Hymenoptera: Formicidae) Nesting in Dead Wood of Northern Boreal Forest
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COMMUNITY AND ECOSYSTEM ECOLOGY Postfire Succession of Ants (Hymenoptera: Formicidae) Nesting in Dead Wood of Northern Boreal Forest PHILIPPE BOUCHER,1 CHRISTIAN HE´BERT,2,3 ANDRE´ FRANCOEUR,4 AND LUC SIROIS1 Environ. Entomol. 44(5): 1316–1327 (2015); DOI: 10.1093/ee/nvv109 ABSTRACT Dead wood decomposition begins immediately after tree death and involves a large array of invertebrates. Ecological successions are still poorly known for saproxylic organisms, particularly in boreal forests. We investigated the use of dead wood as nesting sites for ants along a 60-yr postfire chro- nosequence in northeastern coniferous forests. We sampled a total of 1,625 pieces of dead wood, in which 263 ant nests were found. Overall, ant abundance increased during the first 30 yr after wildfire, and then declined. Leptothorax cf. canadensis Provancher, the most abundant species in our study, was absent during the first 2 yr postfire, but increased steadily until 30 yr after fire, whereas Myrmica alasken- sis Wheeler, second in abundance, was found at all stages of succession in the chronosequence. Six other species were less frequently found, among which Camponotus herculeanus (Linne´), Formica neorufibar- bis Emery, and Formica aserva Forel were locally abundant, but more scarcely distributed. Dead wood lying on the ground and showing numerous woodborer holes had a higher probability of being colonized by ants. The C:N ratio was lower for dead wood colonized by ants than for noncolonized dead wood, showing that the continuous occupation of dead wood by ants influences the carbon and nitrogen dynamics of dead wood after wildfire in northern boreal forests. KEY WORDS ant, wildfire, succession, boreal forest, dead wood Dead wood is an important component of forest eco- called “ecosystem engineers” to highlight their ecologi- systems and can be produced through the gradual sen- cal importance (Folgarait 1998). Ants modify soil physi- escence of individual trees (Rouvinen and Kuuluvainen cal and chemical properties, enhance plant growth, 2001) or from the mass killing of trees by large-scale influence plant and animal distribution, and contribute disturbances such as wildfire (Payette et al. 1989). to overall ecosystem health (Ho¨lldobler and Wilson Dead wood is used by a large array of invertebrates 1990, Lafleur et al. 2002). However, several ant species (Grove 2002, Hammond et al. 2004, Azeria et al. 2012). also nest in dead wood, which provides a warmer nest- Several xylophagous insects feed directly on dead or ing environment than soil (Higgins 2010, Higgins and moribund trees and are thus primary colonizers (Coul- Lindgren 2012). This is particularly important at higher son and Witter 1984). These insects play a major role latitudes where low soil temperature becomes a limit- in initiating cycling of nutrients stored in dead wood in ing factor for nesting of thermophilic insects (Higgins forest ecosystems (Ausmus 1977, Zhong and Schowal- 2010). ter 1989, Siitonen 2001). They dig galleries that Many studies have reported important modifications enhance colonization of dead wood by secondary in soil properties attributable to soil-dwelling ant activ- decomposers (Bruno et al. 2003), to which group sap- ity (Nkem et al. 2000, Frouz et al. 2003, Dostal et al. roxylic ants belong. These are usually found in dead 2005). While building their mounds, ants mix organic wood of mid- to late decay classes, where they excavate and mineral material, thus increasing the concentra- wood and thus contribute to its decomposition (Higgins tions of nitrogen compounds (NH4þ, NO3À) and of other 2010). Ants (Hymenoptera: Formicidae) are among the nutrients (Lafleur et al. 2002, Dostal et al. 2005). Even dominant arthropods of the world terrestrial ecosys- if carbon and nutrient dynamics is a well-known phe- tems (Ho¨lldobler and Wilson 1990). They influence soil nomenon in the process of wood decay (Harmon et al. and ecosystem processes in various ways and have been 1986, Bond-Lamberty et al. 2002, Laiho and Prescott 2004, Boulanger and Sirois 2006), the role of ants in this process is still unknown, as well as the relationship 1 De´partement de Biologie, Chimie & Ge´ographie, Universite´ du between ants and dead wood characteristics (Torgensen Que´bec a` Rimouski, 300 alle´e des Ursulines, Rimouski, QC, Canada and Bull 1995, Lindgren and MacIsaac 2002). G5L 3A1. 2 Natural Resources Canada, Canadian Forest Service, Laurentian In the boreal forest of America, wildfire is the main Forestry Centre, 1055 du P.E.P.S., P.O. Box 10380, Stn. Sainte-Foy, natural disturbance generating dead wood (Pedlar et al. Que´bec, QC, Canada G1V 4C7. 