) within young plantations in northern Victoria

Summary The combined effects of two consecutive simulated partial and total defoliations of upper, lower and total crowns of 1.7-year- old plantings of Eucalyptus globulus during summer on height, stem basal area and volume increment are described. One hundred per cent crown defoliation suppressed height increment relative to the control treatment soon after the second defoliation, whereas the 100% lower crown defoliation boosted height growth throughout the post-defoliation period. Stem basal area increments were significantly reduced only by the 100% total crown defoliation, which also suppressed stem volume increment relative to the other treatments. None of the treatments affected tree survival. The implications of the results for eucalypt plantation managers are that populations of insect pests likely to cause total crown defoliation during summer in young E. globulus stands prior to canopy closure should be controlled at the earliest opportunity with an effective and appropriately registered insecticide. No action is required when moderate to severe defoliation is expected in either the upper or lower crowns. Moreover, pruning of lower crown branches during summer could boost height growth and accelerate canopy closure, a condition which suppresses infestations by light-seeking leaf-consuming leafblister sawflies, leaf beetles and Christmas beetles.

Seasonal variation of branch respiration of a treeline forming (Betula ermanii Cham.) and a montane (Fagus crenata Blume) deciduous broad-leaved tree species on Mt. Fuji, Japan

Summary In this study we focus on four particular aspects in the field of ecological studies of woody tissue respiration: 1) the application of the non-destructive soda lime technique to the in situ measurement of CO 2 efflux rates from branches or stems of standing trees all year round; 2) the investigation of respiration rates of branches of similar diameter but different positions in the canopy; 3) the comparative study of seasonal variation and long-term thermal acclimation of branch respiration along an altitudinal transect up to the treeline; 4) the comparison of branch respiration between a treeline forming ( Betula ermanii ) and a montane ( Fagus crenata ) deciduous broad-leaved tree species in order to evaluate the relevance of woody tissue respiration to tree survival in low temperature climates. No qualitative differences in respiratory behaviour between the treeline forming B. ermanii and the montane F. crenata were found in this study. Significantly higher respiration rates of upper crown branches of both tree species were due to biogenic factors which were spatio-temporally unevenly effective within the crown. In early spring, branch respiration rose independently of xylem temperature. This was caused by an increase in metabolic activity of branch parenchymatous tissues associated with the phenological development of the buds. During summer, the CO 2 efflux of upper crown branches reached up to sixfold higher rates than that of lower crown branches. This was associated with secondary thickening being more pronounced in the upper crown. During winter, higher rates of maintenance respiration in the upper crown reflected different physiological states of branches, probably with respect to protein metabolism involved in processes of cold resistance of live branch tissues. As shown in this study, thermal acclimation of branch respiration is occuring at a similar level as was reported for leaves of herbaceous alpine plants. The tendency for a lower activation energy for respiration towards low temperature climatic conditions points to a physiologically driven increase in respiratory capacity in branches of B. ermanii and F. crenata . In treeline forming tree species a decrease in activation energy may contribute to keep respiratory activity relatively unaffected by large daily temperature fluctuations of more than 25°C during the cold season. In this study, no evidence was found that branch respiration may act as an ecophysiologically limiting parameter for the survival of Betula ermanii at its present upper distribution limit in the Japanese Alps.

The role of epicormic shoot production in maintaining foliage in old Pseudotsuga menziesii (Douglas-fir) trees

Shoots and foliage on branches of old Pseudotsuga menziesii (Mirb.) Franco var. menziesii (coastal Douglas-fir) trees are constantly renewed by epicormic shoot production. Epicormic shoots are produced in all parts of the crown, and epicormic buds remain dormant for 5 or 6 years on average. Epicormic shoot production results in reiteration of shoot cluster units (SCUs), an architectural unit of shoot organization within branches. Five phases of SCU development were identified based on relative age structures of regular and epicormic shoots. SCUs produce epicormic branchlets as early as 3 or 4 years of age, and peak production occurred around 6-13 years. Epicormic branchlets occur toward the proximal end of main axes of SCUs, where regular lateral branchlets are no longer producing new shoots. In some lower-crown branches, nearly 50% of shoots and foliage are epicormic shoots. Demographic analysis of SCUs showed that upper-crown branches are still growing in size, while mid- and lower-crown branches have reached maximum size, and are being maintained by reiteration of SCUs. Epicormic shoot production maintains shoots and foliage of old P. menziesii trees after height growth and crown expansion have stopped and may contribute to prolonging tree longevity.Key words: aging, branch growth, epicormic shoots, longevity, Pseudotsuga menziesii, reiteration.

Spatial distribution and succession of epiphytes on Tsuga heterophylla (western hemlock) in an old-growth Douglas-fir forest

We examined the distribution and abundance of nonvascular epiphytes on western hemlock trees in an old-growth coniferous forest focusing on patterns of epiphyte distribution at different spatial scales, epiphyte abundance amongst trees differing in size, and crown structures associated with epiphyte abundance. Total epiphyte cover was greatest in four canopy microhabitats: the upper canopy strata, crowns of large trees, lower crown branches, and inner branch plots. Epiphyte functional groups were stratified vertically within the stand and horizontally within branches. Alectorioid and "other" lichens were most abundant in the upper canopy and outer branch plots. Cyanolichens and Sphaerophorus globosus (Huds.) Vain. were most abundant in the lower to mid canopy. Although cyanolichens were most abundant in middle branch plots, Sphaerophorus was most abundant in inner branch plots. Bryophytes were most abundant in the lower canopy and inner branch plots. At the stand level, canopy height and tree size were the main influences on epiphytes. Within trees, plots closer to the tree trunk and lower in the crown had the greatest abundance of epiphytes. In this forest, understory trees were colonized first by bryophytes, not by alectorioid and "other" lichens as is common for small trees in young stands.Key words: epiphyte succession, lichens, western hemlock, old growth, forest canopy, crown structure.

