Lai Fern Ow

Comparing the morphology and physiology of trees planted in containers and in-ground sites

Abstract Restricted root volume poses a constraint to the successful establishment of containerised trees. The potential for growth and survival in containers for urban forests is important to ensure a sustainable population of sizeable urban trees given the staggering pace of development. In this study, it was found that the restricted soil environment inside the containers had no effect on the morphometric and physiological characteristics of container trees. A positive relationship was found between xylem pressure potential and Fv/Fm. A stronger correlation between xylem pressure potential and soil water status was observed. This indicated the importance of soil water status for optimal photosynthetic function and overall tree growth. Biomass data indicated that container trees tended to allocate more carbon to leaves, stems and branches while in-ground trees channelled carbon into leaves and roots. The potential for growing trees in containers is a desirable alternative to in-ground planting, providing urban municipalities with the option to save and relocate trees when confronted with development. In doing so, cities can work towards the development of a sustainable population of medium to large urban trees.

Calculating the value of the tropical, urban tree Albizia saman

This study compared estimated appraised value of trees using cost- and benefit-based approaches. Benefit-based appraisals provide estimates which highlight the relative contribution of different benefit types. Cost-based approaches are linked to regional market and nursery stock prices and/or tabulated through a point rating system with the inclusion of a monetary factor. The approaches used were the Council of Tree and Landscape Appraisers trunk formula, and the Helliwell approach. There were striking differences in the appraised value of the same trees (Albizia saman) between the two methods but this tended to be limited to trees of smaller girth sizes. The proposed benefit-based approach used in this study used a product score obtained through the rating of some 11 attributes/factors with no association to a monetary conversion factor (MCF). The same tree species used as in the cost-based methods were used in the benefit-based approach but this approach required the selection of four different specimens ranging from weak to highly desirable. The data collected showed that on each extreme end of the scale, there was some 98.6% difference in appraised value of trees. The key objective in the development of this proposed methodology was to allow for a rapid, effective decision-making process on tree removal and/or replacement for field arborists. Where the situation warrants a cost-based system for issues such as compensation, there are already established cost-based methodologies in place, which can serve this purpose. There is, therefore, no added advantage to introduce a new system with a MCF; rather a simplistic benefit-based methodology was an advantageous alternative. This provided fair and reasonable estimates of the value of trees by illustrating the relative contribution of the different benefits. Ultimately, the employment of both cost- and benefit-based methodologies may be necessary in some situations where a holistic approach is required for tree valuation. Although assigning a monetary value to a tree is based predominantly on the perception of the appraiser, establishing the value of trees is still fundamental to arboriculture and urban forestry. Without an estimate of tree value, there is little to motivate investment in tree management.

