Crown Spread Patterns for Five Deciduous Broad-leaved Woody Species: Ecological Significance of the Retention Patterns of Larger Branches

Patterns of crown spread and branch retention of two shade-intolerantspecies (Betula platyphyllaandB. maximowicziana) were comparedwith three more tolerant species (Quercus mongolica,Acer sieboldianumandMagnoliaobovata). Branching height (height of the lowest living branch)rose more rapidly with age for the twoBetulaspecies than forthe shade tolerant species. Branching heights ofA. sieboldianumandM.obovatawere similar, irrespective of tree height and age, andlarger trees tended to produce wider crowns than theBetulaspecieswhen trees of similar height were compared. In all species,the branch basal area (cross-sectional area of a branch at itsbase) and the leaf area per branch generally increased as thebranch position on a stem became lower. Therefore, retaininglarger branches contributed significantly to the support ofa larger leaf area per tree. The number of larger branches (branchbasal area >80 cm²) for bothBetulaspecies was significantlysmaller than that of the shade tolerant species. The branchretention pattern ofBetulaspecies was probably a consequenceof intolerance of the leaves to shade. The decline ofBetulaspecieswith forest succession is likely to occur through their inabilityto retain branches with a large base area in closed forests.Copyright1997 Annals of Botany Company Shade tolerance; crown spread; branch retention; branch size; broad-leaved woody species; leaf area index per tree     

云南红豆杉人工林萌枝特性

萌枝是许多木本植物维持种群稳定和延续的重要机制之一。本文通过对云南红豆杉人工林萌枝情况的调查,分析了云南红豆杉萌枝特征及其对生长的影响。结果表明：（1）云南红豆杉萌枝现象明显,萌枝率达到88.1%,萌枝类型有树基萌枝和树干萌枝两种,其中树基萌枝是最主要的类型,有树基萌枝的个体达到了总株数的80.0%,树干萌枝率仅为39.6%,约为树基萌枝率的一半,两种萌枝都有的比率为31.5%;（2）云南红豆杉的树基萌枝数量与树高呈正相关关系,与地径呈负相关关系,而树干萌枝数量与树高和地径都没有显著的相关关系。总萌枝数量与树高及地径的相关关系与树基萌枝的一样,但相关性略低。（3）树基萌枝和树干萌枝都会影响云南红豆杉枝叶的空间分布格局,但从植株总体上说,它们对云南红豆杉的枝叶生长量没有显著的影响。     

Assessing internal epicormic dynamics in Quercus alba L. using CT scanning: the strong effects of shoot development and tree growth relative to progeny level genetic variation

Epicormic branches can be a serious silvicultural problem in many Quercus species because of the potential reduction in log value associated with their occurrence. The phenomenon is also problematic for tree improvement since the genetic component of epicormic branching has not been well quantified. The strong influence of ontogeny on epicormic development in Quercus is well established; however, the long-standing assumption that genetic variation also influences epicormics has not been rigorously tested. With trees from two, 25-year-old Quercus alba L. progeny tests in IN, USA, we used computed tomography scanning to characterize internal epicormic development. We sampled trees from upper and lower crown classes of families that had been classified as having low, medium and high numbers of epicormic sprouts. We also measured an array of variables related to growth and competition with the objective of assessing the relative impacts of genetics and vigor on epicormic development. Using generalized linear and linear mixed models, we found that ontogenetic and vigor variables were strongly associated with epicormic structure and development, and that the genetic effect was negligible. The total number of epicormics was most significantly influenced by the number of sequential branches that bore epicormics (p < 0.001) and the proportion of undeveloped epicormics was most significantly influenced by diameter increment (p < 0.001). We propose that a strong focus on individual tree vigor and form in tree improvement could minimize the impact of epicormic branching in Q. alba trees.     

