The Influence of Habitat Type on the Distribution of Carabid Beetles in Traditionally Managed “Dehesa” Ecosystems in NW Spain
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© Entomologica Fennica. 11 October 2006 The influence of habitat type on the distribution of carabid beetles in traditionally managed “dehesa” ecosystems in NW Spain Angela Taboada, D. Johan Kotze, José M. Salgado & Reyes Tárrega Taboada, A., Kotze, D. J., Salgado, J. M. & Tárrega, R. 2006: The influence of habitat type on the distribution of carabid beetles in traditionally managed “dehesa” ecosystems in NW Spain. — Entomol. Fennica 17: 284–295. We investigated the responses of carabid beetles to habitat type at the local scale in traditionally managed “dehesa” ecosystems in NW Spain. The beetles were sampled from two habitat types (central grassland and surrounding forested zone) of five “dehesa” ecosystems, from May to October 2004. A total of 4,374 carabid individuals and 55 species were captured using pitfall trapping. Most of the species were collected from both habitat types, probably due to open spaces created between old-growth trees in the forested zone. Differences in carabid as- semblage composition were found mainly due to Harpalus species characteristic from the central grassland and a few forest specialist species exclusively found in the forested zone. The maintenance of the “dehesa” structure may be of impor- tance for carabid species adapted to the variety of habitats created, and requires the continuation of traditional management practices. A. Taboada and J. M. Salgado, Department of Animal Biology, University of León, Campus de Vegazana s/n, E-24071 León, Spain; E-mail: dbaatp @unileon.es D. J. Kotze, Department of Biological and Environmental Sciences, P.O. Box 65 (Biocenter 3, Viikinkaari 1), FI-00014 University of Helsinki, Finland R. Tárrega, Department of Ecology, Genetics and Microbiology, University of León, Campus de Vegazana s/n, E-24071 León, Spain Received 12 December 2005, accepted 1 March 2006 1. Introduction diversity (Gómez-Limón & De Lucío Fernández 1999). A“dehesa” is an agro-forestry system with Historical land use and management practices, in- extensive grazing (sheep, goats, pigs and cattle); cluding forest burning and cutting to create agri- these multiple land-uses produce a landscape of cultural land and pastures for livestock grazing, high habitat heterogeneity (Blanco et al. 1997). have altered and diversified the landscape in the The resulting anthropogenic mosaic (pasture, ar- Iberian Peninsula (Blanco et al. 1997, Luis- able, woodland) produces a range of environmen- Calabuig et al. 2000). In some cases, these tradi- tal conditions and niches that can enhance diver- tional practices have transformed the forested sity (e.g., Pulido & Díaz 1997, Martín & López land to create “dehesa” ecosystems, where the use 2002). of resources coexists with areas of high biological The origin and evolution of the “dehesa” ENTOMOL. FENNICA Vol. 17 • Carabid beetles in dehesa ecosystems in NW Spain 285 Figure 1. Composition of the dehesa ecosystem and its relation to the surrounding oak forest. a) Aerial view and b) detailed view. Habitat types: G = Central grassland, F = Forested zone, O = Surrounding oak forest. landscape have been intrinsically related to branches (to provide shade, browsing and acorn transhumance pastoral systems for centuries production), and c) the enhancement of tree re- (Blanco et al. 1997). Well-developed “dehesa” generation by the planting of new seedlings systems were established as a permanent feature (Blanco et al. 1997). of the Spanish landscape from the early Middle Here we investigate the responses of carabid Ages, when clearing, thinning and ploughing of beetles to habitat type (defined by the variability continuous oak forests were frequently per- in the composition of the vegetation layer) at the formed. These management practices were de- local scale in traditionally managed “dehesa” veloped in order to obtain regularly-spaced re- ecosystems in NW Spain. We selected a Quercus tained trees (between 30 and 60 trees per ha) and pyrenaica “dehesa” system that typically consists to enhance grassland growth among the trees of two main habitat types: 1) a central grassland (Blanco et al. 1997, Joffre et al. 1999, Pulido et area and 2) a surrounding forested zone charac- al. 2001). Most contemporary “dehesa” ecosys- terised by scattered old-growth trees, which are tems were created during the second half of the maintained for livestock shelter and feeding pur- 19th and the beginning of the 20th centuries as a re- poses (Fig. 1). sult of increased human densities (Pulido et al. We aim to determine if the carabid assem- 2001). blages inhabiting the “dehesa” ecosystem differ The degree of habitat diversity (i.e., differ- between the central grassland and the surround- ences in vegetation structure and composition) in ing forested zone despite their spatial proximity. a “dehesa” ecosystem is mainly dependent on We ask whether differences in environmental management practices and different products ob- conditions due to tree development in