Jones and Henry 2003

Jones GA, Henry GHR. 2003. Primary plant succession on recently deglaciated terrain in the Canadian High Arctic. Journal of Biogeography 30: 277-296.

These authors examined five glacial foregrounds on Ellesmere Island, one intensively and the other 4 “extensively”, to determine patterns of succession among plant communities on sterile ground. The ecological literature recognizes several different modes of succession, including a categorization by Henry and Svoboda (1987) based on the relative strengths of biotic and abiotic factors. This model of succession recognizes 3 modes; directional succession with species replacement, directional succession without species replacement, and non-directional succession without replacement. They are arranged in increasing importance of abiotic factors, referred to here as “environmental resistance”, which operates in opposition to “biological driving forces”.

In temperate regions, where much of the relevant ecological theory has been developed, biotic factors are mainly competition. In the High Arctic, a successional pattern consistent with directional-with-replacement was found, demonstrating that this can occur even in environments with obviously severe abiotic factors. However, these authors argue that the biotic factor driving this succession was probably not competition, because total plant cover remains below 10% by area even at the fourth stage recognized here, and species richness is always very low. The polar oasis landscape with 80-100% plant cover was never reached within the approximately 50-year old glacial forelands examined by these authors, though it is likely that competition is important in that “stage 5” level of High Arctic succession.

Other biotic variables suggested playing a role in successional dynamics in the High Arctic included facilitation and life-history characteristics. These factors are not independent; later successional species such as Salix arctica appear not to be able to establish until soil fertility has been improved by mats of very-early-colonizing mosses, and are long-lived, slow-growing species that contribute little to the early seed bank and seed rain. Thus, multiple plant and environmental characteristics appear to interact when structuring early communities.

I read this paper to try to gain some understanding of ecological succession and the role of time-since-deglaciation among the ecosystems of Alexandra Fjord. Rather than being distinct successional stages in sequence as I had previously supposed, it appears the various lowland ecosystems are all of a similar age, and have different vegetation communities as a result of other factors besides simply relative proximity to the Twin Glacier. Dryas integrefolia and Cassiope tetragona were important parts of this study, and both appear in stage 4, after primary-colonizing mosses, and early-colonizing forbs such as Papaver radicatum and early-colonizing deciduous shrubs like Saxifraga spp. Both Dryas and Cassiope form associations with mycorrhyzal fungi, a requirement that may slow their colonization of novel habitats; earlier-spreading plants do not form these associations, and instead may be limited by seed dispersal.

This was helpful in organizing the structure of the manuscript I am currently working on, which will describe some of the soil biotic communities both in the Alexandra Fjord lowlands and in the adjacent polar desert. It is not a simple story of succession from one ecosystem to the next, but succession does play a role.