Munibe (Ciencias Naturales-Natur Zientziak) • NO. 53 (2002) • 183-204 • ISSN 0214-7688 Distributions of sawflies and aculeates in a heterogenous secondary acid forest in Artikutza (Navarre) (Insecta: Hymenoptera). 1 2 3 LETICIA MARTÍNEZ DE MURGUIA , Mª ANGELES VÁZQUEZ & JOSÉ LUIS NIEVES-ALDREY ABSTRACT The distribution of a sawfly and aculeate species assemblage was investigated by means of six Malaise traps in two adjacent succesional vegetation series, mixed pine forest and beechwood, at the forest reserve of Artikutza (Navarre). Comparisons between vegetation series and trap locations in sawflies, wasps, bees and ants suggested that species distribu- tions could be related to spatial distribution of different feeding, mating nesting and hiber- nating resources. Glades, river banks and dead wood have shown to provide a variety of diversity sources. • KEY WORDS: Distribution, Sawflies, Aculeates, Hymenoptera, Mixed pine forest, Beechwood, Navarre. LABURPENA Malaise erako sei tranparen bitartez ikertu da sinfito eta akuleatuen espezieen banaketa; elkarren jarraian eta alboan dauden bi landaredi-serietan jarri dira tranpak (pinuen baso mis- toa eta pagadia), Nafarroako Artikutzako baso erreserban. Sinfito, erle eta txindurrien kasuan landaredi-seriak eta tranpen kokapena elkarrekin alderatzean, pentsatu da espezieen bana- keta lotuta egon daitekeela elikadura-baliabideen banaketa espazialarekin, ugalketarekin, habiagintzarekin edo hibernazioarekin. Argiguneak, ibai-ibilgua eta zur hila direla medio, dibertsitate iturrien aniztasuna ziurtatzen da. • GAKO-HITZAK: Banaketa, sinfito, akuleatu, Hymenoptera, pinuen baso misto, pagadi, Nafarroa. RESUMEN La distribución de las especies de sínfitos y aculeados ha sido investigada por medio de seis trampas Malaise instaladas en dos series de vegetación adyacentes y sucesivas, bosque 1 Sociedad de Ciencias Aranzadi. Departamento de Entomología. Zorroagagaina, 11 • 20014 Donostia-San Sebastián. 2 Universidad Complutense de Madrid. Departamento de Biología Animal I, Facultad de Ciencias Biológicas. Ciudad Universitaria • 28040 Madrid. 3 Museo Nacional de Ciencias Naturales (CSIC), Dpto. de Biodiversidad y Biología Evolutiva (Entomología). C/ José Gutiérrez Abascal, 2 • 28006 Madrid. 183 LETICIA MARTÍNEZ DE MURGUIA, Mª ANGELES VÁZQUEZ & JOSÉ LUIS NIEVES-ALDREY mixto de pinos y hayedo, en la reserva forestal de Artikutza (Navarra). La comparación entre series de vegetación y localización de las trampas en sínfitos, avispas, abejas y hor- migas sugiere que la distribución de las especies puede estar relacionada con la distribu- ción espacial de los distintos recursos de alimentación, reproducción, nidificación o hiber- nación. Los claros, el cauce del río y la madera muerta proveen variedad de fuentes de diversidad. • PALABRAS CLAVE: Distribución, sínfitos, aculeados, Hymenoptera, bosque mixto de pinos, hayedo, Navarra. w y INTRODUCTION Restoration of natural decidous forests combining with development of recreation values and other sustainable uses are the main concerns in the Aiako Harria natural park (Gipuzkoa) (B.O.P.V. 2002) and the adjacent forest reserve of Artikutza (Navarre). Recording of a sawfly and aculeate species assemblage in this last locality was framed in a wider study in which Hymenoptera were used as an indicator group to assess diversity of semi-natural acid forests in the region (MARTÍNEZ DE MURGUÍA, 2001). Woodland structure determines spatial resource distribution and affects in a great extent insect resource searching strategies (DENNIS, 1997; ROLAND, ET AL. 1997; HUMPHREY ET AL, 1999). Changes in behavior can help identifying activity patches that indicate species strategies and conservation requirements (BELL, 1990). Malaise traps (MALAISE, 1937; TOWNES, 1962) have been shown to provide a useful tool to measure insect flying adult activity and variability among trap locations has been used to identify changes in the use of different resources (STEYSKAL, 1981; MUIRHEAD-THOMSON; 1991, PAPP & JÓZAN, 1995; SHLYAKHTENOK, 1995; PRECHT & CÖLLN, 1996; HAGVAR ET AL, 1998). The aim of this paper is to analyze the spatial activity patterns of sawflies and aculeate wasps, bees, and ants at the space close to the ground b means of Malaise traps in a hete- rogenous forest stand, and identify potential species conservation requirements in relation to structural features. For this purpose we study the taxonomic and quantitative distributions of ecological groupings, as well as of the most abundant species, among six traps covering two successional adjacent vegetation series, mixed pine forest and beechwood. This information could be useful when planning management techniques to promote forest biodiversity. MATERIALS AND METHODS STUDY AREA The study took place in the forest reserve of Artikutza (Goizueta, Navarra) (43°09 28’’- 43°14’52’’ North and 01°45’35’’- 01°49’30’’ West), located in the Cántabro-Euskaldún phy- 184 DISTRIBUTIONS OF SAWFLIES AND ACULEATES IN A HETEROGENOUS SECONDARY ACID FOREST IN ARTIKUTZA (NAVARRE) (INSECTA: HYMENOPTERA) togeografic sector of the Eurosiberian region (Fig. 1). It is characterized by nutrient poor, aci- dic soils with a humus moder of granitic origin, Artikutza that tends to support a vegetation dominated by Quercus robur L. (Hyperico pulchri-Quercetum roboris) and Fagus sylvatica L. (Saxifrago hirsu- tae-Fagetum) (CATALÁN, 1987). Following exten- sive deforestation up to 1925, plantations were established comprising a variety of deciduous species (F. sylvatica L., Quercus spp., Castanea sativa Mill.) and conifers (Pinus sylvestris L., Larix x eurolepis A. Henry, Chamaecyparis law- Fig.1.