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Journal for Nature Conservation 19 (2011) 143–147

Contents lists available at ScienceDirect

Journal for Nature Conservation

journa l homepage: www.e lsev ier .de / jnc

hort communication

ong-lived sustainable microhabitat structures in arable ecosystems, andkylarks (Alauda arvensis)

artin Schönrunsstrasse 34, D-72074 Tübingen, Germany

r t i c l e i n f o

rticle history:eceived 17 March 2010eceived in revised form 8 October 2010ccepted 21 October 2010

eywords:gri-environment schemesird conservationaps in cultivation

n-field measures

a b s t r a c t

To slow down the decline of skylark populations, in agri-environment schemes within-field microhabitatstructures with stunted growth of the vegetation (“scrapes”, “plots”) are created artificially for one yeareach. However, in arable land comparable microhabitat structures may develop spontaneously, and existover long periods, caused by microgeological features, and traditional cultivation practices. Skylarks,and other species of arable ecosystems, may adhere strongly to such structures. In two study areas insouthwestern Germany, with fairly high densities of 0.26–0.42 skylark territories/ha, 80.2% of the territorycentres were situated near such structures; 32.4% were re-used in different years. In combination withthe observation of further farmland species, e.g. arthropods, at these locations, it is suggested that short-lived structures with stunted vegetation may promote predominantly species with shorter life-cycles,

aturally formingegionaltunted vegetationraditional cultivation

while the longer-lived naturally forming structures may be attractive also for species with higher site-fidelity, or with multi-annual life-cycles. In many regions, at least traces of these structures are presentin fields to date, but rapidly vanishing under use of modern agro-machinery, and thus becoming lesseffective in causing patchy, stunted vegetation. Yet, protection of such quasi self-preserving, sustainablemicrohabitat structures, adapted to local conditions, could benefit biodiversity. More studies are neededto understand in more detail the ecological role of these undervalued elements of arable ecosystems.

ntroduction

In order to slow down the decline of skylark (Alauda arvensis,innaeus, 1758) populations, various proposals have been tested inrable land in recent years (e.g. Fischer et al. 2009; Henderson &oombes 2007; Henderson et al. 2007; Morris et al. 2004; StoateMoorcroft 2007; Stöckli et al. 2006; Wilson et al. 2009). Sev-

ral experimental studies reported that within-field measures withtunted growth of the vegetation may be advantageous for thispecies, mainly later in the season when the cereals have grownoo high for nesting, or foraging. For that purpose, unsown patches“skylark scrapes”, or “plots”) or strips, with variable levels of appli-ation of agrochemicals, were created and maintained artificially,ainly within wintercrop fields and mostly for one growing season

nly, i.e. they were rotational (e.g. Fischer et al. 2009; Morris 2007;orris et al. 2004; Odderskær et al. 1997). However, it has appar-

ntly been largely neglected in recent considerations that similaraturally forming microhabitat structures with stunted vegetation

ay exist, and have strong beneficial effects on arable ecosys-

ems, at least regionally. Therefore, this study tested the hypothesishether the distribution of skylarks is influenced by the occur-

E-mail address: Lanexcu@t-online.de

617-1381/$ – see front matter © 2010 Elsevier GmbH. All rights reserved.oi:10.1016/j.jnc.2010.10.003

© 2010 Elsevier GmbH. All rights reserved.

rence of such spontaneously occurring structures, and to whichextent.

Materials and methods

The study was conducted in southwestern Germany in four suc-cessive years (1997–2000, and to a limited extent in the yearsbefore and thereafter), in two separate study areas about 3 km apart(U1: 135 ha, U2: 83 ha), during the second and last thirds of thebreeding season (second third: middle of the breeding season, frommiddle of May to early June; last third of breeding season: frommiddle of June to middle of July). The average number of skylarkterritories was x ± s = 40.3 ± 7.0 in U1 (32.3 ± 11.2 in U2) in the sec-ond third; and 34.5 ± 9.8 in U1 (26.5 ± 7.3 in U2) in the last third ofthe breeding season.

