The Effect of Removing Shrub Cover on Annual Plants and Small Mammals

Biological Conservation 94 (2000) 235±242 www.elsevier.com/locate/biocon

The eect of removing shrub cover on annual plants and small mammals in a coastal sand dune ecosystem

Pua Kutiela,*, Yakim Peledb, Eli Geenb aDepartment of Geography, Bar Ilan University, Ramat Gan 52900, Israel bInstitute for Nature Conservation Research, Tel Aviv University, Ramat Aviv, Tel Aviv 69978, Israel

Received 2 July 1999; received in revised form 14 October 1999; accepted 20 October 1999

Abstract Populations of sand-living organisms in Israel have decreased due to the stabilization of the coastal dunes and their massive cover by a few shrub species. This study examined the impact of the removal of the above-ground shrub growth on sand-living (psam- mophile) annual plants and small mammals. After 3 years, the annual plant composition in the cleared plots was similar to the uncleared plots. However, several species speci®c to open sandy habitats were more abundant after clearing the scrub. This was expressed in the higher Shannon±Wiener diversity index obtained for the cleared plots. Likewise, the small rodents Mus musculus, Rattus rattus, and the shrew Crocidura russula avoided entering the cleared plots, while Gerbillus andersoni allenbyi (an endemic sand-living gerbil) and the Tristram's jird Meriones tristrami were well established there. The deliberate removal of dense shrub cover is proposed as part of the management of Mediterranean coastal dunes, with the intention of preserving the whole shifting dune ecosystem by cheap means and with lower level of human intervention. # 2000 Elsevier Science Ltd. All rights reserved. Keywords: Annual plants; Conservation; Management; Mediterranean; Small mammals

1. Introduction The importance of the coastal strip as a centre of ¯oral and faunal speciation is also manifested in the psam- The Israeli coastal plain is 190 km long and between mophile gerbils and jirds. The only mammal species 1 km wide in the north and 7 km in the south. It includes endemic to Israel, the Buxton's jird (Meriones sacra- sand dunes in various degrees of stabilization, sand- menti), and an endemic subspecies of Anderson's gerbil stone ridges and several types of sandy soils. Most of (Gerbillus andersoni allenbyi subsequently referred to as the coastal plain is extensively populated, developed and Gerbillus allenbyi) are found in this region (Zahavi and polluted. According to a recent survey, only about 17% Wahrman, 1957; Yom Tov and Mendelssohn, 1988). of the Israeli coastal dunes are still of good or reason- Some of the shifting coastal dunes, which are con- able ecological value, while <5% of this area has been sidered ecologically valuable, have been covered during designated as protected open spaces (data provided by the last 50 years by shrubs and dwarf-shrubs. Aerial the Nature Reserves and National Parks Authority). photographs taken in 1944 show that these dunes were In the past, the coastal dunes of Israel oered a rich once active, long, narrow, ridge-like (seif dunes) in variety of vegetation associations, with a high plant shape, with sparse vegetative covering <5% of the area. species richness that comprised many endemic species Since then the dunes have lost their longitudinal shape (Naveh and Kutiel, 1990). Today, 31 endemic plant and have now become crescent-like, with some 80% species (most of them annuals) can be found in the cover of woody vegetation, resulting in their stabiliza- sandy habitats of the coastal plain. This constitutes tion (Kutiel and Sharon, 1996; Barzily et al., 1998). 20% of all endemic species in Israel, and comprises the Some researchers suggest that these changes occurred as highest rate of endemism in one habitat (Shmida, 1982). a result of global and local climatic changes that caused a decline in sand movement with the consequent increase in shrub cover (Netser, 1994). Others, however, * Corresponding author. Tel.: +972-3-531-8773; fax: +972-3- 5344430. claim that the reason may be found in changes in land E-mail address: [email protected] (P. Kutiel). use policies from agriculture and pasturage to nature

