Condition of green ash (Fraxinus pennsylvanica) overstory and regeneration at three stages of the emerald ash borer invasion wave

Abstract

Assessing emerald ash borer (Agrilus planipennis Fairmaire) impacts in North American forests is essential for projecting future species composition of stands invaded by this phloem-feeding pest. We surveyed all species of overstory trees and regeneration in 2010 and 2011 in 24 forested sites with a major component of green ash (Fraxinus pennsylvanica), representing the Core, Crest, and Cusp of the A. planipennis invasion wave across southern Michigan. By 2011, an average of 78.6% ± 0.10%, 44.8% ± 0.11%, and 19.8% ± 0.07% of overstory ash trees representing 87%, 57%, and 14% of the total ash basal area had been killed in Core, Crest, and Cusp sites, respectively. Green ash seedlings, saplings, and recruits were abundant in all sites, but newly germinated ash seedlings were absent in Core sites and scarce in Crest sites. Canopy gaps resulting from current ash decline and mortality increased available photosynthetically active radiation (PAR) and sapling growth in Crest sites, but PAR was low in Core and Cusp sites. Lateral ingrowth of non-ash overstory trees has largely filled canopy gaps in Core sites, and there was little evidence of green ash recruitment into the overstory. Green ash appears unlikely to persist as a dominant species in forests invaded by A. planipennis.Résumé : Il est essentiel d'évaluer les impacts de l'agrile du frêne (Agrilus planipennis Fairmaire) dans les forêts d'Amérique du Nord pour prédire la composition future en espèces des peuplements envahis par ce ravageur qui se nourrit du phloème. Nous avons relevé toutes les espèces d'arbres dans l'étage dominant et la régénération en 2010 et 2011 dans 24 stations forestières du sud du Michigan où le frêne rouge (Fraxinus pennsylvanica Marshall) était une composante majeure et où la vague d'invasion de l'agrile était dans la phase soit croissante, soit culminante, soit décroissante. En 2011, une moyenne de 78,6 ± 0,10 %, 44,8 ± 0,11 % et 19,8 ± 0,07 % des frênes de l'étage dominant représentant 87, 57 et 14 % de la surface terrière du frêne avaient été tués dans les stations où l'invasion était respectivement dans les phases décroissante, culminante et croissante. Les semis, les gaules et les recrues de frêne étaient abondants dans toutes les stations mais les semis récents étaient absents dans les stations où l'invasion était dans la phase décroissante et rares dans les stations où l'invasion était dans la phase culminante. Les trouées dans le couvert causées par le dépérissement et la mortalité courante du frêne ont augmenté le rayonnement photosynthétiquement actif (RPA) et la croissance des gaules dans les stations où l'invasion était dans la phase culminante mais le RPA était faible dans les stations où l'invasion était dans les phases croissante ou décroissante. Le recrutement latéral d'espèces de l'étage dominant autres que le frêne a largement comblé les trouées dans les stations où l'invasion était dans la phase décroissante et il y avait peu d'indice de recrutement de frênes rouges dans l'étage dominant. Il est peu probable que le frê...

Ash regeneration capacity after emerald ash borer (EAB) outbreaks: Some early results

“…Similarly, in southeastern Michigan, Kashian and Witter (2011) observed abundant ash regeneration five years after the initial detection of the infestation, with mean densities of up to 3672 stems/ha for established seedlings and saplings in mesic hardwood stands. Significant decreases in new seedlings over time have also been reported for this region (Kashian andWitter 2011, Klooster et al 2014) and Burr and McCullough (2014) reported that they could not find any new germinants in postinfestation sites in 2010 or 2011 (southeastern Michigan). Ash seeds persist only two to three years in the seed bank (although for black ash some viable seeds have reportedly been found up to eight years; USDA and NRCS 2009) and the rapid depletion of the local seed bank following canopy mortality (Klooster et al 2014) is likely to severely affect the recovery capacity of ash populations by seedling establishment.…”

“…They reported an average DBH of 17 cm for these lingering ash trees which suggests that at least some may represent vigorous post-infestation regeneration. Similarly, Burr and McCullough (2014) reported green ash survival rates ranging from 15% to 32% (depending on DBH) in post-infestation sites. The difference in ash survival among the studies may indicate variations in ash innate resistance to EAB between populations, species or with site conditions.…”

“…Although they can occupy considerably different niches in the landscape, white and green ash are quite similar with respect to the life history traits that will determine their ability to persist under continued EAB presence. With both species, the first flowers may be produced by individuals as small as 8 cm in DBH, although trees are larger (typically 20 cm -25 cm DBH for white ash) before they flower abundantly (Burns and Honkala 1990). For dioecious species like green and white ash, reproduction success at low stem densities can be further delayed by the need for individuals of both sexes to mature within a few hundred metres of each other.…”

“…Despite some similarity in reproductive strategy with American elm, it is therefore doubtful that ash will persist in the landscape in the same way. Like American chestnut however, ash species have good re-sprouting ability (Burns andHonkala 1990, Dietze andClark 2008). In Europe, ash (particularly F. excelsior L.) were among the most commonly coppiced trees (Jansen and Kuiper 2004).…”

Lethal trap trees: a potential option for emerald ash borer (Agrilus planipennis Fairmaire) management

“…trees since it was first identified in North America in 2002 . Ash mortality rates of >95% have been documented in forested areas with a substantial ash component . Recent economic analyses identified A. planipennis as the most destructive and costly invasive forest insect in North America .…”