Vegetation responses to simulated emerald ash borer infestation inFraxinus nigradominated wetlands of Upper Michigan, USA

Abstract

The invasive emerald ash borer (EAB) (Agrilus planipennis Fairmaire (Coleoptera: Buprestidae)) is a significant threat to biodiversity and ecosystem processes in North American forests. Of particular concern is the fate of Fraxinus nigra (black ash), which is frequently a dominant canopy species across much of its range. To investigate the potential vegetation response to the loss of this foundation species, EAB-induced mortality was simulated in F. nigra dominated wetlands of Upper Michigan, USA. No growth response of residual overstory species occurred over the course of three growing seasons, which may in part be attributed to negative effects of post-treatment growing conditions, including prolonged inundation. A significant increase in non-Fraxinus sapling growth rate was observed, however. Mortality of F. nigra did not impact overall stem recruitment or regeneration, although species composition is shifting towards Acer rubrum (red maple) and Betula alleghaniensis (yellow birch) in the seedling layer. The herbaceous community exhibited the greatest response, nearly doubling in areal cover by the end of the study. Importantly, this expanded cover was not associated with decreased establishment of new woody seedlings, suggesting that increased competition between these functional groups has not yet impacted the potential for future recovery of woody vegetation in these forests.

Review of Ecosystem Level Impacts of Emerald Ash Borer on Black Ash Wetlands: What Does the Future Hold?

“…In upper Michigan, throughfall deposition of N was not influenced by girdling, but the ash-cut treatment had higher nitrate deposition than the unharvested control [20]. Preliminary soil data indicate that the ash-cut and girdled treatments had little influence on inorganic soil N concentrations and N availability [20].…”

“…At the Michigan sites, Davis [20] found litter N concentrations in black ash to be greater than non-ash (i.e., red maple and yellow birch) species. Other studies have also found high concentrations of N in ash litter, leading to high turnover rates of ash litter and greater soil N availability compared to non-ash species [21,22].…”

Evaluating Adaptive Management Options for Black Ash Forests in the Face of Emerald Ash Borer Invasion

“…For example, non-ash species, including Quercus macrocarpa, Ulmus americana, and Abies balsamea, made up 16-30% of the basal area across old-growth WFn64 communities in Minnesota [29]. Similarly, black ash abundance ranged from 25% to 85% of basal area in isolated, depressional wetlands in the Upper Peninsula of Michigan, with Betula alleghaniensis and Acer rubrum often constituting the other primary overstory species [30]. The variation in these community types, particularly in relation to the amount of non-ash trees present in the overstory and regeneration layers, is an important consideration when determining vulnerability to EAB impacts and developing appropriate management responses [31].…”

Methods to Improve Survival and Growth of Planted Alternative Species Seedlings in Black Ash Ecosystems Threatened by Emerald Ash Borer

“…All black ash greater than 2.5 cm in diameter were treated in the Girdle and Ash-Cut wetlands. This is a similar design to a sister-study [12] and our intention for the Girdle treatment was to simulate the short-term impacts of an EAB infestation, while the Ash-Cut treatment simulated the long-term impacts of EAB infestation [1]. …”

“…For example, black ash forested wetlands provide habitat and food sources for game birds, small animals, and deer [7], the canopy reduces heat input into streams [8,9], and the root structure maintains soil integrity during rain events, reducing erosion and sediment deposition downstream [10,11]. Current theories predict that cover type changes after EAB infestation will lead to loss of the tree canopy on the landscape and forested wetlands in the short-term will become dominated by a robust herbaceous community [12] and in the long-term possibly a shrub layer consisting of alder (Alnus spp.) [13,14].…”