7    CHAPTER:  Vegetation

7.1    Introduction

At the heart of any successful rehabilitation project is a successful re-vegetation program.  And the best way to achieve a successful revegetation program is to ensure that the right plant is in the right place.

Unfortunately ensuring that the right plant is put in the right place is currently one of the greatest failings in rehabilitation projects.  A recent study, xxxx, has found that in the average success rate of  government sponsored revegetation projects in xxxx is only 20 %.  This means for every $1,000, $800 is being simply wasted.  Of coursse there is always going to be some loss of plants due to unpredictable occurences such as droughts and floods but it is not unrealistic to aim for an 80% success rate not an 80% failure rate.

In order to achieve a successful revegetation project there are 5 key components that need to be balanced.

  1. Biodiversity  (As rich and as indignenous as possible)
  2. Costs  (As low as possible)
  3. Sustainability (for the planted vegatation cover, both in richness and quantity, to continue to exist indefinately)
  4. Provide multiple benefits  (eg assist with erosion control, water filtation etc)
  5. Require minimal maintenance (help minimise the costs associated with ongoing weed and pest control)

As can be seen from the often high failure rates of revegetation projects a sustainable balance between the components listed above is not yet being achieved.  All too often the the drive to minimise intial costs, ie the cost of getting the plants in the ground, is pursued to the exclusion of the other components of a successful revegetation project.  Saving money in year one is a false ecconomy if little thought is given to how many plants, and how many species, will still be alive in 2 years let alone 20 years. 

7.2    Current revegetaion practice

There currently is no standard method of creek revegetation, one that is used in multiple areas so what is detailed here is a collection of typical practices that have been observed and repoted from a range of differnet locations.  Planting practices varry widely from State to State, place to place and person to person.

There are very few revegetation texts specific to revegetating creeks.  What is more that where these texts exist they are not commonly available.  This lack of source documentation, combined with the fact that few revegetaion projects in rural areas proceed with a revegetation or rehabilitation plan in place, ensures a wide variation of techniques are employed.

Currently the type of person tasked with organising a revegetation project will varry from situation to situation.  It may be an employee of a government agency such as a Catchement Management Authority, or similar, it may be a local Landcare coordinator or a knowledgeable member of the community such as the owner of a nursary business.

Common revegetation practice

  1. A project leader is identified
  2. Discussions are held with the land holder
  3. A written agreement may or may not be put in place
  4. An estimame of the size of the project site is made through visiting site and or studying aerial photos.
  5. The number of plants required is calculated using xxxx
  6. The range and mix of species are identified, indigenous species but not always indigenous stock is identified
  7. The project site is spot sprayed prior to planting
  8. Planting occurs at an apropriate time of year
  9. Plants are mixed together more or less randomly
  10. Very little planting occurs in the low flow channel
  11. Plants are planted 2-3 meters apart
  12. Planters are employed often on the basis of cost alone
  13. Planters are paid per plant in the ground
  14.  Milk cartons or plastic sleeves are placed around each plant to protect from wildlife and wind
  15. Follow up weed control or watering is rare

7.3    Assessing the success of a revegetation project

It is difficult to put an empirical figure on what constitutes a failed creek revegetation project due to the large numbr of dependent factors, eg budget, climate, weather, site specific priorities etc.  

Despite the difficulties in assessing success or otherwise of a creek revegetation project there are a range of different assesment methods available (xxxx).  These assessment methods varry in complexity depending on the time and budget available.  Unfortunately in most cases there simply are not the resources to conduct an extensive analysis of the project particularly as this can only be meaningfully done years after the initial plantings have been carried out.  

While detailed analysis of a creek revegetation project is not possible we do need to be able to assess whether there has been a positive outcome or not on ideally every project.  It is only by revisiting past projects can key stakeholders deturmine what does and what doesn’t work in a given area and set of circumstances.

A very simple bench mark assesment that can be carried out by revisiting the project site 5 years after the intitial planting.  At this site visit observation is made of three key components.