Epicormic Bud Development in Quercus robur L. Studies of Endogenous IAA, ABA, IAA Polar Transport and Water Potential in Cambial Tissues10

Seasonal measurements of IAA,³ made using GC-MS, ⁴ indicatedthat in Q. robur the spring initiation of cambial activity andonset of visible bud outgrowth in the canopy is preceded byan increase in cambial region IAA. The effects of notch-girdlescut into the bole indicated that IAA in the cambial region laterwas present in separate physiological pools, with only the polar-transportedfraction affecting epicormic bud outgrowth. The stage in thespring when the epicormic buds grew out coincided with an increaseboth in cambial region IAA and in the capacity of cambial explantsfor IAA polar transport. Thus the stimulus needed by the epicormicbuds to overcome inhibition by polar-transported IAA appearedto be self-generated. The observed effects of exogenous hormoneson epicormic bud outgrowth from stem explants indicated thatthis stimulus might be cytokinin. The seasonal changes detectedin cambial region ABA³ were consistent with a role for stress-inducedABA in the induction of epicormic bud dormancy after canopydevelopment during the summer. No consistent effects of standthinning on cambial region IAA, ABA, water potentials or watercontents were detected, although polar transport of exogenousIAA by cambial region explants removed in the spring was reducedby thinning. Key words: Epicormic buds, cambium, hormones     

Seasonal Changes of Bioelements in the Litter and their Potential Return to Green Leaves in four Species of the Argentine Subtropical Forest

The aim of this work was to analyse the nutrient concentrationsof N, P, Ca, Mg, K and Na in mature leaves, branches and fruitsand to investigate relationships between the contents of thesebioelements in senescent and fresh leaves in four forest species:Gleditsia amorphoides ( Espina Corona), Patagonula americana(Guayaibí),Chlorophora tinctoria ( Mora) and Astroniumbalansae (Urunday). The study site was located in the ColoniaBenítez Estricta Nature Research (Chaco, Argentina).In this subtropical forest, total litter was collected monthlyand was sorted into three groups: (1) leaves; (2) branches andfruit; (3) unidentified. Total dry matter was recorded and analysedfor N, P, Ca, Mg, K and Na. Espina Corona had the highest leafconcentrations of N, while Mora had the highest concentrationsof Ca and Mg. The highest leaf concentrations of P were foundin Espina Corona, Mora and Urunday. No significant differencesin K were found among the different species. Na concentrationswere higher in Espina Corona and Guayaibí than Mora andUrunday. A marked seasonal variability was observed in the concentrationsof N, P and K, with no important differences for Ca and Mg,except in Espina Corona. These variations in nutrient concentrationswere greater in leaves than in branches and fruits. N and Pwere translocated to other tree organs and Ca, Mg and Na wereaccumulated in mature leaves. The bioelement K is the only onethat undergoes leaching and mobilization in all species. ResorbedN and P can be used for the production of new leaf organs inthe following annual cycle. This resorption supports a portionof the production of new foliage, diminishing the demand fromsoil.Copyright 2000 Annals of Botany Company Above-ground production, potential return, nutrient resorption, leaf analysis, tropical forest, Gleditsia amorphoides, Patagonula americana, Chlorophora tinctoria, Astronium balansae, Espina Corona, Guayaibí, Mora, Urunday.     

Irregular Heartwood Formation in Maritime Pine (Pinus pinaster Ait):Consequences for Biomechanical and Hydraulic Tree Functioning