the forested tained (e.g., forage, firewood, charcoal, acorn, area influence the presence of carabid species ac- cork, tannin). Basically, the vegetation structure cording to their habitat preferences [see Reyes- of a “dehesa” is composed of two layers (Joffre et López et al. (2003) for ants]. Shade provided by al. 1999): a savannah-like open tree layer with the scattered trees in the forested zone increases scattered mature oaks (mainly Quercus ilex and microhabitat humidity, decreases temperature Q. suber) and a grass dominated layer (usually and contributes to leaf litter development and or- native annual herbs for grazing). The mainte- ganic matter content (Joffre et al. 1999), leading nance of this two-layered vegetation structure re- also to modifications in the vegetation composi- quires continuous management such as: a) con- tion. These changes in environmental conditions trol of shrub invasion by uprooting, clearing and may make the forested zone suitable for forest ploughing, b) preservation of the old-growth tree specialist species, even though these zones are layer by regular pruning to favour horizontal not considered true forest ecosystems. Open hab- 286 Taboada et al. • ENTOMOL. FENNICA Vol. 17 itat species are expected to thrive in the central caryophyllea, Cynosurus cristatus, Medicago grassland and generalist species are expected to lupulina, Ornithopus compressus, Trifolium ar- be less influenced by the differences between the vense, T. campestre, T. glomeratum, T. pratense, two habitat types. T. strictum,andVulpia bromoides (Díez et al. 1994, 1995). The surrounding forested zone is characterised by a more complex vegetation 2. Material and methods structure consisting of several layers: oak trees, oak saplings, shrubs and annual and perennial 2.1. Study area and sampling method herbs (Table 1). Vegetation sampling in these forested zones The study was conducted in NW Spain (42º36’– were carried out in June–July 2004: (a) under- 42º39’ N, 4º58’–5º05’ W), in the Mediterranean story vegetation cover (shrubs, herbs and sap- Region 980–1,030 m a.s.l. We selected five lings) was visually estimated in 20 systematically Quercus pyrenaica “dehesa” ecosystems [Fes- placed 1 m × 1 m quadrats per site; (b) oak tree tuco heterophyllae–Querceto pyrenaicae sig- characteristics (perimeter, height, canopy diame- metum; Penas et al. (1995)] at least 1 km apart, ter and distance between trees) were measured surrounded by continuous oak forests and with a from 40 trees per site. similar grazing intensity (sheep and goats). Each We used plastic pitfall traps (depth 86 mm, di- “dehesa” ecosystem included the two habitat ameter 60 mm) covered by 10 cm × 10 cm roofs types described above, and we sampled carabid and partly filled with 25% propylene glycol to beetles in five central grassland sites (size range collect the beetles. Pitfall catches reflect carabid 2.09–8.23 ha) and five surrounding forested sites activity-density (e.g., Thomas 1998) that will be (size range 11.50–24.64 ha). referred to here as abundance or number of indi- Grazed and open central grasslands are domi- viduals. Five sampling points were placed in each nated by a variety of herb species such as Aira of the ten sites. Each sampling point consisted of Table 1. Structural characteristics of the vegetation at the five forested zones. Dominant herb (annual and perennial herbs) and scarce (<5% cover) shrub species at each zone are given. Oak saplings (<1m height) are indicated when cover was greater than 2%. Mean ± Standard Deviation distance between oak trees, tree height, perimeter and canopy diameter are also given. Annual herbs Perennial herbs Shrubs Mean ±SD Mean ±SD Mean ±SD Mean ±SD tree dist. tree ht. tree perim. canopy (m) (m) (cm) diam. (m) 1 Aira caryophyllea Agrostis capillaris Crataegus monogyna 7.70 ± 3.76 8.46 ± 4.42 73.33 ± 71.47 6.49 ± 4.66 Cynorosus echinatus Festuca rubra Tuberaria guttata Plantago lanceolata 2 Tuberaria guttata Agrostis capillaris Erica cinerea 7.65 ± 5.32 11.03 ± 4.14 123.40 ± 112.32 7.45 ± 4.97 Carex muricata Halimium umbellatum Festuca rubra Oak saplings 3 Aira caryophyllea Agrostis capillaris Halimium umbellatum 9.66 ± 5.17 10.20 ± 4.70 98.68 ± 102.69 6.83 ± 4.50 Cynosurus echinatus Oak saplings Tuberaria guttata Vulpia bromoides 4 Aira caryophyllea Agrostis capillaris Thymus serpyllum 7.18 ± 4.34 10.18 ± 4.96 87.80 ± 91.43 6.08 ± 4.27 Tuberaria guttata Hieracium castellanum Vulpia bromoides Hieracium gr. pilosella Plantago lanceolata 5 Aira caryophyllea Agrostis capillaries Calluna vulgaris 5.53 ± 3.13 13.88 ± 2.10 86.20 ± 48.26 6.64 ± 3.03 Trifolium campestre Carex muricata Erica umbellate Festuca rubra Lithodora diffusa Hieracium gr. pilosella Thymus serpyllum Oak saplings ENTOMOL. FENNICA Vol. 17 • Carabid beetles in dehesa ecosystems in NW Spain 287 Table 2. Generalised linear model results. df = degrees of freedom. Residual Deviance is the amount of variation not explained by the models; p values in parentheses (boldface if p <0.05; ¤2 distribution). The Central grassland (Grassl.) coefficients are the basic intercepts of the models; Forest = forested zone.