Species diversity, niche metrics and species associations in harvested and undisturbed bogs

Abstract

Abstract. Competition is considered an important force in structuring plant communities and in governing niche relations, but communities recovering from disturbance, may be less governed by species interactions and less orderly organized. To address this issue, we studied species richness, abundance and patterns of association between plant species at three spatial scales (1 m2, 1/25 m2, 1/625 m2) in two ombrotrophic mires in east‐central Sweden. One was at a secondary successional stage following peat extraction 50 yr ago and the other was undisturbed. Peat extraction leads to a change in hydrology which is slowly restored by the formation of new peat. Niche breadth and niche overlap along the gradient of height above the water table were calculated for the five common Sphagnum species occurring at both mires in an attempt to better understand differences in species co‐occurrence at each mire. Species cover differed between the mires, and the number of species per plot was higher in the undisturbed community at all scales, suggesting that the degree of species intermingling was greater than at the harvested site. At all scales, the number of non‐random associations was higher, and niche overlap lower among ecologically similar species (e.g. hollow Sphagnum species) in the undisturbed mire. These differences indicate that random events are important in colonization, and that biotic interactions between neighbours later result in a higher degree of non‐randomness. In addition, we surveyed a number of abandoned peat pit sites to test the effect of disturbance for species composition at a regional scale. Ombrotrophic peat pits contained several Sphagnum species normally associated with minerotrophic mires, and species of wooded mires occurred frequently in peat pits, making them more species‐rich than undisturbed bogs. There were also Sphagnum species new to, or rare in, this part of Sweden which indicates effective long‐distance dispersal. Even 50 yr after peat extraction had ceased, the vegetation had not recovered to its original composition.

Effects of human impact and climate change during the last 350 years recorded in a Swedish raised bog deposit

“…Smaller ditches for peat cutting activities were dug east of the eastern ditch. Exploitation took place mainly during the period AD 1910-1920but lasted until 1953(Soro et al, 1999. During the Second World War peat cutting activity increased temporarily.…”

“…However, evapotranspiration during this period is also relatively low, which would have caused an increase of the water table. During this period peat cutting activities took place in the eastern part of the bog (Lennartsson et al, 1996;Soro et al, 1999) which provides explanation for the lowering in water table. The peat cutting area was nearest to the coring site during the Second World War (AD 1940-45) until the end of the peat cutting activities in AD 1953.…”

Living together and living apart: the sexual lives of bryophytes

“…Under this interpretation, Sphagnum fuscum at Fuglmyra consists of a monogamous couple in a long-term sexual relationship. Because Sphagnum fuscum creates and maintains its own hummock habitat [52], the bog at Fuglmyra could be considered the extended phenotype of a 'diploid' pair of haploid gametophytes producing trillions of spores over hundred of years for the chance that a few lucky spores establish new bogs.…”

Do vegetation patch spatial patterns disrupt the spatial organization of plant species?

“…In addition, during the early stages of colonization, random distributions arise (Kershaw, 1963;Fowler, 1990;Sole and Bascompte, 2006). Above a threshold in abundance, the probability of interactions increases, which triggers the positive feedback mechanisms that underlie plant facilitation (Bertness and Callaway, 1994;Pugnaire et al, 1996;HilleRisLambers et al, 2001) and the system moves toward a more clumped spatial organization (Aarssen and Turkington, 1985;Loehle et al, 1996;Soro et al, 1999;Sole and Bascompte, 2006). Those nonlinear interactions involve amplifications that operate through feedback loops 0ensen, 1998).…”