SEPARATION OF ALLELOPATHY AND RESOURCE COMPETITION BY THE BOREAL DWARF SHRUB EMPETRUM-HERMAPHRODITUM HAGERUP

An experimental technique was used to separate and evaluate the magnit ude of allelopathic interference relative to resource competition by t he boreal dwarf shrub Empetrum hermaphroditum Hagerup (Empetraceae). T o test for resource competition and allelopathy, respectively, Scots p ine (Pinus sylvestris L.) seedlings were grown in both the greenhouse and in the field over a 3 year period, in four different treatments wi thin E. hermaphroditum vegetation: (1) PVC tubes were used to reduce e ffects of interspecific below-ground competition; (2) activated carbon was spread on the soil to adsorb toxins leached from E. hermaphroditu m litter and green leaves, thus reducing effects of allelopathic inter ference; (3) E. hermaphroditum vegetation was left untreated to evalua te inhibiting effects when both allelopathy and resource competition w ere present; (4) PVC tubes, placed in E. hermaphroditum vegetation spr ead with activated carbon were used to determine growth of seedlings w hen both allelopathy and resource competition were reduced. Scots pine seedlings grown in untreated vegetation (with both root competition a nd allelopathy present) had the lowest shoot length and dry weight; se edlings with both allelopathy and root competition reduced (activated carbon in tube) were the largest. Reducing either root competition alo ne (tube treatment) or allelopathy alone (carbon treatment) produced s eedlings of intermediate size, but reduced competition had a greater e ffect than reduced allelopathy (although, in the greenhouse, significa ntly so only for root biomass). In the greenhouse experiment, biomass production of seedlings grown free of both interactions (carbon in tub e) was greater than the simple sum of the growth response to the indiv idual interactions (tube treatment and carbon treatment, respectively) . Larger shoot:root ratios were also found when pine seedlings were gr own without tubes (i.e. when resource competition was occurring). In t he field, the removal of allelopathy (carbon treatments) increased sho ot:root ratio when compared to the removal of resource competition. Th e study showed that two different interference mechanisms of E. hermap hroditum can be separated and quantified, and that below-ground compet ition and allelopathy by E. hermaphroditum are both important factors retarding growth of Scots pine.