The skylark population was recorded during 5–7 counts per sea-son, each with an effort of 30–40 min per 10 ha, resulting in themapping of territory centres which were inferred from specific ter-ritorial behaviour (e.g. starting, and landing points of males duringsong flights, observations of pairs, or of fed unfledged juveniles,

approaches of adults with food, occasionally detection of nests).This specific behaviour was largely restricted to a narrow area,i.e. the ‘territory centre’ of breeding activity, which was fixed as acircular area with a diameter of 15 m. (The outline of the entire ter-

1 Conservation 19 (2011) 143–147

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Fig. 1. Association (%) of centres of skylark territories with microhabitat structureswith stunted vegetation, forming naturally, and/or caused by traditional cultivationpractices; in two study areas (U1, U2) in southwestern Germany, and in each of twoparts of the breeding season during four successive years: comparison of observeddistribution of territory centres (filled symbols) and random distribution (open sym-bols); given as proportion (%) of the total of territory centres, respectively of randompoints, at/near such microhabitat structures. Symbols: m, squares = middle of thebreeding season (three successive seasons); l, circles = last third of breeding season

44 M. Schön / Journal for Nature

itory could be inferred from additional behaviour, e.g. trajectoriesf song flights, fights between males.) All observations of skylarks,nd similarly the microhabitat structures, were recorded on landegister maps (scale 1:2500), showing the traditional arrangementf mostly narrow plots (parcels of land), thus facilitating position-ng. Territory centres were classified as being situated at/near the

icrohabitat structures, or elsewhere. Similarly, the distribution ofinging males of the quail (Coturnix coturnix, Linnaeus, 1758) wasapped, with song locations classified as at/near the structures, or

lsewhere.Microhabitat structures with stunted vegetation were subdi-

ided into three groups; i.e. structures at sites: (a) caused byicro-geological and -climatical conditions, or resulting from tra-

itional cultivation practices; (b) caused by modern cultivationechniques (e.g. clay-covered country lanes at least partly with

solid bed of gravel); (c) at arbitrary places (not a, and not b).icrostructures of type (a) include those caused by: (1) the local

onditions of micro-climate, micro-geology and -topography (e.g.atches with stones, with thin soil cover; wet patches over geo-

ogical layers with springs, shallow depressions with accumulatingtanding water, becoming suitable when drying up later in the sea-on; or shallow, potentially arid elevations); and/or resulting from:2) traditional cultivation practices (e.g. fields with small-scaledentral vaults and marginal depressions caused by ploughing thelods towards the central parts of the parcelles; unconsolidatedraversing field-paths, in parts with compressed bare ground).hus, structures of type (a) are part of the regularly cultivated farm-and. Results reported here refer to (a) only (for b, c, see Schön 1999,004).

The age of a structure may be inferred from direct observationsn the fields (covering > 25 years), from the land register maps (dat-ng from the years 1850 to 1880), in combination with reports onocal history and oral communications by residents (for detailedxamples, see Schön 2000, 2004; see also Appendix C).

tatistics

The observed distributions of territory centres were comparedo random distributions of six sets of random points, which wereenerated for each year and each part of the breeding seasoneparately, with the total of random points equalling the total of ter-itory centres in each combination. Differences were then checkedor significance with Chi square and Binomial tests, and with theonfidence interval of the arithmetic mean of the six sets of ran-om distributions (see also Schön 1999, 2004). In Fig. 1 only thoseesults are included which show differences of observed and ran-om distribution exceeding the 99.9% confidence interval, for eachear separately, corresponding to a level of significance of p < 0.001.

esults

In both study areas (and in adjacent areas), naturally occur-ing microhabitat structures with stunted growth of the vegetationre found regularly, and dispersed over the fields, often within theresent-day plots (average density: 2.0 structures/ha, N = 432, totalor both study areas). These structures persisted in the same placeor several years at least (observed age: >4–6 years for the majorityf structures; in addition: >25 years for several individual struc-ures; unpublished data). For many structures, an even higher agef no less than 130–160 years may be inferred from land registeraps.

