Will & James,Will Blozan wrote:Probably a difference in vector density and mabye tree physiology. I did a study of BBD back in the late 90's in GRSM and the scale was rare in the low elevations and extrememly dense in the high elevations.
Those sound very logical causes to me. Do you know, why is the scale insect dense in the high elevations? Two possible reasons come to my mind:
1. The scale insect is native to Europe (correct me if I am wrong). The climate in the low elevations of GrSM is probably warmer than that in the natural range of the European beech. Perhaps the scale is adapted to climates more like those in the northeast US and in the high elevations of GrSM?
2. Are beech populations more dense in higher elevations? In the low elevations, where species diversity is very high, beech is probably more rare, and thus the scale would also be more rare.
It is interesting (and sad, of course), that so many exotic pests and diseases are so severe to American trees. There are chestnut blight, emerald ash borer, white pine blister rust, hemlock woolly adelgid, Dutch elm disease, beech bark disease, Phytophthora lateralis (for Port Orford-cedar in the west), ... In Europe Dutch elm disease has almost wiped out Ulmus minor, but I do not know any disease fatal to European trees which would be native to North America. This is almost like with Europeans and native Americans: 90% or so of the latter died of old world diseases. Perhaps one thing is the size of the Eurasian continent: more pests and diseases evolved, and the trees developed resistance to wider selection of diseases.
Does this sound logical to you?