Eco-Geographical Relations of the Bj~Rn~Yavascular Flora, Svalbard

Eco-geographical relations of the Bj~rn~yavascular flora, Svalbard TORSTEIN ENGELSKJ0N Engelskjen, T. 1986: Eco-geographical relations of the Bjerneya vascular flora, Svalbard. Polar Research 5n.~19- 127. A renewed survey of the flora of Bjemeya (74" 31") has yielded a total of 54 native vascular species. fi Details of their distribution are provided by local maps and vertical frequency tabulations. Soil preferen- ces of species and various plant communities are outlined. The general climate and microthermal conditions of the prevailing vegetation place Bjemeya as a pronouncedly maritime part of the Svalbard archi- pelago, supporting mainly hygrophilous and chionophilous plant communitites and species. Only half of the island's vascular species persist at elevations above 200 m ad.. corresponding to a heat sum of July and August below approximately 190 Degree-Days. Ice-cored peat mounds coated by Rharomitrium lanuginosum were discovered on plateaux above 400 m elevation. The impact of the Vistula glaciation is discussed in view of Quaternary evidence from the Barents Sea area. Probably only one third of the present vascular flora could endure full-glacial conditions in possible ice-free cliffs on the coast of Bjerneya. Torstein Engelskjon. Botanical Garden and Museum, Universitjl of Oslo, Trondheimsveien 23b. 0560 Oslo 5. Norway. December I985 (revised September 1986). 1. Introduction genera, such as Draba, Dupontia, Festuca, Poten- Since the floristic survey published by Engel- tilla. and Puccinellia s. lat. I generally adopt pre- skjan & Schweitzer (1970) of the vascular flora liminary results from an ongoing cytotaxonomi- of Bjamaya (Bear Island), Svalbard, little cal study of vascular plant species from Bjamoya botanical work was done until 1983, when the and Spitsbergen (Engelskjan & Schweitzer 1970; present author joined an expedition of Tromsa Engelskjan 1979, and unpublished results). Museum to Bjamaya, 9 to 28 August. The nomenclature of bryophyte species fol- New observations of the flora and vegetation lows hell(1956) and Nyholm (1954-69), and during this stay make up the foundation of the of lichens, Santesson (1984) and Walker (1985). present treatment. An outline of the plant communities of Bjamaya is provided, and the thermal and edaphic conditions are related to the deve- 2. The climate of Bjornoya lopment of vegetation and plant distributions The meteorological station is situated on the N within the island. Notes on altitudinal belts are coast, at 74"31'N, 19"E, 15 m above sea level. included, as well as notes on the discovery of The extensive northern plain of the island undu- Rhacomitnum lanuginosum peat mounds at app- lates between 15 and 50 m a.s.1. This relief causes roximately 400 m above sea level on the southern only insignificant deviations from the prevailing mountain plateaux of the island. maritime climate observed at the station. Moun- Distribution maps are given for the 54 native tains to the SE and S reach altitudes from 410 to vascular species. 535 m ad., and temperatures there are lower Brattbakk (1984) visited the island to study the owing to the vertical temperature gradient and potential of the vegetation for reindeer grazing. orographic cloud formation (Steffensen 1969, He contributed an interesting floristic novelty, 1982). The thermal climate of Bjarnaya is shown Saxifaga foliolosa R. Br. in Table 1 and compared with other North At- The taxonomy and nomenclature of Svalbard lantic, Arctic stations. Due to inconsistency of vascular plants are still ambiguous for several the observation material, two sets of mean 80 monthly temperatures are presented. One is for the period 1946-65 and is continuous, with a few breaks of homogeneity due to moving of stations (Steffensen 1969). The other is the Stan- dard normal series (193 1-60) with interpola- tions of breaks during World War I I. Differences between these series reflect a secular decline of temperatures at the end of the 1950s, which lasted up to the late 1960s, e.g. on the island of Jan Mayen (Steffensen 1969, pp. 266-267). Complex phenomena such as secular climatic change could not be dealt with here, although an analysis would be of interest in relation to distribution and performance of North Atlantic, Arc- tic vegetation. Some derived parameters of ecological signi- ficance are listed in Table 2 for the same Arctic stations. Heat sums were calculated as Degree- Days, June-September (DD-4) and July- August (DD-2). all based on the 1946-65 period. Cloudiness and mean annual precipitation are summarized for the period up to 1965, annual sunshine hours are given when available, and wind chill and cooling power calculated according to the formulae of Siple & Passel (1945) and