Increasing Population Density and Seed Production with Altitude in Eritrichium nanum (Boraginaceae)—an Arctic Alpine Obligatory Seeder

Figures & data

FIGURE 1. Map of investigated sites. Measurements: • (population density); ▵ (population density and seed weight); ▴ (population density, seed weight, and seed number). (1) Grauson (Cogne, Val d'Aoste, Italy). (2) Zwischbergen (Saas, Wallis, Switzerland). (3) Claudio e Bruno (Formazza, Piemonte, Italy). (4) Passo Cristallina (Bedretto, Ticino, Switzerland). (5) Pazolastock (Oberalp, Graubünden, Switzerland). (6) Passo Scuro (Leventina, Ticino, Switzerland). (7) Grevasalvas (Maloja, Graubünden, Switzerland). (8) Grialetsch (Sils, Graubünden, Switzerland). (9) Piz Nair (St. Moritz, Graubünden, Switzerland). (10) Piz Lagalb (Bernina, Graubünden, Switzerland). (11) Sass Capell (Arabba, Dolomiti, Italy). (12) Porta Vescovo (Arabba, Dolomiti, Italy). (13) Grosser Hafner (Maltatal, Kärnten, Austria). (14) Faschaunereck (Niedere Tauern, Kärnten, Austria). (15) Reitereck (Niedere Tauern, Kärnten, Austria). (16) Mangart (Tarvisio, Alpi Giulie, Italy). (17) Triglav (Planika, Julic Alps, Slovenia)

FIGURE 2. Population density of Eritrichium nanum in plots of 1 m² (% cover) with altitude in the European Alps. (a) Zwischbergenpass: data of 1996. The population density increases significantly with increasing altitude (R² = 0.581, n = 16, P < 0.001). (b) Permanent plots: data of 1995; Claudio e Bruno, 1996. The population density increases significantly with increasing altitude (R² = 0.741, n = 13, P < 0.001). (c) Eastern Alps: data of 1996; Triglav, 1997; Mangart, 1998. The population density increases significantly with increasing altitude (R² = 0.471, n = 27, P < 0.001). (d) Summary: mean per 100 m section. Data of 1995; Passo Cristallina, 1994; Zwischbergen, Claudio e Bruno, Dolomits, and Austrian Alps, 1996; Triglav, 1997; and Mangart, 1998 (see Table 1). The mean population density per 100 section increases significantly with increasing altitude (R² = 0.659, n = 11, P < 0.01)

FIGURE 3. Seed number of Eritrichium nanum in 13 permanent plots of 1 m² in relation to increasing altitude in the Swiss Alps (data of 1995; Claudio e Bruno, 1996). The seed number increases significantly with increasing altitude (R² = 0.36, n = 13, P < 0.05)

FIGURE 4. Annual variation of flowers, fertilized flowers and seeds of Eritrichium nanum in 8 plots at 3 sites: (a) Piz Nair (1992–1996), (b) Piz Lagalb (1992–1996), (c) Passo Scuro (1994–1997, 1999)

FIGURE 5. Mean seed weight of Eritrichium nanum, of related species (Lappula squarrosa and L. deflexa, to the left) and of species from the same habitat (Leucanthemopsis alpina, Moehringia cilliata, Silene acaulis, Cerastium pedunculatum, Achillea moschata, Minuartia sedoides, Cerastium uniflorum, Saxifraga oppositifolia, Saxifraga exarata and Saxifraga bryoides, to the right)

FIGURE 6. Mean seed weight (mg, n = 50) of Eritrichium nanum in 13 plots of 1 m² in relation to altitude in the European Alps (data of 1990–2001; R² = 0.52, n = 13, P < 0.01)

TABLE 1 List of investigated sites. The population density was investigated in all 69 plots; the seed number/m² in 13 permanent plots at sites 3, 5, 8, and 10; and the seed weight from material originating from sites 2, 3, 5, 8, and 10

TABLE 2 Seed production of Eritrichium nanum (1992–1999)