Wide Crown Research Articles

The growth and genetic potentials of gempol (Nauclea orientalis L.) as shading trees in urban landscapes

Gempol (Nauclea orientalis L.) is a fast-growing species with a wide crown and large diameter. This native species has the ability to replenish soil fertility and to control erosion and may be integrated in urban landscapes for genetic conservation purposes. However, the ecological function of the species as well as the genetic potentials of this species have not been investigated. This study aimed to assess the growth performance and to evaluate the genetic potentials of gempol by utilizing the progeny test stand that was established in 2011 using a Randomized Complete Block Design (RCBD). The area was divided into 10 blocks in which each block was represented by 49 families planted using 4-tree-plot replication. The observation showed that as much as 67% of the trees had a straight stem form with the average score of 4.38. The diameter ranged between 9.17 – 14.23 cm, with a total height that ranged 5.90 – 8.60 m and a crown diameter with a range of 2.06 – 3.32 m. Depending on the traits, the heritability varied between low to high. Clear bole height performed the highest heritability with a value of 0.60 (family) and 0.52 (individual). A Crown diameter indicated a moderate positive correlation with a diameter degree of 0.328 and denoted a strong positive correlation with a total height degree of 0.798.

Disentangling isolated dental remains of Asian Pleistocene hominins and pongines.

Scholars have debated the taxonomic identity of isolated primate teeth from the Asian Pleistocene for over a century, which is complicated by morphological and metric convergence between orangutan (Pongo) and hominin (Homo) molariform teeth. Like Homo erectus, Pongo once showed considerable dental variation and a wide distribution throughout mainland and insular Asia. In order to clarify the utility of isolated dental remains to document the presence of hominins during Asian prehistory, we examined enamel thickness, enamel-dentine junction shape, and crown development in 33 molars from G. H. R. von Koenigswald's Chinese Apothecary collection (11 Sinanthropus officinalis [= Homo erectus], 21 “Hemanthropus peii,” and 1 “Hemanthropus peii” or Pongo) and 7 molars from Sangiran dome (either Homo erectus or Pongo). All fossil teeth were imaged with non-destructive conventional and/or synchrotron micro-computed tomography. These were compared to H. erectus teeth from Zhoukoudian, Sangiran and Trinil, and a large comparative sample of fossil Pongo, recent Pongo, and recent human teeth. We find that Homo and Pongo molars overlap substantially in relative enamel thickness; molar enamel-dentine junction shape is more distinctive, with Pongo showing relatively shorter dentine horns and wider crowns than Homo. Long-period line periodicity values are significantly greater in Pongo than in H. erectus, leading to longer crown formation times in the former. Most of the sample originally assigned to S. officinalis and H. erectus shows greater affinity to Pongo than to the hominin comparative sample. Moreover, enamel thickness, enamel-dentine junction shape, and a long-period line periodicity value in the “Hemanthropus peii” sample are indistinguishable from fossil Pongo. These results underscore the need for additional recovery and study of associated dentitions prior to erecting new taxa from isolated teeth.

