Statistical Analyses
To test the hypothesis that burned habitat was of nutritionally higher
quality than unburned habitats, we analyzed the nutritional quality data
in a hierarchical fashion. For the analysis, we only used species that
were found in both habitat treatment types. Four species that were only
found in the burned habitat (fireweed, quaking aspen (Populus
tremuloides ), little tree willow (Salix arbusculoides ), and
sedges) were removed from the analysis, leaving nine different species
to be included in the analysis (Alnus crispa , Equisetumspp., Salix pulchra , S. glauca , S.
pseudomyrisinites , S. richardsonii , Betula nana , B.
glandulosa , and B. neoalaskana ). We first compared overall
nutritional quality of habitats for all forages combined using a
multivariate analysis of variance (MANOVA) with habitat type, month, and
year as covariates. We tested the interaction between habitat type and
month sampled using an ANOVA, with digestible energy, nitrogen
concentration, percent reduction in proteins from tannins, and
digestible protein as dependent variables. We also calculated the
species diversity of each habitat type using the Shannon-Weiner Index
(Eq. 2), where pi is the proportion of total sample represented by
species i, and H is the diversity of each study site.
H=Σ[(pi)×ln(pi)]. (2)
Comparisons of forest versus burn for individual forage species common
to both sites were done using unpaired t-tests with a Bonferroni
multiple comparison adjustment. All statistical analyses were performed
in R (Marsh et al. 2006), and all comparisons were considered
significantly different at p < 0.05. Individual species
that were found in both burned and unburned habitats, including diamond
leaf willow, dwarf birch, and gray leaf willow, were also compared
individually using unpaired t-tests with a Bonferroni multiple
comparison adjustment to directly compare the two habitat treatment
types.
Results
Over the 2018-2019 field seasons, we sampled the Alphabet Hills burn on
six occasions, five times across the summers of 2018 and 2019 and once
in the winter of 2018-2019. We collected over 500 plant samples, and
measured canopy coverage of moose browses from randomly selected plots
in burned (n = 16) and unburned habitats (n = 10). We
found that the total canopy cover of moose preferred browses were higher
in forested sampling sites than in burned sites. There was a significant
difference between browse canopy cover in the forest compared to the
burn (forest % cover = 10%, SE = 0.019, burn % cover = 9%, SE =
0.01; t = 19.18, p = 0.033) (Figure 2). The burned area
had higher diversity of species (burn H = 1.709, forest H = 1.509) with
four species that were only found in the burned areas including
fireweed, quaking aspen, little tree willow and various mushrooms
(Boletus spp.) that are consumed by moose (Figure 2).