Seedling root growth of six broadleaved tree species grown in competition with grass under irrigated nursery conditions

Pre-treated seeds of ash. silver birch, field maple, hawthorn, rowan and sycamore were sown into open nursery beds half of which were then over-sown with grass seed. After germination most species were harvested at approximately weekly intervals. Height, dry weights, lengths of roots. and numbers of lateral roots and root tips of tree seedlings were assessed. Overall, competition with grass had little effect on seedling size but appeared to reduce development of the lateral root system. However, results were very variable both within and between species. and differences observed were often only indicative and not statistically significant. Competition tended to increase allocation of biomass to roots and the length of the tap-root, but reduced total length of the root system. In general, on a length basis, competition with grass had no effect on the number of 1st order laterals on the tap-root, but the total number of root tips on the root system declined. The response to competition varied with species but differences could not be related simply to competitive ability. The small effects of grass competition may be related to the short duration of the experiment and the irrigation regime used.