  1. Survival rates:  Approxiomately what % of total plants and what % of species planted have survived (70–80 % is considered successful)
  2. Natural regeneration:  Is there substantial natural regeneration underway (if after 5 years there is evidance of approximately 50% of species are regenerating is considered successful)
  3. Weed control:  Do the newly planted species apear to be holding their own against invasive species? (It is a reality that in most cases the land holder will have to conduct an annual weed control program in the creek much as they would on the rest of their property)

7.4    Common reasons revegetation projects fail

The reality is that in most areas of Australia most revegetation projects run the risk of failing due to factors that are out of the contol of those involved in the project.  If there is a major flood in a creek soon after planting, if there is an extended hot, dry spell soon after planting or if stock break though a protective fence then it is likely that significant numbers of newly planted plants will not survive. 

The list of common reasons for revegetaion project failures listed below focuses on decisions that are made which increase the chances that a given revegetation project will fail.

  • Plants are planted in the wrong spot: Many plants will die withing 5 years if planted only 2 meters away from a fast growing gum tree, a plant that needs regular water will struggle on an exposed clay bank etc.
  • Weed competition:  Weed or grass competition is a major cause of plant failures through smothering and or competition for resources in particular water
  • Predation: Rabbits, hares, kangaroos and wallabies all eat the seedlings of many species of native vegetation
  • Stock damage:  Trampling and consumption by stock due to insufficient infrastructure, gates and fences, control and management
  • Timing:  Plants are planted too late in the planting season or are not planted soon enough after leaving the nursery
  • Planting technique:  Plants are not planted deep enough into the ground or are not properly heeled in 

7.5    Preferered revegetation practice

Note:    The second half of this book covers the “Step Method” of creek rehabilitaion.  The Step method is a way in which the current best practice thinking outlined in this book can be put into practice in actual creek rehabiliation situations.

The information provided under this heading is a summary of more detailed information which can be found under the heading of revegetation in the Step Method. 

It is important to acknowledge at the outset that there is not a single “best way” to
revegetate a creek.  Every project due to its location, budget, climate, species availablity etc. is unique, however there are many “truisms” which when combined can form an excellent base line of revegetation practices.  A brief summary of what is currently considered best practice is listed below.

It is impotant to be aware that the suggested range of practices outlined below is different in a number of ways to the “common revegetation practices” described above.  This new way of undertaking revegetation projects aims to improve the likeliehood of achieving successful revegetation outcomes by focussing on all 5 key components of a creek revegetaion project rather than just one or two.

The key difference is an emphasis on sustainalbe long term outcomes not on short term cost driven decissions unsurprisingly have lead to long term repeated and hence expensive failures.

Preferred revegetation process

  1. A project leader is identified
  2. The project leader, with input from major stake holders, creates or has created a revegetation plan (The revegetation plan is often part of a overall creek rehabiltation plan
  3. The size of the project site is calculated using a gps device and includes a rough estimate of the area of the low flow channel, the area of the high flow channel and the area of the verge)
  4. Assess the rights species and mix of plants (see the right plant in the right place below)

7.6    The benefits of vegetation

7.6.1    Stability

Vegetation can provides stability and resistance to erosion in 3 main ways:

  1. In the low flow channel grassy plants such as rushes, reeds and sedge will lie down almost horizontal to the flow of water in high water velocity events like floods.  While these grassy plants are lying flat they act as an effective form of protection against the scouring force of the water.
  2. In the high flow channel the roots of vegetation can both reinforce the soil of the bank limiting erosion while at the same time slowing the speed of the water and reducing is capacity to scour the bank.
  3. On the verge the roots of vegetation, particularly larger species such as trees, can effectively reinforce and strengthen the verges making them less vulnerable to calving and slumping.  At the same time vegetation on the verge is particularly helpful in slowing and reducing the speed and rate at which underground water is entering the channel.   By lowering the quantity and speed at which underground water enters the channel effectively helps reduce the risk of slumping.

7.6.2    Biodiversity

Biodiversity can be considered as comprising two major groups, vegetation and wildlife. Vegetation is essential to creek biodiversity.  The greater the quantity of vegetation, the more indigenous, the more varied and the more established the vegetation in a creek the greater the likelihood of a there being a high and rich level of biodiversity of wildlife both in the water and out.

