Vegetative and Edaphic Responses in a Northern Mixed Conifer Forest Three Decades after Harvest and Fire: Implications for Managing Regeneration and Carbon and Nitrogen Pools

R Kasten Dumroese,Deborah S Page-Dumroese,Martin F Jurgensen

doi:10.3390/f11101040

R Kasten Dumroese, Deborah S Page-Dumroese + Show 1 more

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https://doi.org/10.3390/f11101040

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Abstract

Research Highlights: This experiment compares a range of combinations of harvest, prescribed fire, and wildfire. Leveraging a 30-year-old forest management-driven experiment, we explored the recovery of woody species composition, regeneration of the charismatic forest tree species Larix occidentalis Nutt., and vegetation and soil carbon (C) and nitrogen (N) pools. Background and Objectives: Initiated in 1967, this experiment intended to explore combinations of habitat type phases and prescribed fire severity toward supporting regeneration of L. occidentalis. At onset of the experiment, a wildfire affected a portion of the 60 research plots, allowing for additional study. Our objective was to better understand silvicultural practices to support L. occidentalis regeneration and to better understand the subsequent impacts of silvicultural practices on C and N pools within the vegetation and soil. Materials and Methods: We categorized disturbance severity based on loss of forest floor depth; 11 categories were defined, including controls for the two habitat type phases involved. We collected abundance, biomass, and C and N concentrations for the herbaceous layer, shrubs, and trees using nested quadrats and 6 to 10 experimental units per disturbance category plot. Moreover, we systematically sampled woody residue from transects, and forest floor, soil wood, and mineral soil with a systematic grid of 16 soil cores per disturbance category plot. Results: We found that (1) disturbance severity affected shrub species richness, diversity, and evenness within habitat type phases; (2) L. occidentalis regenerates when fire is part of the disturbance; (3) N-fixing shrub species were more diverse in the hotter, drier plots; (4) recovery levels of C and N pools within the soil had surpassed or were closer to pre-disturbance levels than pools within the vegetation. Conclusions: We confirm that L. occidentalis regeneration and a diverse suite of understory shrub species can be supported by harvest and prescribed fire, particularly in southern and western aspects. We also conclude that these methods can regenerate L. occidentalis in cooler, moister sites, which may be important as this species’ climate niche shifts with climate change.

Highlights

Forest ecosystems are dynamic, driven by disturbance that occurs commonly rather than rarely, and that encompasses a range of spatial, temporal, and severity combinations [1]
After harvest, five of the six Xerophyllum tenax (XETE) plots burned with combinations of prescribed fire and wildfire; the disturbance level increased with fire severity, as measured by the loss of forest floor (Table 1)
Despite soil wood in West 10 being 3 times higher than in undisturbed XETE plots (UX), and despite some XETE plots having no soil wood, we found no significant differences among plots (Table S4)

Summary

Introduction

Driven by disturbance that occurs commonly rather than rarely, and that encompasses a range of spatial, temporal, and severity combinations [1]. The resulting myriad of fire characteristics yields an immense range of disturbance patterns across the landscape [5]. These patterns increase forest heterogeneity, which in turn promotes biodiversity and subsequently contributes to forest resilience [6,7]. Modern silvicultural techniques, such as thinning, harvesting, and prescribed fire, can mimic natural disturbances and implementing these techniques can allow land managers to effectively control species composition, structure, spatial arrangement, and forest function to meet management objectives [8,9]. Exclusion of natural disturbances (e.g., wildfire suppression), which in the case of fire has predominated the landscape in the western USA [10], can alter species composition and stand structure. Lacking implementation of other management activities, these altered conditions can lead to more extreme severities of insect infestation and wildfire [11]

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