The biodiversity of any ecosystem includes all the species present in the standing crop (i.e. the juvenile and adult population) and the pool of species stored in dormant stages (e.g. seed banks, cysts or long-lived larval stages in insects). Our project focuses on soil seed banks. Seed banks are the result of seed accumulation due to past seed production at the site and of seed arrival by dispersal (e.g. by wind or animals). In addition, seed banks are essential to the development of the vegetation: if a new species is to establish itself at a site its seeds have to be, at least for a time, part of the seed bank. In our efforts to understand the biodiversity and dynamics of terrestrial Arctic ecosystems, a better knowledge of what is stored in Arctic soils is fundamental to predicting how the vegetation can respond to change.

Many studies predict that the impact of global change will become greater in the polar regions and in this context so me questions are becoming more and more pressing, among them:

• How will the plant communities present in the Arctic today change in response to longer (or shorter) growing seasons, to dryer (or wetter) summers or to intensive grazing?
• Are some plant communities more likely to respond to change through the establishment of new individuals? Which ones? Why?
• Can we expect new species to colonize the northern regions? Which area should we monitor to measure such changes?
• Could some species already present in the soil (in a dormant stage) contribute rapidly to some vegetation change? This is of special interest since we know that the cold conditions in the Arctic may favour the persistence of viable seeds in the soil for extended periods of time (hundreds of years or more!).

These and many other questions require a thorough study of the re-vegetation potential of Arctic plant communities. Our project addresses these questions by quantifying the seeds present in the soil of two adjacent plant communities (one with abundant plant cover and the other with sparse vegetation) at each site visited throughout the Canadian Arctic.

This project was carried out in close collaboration with other groups studying biodiversity in the same terrestrial habitats across large longitudinal and latitudinal gradients. These gradients have a strong impact on the vegetation and on seed production. Firstly the climatic conditions are colder and dryer further North, and secondly the geology varies greatly throughout the Canadian Arctic. The eastern part is characterized by granitic rocks (pH generally acidic) whereas the central and western parts have sedimentary bedrock (pH generally neutral or alkaline). These gradients also have a third important element: the impact of glaciation on the landscape. In the eastern Arctic, the ice retreated more recently (5 000 to 6 000 years ago in some places) than in the western Arctic where some areas were probably not glaciated during the last glacial period (ice-free for more than 20,000 years!). Of course, parts of the Arctic are still glaciated! These conditions create a mosaic which requires a large scale approach to be properly detected and assessed.

Our specific objectives are:

1. To quantify the abundance and diversity of seeds stored in the soil of two adjacent habitats: How many seeds can we find and from how many species?
2. To compare the seeds that can germinate from these soils to all the seeds present: Are all the seeds present still viable?
3. To compare these results with the plant diversity and abundance present at the site: Are there unexpected species in the seed bank?
4. To identify patterns in soil seed bank diversity and abundance across the various gradients studied: Are there some trends that could serve to predict the re-vegetation potential of these remote habitats?

Field-work on board

This project requires a great deal of vascular plant diversity and abundance in each plant community as well as a careful collection of a known volume of soil from each site. We collaborated with the general Theme B project whose aim was to characterize the plant communities of two typical habitats at each site visited, a mesic habitat (generally heath community with 100% plant cover) and a dryer habitat with scattered plant cover (generally dominated by forbs and cushion plants). This common project involved the measuring of plant abundance and diversity within a 20m x 20m plot in each plant community using 10 random quadrats (50 cm x 50 cm).

Following the common sampling we collected, within the same quadrats (10 per plant community), the top soil (approximately 1 cm) and a deeper horizon (1 to 5 cm) of a 10 cm x 10 cm square. These samples were stored in a freezer at -4°C on board the ship and were brought back to Sweden for germination tests. In addition, in five of the 10 quadrats, a second series of samples was collected exactly the same way and adjacent to the first samples. These soil samples were dried on the ship and sent to Trois-Rivières where they will be sieved and sorted to quantify the total seed bank.

The expedition was a great success since on the first leg it was possible to collect samples at all but one site along the route (8 of 9 sites). On the second leg all sites were sampled (8 of 8 sites).

A story to follow…

The samples collected now require a lot of work before yielding the precious information we need.

The germinable seed bank samples are at present being kept in a cold room in Sweden to imitate field conditions. In December 1999 the samples will be taken out of their dormant stages and put in greenhouses to germinate. Only then will we find out how many seeds are present in the soil samples.

As for the total seed bank samples they will need to be sieved and carefully examined under a dissection microscope in order to identify all the seeds present.

The comparison of results using these two approaches will be a very exciting process and will allow questions to be answered that have not been addressed in the Arctic before. In addition, the integration of our results with the work of our colleagues should yield insightful discoveries about the dynamics and diversity of Arctic terrestrial ecosystems.

Will the poor plateaux of Devon and Ellesmere Islands reveal a potential to resemble the rich hills of Ivvavik?