Salinity Indicator Plants - A guide to spotting soil salting

Salinity in the Loddon Murray Region
Salinity in the Central and Northern Victorian Region
Salinity in the Western Victorian Region
Salinity in the Wimmera Region
Salinity in the Mallee Region

Purpose of this Guide | Using this Site | Salinity Classes and Ranges | Salinity Indicator Plants - Alphabetical Listing - Common Name and Scientific Name

Dryland salinity is a feature of parts of the Victorian landscape, particularly in the western and northern regions of the state and in parts of central Gippsland. It has been estimated to affect between 290,000 and 370,000 ha of land and to have cost $1.8 billion of private and public funds in management during the period 1990-2001 alone. The extent and severity of dryland salinity continues to require assessment as water-table levels, long-term weather patterns, landscape modification and land-use change. For example, during the drought years of 2000-07, water-tables across Victoria displayed a general fall with consequent less expression of salinity in the landscape. After a series of wet years, there would an expectation that landscape salt would become more mobile and surface salinity would be more evident. Land clearance, drainage works, increased tree plantings and continuous cropping may all impact on the level of dryland salinity.

Physical indicators of dryland salinity include groundwater discharge (free surface water or dampness during the summer), mid-slope seepage, bare soil, surface soil salt stains or crystals and soil blackening (organic mater staining). Apart from the latter two, these signs are not always indicative of salinity but may represent recent rainfall events, freshwater springs, overgrazing or trafficking. However, the use of indicator plant species has been commonly employed in combination with physical indicators to assist in dryland salinity assessment.

Plant species have different tolerances to soil and water salinity levels. Salt-tolerant species have physiological mechanisms, such as salt exclusion, intraplant salt translocation (e.g. from sensitive shoots to older leaves or roots), cellular osmotic adjustment (i.e. dilution by increasing water uptake), salt intracellular compartmentation (i.e. accumulation in the spaces between cells) or salt excretion (e.g. through salt glands) that allow them to cope with high environmental salt concentrations. Salt-sensitive species do not have these (or maybe not all of these) coping mechanisms and therefore succumb to wilting due to decreased water uptake, inhibited growth and eventual death, depending on the salt levels encountered and the particular species tolerance level. As a consequence, as soil salinity increases, vegetation becomes more dominated by the more salt-tolerant species. Contrary to popular belief, most salt-tolerant species are not dependent on salt to survive but are often only found in saline conditions. This is because, in non-saline or low salt environments, salt-sensitive species are generally more vigorous than salt-tolerant species and out-compete with them for water and nutrients.

A number of plant species however, grow vigorously in both non-saline and saline environments; available moisture appearing to be the main criterion for their dominance. Therefore, the presence of these species on a site may not be related to salinity but merely to a seasonally or permanently wet site. Common species in this category include; Water Buttons (Cotula coronopifolia), Beard Grass (Polypogon monspeliensis), Buck’s-horn Plantain (Plantago coronopus), Spiny Rush (Juncus acutus) and Common Blown-grass (Lachnagrostis filiformis). For some of these species, increasing salt may increase their presence on site, while for others, increasing salt may decrease their dominance or change their appearance. For example, the leaves of Buck’s-horn Plantain generally become red as salt stress increases. It is important to examine the whole of the vegetation present on a site and look for physical indicators before determining if salinity is present or not.

Dryland salinity is often divided into Primary and Secondary types. Primary or natural salinity existed long before European settlement and is considered to be the result of natural landscape processes. Secondary or induced salinity has occurred since European settlement and is considered to be the result of changes in land and water management practices. Primary salinity can be classified into i) salt marshes and saline swamps, ii) salt lakes, iii) salt flats, playa and salt pans and iv) natural salt springs, seepages and drainage lines. Each of these classes tend to support a particular suite of plant species. In relatively unmodified Primary salinity environments, the major species present are Australian perennial natives. In Secondary saline environments, which have generally been extensively modified, introduced annual species tend to dominate the vegetation.

The role of rainfall amount and seasonal pattern, soil drainage and water retention and subsequent soil moisture is significant in terms of the expression of salt-tolerance, even among salt-sensitive plant species. Where rainfall is higher, where storm events can leach salt from the soil profile or drainage is rapid, plant species can often tolerate higher levels of soil and water salinity than where seasonal growth periods are short and salt accumulates as evaporites on dense clay surface soils. The same species may have less tolerance in the latter situation than in the former. The same is generally true for germination rates and early seedling growth of recruitment plants. Even the most salt-tolerant plant species, generally require seasonal salt leaching and therefore lowering of surface soil salinity before germination can occur.

