# Successional changes and diversity of soil macrofaunal communities of chalk grasslands in Upper-Normandy (France)

Thibaud Decaëns, Thierry Dutoit, Didier Alard

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## To cite this version:

Thibaud Decaëns, Thierry Dutoit, Didier Alard. Successional changes and diversity of soil macrofaunal communities of chalk grasslands in Upper-Normandy (France). Acta Oecologica, 1997, 18, pp.135-149. *hal-05471793*

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# Successional changes and diversity of soil macrofaunal communities on chalk grasslands in Upper-Normandy (France)

Thierry Dutoit (¹*), Thibaud Decaens (²) and Didier Alard (³)

(¹) Université de Provence, Laboratoire de Biosystématique et Ecologie Méditerranéenne, FST Saint-Jérôme, URA 1152, case 421 bis, 13397 Marseille Cedex 20, France.

* Corresponding author: Tel: 04.91.28.87.32; Fax: 04.91.28.87.07

E-mail: thierry.dutoit@bioeco.U-3mrs.fr

(²) O.R.S.T.O.M., Laboratoire d'Ecologie des Sols Tropicaux, 72 route d'Aulnay, 93143 Bondy Cedex, France.

(³) Université de Rouen, Laboratoire d'Ecologie, UFR Sciences, 76821 Mont-Saint-Aignan Cedex, France.

## Abstract

A study of soil macrofaunal communities was made along a secondary plant succession following sheep grazing abandonment in some chalk grasslands of Upper-Normandy (France). 78 taxonomic units were identified. Taxonomic richness was highest in the recently abandoned grassland. Each plot was characterised by its own specific taxonomic groups. The environmental factors which explained the major contrasts between soil macrofaunal communities were the extent of tree colonisation and litter characteristics (C:N, biomass). Successional changes induced major changes in functional groups of soil macrofauna i.e. endogeic species dominated under herbaceous vegetation while epigeic species were more important in woody plots.

**Keywords:** Soil macrofauna, secondary succession, biodiversity, conservation management, chalk grassland, Upper-Normandy, France.

## Résumé

Dans des pelouses calcicoles de Haute-Normandie, une étude des communautés de macrofaune du sol a été réalisée le long d'une succession végétale secondaire après abandon du pâturage ovin. 78 unités taxonomiques ont été identifiées. La richesse taxonomique est la plus forte dans la pelouse abandonnée mais chaque stade de la succession demeure caractérisé par un groupe taxonomique spécifique. Les facteurs environnementaux qui expliquent la distribution des communautés de macrofaune du sol sont le taux de colonisation par les arbres et les caractéristiques de la litière (C/N, biomasse). Les changements végétaux successionnels induisent également des modifications des groupes fonctionnels de macrofaune du sol. Les espèces endogées dominent sous la végétation herbacée tandis que les espèces épigées sont plus nombreuses sous les parcelles boisées.
# INTRODUCTION

Chalk grasslands are characterized by their high diversity and species richness. In north western Europe, these ecosystems, derived from human forest clearing, were used as sheep walks for many centuries (TANSLEY, 1939). Since the abandonment of this practice in the 1950s, natural successional processes have led to scrub and woodland extension (SMITH, 1980) and/or to the development of species-poor coarse grasslands (WILLEMS & BOBBINK, 1990). Plant and insect diversity of calcareous grassland are threatened by a lack of grazing, either by domestic (BOBBINK, 1987) or wild animals (THOMAS, 1962). The aims of management plans for chalk grassland ecosystems are generally to remove part of the herbaceous layer of grasslands where grazing has ceased, in order to maintain the diversified flora of the mown or grazed stands (SUTHERLAND & HILL, 1995). The management systems which can achieve these objectives have been discussed in general terms by WELLS (1965) and they are now applied in chalk grasslands in many countries of north-western Europe (HILLIER et al., 1990; DUTOIT & ALARD, 1996 for review).

Effects of various management options (i.e., grazing, mowing, abandonment, etc.) on plant communities (WELLS, 1969) and above-ground invertebrates (MORRIS, 1969; BROWN & GANGE, 1985) have been studied to support management plans. Nevertheless, very little is known about the richness and diversity of soil invertebrate communities in calcareous soil ecosystems and their dynamics during secondary plant successions after the cessation of grazing, except for nematodes (HODDA & WANLESS, 1994a,b; WASILEWSKA, 1994).

An understanding of the dynamics of soil macrofaunal communities under different management regimes is as important as knowledge of the evolution of communities of plants or above-ground fauna (SOLBRIG, 1991) because soil macrofaunal communities play a key role in the soil system (BOND, 1994). Their diversity and distribution among functional groups is highly relevant to the development of major soil processes. As a result, any attempt to modify their structure may affect these processes. Soil invertebrates participate in the formation of a highly active mull by improving microbial activity (SCHEU, 1990) and influence nutrient cycling (STORK & EGGLETON, 1992). Some taxonomic groups (earthworms) also play an important role in determining vegetation pattern by selectively transporting seeds from the seed bank (WILLEMS & HUIJSMAN, 1994) or enhancing seedling growth in their casts (THOMPSON et al., 1994).

The aim of the study was to identify the main soil macrofaunal communities in chalk grasslands and their changes in density and biomass during a post-pastoral secondary succession which occurs in Upper-Normandy (France). The effects of changes in plant composition on soil macrofaunal community characteristics were also tested (i.e. evenness, diversity, species richness).

# STUDY SITES

Six plots were chosen to represent a successional sequence that characterize chalk grassland secondary successions in Upper-Normandy. These plots were on three sites, plot 1 on site 1, plots 2-5 on site 2 and plot 6 on site 3.

