Abstract
Black ash (Fraxinus nigra Marsh.) exhibits canopy dominance in regularly inundated wetlands, suggesting advantageous adaptation. Black ash mortality due to emerald ash borer (Agrilus planipennis Fairmaire) will alter canopy composition and site hydrology. Retention of these forested wetlands requires understanding black ash’s ecohydrologic role. Our study examined the response of sap flux to water level and atmospheric drivers in three codominant species: black ash, red maple (Acer rubrum L.), and yellow birch (Betula alleghaniensis Britt.), in depressional wetlands in western Michigan, USA. The influence of water level on sap flux rates and response to vapor pressure deficit (VPD) was tested among species. Black ash had significantly greater sap flux than non-black ash at all water levels (80–160% higher). Black ash showed a significant increase (45%) in sap flux rates as water levels decreased. Black ash and red maple showed significant increases in response to VPD as water levels decreased (112% and 56%, respectively). Exploration of alternative canopy species has focused on the survival and growth of seedlings, but our findings show important differences in water use and response to hydrologic drivers among species. Understanding how a replacement species will respond to the expected altered hydrologic regimes of black ash wetlands following EAB infestation will improve species selection.
Highlights
Emerald ash borer (EAB, Agrilus planipennis Fairmaire), an exotic insect native to Asia and first detected in southeastern Michigan, USA, in 2002, has been spreading outward after introduction [1,2].EAB has caused a regional trend of declining native ash (Fraxinus spp.) populations in the Great LakesStates observable since 2004 [3]
The difference between black ash and non-black ash sap flux rates was the difference between black ash and non-black ash sap flux rates was greatest at low water greatest at low water levels, and lowest at high water levels, which is contrary to the second levels, and lowest at hypothesis
Some adaptation or suite of adaptations have resulted in black ash remaining historically dominant at these sites. One expression of these adaptations is an increase in sap flux with receding water levels, so that forest canopy transpiration would be reduced most at times of low water levels following the loss of ash
Summary
Emerald ash borer (EAB, Agrilus planipennis Fairmaire), an exotic insect native to Asia and first detected in southeastern Michigan, USA, in 2002, has been spreading outward after introduction [1,2].EAB has caused a regional trend of declining native ash (Fraxinus spp.) populations in the Great LakesStates observable since 2004 [3]. EAB has caused a regional trend of declining native ash (Fraxinus spp.) populations in the Great Lakes. The loss of native ash throughout their ranges in North America has been shown to have important economic [4], cultural [5], and ecological [6] impacts. The northwestern periphery of the expanding infestation includes areas where black ash (Fraxinus nigra Marsh.) plays an important role on the landscape [7] (Figure 1). Black ash grows on wet sites with persistently high water tables or seasonal inundation [8]. These wet sites are classified as northern hardwood swamps
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