Impacts of Mastication: Soil Seed Bank Responses to a Forest Thinning Treatment in Three Colorado (USA) Conifer Forest Types

Akasha Faist,Heather Stone,Erin Tripp

doi:10.3390/f6093060

Akasha Faist, Heather Stone + Show 1 more

Open Access

https://doi.org/10.3390/f6093060

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Journal: Forests	Publication Date: Aug 31, 2015
Citations: 53	License type: CC BY 4.0

Affiliation: University of Colorado Boulder, Museum of Boulder

Abstract

Mastication is a forest fuel thinning treatment that involves chipping or shredding small trees and shrubs and depositing the material across the forest floor. By decreasing forest density mastication has been shown to lessen crown fire hazard, yet other impacts have only recently started to be studied. Our study evaluates how mastication treatments alter the density and composition of soil seed banks in three Colorado conifer forest types. The three forest types were (1) lodgepole pine, (2) ponderosa pine and (3) pinyon pine-juniper. Results showed that masticated sites contained higher seed bank densities than untreated sites: a pattern primarily driven by treatment effects in ponderosa pine forests. The seed bank was dominated by forbs regardless of forest type or treatment. This pattern of forb dominance was not observed in the aboveground vegetation cover as it demonstrated more even proportions of the functional groups. Graminoids showed a higher seed density in treated sites than untreated and, similarly, the identified non-native species only occurred in the treated ponderosa pine sites suggesting a potential belowground invasion for this forest type. These results suggest that presence of masticated material might not be creating a physical barrier hindering the transfer of seeds as predicted.

Highlights

Following decades of fire suppression and climate change, the severity and frequency of forest wildfires are increasing across multiple ecosystems [1,2,3,4,5,6]
While highly variable in their ecological responses, mastication treatments often create an open canopy allowing for the inclusion of light, enhance soil moistures and increase plant available N and vegetation cover [16,17,18,19,20,21,22,23,24,49], which in turn increase the potential for seed rain and overall storage in the seed bank
Through understanding soil seed bank compositions we can begin to predict the potential future of the aboveground vegetation community and effects of a forest thinning treatment on the vegetation community as a whole

Summary

Introduction

Following decades of fire suppression and climate change, the severity and frequency of forest wildfires are increasing across multiple ecosystems [1,2,3,4,5,6]. Increasing fire hazards and fuel densities coupled with human encroachment into the wildland urban interface have prompted managers to implement fuel reduction treatments to reduce potential crown fire hazard and threat to property [3,5,7,8,9,10]. One such fuels reduction treatment is mastication or the chipping or shredding of unwanted small diameter trees and shrubs, followed by broadcasting this material, commonly called mulch, across the treatment area [10,11]. At stand level scales, such as over an entire thinning project, mulching has been shown to increase plant diversity and cover due to an increase in light and the maintenance and enhancement of soil moisture [16,18,20]

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