Successional processes in chalk grassland are complex and can be described as multidirectional. These sites have been ordered to represent an approximate (potential) succession sequence (fig. 1). It must be emphasized that any particular site has
<figure><img src="image_3.png" /><figcaption>FIG. 1. — Schematic secondary successions occurring in chalk grasslands in Upper-Normandy represented as a multidirectional process depending on temporal and spatial patterns which characterized the plots.</figcaption></figure>

been, or is likely to go, through all the described stages (DUTOIT, 1996; DUTOIT & ALARD, 1995b). Clearly, some of the stages are succession alternatives, e.g. pine wood in site 3. In the same way, a scrub community dominated by *Crataegus monogyna* and *Cornus sanguinea* are not absolutely a necessary stage in the development of maple wood in plot 5. Sites dominated by woody species have been ordered solely on the basis of the time elapsed since the abandonment of sheep grazing in 1950. This was estimated from old aerial photographs (DUTOIT & ALARD, 1995a). Similar considerations can be applied to the plots with only herbaceous vegetation. The enclosure plot in site 2 was the hypothetical starting point of post pastoral succession after one year of grazing abandonment which continued on the grassland of site 1. The tall grassland in site 2 corresponded to a grassland abandoned since 1950 (LIGER, 1952). As a whole, if successional changes lead to an overall extension of woody species, the contrasting dynamics leading to the development of tall grassland, scrub encroachment or forest pioneer are to be linked with former land uses as well as competitive or dispersal plant strategies (WELLS *et al.*, 1976; DUTOIT & ALARD, 1995a).

These sites represent a set of 6 plots with different management as described below. Nomenclature for vascular plants follows TUTIN *et al.* (1964-1980).

## Site 1. Val de Lescure, Amfreville-la-Mivoie (1°7'42"E, 49°25'5"N)

Plot 1 (Grazed Grassland) was an enclosed pasture (6.5 ha) heavily grazed by sheep and horses (1.5 livestock units/ha). The vegetation was a very short sward dominated by small perennial herbs
such as *Festuca cf. lemanii*, *Carex flacca* and *Lotus corniculatus*. Bare ground patches, non palatable plants and weeds indicative of overgrazing were locally abundant (*Eryngium campestre*, *Verbascum nigrum*, *Cirsium acaule*, *Origanum vulgare*).

## Site 2. Roches de Saint-Adrien, Belbeuf (1°7'30"E, 49°22'22"N)

Plot 2 (Ungrazed Grassland) was a fenced area (0.7 ha) where sheep grazing (4 sheep/ha/year) was abandoned in January 1992, twelve months before sampling. The vegetation was dominated by *Sesleria albicans*, *Brachypodium pinnatum* and some annual weeds (*Medicago lupulina*, *Linum catharticum*, etc.) which occurred in bare areas created by sheep trampling.

Plot 3 (Abandoned Grassland) was a 0.5 ha area immediately adjacent to the fenced enclosure. In this plot, sheep grazing was abandoned in 1950. The vegetation was a tall grassland dominated by tussock species (*Brachypodium pinnatum*, *Sesleria albicans*) with encroachment of some scrub species (*Rosa canina*, *Cornus sanguinea*, *Viburnum lantana*, etc.).

Plot 4 (Scrub) was adjacent to the tall grassland and corresponded to a uniform stand of *Crataegus monogyna* and *Cornus sanguinea* scrub (0.5 ha) aged 40 years. *Viola hirta* and *Origanum vulgare* were the commonest species of the herbaceous vegetation.

Plot 5 (Maple Wood) corresponded to a woody vegetation (0.5 ha) where the tree canopy, dominated by *Acer pseudoplatanus* and *Fraxinus excelsior*, was virtually closed. The scrub layer was mostly composed of *Corylus avellana*, *Sambucus nigra* and *Crataegus monogyna*. The herbaceous layer was dominated by *Mercurialis perennis*.

## Site 3. Belles-Roches, Brosville (1°7'12"E, 49°9"N)

Plot 6 (Pine Wood) had a woody vegetation (14.5 ha) exclusively composed of *Pinus sylvestris* which invaded the grassland since grazing ceased in 1947 (DUTOIT *et al.*, 1995). An herbaceous vegetation dominated by two grasses (*Brachypodium pinnatum*, *Sesleria albicans*) and one sedge (*Carex flacca*) indicated that more light reached the soil surface than in the scrub and maple wood plots.

# MATERIALS AND METHODS

## Sampling of soil macrofauna

Every two months, from March 1994 to January 1995, 5 soil samples of 25x25x10 cm were taken in each plot along a transect whose origin and direction were randomly chosen. Two complementary methods were used for soil macrofauna sampling:

(i) Hand sorting, following the method recommended by the Tropical Soil Biology and Fertility program (LAVELLE, 1988; ANDERSON & INGRAM, 1993; DECAËNS *et al.*, 1994). Soil monoliths were dug out with a spade, divided into 3 strata (i.e. litter, 0-5 and 5-10 cm) and carefully hand sorted in a large plastic tray.

(ii) Earthworms from deeper soil layers were extracted with formalin. Twice 2,5 l of 0,05% formalin were applied to the soil (BOUCHÉ, 1972). After 10 minutes, earthworms were collected and the soil was rapidly dug out up to 10 cm and hand sorted.