- Geographical situation of the forest reserve of Artikutza (Navarre, Spain). soniana (A. Murray) Parl.) (CATALÁN, ET AL, 1989). The present-day landscape supports a heterogenous mosaic of remanent forest, pine plan- tations and derived secondary mixed forests. Sampling was conducted in 5 ha located in the northwest of the reserve (30TWN972868 U.T.M.) at an elevation of 575-652 m altitude and includes two adjacent successional series defined by a stream: mixed pine forest and beechwood. The mixed pine forest represents a secondary forest (70 years old) dominated by pine, oak and beech, and the beechwood is partially restocked with young plantings and surrounded by conifer plantations. Other tree species are C. sativa Mill., Taxus baccata L., Salix atrocinerea Brot., Fraxinus excelsior L., Betula celtiberica Rothm.& Vasc. and Sorbus aucuparia (L.) Crantz. The shrub and her- baceous zones are composed of F. sylvatica L., Ilex aquifolium L., Blechnum spicant (L.) Roth., Deschampsia flexuosa (L.) Trin., Vaccinium myrtillus L., Euphorbia amygdaloides L., Daphne laureola L., and Oxalis acetosella L. Adjacent to clearcut areas the following spe- cies are common: Crataegus monogyna Jacq., Corylus avellana L., Pyrus cordata Desv., Malus sylvestris Miller, Pteridium aquilinum (L.) Kuhn., Erica vagans L. and Asphodelus albus Miller (CATALÁN, 1987). Scarce coverage of the herb and shrub layers leave large understory areas covered only by a litter layer of variable depth depending on the slope. Under high humidity conditions, the mossy layer is well developed on soil, stumps and the north side of tree trunks. Site characteristics as pine advanced age, clearings and restoc- kings, are responsible in a great extent for the important amount of dead wood, that accu- mulates particularly in the stream banks. SAMPLING DESIGN AND DATA COLLECTION TOWNES (1972) modified Malaise traps supplied by Marris House Nets (United Kingdom) were used in this study. They are bidirectional (203 cm front height, 112 cm back height, and 122 cm wide by 183 cm long) black with the roof white and fine mesh (0.3 mm) (Fig. 2). Trap collection jars were filled with 70 % ethanol along with three drops of glycerine to soften specimens. 185 LETICIA MARTÍNEZ DE MURGUIA, Mª ANGELES VÁZQUEZ & JOSÉ LUIS NIEVES-ALDREY Figure 2.- Malaise trap model used (trap M-2). A total of six Malaise traps were placed, three in each vegetation series: M-1, M-2 and M-3 in the mixed pine forest and H-1, H-2 and H-3 in the beechwood (Table I). Traps were settled along the direction of the slope, NE-SO in the mixed pine forest and NO-SE in the beechwood but all had similar orientation of the colector pole (SO) and direction of cap- tures (N-S). First trap in each vegetation series was placed at 50 m from the ride and follo- wed in the direction of the slope by a second one and from this one a third one, at about 100 m of distance in between traps. Heterogenous tree coverage and differences in the slope in each of the series resulted in particular trap locations. In the mixed pine forest, trap M-1 was located at the edge of a clearcut, trap M-2 in open forest and trap M-3 was under a mature beech in an area of major pine densities. In the beechwood, trap H-1 was ORIENTATION ORIENTATION COLLECTOR ORIENTATION TRAP TRAP ALTITUDE SLOPE HILL POLE CAPTURES DISTANCES ▼▼▼ ▼▼ ▼ ▼ MIXED PINE FOREST M-3 NE-SO N216E N-S 652 m 20º 82 m M-2 NE-SO N210E N-S 631 m 15º 121 m M-1 NE-SO N230E N-S 611 m 12º 206 m BEECHWOOD H-3 NO-SE N242E N-S 620 m 9º 92 m H-2 NO-SE N210E N-S 595 m 18º 206 m H-1 NO-SE N235E N-S 576 m 19º 75 m Table I.- Trap locations parameters in two adjacent vegetation series, mixed pine forest and beechwood (Artikutza, Navarre). 186 DISTRIBUTIONS OF SAWFLIES AND ACULEATES IN A HETEROGENOUS SECONDARY ACID FOREST IN ARTIKUTZA (NAVARRE) (INSECTA: HYMENOPTERA) under a big beech in a steep slope which affected in a lesser extent to trap H-2, settled near a small clearcut and surrounded by a shrub beech layer, and trap H-3 standed under the shade of a mature beech on a landing. Sampling was conducted continuously during two seasonal cycles, from May 1995 to April 1997, and produced a total of 46 samples per trap in 733 days. Species identification was made available by several taxonomists: G. Llorente Vigil (Symphyta), M.D. Martínez (Formicidae), S.F. Gayubo (Sphecidae), C. Ornosa (Bombinae), M. Díaz (Eumeninae), J.P. Pedrero (Pompilidae).