ASSESSMENT OF TEAK PRODUCTION CHARACTERISTICS USING 1 M SPACING IN A PLANTATION IN NICARAGUA

Cette étude s’est déroulée dans une plan- tation forestière en Amérique centrale, proche de la ville de Diriamba au Nica- ragua, où des plantations de teck sur 48,9 ha, dans une zone de reboisement de 76,5 ha, sont renouvelées depuis 2006 (2006 : 7,90 ha ; 2007 : 13,63 ha ;2008 : 11,93 ha ; 2009 : 12,87 ha ; 2010 :21,70 ha). Cette plantation sort de l’ordi- naire du fait de l’espacement de 1 x 1 m des arbres et des facteurs écologiques limitants de cette zone tropicale aride. L’espacement de 1 x 1 m a été choisi pour favoriser la croissance en hauteur et obtenir ainsi des tiges de haute taille, et pour limiter les ramifications afin d’éviter la formation de houppiers importants. Cela permet de démarrer une production de poteaux de teck, adaptés à certaines constructions, dès la première coupe d’éclaircissement. Les paramètres de croissance des tecks (hauteur, circonfé- rence) ont été mesurés dans les placettes expérimentales mises en place en 2011. Des données complémentaires (morta- lité, arbres cassés ou tordus) ont égale- ment été relevées. Une méthodologie de terrain a été développée et les résultats restitués sous forme de tableaux et gra- phiques. Une évaluation statistique des paramètres de croissance a été menée à partir des mesures prises sur les placettes expérimentales délimitées dans la planta- tion. Les jeunes arbres plantés la même année ont été comparés selon leur prove- nance en termes de hauteur, de circonfé- rence, de productivité et de mortalité. Au total, 10 955 arbres sur 143 placettes ont été mesurés. Sur ces peuplements de 1 à 5 ans d’âge, le bois sur pied total est estimé à 1 287,89 m3, la masse moyenne de bois à l’hectare à 17,89 m3, la hauteur moyenne des peuplements à 3,03 m et la circonférence moyenne à hauteur de poitrine à 2,74 cm. Les arbres cassés représentent 5,64 %, les arbres tordus 5,66 % et la mortalité moyenne s’établit à 21,48 %.

Response of species and stand types to snow/wind damage in a temperate secondary forest, Northeast China

Snow/wind damage is one of the important natural disturbances in forest ecosystems, especially in a montane secondary forest. However, the effects of snow/wind damage remain unclear which affects the management of these forests. Therefore, we investigated the responses of species, individual tree traits and stand structure to snow/wind damage in a montane secondary forest. Results show that, amongst the canopy trees, Betula costata exhibited the most uprooting, bending and overall damage ratio (the number of damaged stems to the total number of stems in a plot); Quercus mongolica showed the highest breakage ratio and Fraxinus mandshurica and Juglans mandshurica the least overall damage ratios. Among the subcanopy trees, Carpinus cordata, Acer mono, Acer tegmentosum and Acer pseudo-sieboldianum showed the least uprooting and breakage, and the most bending damage. A. pseudo-sieboldianum demonstrated the lowest breakage and highest bending damage ratios. These findings indicate that different species have various sensitivities to snow/wind damage. Larger trees (taller, wider crowns) tend to break and become uprooted, while smaller trees are bent or remain undamaged, suggesting that tree characteristics significantly influence the types of damage from snow and wind. Stands of Q. mongolica and B. costata had the highest damage ratios, whereas A. pseudo-sieboldianum had the lowest snapping ratio. In summary, the severity and type of snow/wind damage are related to individual tree attributes and stand-level characteristics. Therefore, selection of suitable species (e.g., shorter, smaller with deep root systems, hard wood, bending resistance and compression resistance) and appropriate thinning are recommended for planting in the montane secondary forests.

Novel aesthetic treatment of bilateral gemination of maxillary central incisors

Abstract The fusion of adjacent tooth buds and the formation of a single tooth or the gemination of a single tooth are rare and occur less often bilaterally in the permanent dentition. Following a brief literature review, this case report describes the multidisciplinary treatment of an adolescent patient who presented with the bilateral gemination of the permanent central incisors. It was planned to restore the teeth using porcelain laminated veneers after the completion of orthodontic treatment. The wide crown of the geminated incisors was restored, to mimic the morphology of two teeth, comprising a wider central and a narrower lateral incisor. In carefully selected cases, this conservative treatment option preserves the physiologic function of the teeth and the periodontal ligament.

