The impact of Sydney's driest start to a year in half a century is starting to spread from lawns and playing fields to the trees hanging over them, with exotic conifers among the first to wilt.

Pines, cedars and junipers and other northern hemisphere conifer species are showing up as early arboreal victims of the drought, according to Brendan Choat, an expert in tree responses to drought from Western Sydney University.

The conifers "get hit sooner and harder than the natural species", Associate Professor Choat said.

While there are only sporadic signs of dying trees so far, owners should expect instances of "the Christmas tree effect". That's when conifers "all of a sudden go crispy and brown", once water supply is cut off, he said.

Even though many types of pines have been picked for their hardiness, their disadvantage during drought is the shallowness of their root systems. Eucalyptus species, by contrast, typically sink deeper roots, allowing them to tap aquifers that are yet to dry out.