Sigmund Hågvar

Primary Succession of Soil Mites (Acari) in a Norwegian Glacier Foreland, with Emphasis on Oribatid Species

Abstract The distribution of soil mites was studied in the foreland of the Hardangerjøkulen glacier in central south Norway, close to a glacier snout, which has been receding since 1750. Twenty sampling plots were distributed along a gradient spanning from 30 to 230 years, and five additional plots were in 10,000-year-old soil nearby. To standardize the microhabitat, all 320 soil cores (each 10 cm2 and 3 cm deep) were taken in Salix herbacea vegetation. The main focus was on oribatids, and most juveniles were identified to species. Two small, parthenogenetic species were pioneers, with high abundance in young soil: Tectocepheus velatus and Liochthonius cf. sellnicki, although their dominance values decreased sharply with time. The youngest soils also contained unidentified Actinedida and Gamasidae, and pitfall traps revealed the rather large, predatory actinedid species Podothrombium strandi. The number of oribatid species increased gradually with soil age. The oldest soil contained 19 oribatid species, but only six of them, all in low densities, were unique to this soil. Parthenogenetic species were present in all age classes of soil. Although there exist few earlier studies on mite succession in glacial foreland soil, mites are clearly among the earliest colonizers along receding glaciers.

Primary Succession of Springtails (Collembola) in a Norwegian Glacier Foreland

Abstract The Collembola succession was studied in the Hardangerjøkulen glacier foreland in south-central Norway. Twenty sampling plots 30 to 230 years of age were distributed along a chronosequence where a glacier snout had been receding since 1750. Also, five plots 10,000 years of age were sampled. All soil samples were taken in Salix herbacea vegetation, in order to standardize the microhabitat. The youngest zone (30–50 years) contained 14 springtail species, mainly large, surface active generalists. Additional pitfall catches here revealed considerable surface activity of several species, also on vegetation-free areas. Even a three-year-young moraine contained at least three springtail species. Most pioneers also occurred in older soils. The cumulative number of species increased rapidly up to about 70 years, at which age 72% of all species had been recorded. Only five species in low numbers were confined to 10,000-year-old soil. A high density of Folsomia quadrioculata and F. brevicauda was noted at 50–70 years of age, and of Tetracanthella brachyura at about 100 years. Compared to oribatid mites, a higher number of springtail species colonized pristine ground. While the two pioneer oribatids were parthenogenetic, the dominant springtail pioneers were bisexual. Springtails are among the earliest colonizers along receding glaciers.

Ancient carbon from a melting glacier gives high 14C age in living pioneer invertebrates

Glaciers are retreating and predatory invertebrates rapidly colonize deglaciated, barren ground. The paradox of establishing predators before plants and herbivores has been explained by wind-driven input of invertebrate prey. Here we present an alternative explanation and a novel glacier foreland food web by showing that pioneer predators eat locally produced midges containing 21,000 years old ancient carbon released by the melting glacier. Ancient carbon was assimilated by aquatic midge larvae, and terrestrial adults achieved a radiocarbon age of 1040 years. Terrestrial spiders, harvestmen and beetles feeding on adult midges had radiocarbon ages of 340–1100 years. Water beetles assumed to eat midge larvae reached radiocarbon ages of 1100–1200 years. Because both aquatic and terrestrial pioneer communities use ancient carbon, the term “primary succession” is questionable in glacier forelands. If our “old” invertebrates had been collected as subfossils and radiocarbon dated, their age would have been overestimated by up to 1100 years.