Functional traits shape size-dependent growth and mortality rates of dry forest tree species

Aims: Functional traits have emerged as an important tool to evaluate plant performance. However, the environmental conditions and ecological pressures that plants face change with their size, and the relationship between traits and plant performance should therefore be size-dependent, which has rarely been tested. Methods: Here, we evaluated over a broad range of tree sizes the interspecific relationship between tree growth and mortality and eight functional stem, leaf and seed traits. We did so across 59 tree species in Brazilian dry forests and evaluated whether the relationships found for wet forest types in the literature also hold for dry forests, where water rather than light might limit tree performance. Important Findings: We indeed found a strong size-dependent relationship between demographic rates and functional traits. At small sizes, when trees are in the shaded understory, species with functional trait values that enhance light capture or shade tolerance (i.e. higher maximum adult stature, taller heights, wider crowns, higher seed mass) have higher growth and/or lower mortality rates (MR). This relationship disappears at larger sizes when trees attain better light conditions in the canopy. Drought adaptations play only a role at larger tree sizes; once trees are in the dry and exposed canopy, species with higher wood density (an indicator of cavitation resistance) have lower MRs. Our study shows that both drought and shade adaptations are important in this dry forest, and that the relationships between functional traits and plant performance changes with plant size. Plant size should therefore explicitly be included as an axis of variation in functional analyses, to better understand the relationship between functional traits and demographic rates.

Macroevolutionary assembly of ant/plant symbioses: Pseudomyrmex ants and their ant-housing plants in the Neotropics.

Symbioses include some of the clearest cases of coevolution, but their origin, loss or reassembly with different partners can rarely be inferred. Here we use ant/plant symbioses involving three plant clades to investigate the evolution of symbioses. We generated phylogenies for the big-eyed arboreal ants (Pseudomyrmecinae), including 72% of their 286 species, as well as for five of their plant host groups, in each case sampling more than 61% of the species. We show that the ant-housing Vachellia (Mimosoideae) clade and its ants co-diversified for the past 5 Ma, with some species additionally colonized by younger plant-nesting ant species, some parasitic. An apparent co-radiation of ants and Tachigali (Caesalpinioideae) was followed by waves of colonization by the same ant clade, and subsequent occupation by a younger ant group. Wide crown and stem age differences between the ant-housing genus Triplaris (Polygonaceae) and its obligate ant inhabitants, and stochastic trait mapping, indicate that its domatium evolved earlier than the ants now occupying it, suggesting previous symbioses that dissolved. Parasitic ant species evolved from generalists, not from mutualists, and are younger than the mutualistic systems they parasitize. Our study illuminates the macroevolutionary assembly of ant/plant symbioses, which has been highly dynamic, even in very specialized systems.

Computational Study of Subdural Cortical Stimulation: Effects of Simulating Anisotropic Conductivity on Activation of Cortical Neurons.

Subdural cortical stimulation (SuCS) is an appealing method in the treatment of neurological disorders, and computational modeling studies of SuCS have been applied to determine the optimal design for electrotherapy. To achieve a better understanding of computational modeling on the stimulation effects of SuCS, the influence of anisotropic white matter conductivity on the activation of cortical neurons was investigated in a realistic head model. In this paper, we constructed pyramidal neuronal models (layers 3 and 5) that showed primary excitation of the corticospinal tract, and an anatomically realistic head model reflecting complex brain geometry. The anisotropic information was acquired from diffusion tensor magnetic resonance imaging (DT-MRI) and then applied to the white matter at various ratios of anisotropic conductivity. First, we compared the isotropic and anisotropic models; compared to the isotropic model, the anisotropic model showed that neurons were activated in the deeper bank during cathodal stimulation and in the wider crown during anodal stimulation. Second, several popular anisotropic principles were adapted to investigate the effects of variations in anisotropic information. We observed that excitation thresholds varied with anisotropic principles, especially with anodal stimulation. Overall, incorporating anisotropic conductivity into the anatomically realistic head model is critical for accurate estimation of neuronal responses; however, caution should be used in the selection of anisotropic information.

