Insect pests, warming, and the future of forests. Emily K. Meineke, Elsa Youngsteadt, Adam G. Dale, Robert R. Dunn, & Steven D.

Transcription

1 Insect pests, warming, and the future of forests Emily K. Meineke, Elsa Youngsteadt, Adam G. Dale, Robert R. Dunn, & Steven D. Frank

2 Over 50% of people worldwide live in cities.

3 City environments are increasingly more important for human health and wellbeing worldwide.

4 Ecosystem services by urban trees Carbon sequestration (10% in US) Air filtering Storm water filtering Cooling Shade

5 Trees make us healthier. More canopy cover --> Less asthma in kids Heavier infants Lower mortality in seniors Lower mortality from lung and heart diseases

6 Urban trees are stressed. Planted in sidewalks Drought stress Nutrient stress More herbivorous insects

7 Herbivorous Pests More in urban than rural areas Why?

8 Two prevailing theories Natural enemies are less effective.

9 Two prevailing theories Host plants are stressed. Photo: Nicholas A. Tonelli

10 Do not consistently predict pest abundance Do not explain variation within cities Alternative: The urban heat island effect is the most important driver of insect pest abundance in cities.

11 The Urban Heat Island Effect Cities up to 12 C warmer

12 Causes: Impervious surfaces Less tree cover Heat from vehicles AC/heating units

13 Urban warming >> more insect pests on trees? Warming can cause insects to: Develop faster Survive better Produce more young

14 Study organism: Scale insects Noticeably more abundant in cities Sap-sucking pests on grasses, shrubs, and trees

15 Hypothesis 1 Urban warming leads to higher scale insect abundance on street trees.

16 Study system Oak lecanium scale

17 Study system Willow oak

18 Some parts of the city are hotter than others. RDU Airport Umstead State Park 12 C spread

19

20 20 hot, 20 cold sites Various life stages

21 Hot sites are warmer Up to 2.4 C F 1, 10 = 7.90, P = Up to 3.8 C F 1, 10 = 6.42, P =

22

23 6 more 9 more 5 more

24 Scale insects of red maple: Diaspididae Photo: Adam Dale Photo: Adam Dale Gloomy scale (Melanaspis tenebricosa) Xylem feeders Cause branch dieback, death

25 Gloomy scale abundance increases with urban temperature. Generalized linear model 2 X 1 = 35.67, P <

26 Hypothesis 1: Urban warming leads to higher scale insect abundance on street trees. More scale insects across urban habitats More herbivore pressure on trees Danger for urban trees now and as urban warming continues to become more intense Bad for humans, because we rely on trees What about global climate warming?

27 Hypothesis 2 Scale insects become more abundant in response to experimental warming that simulates broad scale climate warming.

28 Duke Forest open-topped warming chambers 12 chambers 5-m diameter Forced air system Ambient to C

29 Red maple saplings in 11 chambers

30 Scale insect abundance increased with experimental warming. Generalized linear model 2 X 1 = 15.79, P <

31 Hypothesis 3 Other insect pests become more abundant in response to experimental warming. Oak leaf Phylloxera

32 Phylloxera abundance June average temperature

33 Hyp 1: Urban warming leads to higher scale insect abundance in cities. Hyp 2: Scale insects become more abundant in response to experimental warming that simulates broad scale climate warming. Hyp 3: Other insect pests become more abundant in response to experimental warming.

34 Organisms that can survive in cities may be better at tracking global warming.

35 Implications for Forestry Global climate warming may cause widespread herbivore outbreaks. More pesticides More dead and unhealthy trees Clearly bad for human wellbeing Ongoing research: Ecosystem services

36 Acknowledgements We thank Sally Thigpen, Joe Sexton, Dean Urban, Dave Stephan, Uchenna Nwoko, George Washburn, Christi Mikeski, Sarah Widney, Rob Austin, Steve Bambara, and Andrew Ernst for their help with this work. USGS Southeast Regional Climate Science Center NASA Biodiversity Grant (ROSES- NNX09AK22G) NSF Career grant ( ) USDA Southern Region IPM ( ) NCSU Department of Entomology EPA STAR Fellowship.

37 Log average scale abundance per stem Scale abundance increases with urban temperature. F 1,10 =7.613, P=0.0202, Adj R2= May average daytime temperature

38 Duke Forest warming chambers Experiment set up in 2008 Total 36 open top chambers 12 open-bottom chambers to allow free movement Control chambers, no heating Heated chambers have target temperatures between 1.5 and 5.5 C above ambient. Pelini et al. 2011

39 Ecosystem services by trees Urban trees store 700 million tons of carbon per year (Nowak and Crane 2002). The US emits 6,700 million tons (EPA). 10% Importance of shade Proxy: tree growth Hypotheses: 1. Hotter trees have more herbivores. 2. Herbivores and warming both inhibit tree growth. 2A. Herbivores inhibit tree growth, while warming enhances it.