Skylarks may adhere strongly to such long-term microhabitat

tructures, and to the immediately adjacent areas, showing a pref-rence for and the re-use of such structures over several yearsFig. 1; for each year separately: significant differences, p < 0.001).

(four successive seasons); small symbols: single years; 1 = 1997, 2 = 1998, 3 = 1999,4 = 2000; large symbols: average of the total of years, given as arithmetic mean ± SD(standard deviation); N = total of territories for all of the years.

This predilection was similar in both study areas, and in both partsof the breeding season (m, l), with a slightly smaller variance in U1(Fig. 1). A similar preference was shown by the quail (for each year:significant differences, p < 0.02, N = 56). In the studied populationof skylarks, with fairly high densities of 0.26–0.42 territories/ha (inthe middle of the breeding season), 398 of 496 (80.2%) territorycentres were situated at such naturally forming long-term micro-habitat structures, and 89 of 275 (32.4%) such micro-structureswere used more than once as a territory centre during four sub-sequent seasons (totals for the two study areas).

Discussion

Could naturally forming structures diminish skylark decline?

In arable land (and in grassland), microhabitat structures withstunted and sparse vegetation, and of variable size, may occur spon-taneously, and exist to a varying extent for long periods (decades,or even centuries). These structures may be caused by local micro-climatical, micro-geological and micro-topographical conditions,and/or result from local traditional cultivation practices appliedover long periods, i.e. from historic crop husbandry (for detailedexamples, see Schön 2000, 2004). Such structures with stunted veg-etation, and the preference of skylarks and other species of arableecosystems for them, are obviously not limited to the study areas,but may be found in various parts of Europe (occasional obser-vations, Schön unpublished data). In many regions, only traces ofthese structures have been outlasting till today (see also Newton

2004). To a minor extent, patches of sparse vegetation may also bebrought about by modern farming practices, if in places too smallquantities are erroneously sown, or sprayed. At such places, the useof the agro-machinery may be hampered, e.g. by stony soil.

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Similarly, other species of larks may also adhere to such patchesf sparse vegetation in fields (Thekla lark Galerida theklae in thealearic Mediterranean region: even within fields with a low cropensity, i.e. with wide-spaced rows; woodlark Lullula arborea: onmall field strips with bare ground, within an under-grazed heath,uring periods of rain; Schön unpublished data, Schön 2000).

The decline of species of arable ecosystems may be due to a vari-ty of interacting factors, which can vary regionally. Thus in thease of the skylark, in addition to progressive agricultural intensi-cation, climate and its changes, food abundance and accessibility,r predators may affect different populations to a varying extent.owever, tall, dense vegetation is likely to be a major limiting factor

or populations on modern farmland (Donald 2004; Newton 2004;eibel et al. 2001; Wilson 1997; Wilson et al. 2005, 2009). In this

ituation, the naturally occurring microhabitat structures may beost probably beneficial, if still present in sufficient frequency, and

n suitable locations within fields (for differences of modern andistoric structures, see Appendix A). Thus, the fairly high territoryensities in the study areas U1 and U2 may be due to the presencef these naturally occurring structures. The slightly smaller vari-nce in U1 in the preference for the structures (Fig. 1) may be dueo the larger size of the plots in U1 (arithmetic mean of plot size forll four years, in U1: x ± SD = 1.29 ± 0.24 ha; in U2: 0.84 ± 0.03 ha).est site selection in U1, therefore, may be restricted to a largerxtent to such naturally occurring structures.