Primary Succession of Surface Active Beetles and Spiders in an Alpine Glacier Foreland, Central South Norway

Abstract Spiders and beetles were pitfall-trapped in the foreland of the receding Hardangerjøkulen glacier in central south Norway. At each of six sampling sites, ages 3 to 205 years, twenty traps covered the local variation in moisture and plant communities. Thirty-three spider species and forty beetle species were collected. The species composition was correlated to time since glaciation and vegetation cover. A characteristic pioneer community of spiders and mainly predatory beetles had several open-ground species, and some species or genera were common to forelands in Svalbard or the Alps. While the number of spider species increased relatively constant with age, the number of beetle species seemed to level off after about 80 years. Half of the beetle species were Staphylinidae, and contrary to Carabidae, most of these were rather late colonizers. Most herbivore beetles colonized after more than 40 years, but the moss-eating Byrrhidae species Simplocaria metallica and also certain Chironomidae larvae developed in pioneer moss colonies after 4 years. The large Collembola Bourletiella hortensis, a potential prey, fed on in-blown moss fragments after 3 years. In the present foreland, chlorophyll-based food chains may start very early. Two pioneer Amara species (Carabidae) could probably feed partly on seeds, either in-blown or produced by scattered pioneer grasses.

Aerial Dispersal of Invertebrates and Mosses Close to a Receding Alpine Glacier in Southern Norway

Abstract The 73 km2 large Hardangerjøkulen glacier in alpine, south Norway is receding. By using sticky and fallout traps, we studied the aerial transport of invertebrates in a foreland with a well-documented succession of mites, springtails, spiders, and beetles. Since mosses are pioneer plants and also food for certain pioneer invertebrates, airborne fragments of mosses were also included in the study. Sampling on 3- to 6-year-old ground revealed aerial transport of several species of mites and springtails. During 4 weeks, the fallout of microarthropods was calculated at around 1000 specimens per m2. This number may depend strongly on local variations in climate and must be treated with care. Besides typical pioneer species, some species assumed to depend on older soil were also trapped. This indicates that the ability to survive is more limiting than the ability to disperse. A few spiders assumed to have the capability for “aerial ballooning” were trapped. Moss fragments, including bulbil diaspores, were common in both trap types. Diptera were sometimes taken numerously, and in sticky traps mainly in those facing away from the glacier. Most aerial transport occurred below 0.5 m height, and the presence of sand grains in sticky traps up to this level illustrated the mechanical force of wind transport. We conclude that aerial transport helps colonization of several non-flying pioneer organisms like mites, springtails, aphids, and mosses.

Retention of Forest Strips for Bird-life Adjacent to Water and Bogs in Norway: Effect of Different Widths and Habitat Variables

In Fennoscandinan forestry, retention of forest strips as a buffer adjacent to water and bogs has long been recommended, but their biological value is poorly known and practice varies greatly. This study explored the value for breeding birds of retaining buffer strips of different width and structure, after clear-cutting in coniferous forest. The presence of birds during their nesting season was inventoried in 370 strips in south-eastern Norway. The species number per 100 m strip length increased with increasing strip width up to about 30 m width, and then remained constant up to 70–100 m width. Generalist species dominated all width categories. Important habitat factors other than strip width were basal area of spruce, short visibility and tree height. Although 11–20 m wide strips had the highest density of species and individuals per hectare, buffer strips of about 30 m width may be recommended, as narrower strips had fewer species per unit length of edge.

Food Choice of Invertebrates During Early Glacier Foreland Succession

Abstract Bryophytes from seven different genera colonized 3- to 6-year-old ground near a receding glacier in central South Norway. Microscopic studies of the gut content in pioneer invertebrates revealed that mosses were grazed upon by four species: an abundant and large Collembola (Bourletiella hortensis), a moss-eating Byrrhidae beetle (Simplocaria metallica), and two omnivorous Carabidae beetles (Amara alpina and A. quenseli). The three most abundant moss species were preferred by the moss-eaters: Pohlia filum, Ceratodon purpureus, and Bryum arcticum. Special parts of the moss plant could be selected. Three other Collembola species present were classified as herbivores because they had diatom algae in their gut, indicating that they grazed on terrestrial biofilm. Chironomidae midges hatching from young ponds represented an important element in the gut content of three common predators: the Opiliones Mitopus morio, and two Carabidae beetles Nebria nivalis and Bembidion hastii. The present data show that chlorophyll-based food chains start almost immediately on bare ground, but in a rather invisible way by tiny pioneer mosses and terrestrial biofilm with diatom algae. Pioneer mosses may be regarded as “drivers” in early animal succession, before higher plants establish. Since several of the pioneer invertebrates were herbivores or omnivores, the present community did not fit with the “predator first” hypothesis.