As the proportion of sapwood (SW) transformed into heartwood(HW) is irregular both radially and longitudinally in trunksof Maritime pine (Pinus pinaster Ait.), it has been suggestedthat HW formation is a developmental process, regulated internallywithin the tree. In trees where stem growth is eccentric dueto stem lean or wind action, the number of annual growth ringsof SW transformed into HW is greater on the compressed sideof the tree. To determine the contribution to bending stiffness,if any, of this prematurely formed HW, four point bending testswere carried out on fresh HW and SW samples taken from the samegrowth ring, or neighbouring growth rings, at different cross-sectionalpositions at a height of 2 m from six 52-year-old Maritime pines.The mean (±s.e.) modulus of elasticity (E) was 7.6 ±0.3 GPa (longitudinal direction) for all samples. No significantdifferences in E were found between HW and SW; thus HW doesnot play a significant mechanical role in bending stiffness.To test a second hypothesis that early HW formation on the compressedside of trees may maintain a constant, optimal volume of SWaround the tree, the Pipe Model Theory was applied to 12 52-year-oldleaning Maritime pines (angle of lean varied from 0–22°).The surface area (S) of the SW was determined at different heightsup the trunk and correlated with crown surface area (S_crown).Regressions between S_SWandS_crown were highly significant, therebysupporting the theory that HW formation and extension is controlledinternally in Maritime pine. HW formation in Maritime pine thenserves to maintain an optimal proportion of functional SW whichis an important criterion for survival in a species often subjectedto severe drought for long periods. Copyright 2001 Annals ofBotany Company Heartwood, sapwood, bending test, Pipe Model Theory, Pinus pinaster     

Plastic Response of Crown Architecture to Crowding in Understorey Trees of Two Co-dominating Conifers

Crown architecture and growth rate of trunk height, trunk diameterand lateral branches of understorey trees (5–10m tall)were compared between two co-dominating conifers,Abies sachalinensisandPiceaglehnii, in relation to the index of local crowding intensity,W,represented as a function of density, distance and basal areaof taller neighbours. For the two conifers, the growth of trunkheight and diameter was decreased and crowns became flat withincreasingW, keeping crown projection area. Self-pruning oflower branches was more intense inAbiesthan inPiceain crowdedconditions, while both conifers showed similar crown forms inless crowded conditions. These results suggest that the growthin lateral branches exceeded that in height in crowded conditions,especially inAbies. Tree age of both conifers increased withincreasingW, resulting from the low growth rate in crowded conditions.The age of the longest and lowest branch ofPicea, up to 150years, was positively correlated with the tree age ranging from70 to 250 years, whereas that ofAbieswas constant at around30 years irrespective of tree age varying from 40 to 140 years.This result agrees with the observation that agedAbieshad moreflat-shaped crowns than in agedPiceain crowded conditions. Theseresults suggest that each conifer adapted to crowding in differentways: high elongation of branches with high turnover rate forAbiesandviceversaforPicea. Abies; crown form; neighbourhood interference; Picea; plasticity     

Changes in Oregon white oak (Quercus garryana Dougl. ex Hook.) following release from overtopping conifers

Oregon white oak or Garry oak (Quercus garryana Dougl. ex Hook.) is a shade-intolerant, deciduous species that has been overtopped by conifers during the past century in parts of its range due to an altered disturbance regime. We examined the response of suppressed Oregon white oak trees in western Washington, USA, to three levels of release from overtopping Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco). We treated individual oak trees with either full release from competition, partial (“half”) release from competition, or a stand-level thinning of Douglas-fir not directed toward release (control). Five years after treatment, oak trees had suffered no mortality or windthrow. Stem diameter growth was 194% greater in the full-release treatment relative to the control. Acorn production varied widely by year, but in years of higher production, acorn production was significantly greater in both release treatments than in the control. Frequency of epicormic branch formation was significantly increased for years 1 and 2 by the full release; the greatest response occurred between 2 and 6 m above ground level. The greatest number of epicormic branches formed on trees on which the majority of original limbs had died back prior to treatment. Trees with relatively less crown dieback at the time of treatment generally had greater stem growth and acorn production responses to release treatments. Our findings indicate that these released Oregon white oak trees are beginning to recover after an extended period of suppression.     

The Effect of Bud Position on Branch Growth and Bud Abscission in Quercus petraea (Matt.) Liebl.