Reduction in branch sapwood hydraulic permeability as a factor limiting survival of lower branches of lodgepole pine

Branch sapwood hydraulic permeability, tracheid size, and earlywood to latewood ratio of annual rings were examined in lower and upper branches of closed-canopy and open-grown lodgepole pine (Pinus contorta Dougl. ex Loud.) trees. Hydraulic permeability, expressed on either a leaf area or sapwood area basis, was lower in lower branches (0.16 × 10-5 and 5.82 × 10-5 m2, respectively) than upper branches (0.26 × 10-5 and 10.47 × 10-5 m2, respectively) and was related to narrower tracheids in the sapwood of lower branches. Earlywood/latewood ratio declined in the lower branches of shaded trees. The hydraulic conductivity of upper and lower branches in closed canopy trees was reduced by drilling small holes radially through the stem. Stomatal conductance was lower, and after a growing season there was greater foliage mortality in drilled lower crown branches than in similarly treated upper branches, suggesting that the hydraulic conductivity of lower branches was closer to the lower limit required to maintain foliage than in upper branches. These data suggest that high foliage mortality and eventual death of lower branches does not occur solely because of low light but also from reduced stomatal conductance and photosynthesis resulting from shade-initiated reductions in earlywood, tracheid diameter, and branch hydraulic conductivity.

Reduction in branch sapwood hydraulic permeability as a factor limiting survival of lower branches of lodgepole pine

Branch sapwood hydraulic permeability, tracheid size, and earlywood to latewood ratio of annual rings were examined in lower and upper branches of closed-canopy and open-grown lodgepole pine (Pinus contorta Dougl. ex Loud.) trees. Hydraulic permeability, expressed on either a leaf area or sapwood area basis, was lower in lower branches (0.16 × 10-5 and 5.82 × 10-5 m2, respectively) than upper branches (0.26 × 10-5 and 10.47 × 10-5 m2, respectively) and was related to narrower tracheids in the sapwood of lower branches. Earlywood/latewood ratio declined in the lower branches of shaded trees. The hydraulic conductivity of upper and lower branches in closed canopy trees was reduced by drilling small holes radially through the stem. Stomatal conductance was lower, and after a growing season there was greater foliage mortality in drilled lower crown branches than in similarly treated upper branches, suggesting that the hydraulic conductivity of lower branches was closer to the lower limit required to maintain ...

Developmental control of xylem hydraulic resistances and vulnerability to embolism in Fraxinus excelsior L.: impacts on water relations

The hydraulic properties and leaf gas exchanges of Fraxinus excelsior L. branches differing by their age and their vertical crown position, but in comparable ambient air conditions (vapour pressure deficit and global radiation) were compared. The variations in leaflet water potential ψleaflet, leaflet stomatal conductance and transpiration rate, E, were small between different branches of the same crown. Whole branch hydraulic resistances (r branch ), and partitioning between leaf (r leaf ) and xylem resistance (r xylem ) were assessed with a high pressure flowmeter. r leaf represented 90% and 10% of r branch for upper and lower crown branches, respectively. The changes resulted from increases in r xylem caused by the formation of short shoot internodes mostly located in secondary axes. However, leaf area-specific branch resistances (r branch =r branch x LA) were nearly constant throughout the crown. This was consistent with the vertical variations in ψ leaflet because r branch x E represents the water potential drop from the trunk to the leaves. Because r xylem was higher, lower ψxylem values were predicted in lower crown rachises. However, rachises from lower crown branches were less vulnerable to embolism than in upper branches ( ψxylem at onset of embolism, ψ cav, were -3 and -2MPa, respectively). It was concluded that r xylem increased with branch age, but r* branch remained constant because LA decreased. As a consequence, E was maximized and ψxylem remained above ψcav, This suggested that, in Fraxinus, leaf gas exchanges and leaf areas were coupled with xylem hydraulic capacities probably through a control of bud activity.

Distribution of Pandora Moth 1 Egg Masses and Pupae near Jacob Lake, Arizona

The distribution of egg masses and pupae of the pandora moth, Coloradia pandora Blake (Lepidoptera: Saturniidae), were studied near Jacob Lake, Ariz. Numbers of egg masses(EMs) per branch on the foliage of trees over 30 cm at breast height (DBH) were insignificantly greater in heavily defoliated stands than on trees the same size in lightly defoliated stands. Numbers were greatest on lower crown branches, least on upper crown branches. EMs per branch on the foliage of trees 18 to 24 cm DBH were significantly greater in heavily defoliated stands than in lightly defoliated stands, but they did not generally change significantly from the top of the crown to the bottom in either stand. Eggs per EM averaged 11. Numbers of EMs/900 cm2 on boles were greatest in the first 30 cm above ground. Pupal densities averaged about 3/900 cm2 or 32/m2 of ground surface.