Geographic variation in seed-setting by heather (Calluna vulgaris (L.) Hull) in the Scottish Highlands
To assess the influence of oceanicity, altitude and latitude on spatial and temporal variations in the fecundity of heather (Calluna vulgaris (L.) Hull) in Scotland.Location
Mountain study areas located throughout the Highlands of Scotland.Methods
Seed-set was assessed as the number of seeds per heather capsule. At each mountain, the mean number of seeds per capsule was recorded at five sites spaced at 150 m height intervals up to heather’s upper altitudinal limit. Germinability was measured by incubating seeds at 20 °C after chilling at 2–3 °C for 6 weeks. Collateral cultivation of heather cuttings taken from sites below 450 m and above 900 m determined whether seed-setting and germinability were under genetic or environmental control.Results
Neither seed-setting nor germinability was under genetic control. Seed-setting generally declined with increasing site oceanicity and altitude but the effect of latitude was ill-defined. Mean maximum temperature and total rainfall during August–September were the principal environmental controls. Germinability varied less widely but tended to be least towards heather’s upper altitudinal limit.Main conclusions
Seed-setting by heather varied in both space and time, depending mainly on late summer warmth. It was always copious below about 600 m but was sparse or even failed altogether on higher ground, particularly in the hyperoceanic west Highlands.