Introduction

Ecologists and wildlife managers generally agree that throughout the world, large-scale disturbance, such as wildfire, can be beneficial for species of large herbivores that are adapted to seral plant communities. Burned plots in states like Colorado and Nevada have been shown to increase crude protein intake for mule deer (Odocoileus heminonus ) and bighorn sheep (Ovis canadensis ) in grassland and montane shrub communities (Hobbs and Spowart 1984). Higher abundances of bison (Bison bison ) were found in recently burned watersheds within the Konza Prairie Research Natural Area in Northern Kansas (Knapp et al. 1999). In summer, these herbivores select grasses and herbaceous plants that respond rapidly to the release of post-fire nutrient deposits (Boerner 1982). In boreal forest ecosystems, post-fire stands are commonly assumed to support higher populations of moose (Alces alces ) than adjacent unburned stands, but quantification of the impacts of fire on moose population productivity is limited. Fire, both natural and prescribed, is considered beneficial to moose because deciduous woody browses and herbaceous foods (e.g., Chamerion angustifolium ) respond rapidly to post-fire conditions, increasing food abundance significantly (Landhausser and Wein 1993). Studies focusing on vegetation after fire show high variability with respect to both the biomass productivity and the species composition that regenerates (Rau et al. 2008, Johnstone et al. 2010).
Although there is significant evidence suggesting that browse biomass density increases after fire, there is little regarding the effect of fire on plant chemistry after fire (Bryant et al. 1983, Maier et al. 2005, Joly et al. 2016, Brown et al. 2018). Alteration of plant chemistry after fire could have dramatic effects on the overall palatability, and therefore the nutritional quality, of browse species. Globally, herbivores are limited by the availability of nitrogen, the element necessary for making protein and therefore building muscle. Nitrogen concentration in boreal plants is a limiting factor for the plants themselves and may be a limiting factor for herbivore growth and reproductive success (McArt et al. 2009, Gundale et al. 2010). Low resource environments, including the boreal forest, are dominated by plants such as evergreens that are slow growing, even when provided with an optimal supply of resources (Chapin, 1991, Gundale et al. 2010). Slow growth in these plants is attributed to an inability to quickly uptake nutrients, a higher allocation to survivorship traits such as chemical defenses, and internal constraints to growth (Chapin, 1991). Due to these growth limitations, nutrients may be leached out of a system before the species has the chance to sequester them (Chapin, 1991, Gundale et al. 2010), although fire has been found to increase nutrient availability. Deciduous species located in nutrient-limited stands have a greater proportion of secondary metabolites than in more productive ecotones, making them less usable by associated herbivores (Gundale et al. 2010). This defense strategy makes these plants less palatable to herbivores.
Nutritional carrying capacity is limited by two elements of a habitat: forage availability and forage quality. Both of which may be significantly altered after a disturbance such as fire. This potential tradeoff between higher availability of browse and potentially lower quality could affect moose productivity and movement. Hobbs and Swift (1985) showed that in high biomass areas nutrient intake is limited by the nutritional quality of the food source. If browse availability increases significantly in burned stands, but the nutritional quality declines, then moose density may increase, at the cost of per capita fitness (Hobbs and Swift 1985, 1988).
The response of moose to fire depends on browse biomass and diversity, and nutritional quality, including plant defenses (Hobbs and Swift 1985, Hobbs 2003). We measured these funda-mental characteristics in a 16-year-old prescribed burn in the Nelchina Basin and in its adjacent unburned forests. The Nelchina Basin located west of Glenallen, AK, supports one of the highest moose harvests in the state (Boertje et al. 2007), drawing in hunters from throughout south-central and interior Alaska (Figure 1).