Managing the landscape: using soil information for investigating and predicting water and vegetation conditions.
Resource Information Systems
Department of Land and Water Conservation
PO Box 3720, Parramatta, NSW 2124
(Phone) 02 9895 6172, (Fax) 02 9895 7985
The NSW Department of Land and Water Conservation soil landscape mapping program provides information to the public concerning soils and landscapes. Mapping of Soil Landscapes provides an overview of landscape processes, vegetation conditions, geomorphic characteristics, land degradation, potential issues, and hydrological conditions. Soil Landscape information is therefore a useful tool when investigating other environmental factors such as water or vegetation condition within a landscape.
Soil Landscape information has been extrapolated to produce maps of potential native vegetation communities according to soil type in areas that have been cleared. These and other products can also be used to determine the suitability of certain species for rehabilitation or Landcare projects.
Soil characteristics and surface conditions directly affect water yields and quality of both surface and ground water. Soils information is important for making ground water vulnerability maps and for modelling the likelihood of eroded soil particles entering water bodies. Additionally, soil information can be used to predict and help quantify potential recharge (input) and saline discharge (output) points within the landscape.
This poster demonstrates the links between soil, water and vegetation information. Examples are provided which demonstrate how these links can be applied to wise land management.
For Natural Resource Management to be effective all components of the landscape and their interactions should be considered and understood. In New South Wales the Native Vegetation Conservation Act 1997 and the Water Management Act 2000 take into account the impact on the soil of changes to native vegetation and water respectively. This paper outlines examples of applications that use soils information to contribute to better native vegetation and water management decisions.
Soil Landscape Mapping and Reconstruction of Native Vegetation Distribution
Soil is a naturally occurring body and its distribution is influenced by parent material, climate, topography and organisms over time. The same processes have also influenced vegetation distribution. This means that soils information is applicable for vegetation mapping and vice versa.
Soil surveyors pay particular attention to the native vegetation during the mapping process and often develop relationships between soil type and plant species. The standards for vegetation structure assessment used by soil surveyors (MacDonald et al, 1990) are the same as those used by vegetation mappers and are universally used by land resource assessors. The extent of vegetation information collected by soil surveyors is indicated by the vegetation records currently in the NSW Soil and Land Information System (SALIS): information on 21,155 species, 22,292 communities (Figure 1) and 15,176 growth forms at approximately 23,000 sites.
Figure 1: A map showing vegetation community distribution at soil profile description points.
In areas where native vegetation has been extensively cleared soils remain mappable. By extrapolating from remant vegetation across the same soil type it is possible to construct preclearing native vegetation maps. The first native vegetation map (Figure 2) was constructed by Tulau from data he collected in the process of mapping Soil Landscapes of the Cooma 1:100,000 Sheet (Tulau, 1994) by using plant communities determined by Costin (1954). Subsequently Eddie produced a Macksville Nambucca Soil Landscape Derivative Map showing native vegetation communities according to the Soil Landscapes of the Macksville and Nambucca 1:100 000 Sheets (Eddie, 2000). The Macksville Nambucca native vegetation distribution map is of particular significance, as Michael Eddie also developed a structural vegetation key, which can be applied across NSW.
Figure 2: Cooma Native Vegetation derivative map.
Reconstruction of native vegetation communities across previously cleared land is of interest to Catchment Management Boards as they can then compare it with existing native vegetation to gain an indication of what is remaining compared to potential extent of various communities.
Austin et al., (2000) have examined nine 1:100 000 sheets extending from south east of Cowra to north west of Condobolin (Figure 3). As part of this study he assembled detailed vegetation information from over 1195 sites and compared native vegetation species distribution against all available data sets. Austin et al., (2000) concluded that Soil Landscape Maps were the best indicators of individual species "soil landscape attributes offered the potential to add powerful predictive capability to models for species distribution and abundance" (Austin et al., 2000, page 51).