0006-3207/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved. PII: S0006-3207(99)00172-X 236 P. Kutiel et al. / Biological Conservation 94 (2000) 235±242 conservation. Until recently, the policy of the Israeli occurred in the dunes during the last 50 years (Kutiel Nature Reserves Authority has been to totally prohibit and Sharon, 1996; Kutiel et al., 1997; Peled, 1997). pasturage or any human intervention in the areas under This study attempted to examine the impact of the its control. This, according to the latter researchers, has removal of the above-ground growth of woody vegeta- led to the dominance of perennial vegetation along the tion cover on the composition of annual plants and coastal plain and the stabilization of the dunes (Barzily small mammals, their richness (number of species) and et al., 1998). It is also possible that the simultaneous diversity. Our hypothesis was that psammophilic species eects of both factors caused the dense cover of woody (such as the endemic rodent G. allenbyi and the annual vegetation. Whatever the reason, it is clear that the plant species Senecio joppensis) would be relatively more dunes are no longer active. The ecological signi®cance abundant in the cleared plots while a more even dis- of this fact is expressed by changes in the landscape tribution would be found in the control (uncleared) features and in the ¯ora and fauna composition of the plots. ecosystems that are characteristic of shifting and semi- stabilized coastal dunes (Kutiel and Sharon, 1996; Kutiel et al., 1997; Peled, 1997). These, now stable areas 2. Study site require eective management for the conservation of this ecosystem. The research concentrated on the semi-stabilized In 1995, a management experiment was begun in the dunes in the area of the Nahal Alexander National Nahal Alexander National Park to preserve and encou- Park. The park is bordered on the west by the settle- rage the growth of psammophilic annual plant and ani- ment of Michmoret, on the south and southeast by the mal populations. Some of these organisms have been settlements of Ho®t and Geulei Teiman, in the east by designated by the IUCN as rare or endangered species. the industrial area of Emeq Hefer, and in the north by The current relative contribution (cover and number of the park's coastal woodland of carob (Ceratonia siliqua) individuals) of these plants and animals is small in this and lentisc (Pistacia lentiscus; Fig. 1). The dominant area, presumably because of the changes that have plant association of the dunes is Artemisia monosperma

Fig. 1. Research location (1, 2, and 3 are uncleared plots, 10,20 and 30 are cleared plots). P. Kutiel et al. / Biological Conservation 94 (2000) 235±242 237 and Retama raetam, with >80% cover (Kutiel et al., consecutive nights. Traps were placed simultaneously 1997; Peled, 1997; Kutiel, 1998a). The climate is Medi- for each set of plots on the same nights in order to terranean with an average annual precipitation between minimize variations due to change in weather or moon 500 and 600 mm. condition. Traps were set at dusk and examined the following morning. During the day the traps were closed. In the winter months, traps were covered with 3. Methods small plastic bags to keep the rain out and partly ®lled with cotton wool to improve insulation. Trapped ani- In late summer (September) of 1995 all the above- mals were categorized by species, toe clipped for indivi- ground woody vegetation was removed from three dual identi®cation, and released at the capture site. plots, 50Â50 m each, separated from each other by a Species diversity was calculated based on the Simpson distance of >200 m. Because of the status and small size index (1949) according to the following formula, of the study site, the Nature Reserves and National Parks Authority limited the number of cleared plots. Xs C p2 The vegetation was removed manually (with the aid of i i1 saws and pruning hooks) in order to minimize damage to the soil. The uncleared (control) plots were located 50±200 m away from each of the cleared plots (Fig. 1), where s is the number of species and pi is the relative and chosen to be similar as possible in respect to plant contribution of the species to the total number of indi- cover and composition, so that the only dierence viduals. This index is aected by the dominant species among them was expected to result from the clearing. (Krebs, 1989). Vegetation observations (plant composition and total and relative cover) were carried out in a 1000 m2 (20Â50 m) area in each of the six plots at the peak of the ¯ow- 4. Results ering season (the beginning of March), 3 years after the removal of the woody plants. The total ground cover 4.1. Vegetation and relative cover for each species was estimated visually as a percentage. Identi®cation of plant species was The vegetation cover of the cleared plots was 65% on based on Zohary and Feinbrun-Dothan (1966±1985). average as opposed to 81% for the control plots. The Charting of the plots was done according to the system former comprised 57% annual plants