Natural establishment of indigenous trees under planted nuclei: A study from a clear-felled pine plantation in an afrotropical rain forest

Applied nucleation has been proposed as a cost-effective reforestation alternative to large-scale re-planting or establishing plantations with exotic tree species. We tested applied nucleation in a regenerating clear-cut pine plantation in Kibale National Park, Uganda, where natural succession had been slow. We planted Neoboutonia macrocalyx, a relatively common indigenous pioneer tree species with animal dispersed seeds and a wide crown, in the pine plantation clear-cuts as seeds and transplanted seedlings. After six years of monitoring the growth of the nucleus trees we identified all naturally recruited seedlings under the nuclei and adjacent control sites without planted nuclei. We monitored the growth and turnover of the recruited seedlings for one year and examined the ground vegetation structure under the nuclei and control sites. We found that the N. macrocalyx nucleus trees had survived equally well if planted as seeds or transplanted seedlings and had attained heights up to ten meters tall. Understory vegetation structure under the established nuclei was less dense (P=0.001) and shorter (P=0.039) compared to control sites. We also found that natural recruitment of indigenous tree species under the nuclei was higher compared to control sites. The seedling density under the nuclei was significantly higher (P=0.035), and there was a significant difference in the composition of seedling communities (P=0.0001) with a larger number of different tree species found under the nuclei. We found that a viable seedling community had been established with a good potential to take over when planted nucleus trees eventually die. Our results show that planting nucleus trees can increase recruitment of indigenous tree species in locations where natural succession is otherwise slow.

Variation in biomass distribution and nutrient content in loblolly pine (Pinus taeda L.) clones having contrasting crown architecture and growth efficiency

Loblolly pine (Pinus taeda L.) is well adapted across an extensive range of sites, is responsive to silvicultural treatments, and has undergone genetic improvement through traditional tree breeding programs, with selection based primarily on rapid growth and disease resistance. Loblolly pine clones with contrasting crown architecture provide an opportunity to better understand the mechanistic relationships among stem growth, biomass partitioning, and component nutrient content. We assessed inventory data from four clones which exhibited a range of crown widths. Using a subset of three clones, we measured crown sizes, crown volume, biomass allocated to components (foliage, branches, stemwood and bark), and component nutrient concentration and content to assess variation in allocation and growth efficiency. Clonal variation in biomass distribution patterns helped explain variation in growth efficiency between the narrow crown clone (ARB-1) and wide crown clone (ARB-4). Clone ARB-1 was more efficient at producing stem biomass increment per unit foliar biomass and unit foliar nutrient content than clone ARB-4; this was consistent with the concept of a crop ideotype. This study provides new information useful for improving our understanding of the relationships among crown structure, biomass distribution patterns, growth efficiency, and tree productivity, and may help guide clonal tree population management.

THE EFFECTS OF TREE SPECIES ON REDUCTION OF THE RATE OF NOISE POLLUTION AT THE EDGE OF HYRCANIAN FOREST ROADS

Plants have an effective role in reducing noise pollution. The aim of this study was to evaluate the impact of broad-leaved and coniferous species on reducing noise pollution according to the distance from the sound source and the tree species type. For this purpose, 25 plots for coniferous species and 25 plots for the broadleaved species was selected. The decibel-meter (Casella Enhances CEL-630) and the trumpet (FIAMM) of machine were used to measure the sound level. Results indicated that the tree at the edge of the forest roads causes to decrease noise pollution. As, there was a significant difference between the distance of 300 meter as compared with the distances of 20 meter and 100 meter for the broadleaved species (P<0.05). We also found an inverse relationship between frequency of broadleaved and coniferous trees and the rate of sound level (R2 = 0.94 for coniferous; R2 = 0.89 for hardwood). In plots consist of broadleaved species, the sound level at the distances of 20, 100 and 300 meter have been reduced 10.6, 14.5 and 19.4 dB, respectively. This difference with considering these distances was respectively 10.4, 14.3 and 16.8 dB for coniferous species. It is suggested that the species with low H:D ratio (Height of tree: DBH) and wide crown used to decrease noise pollution. The coniferous species which is grown dense can be used to provide aesthetic quality and increase number of stories.

