| Summary: | Maritime tree limits are rarely defined or addressed in the scientific literature. It has been proposed that maritime tree limits are ultimately set by airborne salt inducing top shoot dieback. The maritime tree limit would then be at the point of zero average net height increment. In order to evaluate this hypothesis, survival, top shoot lengths, shoot dieback and net height increment were monitored during a six year period in an experimental belt of black cottonwood (Populus trichocarpa) clones extending 693 m inland from an exposed 29 m high sea cliff on Heimaey Island off the south coast of Iceland (63° 26’ N, 20°18’ W, 37-50 m a.s.l.). Survival and net height increment increased with distance from the coast line. Zero net height increment during six consecutive years of study was at 510 m from the coastline. Annual net increment at 600 and 693 m from the coast was 1.6 and 3.3 cm year-1, respectively. Survival rate of all clones combined was significantly explained by a logit model of the inverse of the distance to the coast. According to that model estimated limits of 1%, 50% and 75% survival were at 109, 280 and 448 m from the cliff, respectively. Trjámörk við sjó eru sjaldséð umræðuefni í vísindaritum. Á það hefur verið bent að nærri opnu hafi setji kalskemmdir á toppsprotum vegna sjávarseltu trjágróðri hæðarmörk. Trjámörk við sjó verða þar sem kalskemmdir eru jafnar eða meiri en hæðarvöxtur trjánna þannig að trén hækka ekkert. Til að meta þessa tilgátu var fylgst með lifun, lengdarvexti toppsprotans, lengd sprotakals og hækkun trjánna á sex ára tímabili í klónatilraunabelti af alaskaösp (Populus trichocarpa) sem náði 693 m frá skjóllausum 29 m háum sjávarhömrum á Heimaey (63° 26’ N, 20°18’ W, 37-50 m y.s.). Trén hækkuðu hraðar og lifun var betri með aukinni fjarlægð frá hafi. Nær ströndinni en 510 m hækkuðu trén ekkert á þessu sex ára tímabili. Árleg hækkun trjánna var 1,6 cm ár-1 við 600 m en 3,3 cm ár-1 693 m frá ströndinni. Lifun allra asparklóna mátti skýra með logit-falli af andhverfu fjarlægðar ...
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