Performance of Three Warm Season Turfgrasses under Linear Gradient Irrigation

Drought is an environmental stress that will lead to the decline and loss of turfgrass. Most areas of Singapore, require irrigation to maintain desirable turfgrass quality. As water conservation has become an important issue, researchers have put significant effort into developing and evaluating turf species with exceptional drought resistance (Carrow, 1995; Peacock, 2001; Fu et al., 2004; Barton and Colmer, 2006; Huang, 2008). The results from these studies suggest that turfgrasses differ in their performance during drought stress. In a study by Songul et al. (2011), rankings of relative drought resistance under Mediterranean conditions of Turkey indicated that relative drought resistance was superior for Cynodon dactylon x C. transvaalensis (Hybrid green couch), Bouteloua dactyloides (buffalo grass), and Paspalum notatum (bahia grass). Conversely, drought resistance was less ideal for Paspalum vaginatum (seashore paspalum), Eremochloa ophiuroides (centipede grass), Zoysia matrella, and Festuca arundinacea (tall fescue). In another field observation by SeedLand® (LawnGrasses.com), grasses for drought resistance were ranked in the order of Cynodon dactylon x C. transvaalensis, Paspalum notatum, Zoysia matrella, Eremochloa ophiuroides, Festuca spp, and Stenotaphrum secundatum (St. Augustine grass). Noteworthy however, that Morris and Shearman (2007) suggested that variations in the rankings of drought resistance may be a result of the varying climatic conditions of the various sites, the assessment method, and duration of the drought. Zoysia matrella, Stenotaphrum secundatum, and Axonopus compressus (broadleaf carpet grass) are the most commonly used turfgrass species in Singapore, but the use of Cynodon dactylon has increased in recent years because of the ability to tolerate drought. This grass has been used as an alternative to ABSTRACT. The appropriate level of irrigation for turfgrasses is vital to the performance of the turfgrass as well as conservation of water. Linear gradient irrigation system (LGIS) facilitates long-term study of turf performance under continuous irrigation gradients at extreme ends of the irrigation scale. The objectives of this study were to: a) determine the minimum irrigation requirements and relative drought resistance in three warm season turfgrasses; and b) evaluate the medium to long-term effects of irrigation levels on turf persistence, weed invasion, and susceptibility to diseases. Results suggest that grasses differed in drought resistance and persistence under variable irrigation regimes. Irrigation (Ep) required for consistent acceptable turf quality for respective grasses was Cynodon dactylon x C. transvaalensis (61%), Zoysia matrella L. Merr (73%), and Stenotaphrum secundatum ‘Palmetto’ (86%). Brown patch infection was most prevalent in Stenotaphrum secundatum ‘Palmetto’ at 12 and 125% Ep irrigation. Cynodon dactylon x C. transvaalensis and Zoysia matrella L. Merr were better able to adapt to the various irrigation regimes, and this ability allowed these species to resist drought, and maintain turf coverage which in turn, kept weeds and the occurrence of diseases at bay. Ranking these grasses for their drought tolerance abilities showed that Cynodon dactylon x C. transvaalensis had the most outstanding resistance against drought, followed by Zoysia matrella L. Merr, and lastly, Stenotaphrum secundatum ‘Palmetto’. Despite having the highest irrigation requirement, Stenotaphrum secundatum ‘Palmetto’ was still not able to maintain persistence at high irrigation regimes. Likewise, this grass also lost turf coverage at low irrigation levels.

Effect of Compost and Hydroabsorbent Polymer on Tree Growth and Soil Properties in a Tropical Urban Environment

ABSTRACT Horticultural application of hydroabsorbent polymer (HP) has drawn research attention due to its perceived benefits to plant growth. Few studies have compared the use of compost and HP amendments on tree establishment in tropical urban environments. An experiment was conducted to assess the effect of compost (40% v v–1) and HP (3 and 5 kg m–3) on the growth of two native tree saplings (Calophyllum soulattri and Syzygium myrtifolium) in loamy and sandy soils. The HP treatments significantly affected soil pH and extractable phosphorus (P) and potassium (K), whereas combined application of compost and HP (5 kg m–3) resulted in significantly higher nitrogen (N) in both soil types. Plant diameter and height were significantly higher following HP application. This experiment demonstrates the efficacy of HP that can cater the plant requirements at the initial growth stages which are crucial for their successful establishment in tropic urban degraded soils.

Effects of varying establishment approaches on the growth of urban street trees

ABSTRACT Limited rooting space is frequently a major impediment to the growth of street trees. Different approaches to enhance the soil volume accessible to roots have been implemented in urban cities within the last decade. This survey observed the growth and health of trees planted in a) structural, load-bearing soil; b) biochar-stone-based load-bearing soil; and c) planting pits installed with structural cells. These alternative planting methods were compared against trees grown in conventional planting pits. The experimental trees were either street trees or sited within a plantation with similar soil conditions. The results indicated that tree growth and health ratings were found to be superior in the order of, planting in pits with structural cells, load-bearing material of structural soil and the biochar-stone blend, and conventional planting pits. Tree growth in structural cells was found to be 37% higher than conventional planting pits. As such, these approaches can be considered at sites where conventional pits cannot be used for tree establishment. Tree growth in pits with structural cells is therefore recommended wherever space for large planting pits is limited and when trees need to be sited close to infrastructure.