A positive effect of the naturally occurring structures is largelynferred from high density in this study. But high territory den-ity need not necessarily be combined with high breeding success.herefore, the naturally occurring patches of stunted vegetationight be a pitfall (sink) for a skylark population, with high attrac-

iveness yet low breeding success, even for birds from surroundingreas. However, it is rather improbable that such a worst casessumption is valid for the studied population for several reasons.lthough breeding success was not recorded quantitatively in thistudy, at least part of the skylark population has been breeding reg-larly and successfully at or near such structures (ad hoc searches

ocated about 20 successful breeding attempts in each year). More-ver, immigration from surrounding farmland might have occurredo a minor extent only, as territory densities in these areas werepparently lower than, or at most equal to the density in the studyreas (Schön unpublished data). In addition, these structures, withmixture of bare or sparsely vegetated ground and adjoining higheregetation, rather fully reflect the habitat preferences of the sky-ark (e.g. Donald 2004; Schläpfer 1988; Wilson et al. 2009), and

ere often used for feeding as well. Finally, high densities andigh breeding success in former times were often reported fromreas with traditional cultivation practices, i.e. with such historictructures (e.g. Glutz von Blotzheim & Bauer 1985; Schläpfer 1988,001). Thus, it appears reasonable to assume that these structuresre most probably beneficial. Further research would be needed todentify in detail the factors which influence territory density andreeding success in areas with the naturally occurring structures.

Where still present, the naturally forming or historic structuresre apparently associated with rather high densities of skylarkerritories. Thus in the study areas, maximum densities rose to.42 (total average for both study areas), 0.55, or even up to 1.11nd 1.36 territories/ha (in one study area, or in parts of them;ee also Schön 1999, pp. 89–90; Schön 2004, p. 36), without anydditional conservation measures. This compares favourably withensities on present-day, intensively cultivated land; e.g. withean and maximum densities on arable (0.28) and mixed farmland

0.23 territories/ha; averages from studies of the last five decades,

onald 2004, p. 59); or even in areas with artificially created struc-

ures, with densities increasing from 0.18 (controls without) tomaximum of 0.31 nests/ha (experimental fields with “patches”,orris et al. 2004, p. 159). Furthermore, the naturally forming or

ervation 19 (2011) 143–147 145

historic structures (or at least traces of them on formerly small-parcelled fields) are usually dispersed in rather high densities overlarge areas (of more than 5 km2; observations in several regions,Schön unpublished data). In this way, a benefit may extend to thepopulation level. Similarly, artificially created structures, such as“patches”, should be frequent and present on large areas, to ame-liorate skylark densities on a regional scale (e.g. SE-England, seeWilson et al. 2009).

Preservation of vanishing historic habitat features?

In practice, it may be difficult for humans to detect the natu-rally occurring microhabitat structures, often being inconspicuousespecially within large fields, and in fields with tall sward, and inparticular for people not acquainted with local conditions (see alsoAppendix C). These structures may vary in size from year to year,depending on weather, type of crop, and cultivation techniques.Moreover, use of modern large-sized machinery can cause micro-depressions, or -elevations to be largely levelled out, or filled updue to abrasion of soil; and any stones coming up by tilling may becrushed or removed from the fields. With the advent of satellite-based position finding systems, such “less productive” patches caneasily be (re-)located in fields (“precision farming”). Therefore,these naturally forming structures are widely and often rapidlyvanishing through the use of modern agro-machinery.

Hence, the state of these microhabitat structures appears tobe of crucial importance. Under large-scale, intensive cultivationpractised just for a short period, even remnants of the formerlysmall-parcelled field boundaries may allow for relatively highdensities of the skylark, at least in the years directly followingconsolidation of the farmland. But with the continued practice ofmodern agro-industrial farming, the vanishing traces of such struc-tures will become less and less effective in causing stunted growthof the vegetation (for re-formation of structures, see Appendix B).

These various obstacles may explain why such microhabitatstructures forming naturally and/or caused by traditional cultiva-tion apparently have received little attention (e.g. Fischer et al.2009; Morris 2007; Morris et al. 2004; Stoate & Moorcroft 2007),particularly if these structures are situated within fields, and areperceived largely as rather transitory, historic features (but seeSchläpfer 1988, 2001; also: Buckingham 2001).

