Ffd First Flowering

Fig. 4.24 A triangular ordination of flowering phenology in 80 species from Latnjajaure, Swedish Lapland. FFD, first flowering day (Julian day number); PI, phenology index; E, early; L, late; and D, delayed. The dates when 10%, 50%, and 90% of the valley is snow free are inserted as lines. The dotted circles represent two species each. Abbreviations: Aa, Arctostaphylos alpina; Aba, Arabis alpina; Ana, Antennaria alpina; Bn, Betula nana; Ca, Cerastium alpinum; Cb, Cardamine bellidifolia; Ch, Cassiope hypnoides; Cr, Campanula rotundifolia; Cs, Calamagrostis stricta; Ct, Cassiope tetragona; Cu, Campanula uniflora; Cxa, Carex atrofusca; Cxa-s, Carex aquatilis ssp. stans; Cxb, Carex bigelowii; Cxc, Carex capillaris; Cxf, Carex fuliginosa; Cxl, Carex lachenalii; Cxp, Carex parallela; Cxr, Carex rariflora; Cxru, Carex rupestris; Cxs, Carex saxatilis; Dd, Draba daurica; Df, Draba fladnizensis; Dl, Draba lactea; Dn, Draba nivalis; Do, Dryas octopetala; Ea, Eriophorum angustifolium; Ef, Euphrasia frigida; Eh, Empetrum hermaphroditum; Es, Eriophorum scheuchzeri; Eu, Erigeron uniflorus; Fv, Festuca vivipara; Gn, Gentiana nivalis; Gt, Gentianella tenella; Ha, Hierochloe alpina; Jb, Juncus biglumis; Jt, Juncus triglumis; La, Lychnis alpina; Lza, Luzula arcuata; Lzs, Luzula spicata; Mb, Minuartia biflora; Mr, Minuartia rubella; Ms, Minuartia stricta; Od, Oxyria digyna; Pal, Poa alpina; Par, Poa arctica; Ph, Pedicularis hirsuta; Pha, Phippsia algida; Phc, Phyllodoce caerulea; Piv, Pinguicula vulgaris; Pl, Pedicularis lapponica; Pn, Potentilla nivea; Poc, Potentila crantzii; Pog, Poa glauca; Pov, Polygonum viviparum; Pp, Poa pratensis; Pyn, Pyrola norvegica; Ra, Ranunculus acris; Rg, Ranunculus glacialis; Rl, Rhododendron lapponicum; Rn, Ranunculus nivalis; Rp, Ranunculus pygmaeus; Rr, Rhodiola rosea; Sa, Silene acaulis; Sh, Salix herbacea; Sp, Sibbaldia procumbens; Sw, Silene wahlbergella; Sxa, Saxifraga aizoides; Sxc, Saxifraga cernua; Sxcp, Saxifraga cespitosa; Sxn, Saxifraga nivalis; Sxo, Saxifraga oppositifolia; Sxr, Saxifraga rivularis; Sxs, Saxifraga stellaris; Sxt, Saxífraga tenuis; Ta, Thalictrum alpinum; Tp, Tofieldia pusilla; Ts, Trisetum spicatum; Va, Veronica alpina; Vu, Vaccinium uliginosum. (Reproduced with permission from Molau et al., 2005.)

Saxifraga Stellaris
Fig. 4.25 Saxifraga oppositifolia flowering profusely at the limit of its most northerly distribution 83° N in Peary Land (Greenland) and showing the tufted arctic form that is common at high latitudes. (Photo Dr Jean Balfour.)

next generation, even though they may have failed to produce seed (Teeri, 1973).

A comparative study of the alpine sedges Carex curvula and C. firma has shown that like Saxifraga oppositifolia, both Carex species are highly dependent on the date of snowmelt for the timing of their reproductive processes (Wagner & Reichegger, 1997). Both species can compensate for late snowmelt by shortening the time that is required for the emergence of their flowers to as little as 8 days with C. firma and 14 days with C. curvula. Despite this flexibility, both these species exhibited the characteristic impoverishment of seed production common to early flowering species with the proportion of ovules that ripened to mature seeds (S/O ratio) being only 0.3 in C. firma and 0.64 in C. curvula. Seed germinability from these marginal sites was poor with none for the C. curvula seeds and only 20% of the C. firma seeds germinating during a two-year period of observation. In the more sunlit sites seed germination was more successful than from the shaded northern slopes with up to 28% of C. curvula seeds germinating over two years. Clearly these studies show that length of growing season rather than temperature makes the sites marginal for sexual reproduction. Predictions as to the effects of climatic change on these alpine species will not depend directly on temperature but on depth of snow banks and the length of the potential growing season.

It is therefore not surprising that in relation to flowering and seed production, the arctic flora shows strong correlations between flowering phenology and snow cover duration, combined with particular reproductive strategies for early and late flowering species. Gynodioecious and dioecious breeding systems are abundant only among early flowering species, whereas apomixis and vivipary are restricted to the late flowering species. The variation in ploidy levels among species increases from early to late flowering. As an overall generalization, these differing reproductive strategies characterize the early flowering groups as preferring the risks that are associated with pollen production and dispersal while late flowering groups face the risks of reproduction as seed producers (Molau, 1993a).

