http://www.researchonline.mq.edu.au/vital/access/services/Feed ${session.getAttribute("locale")} 5 http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:20484 Production and distribution of fine roots (≤2.0 mm diameter) are central to belowground ecological processes. This is especially true where vegetation serves as a pump to prevent saturation of soil and possible drainage of excess water into or from potentially toxic waste material stored underground or in mounds aboveground. In this study undertaken near Sydney in Australia, we determined fine root biomass and evapotranspiration (ET) on a waste disposal site restored with either a 15-year-old grass sward or plantations of mixed woody species that were either 5 years old (plantation-5) with a vigorous groundcover of pasture legumes and grasses, or 3 years old (plantation-3) with sparse groundcover. These sites were compared with nearby remnant woodland; all four were located within 0.5-km radius at the same site. Ranking of fine root biomass was in the order woodland (12.3 Mg ha⁻¹) > plantation-5 (8.3 Mg ha⁻¹) > grass (4.9 Mg ha⁻¹) > plantation-3 (1.2 Mg ha⁻¹) and was not correlated with nutrient contents in soil or plants, but reflected the form and age of the vegetation covers. Trends in root length density (RLD) and root area index (RAI) followed those in root biomass, but the differences in RAI were larger than those in biomass amongst the vegetation covers. Annual ET in the dry year of 2009 was similar in the three woody vegetation covers (652–683 mm) and was at least 15% larger than for the grass (555 mm), which experienced restrained growth in winter and periodic mowing. This resulted in drainage from the grass cover while there was no drainage from any of the woody vegetation covers. In plantation-5, root biomass, RAI and RLD were reduced in the rain shadow side of the tree rows. Similarly, the amount and depth of rooting in the groundcover were reduced close to the trees compared to midway between rows. Differences in the root variables were larger than those in ET, which suggested that more roots were produced than were needed for water uptake and/or presence of considerable amounts of necromass. We conclude that vegetation covers, such as plantation-5 consisting of widely spaced trees and a heavy groundcover containing winter-active pasture legumes, will promote year-round water-use with a reduced risk of deep rooting that could breach buried wastes. This function could be sustained through progressive thinning of trees to account for not more than 25% of the whole canopy cover; this will minimize competition for limited soil-water and thereby constrain deep rooting as vegetation ages and attains climax. 2012-07-19T22:51:22.974Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:11150 Trends in global soil moisture are needed to inform models of soil–plant–atmosphere interactions. Predawn leaf water potential (Ψpd), a surrogate for soil moisture and an index of plant water stress, has been routinely collected in Australian forests, woodlands and savannas, but the associated leaf area index (LAI) has seldom been available to enable the preparation of a Ψpd on LAI relationship. Following an analysis of Ψpd and MODIS LAI data from Australian forests, woodlands and savannas, we identified patterns in Ψpd which provide an understanding of the role of soil-moisture status in controlling LAI. In the savanna of northern Australia, the MODIS LAI product had a basal value of 0.96 during the dry season as compared with a mean value of 2.5 for the wet season. The dry season value is equivalent to the LAI of the tree component and corresponds with ground-truthed LAI. Ψpd is lowest (more negative) during the height of the dry season (late October) at -2.5 MPa, and highest (-0.1 MPa) during the wet season (early March). We present two models which predict Ψpd from the MODIS LAI product. These may be useful surrogates for studying trends in soil moisture in highly seasonal climates and may contribute to climate change research. 