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Tuatara: Volume 1, Issue 2, May 1948

The Place of the Botanist in Soil Conservation

page 19

The Place of the Botanist in Soil Conservation

The authority for soil conservation to be placed on a State and Local Body basis came with the passing of the Soil Conservation and Rivers Control Act in 1941, under which authority was given for the formation of the Soil Conservation and Rivers Control Council and Catchment Boards; under the terms of this Act, the primary objects of these bodies were (1) the promotion of soil conservation and (2) the prevention and mitigation of soil erosion.

The problems of soil conservation cannot be solved by the work of any one branch of science, and it is only by the combination of the skills of agronomists, agrostologists, agriculturalists, botanists, foresters, pedologists and engineers working simultaneously that successful results can be secured. In New Zealand, due to wartime difficulties the putting into operation of a soil conservation programme has been delayed, and until recently, work has been largely confined to river control by engineering means. Now that soil conservation is an accepted fact, the scope of work will become infinitely greater with passage of time.

A basic principle in soil conservation is protection of the soil by vegetative cover, with or without assistance from engineering structures, while on arable land the emphasis is on improved cultural technique. In New Zealand, soil conservation is concerned in the main with country with depleted vegetative cover, country which was originally covered with either tussock grassland or forest; thus, the maintenance or regeneration of an adequate vegetative cover over some millions of acres is the problem confronting New Zealand. In this task, the botanist is called on to play an important part.

Vegetation surveys are essential in providing basic information, this being useful not only by itself, but it can be used in combination with data from other types of surveys, e.g., soil surveys in the preparation of land utilization schemes. In New Zealand there has been no systematic vegetation survey of the country as a whole, and when it is proposed to carry out conservation measures it is usually necessary to carry out such a survey of the particular region. Vegetation surveys have been carried out by the Botany Division, Department of Scientific and Industrial Research, for the Soil Conservation and Rivers Control Council, District Soil Conservation Committees and Catchment Boards, and there are at present others waiting to be carried out. Such surveys may be made of a single catchment, or of a region em- page 20 bracing a number of catchments, or as was recently done, of a projected Soil Conservation Reserve. By this means a picture of the vegetation of a region is presented, showing the main associations, and from which can be determined in broad outline those areas requiring conservation measures in terms of improved vegetative cover.

It is necessary when dealing with depleted tussock grassland and burned and/or cut over forest land to make more detailed investigations than are carried out during a vegetation survey; these are essential in studying the present state of the vegetation, and where reseeding has taken place, to study the process of establishment of the sown species, or where these fail to establish the cause of the failure. In these detailed investigations, use is made of unit areas of vegetation termed “quadrats,” the study of a number of which yields a picture of the structure of the particular association. Investigations of this nature have been carried out by the Botany Division, D.S.I.R., at the Molesworth run, Marlborough, in connection with the rehabilitation of depleted tussock grassland. Various types of quadrats can be used, depending on the purpose of the particular investigations (list quadrats, basal area quadrats, clip quadrats, etc.), and although not all have been used in New Zealand it seems likely that all will be required to elucidate the different facets of the problems presented. For investigation of the effect of altitude, slope and aspect, use is made of “belt transects,” this method being used by the Soil Conservator of the North Canterbury Catchment Board in study of depleted tussock grassland. The interpretation of photographic records of vegetation is another sphere of activity for the botanist.

The introduction of plant species for soil conservation purposes is an important and exacting activity which should be carried out by the botanist, since in other hands it can have serious effects, such as introduction of undesirable species. A complete record of such introductions is essential, covering origin, habit and general characteristics in the experimental plantings, correctness of identity, suitability for projected plantings in New Zealand, and loci of distribution after trial period. New introductions should be carefully observed in the initial experimental sowings, and if they prove suitable for further sowings in other areas, their behaviour in the new habitats should be further observed—only by meticulous care can plant introduction be really beneficial, and the possibility of undesirable plants gaining access and distribution due to inaccurate naming of original seed, or failure to appreciate harmful habits under local conditions, be greatly reduced.

Taxonomy, although regarded by some people as largely academic, is of importance in soil conservation. As mentioned above, the taxonomist has a definite responsibility in plant introduction. The ecologist in his vegetation surveys and more detailed work requires that the flora with which he deals be systematised; work carried out since the publi- page 21 cation of Cheeseman's “Manual of the New Zealand Flora” in 1925 has shown that there is urgent necessity for taxonomic investigation of the indigenous flora, to provide a basis for many types of botanical inquiry. It is evident that distinct geographic and ecological entities are contained in the earlier botanists' conception of a single species, and it is essential that the exact status of these entities be worked out; from the soil conservation viewpoint, this is particularly the case with species or groups which show promise for conservation, for example, the Gramineae. Correctness of determination is essential when dealing with the willows (Salix sp.) and poplars (Populus sp.) which have important uses in river control and stabilization of slumping hillsides, and equally so with any other plants used for conservation purposes.

As distinct from investigation of introduced species for soil conservation purposes, there is need for investigation of indigenous species for the same purpose. Ecological work to date has shown that certain species offer possibilities for the revegetation of depleted land—as an example one can cite the native blue wheat grass (Agropyron scabrum) which is composed of a large number of geographic types covering divers habitats. The above mentioned species is being studied by the Botany Division, D.S.I.R., plants being grown from seed from many localities, and selection of desirable types being made from this representative collection. Further ecological work will, no doubt, reveal other indigenous species which would fulfil needs of the conservation programme. The writer has made experimental sowings of the native silver tussock (Poa caespitosa) from several sources on depleted country in Marlborough, in an endeavour to establish scattered tussocks, to act as nurse plants for more palatable grassland species.

Although the necessity has not yet arisen in New Zealand as in other countries, where the value of a species for soil conservation, although normally regarded as a weed, has to be equated against its harmful effects on agriculture, etc., the services of the botanist are useful; for instance, it might be necessary to decide whether or not sowings of gorse or some other weed are warranted for soil conservation purposes, and whether the benefits would outweigh any possible detrimental effects.

Close liaison between the botanists and the pedologists would be of value, not only to these two branches of inquiry, but to soil conservation, since integration of the results of both types of workers would provide basic information on land capability. A closer investigation of both indicator plants and indicator associations would be of material value—we do know that such plants as Gnaphalium subrigidum and Asplenium anomodum are usually characteristic of calcareous regions, and it might be that indicators of other parent materials and soils derived therefrom will be discovered. Such information would be of significance in determining the best methods of land utilization.

page 22

The above account is intended to cover in broad outline some of the aspects of the work of the botanist in soil conservation; although the spheres of the ecologist and taxonomist have been mentioned, it must not be thought that there is no scope for the physiologist—there is a large field in the investigation of the problems of “experimental ecology”; all types of botanical work are needed to help solve the problems of soil conservation.