Linking size‐dependent growth and mortality with architectural traits across 145 co‐occurring tropical tree species

Tree architecture, growth, and mortality change with increasing tree size and associated light conditions. To date, few studies have quantified how size-dependent changes in growth and mortality rates co-vary with architectural traits, and how such size-dependent changes differ across species and possible light capture strategies. We applied a hierarchical Bayesian model to quantify size-dependent changes in demographic rates and correlated demographic rates and architectural traits for 145 co-occurring Malaysian rain-forest tree species covering a wide range of tree sizes. Demographic rates were estimated using relative growth rate in stem diameter (RGR) and mortality rate as a function of stem diameter. Architectural traits examined were adult stature measured as the 95-percentile of the maximum stem diameter (upper diameter), wood density, and three tree architectural variables: tree height, foliage height, and crown width. Correlations between demographic rates and architectural traits were examined for stem diameters ranging from 1 to 47 cm. As a result, RGR and mortality varied significantly with increasing stem diameter across species. At smaller stem diameters, RGR was higher for tall trees with wide crowns, large upper diameter, and low wood density. Increased mortality was associated with low wood density at small diameters, and associated with small upper diameter and wide crowns over a wide range of stem diameters. Positive correlations between RGR and mortality were found over the whole range of stem diameters, but they were significant only at small stem diameters. Associations between architectural traits and demographic rates were strongest at small stem diameters. In the dark understory of tropical rain forests, the limiting amount of light is likely to make the interspecific difference in the effects of functional traits on demography more clear. Demographic performance is therefore tightly linked with architectural traits such as adult stature, wood density, and capacity for horizontal crown expansion. The enhancement of a demographic trade-off due to interspecific variation in functional traits in the understory helps to explain species coexistence in diverse rain forests.

Do wide crowns in arid woodland trees reflect hydraulic limitation and reduction of self-shading?

In arid regions many tree species develop broad crowns. A number of hypotheses involve trade-offs between growth in height and horizontal spreading, but there is no explanation for the switch from vertical to horizontal growth during development. Using Acacia papyrocarpa Benth as a model, we measured tree height and crown shape across different sites and topographic positions. We also measured δ13C of phyllodes from crown tops and lateral spreading branches. Trees were significantly taller at the base of a hill, where water availability is typically greater, than on the adjacent steep hillslope. In contrast, δ13C from the treetops was not significantly different across this topographic gradient, despite variation in tree height. In addition, δ13C was higher at treetops than in lower, lateral branches. These observations are consistent with hydraulic limitation to tree height. The shape of mature and young crowns in open environments was not symmetrical. At all sites, branches were shortest, but tree crowns tallest, on south-facing (i.e. shadiest) aspect of crowns. This suggests that light limitation may also affect crown development. If upper branches become water-limited and lower branches light-limited, then middle lateral branches become the less-stressed part of the crown and may grow more, producing a broad crown.

Differentiation in architectural properties and functional traits of forest-floor saplings among heath, peat swamp, and mixed dipterocarp forests

There are physiognomically distinctive forest types in lowland tropics reflecting variation in edaphic conditions. Tree saplings that contribute to forest regeneration are expected to show morphological properties in response to forest environment. However, it remains unknown how sapling properties are similar or different across forest types. We examined architectural and functional traits of forest floor saplings across heath, peat swamp, and mixed dipterocarp forests that characterize lowland forests in Kalimantan, Indonesia. Saplings (150-310 cm tall) of 41 species, which represent each forest type, were selected under the canopy of developed forest stands. Among these, we chose one species found in all forest types and two species in heath and peat swamp forests. Significant differences in crown allometries were found across forest types and across species. Saplings in mixed dipterocarp forest had thicker trunk and wider crown at the same sapling height compared to other forests and they had higher specific leaf area, higher mass-based leaf nitrogen content and lower wood density. Heath forest saplings showed lowest leaf nitrogen content and highest wood density. Species with across forest-type distribution showed intra-specific variation in sapling traits, and which was similar to the difference among forest types. We conclude that saplings show morphological response to nutritional and water conditions that characterize forest types.