2002). While postfire succession of saproxylic beetles 3 Corresponding author, e-mail: Christian.Hebert@NRCan-RNCan. have received some attention over the past decade (Sii- gc.ca. 4 Universite´ du Que´bec a` Chicoutimi, 555 de l’Universite´, Sague- tonen 2001, Grove 2002, Saint-Germain et al. 2004, nay, QC, Canada G7H 2B1. Boulanger and Sirois 2007), few studies have addressed VC The Authors 2015. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For Permissions, please email: [email protected] October 2015 BOUCHER ET AL.: ANT POSTFIRE SUCCESSION IN DEAD WOOD 1317 postfire succession of saproxylic ants. In fact, the few and Franks 1995, Debout et al. 2007), we defined an studies that have addressed postfire succession of ants ant nest as a group of worker ants taking care of a have mostly focused on ground-nesting (Lafleur et al. brood, with or without the presence of a queen. For 2006) or ground-dwelling and arboreal ants (Rodrigo each piece of dead wood housing one or more nests, and Retana 2006). Moreover, ecological succession of we recorded values for the following attributes: number saproxylic ants is poorly known in the boreal forest, par- of woodborer holes, position (snag or log lying on the ticularly with respect to changing habitats resulting ground), stump diameter (cm), length or height of the from fire disturbances (Lafleur et al. 2006). dead wood piece (cm), bark cover (%), maximal length The present study aims to 1) characterize the tempo- of twigs (cm), contact with the ground (%), moss and ral colonization of dead wood by ants along a postfire lichen cover (%), and decay class according to the crite- chronosequence in northern boreal forest; 2) deter- ria shown in Table 1. In order to identify attributes mine which characteristics of dead wood favor nesting favoring ant colonization, we also sampled, for compari- by ants; and 3) assess the influence of ants on cycling son purposes, 5–10 noncolonized pieces of dead wood of carbon and nitrogen stored in dead wood. in each plot and described them with the same attrib- utes. All noncolonized pieces were described in plots with less than five pieces of dead wood. Materials and Methods To compare biological traits of ant species nesting in Study Area. The study was carried out in the low- dead wood, we estimated the volume (Vcylinder ¼ pr2h) lands of the James Bay area, within a 100-km radius of of each nest by measuring the length and thickness of the Town of Radisson (53 790 N, 77 620 W; Fig. 1). the cavity occupied within each piece of dead wood The study area is located on the Precambrian geologi- (Foitzik and Heinze 1998). In addition, we noted if cal formation of the Canadian Shield, which is charac- ants were using the space between the piece of dead terized by a low-altitude (100–200 m) undulating wood and the ground, the space between the bark and plateau dissected by depressions. The surficial deposits the wood, or the wood itself. In the latter case, we also in this landscape correspond primarily to ablation tills noted if ants were mostly using the periphery or the and glaciofluvial sands on uplands and marine clays in center of the debris. We used a vacuum to collect a lowlands (Stockwell et al. 1968). This region is charac- minimum of 20 specimens from each nest, which were terized by a subarctic climate with warm and short kept in 95% ethanol until species identification. Vouch- summers followed by long and cold winters. Annual ers are kept at the Universite´ du Que´bec a` Rimouski temperature averages À3.6C, with a mean maximum (Rimouski, QC, Canada). of 13C in July and a mean minimum of À23C in Jan- In order to estimate the role of ants in wood decom- uary. Annual precipitation averages 684 mm, of which position, we collected two wood samples of the same 246 mm fall as snow (Environnement Canada 2003). decay class (one from a colonized and one from a non- Forest dynamics are primarily influenced by a 100-yr colonized piece of dead wood) in each plot of the con- fire cycle (Payette et al. 1989, Parisien and Sirois 2003). trol sites, as well as from plots of the 1989, 1988, 1973, Black spruce (Picea mariana [Mill.] BSP) is the most and 1941 burns. These sites were selected because common tree species in the region, along with jack they contained at least one ant nest per plot. Wood pine (Pinus banksiana Lamb.) in fire-prone sites such disk samples (5 cm thick) were collected using a bow as those studied here. The understory vegetation is saw, placed in sealed plastic bags to avoid dessication, mainly composed of ericaceous shrubs and the forest and stored at À20C. Finely ground subsamples (3 g) floor is covered either by lichens of the genus Cladina were analyzed to determine carbon and nitrogen con- or by pleurocarpous mosses. tents by high temperature combustion and thermocon- Sampling sites were located within 10 black spruce ductometric detection (2400 CHN Elemental Analyzer, stands that respectively burned in 2002, 2001, 1998, PerkinElmer Corp., Norwalk, CT).