Are long-lived structures different?

The microhabitat structures in arable land may fulfill the dif-ferent demands of a species to a different degree; microhabitatsbeing suboptimal for nesting may be valuable for foraging (Fischeret al. 2009; Morris et al. 2004), or preening. Moreover, the mostlyannual artificially created (rotational) structures, and the sponta-neously occurring structures existing for long periods at the samesite (non-rotational, semi-permanent) may differ in their relevanceto wildlife species. Thus, ecological differences between short- andlong-lived structures may be expected. Durable structures exist-ing for periods of many years may also attract species with highersite-fidelity, or less mobile species, by allowing for traditions in(micro-) habitat use (observations for various species of semi-colonial hymenoptera, of orthoptera, coleoptera, rare species ofweeds, and even amphibians; Schön 2000, and unpublished data).In general, at sites existing for one season only predominantlyspecies with rather short life-cycles and lower site-fidelity might bepromoted, while even species with longer, multi-annual life-cyclesmight find opportunities to survive at sites with durable micro-

habitat structures in arable land (according to the life-history traitsof r- and K-selection, respectively). It is still necessary to under-stand in more detail in which way plant and animal species inarable ecosystems may benefit from such semi-permanent, natu-

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ally occurring structures, varying in state and frequency betweenifferent regions. Future studies focussing on these aspects woulde very valuable for conservation too (for invertebrates as food,.g. Henderson et al. 2007; Smith & Jones 2007; Smith et al. 2009;eibel et al. 2001).

omplementary conservation measures

Obviously, one of the main challenges in modern agriculturaland-use is to provide space for temporal and spatial “gaps in cul-ivation” (Schön 2000), in order to promote the conservation ofarmland species, and to implement the concept of sustainabil-ty (Stoate & Moorcroft 2007; Wilson et al. 2009). Taking intoccount the distribution of patches where natural preconditionsavour stunted growth of the vegetation may facilitate the creationf artificial, self-renewing, and quasi self-preserving microhabitattructures with stunted, sparse vegetation. Thus, the expendituresor conservation measures might be diminished, and their dura-ility could be enhanced (Schön 1999, 2004). With respect togro-technical needs, a disadvantage of the naturally forming struc-ures is that they cannot be moved freely, or only to a very limitedxtent, to places where they might be tolerable (for detailed sug-estions, see Schön 2000, pp. 194ff.).

Evidently, naturally occurring and artificially created microhab-tat structures should not be viewed as alternatives, but rather asomplementary. In areas where these naturally forming and his-oric features are still widespread, their preservation should attainigh priority in regional conservation schemes, on the assump-ion that these structures are most probably beneficial to variousarmland species. Farmers should be informed about the greatcological importance of these structures, and their preservationhould be supported through targeted payments within the scopef local agri-environment schemes, particularly for those struc-ures at isolated sites within the present fields (for a procedureor implementation, see Appendix C). Conversely, in areas withigh-intensity farming, where only few of such naturally occur-ing structures are left, the creation of artificial structures (e.g.lots) may be a better option to improve the fields as habitatsor the skylark and other farmland species (Fischer et al. 2009;

ilson et al. 2009). Particularly in areas where winter croppings dominating, artificial microhabitat patches with stunted veg-tation may be effective at rather low cost (Morris et al. 2004;orris 2007). The laying out of fallow patches for several years,hich are non-rotational during this period, in combination withlow-intensity cultivation in spring, could possibly increase the

enefit of such measures, similar to the long-lived historic struc-ures. Thus, by adaptation to the differing local conditions, andraditions in historic cultivation practices, the efficiency of conser-ation actions could be improved on a regional scale (Kleijn et al.006; Whittingham et al. 2007; Wilson et al. 2009), and in specificombinations, the ecological value of the various measures mighte mutually increased (see Appendix C).

