Demography of Short-Lived Plants in Chalk Grassland. II. Control of Mortality and Fecundity

Abstract

(1) Factors affecting the germination, survival and reproduction of field populations of a hemiparasitic summer annual (Euphrasia pseudokerneri) and two strict biennials (Linum catharticum and Gentianella amarella) were examined at two chalk grassland sites. Data are also provided on a second annual (E. nemorosa). (2) In the field, germination of E. pseudokerneri, Linum and Gentianella was restricted to a narrow 'window' of germination sites where mean turf height was only 1-3 cm. All three species germinated poorly in longer turf, and E. pseudokerneri and Linum also germinated less well in very short areas. Survival of E. pseudokerneri, Linum and Gentianella, and reproductive output of Gentianella, were higher in areas of short turf. Overall, Gentianella was the most sensitive to turf height and Linum the least. (3) Mortality rates of E. nemorosa, Linum, and (especially) E. pseudokerneri were higher during dry periods even over three years of normal rainfall, but Gentianella was not affected. (4) Experimental treatments, applied in the field, showed that E. pseudokerneri survival was decreased by adding nitrate, and increased by clipping the turf, by adding water and by excluding rabbits; E. pseudokerneri fecundity was increased by excluding rabbits and by adding phosphate; and Linum survival and fecundity were increased by regular applications of snail poison. (5) The performance of each species was affected by a unique suite of factors which varied between years.