Molau describes such early flowering species as pollen-riskers. Although pollen may be wasted in these species the seeds that are produced have ample time for ripening. The converse situation of late flowering has a greater probability of achieving pollination but a deterioration in growing conditions at the end of the growing season can bring about a failure of seed ripening and such species are described as seed-riskers. A ten-year study of time of flowering in Swedish Lapland (Molau et al., 2005) has shown that there is a regular pattern in the timing of flowering between the different species, and the seed-riskers are identified as the group most likely to benefit from climatic warming (Fig. 4.24).

4.8.1 Annual arctic plants

In the Arctic the reproductive season is so short that most species are perennials and annual species are few. Probably the largest annual plant in the Arctic is the mastodon plant Tephroserispalustris subsp. congesta

(syn. Senecio paludosus; Figs. 4.26-4.27). In the early stages of growth, the leaves, stem, and flower heads are covered with translucent hairs, producing a 'greenhouse effect' close to the surface of the plant, essentially extending the growing season by a few vital days by allowing the sun to warm the tissues, and preventing the heat from escaping. It is claimed that the species is 'semelparous^ (flowering once), and dies completely after having flowered and produced seed. However, in high latitudes, plants in which the flowers of the first year are killed by early frost may flower and fruit the following year (Aiken et al., 1999). The species is widespread, occurring throughout the northern hemisphere from Canada across Beringia to Eurasia. The most northerly occurrence is at 72° N on Prince Patrick Island, one of the most inaccessible islands in the Canadian Arctic and surrounded by sea ice all year round (Figs. 4.26-4.27).

Other annual species found in the Arctic are in the Polygonaceae and include Ray's knotweed (Polygonum oxyspermum subsp. rayii) and the widespread and ancient Iceland purslane (Koenigia islandica). Ray's knotweed is a declining Atlantic species which extends its distribution to the arctic coasts of Norway and the Kola Peninsula but occurs sporadically, particularly in the more northern shores of the British Isles (Fig. 4.28).

Koenigia islandica (Fig. 3.5) deserves special discussion for our understanding of how it achieves its remarkable ability to complete its life cycle in a single cool, short growing season at high latitudes. The genus as a whole comprises six species that exemplify their derivation from montane ancestors of a small group of high mountain dwelling species displaying adaptive radiation into diverse areas with short growing seasons. Five out of the six species are now confined to high mountain areas in south-eastern Asia, primarily in the Himalayas, whereas the sixth, Koenigia islandica, has spread to arctic and alpine areas in the northern hemisphere and even penetrated to the fringes of Antarctica in the Tierra del Fuego (Fig. 3.5).

Iceland purslane (Koenigia islandica) shows a progressive reduction in size in regions with very short summers and severe climatic conditions (Hedberg, 1997). Despite the reduction in size of the vegetative parts the seed is notably large for such a small plant. This is, however, a general characteristic of many annual species that use a plentiful maternal endowment in seed

Mastadon Locations
Fig. 4.26 Canadian distribution of the mastodon plant (Tephroseris palustris), the largest annual plant to be found in the Canadian Arctic with its most northerly location at 77° N on Prince Patrick Island. (Reproduced with permission from Aiken et al, 1999.)
Plants Found Alabama
Fig. 4.27 Mastodon plant Tephroseris palustris var. congesta the largest annual plant to be found in the Canadian Arctic. (Reproduced with permission from Aiken et al., 1999.)

reserves to facilitate prompt growth and the avoidance of an initial lag phase in their development. A study of the germination, growth and flowering of this arctic-alpine annual (Heide & Gauslaa, 1999) found that seeds germinated poorly at temperatures up to 18 °C, with an optimum at 24 °C (89% in 10 days). Scarified seeds germinated rapidly, and reached 100% germination in 3 days at 21 °C. Flowering was extremely rapid and independent of day length, even in a high-arctic population from 79° N. In full summer daylight anthesis was reached 24 days after germination and seeds ripened after a further 12 days at 15 ° C. It was concluded that a conservative seed germination strategy, diminutive size and rapid development together with low temperature optima for growth and reproduction, and indifference to day length for flowering are all important adaptations for the success of an annual plant in high-arctic and highalpine environments.

Ecological Limits

Fig. 4.28 Ray's knotweed (Polygonum rayii) growing as an annual plant on the north-west coast of Orkney at the end of the growing season in October. This species can grow as an annual or sometimes as a biennial or short-lived perennial and has a distribution range that reaches arctic shores (see text). (Inset) Detail of flowering shoot.

Fig. 4.28 Ray's knotweed (Polygonum rayii) growing as an annual plant on the north-west coast of Orkney at the end of the growing season in October. This species can grow as an annual or sometimes as a biennial or short-lived perennial and has a distribution range that reaches arctic shores (see text). (Inset) Detail of flowering shoot.

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