The time at which a bud began to expand was related to its positionnot only on an individual shoot but also within the crown. Thedistribution of buds and branches on the shoot was uneven; theshoot tip, where they were densely clustered, was termed the‘whorl; and the remainder of the shoot, where they werewidely spaced, the ‘interwhorl’ stem. In spring,the terminal bud started expanding before the ‘whorl’buds which preceded the ‘interwhorl’ stem buds;completion of the flush of growth, determined by the end ofleaf expansion, occurred in the reverse order, ‘interwhorl’> ‘whorl’ > terminal. Similarly bud expansionstarted at the top of the crown and progressed downwards, andthe first shoots to complete their flush were at the bottomof the crown. Approximately 60% of the buds on each shoot beganexpanding in spring but only about half of these formed branches.Bud abscission began in May and by Sep. 45% of buds originallypresent had abscised. Most of-the buds that did not abscisewere the small buds at the base of the shoot that were not originallyassociated with a leaf. Approximately 42% of ‘whorl’buds and 28% of MnterwhorP stem buds formed branches. ‘Whorl’branches were approx. 60% longer that ‘interwhorl’stem branches; buds on the lower surface of the shoot producedlonger branches than those on the upper surface. The implicationsof the results for the development of crown form and selectionof superior oak are discussed. Quercus petraea, oak, buds, branches, crown form     

Low light reflectance may explain the attraction of birds to defoliated trees

Plants use volatile organic compounds to attract invertebratepredators and parasitoids of their herbivore pests. Recently,it has been suggested that plants, either through visual orolfactory cues, may also "cry for help" from vertebrate predatorssuch as birds. We show that in a laboratory choice test, passerinebirds (Parus major and Cyanistes caeruleus) were attracted tothe intact branches of trees (Betula pendula) suffering fromfoliar damage caused by herbivore larvae (Epirrita autumnata)in nontest branches. Species, age, or sex of the experimentalbird or lighting (ultraviolet [UV] or non-UV) did not affectthe preference. However, the birds made a clear choice betweenthe treatments when the trees came from a forest patch receivingmore sunlight, whereas no obvious choice was observed when thetrees came from a shadier forest patch. Results of the choicetest were supported by the spectral reflectance of tree leaves.In the sunnier forest patch, control trees reflected more visiblelight than the herbivore trees, whereas no such difference wasfound in the shadier forest patch trees. We suggest that avianpredators use their vision within visible wavelengths to findinsect-rich plants even when they do not see the prey itemsor damaged leaves.     

The occurrence of non-ring producing branches in Abies lasiocarpa

Lack of annual growth ring production at the base of branches in the lower portion of the crown is a commonly observed phenomenon. In this study, branches with missing rings were found on 47 of 49 Abies lasiocarpa trees sampled. The number of missing rings on the lowest live branch in the crown averaged 12, and ranged as high as 28. The lower one-third of the live crown tended to consist of branches without rings; these branches contained an average of 30% of the total crown leaf area. The ratio of foliage weight to total branch weight, in combination with position of the branch in the canopy, was an effective discriminator of non-ring producing branches. This suggests that both structural and environmental factors influence the cessation of ring production. The potential ecological implications of branches that fail to produce rings are discussed.     

Persistence of<Emphasis Type="Italic">Pseudotsuga menziesii</Emphasis> (Douglas-fir) in temperate coniferous forests of the Pacific Northwest Coast,USA

Old-growthPseudotsuga-Tsuga forests of the Pacific Northwest Coast of North America are characterized by the presence of large, old trees ofPseudotsuga menziesii var.menziesii (Douglas-fir). Colonizing soon after a stand-replacing disturbance,P. menziesii persists in these forests, coexisting for centuries with the late-successional species.P. menziesii survives by maintaining emergent status in the uppermost part of the forest canopy, above the crowns of competing late-successional species. After reaching maximum tree height and crown size,P. menziesii maintains shoots and foliage of the established crown by epicormic shoot production. In this review, we propose that attaining emergent status in the upper canopy combined with the process of crown maintenance contributes to the persistence ofP. menziesii into later stages of succession, making this species a long-lived pioneer that between infrequent disturbances can coexist with late-successional species for centuries.     