Not only does salt concentration on a site vary depending on the season of the year (i.e. lowest with winter and spring rainfall and highest with summer drought), most saline sites are variable in terms of salt distribution across their surfaces. Slightly elevated areas may have a lower salt level than slightly depressed areas. Sandier surfaces may allow more rapid leaching of salt than clay surfaces. Salt-tolerant bushes and shrubs may provide enough organic litter below their canopy to allow sufficient salt dilution for the successful germination of more salt-sensitive species. As a consequence of this variation, it is not uncommon to find a mosaic of plant species of varying salt-tolerance across a site. In particular, annual salt-sensitive species with a short growing cycle (e.g. Soft Brome, Silver Grass, Burr Medic) can often establish on a saline site, grow rapidly to maturity and set and disperse seed before the extreme stress of summer salt concentration sets in.

Because salt is highly soluble in water and is transported by such, saline environments are often also wet environments, or at least seasonally wet. As well as varying in salt-tolerance, plant species also vary in water-logging tolerance. Species can be salt- and water-logging sensitive (e.g. Kangaroo Grass) or salt- and water-logging tolerant (e.g. Australian Salt-grass) or salt-sensitive and water-logging tolerant (e.g. Swamp Wallaby-grass) or salt-tolerant and water-logging intolerant (e.g. Coastal Blown-grass) or with varying degrees of salt-tolerance and water-logging tolerance. However, salt-tolerance can also vary for a particular species, depending on the duration of water-logging. The interrelationship between salinity and water-logging for many species is often unclear or completely un-researched. Nevertheless, a knowledge of water-logging on a site undergoing salinity assessment is an important aspect to take into consideration when examining the suite of plant species present.

The following web pages describe both Australian and introduced plant species commonly found on Primary or Secondary salinity sites throughout Victoria. They provide some basic plant descriptions and notes on likely habitat to assist the reader in classifying the severity of salinity at a site under investigation. This guide should not be used as a final arbitrator of salinity class (that being the role of laboratory soil and water testing) but can be useful as a first stage of assessment.

Purpose Of This Guide

The original Spotting Soil Salting field guide was conceived as a statewide guide that could be used to identify some of the common salt tolerant plants found across Victoria and assign a salinity rating based on the plants present. However, salinity indicators vary across the state. For example plants found at saline sites in north west Victoria may not be present at discharge sites in the Western District. This version of the field guide aims to provide reference material for specific regions of the state.

Using this site

This site provides information, using photos and descriptive text, to guide you in recognising plants associated with groundwater and soil salting. The site describes a range of Victoria's most common plants found growing on saline sites. The guide is divided into major regions across Victoria where the same or a similar range of plant species exhibiting a consistent response to salinity might occur. Note that not all listed plants for your region may be found in your particular district. Other factors, such as soil type, climate, topography, flooding frequency and duration and land management and history will have a role in determining which species grow where.

While some plants will be easily recognized from the photographs, others may need reference to the descriptive text, drawings and definitions. But don't let this put you off. Identifying plants is like anything else: it gets easier with practice. Over time, you should be able to identify the most common species associated with salinity in your district and thereby recognize emerging salinity areas requiring further investigation with soil and/or groundwater analysis.

The steps to using this guide for the first time are as follows:
1. Examine the photographs and descriptions associated with the salinity classes provided in the table below and determine which best suits the situation under investigation.
2. Choose the region or subregion of interest from the clickable list or map provided.
3. Focus on the plant species list associated with the salinity class you have determined.
4. Examine individual species by clicking on their common name.

Salinity Classes and Ranges

The following table provides approximate ranges for salinity classes used in this guide. For further information and photographs associated with these classes, click on the links within the table.

Salinity Class	ECe (dS/m)	EC 1:5 Sandy loams (dS/m)	EC 1:5 Clay loams to light clays (dS/m)	EC 1:5 Medium to heavy clays (dS/m)
S0 - Non Saline	< 2	< 0.2	< 0.2	< 0.3
S1 - Slightly Saline	2 - 4	0.2 - 0.3	0.2 - 0.4	0.3 - 0.6
S2 - Moderately Saline	4 - 8	0.4 - 0.7	0.5 - 0.9	0.7 - 1.3
S3 - Highly Saline	8 - 16	0.8 - 1.5	1.0 - 1.8	1.4 - 2.7
S4 - Extremely Saline	> 16	> 1.5	> 1.8	> 2.7