So, further studies and discussion may still give rise to newptions for “aiding nature” by revealing deeper insights into thenter-relations of micro-geology, -topography, of cultivation prac-ices, and wildlife in agricultural ecosystems, thus broadening thecological scope of conservation (various proposals in: Douglast al. 2010; Field et al. 2007; Henderson et al. 2007; Newton 2004;mith et al. 2009; Stoate & Moorcroft 2007; Stöckli et al. 2006;ilson et al. 2005).

cknowledgements

The detailed reviewing of earlier drafts by Dr. J. Prop, and bynonymous referees was of great help, especially the commentsnd suggestions of Dr. T. Morris.

ervation 19 (2011) 143–147

Appendix A. Differences between modern and historiclinear microhabitat structures

In intensively cultivated present-day fields, skylark nests nearlinear structures, like tramlines, often have a lower breeding suc-cess. This is attributed to the nest sites being rather easily accessibleto predators (e.g. Donald 2004; Fischer et al. 2009). On the otherhand, in low-intensity farmland with numerous linear microhabitatstructures caused by traditional cultivation practices (see Methods;Schläpfer 1988; Schön 2000), nests were successful to a high pro-portion (e.g. Schläpfer 1988, 2001). Obviously, the linearity of thesehistoric structures did not result in a substantial reduction of breed-ing success. This might be due to differences between historic andmodern structures. As a consequence of the small-parcelled, low-tech traditional cultivation of farmland, the historic structures wererather numerous, and not as homogenous as e.g. modern tramlines(Schön unpublished data). Thus, the effort for nest predators wouldhave been increased. Accessibility was balanced to a greater extentagainst frequency and heterogeneity of these historic structures(for homogeneity caused by agricultural intensification: Wilsonet al. 2005).

Appendix B. Re-formation of microhabitat structures

In the long run, even in intensively cultivated fields completelylevelled out, such microhabitat structures may develop again afterlong-lasting periods of drought or rain, followed by duststorms,and inundations, causing shifts of huge amounts of soil. But thisre-formation of microhabitat structures occurs mostly on a largerscale, compared to the small-scaled structures produced by tradi-tional cultivation practices (observations in various regions, Schönunpublished data).

Appendix C. Suggestions for an implementation procedure

It would be advantageous to combine naturally occurring andartificially created microhabitat structures: by encouraging farmersto preserve the naturally occurring patches already existing in thefields, with a rather random arrangement, as well as by promoting aplanned layout of artificially created in-field patches and marginalstrips. It may be useful to proceed in two steps. Firstly, the potentialsites of such naturally occurring structures should be mapped (e.g.patches with thin soil cover, bare ground, or doline depressions), bycombining: (a) detailed land register maps (scale 1:2500), with theolder editions showing the situation before consolidation of farm-land often being of greater use, with support of digital GIS programs(cf. Stöckli et al. 2006); with (b) aerial photographs (1:2500), takenpreferably in autumn, or in early spring, and in combination witholder series from former decades; and with (c) local inventories ofmicro-geology and soil (according to experiences covering morethan 25 years, Schön unpublished data; see also Schön 2000). Inaddition, the residents’ knowledge of local conditions should beused extensively. Local farmers that are often bound up with theirlands for several generations are mostly well acquainted with localgeological features, or the former arrangement of parcels, and par-ticularly with places of stunted growth of the crop within theirfields (oral communications). Contrarily, people not acquaintedwith local conditions and following a scheme rather routinely(“experts”) might easily overlook some inconspicuous structures(own experiences). Still, taking such an inventory would be possiblewith limited effort, at least in Germany, especially in regions with

formerly small-parcelled fields that are merged after consolidationinto larger field units just recently.

In a second step, the preservation of any site with such structuresin a field should be rewarded in public and by financial support

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“eco-patchworker of the year”, “living with stones, and depres-ions in a field”). To this purpose, the existing agri-environmentchemes would have to be supplemented, giving a higher rate tosustainable” microhabitat structures already existing in the fields.

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