All invertebrates were killed and kept in 75% alcohol, except earthworms which were first fixed in 5% formalin over 3 days. Herbaceous plants and moss cover were determined using 50 × 50 cm square quadrats, litter using 25 × 25 cm quadrats and herbaceous roots with a cylinder, 10 cm diameter and 12 cm depth. Samples were dried at 75°C over 24 hours before counting and weighing. The soil
analyses were carried out using standard soil analytical procedures (ALLEN *et al.*, 1974). The percentage of tree cover was estimated with aerial photographs.

## Data processing

BOUCHÉ (1972) was used to identify Lumbricidae, PERRIER (1927-1940) and JONES (1990) for others groups. Many of the animals other than earthworms have been identified as immature stages using PAULIAN (1990). Earthworms were identified to species and other animals to families. Densities and biomasses of the 13 major taxonomic units (the others were too infrequent) were divided into three ecological groups (BRIONES *et al.*, 1995) i.e. epigeic (macrofaunal communities which have all their biological cycle on the soil surface or just under the soil surface), endogeic (macrofaunal communities which have all their biological cycle in the soil) and anecic (macrofaunal communities which have their biological cycle part on the soil surface and part in the soil).

Taxonomic richness (R) was estimated as the number of families found in one plot. Diversity (H) and Evenness (H') were calculated using the Shannon index from macrofauna population densities (table II, fig. 4). Differences in mean density, biomass and diversity index were statistically tested by the Fisher parametric test. Two multivariate analyses were performed using the Mac Mul and Graph Mu software (THIOULOUSE, 1990):

(i) A principal component analysis (PCA), performed on a [12 variables × 6 samples] matrix, in order to identify the main gradients in vegetation and soil likely to play a role in the distribution of macrofaunal communities (table I).

(ii) A correspondence analysis (CA), performed on a [20 variables × 6 samples] matrix, in order to compare the structure of invertebrates communities (density & biomass) in the different sites (table II & Appendix).

<table><caption>TABLE I. - Vegetation and soil characteristics of the six plots (C: carbon; O.M.: organic matter; CEC: cation exchange capacity).</caption><thead><tr><th>Plots<br>(vegetation)</th><th></th><th>Moss<br>(g/m²)<br>dry weight</th><th>Herbaceous<br>(g/m²)<br>dry weight</th><th>Roots<br>(g/m²)<br>dry weight</th><th>Litter mass<br>(g/m²)<br>dry weight</th><th>Litter<br>(C/N)</th><th>Tree cover<br>(%)</th></tr></thead><tbody><tr><td>Grazed Grassland</td><td>n=6</td><td>0</td><td>187</td><td>637</td><td>57</td><td>29</td><td>0</td></tr><tr><td>Ungrazed Grassland</td><td>n=6</td><td>0</td><td>573</td><td>838</td><td>93</td><td>35</td><td>0</td></tr><tr><td>Abandoned Grassland</td><td>n=6</td><td>5</td><td>722</td><td>914</td><td>153</td><td>36</td><td>5</td></tr><tr><td>Scrub</td><td>n=6</td><td>137</td><td>16</td><td>593</td><td>228</td><td>27</td><td>90</td></tr><tr><td>Maple Wood</td><td>n=6</td><td>27</td><td>75</td><td>533</td><td>304</td><td>22</td><td>100</td></tr><tr><td>Pine Wood</td><td>n=6</td><td>323</td><td>231</td><td>914</td><td>264</td><td>57</td><td>70</td></tr></tbody><thead><tr><th>Plots<br>(soil)</th><th></th><th>Clay<br>(%)</th><th>Silt<br>(%)</th><th>Sand<br>(%)</th><th>C<br>(g/kg)</th><th>O.M.<br>(g/kg)</th><th>CEC<br>(Cmol/kg)</th></tr></thead><tbody><tr><td>Grazed Grassland</td><td>n=6</td><td>37.4</td><td>48.9</td><td>13.7</td><td>39.2</td><td>67.4</td><td>10.1</td></tr><tr><td>Ungrazed Grassland</td><td>n=6</td><td>68.5</td><td>21.5</td><td>10</td><td>38.9</td><td>66.9</td><td>10.9</td></tr><tr><td>Abandoned Grassland</td><td>n=6</td><td>74.1</td><td>22.5</td><td>3.4</td><td>54.1</td><td>93.1</td><td>16.6</td></tr><tr><td>Scrub</td><td>n=6</td><td>76.5</td><td>19.5</td><td>4</td><td>54.6</td><td>93.9</td><td>24.3</td></tr><tr><td>Maple Wood</td><td>n=6</td><td>71.3</td><td>23</td><td>5.7</td><td>63.4</td><td>109</td><td>30.3</td></tr><tr><td>Pine Wood</td><td>n=6</td><td>61.4</td><td>22.7</td><td>15.9</td><td>56.8</td><td>97.7</td><td>17.7</td></tr></tbody></table>
Key of codes used in PCA and CA, for the different plots, variables and taxonomic groups are given in table III.

## RESULTS

78 taxonomic units of soil invertebrates were recognised during the study (Appendix). Multivariate analysis of environmental factors (fig. 2) and macrofaunal communities (fig. 3) reveal two factors which are responsible for respectively 91.7% (PCA) and 80.7% (CA) of the total variance observed.

The first environmental factor was identified as the effect of the vegetation structure (tables I & III). It accounted for 75.8% of the environmental variance (PCA), 46.7% of the variance in invertebrate communities (CA), and separated herbaceous plots from woody plots (fig. 2). In grasslands, the predominance of endogeic groups of Coleoptera (Melolonthidae, Nitidulidae) and the presence of the earthworm *Appo-rectodea caliginosus* can be noted. In contrast, large epigeic populations, i.e. Isopoda (Oniscidae) and Hymenoptera (Formicidae), were recorded in wooded plots. The second factor explained 15.9% of the environmental variance, 34% of the community variance and opposes the grazed grassland and deciduous woody plots, with low herbaceous shoot biomass, root biomass and C:N litter value (tables I & III), to the pine wood and other non-grazed grasslands (fig. 2).

