Effects of intensive cattle trampling on soil-plant-earthworms system in two grassland types

Soil Bid. Biochem. Vol. 23. No. I?, pp. 1661-1665. 1992 Printed in Great Bntain. All rights reserved

Copyright

0038-0717/92 55.043 + 0.00 IC 1992 Pergamon Pxss Ltd

EFFECTS OF INTENSIVE CATTLE TRAMPLING ON SOIL-PLANT-EARTHWORMS SYSTEM IN TWO GRASSLAND TYPES D. CLUZEAU,‘* F.BINET,'F.VERTES,'J.C. SIMON,'J.M. RIVIERE' and P. TREHEN’ ‘Universitt de Rennes I, URA, CNRS 696, Laboratorie d’Ecologie du Sol et Biologie des Populations, Station Biologique de Paimpont, F.35380 Plelan Le Grand, *INRA, Station agronomique, 4 rue de Stang-Vihan, F.29000 Quimper and ‘ENSAR, Chaire de Pedologie, 65 rue de St Brieuc, F.35042 Rennes Cedex, France

Summary-An experimental study of the consequences of intensive cattle trampling was carried out pure white clover and on a perennial rye-grass-white clover association. Direct and indirect elfects of trampling on earthworm and plant communities and on soil structure were found. Trampling led to destruction of a large portion of the aerial system, stolons and roots, with removal of some of the vegetation cover (soil at least 50% bare). From a general view, tramphng in experimental plots induced a large decrease (from 70 to 86%) of earthworm density and biomra. The functional structure was modified for the benefit of large size species. Small size species were more sensitive: some species, such as Lumbricus casraneus and Allolobophora chlorotica chlorotica typica disappeared. An increase of the proportion of adults could be related to larger sensitiveness of juvenile individuals in the same population and explained a significant increase of the individual mean weight. Different responses existed in function of the grassland type related to depth.

INTRODlJCllON Trampling by cattle during certain periods of the year may substantially damage the main components of the grassland system (plants, soil structure and soil biology), destroying vegetation, compacting the soil

and disturbing edaphic biological activities. The effects of trampling on plant productivity, root growth and physical soil properties have been studied by Monnier and Stengel (1982) and Vertes et al. (1988). Conversely, the effects of soil compaction on earthworm populations have rarely been measured, with existing research focusing on the effects of soil compaction caused by trampling (Chappel et al., 1971; Pierce, 1984) and the passage of farm machinery (Aritajat et al., 1977, Bostrom, 1986; Cluzeau et al., 1987). A study was made of the direct and indirect effects of trampling by cattle on earthworm and plant communities and soil structure, with trampling isolated from other environmental factors such as grazing specificity and dung deposition. EXPERIMENTAL DESIGN ANDSAMPLINCMETHOD Site

Plots located south of Quimper (southern Brittany, France) were planted with either clover alone or with a mixture of clover and rye-grass in spring 1985 and *Author for correspondence.

mowed 5 times yearly until subjected to trampling in 1987-1988. The soil, brown with a sandy loam texture (48% sand: 35% silt: 18% clay) and granite subsoil, is rich in organic matter (5%). This soil type is well-structured and resistant. Methods

Figure 1, representing the experimental site, indicates the zones for effecting culture profiles and sampling for earthworm study. Two types of vegetation cover were taken into account: white clover only (WC) (Trifolium arvensis) and perennial rye-grass (Lolium perenne) white clover association (WC-PRG). The plots were twice subjected to heavy trampling at different dates: December 1987 (winter trampling) and March 1987 (spring trampling). Twelve cattle were allowed to trample the plots over 120m2 (density: 1 animal 10me2) for 45 min in each trampling period. Trampling was extremely heavy, corresponding to that at a pasture entrance-way. The following variables were analysed: vegetation (growth and morphology), soil (cultural profile, bulk density and infiltrability) and earthworm populations (abundance and structure, age ratio and mean individual weight by age group). All sampling took place 1 month after spring trampling. Earthworm

sampling

Earthworm sampling was effected by washing and screening, followed by manual sorting under a 1661

D.

1662 WINTER

4

CLUZEAU

et al.

LEAF BIOMASS (t/ha)

TRAMPLING C

I

_---- WC

WC-PRG -----

4

3 2

i

6m

i -A*

SPRING

1 TRAMPLING

Fig. I. Experimental site with plots studied (hatched zones). modifying

0 1

glass in order to extract all individuals

(adults and juveniles) and cocoons. Five, 0.10 mz surface samples were taken from each treatment. Each sample was divided into two depths (O-IO and IO-20cm). The results present are the means of the 5 sample units.

2 3 4

Computation of disturbance coeficient

STOLON BIOMASS (t/ha)

The disturbances in earthworm populations caused by trampling were evaiuated by means of a disturbance coefficient (CPa):

Fig. 2. Trampling effects on aerial biomass of white clover (hatched) and perennial rye-grass (shaded), and of the stotons: I, = 14 April 1988-t, = 7 May 1988.

