This thesis is about coexistence mechanisms in a guild of seven species of annual
plants that inhabit dry, open, compacted ground in Silwood Park, Berkshire.
Annual plants were chosen for the study because of the importance of obtaining
whole-generation estimates of the vital rates, and because short-lived plants help/hold
out the prospect of being able to assess the importance of year-to-year variation in
the rates of recruitment, growth, survival and fecundity.
The field work was carried out at Pound Hill for the seed bank experiment, at Walled
Garden for the seed dispersal experiment and at Ashurst for the main experiment in
Silwood Park, Berkshire. The location was chosen because the area was already
fenced and beds were laid out for a previous pilot study experiment in 1996.
The intention was to have a range of contrasting ecologies within our guild of annual
plants. All species were capable of germination in autumn followed by over-winter
survival as rosettes, and then rapid growth and early seed set in spring. Some species
were immediately precluded from consideration as a result of their thuggish
behaviour in the pilot studies.
The final choice consisted of a grass (Aira praecox), a legume (Ornithopus
perpusillus), three contrasting herbs (Myosotis discolor (Boraginaceae), Cerastium
glomeratum (Caryophyllaceae) and Veronica arvensis (Scrophulariaceae)), and two
tiny crucifers (Erophila verna and Arabidopsis thaliana). All were locally frequent
on gravel paths and other compacted open habitats within Silwood Park.
The thesis describes 7 separate replicated experiments, each carried out over 5
years: monocultures of each of the seven species; saturation sowing; two-species
mixtures (21 of them) and multispecies mixtures.
I show clear pattern of year effects in both inter and intra-specific density dependence. The time series experiments are backed up by quantification of seed dispersal
and seed bank dynamics
