Seed banks in alpine soils
The concept of seed banks
The viable seed population in soils is described as a "seed bank". The concept includes, that seeds are buried and survive for more than a season (or winter) in the soil remaining dormant. Seed banks are a pool of genotypes for future recruitment. Seed longevity in alpine soils is poorly known, but the general view is that at least in early successional alpine habitats most seeds germinate in the season after dispersal. Erschbamer et al. (1997) found, however, surprising high numbers of seeds in moraine soils. It should be noticed that soils generally are not a safekeeping place and seed banks are constantly plundered by predators and are prone to the attack of fungi.
Stored at low temperatures alpine seeds were found to remain viable over several years. At freezing temperatures, seed longevity seems to be almost unlimited.
| Number of seeds in alpine soils | |||
| Type of vegetation, site |
Number of all species
(seed bank only) |
Seed bank
(n m-2) |
Ref.a |
| Dolomite grassland, Alps (2400 m) | 35 (11) | 1400 | 1 |
| Acidic silicate grassland, Alps (2450 m) | 44 (15) | 1900 | 1 |
| Open grassland/fellfield, Alps (2600 m) | 57 (33) | 1350 | 2 |
| Carex firma community, Alps (2300 m) | 56 (22) | 1500 | 2 |
| Festuca grassland, Caucasus (2750 m) | 55 (24) | 1190 | 3 |
| Tall herbfield, Caucasus (2700 m) | 38 (16) | 3850 | 3 |
| Snowbed, Caucasus (2700 m) | 22 (19) | 2800 | 3 |
| Geum turf, Beartooth Mts. (3200 m) | 54 (44) | 3800 | 4 |
Examples for emergent seed bank sizes in alpine vegetation (rounded numbers from
germination trials in warm greenhouses). Species numbers include all, even very rare
species. Aliens never exceeded 3 species.
a
1, Hatt (1991);
2, Diemer and Prock (1993);
3, Onipchenko (1994);
4, Chambers (1993)
Dormancy
As in species from the lowland the behavior of alpine species in germination studies is highly variable and species specific. Nevertheless, most germination events at high altitudes occur early after snow-melt, when soils are still wet. The short vegetation period is a challenge for the success of most seedlings.
Dormancy, enforced by unfavorable environmental conditions seems to be a rather general feature for alpine plants at the end of the growing season. Indeed, under laboratory conditions seeds of most alpine species germinate readily after a period of wet-cold storage.
Remarkably, Söyrinki (1938) who screened a large number of alpine species for their germination behavior observed that after a first rapid wave of germinations, almost a third of the studied species exhibited additional germination events delayed over several weeks, thereby probably reducing the risk of recruitment failure in a bad season.
Environmental conditions at high altitudes limit considerably germination success. In the field, the percentage of germinating seeds is usually very low (between less than 1 % and at maximum 10-15 %). Temperature is the prevailing factor influencing germination of alpine species. Surprisingly high temperatures are required for optimal germination in cold climates (Fig. 1). Similar results were obtained for tropical alpine species (Fig. 2).