Along the potential succession, the relative contribution of endogeic invertebrates was high in the grazed grassland (78% of total biomass) and decreased during colo-

<figure><img src="image_4.png" /><figcaption>FIG. 2. - PCA carried out on the vegetation and soil variables of six plots of a potential secondary succession in chalk grasslands. (B) Biomass. See text for the designation of groups (GG: grazed grassland; UG: ungrazed grassland; AG: abandoned grassland; S: scrub; MW: maple wood; PW: pine wood).</figcaption></figure>
<table><caption>TABLE II. - Macrofaunal density (Ind/m²) and biomass (g. fresh weight/m²) in the six plots (standard error in brackets).</caption><thead><tr><th rowspan="3"></th><th colspan="6">Grasslands</th><th colspan="2">Scrub</th><th colspan="4">Woods</th></tr><tr><th colspan="2">grazed</th><th colspan="2">ungrazed</th><th colspan="2">abandoned</th><th rowspan="2">Ind./ m²</th><th rowspan="2">g./m²</th><th colspan="2">maple</th><th colspan="2">pine</th></tr><tr><th>Ind./ m²</th><th>g./m²</th><th>Ind./ m²</th><th>g./m²</th><th>Ind./ m²</th><th>g./m²</th><th>Ind./ m²</th><th>g./m²</th><th>Ind./ m²</th><th>g./m²</th><th>Ind./ m²</th><th>g./m²</th></tr></thead><tbody><tr><td><strong>Anecic fauna</strong></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td><em>Lumbricidae</em></td><td>16<br>(4)</td><td>15.4<br>(4.1)</td><td>50<br>(8)</td><td>38.6<br>(7.6)</td><td>27<br>(4)</td><td>38.5<br>(6.8)</td><td>22<br>(4)</td><td>34.4<br>(9.5)</td><td>12<br>(3)</td><td>14.6<br>(5.7)</td><td>21<br>(4)</td><td>22.3<br>(4.5)</td><td></td></tr><tr><td>Anecic Formicidae</td><td>883<br>(371)</td><td>1.2<br>(0.5)</td><td>689<br>(412)</td><td>1.0<br>(0.8)</td><td>432<br>(134)</td><td>0.3<br>(0.1)</td><td>327<br>(106)</td><td>0.7<br>(0.2)</td><td>2<br>(1)</td><td>0.0<br>(0.0)</td><td>78<br>(69)</td><td>0.3<br>(0.2)</td><td></td></tr><tr><td><strong>Endogeic fauna</strong></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td><em>Lumbricidae</em></td><td>223<br>(26)</td><td>74.9<br>(11.2)</td><td>361<br>(28)</td><td>90.7<br>(12.0)</td><td>187<br>(17)</td><td>65.4<br>(8.7)</td><td>314<br>(27)</td><td>45.2<br>(4.4)</td><td>422<br>(28)</td><td>46.6<br>(3.8)</td><td>138<br>(13)</td><td>28.0<br>(3.6)</td><td></td></tr><tr><td>Coleoptera</td><td>62<br>(13)</td><td>4.0<br>(0.8)</td><td>37<br>(6)</td><td>5.9<br>(1.2)</td><td>17<br>(10)</td><td>0.7<br>(0.5)</td><td>15<br>(11)</td><td>0.1<br>(0.1)</td><td>15<br>(3)</td><td>0.4<br>(0.1)</td><td>3<br>(1)</td><td>0.0<br>(0.0)</td><td></td></tr><tr><td><strong>Epigeic fauna</strong></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td><em>Lumbricidae</em></td><td>16<br>(9)</td><td>2.6<br>(1.8)</td><td>9<br>(3)</td><td>0.9<br>(0.3)</td><td>12<br>(4)</td><td>1.0<br>(0.4)</td><td>37<br>(18)</td><td>1.9<br>(1.0)</td><td>88<br>(10)</td><td>6.7<br>(1.3)</td><td>18<br>(5)</td><td>1.0<br>(0.3)</td><td></td></tr><tr><td>Epigeic Formicidae</td><td>0<br>(0)</td><td>0.0<br>(0.0)</td><td>0<br>(0)</td><td>0.0<br>(0.0)</td><td>0<br>(0)</td><td>0.0<br>(0.0)</td><td>111<br>(41)</td><td>0.1<br>(0.0)</td><td>337<br>(164)</td><td>0.3<br>(0.1)</td><td>0<br>(0)</td><td>0.0<br>(0.0)</td><td></td></tr><tr><td>Coleoptera</td><td>16<br>(4)</td><td>0.3<br>(0.1)</td><td>19<br>(4)</td><td>0.3<br>(0.1)</td><td>6<br>(3)</td><td>0.0<br>(0.0)</td><td>6<br>(2)</td><td>0.1<br>(0.1)</td><td>15<br>(3)</td><td>0.5<br>(0.2)</td><td>18<br>(3)</td><td>0.1<br>(0.0)</td><td></td></tr><tr><td>Chilopoda</td><td>16<br>(5)</td><td>0.1<br>(0.0)</td><td>68<br>(10)</td><td>0.7<br>(0.2)</td><td>58<br>(9)</td><td>0.6<br>(0.1)</td><td>61<br>(9)</td><td>0.3<br>(0.1)</td><td>63<br>(8)</td><td>1.0<br>(0.2)</td><td>39<br>(8)</td><td>0.5<br>(0.1)</td><td></td></tr><tr><td>Diplopoda</td><td>0<br>(0)</td><td>0.0<br>(0.0)</td><td>2<br>(1)</td><td>0.0<br>(0.0)</td><td>1<br>(1)</td><td>0.2<br>(0.2)</td><td>3<br>(2)</td><td>0.0<br>(0.0)</td><td>3<br>(1)</td><td>0.0<br>(0.0)</td><td>9<br>(2)</td><td>1.4<br>(0.4)</td><td></td></tr><tr><td>Isopoda</td><td>1<br>(1)</td><td>0.0<br>(0.0)</td><td>81<br>(21)</td><td>0.8<br>(0.2)</td><td>31<br>(7)</td><td>0.3<br>(0.1)</td><td>21<br>(5)</td><td>0.2<br>(0.0)</td><td>85<br>(18)</td><td>1.6<br>(0.4)</td><td>37<br>(7)</td><td>0.7<br>(0.4)</td><td></td></tr><tr><td>Araneida</td><td>11<br>(2)</td><td>0.1<br>(0.0)</td><td>12<br>(2)</td><td>0.1<br>(0.0)</td><td>13<br>(3)</td><td>0.1<br>(0.0)</td><td>12<br>(3)</td><td>0.1<br>(0.1)</td><td>6<br>(2)</td><td>0.0<br>(0.0)</td><td>7<br>(2)</td><td>0.1<br>(0.1)</td><td></td></tr><tr><td>Gastropoda</td><td>3<br>(1)</td><td>1.0<br>(0.5)</td><td>5<br>(2)</td><td>0.7<br>(0.3)</td><td>7<br>(2)</td><td>6.7<br>(3.4)</td><td>6<br>(2)</td><td>1.1<br>(0.6)</td><td>78<br>(14)</td><td>9.5<br>(2.1)</td><td>37<br>(6)</td><td>14.8<br>(3.9)</td><td></td></tr><tr><td>Other invertebrates</td><td>12<br>(3)</td><td>0.9<br>(0.3)</td><td>32<br>(7)</td><td>0.6<br>(0.2)</td><td>48<br>(29)</td><td>0.4<br>(0.2)</td><td>33<br>(10)</td><td>0.7<br>(0.2)</td><td>32<br>(10)</td><td>0.6<br>(0.1)</td><td>16<br>(8)</td><td>0.9<br>(0.5)</td><td></td></tr></tbody><tfoot><tr><td><strong>Total</strong></td><td><strong>1259<br>(375)</strong></td><td><strong>100.5<br>(14.0)</strong></td><td><strong>1365<br>(408)</strong></td><td><strong>140.3<br>(17.2)</strong></td><td><strong>839<br>(150)</strong></td><td><strong>114.1<br>(12.5)</strong></td><td><strong>968<br>(154)</strong></td><td><strong>84.9<br>(11.8)</strong></td><td><strong>1159<br>(178)</strong></td><td><strong>81.7<br>(7.7)</strong></td><td><strong>421<br>(24)</strong></td><td><strong>70.2<br>(8.2)</strong></td><td></td></tr></tfoot></table>