2011-01-07T12:11:13.530Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:11158 Article first published online: 17 JUN 2009. Leaf area index (LAI) is a key physical variable which controls the exchange of water and CO₂ between the earth and the atmosphere. Recent improvements in the quality of satellite-derived estimates of LAI, specifically the MODIS LAI product, have led to increased confidence in their operational use. In this study, we examined the relationship amongst MODIS LAI (Collection 5), pre-dawn leaf water potential (Ψpd) (a surrogate for plant water availability), vegetation water use (ET) and pan evaporation (E₀) in forest, evergreen woodland, open shrubland and savanna in Australia. We present three models which demonstrate how the MODIS LAI product can be used to make spatially explicit predictions of the state of three key physical variables, namely Ψpd, the aridity index and vegetation water use. The LAI-Ψpd model explains how plant available soil moisture can be predicted at a continental scale for intact forests, woodlands and savannas. In a similar manner, the aridity index (mean annual rainfall/E₀ ) shows a powerful relationship with the MODIS LAI values. Using vegetation water use data from 16 field campaigns and published studies, we developed a MODIS LAI-ET model that provides the ability to predict both site and catchment-scale annual evapotranspiration. We test the model against independent estimates of site and catchment-scale vegetation water use. 2011-01-07T12:10:56.537Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:11089 Leaf area index (LAI) is one of the most important variables required for modelling growth and water use of forests. Functional–structural plant models use these models to represent physiological processes in 3-D tree representations. Accuracy of these models depends on accurate estimation of LAI at tree and stand scales for validation purposes. A recent method to estimate LAI from digital images (LAID) uses digital image capture and gap fraction analysis (Macfarlane et al. 2007b) of upward-looking digital photographs to capture canopy LAID (cover photography). After implementing this technique in Australian evergreen Eucalyptus woodland, we have improved the method of image analysis and replaced the time consuming manual technique with an automated procedure using a script written in MATLAB 7.4 (LAIM). Furthermore, we used this method to compare MODIS LAI values with LAID values for a range of woodlands in Australia to obtain LAI at the forest scale. Results showed that the MATLAB script developed was able to successfully automate gap analysis to obtain LAIM. Good relationships were achieved when comparing averaged LAID and LAIM (LAIM = 1.009 – 0.0066 LAID; R² = 0.90) and at the forest scale, MODIS LAI compared well with LAID (MODIS LAI = 0.9591 LAID – 0.2371; R² = 0.89). This comparison improved when correcting LAID with the clumping index to obtain effective LAI (MODIS LAI = 1.0296 LAIe + 0.3468; R² = 0.91). Furthermore, the script developed incorporates a function to connect directly a digital camera, or high resolution webcam, from a laptop to obtain cover photographs and LAI analysis in real time. The later is a novel feature which is not available on commercial LAI analysis softwares for cover photography. This script is available for interested researchers. 2011-01-06T05:01:47.392Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:11076 Revegetation is critical to restoring hydrological function on waste disposal sites in order to minimize runoff and drainage and safeguard the water quality of the catchment. In this study, we determined the components of soil–water balance between late 2006 and the end of 2008 for three vegetation types established over sites used for waste disposal: (i) a juvenile plantation of mixed Australian woody species; (ii) a block of mixed tree seedlings; (iii) and an ungrazed grass pasture. These were compared against a nearby natural woodland taken as an analogue of a pre-existing hydrological state. Evapotranspiration (ET) was the major component of the soil–water balance in all the four vegetation types. In the plantation and woodland, ET accounted for 60–93% of the annual rainfall compared to 44–88% in the grass and seedling blocks. While the balance of rainfall was largely lost to runoff in the plantation and the woodland, it was split almost equally between runoff and drainage in the other two vegetation covers. The plantation maintained parity in its ET with woodland due to groundcover that contributed at least 70% of the water use, while seasonal growth and periodic mowing reduced ET from the grass. Over the 2 years, the height of the deep (∼19 m above sea level) water table under the plantation and grass declined by an average of 0·3 m, while it rose by a similar magnitude in the woodland. The height of the shallow water table (∼8 m above sea level) showed no consistent change. We conclude that, with a good groundcover of mixed herbaceous species, a juvenile plantation can restore hydrological function and minimize deep recharge of a waste disposal site to the status of that under a pre-existing undisturbed woodland. 2011-01-05T06:50:05.740Z ]]>