(Absolute Abundance Disturbance) - (Absolute Abundance Control) CPa = (Absolute Abundance Control) The above coefficient is subject to two constraints: (1) variation in abundance is not taken into account and (2) high- and low-density species are not differentiated. RESULTS

compacted under both types of cover. The method utilized to measure bulk density (cylinders, etc.) did not enable determining the significance of compaction. However, differences in water retention were evaluated, with cubes of trampted soil starting to dry out earlier, more rapidly and extensively (Vertes et al., 1988). E,$ects on earth~oTm po~iatio~

Effects of trampling on vegetation Trampling led to destruction of a large portion of the aerial system, stolons and roots, with opening of the vegetation cover (soil at least 50% bare). The degree of damage was evaluated after initial regrowth and the main results are summarized in Fig. 2. Reconstitution of the aerial portions occurred as of the second regrowth, whereas that of stolons required about I yr. WC and WC-PRG plots showed different effects: after trampling, clover was at a disadvantage with ryegrass in competing for light (although initially protected from crushing by the ryegrass root mass) (Vertes et al., 1988; Vertes, 1989). EApcts on soil Cultural profiles after planting revealed destruction of much of the root system at a S-15 cm depth, a zone

We consider that the biological parameters measured allow specification of the types of disturbance caused by trampling. Changes in the vertical distribution of species indicate the effects of trampling on the soil profile. The relative sensitivity of different species to trampling was evaluated by taking into account overall abundance, structure (abundance, age distribution and individual weights) and the number of cocoons. Trampling did not influence the vertical distribution of individuals and cocoons (90% were Iocated at 0-1Ocm depths). Piearce (1984) reported a decrease of 94 to 67% at O-10 cm. However, this finding was not significant considering the low number of individuals present. Trampling led to a significantly greater reduction in overall abundance under WC-PRG than under

Table 1. Number find. m-‘) and biomass (g m-‘) and cocoons number presented as means f SD in various treatments. (For abbreviations, see Fig. I and text.) Worms

Grassland WDe

Experimental olots

WC

Untreated Trampled

WC-PRG

Untreated Tramoled

Number 806 f 152’ 230& 174 418 2 8.5’ ss+43

Biomass

Number of cocOO”S

124 + 16’ 67 & 22 69 + 20’ 16 -+ 13

394 & 131 NS 182 & 137 308 + 193 NS 134+52 -

Significance lcvcls between plots: lP < 0.05; NS = not significant. Mann-Whitney-test.

Cattle trampling and soil-plant-earthworms

q m

WC WC-WG

I663

system

[Fig. 5(b)]. The epigeic species L. r. rubellus is only consisted of juveniles after trampling. Under WC-PRG, juvenile mean weight in trampled plots was lower for all species (minimum decrease of 25-30%) (Fig. 6). Mean adult weight showed a similar, but less marked tendency in both types of grass cover. DlSCUSSION

-1

1 0 DirNrbmce coefficient

2

Fig. 3. Disturbance coefficient of the specific different earthworm population numbers. (For abbreviations, see Fig. I and text.)

WC, with respective decreases of 85 and 70%. for abundance, and 77 and 50%, for biomass (Table 1). There was a non-significant 50% reduction in the number of cocoons, related to heterogeneous spatial distribution. Specific population numbers decreased under WC after trampling, with disappearance of the epigeic species Lumbricus castaneus. The numbers of L. friendi and Allolobophora chlorotica chlorotica albinica showed a nonsignificant increase (Fig. 3). Under WC-PRG, all species were reduced. Except for Aporrectodea nocturna, damage appeared greater under WC-PRG, with two species eradicated, the epigeic L. castaneus and the endogeic Allolobophora chlorotica choloritica typica (Fig. 3). Species living near the soil surface were the most disturbed: L. castaneus disappeared. However, Lumbricus rubellus rubellus showed a capacity to resist trampling. Anecic species appeared the least sensitive to trampling. However, Aporrectodea nocturna tended to predominate over L. friendi under both grass conditions. The response of endogeic species varied, with Allolobophora chlorotica chloritic albinica resisting better than Aporrectodea caliginosa caliginosa and Allolobophora rosea rosea. Trampling tended to decrease the number of cocoons more or less markedly depending on the biology of the species (Fig. 4): the number of cocoons of epigeic species decreased by 90%, for L. castaneus, and by 50-65%, for L. r. rubellus, whereas the decrease for anecic and endogeic species was only 23-37% and 32-57%, respectively. The number of juveniles fell sharply in trampled WC (by lo-SO%), while the number of adults showed little change [Fig. 5(a)]. Hence, the change in population structure consisted of a marked increase in the proportion of adults. In species with a significant proportion of juveniles, juvenile mean weight was higher after trampling (Fig. 6). Under trampled WC-PRG, the proportion of juveniles in the three endogeic species A. rosea, A. caliginosa and A. c. c. albinica and in the anecic species A. nocturna showed a significant decrease

Type of vegetation cover affected the development of lumbricid populations. Population density was initially twice as high in clover as in the grass combination. The differences in initial numbers may be explained by either of the following hypotheses:

(1) Soil obstruction by the ryegrass root system in the combination limits the available space for earthworms in the upper IOcm (hence lower initial abundance under the WC-PRG combination).

