It’s not easy for trees to grow, much less, thrive in cities. Cities are warmer than natural areas where trees evolved. City soil is typically drier than natural soil too. Both of these problems – heat and drought – are caused in large part by impervious surfaces that absorb heat but deflect water.

Gloomy scales on a red maple branch. Photo: AG Dale.

In previous papers, we have shown that the urban heat island effect can increase pest abundance on trees. Oak lecanium scales become more abundant due to greater survival on hot trees. Gloomy scales become more abundant because on warm trees more of them survive and they produce three times as many eggs.

Adam measuring photosynthesis on a tree he has been watering with the green water bag around its trunk. Photo: AG Dale.

In a new paper, Adam Dale (former PhD student now at University of Florida), shows that

Gloomy scale embryos  that Adam counted to assess the effects of heat and drought on fecundity. Photo: AG Dale.

drought, in addition to heat, is also an important mechanism by which gloomy scale abundance increases on urban red maples. This is among the best evidence that heat and drought – two major consequences of urbanization and of climate change – combine to benefit pests and thus must be studied in concert. Read more about it in Adam’s blog post.


This article is published in the journal PLoS One. Find the entire article here:

Also, a UF press release can be found here:

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