and only 8% per- designed by Whittaker (1975), and described in studies ennials, with the opposite being found for the control by Naveh and Whittaker (1979) and Shmida (1984). The plots (75% cover by perennials and 6% by annual system is based on documenting the relative cover of plants; Table 1). However, the total and the average plant species in small squares; subsequently enlarging number of species found in control plots were higher the observed area until the dimensions of the entire plot than in the cleared plots. Conversely, the average spe- is included. cies diversity found in the control plots was low (1.18) Species diversity was calculated based on the Shan- compared to that of the cleared plots (1.94; Table 1). non±Wiener Index according to the following formula, Plant composition for both types of plots did not signi®cantly dier especially in regard to the annual plants XS 0 H pi ln pi i1 Table 1 Characteristics of the vegetation in control and cleared plots from which woody plants had been removed three years previouslya,b where s is the number of species and pi is the relative contribution of the species to the total cover. This index Characters Control Cleared ZP takes into account the number of species and the rela- Total number of species 47 42 tive contribution of each species to the overall plant Average number of species 31.36.7 27.35.7 1.09 0.27 cover (Kutiel, 1998b). per plot Trapping of small mammals was done in two pairs of Number of psammophilic 22 18 plots (1 and 10, 2 and 20). Each plot was 50Â50 m. species Number of endemic species 2 2 Trapping began in December 1995 and continued to Species diversity H0 Index 1.20.8 1.90.4 1.53 0.13 September 1996, a total of 5184 trap/nights. Thirty-six Total cover (%) 80.718.9 65.08.7 1.16 0.25 Sherman collapsible traps (23Â8Â9 cm), baited with Annual plant cover (%) 6.32.1 57.012.5 1.96 0.049 bread and peanut butter, were set in the central 50Â50 m Perennial plant cover (%) 74.317.2 8.06.1 1.96 0.049 area in the centre of each of these plots on a 10-m a n=3; S.D. grid. Each month, every plot was sampled for four b Mann±Whitney U test was used in all comparisons. 238 P. Kutiel et al. / Biological Conservation 94 (2000) 235±242 that characterize sandy habitats (Table 2). In all, 57 Table 2 species were found on both types of plots, of which 32 The average cover % of annual (A) and perennial (P) species in the species were common to both types of plots, 10 species control (UC) and cleared (C) plotsa were not found in the control plots, and 15 species were Species Status UC C absent from the cleared plots. The plants not present in the cleared plots were perennials (seven species), like the Achyranthes aspera A<1 climbing Rubia tenuifolia and Phagnalon rupestre, which Ainsworthia trachycarpa A<1 Alopecurus utriculatus A<1<1 did not regenerate after removal of the vegetation, and Anagallis arvensis A<1<1 some annuals typical of the Mediterranean batha Arenaria leptoclados A,S <1 <1 (dwarf-shrub communities), such as Ainsworthia tra- Artenmisia monosperma P,S 25 12 chycarpa and Alopecurus utriculatus. All the species that Asparagus stipularis P<1 were not found in the control plots but did appear in the Astragalus boeticus A<1 cleared plots were annuals, of which three are de®ned as Avena barbata A<1 ruderal species, namely Euphorbia peplus, Chenopodium Brassica tournefortii A,S <1 6 Bromus rigidus A<11 murale and Lavatera cretica (Table 2). In spite of the Chenopodium murale A<1 similarities in species composition between the cleared Corynephorus divaricatus A,S <1 3 and control plots, essential dierences were found in the Crepis aculeata A,S < 11 evenness among species, as expressed in the species Crucianella macrostachya A,S <1 1 diversity. Cutandia philistaea A,S <1 6 Several annual species speci®c to sandy habitats were Cyperus capitatus P,S <1 more prevalent in the cleared plots than in the control Daucus litoralis A,S 1 10 areas in terms of cover: Rumex pictus, and Daucus gla- Ephedra spp. P<1<1 Ephedra camplyopoda P<11 ber were 30 times more abundant, Crepis aculeata and Euphorbia peplus A<1 Brassica toumefortii 10 times more abundant, Cutandia Euphorbia terracina P,S 1 philistaea six times, and Corynephorus divaricatus twice Geranium robertianum A9<1 as abundant as in the control plots (Table 2). The cover Heterotheca subaxillaris P,S <1 3 of the two perennial species, Artemisia monosperma and Hormuzakia aggregata P,S 1 1 Retama raetan, which were abundant in the cleared I¯oga spicata A,S <1 1 plots before the removal of vegetation (53 and 25%, Inula viscosa P<1 respectively), approached 5 and 