Response of eucalypt species to drought

The response of three eucalypt species (Eucalyptus pulchella, Eucalyptus coccifera and Eucalyptus delegatensis) to a severe drought in the summer of 1982/83 was examined at Snug Plains, south-eastern Tasmania. Few large differences in leaf water potential (Ψ_l) or stomatal conductance (gs) were apparent even at the height of the drought when both Ψ_l and soil water potentials (Ψ_s) reached ca. — 4.5 MPa. However, E. pulchella maintained a higher relative water content (RWC) in its leaves than E. coccifera and E. delegatensis, and showed less severe crown damage. After the first light rains substantial interspecific differences in Ψ_l and gs occurred. Eucalyptus pulchella restored normal Ψ_l, gs and RWC more rapidly than the other two species and, even for severely droughted trees, crown growth commenced via epicormic buds near the ends of its branches while for E. delegatensis and E. coccifera crown regeneration was via epicormic buds arising from stems and larger branches. This resulted in a change in dominance in certain stands and showed that E. pulchella was more drought-resistant than E. coccifera, which was in turn more resistant than E. delegatensis. This conclusion was confirmed during competition experiments using potted seedlings. However, potted seedlings differed from mature field trees by maintaining moderate gs at high vapour pressure deficits and closing stomata at Ψ_l below ca. — 2.0 MPa. Substantial variation in the severity of drought symptoms was observed over short distances. This variation appeared to be determined by the moisture-holding capacity of the soil and the biomass of the stand. Although differences in the rooting patterns of seedlings were evident, field measurements of Ψ_l and Ψ_s suggested that all three species were exploiting the same water resource. In contrast to previous studies, the results suggest that large interspecific differences in tissue hydration and crown damage may be present, even though differences in Ψ_l, gs and characteristics of the root system may appear small.     

Stem Diameter Growth of Scots Pine Trees after Increased Mechanical Load in the Crown during Dormancy and (or) Growth

A field experiment with a 2 x2 factorial block design (W_xS_x)was conducted in northern Sweden where the mechanical loadsin the crowns of sixteen 2.5m high Scots pine (Pinus sylvestrisL.)trees were increased during one winter (W₁, dormant period)and (or) summer (S₁, growth period). Trees treated were loadedwith five 2kg bags hung over mid-crown branches close to thestem, i.e. 10kg per tree. After treatment, all trees were leftto grow untreated for one additional year. Trees were then cutat ground level and annual ring widths for the last 5 yearswere measured on stem discs taken at 1, 5, 10, 15, 20, 30 and50% of tree height. Differences between treatments were analysedwith two-way factorial ANOVA. Accumulated treatment responsewas positive for winter loading (W₁S_x) at all levels, and statisticallysignificant at 1, 15 and 20% of tree height. Summer loading(W_xS₁) had positive effects at the lowest and middle parts ofthe stem, and negative in between. No statistically significanttwo-way interaction (W xS) was observed. Results support thehypothesis that Scots pine trees can retain information aboutmechanical forces acting on their stems during winter, and respondto this during the following growth period. The results alsosuggest that stem form of trees in boreal forests may be stronglyaffected by winter conditions. Stem form; mechanical perturbation; Scots pine; Pinus sylvestris; dendrometer; diameter; growth; dormancy; thigmomorphogenesis; wind; sway     

