Long-Term Seeding Outcomes in Slash Piles and Skid Trails after Conifer Removal

Becky K Kerns,Dana Ikeda,Michelle A Day

doi:10.3390/f11080839

Becky K Kerns, Dana Ikeda + Show 1 more

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https://doi.org/10.3390/f11080839

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Abstract

Conifer removal in interior woodland ecosystems of the western US is a common management treatment used to decrease fire hazard and shift woodlands to more historical states. Woody material is frequently removed by skidding material off site and via slash pile burning. Assessing the long-term outcomes of seeding treatments after such ground disturbing activities is critical for informing future management and treatment strategies. Using two designed experiments from a central Oregon juniper woodland, we resampled slash piles and skid trails 8 years after seeding. Our objectives were to assess the long-term vegetation response to conifer removal, ground disturbance, and seeding source (cultivar and local) in slash piles and skid trails. We found that seeded species persisted in the long term, but abundance patterns depended on the species, seed source, and the type of disturbance. In general, there were more robust patterns of persistence after pile burning compared to skid trails. Seeding also suppressed exotic grass cover in the long term, particularly for the local seed source. However, the invasion levels we report are still problematic and may have impacts on biodiversity, forage and fire behavior. Our short-term results were not predictive of longer-term outcomes, but short- and long-term patterns were somewhat predictable based on species life history traits and ecological succession. The use of a mix of species with different life history traits may contribute to seeding success in terms of exotic grass suppression. Lastly, our results suggest that locally adapted seed sources may perform as well or better compared to cultivars. However, more aggressive weed treatments before and after conifer removal activities and wider seeding application may be needed to effectively treat exotic grass populations.

Highlights

Conifer encroachment and densification are global phenomena that have been documented in numerous ecosystems, including dry conifer forests and woodlands, oak woodlands, mountain meadows, shrublands and grasslands [1,2,3,4,5]
We examine the long-term effects of locally sourced and cultivar seeding treatments in slash piles and skid trails after the mechanical removal of western juniper in central Oregon in an effort to facilitate the cover of native species, suppress exotic weeds, and enhance native plant diversity post-treatment
We found no evidence that juniper removal followed by slash pile burning and seeding influenced total plant cover in the long term, but strong evidence that seeding had a long-term impact on seeded species cover (PSSP, ELEL and ACMI) (Figure 4)

Summary

Introduction

Conifer encroachment and densification are global phenomena that have been documented in numerous ecosystems, including dry conifer forests and woodlands, oak woodlands, mountain meadows, shrublands and grasslands [1,2,3,4,5]. Conifer encroachment and densification in the western US have resulted in: (1) the listing of over 350 sagebrush dependent plants and animals as species of concern [15,16]; Forests 2020, 11, 839; doi:10.3390/f11080839 www.mdpi.com/journal/forests (2) increasing woody fuels and crown fire potential [17]; and (3) the alteration of ecosystem functioning through changes in hydrological processes [18]. Owing to the potential for negative effects associated with conifer encroachment, land managers have sought to remove or reduce trees such as western juniper through mechanical cutting and burning in an effort to halt or reverse ecosystem type conversion and decrease woody fuels. Pile burning initially removes all aboveground vegetation, and can result in soil blackening or reddening, increases in soil nutrient availability and hydrophobicity [21,22,23,24,25,26,27]

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