Abstract
Large-scale disturbances such as ice storms may increase in frequency and intensity as climate changes. While disturbances are a natural component of forest ecosystems, climatically driven alteration to historical patterns may impart fundamental change to ecosystem function. At Hubbard Brook Experimental Forest, NH, experimental ice storms of varying severity were applied to replicate plots of mature northern hardwoods to quantify their effects on forested ecosystems. We assessed ice storm treatment effects on insectivorous foliage-gleaning birds and evaluated insectivore predation on model caterpillars in the understory vegetation. These birds are charismatic, of conservation concern, and are major predators of caterpillars. In turn, lepidopterans are the dominant herbivores in temperate forests and are integral to ecosystem function. We predicted that avian abundance would increase due to additional structural heterogeneity caused by ice treatments, with a concomitant increase in caterpillar predation. Point counts were used to measure insectivorous bird activity in the ice storm experiment plots and additional control plots before and after treatments. We deployed and retrieved plasticine model caterpillars and estimated predation from characteristic marks to these surrogates. Abundance of foliage-gleaning birds was higher in the ice storm plots and birds responded to treatments as a single diffuse disturbance rather than on an individual plot level. All species except one were observed both before and after the ice treatments. Surprisingly, predation on caterpillar models was unaffected by ice storm treatments but rather was a function of caterpillar density. The increase in avian abundance in the ice storm treatment plots corroborates other studies of bird responses to relatively small-scale disturbances in forests and the limited change in species composition was expected given the plot size. We conclude that ice storms may provide beneficial changes for foliage-gleaning birds in the growing season following the disturbance.
Highlights
Concomitant with warming temperatures, climate change is predicted to increase the frequency, intensity, and timing of extreme weather events (Cook and Seager, 2013; Wuebbles et al, 2014)
Ice storm experiment (ISE) plots encompassed ∼100 yr old mixed hardwood stands co-dominated by American beech (Fagus grandifolia), sugar maple (Acer saccharum), and yellow birch (Betula alleghaniensis)
We found some evidence that the increase in abundance was a response to the suite of treatments that created a diffuse disturbance in the roughly 100 × 300 m area containing all eight treated plots and two control plots, due to model selection uncertainty the evidence is not conclusive
Summary
Concomitant with warming temperatures, climate change is predicted to increase the frequency, intensity, and timing of extreme weather events (Cook and Seager, 2013; Wuebbles et al, 2014). These alterations to natural cycles are directly linked to increases in anthropogenic greenhouse gas emissions (Lambert and Fyfe, 2006; Cook and Seager, 2013) and will likely be more damaging to ecosystems than gradual temperature changes, at least over the short term (Dale et al, 2001; Arnone et al, 2011). Climate change may increase ice storm frequency and severity as well as shift the current ice belt northward (Dale et al, 2001; Cheng et al, 2011; Klima and Morgan, 2015; Swaminathan et al, 2018)
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