7.6.3    Improved farm productivity

Vegetation in and around a creek can lead to a range of changes that will help farm productivity, particularly if the creek is fenced out to exclude stock and protect the vegetation:

  • More sheltered paddocks
  • Less land lost to erosion
  • Less farm infrastructure lost or damaged by erosion
  • More birds to control insects
  • A more interesting and pleasant work environment for the farmer and his employees
  • Improved stock health, if they are drinking water pumped from the creek which has cleaner water as a result of increased vegetation
  • Assist with retention of water in the landscape
  • Less stock loss from animals being trapped or falling into the creek

7.6.4    Nutrient retention

Where there is a healthy and balanced cover of vegetation in a creek a considerable amount of organic matter and sediment from further up stream can be trapped over time by the vegetation.  As this new organic material breaks down a wide range of plants and animals can use the new nutrients and minerals that were not previously available. 

7.6.5    Sediment accumulation

As with the retention of nutrients, a healthy and balanced cover of vegetation in a creek will, over time, trap significant amounts of sediment.  Over time trapped sediment will build up on the bed of the creek flattening out the bottom of an incised channel and making growing conditions more suitable for a range of marshy plants, plants that will in turn trap more sediment. 

7.6.6    Retention of water in the landscape

One of the significant problems associated with severely incised creek channels occurs when the depth of the channel reaches the water table.  Once a creek channel has reached the level of the surrounding water table the water in the water table can begin to quickly drain into the creek, with the corresponding result being much like  pulling the plug out of a bath full of water.  While an appropriate cover of vegetation in a creek will not fully “replace the plug” it will help slow down the transfer of water from the water table and into the creek channel.  This assistance in retaining water in the surrounding landscape can make pos slowing down the removal of water from the landscape can have positive benefits both for biodiversity in the area as well as ajoining farms

7.6.7    Cleaning and oxygenating the water

Where water passes though thick vegetation either on the verge or in the creek channel, in partiular in the low flow channel where the density of grassy plants is highest, the vegetation can filter out a significant range of pollutant.  For example studies have shown that even a grassy strip xxxx meters wide on the verge of a creek can filter out xxxx.

The other advantage of water passing trough vegetation is that the resulting turbulance will help re-oxygenate passing water.  Adequately oxygenated water is important to the health of many instream animal species and as a result is important to the health of biodiversity in the creek in general.

7.7    Limitations of vegetation 

While a balanced cover of healthy vegetation provides many benefits there is a point where vegetation, no matter how suited to a given site, will be able to achieve the desired outcome.  This is particularly true in the case of erosion.  At steep gradients, often in gullies and where step erosion is occuring, even relatively low water flow events erosion will continue despite vegetation.  And in high flow events significant erosion events will happen washing away the vegetation as well as the banks and bed of the creek.  In situations such as this either hard works will need to be considered or there needs to be an acceptance that erosion will continue until the landscpae of the creek changes, ie banks reach an angle of repose. 

If hard works are not an option it is important for the landholder to understand that the landscape of the creek will change and make plans accordingly, for example making sure that the fenced of verges of the creek are particularly wide to allow the banks to lie back over time as they move towards an angle of repose.  Where ongoing erosion is predicted particular attention should be paid to instream plantings which can help stabilise newly damaged banks and trap sediment loads being added to the creek flow.

In addition to the limitations of vegetation to achieve goal there are also a number of potential downsides which need to be taken into consideration:

  • If stock are fenced out of a creek then an alternative system of stock watering may need to be put in place
  • Heavy vegetation cover can provide shelter for pests such as foxes, cats and rabbits
  • A heavy cover of vegetation can make locating and dealing with weeds more difficult 
  • Some native species can spread into padocks from the fenced out creek area (grazing and normal farming practices will ensure that this is rarely a major problem

7.8    The right plant in the right place

7.8.1    Introduction

The key to the long term success of a revegetation project can be broadly measured by 3 interdependent objectives:

  1. How many of the newly planted plants survive.
  2. How many of the planted plants successfully reproduce.  
  3. How succesfully the revegetaion project achieves its goals eg controlling erosion.

For these three objective to be met it is critical that the right plants are planted in the right place.  

