Effects of various stripping regimes on foliage production of some browse bushes of the Sudano-Sahelian zone**

Mohamed Idrissa Cisse

Ecologist to the Joint ILCAlMali Programme

1. Introduction

2. Methodology

3. Results

3.1 Effects of stripping on annual production

3.2 Aftereffects of treatments one year later

4. Discussion

5. Summary and conclusion

Bibliography,

1. Introduction

In the Sahel zone many varieties of bush are hungrily sought after by livestock, which browse on their leaves and branches and sometimes their flowers and fruit. Frequently they present a stunted habit as a result of the intensive utilization to which they are subject.

In the context of the ILCA programme in Mali it seemed important to study the reaction of bushes to browsing, even if the experiment could not be carried out on the most favourable basis, i.e. with utilization by animals. Utilization by animals was simulated by means of stripping : this had a twofold purpose, that of monitoring the development of leaf production during the growth season on the one hand, and on the other that of studying the influence stripping interval and method, and date of first stripping, on total leaf production.

The study involved three species: Combretum aculeatum Vent. (Combretaceae), Cadaba farinosa Forsk. (Capparidaceae), and Feretia apodanthera Del. (Rubiaceae). The site of the experiment was the ranch of the Station d'Elevage et de Recherches Zootechniques in Niono, situated in the fossil alluvial plain of the Niger, in the Sudano-Sahelian zone.

2. Methodology

Total or partial stripping was carried out on a batch of five stocks for each variety and treatment. The leaves and young branches harvested were ovendried. The treatments consisted of comparing the production of:

a) Stock subjected to total stripping every 15 days (coded TS 15) to others stripped every 30 days (coded TS 30);

b) Stocks stripped completely with those partially stripped and coded PS (alternate stripping of half the plant every month);

c) Staggering of the date of first stripping over 30 consecutive days for specific stocks coded TSDO to TSDN, which were subsequently stripped totally every 15 days, enabling the development of foliage production over time to be monitored and the influence of the date of first stripping to be measured every fortnight. 

The aftereffects of treatments were studied the following year by comparing the production of new shoots to that of control plants measured at their maximum productivity. These results are only available for Cadaba farinosa and Combretum aculeatum.

3. Results

3.1 Effects of stripping on annual production

3.1.1 Seasonal evaluation of production

Figure 1 enables the development of foliage production to be compared for three species over time. Owing to the absence of any form of utilization, the biomass development describes a looped curve reflecting foliage production, which characterizes the climb of the curve, and the fall of leaves.

Figure 1. Comparison of seasonal trend's in foliage production for 3 browse bushes.

Although the shape of the three curves is identical, it is easy to see that the peak did not occur at the same period. It occurred in August for Cadaba, in September for Feretia, and in October for Combretum. Moreover, it does not reach the same value for the three species: Combretum was the most productive, followed by Feretia. Although leaves fell more rapidly in Cadaba, in Feretia the leaves dry on the tree and defoliation occurs slowly during the dry season. The curve is modified by the interval and method of utilization.

3.1.2 Influence of stripping interval and method on total production

Table 1 illustrates the influence of stripping interval and method on the three species. The following may be noted for the three species:

a) A drop in production according to interval; the production of the stocks which were totally stripped every 30 days was higher than those subjected to total stripping every 15 days.

b) Given the same pattern, partial stripping (PS) results in more foliage than total stripping.This emerges less clearly for Cadaba where production in TS 30 was slightly higher than that of stocks which were partially stripped, but this can be interpreted in terms of the effect of a treatment initiated at an advanced stage of the plant cycle.

Although in Combretum and Cadaba stripping had a depressing effect on total production, in Feretia it had a stimulating effect, since cumulative production in individuals subjected to a total stripping regime every 30 days and to partial stripping emerges as more productive than the maximum obtainable without treatment.

Table 1. Cumulative average foliage production as a function of stripping interval and method in three browse bushes

Treatment	Cumulative production in g of DM/stock and species
	Combretum aculeatum	Cadaba farinosa	Feretia apodanthera
Control (max. biomass)	655	183	334
Total stripping every 15 days	190	125	280
Total stripping every 30 days	275	140	444
Partial stripping	335	122	581

3.1.3 Influence of date of first stripping on total production

The results comparing the influence of first stripping date for the three species are given in Table 2, which shows cumulative production for each species and stock subjected to a total stripping regime every 15 days, beginning at 30 day intervals throughout the growth season and successively designated TSD0, TSD1, TSD 5.

Table 2. Average cumulative foliage production as a function of date of first stripping three browse bushes

In the three species, when the first stripping occurs while the production curve is climbing (see Figure 1) regrowth is more marked and stronger than when it occurs during the descending phase. In Combretum and Cadaba, highest total production is obtained when first stripping occurs when maximum production is reached (TSD 3 for Combretum and TSD 1 for Cadaba). The same is not true, however, for Feretia, in which the best date occurs at the beginning of the upward part of the case (TSD 1).

3.2 Aftereffects of treatments one year later

The aftereffects of the treatments were only studied for Cadaba farinosa and Combretum aculeatum. The effects were estimated one year after treatment by comparing the maximum production of individuals which had never been stripped (the control batch) to that of the regrowth on stocks which had been treated. As regards the latter, we considered the production of the old stems and that of new shoots separately, and analysed the influence of interval, method and date of first stripping.

3.2.1 Aftereffects of stripping interval method

One year later, in Cadaba and in Combretum, the depressing effect of stripping whether total or partial, could still befell, as shown in Table 3.

