To Graze or Not to Graze
This is the big questionBy Ian Sharpe
In my business, as an ecologist for nature conservation authorities, one often hears a landowner use the phrase ‘but there is plenty of grass’ when surveying the pasture on his property. This misconception has lead to overstocking of game species and the resultant decline in the potential of the property to support a certain number of animals. Accelerated erosion and encroachment of trees and other herbaceous species is the end result.
Migration of animal herds was a reality in days gone by but the advent of fences has made these herds sedentary. Under this restriction animals are now forced to remain in a specific area and the grass sward has no respite that migration would provide. This is compounded by the provision of artificial water points where localised overgrazing leads to the creation of piospheres.This type of zone is characterised by pasture condition improving as one move further away from the water point. The grazing pressure and trampling effect is greatest at the central point of the piosphere. Getting back to the roots so to speak, grass is one of the components of the primary producers in the food chain.
Together with trees and other herbaceous plants, grass is one of the primary suppliers of nourishment to the second level of the food chain namely the herbivores. Most of the large herbivores commonly found in our area are grazers and therefore preferably utilisers of grass. In times of drought or extended dry periods, some species may switch to browsing to ensure their survival.Do grazers utilise all species of grass? Under normal conditions the answer is 'no' as there are many factors that influence the palatability of a grass species. As indicated in Photo 1, game will select palatable grass species and ignore other species for a number of reasons. Factors such as structure, taste, texture or accessibility will determine the suitability for a grazer.
The structure of a tuft in the sense that it may be dominated by inflorescence-bearing culms (flowering grass stems) with limited leaf production would make the particular grass species unpalatable to grazers. Many of the pioneer grass species that grow in tough conditions have this type of characteristic.In other instances only the new leaf sprouts of early season growth are selected in some of the tall grass species as access is difficult once the hard and thick stems are present later in the season. Chemical compounds in certain grasses serve as deterrents to grazing and are therefore avoided by most game species.
Names such as 'turpentine grass', 'quinine grass', 'stinking grass' or 'sour grass' bear witness to unpleasant tasting species. Photo 2 illustrates a dense stand of grass that is avoided by grazers due to the presence of unpalatable grass species. Under certain conditions such grasses may be utilised e.g. if growing on enriched soils such as found on termite mounds or when under drought conditions where nothing else is available. Texture of the leaves of the grass tuft may also make grasses unpalatable. During the rainfall months the leaves may be soft enough to eat but once the tuft dries at the onset of the dry winter period, grazers will avoid such grass species. Accessibility refers to the potential availability of a grass tuft to be utilised by a grazing animal.
Grazers are divided into two groups, namely bulk grazers and selective grazers. The first is adapted to dealing with long grass, taking large bites at a time, but do not have the ability to graze closer to the ground surface.
Once an area has been 'opened up' by a bulk grazer, the food source becomes more accessible to selective grazers that have the ability to grazer close to the ground surface. In this way both groups can benefit from the same preferred grass species no matter how dense the tuft or grass sward. The status of the grass sward is also influenced by the physical terrain upon which it is growing. Slope aspect influences soil fertility. Soil depth determines grass sward density to a large degree. Seep-lines are only suitable to specialised plant species.
Cover provided by trees and shrubs protect grass tufts from premature dehydration. The slope, referred to as a catena system, usually is characterised by leached sandy soils on the crest and more fertile mineral-rich soils in the bottomlands.
A seep-line may be found along the slope where an impervious layer forces water in the soil to move sideways and out on to the surface creating hygromorphic (wetter) conditions. The soils found on crests are usually sandy and therefore lack the ability to hold moisture for extended periods and are low in nutrients. As a result the quality of the grasses growing on the crests is poor and percentage cover low.Due to leaching, minerals are deposited lower down the slope and therefore the fertility and clay content of the soils of the bottomlands are higher, most suitable for the establishment of preferred palatable species. The depth of soil various considerably, limiting the establishment of grass where the soils are very rocky or shallow. Deeper soils are able to support healthy root systems and hold more moisture.
The cover provided by trees and shrubs promotes the growth of palatable species as moisture in the soil is retained for extended periods and protection provided against direct sunlight. Grass species growing in the open are often hard and coarse, drying prematurely at the end of the rainfall season. Animals have preferences where the grass species they select to feed on are concerned.Therefore it is essential that pasture is managed in such a way as to protect the preferred species. Intensive grazing over extended periods has a negative effect on the preferred grass species and promotes the growth of unpalatable species through the lack of competition. Excessive use of fire can create a fire climax where species that respond well to regular burning start to dominate.
In this way, the ecological status of the pasture on a specific property can decline. How can one determine the best management practices? It should be noted that with cattle farming a system of rotational grazing is applied that provides the grass of a specific camp a period of rest and recovery. With game this is different as there is no control on which areas are to be utilised at any given time.The only way to encourage game to move into new areas is through the manipulation of watering points or selective burning of sections of a property. Probably the most important aspect of pasture management is monitoring of condition on a regular basis.
This is done by identifying the different vegetation types of a property and then to pro rata place monitoring points in each of the vegetation units.
The most important part of such a monitoring process is to determine the ecological value of the grass sward. A quantitative assessment of the grass species at a monitoring point is done by identifying species present and allocating a grazing value to each species.Regular monitoring provides a trend that is indicative of what impact grazing is having on the property. Other aspects of the grass sward such as percentage cover and tuft size are also recorded to monitor trends in grass tuft establishment. Many land owners or managers see supplementary feeding as the solution to the lack of grazing.
This, in my opinion, is the first sign of poor management practices. Continual supplementary feeding does not relieve the pressure on the grass sward. It only postpones the decline in the ecological value of the grass sward; grazers still utilise the natural grazing available even though supplementary fodder is provided thus the pressure continues throughout the period of supplementary feeding.The only way to protect pasture condition is to reduce grazing pressure - animal populations cannot be allowed to increase continuously where there is no system of reducing their numbers. The situation as seen in Photo 4 can in no way be mitigated by the provision of supplementary feeding.
It took two seasons of average rainfall for this section of pasture to recover - with continual heavy grazing this would never have been possible! The natural environment in our area supports a number of industries including tourism and game farming. Protection of this resource is tantamount to the future of these industries. Exploitation will only have one result. It should always be remembered that the environment is not reliant on tourism or game farming for its future but that the converse is true.Many are inclined to advocate tourism as the saviour of our region – this is far from the truth. Our priority is soil conservation and with this obviously the protection of the vegetation that it supports. Only then does the conservation of animals enter the picture. The importance of tourism may possibly be given fourth position but this is debatable too.
The misconception that tourism, sometimes called ‘eco-tourism’ (a term I still fail to digest), is top of the pyramid needs to be exposed for the lie that it is. Without the environment, in a healthy state, there just would not be any tourist attraction in our region.Poor pasture management leads to poor pasture condition which results in poor animal condition. Poor animal condition leads to increased disease ending in a high proportion of fatalities.
The natural environment is a dynamic system that responds primarily to climatic conditions. As a result it can only support a certain level of utilisation as determined by production within the primary level of the food chain. Therefore the implementation of adaptive management on any property is essential.
The smaller the property the more intensive management should be because the effect of poor management will manifest itself quicker and more intensely. Finally it would suffice to say that ‘grass is not always what it appears to be’.
Some are good and some not so good, but all in all, grass is still there to protect the soil from erosion and to nourish the herds that feed on it. Look after your grass sward and it will look after your investment in the natural environment, whatever that may be.