nisation by woody plants. This is marked by the appearance of epigeic groups such as epigeic earthworms (25 to 28 % of total biomass for the woody plots).

In the grazed plot, the quality of the litter brought to the soil allowed the maintenance of a macrofaunal population with a medium biomass and high density (table II). Contributions to the density of anecic ant populations (70%) is particularly important in this plot. The highest biomass and density measured in this study were observed in the ungrazed grassland while a lower biomass and density were observed
<table><caption>TABLE III. - Factorial coordinates of variables and taxonomic groups on the first two factors extracted respectively from the PCA and CA.</caption><thead><tr><th rowspan="2">Variables used<br>for the PCA</th><th colspan="2">Factorial coordinates</th><th rowspan="2">Taxonomic groups used<br>for the CA</th><th colspan="2">Factorial coordinates</th></tr><tr><th>Factor I<br>75.79%</th><th>Factor II<br>15.91%</th><th>Factor I<br>46.66%</th><th>Factor II<br>34.03%</th></tr></thead><tbody><tr><td colspan="6" style="text-align: center; font-weight: bold;">Density</td></tr><tr><td>Herbaceous biomass</td><td><strong>19.85</strong></td><td><strong>- 14.74</strong></td><td>Anenic earthworms</td><td>- 0.32</td><td>0.27</td></tr><tr><td>Moss biomass</td><td>- 7.51</td><td>- 6.06</td><td>Epigeic earthworms</td><td>0.35</td><td>- 0.06</td></tr><tr><td>Root biomass</td><td>6.46</td><td><strong>- 13.89</strong></td><td>Endogeic earthworms</td><td>- 0.15</td><td>- 0.05</td></tr><tr><td>Litter biomass</td><td>- 8.3</td><td>- 2.07</td><td>Epigeic Formicidae</td><td><strong>1.25</strong></td><td>- 0.76</td></tr><tr><td>Tree and scrub cover</td><td><strong>- 45.57</strong></td><td>- 5.55</td><td>Epigeic Coleoptera</td><td>- 0.22</td><td>0.35</td></tr><tr><td>Litter C:N ratio</td><td>- 3.42</td><td><strong>- 9.36</strong></td><td>Endogeic Coleoptera</td><td><strong>- 0.75</strong></td><td>- 0.42</td></tr><tr><td>Clay content</td><td>- 1.02</td><td>3.04</td><td>Chilopoda</td><td>0.07</td><td>0.24</td></tr><tr><td>Silt content</td><td>3.21</td><td>- 0.47</td><td>Diplopoda</td><td>0.35</td><td><strong>1.22</strong></td></tr><tr><td>Sand content</td><td>- 2.19</td><td>- 2.57</td><td>Isopoda</td><td>0.07</td><td>0.38</td></tr><tr><td>Organic carbon</td><td>- 7.32</td><td>- 2.33</td><td>Gastropoda</td><td>0.64</td><td>0.72</td></tr><tr><td>Organic matter</td><td><strong>- 12.58</strong></td><td>- 4.03</td><td colspan="3" style="text-align: center; font-weight: bold;">Biomass</td></tr><tr><td>Cation Exchange Capacity</td><td>- 5.89</td><td>- 0.95</td><td>Anenic earthworms</td><td>0.01</td><td>0.11</td></tr><tr><td></td><td></td><td></td><td>Epigeic earthworms</td><td><strong>0.73</strong></td><td>- 0.44</td></tr><tr><td></td><td></td><td></td><td>Endogeic earthworms</td><td>- 0.1</td><td>- 0.13</td></tr><tr><td></td><td></td><td></td><td>Epigeic Formicidae</td><td><strong>1.43</strong></td><td><strong>- 0.77</strong></td></tr><tr><td></td><td></td><td></td><td>Epigeic Coleoptera</td><td>0.45</td><td>- 0.39</td></tr><tr><td></td><td></td><td></td><td>Endogeic Coleoptera</td><td><strong>- 0.84</strong></td><td>- 0.4</td></tr><tr><td></td><td></td><td></td><td>Chilopoda</td><td>0.51</td><td>0.09</td></tr><tr><td></td><td></td><td></td><td>Diplopoda</td><td>0.35</td><td><strong>1.86</strong></td></tr><tr><td></td><td></td><td></td><td>Isopoda</td><td><strong>0.82</strong></td><td>0.09</td></tr><tr><td></td><td></td><td></td><td>Gastropoda</td><td>0.6</td><td><strong>0.81</strong></td></tr></tbody></table>

