The long term effects of clearcutting on the diversity and abundance of Oribatid (Cryptostigmata) mites of Western Newfoundland balsam fir (Abies balsamea) forests

Dwyer, Eileen E. (1995) The long term effects of clearcutting on the diversity and abundance of Oribatid (Cryptostigmata) mites of Western Newfoundland balsam fir (Abies balsamea) forests. Masters thesis, Memorial University of Newfoundland.

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Abstract

In an attempt to assess long-term effects of clearcutting on oribatid mite populations, oribatid species diversity and distribution were examined in three different aged forest stands (old - uncut, 60 years and 40 years old regrowth) within balsam fir (Abies balsamea) - fern (Dryopteris) (FD) and a balsam fir - horsetail (Equisetum) (FE) forest types. A total of 360 and 120 soil samples (10 cm x 10 cm x 10 cm) were taken from the two forest types, respectively. Each sample was subsequently divided into upper and lower 5 cm halves to assess vertical distribution of mites. Both species diversity and abundance decreased with increasing soil depth. In addition, relative abundances of smaller oribatid species such as Oppiella washburni and Suctobelbella spp. increased in the lower layers whereas larger species such as Parachipteria travei decreased. -- A series of microhabitat samples were also collected in the balsam fir - fern forest to include as many oribatid species as possible. One species, Eueremaeus marshalli, occured only in microhabitat samples. Average abundances of oribatid mites per sample ranged from 344 to 1894 in FD and from 501 to 886 in FE forest types. -- In total, 91 species representing 41 families were collected including 17 new generic and 35 new species records for Newfoundland. Haplozetes sp. was also collected representing a new genus record for Canada. The ecology of all species collected is described. The number of species occurring in any one site ranged from 55 to 65 in the FD sites and from 51 to 59 in the FE sites. Populations in both forest types were dominated by the same common species: Eniochthonius minutissimus, Synchthonius crenulatus, Steganacarus thoreani, Nanhermannia bryophila, Tectocepheus velatus, Oppiella washburni, Suctobelbella spp. and Parachipteria travei. Several species were collected from only one forest type and may be useful indicators of differing environmental conditions. In particular, Epidamaeus longitarsalis, Eupterotegaeus sp., Fuscozetes setosus and Dentachipteria sp. were characteristic of FD sites whereas Gozmanyina majestus, Ceratozetes gracilis, Sphaerozetes arcticus, Eupelops sp. and Propelops canadensis were characteristic of FE sites. -- Separation of the sample sites through cluster and TWINSPAN analysis indicated differences in species diversity and relative abundances between age classes of both FD and FE forests. However, this separation was most pronounced between the sites of FD forest. Species richness and diversity tended to be highest in the forty year old sites of the FD forest and in the old sites of the FE forest. -- Oribatid population data from the FD forest was further assessed in relation to soil and vegetation data from the sites using principle components and discriminant function analysis. This indicated that different forest ages were associated with different soil and vegetation characters as well as different mite species. -- Long-term effects of clearcutting vary between forest types and are more obvious in species diversity and relative abundances than in total oribatid abundances. These variations in oribatid community structure between the forest age classes are apparently related to successional changes in the maturing forests.

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