By Selwyn Green: Xanadu Resident Conservationist
Many living organisms are dependent on grass as a source of food, e.g. Many species of antelope (grazers), birds, rodents and insects.
Grasses are also important in that they stabilize the soil and prevent soil erosion by protecting the soil from heavy rain runoff and high winds, grass also controls soil temperature.
The importance of identifying the different grasses in the nature estate is to understand the following:
Production: The ability to produce a low or high-leaf material.
For example, understanding whether the grasses in the estate are perennial (Normally produce high leaf material) or annual (which puts more energy into seed production).
Palatability: This enables the nature estate management to understand the general acceptability of the grass for grazers, this is influenced by the nutritional value and digestibility.
Nutritional value: An indication of the amount of nutrition the grass contains.
The nutrients are produced by the soil (therefore soils are a very important component of the ecological system) and photosynthesis, and the most important part of the nutritional value is the crude protein value.
Understanding the nutritional value of the grasses in the estate is important when it comes to making decisions on how to stock the nature estate.
Growth vigour: For the nature estate to stock the estate correctly, the management team will need to understand the ability of the grasses to rapidly regrow post-grazing and the ability of the grasses to produce sufficient material to be grazed again. Understanding the growth vigour is essential to run the nature estate efficiently and to ensure that no overgrazing occurs.
Digestibility: The fibre content determines the digestibility of the grass, this is mainly the lignin and the cellulose of the leaves of the grasses.
Should the grass have a high fibre content the lower the digestibility of that species of grass will be.
It is also worth mentioning that many grasses contain Silica (SiO2) particles in the epidermis of the leaves, the Silica particles are indigestible.
Understanding the digestibility of the grasses present will enable the estate management to make the right decisions, when stocking the estate.
Habitat preference: Grasses that grow in nitrogen-rich soil, will usually have a higher nutritional value and grasses that grow in wet conditions i.e. on the boundaries or within a wetland will have higher leaf production.
Further reasons why the identification of grasses is important and the importance of grasses
· Establish a veld management plan (sourveld (sour grasses) or sweetveld (sweet grasses))
· Establish the grazing capacity of the nature estate
· Soil erosion management
The Ecological Status of Grasses
The ecological status of grasses refers to the ranking of grasses according to their reaction to different levels of grazing.
The different grass species react in two distinct ways:
1. It will either increase in number when grazed on
2. Decrease in number when grazed on
From the above, we are able to group different grass species in the following groups:
· Decreasers – grass species that are abundant in good veld but decrease in number when overgrazed or undergrazed. These grasses are preferred by grazing animals. They are climax grasses that are highly palatable and nutritious.
· Increaser I – this group of grasses are abundant in underutilized veld. They are usually unpalatable, robust climax grasses and can grow without defoliation.
· Increaser II – are abundant in the overgrazed veld. These grasses increase due to overgrazing and are mostly pioneer and sub climax grasses
· Increaser III – commonly found in overgrazed veld. They are usually unpalatable dense climax grasses. They are competitive and increase in numbers when palatable grasses are weakened.
· Invaders – these plants are not indigenous to the estate. These plants include annual weeds or perennial invasive species. There are many examples of these plants within the grassland of Xanadu Nature Estate.
Note: The introduction and the ecological state of the grasses form the foundation for explaining the importance of managing the veld condition at the Xanadu Nature Estate the way it is currently being done.
Mowing is the worst form of veld management possible in a natural occurring grassland, which is one of the most important biomes in South Africa and unfortunately the least conserved.
The management of the estate introduced mowing as a means of maintaining the aesthetics of the estate and as a form of veld management. Initially, the grassland was cut 3 times monthly, which was detrimental to the veld condition and soil health maintenance.
Studies that have been conducted on grassland and soils due to the application of mowing have shown that mowing is a destructive means of veld management and should be kept to the bare minimum should this be the method of veld maintenance. To quote test work results on grasslands that have been mowed:
· It reduces the vigour of the grass sward.
· It reduces the canopy and basal cover of the grass sward (the portion of earth covered by grass cover)
· It increases the runoff of rainwater
· It results in increased soil erosion
This is also true of the annual burning of a grassland, grasslands should only be burned at intervals of 3 to 4 years, depending on whether it is sourveld or sweetveld or in a low or high rainfall area. In reality, a grassland should ideally be mowed only once every four years, but burning is considered the more appropriate method for veld management in a grassland setting.
Mowing significantly decreases the soil’s available Nitrogen, Potassium and Phosphorus, all important elements required for good healthy grass and nutrition for grazing animals. Soil micro-organisms are destroyed when heavy machinery passes over caused by compaction and disturbance.
Mowing reduces the growth efficiency of the plant. It was found that many grass species’ growth is stunted due to mowing in that it causes extensive destruction of the culm of the plant, transports water and nutrients and is leaf-bearing and the rhizomes (modified culms under the soil).
Basically, mowing destroys biodiversity, species richness (SR) and harvested biomass (HB).
So, to get to the question of whether “to mow or not to mow”. No, we should not mow a natural grassland.
Xanadu Nature Estate Ecological Management Plan:
The management of the estate cannot block burn (the preferred method of veld management).
Therefore, mowing is the secondary method, with all its destructive characteristics is probably the only acceptable method of veld management remaining.
To optimize the management of the grassland within the estate, the block method of conservation was recommended and agreed on.
The estate has been divided into blocks which are the mowed on a rotational basis. The rotations are shorter than the recommended period which is a 3-to-4-year rotation, presently a 2-year rotation plan has been implemented.
It is also important to take note that the mowing or burning of a grassland should be conducted within the correct seasonal window.
Grass should never be cut in:
· Spring, when grass is in its new growth stage.
· Summer, when the grass is producing seed
· Autumn, when the seed is being dispersed
· Winter is when the grasses need all the stored nutrition that has been stored throughout the seasons.
The best time to cut grass is between seasons, Late winter – and early spring (just prior to the first rains).
This is a short summary of why the grassland area within the estate is mowed in blocks and why it is not mowed on a regular basis. One must consider, that we as residents chose to live in a nature estate. We are custodians of a very special piece of remaining natural land within an urban environment, co-existing with nature. We should consider aesthetics as being a healthy environment with an abundance and biodiverse flora and fauna life.
As a conclusion and a point of concern
Two veld condition analysis surveys have been conducted within the estate over the past 4 years.
The estate’s grasslands are considered to be in poor to moderate condition. We can improve the state of our grassland by minimizing mowing further and cutting during the correct periods within the year. The introduction of burning can be considered, but this is highly unlikely to be an acceptable method of veld management within Xanadu Nature Estate.