Measuring tree height: a quantitative comparison of two common field methods in a moist tropical forest

SummaryTree height is a key variable for estimating tree biomass and investigating tree life history, but it is difficult to measure in forests with tall, dense canopies and wide crowns. The traditional method, which we refer to as the ‘tangent method’, involves measuring horizontal distance to the tree and angles from horizontal to the top and base of the tree, while standing at a distance of perhaps one tree height or greater. Laser rangefinders enable an alternative method, which we refer to as the ‘sine method’; it involves measuring the distances to the top and base of the tree, and the angles from horizontal to these, and can be carried out from under the tree or from some distance away.We quantified systematic and random errors of these two methods as applied by five technicians to a size‐stratified sample of 74 trees between 5.7 and 39.2 m tall in a Neotropical moist forest in Panama. We measured actual heights using towers adjacent to these trees.The tangent method produced unbiased height estimates, but random error was high, and in 6 of the 370 measurements, heights were overestimated by more than 100%.The sine method was faster to learn, displayed less variation in heights among technicians, and had lower random error, but resulted in systematic underestimation by 20% on average.We recommend the sine method for most applications in tropical forests. However, its underestimation, which is likely to vary with forest and instrument type, must be corrected if actual heights are needed.

Short-Term Fading Behavior in High-Speed Railway Cutting Scenario: Measurements, Analysis, and Statistical Models

Cuttings are widely used in high-speed railway (HSR) transportation to ensure the flatness of rails. The special structure of cuttings results in rich reflection and scattering, and creates dense multipath components. This paper presents a series of measurements of the propagation channel at 930 MHz conducted along the “Zhengzhou-Xi'an” HSR of China, to characterize the small-scale fading behavior of rail-cutting scenarios as a function of the geometry of cuttings, including crown width and bottom width. Raw data are collected in six cuttings (five cuttings are used for developing the model, while the other one is used for validation) in rural and suburban environments. We propose a set of effective methods to statistically model the spatial/temporal variations - including fade depth (FD), level crossing rate (LCR), average fade duration (AFD), and Ricean <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</i> -factor - as a function of the structural parameters of cuttings. Akaike's Information Criterion (AIC)-based evaluation indicates that the Ricean distribution is the best to describe small-scale fading. In addition, the rich multipath and directionality of the transmitting antennas lead to a non-monotonous dependence of the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</i> -factor on the distance between transmitter and receiver. The autocovariance function of the deviation of the extracted <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</i> -factors from the proposed model is presented and the coherence length is investigated. Our results show that even though a cutting is a scenario with severe fading, a “wide” cutting (i.e., with both wide crown and bottom widths) is conducive to the reduction of the severity of fading.

Habitat Complexity andCaryocar brasilienseHerbivores (Insecta: Arachnida: Araneae)

Caryocar brasiliense Camb. (Malpighiales: Caryocaraceae) trees have a wide distribution in the cerrado. This plant is protected by federal laws and is left in deforested areas of the cerrado. This situation increases the damage to leaves, flowers, and fruits from chewing insects. We studied the effect of habitat complexity and plant architecture on the diversity and abundance of the Lepidoptera, Coleoptera, and Hymenoptera herbivores and their predators on trees of C. brasiliense in cerrado, pasture, and on the Campus of the Federal University of Minas Gerais. We observed 13 rare, 2 common, and 1 constant species of herbivores insects; and 3 rare, 8 common, and 1 constant species of predators on trees. Higher diversities and number of species of herbivores insects and their predators were observed in pasture than in the cerrado and on the campus of the Federal University of Minas Gerais. Herbivorous insects were most abundant in pasture and least abundant on the university campus. Predators were most abundant in pasture and least abundant in the cerrado. Ants, spiders, and predatory bugs are important in the reduction of the defoliators and leaf miners insects. The percentages of defoliation and populations of defoliators and ants were higher on C. brasiliense trees with wider crowns. We found a positive correlation of soil aluminum concentration with percent defoliation and numbers of lepidopteran leaf miners. On the other hand, increased soil pH was correlated with reduction in percent defoliation and numbers of lepidopteran leaf miners.