in the abandoned grassland. In the woody plots (scrub and maple wood) the epigeic fauna was mostly composed of small arthropods. This may explain the relatively low biomass and the high density respectively observed in scrub and maple wood. The lowest density and biomass were recorded in the pine wood.

Species diversity (Shannon index) and evenness showed no significant differences between each plot (fig. 4). If an increase in diversity and evenness could be observed from the grazed grassland to the abandoned grassland, no significant increase in evenness, species richness and species diversity could be observed from the scrub to maple wood plots. The highest value of evenness was calculated in the pine wood plot.

## DISCUSSION

Macrofaunal density and biomass in the different plots are influenced by environmental factors which determine the composition and structure of their communities along secondary plant successions of chalk grasslands.

In the grazed plot, standing biomass of the herbaceous layer decreased under the effect of grazing (HUTCHINSON & KING, 1980). The low value calculated for the diversity and evenness of these plots could be linked with the spatial and temporal heterogeneity of the litter which is in the form of animal dung and faeces (HIRSCHBERGER &
<figure><img src="image_5.png" /><figcaption>FIG. 3. - CA carried out on soil macrofaunal taxonomic groups which characterize six plots of a potential secondary succession in chalk grasslands (B) biomass, (D) density. See text for the designation of groups (GG: grazed grassland; UG: ungrazed grassland; AG: abandoned grassland; S: scrub; MW: maple wood; PW: pine wood).</figcaption></figure>

BAUER, 1994). Abandonment of grazing leads to a rapid development of the herbaceous vegetation and a subsequent accumulation of a litter layer which protects the soil from drought and extreme temperatures (SCHEU, 1990) giving the characteristic local climate of chalk grasslands (RORISON et al., 1986). Colonisation by tussock grasses (Brachypodium pinnatum) has created a mosaic of different microhabitats (i.e. patches of short and tall vegetation). Spatial variability of the plant cover was assumed to increase the diversity of other functional groups and could be responsible for the high taxonomic richness observed in the ungrazed plot (BABEL et al., 1992). The decrease in taxonomic richness in the abandoned plot may have resulted from the domination of a dense herbaceous vegetation with a high C:N litter layer (SCHEU, 1992; BOBBINK & WILLEMS, 1993) and a subsequent reduction in the diversity of microhabitats.

Colonisation of the grasslands by woody deciduous species significantly modified composition and structure of macrofaunal communities. Woody environments present characteristics that favour the development of epigeic macrofauna i.e., low light intensity, buffered micro-climatic conditions and a thick litter layer providing new habitats and food supply with a low C:N ratio. The very low nutrient value of the litter in the pine wood in the form of non palatable pine needles reduced taxonomic richness, discouraged earthworms and favoured the development of other epigeic groups especially Gastropoda (Pomatiidae) and Diplopoda (Glomeridae, Iulidae). The range of fauna found in the pine woodland is different from that to be expected in mature pine forest, e.g. helicid, pomatiid snails and the earthworm Apporectodea longa is not found in soils of low pH which are characteristic of late successional
<figure><img src="image_6.png" /></figure>

<figure><img src="image_7.png" /></figure>

<figure><img src="image_8.png" /><figcaption>FIG. 4. - Soil macrofaunal richness (R), diversity (H) and evenness (H'), calculated from macrofaunal population densities of the six plots (table II). The error bars correspond to the standard errors. (GG: grazed grassland; UG: ungrazed grassland; AG: abandoned grassland; S: scrub; MW: maple wood; PW: pine wood).</figcaption></figure>

stages of coniferous woodland. The presence of such fauna in our pine wood plot reflects the fact that successional changes still have a long way to go in the subterranean fauna. However, spatial and temporal homogeneity in the litter enhanced diversity which here reached the highest value recorded in the study.