12%, respectively Lagurus ovatus A,S <1 <1 Lavatera cretica A<1 3 years after the treatment. The annual species that Leopolidia bicolor P,S <1 was most common in the control plots was Geranium Lolium rigidum A,S <1 robertianum. Lotus peregrinus A1 Lycium schweinfurthii P,S <1 4.2. Small mammals Maresia pulchella A,S <1 <1 Ononis hirta A<1 The gerbil (Gerbillus allenbyi) was the most abundant Ononis serrata A,S <1 small mammal in the study area, comprising nearly 60% Papaver subpiriforme A<1 Paronychia argentea A,S 1 <1 of trapped individuals, followed by the house mouse Phagnalon rupestre P1<1 Mus musculus (30%; Table 3). The three other species, Pistacia lentiscus P1<1 the Tristram's jird (Meriones tristrami), the brown rat Polycarpon succulentum A,S <1 1 (Rattus rattus) and white-toothed shrew (Crocidura rus- Polygonum palaestinum P,S,E <1 <1 sula) comprised roughly one-tenth of the total captures. Prasium majus P2<1 Control and cleared plots revealed very dierent species Retama raetam P,S,E 53 5 distributions (Table 3). M. musculus, M. tristrami, R. Rubia tenuifolia P14 rattus and C. russula were rarely captured in the cleared Rumex pictus A,S <1 34 Sececio vernalis A<15 plots, and then only in peripheral traps (Table 3). Solanium luteum A<1 However, G. allenbyi was caught throughout all the Sonchus oleraceus A1<1 plots and produced 86% of captures in the cleared plots. Strellaria pallida A<1<1 In the control plots, 47% of captures were G. allenbyi Trisetaria linearis A,S 1 and 41% were M. musculus, the other three species Urospermum picroides A<1<1 combined providing 12% of captured individuals. Valantina hispida A<1<1 Values of Simpson's index of dominance were sig- Verbascum sinuatum P<1 ni®cantly higher for the cleared plots (2.2770.593 Vicia sativa A<1 Vicia villosa A<1<1 (S.D.) than in controls (1.2630.517) (Mann±Whitney test: Z=4.34, P<0.001). The occurrence of small a S, species typical of sandy habitats; E, endemic. P. Kutiel et al. / Biological Conservation 94 (2000) 235±242 239

Table 3 in the previously undisturbed habitat (Armesto and Number of individuals captured in the control and cleared plots dur- Pickett, 1985; Kutiel, 1993, 1997; Kobayshi et al., 1997). ing the ®rst year after the shrub removal The rate of change is a function of various factors, such Control Cleared as the type of disturbance, its intensity and frequency, its timing, and the original conditions of the habitat Species Number Percentage Number Percentage (Peet et al., 1983; Armesto aned Pickett, 1985; Carson Gerbillus allenbyi 124 47.1 107 85.6 and Pickett, 1990; Chaneton and Facelli, 1991; Kutiel, Meriones tristrami 3 1.1 8 6.4 1993, 1997; Chambers and Samways, 1998). The accep- Mus musculus 109 41.4 6 4.8 ted theory is that species richness and diversity after a Rattus rattus 12 4.6 1 0.8 Crocidura russula 15 5.7 3 2.4 disturbance will be maximized when the disturbance occurs at a medium intensity and low frequency (for Total 263 100.0 125 100.0 example: van der Maarel, 1971; Grime, 1979; Huston, 1979), or when the availability of the resources is at a medium rate (Tilman, 1982). mammal species in control and cleared plots was sig- Vegetation in the Mediterranean Basin has developed ni®cantly dierent ( 2 61:7, df=3, P<0.001; data for over thousands of years according to natural processes M. tristrami and R. rattus were combined to avoid such as climate change and human intervention (e.g. expected values <5). However, partition of the degrees woodcutting, ®re and pasturage; Naveh, 1985; Shmida, of freedom in the 2 test showed the dierence to be 1985). Under these conditions the trees and shrubs are only in the numbers of M. musculus (Table 4; Siegel not capable of covering the area with a dense and con- and Castellan, 1989). No signi®cant dierences were tinuous cover, thus allowing herbaceous plants, and observed for the psammophilic species G. allenbyi and especially annuals, to exploit the patches of open space. M. tristrami. These patches oered resources, such as light and high temperatures, which the herbaceous plants could not have received under the cover of tall plants. Researchers 5. Discussion like Shmida (1985) and Naveh (1985) see these combined processes as contributing to the formation of the Removal of the vegetation, whether deliberate or landscapes of the Mediterranean Basin and to the rich- unintentional (®res, pasturage and trampling), causes ness and diversity of species, which are among the changes in the physical environment, such as increased highest in the world at the level of community diversity daylight intensity, temperature and evaporation rate at (a