Table 3. Aftereffects of stripping interval and method in two browse bushes

Treatments	Average foliage production in g. of DM/stock
	Combretum aculeatum			Cadaba farinosa
	Old stems	New shoots	Total	Old stems	New shoots	Total
Control (never stripped)	–	–	715	–	–	170
Total stripping every 15 days	1	0	1	39	0	39
Total stripping every 30 days	321	5	326	75	0	75
Partial stripping	60	0	60	57	0	57

It could be seen in the marked drop in production of individuals which had been treated compared with the control group, adding emphasis to the trends recorded for the preceding year (see 2.1.2).

In Cadaba no new shoots were put out. The depressing effect ranged from 31 to 77% for a total stripping regime every 15 days, from 22 to 55% for total stripping every 30 days and from 33 to 65% for partial stripping.

In Combretum, although stocks subjected to total stripping every 15 days as well as those partially stripped were no longer in a position to put out new shoots, individuals which were entirely stripped every 30 days did put out shoots and production increased slightly, with an attenuation of the depressing effect from 58 to 54%.

These results are rendered all the more interesting by the fact that the difference between average maximum production in the two years is not statistically significant for the two species.

3.2.2 Aftereffects of date of first stripping

The resulting aftereffects of staggered stripping are shown in Table 4, which compares the production recorded for the two bushes.

Table 4. Comparative aftereffects of date of first stripping in two browse bushes

It emerges that in Combretum and Cadaba the periods in which the after effects of treatments were beneficial did not coincide and were even out of phase.

In Combretum recovery was better if the treatment of the preceding year occurred late. Thus, for example, the production of TSD0, TSD1 and TSD2, in which treatment began while the growth curve was rising, was below that of the control group. Again, the production of stocks treated while the curve was dropping was higher than that of the control group and grew regularly from TSD3 to TSD4.

This relative increase in production is probably due to less marked mortality in the stocks, which react by putting out new shoots, the production of which is added to that of the old stems.

In Cadaba, individuals stripped during the declining production phase did not recover well. Moreover, stripping did not trigger off any new shoots in the subjects treated, except in stocks TSD 2, in which, however, production remained low.

4. Discussion

Although many experiments simulating browsing via a cutting method have been carried out on both perennial and annual grasses, as far as I am aware few authors have dealt with this topic in relation to browse trees. This fact restricts the discussion of results. However, it should be noted that there is some analogy between the influence of stripping interval on bushes and that of cutting on perennial grasses. The analogy is reflected in the drop in production in accordance with the utilization interval. Short intervals provide less browse than longer ones, and in addition they prejudice the survival of the plants, which may even lose the ability to put out new shoots. This tendency is particularly marked if stripping occurs late in relation to the onset of the plant cycle. The drop in production as a result of the stripping interval could be explained, as is the case for perennial grasses, in terms of the exhaustion of root reserves on which regrowth depends.

Partial stripping is more productive than total stripping. It is interesting to note this fact, since partial stripping more closely resembles utilization by animals. Animals never in fact strip a bush totally bare, but make do with small mouthfuls snatched sparingly from different parts of the bush. This is why in the real life situation bushes suffer little, although they are subjected to a far more rapid interval, than the 15 days pattern which we tested, unless they are subjected for a very long period to this kind of selective browsing, as is the case on the livestock ranch at the Niono station, where the bushes have developed a dense, rounded habit with branches which have become inextricable.

As regards the date of first stripping, the best period, as in the case of perennial grasses, is while the growth curve is rising when regrowth is at its strongest. The period at which cumulative production reaches its maximum appears to be the best in quantitative terms, but is this also true in terms of quality? It should be noted that this varies from one species to another (see 2.2). The aftereffects one year following treatment (see 2.2) can be beneficial if the plant reacts to stripping by putting out new shoots to compensate for the death of old stems. This was the case for Combretum aculeatum, for which it would be interesting to subject the TSD batch to a total stripping regime every 30 days, after maximum production had been reached. This is an interval which will result in their putting out new shoots, even one year later.

These results provide few indications as to the optimum utilization rate for these browse plants. However, this has been no more than a first approach, and certainly an indirect one, to the effect of browsing on the production of ligneous forage plants. An approach by a direct method would appear to be necessary.

5. Summary and conclusion

Partial and total stripping at 15 and 30 days intervals, simulating different browsing methods and intensities, as practised on Combretum aculeatum, Cadaba farinosa and Feretia apodanthera in the Sudano-Sahelian zone showed that the interval, method and date of first utilization have an influence on the foliage production of the current year and may also affect the production of the following year. Stripping may have either a depressing effect (Cadaba and Combretum) or else a stimulating effect (Feretia) on the foliage production of the current year. In both cases a drop in production in accordance with the stripping pattern was recorded and, given the same stripping interval, partial stripping appeared more productive than total stripping.

The highest total cumulative production was obtained when first stripping occurred while the growth curve was climbing. However, the optimum result differs from one species to another, and is obtained either when first stripping occurs after maximum production (October for Combretum and August for Cadaba), or when treatment is carried out as the growth curve begins to rise (Feretia).

The impact of treatment during the following year was beneficial only when the plant put out new shoots to compensate for the death of stems, as was the case for Combretum.

Bibliography,

Cissé, M.I. (1976). 'Influence de l'exploitation sur la qualité d'un pâturage soudano-sahélien'. These 3ème cycle, C.P.S., E.N. Sup. Bamako.

Hiernaux, P. (1978); Cissé, M. (1979) et Diarra, L.. 'Rapports annuels d'activité Section Ecologie'. Pâturages naturels du CIPEA/MALI. (mimeo) CIPEA.