Recent severe fires in the boreal forest have resulted in an increase in deciduous dominated areas, as opposed to the historical coniferous dominance. In Alaska, deciduous trees are the preferred forage of moose (Alces alces), thus changes in fire severity could create more available habitat and forage. Our goal was to study the individual response of Alaskan paper birch (Betula neoalaskana) to simulated summer moose browsing, as well as the response of the surrounding plant community. In 2014, in interior Alaska, we established six post-fire sites (2004 burn) ranging in deciduous dominance. At each site we simulated a range of leaf-stripping intensities (zero to 100%) on 60 birch saplings. For each birch sapling, we measured multiple woody and leaf growth traits, as well as shoot morphology before, and one year after, the stripping treatment. In 2015 we collected long-shoots to calculate resin gland density, a proxy for chemical defense. At one of the six sites, we also established moose exclosures (n=3) to monitor Picea mariana and Populus tremuloides responses to 100% leaf-stripping of birch in half of each exclosure. Before, and one year after treatment, we measured tree growth of all three species inside exclosures.
Results/Conclusions
Leaf-stripping had significant, negative effects on growth and defense of birch one year after the treatment. Height growth in all leaf-stripping categories was significantly less than the control trees (p<0.001) with an average growth of 15cm to a loss of 5cm in height, for control and 100% stripping treatment respectively. The ratio of short to long shoots increased 4-fold in the 100% stripping treatment, with some trees producing zero long-shoots in 2015. Furthermore, there was a significant increase in the short to long-shoot ratio for three leaf-stripping treatments (p=0.05, 0.003, <0.001 for 60, 80, and 100% respectively). Leaf length was also affected by leaf-stripping, however only the 100% treatment experienced a significant increase in leaf length (p=0.01). Preliminary results suggest that fewer resin glands are produced by leaf-stripped birch, with 20% less in the 100% stripping treatment. The negative effects (height, shoot production) on crown elongation of birch has no effect on the height growth of other tree species in the community one year after treatment. Small scale (browsing) disturbances, mediated by large scale (fire) disturbances, can affect multiple functional plant traits, however community responses will take more than a year to occur.