Some of the factors to keep in mind when considering the best location for a given species include:

  • Moisture requirements eg putting wet plants in wet areas 
  • Different root structures eg putting plants with matted root structures in areas prone to erosion.
  • Light requirements eg water plants often need resonable light levels to thrieve.
  • What species are compatable with other species eg a dense cover of Eucalypts can quickly out compete and kill a wide range of other native species.
  • The distance different species are planted apart eg gum trees that can grow to have have a canopy of 20-30m should be planted further apart than native grasses which may have a cannopy when fully gown of less than 1m.

The above may seem self evident however historically these issues have not influenced revegetation plans to the level they could for the following reasons:

  • Lack of knowledge about the specific requirements of specific species.
  • Lack of a planting plan.
  • Difficulty in directing and or educating planters about the correct location for different species.
  • The cost of doing the above.

It is true that ensuring the majority of plants are planted in the right place is more expensive than planting them more or less randomly...... initially.  However if the project fails due to the right plants not being planted in the right place then money and enthusiasm has been wasted.

For gaining a better understanding of ways in which the cost of planting the right plant in the right place can be minimized view the heading Planting xxxx.

7.8.2    Local and indigenous

It is generally accepted that it is important to use Indigenous plants in any revegetation project.  However while most people generally understand the term Indigenous to mean plants that would have grown on or "near" their revegetation site, they are often unclear about how big an area "near" actually is.  This lack of clarity about the size of an Indigenous area also leads to confusion about where an Indigenous area stops and the Local area begins.  

Unfortunately there does not seem to be an easily understood definition of exactly what an area of Indigenous vegetation area is, take the definition of Indigenous vegetation that comes up on Google:
"Indigenous vegetation:  Any local indigenous plant community containing throughout its growth the complement of native species and habitats normally associated with that vegetation type or having the potential to develop these characteristics. It includes vegetation with these characteristics that has been regenerated with human assistance following disturbance, but excludes plantations and vegetation that have been established for commercial purposes. (http://www.biodiversity.govt.nz)

In Victoria the State has been devided up into a range of different Environmental Vegetation Classes, or EVC's these EVC's identify the species that would have existed in a particular location prior to 1750.  This classification system is very useful for deturmaning appropriate species and does go some way towards helping define what is Indigenous however this system does not currently opperate in all States and Territories.

Also is should be noted that while the use of Indigenous plants should be strongly encouraged there are also occassions when Local as well as Indigenous plants should be considered.
Take for instance a former swamp that is now a deeply incised Creek.  In this highly modified environment there are often tall bare clay banks, active erosion and regular high speed water flow events, none of which would have existed previously in the swamp.   In this situation a revegetation project that used only Marsh plants would almost certainly fail.  In the circumstance of a highly modified environment it makes sense to to not only use Indigenous plants but to consider appropriate plants from the Local, surrounding area also.

7.8.3    The importance of indigenous plant stock

Many species of native plants have a wide natural range however within that range there are often a significant genetic variations.  These genetic variations have evolved over thousands of years and permit the same species to thrive in a range of different environments. It is this natural variablity and genetic diversity within a species which makes the species as a whole more robust and able to adjust to long term changes in  environmental conditions.

However more than just making the species as a whole more robust understanding which genetic combination is appropriate for a given site can make significant differences to growth and regeneration rates. In fact research has shown that plants planted in the specific local conditions that it has evolved in can grow at rates up to twice as fast as the same species with different genetic material in the same location while at the same time producing up to twice as much viable seed.

It is this combination of maintaining genetic diversity within a species and obtaining healthy plants that it is desirable to use Indigenous stock.

7.8.4    Self regenerating plants

As we have seen above Indigenous stock planted in the right location will give any revegetation project a significantly improved chance of success.   However it is not enough to have healthy plants in the right place, what is most critical is that there plants regenerate naturally, either by seed or suckering.  A revegetation project may look great for a number of years but if there is not a significant amount of regeneration then ultimately the project will fail and the initial funding and effort will have been wasted.

Therefore when choosing plants for a revegetation project it is important to choose species where there is a realistic expectation that ALL the species that are to be planted will eventuall naturally regenerate.

Two possible exceptions to the aim of having all species regenerate naturally could be trees that can be expected to live for hundreds of years or Nursery plants.  Nursery plants are planted to help protect the rest of the revegetation projects while it gets estalished.