It is understood (University of Florida www.ufl home page) that Camphor Laurel was a problem weed in South Florida by 1930.
According to University of Florida researchers in Education and Zoology most concerned about the serious spreading infestations of Camphor Laurel in Florida (not only southern California), frog-loss is high on the Agenda of 'probable causes' due to Camphor.
The man who is historically the largest exporter of Australian camphor laurel timber, Roy Hepburn of Lennox Head, reported in the 1950s that tadpoles in wet season pools under camphor laurels were dying. He was also the first to assert that camphor hybrids were becoming more toxic.
First experimentation to prove that northern NSW Camphor oils (of fruit, leaves, root etc) kill frog and Cane Toad larvae - tadpoles in small soil-water sized pools - was also conducted in NSW Northern Rivers. With just a couple of squeezed drops of liquid extract from fruit, leaves or root, in 250mls of water, tadpoles appear first anaesthetized, and (cf. all control specimens healthy) all die with 48 hours (Friend, 1998).
Bushwalking anecdotal evidence of a serious environmental problem is first recorded by Friend, where in Camphor infested steep creek gullies no frogs or Common Toadlet called, as distinct from an adjacent Camphor-free gully on the same soil type where Common Toadlet creek litter living species was common, and calling in season 'Frog Chorus'; below the junction of these two ephemeral creeks (unnamed) the Frogs calling stopped exactly there!
Terania Creek and Tuntable Creek, north of Lismore NSW, in their Camphor infested length approximately half-way upstream from The Channon now has virtually no resident population of any frog tadpoles, nil recently (3years) sighted frogs and (as a result?) a depauperate to zero populationof frog-eating Reptiles e.g. the common Water Dragon. (cf. Upstream Camphor-free subcatchments and dams in Terania Creek which are still abundant with frogs, N.B.: Observations of remnant frogs near, under or in Camphor trees does not prove that a species will achieve breeding success, although certain Camphor chemotype/s may be tolerated in small numbers.)
Friend (1988) co-published scientific results of the first Australian research experimentation with three Northern Rivers species of amphibian tadpoles, that proved local Camphor Laurel tree parts randomly selected from nearby hill slopes caused death of 100% tadpoles within short time periods.
The most toxic plant parts (to frogs) were found to be roots and green fruit berries. Kew Botanic Gardens (1999) confirmed that the roots of Camphor Laurel trees have almost microscopic oil exudation glands all along any-sized roots underground.
In such rich soils as NSW's North Coast enjoys, this tree discharges volumes of waste oils or toxins to soils and soil water, especially observable in-stream at times of peak wet periods. An identified evolutionary need is for the tree to be able to resist themselves from the vagaries of aggressive root-eating beetles and moth larvae.
Apparently, for some chemotypes, colourless toxins (e.g. the alkaloids linolitsene and reticuline) predominate whilst in others, yellow coloured (e.g. Safrole and orange coloured waste oils and toxins seem to predominate). In all cases it does appear that all frog and toad-toadlet species are susceptible.
See also: long-standing research results neglected