No abstract

A Minolta SPAD-502 leaf chlorophyll meter was used for nondestructive data collection on the chlorophyll and nitrogen (N) status of benjamin fig (Ficus benjamina) and cottonwood (Populus deltoides) to quantitatively evaluate foliage quality. The goal was to provide a specific calibration for interpreting SPAD data within a media study for each species. Triplicate SPAD readings were collected from each of six leaves, sampled from forty plants per species, then processed for foliar analysis. Leaf tissue disks were also collected directly over SPAD testing sites for chlorophyll concentration measurement. Significant linear correlations were found between SPAD data and chlorophyll concentrations (r2 = 0.90 in benjamin fig and r2 = 0.91 for cottonwood). A significant, but lower correlation was found between SPAD data and N concentration. The SPAD-N correlations improved from the fifth month to the ninth month harvest (r2 = 0.32 to 0.53 for benjamin fig and 0.26 to 0.42 for cottonwood). The SPAD-502 could be useful for in landscape plant management, and in time for production situations, but baseline data is needed. Consistent protocol in sample collection and seasonal timing is needed prior to use as a predictor for tissue N levels. Development of species, and perhaps cultivar, specific baseline data and sampling procedures will need development, but could yield a rapid, quantitative, in expensive field diagnostic for foliage quality for making cultural management decisions.

No abstract

No abstract

Acer platanoides L. individuals were dissected to determine if branch allometry changed as branches increased in length. Branches were found to transition from a log-log curvilinear relationship to a linear relationship when above 3,000 mm in length. The log-log linear relationship was best modeled with the elastic similarity model. The total number of subordinate lateral branches was found to increase rapidly after the primary branch length surpassed 3,000 mm, suggesting that branches are transitioning to a structural role as size increases. The shift in allometry appears to correspond to a shift from increasing slenderness ratio (length/radius) with increasing branch length to decreasing ratio, and is likely due to a transition from flexible sun branches to stiffer structural branches.

Tree biomechanics studies using dynamic methods of analysis are reviewed. The emphasis in this review is on the biomechanics of open-grown trees typically found in urban areas, rather than trees in forests or plantations. The distinction is not based on species but on their form, because open-grown trees usually grow with considerable branch mass and the dynamic response in winds may be different to other tree forms. Methods of dynamic analysis applied to trees are reviewed. Simple tree models have been developed to understand tree dynamic responses, but these largely ignore the dynamics of branches. More complex models and finite element analyses are developing a multimodal approach to represent the dynamics of branches on trees. Results indicate that material properties play only a limited role in tree dynamics and it is the form and morphology of the tree and branches that can influence the dynamics of trees.

No abstract

Over the last 30 years, researchers have begun to employ biomechanical principles to understand the stability of urban trees. This review concentrates on literature pertaining to trees in temperate urban landscapes, but also includes relevant work from other disciplines and climates as appropriate. The load-bearing capacity of a tree depends on its size and shape and the material properties of its wood. As the trunk and branches increase in diameter, their load-bearing capacity increases. Material properties (e.g., moduli of elasticity and rupture) describe intrinsic wood stiffness and strength, which influence deflection under load and load-bearing capacity, respectively. In wood, material properties vary in relation to a variety of factors, including the direction of loading, moisture content, and tree age. Wood decay reduces a tree’s load-bearing capacity. Although practitioners have developed guidelines to assess its effect, existing guidelines should be investigated, refined or rejected on the basis of rigorous scientific testing. Static load tests have been developed to address this question, as well as investigate the likelihood of uprooting, which accounts for up to 35% of tree failures. While much has been learned, many questions remain about the static load-bearing capacity of trees growing in urban landscapes.