diversity). Thus, the prevention of such processes, ground level. This, in turn, leads to changes in vegeta- including human interference, may lead to cover of tion composition, species richness and species diversity areas by high and dense woody plants, driving the her- (Liddle and Moore, 1974; Armesto and Pickett, 1985; baceous plants to the periphery. Under such conditions, Kutiel, 1993, 1997; Vestergaard, 1994; Kooijman and the richness and diversity of plant species will be lower van der Meulen, 1996; Kobayashi et al., 1997; Schlapfer than those existing in disturbed areas (Abul-Fatih and et al., 1998). The removal of dominant perennial vege- Bazaz, 1979; Armesto and Pickett, 1985; Shmida, 1985; tation in a given area is usually accompanied by the Carson and Pickett, 1990; Chaneton and Facelli, 1991; dominance of herbaceous plants and in an increase in Kutiel, 1993, 1997; Kobayashi et al., 1997). species richness and diversity (Vestergaard, 1994; Col- The annuals in the Retama raetam. Artemisia mono- lins et al., 1998; Schlapfer et al., 1998). These changes sperma community are scattered over the area in small are due to the increase in resource availability (such as patches, close to the shrubs or beneath or among them light and water) which bene®ts the less common species according to their adaptation to the existing conditions of these micro-habitats (Tielborger and Kadmon, 1995). The relative contribution of each of the annual species Table 4 in these areas was <1%, except for Geranium robertia- Chi-square test for describing of distribution of ®ve species of small num, whose cover reached 9%. In Mediterranean area mammals between cleared and control plotsa this species generally grows in shrublands, and in sandy Speciesb 2 df P areas is found only under the canopy of perennial Ga. Mt 3.35 1 N.S. plants. In spite of the relatively high species richness Ga, Mt, Mm 63.88 1 <0.001 found in the undisturbed plots, the Shannon±Wiener Ga, Mt, Mm, Rr 3.26 1 N.S. diversity was low, since three woody species (R. raetam, Ga, Mt, Mm, Cr 1.56 1 N.S. A. monosperma and Rubia tenuifolia) dominated the a Partition of the degrees of freedom are presented. vegetation cover and the remaining species, most of b Ga, Gerbillus allenbyi, Mt, Meriones tristrami, Mm, Mus muscu- which are annuals, had cover of <1%. The removal of lus, Rr, Rattus rattus, Cr, Crocidura russula. the perennial vegetation increased the availability of 240 P. Kutiel et al. / Biological Conservation 94 (2000) 235±242 daylight at ground level. This led to an increase in our study, similar trends as for the psammophilic evenness among species. In the months of December annuals were found for the small mammals. The non- 1997 and January 1998 there was a massive germination psammophilic M. musculus displayed a signi®cant of annual plants, which in March approached 57% (out preference for the control plots. This trend was not of 65% for the overall vegetation cover). The composi- signi®cant in the other non-psammophilic species (R. tion of species was similar to that of the control areas rattus and C. russula) largely due to small sample size, resulting in similar species richness. Because the woody but their restriction to peripheral traps emphasises this vegetation was removed before the rains began and preference. before the growing season, all the species that germi- The psammophilic gerbil G. allenbyi showed a distinct nated and appeared in the area were present in the seed preference for the open plots as shown by the almost bank already existing in the soil. The species that were two-fold increase in the relative number observed absent from the cleared areas were the woody perennial between control and cleared plots (47 and 86%, respec- plants that had not regenerated after the treatment. This tively). The latter ®gure was similar to the combined was probably because of the absence of suitable condi- proportion of G. allenbyi and M. musculus in control tions for germination and vegetative regeneration. For plots (89%). However, since the actual number of ger- example, the climber Rubia tenuifolia usually grows bils did not increase in the cleared plots where mice were under conditions of shade and, therefore, under full absent, this suggests little competition between the two light and arid conditions, this plant would ®nd it di- species. Although 72% of the individuals of M. tristrami cult to germinate and grow. were trapped in cleared plots, the numbers were too low More important than the richness or diversity of spe- to show signi®cance (Table 3). cies in an area chosen as a nature reserve or a national