Some taxonomic units were confined to one or two plots *i.e.* the epigeic earthworm *Dendrobaena mammalis* in the pine wood, Allelulidae and Cantharidae (Coleoptera) in the ungrazed plot and *Seegestriidae* (Araneida) in the abandoned grassland. Some of them, like the spider *Atypus affinis*, which were found in the scrub plot, could be considered of nature conservation interest as their habitat are being strictly limited to chalk grasslands in north western Europe (JONES, 1990). The exclusive presence of the calcicolous earthworm *Allolobophora muldali* in scrub and maple wood is also worth mentioning due to its autecological significance as a strictly neutrophilous species (BOUCHÉ, 1972).
The structure of soil macrofaunal communities depends more on the quality of food supply than on processes of predation or competition (WATKIN & WHEELER, 1966; PRICE, 1984; LAVELLE, 1985). Very many soil animals are generalist feeders compared with above-ground fauna. The diets of saprovores can necessarily include a wide variety of substrates and provide less opportunity for specialisation than occurs in herbivores and predators (CURRY, 1994). Soil macrofaunal species are influenced by the form and quality of litter falling on the soil, which is at first dependent on the nature and structure of plant communities (ANDERSON, 1977). More than a source of food, this litter constitutes a habitat for many soil macrofaunal species. In these conditions, functional groups (i.e. anecic, epigeic, endogeic) or even specific groups (taxonomic) cannot survive when major changes occur in food supply and habitat conditions along the succession (i.e. change in litter quality between grazed and abandoned plots, appearance of a thin moss layer under woody plots, etc.). As a consequence, some functional units or some specific taxonomic units can only be present under one stage of the secondary succession for plants as for invertebrates (DUFFEY *et al.*, 1974). Similar results have been obtained by BARA and VANDERHEYDEN (1985) for the distribution of vagile arthropod communities along a secondary succession series on a chalk grassland in Belgium.

Conservation management of chalk grasslands which was almost designed for plant and above-ground insect communities must also take into account the soil macrofauna of these ecosystems. Rotational management systems implemented to maintain species-rich plant communities (WELLS, 1980), invertebrate communities (MORRIS, 1971) or snails (RUESINK, 1995) could also be suggested for the conservation of species-rich soil macrofaunal communities. In fact, chalk grassland sites and their potential secondary successions can be considered as hotspots of biodiversity (PRENDERGAST *et al.*, 1993) and conservation management systems must take into account their global biological diversity. Soil macrofaunal communities must also be considered as functional groups to understand their key role in soil and vegetation processes (LAVELLE *et al.*, 1994).

## ACKNOWLEDGEMENTS

We are grateful to the Regional Natural Conservatory of Upper-Normandy and the Axa-Insurrances society for permission to work in the natural reserve of Saint-Adrien. This study has been partly supported by the France Fund (Salavin-Fournier Price) and the French Ministry of Environment (DGAD-SRAE n° 94220). We thank Dr. Terry WELLS (Institute of Terrestrial Ecology), Jo WILLEMS (University of Utrecht) and Patrick LAVELLE (ORSTOM) and two anonymous referees for providing useful comments on an earlier version of the paper

APPENDIX. - List of the taxa collected in the soils of the six plots during the sampling period (GG: grazed grassland; UG: ungrazed grassland; AG: abandoned grassland; S: scrub; MW: maple wood; PW: pine wood).

<table><thead><tr><th>Taxa</th><th>Sites</th><th>Taxa</th><th>Sites</th></tr></thead><tbody><tr><td><strong>Lumbricidae</strong></td><td></td><td><strong>Diplopoda</strong></td><td></td></tr><tr><td><strong>Endogeics</strong></td><td></td><td>Polyxenidae</td><td>- - - S MW -</td></tr><tr><td><em>Allolobophora chlorotica</em><br>(Savigny, 1926)</td><td>GG UG AG S MW PW</td><td>Glomeridae</td><td>- UG AG - - PW</td></tr><tr><td><em>Allolobophora rosea</em><br>(Savigny, 1926)</td><td>GG - AG S MW PW</td><td>Iulidae</td><td>- UG - S MW PW</td></tr><tr><td></td><td></td><td><strong>Araneida</strong></td><td></td></tr></tbody></table>
APPENDIX. - List of the taxa collected in the soils of the six plots during the sampling period (GG: grazed grassland; UG: ungrazed grassland; AG: abandoned grassland; S: scrub; MW: maple wood; PW: pine wood). (continued)

