Efficient application of a browsing repellent: Can associational effects within and between plants be exploited?

Abstract

Browsing can reduce forest productivity, particularly when the apical shoots of trees are damaged. Repellents are used widely to reduce browsing, but application is costly. To improve efficiency, it may be possible to take advantage of associational plant refuge effects, requiring repellents to be applied only to some trees or parts of trees, or reapplied less frequently. Using captive moose (Alces alces) and constructed stands of Scots pine (Pinus sylvestris), we tested for potential refuges by applying a commercial repellent (HaTe2) to all, alternate or none of the apical shoots, or all of the previous-year apical shoots. We also tested for potential refuges under field conditions, applying the repellent to all, alternate or none of the apical pine shoots in forest stands. Captive moose (two individuals in a 2.1-ha enclosure, ~ 95 individuals km⁻²) browsed 100% of trees, but were significantly less likely to browse apical shoots treated with repellent. Associational refuge was ineffective both within and between trees. In the field (0.84 moose km⁻²), only 1.3% of trees sustained browsing damage. Applying the repellent to the apical shoots of pines had no direct repellent effect nor any within-plant associational effects. Trees with treated apical shoots provided some protection for untreated neighbouring trees, but this was not biologically meaningful given the low percentage of trees browsed overall. Here, a simple captive experiment was not predictive of the browsing response observed in the field, demonstrating the need to test repellent application strategies in situ.

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