The fact that no small mammals were trapped in the park is the question of whether the plants characteristic cleared plots during the ®rst 3 months after cutting to this region exist in populations large enough to avoid suggests that they moved out immediately after the extinction. Indeed, species such as Rumex pictus, Daucus clearing and recolonised only when the annual plants glaber, Crepis aculeata, Brassica toumefortii and Cutan- had re-established. dia philistaea, which are considered characteristic of shifting dunes and semi-stabilized dunes, were most abundant in the cleared plots. In the ®rst year after 6. Conclusions removal of the vegetation, Senecio joppensis (an endemic annual to the coastal dunes) was most abundant, while by We conclude that our hypothesis has been veri®ed: the third year, Rumex pictus was the dominant species. the removal of dense vegetation from semi-stabilized Tielborge and Kadmon (1995) worked on the Nitzana coastal dunes caused these areas to become colonised by Dunes in Israel (annual average precipitation of 78 mm) psammophilic plants and animals more characteristic of studying the in¯uence of perennial shrubs on the pattern open areas. A reservoir of seeds of all the species char- of the distribution of annual plants in this area. They acteristic of this habitat can be found in this ecological found that many species, including Rumex pictus, prefer system. However, under conditions of almost complete to grow under shrub canopies. It would appear that rate dominance of one or more woody perennial plants (such of seed production and percentage of germination of as Retama raetam and Artemisia monosperma), the her- these species are higher for individual plants that grow baceous types are suppressed. While the richness and under the shrubs than for those growing in open areas. diversity of the species of small mammals decreased in It is possible that in an area with 500 mm or more rain, open areas, richness of plants species did not show any as in our study area, water is not a limiting factor for marked change in these locations as compared to areas the sandy annual plants that grow during the rainy of dense vegetation, although plant species diversity was season and have only a short life span. Under these higher. An important result of this experiment was that conditions there is no relative advantage of positions small mammals and annual plants that were most under shrub canopies over those in open areas, and the abundant in the cleared open areas were also those that opposite may even be true. In dense vegetation, annuals were speci®c to semi-stabilized sand dunes. In practice, like Rumex may not be able to complete their life-cycle, the merit of decreasing the number of small mammal whereas in open areas they are able to ¯ourish. species was an exclusion of the undesirable species from There have been only a few studies that followed the this ecological system. eect of vegetation removal on vertebrates and these It remains to extend our study over a larger area in have mostly related to voles (Birney et al., 1976; Taitt order to evaluate any undesirable eects of such vegeta- and Krebs, 1983; Lemen and Clausen, 1984; Edge et al., tion clearing, and to optimize the pattern of clearing on 1995). All studies recorded a short-term decline in vole larger scales. Nahal Alexander National Park is rela- population size, and a rapid population increases to the tively small so a management plan that involves partial pre-mowing state immediately after plant recovery. In clearing using mechanical tools is feasible. However, P. Kutiel et al. / Biological Conservation 94 (2000) 235±242 241 this is impractical over larger areas. Subjecting an area Mediterranean ecosystem in Israel. Earth Surface Processes and to short periods of intensive grazing by camels may be Landforms 19, 187±194. an alternative scheme, but we would need to investigate Kutiel, P., 1997. Spatial and temporal heterogeneity of species diversity in a Mediterranean ecosystem following ®re. International the level of grazing required and evaluate the eects of Journal of Wildland Fire 7, 307±315. this herbivore on the populations of small mammals. Kutiel, P., 1998a. Possible role of biogenic crusts in plant succession on the Sharon sand dunes, Israel. Journal of Plant Sciences 46, 279± 286. Acknowledgements Kutiel, P., 1998b. Annual vegetation of the coastal sand dunes of the northern Sharon, Israel. Israel Journal of Plant Sciences 46, 287± 298. Our deep gratitude is expressed to Yoel Melamed and Kutiel, P., Sharon, H., 1996. 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