Vinje (1962). A special feature of Bjamaya and other Arctic islands is the foggy summer. The number of days with fog occurring at 7, 13, or 19 C.E.T. is given in Table 3A for the months June-September. We see that Hopen is most frequented by Arctic seafog. A closer study of the original tables (Stef- fensen 1969, Table 11) reveals that Bjamaya tends to have foggy and overcast days concentra- ted to July and August, which is also reflected in the low number of annual sunshine hours. The figures from Isfjord Radio on the W coast of Spitsbergen indicate a more favourable radiation climate. Bjamaya compared with North Norway (Table 3B) shows a much higher fog incidence than Vardo, which is also exposed to drifting fog from the Barents Sea. The thermal regimen of Bjamaya is comparable to that of Jan Mayen, but is less oceanic with regard to annual amplitude of temperature and total precipitation. Hopen is cooler than Bjarnoya throughout the year, whereas Isfjord Radio experiences slightly higher July tempera- 81 Table 2. Some basic and derived climatological parameters from Bjamoya and some other Norwegian Arctic stations. Data compiled from Steffensen (1969) and Andresen (1979). Comparable, 1946- 65 20 year means. Wind chill/cooling power computed according to Siple & Passel (1945) and Vinje (1962). Station Precipi- Degree-Days Sunshine Clear Overcast Wind chilVcooling power tation June- July- hours, days, days, June July August mm Sept. August annual June- June- DD-4 DD-2 Sept. Sept. Bjornaya 357 405 265 613* I .7 93.3 898132 822129 835/30 Jan Mayen 698 475 3 10 1) 1.1 86.4 856129 7801'27 758126 Hopen 368 145 130 2) 3.6 88.4 875/28 822/26 807/26 Isfiord Radio 378 355 270 1066** 4 73 876/30 804/28 823/29 * 1960-65 I) No record; mean cloud cover 6.7 octas ** 1956-65 2) No record; meancloud cover6 octas Table 3. Fog conditions on Bjamaya and some other exposure to this factor than the other Arctic sta- Norwegian Arctic and hemi-Arctic stations. 1946-65 tions considered during the summer months. means. However, Semlja Frantsa Josifa, at nearly 82"N, A) Cases of fog as number of days through June- has an even less favourable thermal climate September with fog at specified hours. Data from Stef- (Miiller 1982), as have Kong Karls Land and fensen (1969). Sjuoyane in the far north and east in the most sea Station At 07 At 13 At 19 ice frequented parts of Svalbard (Norsk Polar- institutt, unpublished observations). Bjamaya 19.3 14.6 17.9 Jan Mayen 16.8 12.7 12.2 The annual precipitation on Bjornoya is below Hopen 19.6 17.1 20.0 400 mm like in most Arctic regions. High humidi- Isfjord Radio 7.1 4.9 6.6 ty of the ground and vegetation cover is main- tained by the low temperatures and heavy cloud B) Monthly fog frequency: Percentage of days with cover, and fog precipitation is also considerable. cases of fog at Bjamaya and at Varda, East Finnmark, Accordingly, Bjornaya has a maritime Arctic North Norway. climate with low temperatures and humid con- Station June July August September ditions. At comparable latitudes in the North Atlantic this climatic oceanity is only surpassed 14 24 22 II Bjamaya by Jan Mayen. Varda 4 5 7 I 3. The vertical temperature gradient tures than Bjarnoya. Other stations in Spits- Data from radiosonde ascents between 10 and bergen are not compared in detail here, but inner 22 August 1983 were utilized to estimate the air Isfjord (Longyearbyen) has higher summer ave- temperatures at higher levels of Bjornoya. The rages and maxima than Isfjord Radio, and less upper air soundings start from the meteorologi- fog. cal station and are performed regularly at 1200 The heat sums for June-September and and 2400 hrs. G.M.T. The air temperature July-August (Table 2) place Bjamaya in a posi- decreases linearly with altitude, but stratification tion between Jan Mayen and Isfjord Radio, and inversions occur at various levels. The first whereas Hopen is much cooler than most other of these so-called significant levels is usually stations. crossed between 950 and 850 mb air pressure, The indices of wind chill and cooling power which corresponds to 500-1300 m above sea entered in the same table reflect the combined level. The temperatures t, and t2 at levels HI and cold and wind stress on animals and plants. We H2 are inherent in the simplified barometric for- note that Bjornaya has a more pronounced mula: 82 P: - P, ti + I? a reference site on the N coast (Fig. I), but I H: = 1600 . (I + 0.004 -) visited most parts of the island during altogether P: + PI 2 six weeks in 1967 and 1983, recording the main plant communitites. Cryptogams were collected (Bliithgen & Weischet 1980) from representative sites, totalling 220 samples of mosses, 35 of liverworts, 150 of lichens, and a Here.

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