Stand and individual tree characteristics associated with Enaphalodes rufulus (Haldeman) (Coleoptera: Cerambycidae) infestations within the Ozark and Ouachita National Forests

Emergent insects, pathogens and drought shape changing patterns in oak decline in North America and Europe

“…Irrespective of topography, red oak mortality was greater in plots with higher E. rufulus population densities (Fierke et al, 2007), which suggests that at high population levels, E. rufulus became a more aggressive mortality agent. After the outbreak, a retrospective study confirmed that, compared to other xeric sites with lower borer densities, live Q. rubra basal area was reduced in xeric areas that sustained higher borer densities (Haavik and Stephen, 2010b). In short, the total amount of oak mortality and dieback was greatest -and E. rufulus populations were highest -on sites with inherently stressful growing conditions.…”

“…These results may be, in part, because different oak species reach maturity at different ages and sizes (Guldin et al, 2006). In contrast, studies that examined species of red oak separately, found relatively more mortality in overtopped (suppressed and intermediate) crown positions than in dominant and co-dominant positions (Fan et al, 2008(Fan et al, , 2011Haavik and Stephen, 2010b). Suppressed oaks also supported higher E. rufulus larval survivorship, though not necessarily higher borer densities, than co-dominant oaks (Haavik and Stephen, 2010b).…”

“…In contrast, studies that examined species of red oak separately, found relatively more mortality in overtopped (suppressed and intermediate) crown positions than in dominant and co-dominant positions (Fan et al, 2008(Fan et al, , 2011Haavik and Stephen, 2010b). Suppressed oaks also supported higher E. rufulus larval survivorship, though not necessarily higher borer densities, than co-dominant oaks (Haavik and Stephen, 2010b). Although some studies of previous oak decline events found that declining oaks were older than healthy oaks (Tainter et al, 1990;Jenkins and Pallardy, 1995), we did not find any evidence for this .…”

“…drought and ensuing E. rufulus infestation) survived this event. Of oaks growing on the same aspect and slope position, healthy survivors were often larger in diameter and possessed higher radial growth rates over the past two decades than their declining or dying counterparts (Haavik and Stephen, 2010b). Q. rubra that sustained low borer infestations, compared with those that were dying and had severe borer infestations, exhibited higher indices of vigor (5-y basal area increment: sapwood area, Haavik et al, 2010), and greater capacity for resistance to E. rufulus .…”

Temporal aspects ofQuercus rubradecline and relationship to climate in the Ozark and Ouachita Mountains, Arkansas

“…We collected increment cores from 35 Q. rubra at each stand, or from all live trees present,~105 trees per study site, and cross sections from ∼20 dead standing or fallen Q. rubra per site. Overall sample sizes were 815 live and 161 Q. rubra that died between 1990 and 2008 (Haavik and Stephen 2010a). We extracted one increment core per live tree on the west-facing side of the bole (parallel to the slope) at breast height.…”