Summertime and the Living is Easy—ummm, not really. Drought Stresses the Flora of Acadia National Park  

The iSWOOP project is dedicated to making the scientific research underway at national parks more apparent to the public, especially visitors. Wildlife and plant communities change over time in concert with changes in climate and geology. Most of us begin grasping change over time by thinking about conditions at one point in time.  Before the summer of 2016 is a distant memory, I wanted to ask rangers to reflect on conditions.

I asked Jesse Wheeler, invasive plant ecologist at Acadia National Park, if the dry summer had a noticeable impact on plant life. Small talk in New England often turns to the weather. In Maine, if visitors from away complain, our standard answer is “Just wait five minutes,” but this summer day after day was sunny and dry. Hikers saw fewer mosquitoes and ticks than in a year with more rain. Stargazers had beautiful clear nights.

What about for plant life? Were the trees stressed? Which pests were gaining a competitive advantage? Which plants were the losers and winners this summer? What does it mean for park management?

Wheeler said he observed effects in various parts of the park (meadows, bogs, forest). His observations follow:

Absolutely, the impact from forest pests and diseases plays out differently in dry and wet years. The native alder flea beetle (Altica ambiens) appeared to have had a boom year. While working in several wetlands of the park this summer, I observed large infestations of the larval stage feeding on speckled alder particularly the Kent Field area between Schooner Head Road and Champlain Mountain (see photo).

Trees are always under stress, from something.

When wet, fungi can do severe damage. When a dry spell lingers, fungi might do less harm.

The shoot blight fungi, Sirococcus conigenus, which is native to Maine, has been causing problems for red pines. It shows up on new shoots where the blight kills clusters of needles at the end of pine branches. Favored by wet conditions, in spring and early summer, these native fungi likely didn’t fare well with a lack of rain and fog during this time period of 2016. Trees got a bit of a break from the fungal blight.

However, the dry spring weather gave an advantage to defoliators as they accomplished their work of stripping trees of leaves. In wet years or years with average precipitation, native fungi keep the viburnum leaf beetle in check. But in dry years the invasive non-native beetle devastates native arrow-wood viburnum shrubs.

The take home point? The dry season could spell some relief from conifer needle and shoot diseases. On the other hand, that is not guaranteed as timing of moisture, spore production and tissue vulnerability may come together. In a system there are multiple factors that support or undermine plant health (Maine Forest Service, 7/25/16 Insect & Disease Conditions Update). Whether it’s wet or dry habitat, most of our native plant species are adapted for relatively consistent moisture levels, not large deficits of water. We have to brace for diebacks, large losses of habitat that will re-form (re-populate) with a different mix of plants and animals.

signs_of_drought_alder_acadia

Leaf damage typical of infestations of Alder leaf beetle, where the larval stage skeletonizes alder shrubs as seen here in Acadia National Park in 2014 (NPS photo).

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