<table><thead><tr><th>Taxa</th><th>Sites</th><th>Taxa</th><th>Sites</th></tr></thead><tbody><tr><td><strong>Allolobophora icterica</strong><br>(Savigny, 1926)</td><td>- UG AG S</td><td>Theridiidae</td><td>- UG - MW -</td></tr><tr><td><strong>Allolobophora muldali</strong><br>(Omodeo, 1956)</td><td>- - S MW -</td><td>Clubionidae</td><td>- UG - MW -</td></tr><tr><td><strong>Apporectodea caliginosus</strong><br>(Savigny, 1926)</td><td>GG UG AG S</td><td>Zodariidae</td><td>GG UG AG S MW PW</td></tr><tr><td><strong>Octalasion cyaneum</strong><br>(Savigny, 1926)</td><td>GG - AG - MW PW</td><td>Zoridae</td><td>GG UG - MW -</td></tr><tr><td><strong>Anecics</strong><br>Lumbricus terrestris<br>(Linne, 1758)</td><td>GG UG AG S MW PW</td><td>Thomisidae</td><td>GG UG AG S MW -</td></tr><tr><td><strong>Lumbricus festivus</strong><br>(Savigny, 1926)</td><td>- UG - S MW PW</td><td>Argiopidae</td><td>- - MW -</td></tr><tr><td><strong>Apporectodea longa</strong><br>(Savigny, 1926)</td><td>GG UG AG S MW PW</td><td>Opilionidae</td><td>GG UG AG S MW -</td></tr><tr><td><strong>Epigeics</strong><br>Lumbricus castaneus<br>(Savigny, 1926)</td><td>GG UG AG S MW PW</td><td>Gnaphosidae</td><td>GG - - MW -</td></tr><tr><td><strong>Dendrobaena mammalis</strong><br>(Savigny, 1926)</td><td>- - - - PW</td><td>Philodromidae</td><td>- UG - PW</td></tr><tr><td><strong>Hymenoptera</strong><br>Formicidae</td><td>GG UG AG S MW PW</td><td>Lycosidae</td><td>GG UG AG S PW</td></tr><tr><td>Myrmosidae</td><td>GG - AG - -</td><td>Atypidae</td><td>- - S -</td></tr><tr><td>Braconidae</td><td>- UG - -</td><td>Liocranidae</td><td>GG - AG S -</td></tr><tr><td>Apidae</td><td>GG UG AG - -</td><td>Segestriidae</td><td>- - AG - -</td></tr><tr><td>Ichneumonidae</td><td>- - AG - MW -</td><td>Folcidae</td><td>- - S MW -</td></tr><tr><td>Symphita</td><td>GG - - - -</td><td><strong>Isopoda</strong><br>Oniscidae</td><td>GG UG AG S MW PW</td></tr><tr><td><strong>Coleoptera</strong><br>Curculionidae</td><td>GG UG AG S MW -</td><td><strong>Lepidoptera</strong><br>Notodontidae</td><td>- - AG - PW</td></tr><tr><td>Elateridae</td><td>- UG - MW -</td><td>Noctuidae</td><td>GG - AG S MW -</td></tr><tr><td>Melolonthidae</td><td>GG UG AG S -</td><td>Lasiocampidae</td><td>- - - PW</td></tr><tr><td>Scarabaeidae</td><td>GG UG AG S -</td><td>Geometridae</td><td>- UG - PW</td></tr><tr><td>Hysteridae</td><td>GG - - - -</td><td>Tortricidae</td><td>- - S -</td></tr><tr><td>Mordellidae</td><td>- UG - - PW</td><td>Satyridae</td><td>GG - AG S -</td></tr><tr><td>Dermestidae</td><td>GG - AG S MW PW</td><td>Pieridae</td><td>GG UG AG S -</td></tr><tr><td>Nitidulidae</td><td>- - MW -</td><td><strong>Gastropoda</strong><br>Limacidae</td><td>- UG AG S MW -</td></tr><tr><td>Chrysomelidae</td><td>GG UG AG - MW PW</td><td>Arionidae</td><td>- UG AG S MW PW</td></tr><tr><td>Carabidae</td><td>GG UG AG S MW -</td><td>Helicidae</td><td>GG UG AG S MW PW</td></tr><tr><td>Anthicidae</td><td>- - MW PW</td><td>Clausiliidae</td><td>- - MW -</td></tr><tr><td>Alleculidae</td><td>- UG - -</td><td>Zonitidae</td><td>- UG - MW -</td></tr><tr><td>Tenebrionidae</td><td>GG - - - -</td><td>Pomatiidae</td><td>- - AG S MW PW</td></tr><tr><td></td><td></td><td><strong>Dermaptera</strong></td><td>- UG - S MW -</td></tr><tr><td></td><td></td><td><strong>Heteroptera</strong><br>Reduvidae</td><td>- UG - MW -</td></tr><tr><td></td><td></td><td>Lygeidae</td><td>- - AG - -</td></tr><tr><td></td><td></td><td>Capsidae</td><td>GG UG - S - PW</td></tr><tr><td></td><td></td><td><strong>Hemiptera</strong><br>Cicadidae</td><td>GG - AG - MW -</td></tr></tbody></table>
APPENDIX. - List of the taxa collected in the soils of the six plots during the sampling period (GG: grazed grassland; UG: ungrazed grassland; AG: abandoned grassland; S: scrub; MW: maple wood; PW: pine wood). (continued)

<table><thead><tr><th>Taxa</th><th>Sites</th><th>Taxa</th><th>Sites</th></tr></thead><tbody><tr><td>Cerambycidae</td><td></td><td>Nevroptera</td><td></td></tr><tr><td>Staphylinidae</td><td>GG UG AG S MW</td><td>Cercopidae</td><td>- MW</td></tr><tr><td>Cantharidae</td><td>- UG - MW PW</td><td>Chrysopidae</td><td>- UG AG MW</td></tr><tr><td>Diptera</td><td>GG UG AG S MW PW</td><td>Diplura</td><td>- MW</td></tr><tr><td>Chilopoda</td><td></td><td>Orthoptera</td><td></td></tr><tr><td>Scolopendridae</td><td>GG UG AG S MW</td><td>Grillidae</td><td>- PW</td></tr><tr><td>Lithobiidae</td><td>GG UG AG S MW PW</td><td>Blattidae</td><td>- UG AG PW</td></tr><tr><td>Geophilidae</td><td>GG UG AG S MW PW</td><td></td><td></td></tr></tbody></table>

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