Cities as surrogates for global change

Entire hillsides covered in brown, dead trees killed by mountain pine beetles. Photo: William M. Ciesla, Forest Health Management International,

The climate has been warming for decades with real consequences for our economy and native ecosystems. One example comes from mountain pine beetles, which are native to western mountain states. This beetle’s northern range is restricted by cold temperature, so as the climate has warmed mountain pine beetles have moved farther and farther north. The trees in these northern forests are under stress from warming and can’t defend themselves the way trees in the native range can. So, mountain pine beetles have decimated millions of acres of forest, ruining millions of dollars of lumber, increasing fire severity, and threatening plant and animal species.

Looking back, it is easy to see the effects of climate on pests. But how can we predict which herbivores may become pests in the future or which trees may die from heat and drought stress? Knowing this could help land managers prepare and mount a response.

An experimental warming chamber at Duke Forest. Figure from Stuble KL, Patterson CM, Rodriguez-Cabal MA, Ribbons RR, Dunn RR, Sanders NJ. (2014) Ant-mediated seed dispersal in a warmed world. PeerJ 2:e286. DOI: 10.7717/peerj.286/fig-1

Many experiments have been conducted to understand how climate warming will affect plants and animals. The biggest have warmed forest patches with heaters or heat lamps to see how plants and animals (usually insects) respond. We have learned a lot from this type of experiment but we are limited by the size of forest patch that can be warmed (up to a few meters) and for how long it can be warmed (several years).

Current conditions in cities are similar to those expected under climate change. Image: Lahr EC, Dunn RR, Frank SD. (2018) Getting ahead of the curve: cities as surrogates for global change. Proc. R. Soc. B 285: 20180643.

Our lab and others have taken a different approach. We conduct research in cities. Cities may seem like the least natural places on earth and weird places to study nature. However, cities do have many of the same plants (think trees like oaks, maples, tulip poplar) and animals (especially insects) as natural areas. More importantly for our research, cities are generally a couple degrees hotter than natural areas, which is how much the climate will likely warm in the next hundred years.

Our favorite study subjects are scale insects. These tiny herbivores suck juices from trees and if they become very abundant can reduce tree growth and health. There are hundreds of scale insect species in the eastern US. We have found two, gloomy scale and lecanium scale, that become hyperabundant and harmful to trees due to just 2°C of warming in cities. We predict these are two species that may become problems in natural forests as the climate warms.

Gloomy scales cover a maple branch near downtown Raleigh. Photo: Adam Dale

We are not the only scientists using cities as surrogates for climate change. However, this line of research is in its infancy. We conducted a literature review, led by postdoc Nora Lahr, to compile all the research we could find in which cities were used to predict the effects of climate change. A review of this kind not only pulls work together in one place it also helps to identify gaps in research, methodological problems, and fruitful future directions. There are obviously limits to the ways in which cities, or experimental approach, can be used to predict future effects of climate change. However, studying trees, ants, bees, microbes, and other living things in cities is valuable and might just provide some advance warning of ecological changes to come.

Read the full paper here:

Lahr, E.C., Dunn, R.R., and Frank, S.D. (2018) Getting ahead of the curve: cities as surrogates for global change. Proceedings of the Royal Society B, 285: 20180643.

2018-07-18T19:49:41-04:00 July 18th, 2018|Categories: Lab Happenings, Urban Ecology|Tags: , , , , |

About the Author:

Steve Frank
I am broadly interested in the ecology and management of arthropod pests. Herbivorous arthropods cause extraordinary damage to plants in agricultural, urban, and natural ecosystems. Understanding interactions between pests and their environment, plant hosts, and natural enemies can improve management practices and reduce pesticide applications.