Non-structural carbohydrate pools in a tropical forest

The pool size of mobile, i.e. non-structural carbohydrates (NSC) in trees reflects the balance between net photosynthetic carbon uptake (source) and irreversible investments in structures or loss of carbon (sink). The seasonal variation of NSC concentration should reflect the sink/source relationship, provided all tissues from root to crown tops are considered. Using the Smithsonian canopy crane in Panama we studied NSC concentrations in a semi-deciduous tropical forest over 22 months. In the 9 most intensively studied species (out of the 17 investigated), we found higher NSC concentrations (starch, glucose, fructose, sucrose) across all species and organs in the dry season than in the wet season (NSC 7.2% vs 5.8% of dry matter in leaves, 8.8/6.0 in branches, 9.7/8.5 in stems, 8.3/6.4 in coarse and 3.9/2.2 in fine roots). Since this increase was due to starch only, we attribute this to drought-constrained growth (photosynthesis less affected by drought than sink activity). Species-specific phenological rhythms (leafing or fruiting) did not overturn these seasonal trends. Most of the stem volume (diameter at breast height around 40 cm) stores NSC. We present the first whole forest estimate of NSC pool size, assuming a 200 t ha^–1 forest biomass: 8% of this i.e. ca. 16 t ha^–1 is NSC, with ca. 13 t ha^–1 in stems and branches, ca. 0.5 and 2.8 t ha^–1 in leaves and roots. Starch alone (ca. 10.5 t ha^–1) accounts for far more C than would be needed to replace the total leaf canopy without additional photosynthesis. NSC never passed through a period of significant depletion. Leaf flushing did not draw heavily upon NSC pools. Overall, the data imply a high carbon supply status of this forest and that growth during the dry season is not carbon limited. Rather, water shortage seems to limit carbon investment (new tissue formation) directly, leaving little leeway for a direct CO₂ fertilization effects.     

The Relationship Between Size of Shoot Apices and Morphological Features of Mature Leaves and Stems of Four Species of Angiosperm Trees

Shoot apex, leaf and stem growth parameters for four speciesof deciduous trees were measured. Only in elm was there a correlationbetween the size of shoot apical meristems and mature leaves.In ash, basswood and cottonwood there was no significant differencebetween size of shoot apices of sucker and canopy branches,despite significant differences in lamina size. In the suckerbranches of all species studied there occurred an early, lateralexpansion of the subapical region of the shoot apical meristem.This correlated well with the greater diameter of stem and pithregions of sucker branches. In addition, the season's annualring of xylem was greater in basswood, cottonwood and elm. Diametersof vessel elements were greater in sucker than canopy branchesin three of the four species. Total branch and internode andnumber of nodes per branch were significantly greater for suckerbranches than canopy growth of all species studied. A hypothesis is proposed to explain the development of the verylarge surface area of leaves on sucker branches. This hypothesisis based on the position of sucker branches in relation to theroot system and involves differences in water stress known tobe present in all plants.Copyright 1993, 1999 Academic Press Sucker leaves, canopy leaves, Fraxìnus pennsylvanica Marsh, green ash, Ulmus amerìcana L., American elm, Populus deltoides Marsh, cottonwood, Tilia americana, basswood     

Microbat responses to forest decline

Tree declines have been recorded across forests and woodlands on most continents, causing tree mortality over thousands of square kilometres, yet the impact of tree declines upon mammals have only rarely been quantified. Once the dominant tree over the western parts of the Swan Coastal Plain in Western Australia, tuart (Eucalyptus gomphocephala) forest has been reduced to less than a third of its former range through clearing for agriculture and urban development. Additionally, over the last 30 years, the remnant population has been heavily impacted by a decline that has an unknown cause, but is likely related to a root pathogen coupled with abiotic factors (reduced rainfall, increased salinity and elevated temperatures). Tuart decline is evident as marked canopy dieback, replacement with epicormic growth and increasing bare branches, while leaf litter is lost from the tree surrounds. We examined the effect of tuart decline and other vegetation measures upon bat activity using auditory monitoring. Vegetation structure was correlated with Vespertilionidae bat activity. Falsistrellus mackenziei were more likely to forage around healthy canopies (activity positively correlated with tuart crown density and negatively correlated with tuart crown dieback). By contrast, the other three taxa were more often encountered in declining rather than healthy tuart sites. Chalinolobus gouldii was positively associated with tuart crown dieback. Activity of Vespadelus regulus and Nyctophilus spp. (species not distinguishable from their calls) were significantly positively correlated with an open tall canopy (positively with cover of plants >10 m tall and negatively with overall canopy cover density). There were no vegetation measurements that were strong predictors of activity of two Molossidae species (Ozimops kitcheneri and Austronomus australis), which intercept insects above the forest canopy. This study clearly reveals different factors influencing the activity of bat taxa, which are likely related to where they feed and their manoeuvrability around tree canopies.