Effects of variable rate aerial application of Vision on moose (Alces alces) winter browsing and hardwood vegetation

Abstract

Experimental aerial treatment of 7 mixedwood areas in late summer for conifer release with Vision® at 0.80, 1.06, and 1.60 kg a.e./ha, decreased living hardwood stem densities after ten months by 42, 61 and 42% respectively on treated plots, while controls increased by 13%. Twenty two months after treatment stem densities were reduced (from pre-spray levels) by 48, 65 and 61%; controls increased 19%. Greatest numbers of stems occurred on moderately deep, fresh soils. After treatment, winter browsing rates decreased in both six and 18 months post spray on all plots and were consistently higher on controls when compared with treated sub-blocks. Decline was progressive over two years after treatment on sprayed areas but recovered in the second year on controls. The two highest application rates had the lowest browsing levels. Conversely, winter track data showed no differences in moose use between sprayed areas and controls, nor any difference among treatments. This suggested moose still traveled through sprayed areas, but did not stop to browse. In addition to stem density counts, cover (%) for both herbs and hardwoods were estimated to evaluate the effectiveness of Vision® as a conifer release. Hardwood cover was reduced significantly by all application rates; differences among treatments were not significant. Herbaceous ground cover was reduced approximately 20% on all treated areas one season after spray but by next year these sprayed areas had recovered to equivalent levels as controls. Neither crop tree diameter nor height growth was affected by Vision® application at this early stage of the experiment. Moose densities within these study areas appear to be low enough that food is not a limiting factor. The small amount of spraying in Ontario (relative to the productive forest land base) is not expected to affect moose populations. However, in areas with high concentrations of sprayed cutovers there should be concern. Results of this short term study suggest that 0.80 kg a.e./ha controlled hardwood and herbaceous competition as well as 1.06 & 1.60 kg a.e./ha. However, the lowest application rate showed signs of increased moose use two years post spray compared with the two higher rates. Consequently, when spray programs are concentrated in one management unit, the 0.80 kg a.e./ha rate is recommended.