Graduate Thesis Or Dissertation
 

Early-successional vegetation dynamics and microsite preferences following post-fire forest restoration in southwestern Oregon

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/b8515r02h

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  • Reforestation-based restoration of severely burnt plantations is one of the primary management activities following wildfire on U.S. federal lands. Restoration effects on early-seral plant and cryptogam communities have not been documented. The objectives of this study were, in severely burnt plantations two to four years post-fire, to examine the: (1) temporal patterns of succession within and among structural layers and influence of site conditions on these patterns, (2) effects of restoration treatments on composition and succession of early-seral vegetation, including terrestrial cryptogams, on moderate and harsh aspects, and (3) the role of microsites and bryophytes in germination and establishment of vascular plants. Structural layers established rapidly after wildfire in plantations following an initial floristics model of succession. Succession within and among structural layers occurred simultaneously but at different rates and with different drivers. Successional starting points differed based on fire severity, site history, species life history traits, topography and pre-disturbance plant community. Multiple successional trajectories were evident in severely burnt plantations based on varying initial species compositions. Restoration treatments, characterized by conifer planting and removal of woody shrubs, altered plant community composition and succession. Cover of bryophytes and shrubs initially decreased in areas with vegetation removal compared to areas without vegetation removal but bryophyte cover recovered over time. Exotic and annual herb cover increased with vegetation removal on harsh aspects by year four post-fire compared to areas without vegetation removal. Effects of vegetation removal on trait group cover were more pronounced on harsh aspects for groups with mostly herbs and on moderate aspects for groups with mostly shrubs and bryophyte communities. Microsites were heterogeneous following wildfire and restoration. Early-seral bryophytes preferentially occupy microsites with undisturbed soil and lower litter and overstory cover. Growth, but not germination, of early-seral vascular plants was lower on burnt bryophyte seedbeds than other seedbeds. Growth and germination of some conifers were higher on unburnt bryophyte seedbeds than other seedbeds. Results suggest that restoration activities shortly after fire had minimal effects on early vegetation cover, but altered early-seral vegetation composition and successional trajectories. Furthermore, early-seral bryophytes played a critical role in succession and establishment of other vegetation.
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