Figure 3: Study Area
Vegetation Applications – Modelling and Mapping Species Suitability
1) The Identification of plantation expansion opportunities in New South Wales project (Bureau Resource Sciences, 2000) has used a model to assess species suitability and yeild potential across New South Wales for the Comprehensive Regional Assessments of the North East and Southern Comprehensive Regional Assessments. Maps of estimated soil depth, soil profile plant available water storage and soil fertility where produced for this process. In addition areas of unusual soil were delineated to aid in determination of endangered species and unusual species assemblages.
2) The Plantgro program was developed from the innovative ‘Matching Plants and Land’ approach of Clive Hackett (1988) where species growth potential is defined according to growth performance with regard to climate and soil parameters such as minimum temperature, solar radiation, soil aeration, water supply and pH nutrient availability. To date Plantgro contains species requirements for some 1800 species. Plantgro species data can be matched against soil and climate conditions at any particular site to determine how well a species will grow at that location and to investigate what species will grow best at a particular location. Soil Landscape map unit descriptions contain all soils information required to run PLANTGRO. Climate information can be obtained from Meterological Records or from spatial climate extrapolation programs such as ANUCLIM (http://cres.anu.edu.au/outputs/anuclim.html) or SILO (http://www.bom.gov.au/silo). Application of plantgro extends far beyond assessment of growth for native plants and has much commercial potential.
Soil Degradation Assessment on Clearing.
The Native Vegetation Management Act 1997 "aims to increase and improve vegetation cover by preventing inappropriate clearing" (Department of Land Water Conservation, 1999). Soil Landscape maps when combined with rainfall erosivity data show the relative risk of sheet and rill and wind erosion that may result from clearing. Figure 4 shows erosion risk across NSW (Environment Protection Authority, 2000). Similarly soil landscape information can be used to determine what changes in recharge may occur following clearing - where changes in transpiration and run-off are included in water balance modelling.
Figure 4: Inherent Sheet Erosion Risk for NSW
Future Trends in Soils and Native Vegetation Mapping
The Resource And Conservation Assessment Council has commissioned a Western Regional Assessment of the Southern Brigalow Bioregion. This regional assessment includes geology, soil landscape, native vegetation and other assessments for determining optimum usage of crown land. The soil landscape mapping program is using climate variables, geological information, gamma radiometrics, magnetics and digital elevation derived indices including compound topographic index and local relief to model landscapes. This is an example of a quantified approach to land resource assessment, this is commonly referred to as ‘Enhanced Resource Assessment’ where soil type boundary deductions can be reproduced over large domains (http://www.dnr.qld.gov.au/resourcenet/land/era/index. html). In the Southern Brigalow project the environmental variability will be sampled for vegetation and soil attributes. It is expected that relationships between soils and vegetation mapping methods will merge as a result of this project.
Water and Soil Management
Water Balance Modelling
Water leaching past the root zone is known as recharge. Increased recharge raises water tables and can mobilise salt stores. This can result in salination of land and water bodies. Besides quantification of salt storage in soils, soil survey provides landscape wide estimates of soil parameters and water balance including; runoff coefficients, infiltration rates, plant available water storage capacity and rooting depths. These are estimated from field and laboratory data included in the Soil Landscape Reports. Water balance models can be used to estimate relative differences in recharge between locations and between land uses.
By overlaying Soil, Climate and Land Use map layers across the landscape it is possible to produce maps of relative recharge rates across whole catchments. This approach has been used by Ringrose-Voase et al., (2000) in the Liverpool Plains for scenario modelling under present land use (Figure 5) and alternative land use (Figure 6). Whilst this approach does not accurately predict changes in water tables or catchment discharge it is arguably the best practical tool for scenario modelling showing relative changes in recharge as a result of land use changes across the landscape. This can be contrasted with the practice of water table monitoring – a practice which tracks changes but is difficult to directly link water table height trends to land use change on particular land parcels. Ultimately to effectively address salinity the root cause of the problem – excess recharge must be addressed in targeted areas where greatest reduction in recharge and most effective reduction in salt mobilisation is achieved.