(2) Food supplied by the clover root system has

a higher nitrogen content (hence higher initial abundance under WC).

These differences are enhanced after trampling by cattle, leading to a marked reduction in earthworm populations. The observed decline is consistent with findings by Chappell et al. (1971) Aritijat et al. (1977), Bostrom (1986) and Cluzeau et al. (1987) in soil compacted by farm machinery, and by Piearce (1984), in a pasture entryway. Furthermore, the effects of trampling on vegetation, particularly WC, involve substantial root destruction. It is difficult to distinguish between direct (mortality due to crushing) and indirect (sublethal effects due to environmental changes) effects, both as regards vegetation and lumbricids. There is a general decrease in populations of earthworms in soils compacted by farm machinery. However, few studies have analysed selection pressures on different populations. The response varies by species and age class and with the type of vegetation cover. Em

cl

L-St.

WC WGFUG

Lr. rub. L friendi

-1

0 1 Disturbance coefficient

Fig. 4. Disturbance coefficient of the number of earthworm cocoons (endogeic species are regrouped in only one class). (For abbreviations, see Fig. I and text.)

D.

1664

(a)

WC-PRG

Untreated

Lrub.

Acca

WC-PRG

Lwb.

uri-

CLUZEAU

(b)

fkxa

WC Untreated

Amsa

WC Trampled

Trampled

Am%

et al.

Amam

Fig. 5. Age-ratio distribution of earthworm populations in various treatments. (For abbreviations, see Fig. 1 and text.)

Specific resistance to trampling is a function of morphology (size and musculature) in combination with location in the soil. Thus, L. cataneus, a strictly

-1

I 0 Disnthawc codfkient

Fig. 6. Disturbance coefficient of the juvenile mean weight. (For abbreviations, see Fig. I and text.)

epigeic species of small size, disappears, irrespective of sward type. Conversely, L. r. rubellus, a mediumsized epigeic species capable of shallow burrowing (Springett, 1983), possesses the capacity to resist trampling. However, as observed by Piearce (1984), the latter species is more sensitive than large- sized (L. friendi and A. n5ctur~u~ and strictly endogeic species (A. c. chlorotica, A. c. cafiginosa, A. r. rosea). Similarly, cocoons of endogeic and anecic species, deposited more deeply underground (inside or at the base of the root hair), are less disturbed. In terms of age classes, juveniles are more vulnerable to the direct effects of trampling than adults, irrespective of grass type. This finding is consistent with Rundgren (1975), who showed that small juveniles of A. c. caliginosa are located at a depth of O-5 cm, whereas adults and large juveniles burrow more deeply.

Cattle trampling and soil-plant-earthworms

system

1665

Vegetation type affects the development of lumbticid populations since population densities were initially twice as high in WC than WC-PRG, and

Acknowledgemenfs-The authors are very grateful to MS G. Chaminade, H. Gamier and Mr M. Lefeuvre for their technical help.

trampling by cattle exacerbates this difference. This may be explained by:

REFERENCES

(1) The greater capacity of the populations under WC to recover may be enhanced by a higher supply of dead organic matter (more root destruction in WC). The growth of young individuals is promoted: juvenile mean weight increased in WC and decreased in WC-PRG (Fig. 6). (2) Population recovery may also be influenced by soil structural changes. The greater soil compaction under WC-PRG was associated with a reduction in porosity and hence water circulation. This may lead to more restricted earthworm movements and a decreased food supply. The present work constitutes an initial approach to understanding the effects of trampling on three major components of the grassland system: soil, vegetation cover and lumbricids. The complexity of flora-fauna interactions makes it difficult to interpret the effects of trampling. Validation of the hypotheses proposed requires new studies specifying the effects of this disturbance on (1) the vertical distribution of individuals (at O-10 cm depths), and (2) the protective role of vegetation. In addition, greater distinction between immediate and longer term effects is required.

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Cluzeau D., Lebouvier M., Trehen P., Bouche M. B., Badour C. and Perraud A. (1987) Relations between earthworms and agricultural practices in the vineyards of Champagne. Preliminary results. In On earfhw~orms (P. Omodeo, Ed.), pp. 465-484. Mucchi. M_odena. Monnier F. and Stengel P. (1982) Sfrucrure ef Erar Physique du Sol. Encyclopedic des techniques agricoles, Pans. Piearce T. G. (1984) Earthworm populations in soils disturbed by trampling. Biological consermrion 29, 241-252. Rundgren S. (1975) Vertical distribution of lumbricids in southern Sweden. Oikos 26, 299-306. Springett J. A. (1983) Effect of live species of earthworm on some soil properties. Journal of Applied Ecology 20, 865-872.

Vertes F. (1989) Effets due pietinement des bovins sur le trefle blanc pur ou en asseciation. In XYfPmeCongr& International des Herbanes. DD. 1063-1064. Nice, France. Vertes F., Le Corre L., Simon J.-C. and Riviere J. M. (1988) Effets du piitinement de printemps sur un peuplement de trtfle blanc pur ou en association. Fourrages 116, 347-366.