Gall mite (Eriophyes laevis) infestation and leaf removal affect growth of leaf area in black alder (Alnus glutinosa) short shoots

We measured the effects of Eriophyes laevis mite galls on the relative growth of short shoot leaf area of Alnus glutinosa. A portion of leaves was artificially removed from a set of short shoots with both high and low gall density to cause local stress conditions. Nontreated high and low gall density short shoots were used as controls. The results show that the relative growth of leaf area measured for short shoots is negatively affected by high gall density. Artificial leaf removal, on the other hand, had positive effects on leaf area growth. Interestingly, the growth of leaf area did not differ for high gall density short shoots with leaf removal and noninfested short shoots with no leaf removal. This result may be caused by the combined, opposite effects of leaf removal and gall infestation.