Figure 5: Annual Drainage on the Liverpool Plains under Current Land Use
Figure 5: Annual Drainage on the Liverpool Plains under an Alternative Cropping Scenario
Water balance modelling is the basis for determining optimal irrigation scheduling to minimise recharge.
Soil point derivative maps for irrigation management
In 1998 a six week trial water reforms project (Using Soil Information to help Increase Water Use Efficiency and help protect Ground Water Assets) involved a team of 24 recent graduates collecting soil information in the Murray Darling Basin. 8,900 soil profiles were gathered from existing records and digitised as part of this process. The information collected was manipulated and categorised according to soil hydrological parameters relevant to water balance modelling and irrigation scheduling. Figure 7 shows the distribution of soils with differing hydraulic conductivity, which has implications for irrigation management- especially for reduction of recharge. Figure 8 shows the distribution of soils across NSW with differing plant available water holding capacity. Both maps illustrate that these soil parameters are variable across the state- even within irrigation areas. These maps are used as tools to encourage better water use efficiency through the adoption of irrigation schedules which relates to both crop growth and soil type.
Figure 7: The distribution of soils with differing hydraulic conductivity
Figure 8: The distribution of soils across NSW with differing plant available water holding capacity
Ground water Vulnerability Soil Mapping Inputs
Ground water vulnerability is the potential for an aquifer to become polluted (Piscopo et al., 1997). Many factors are important in the assessment of groundwater vulnerability, including characteristics of earth materials far below the soil profile, however, soil characteristics are often important, relatively active and relatively easily controlled components of ground water vulnerability. Soil characteristics such as biological activity, cation and anion exchange capacity and residence times (determined by assessment of hydraulic conductivity and plant available water holding capacity) can be important in the absorption of pollutants. Soils information is regularly used for ground water vulnerability assessments.
This paper demonstrates that there are manifold uses for soil landscape information which are of great assistance in the management of vegetation and soils. Significant portions of NSW do not have soil landscape or other usable soil information, however over the last decade mapping coverage has increased dramatically. With appropriate resources and use of technology completion of coverage can be achieved within four years.
Simultaneously there is a need to make information relevant to native vegetation and water management. Use of the internet and digital presentation tools is an obvious solution.
Austin, M.P., Cawsey, E.M., Baker, B.L., Yialeloglou, M.M., Grice, D.J. and Briggs S.V. (2000). Predicting Vegetation Cover in the Central Lachlan Region, CSIRO Division of Wildlife and Ecology.
Bureau of Resource Sciences (2000). Identification of plantation opportunities in New South Wales - Southern NSW CRA Region, Bureau of Resource Sciences.
Costin, A.B. (1954). A study of the ecosystems of the Monaro region of New South Wales with special reference to soil erosion, Soil Conservation Service of NSW.
Department of Land and Water Conservation (1999). Guidelines for clearing vegetation under the Native Vegetation Act 1997, Department of Land and Water Conservation.
Eddie, M.W. (2000). Soil Landscapes of the Macksville and Nambucca 1:100 000 Sheet Report, Department of Land and Water Conservation.
Environment Protection Authority (2000). New South Wales State of the Environment 2000, Environment Protection Authority, Sydney.
Hackett, Clive (1988). Matching Plants and Land, CSIRO, Melbourne.
McDonald, R.C., Isbell, R.F., Speight, J.G., Walker, J. and Hopkins, M.S. (1990). Australian Soil and Land Survey - Field Handbook, Second Edition, Inkata Press, Melbourne.
Piscopo, G., Please, P. and Sinclair, P. (1997). Murrumbidgee Catchment Groundwater Vulnerability Map Explanatory Notes, Department of Land and Water Conservation.
Ringrose-Voase, A.J. and Cresswell, H.P. (2000). Measurement and Prediction of Deep Drainage under Current and Alternative Farming Practice, A final report prepared for the Land and Water Resources Research and Development Corporation, CSIRO Division of Land and Water, Consultancy Report.
Tulau, M.J. (1994). Soil Landscapes of the Cooma 1:100 000 Sheet Report, Department of Conservation and Land Management.