Understory light predictions in mixed conifer mountain forests: Role of aspect-induced variation in crown geometry and openness

Predicting light availability in forest understory is a key step in the modeling of forest dynamics. Aspect is often the main source of environmental variation in mountain forests, and so aspect-induced differences in crown geometry and transparency can be expected to affect light transmission through the canopy and modify understory light predictions. To gain a better understanding of the effects of aspect on the light interception capacity of forest trees, we determined crown allometry and crown openness (CO) in 120 adult trees of three common conifer species in the Pyrenees (mountain pine, Scots pine and silver fir), sampled in eight montane-subalpine forests that each included two contrasting aspects. CO was calculated from digital photographs and several crown outlines were automatically determined to prevent user bias. We also calculated crown irregularity as the difference between crown surface area for the tightest and loosest outlines. Predictions of understory light availability obtained from a forest dynamics model were compared with actual values obtained from 115 hemispherical photographs. Crown length and CO varied across species following previous rankings of shade tolerance. Both pines had longer and wider crowns in the north aspect, whereas fir crown geometry was not affected by aspect. CO depended largely on the method chosen for determining crown outline, ranging from 0.10 to 0.56, and the tightest outline provided the best predictions of understory light (slope=0.89, R2=0.46). CO was also significantly affected by tree size and plot aspect (p<0.001): crowns in southern-oriented plots were more open for mountain pine and silver fir, whereas Scots pine showed the opposite trend. Predictions of understory light were significantly improved when crown geometry and openness were allowed to vary according to plot aspect (slope of the regression: 0.95, R2=0.50). Our results suggest that aspect should be explicitly considered when modeling ecological processes and dynamics in mixed mountain forests given its influence on both abiotic conditions and crown responses to them.

Architecture of Iberian canopy tree species in relation to wood density, shade tolerance and climate

Tree architecture has important consequences for tree performance as it determines resource capture, mechanical stability and dominance over competitors. We analyzed architectural relationships between stem and crown dimensions for 13 dominant Iberian canopy tree species belonging to the Pinaceae (six Pinus species) and Fagaceae (six Quercus species and Fagus sylvatica) and related these architectural traits to wood density, shade tolerance and climatic factors. Fagaceae had, compared with Pinaceae, denser wood, saplings with wider crowns and adults with larger maximal crown size but smaller maximal height. In combination, these traits enhance light acquisition and persistence in shaded environments; thus, contributing to their shade tolerance. Pinaceae species, in contrast, had low-density wood, allocate more resources to the formation of the central trunk rather than to branches and attained taller maximal heights, allowing them to grow rapidly in height and compete for light following disturbances; thus, contributing to their high light requirements. Wood density had a strong relationship with tree architecture, with dense-wooded species having smaller maximum height and wider crowns, probably because of cheaper expansion costs for producing biomechanically stable branches. Species from arid environments had shorter stems and shallower crowns for a given stem diameter, probably to reduce hydraulic path length and assure water transport. Wood density is an important correlate of variation in tree architecture between species and the two dominant families, with potentially large implications for their resource foraging strategies and successional dynamics.

Occlusion regulates tooth-root elongation during root development in rat molars

Occlusion is commenced by contact of a tooth with an opposing tooth and is the mechanical force working against the periodontal ligament (PDL). However, the influences of occlusion during root development remain uncertain. By extracting the unerupted counterpart molars of rats, we established a non-occlusal model that directly examined the effects of the absence of occlusion in developing molars using micro-computed tomography (μ-CT) and histological procedures. The μ-CT data for experimental molars confirmed no attrition and hypogenesis of the alveolar bone. Root lengths in experimental groups increased more than in control groups. Histological findings of experimental molars showed a wide crown pulp, a long and narrow root, immature Sharpey's fibers, and hypogenesis of cementum. Proliferating cells localized in Hertwig's epithelial root sheath (HERS), the apical pulp, and the PDL of experimental teeth. Furthermore, cell-proliferative activity in experimental roots exceeded that in normal roots. These data indicate that cell proliferation is decreased by occlusion during root formation. Thus, occlusion is one factor that regulates root elongation.