A melting glacier feeds aquatic and terrestrial invertebrates with ancient carbon and supports early succession

ABSTRACT More than 5000-yr-old organic material was released by a melting glacier in central southern Norway. The ancient carbon was bioavailable and supported early food chains. This was shown through high radiocarbon age in living aquatic and terrestrial invertebrates. Young ponds acted as biological oases, where ancient carbon was assimilated by larvae of various Diptera: mainly Chironomidae, but also Tipulidae and Limoniidae. Within ponds, even predatory diving beetles had a high radiocarbon age. Adult chironomid midges with a radiocarbon age of 1040 yr transported ancient carbon to terrestrial predators among beetles, spiders, and harvestmen. Ancient carbon was also assimilated by chironomid larvae downstream in the glacier-fed river, and radiocarbon dating of chironomid larvae from glacial rivers will thus be an easy way to check whether a given glacier releases bioavailable ancient carbon. Our study indicates that the ancient organic particles were very small. We refer to studies from other countries showing that glaciers collect and release ancient carbon in the form of tiny, long-transported and biodegradable aerosol particles, which stem from the incomplete combustion of radiocarbon-depleted fossil fuels. All our results would fit with this mechanism.

Succession of beetles (genus Cis) and oribatid mites (genus Carabodes) in dead sporocarps of the red-banded polypore fungus Fomitopsis pinicola

Abstract Dead sporocarps contribute to forest biodiversity by supporting a specialised decomposer fauna. However, detailed succession studies are few and microarthropods are rarely included. In a spruce-dominated forest reserve near Oslo in southern Norway, sporocarps of Fomitopsis pinicola with known age since death (0–5 years) were sampled and invertebrates extracted by Tullgren funnel. While living sporocarps of this species were rarely attacked by tunnelling invertebrates, dead sporocarps were rapidly colonised by a diverse fauna. The youngest pore layers were consumed first, and after five years, the remaining parts were strongly fragmented. Among 16 beetle species, Cis glabratus and Cis quadridens dominated. Another abundant group in dead sporocarps was oribatid mites belonging to the genus Carabodes, with a total of 10 species. Seven of these colonised during less than one year. While there were few significant changes in the density of adult Cis specimens during decomposition, and C. glabratus dominated all years, the Carabodes community underwent considerable changes. Carabodes femoralis dominated during the three first years, after which Carabodes areolatus and Carabodes reticulatus took over the dominance. These three Carabodes species are rare in Norwegian coniferous forest soil. Dead sporocarps of various polypore fungi may represent important microhabitats for sustaining the diversity of Carabodes mites in Fennoscandian coniferous forests.

Mites of the genus Carabodes (Acari, Oribatida) in Norwegian coniferous forests: occurrence in different soils, vegetation types and polypore hosts

Oribatid mites (Acari) represent a considerable part of the biodiversity in Fennoscandian forests, but our knowledge about their habitat requirements is limited. We studied 10 Carabodes species in the forest floor of seven coniferous forest types, and in dead fruiting bodies (sporocarps) of 6 species of wood-living polypore fungi in southern Norway. The most common Carabodes species in soil were rare in sporocarps, and vice versa. The density of several ground-living species was significantly influenced by vegetation type and soil type. Carabodes willmanni and C. subarcticus were considered as lichen feeders on the ground, and occurred abundantly in Cladonia-rich pine forests. Three species, C. femoralis, C. areolatus and C. reticulatus, seem to be sporocarp specialists. Their relative numbers were rather similar in dead sporocarps of five different fungal species, including annual and perennial sporocarps, soft and hard. This was in contrast to beetles from the same sporocarps, which in a previous study proved to be strongly host-specific. Although being tolerant to different fungal species, the association of certain Carabodes species to dead sporocarps could make them vulnerable in forests with little dead wood and few sporocarps.