Synthesis of Research Into the Long-term Outlook for Sierra Nevada Forests Following the Current Bark Beetle Epidemic
Synthesis of Research Into the Long-term Outlook for Sierra Nevada Forests Following the Current Bark Beetle Epidemic

Author:

Publisher:

Published: 2019

Total Pages: 27

ISBN-13:

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This paper summarizes the 2012-2017 bark beetle epidemic in the Sierra Nevada and its implications for long-term changes in tree species composition and forest structure. Preliminary plot and landscape-scale data are reviewed, showing higher levels of mortality for pine species and greater impacts in the southern Sierra Nevada compared to the northern portions of the range. The federal government owns approximately three quarters of the forested area impacted by high levels of tree morality, with the remainder of the land controlled by nonindustrial (18%) and industrial (6%) ownerships. The accumulation of dead and downed fuel and standing dead trees is expected to increase fire intensity and severity, and pose significant hazards for fire control efforts. Potential long-term changes in Sierra Nevada forest composition were explored with a GIS analysis conducted for the Sierra National Forest, located in the southern Sierra. GIS layers included very high fire threat, aspect, high tree mortality, topographic position classification, and climatic exposure. A factor of one was assigned to each parameter (i.e., no weighting for any of the variables). The modeling showed that 4% of the Sierra National Forest is at very high risk for type conversion from mixed conifer to shrublands, and 12% is at high risk. This information can inform landowners regarding the general locations where successful reforestation will be most challenging, as well as illustrate the scale of concern for one national forest in the southern Sierra Nevada. Changes to disturbance regimes, continuing land use changes, and climate change with associated species shifts pose significant challenges for maintaining healthy and resilient forests in the Sierra Nevada. Significant unknowns exist regarding the future species composition for vast portions of this region, but type conversions from mixed conifer to shrublands or oak/grass/woodland appear likely for some areas. Recommended best management practices focus on reducing tree densities, achieving successful reforestation, and using adaptive management in the face of currently unknown future changes in growing conditions. With the exception of the bark beetle epidemic in southern California in the early 2000s, lessons learned from other locations in western North America that have had sustained bark beetle epidemics in the past decade are not directly applicable to Sierra Nevada, with its Mediterranean climate, complex topography, and mixed-conifer forests. For these reasons, ongoing research efforts to characterize and understand tree mortality drivers and changes in forest structure and composition in the Sierra Nevada are extremely important.

Grazing in Future Multi-scapes: From Thoughtscapes to Landscapes, Creating Health from the Ground Up
Grazing in Future Multi-scapes: From Thoughtscapes to Landscapes, Creating Health from the Ground Up

Author: Pablo Gregorini

Publisher: Frontiers Media SA

Published: 2022-09-27

Total Pages: 649

ISBN-13: 288976463X

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This Research Topic is hosted in partnership with the "Grazing in Future Multi-Scapes" international workshop. The workshop will be held online, 30th May - 5th June 2021. Throughout different landscapes of the world, “grazing” herbivores fulfill essential roles in ecology, agriculture, economies and cultures including: families, farms, and communities. Not only do livestock provide food and wealth, they also deliver ecosystem services through the roles they play in environmental composition, structure and dynamics. Grazing, as a descriptive adjective, locates herbivores within a spatial and temporal pastoral context where they naturally graze or are grazed by farmers, ranchers, shepherds etc. In many cases, however, pastoralism with the single objective of maximizing animal production and/or profit has transformed landscapes, diminishing biodiversity, reducing water and air quality, accelerating loss of soil and plant biomass, and displacing indigenous animals and people. These degenerative landscape transformations have jeopardized present and future ecosystem and societal services, breaking the natural integration of land, water, air, health, society and culture. Land-users, policy makers and societies are calling for alternative approaches to pastoral systems; a call for diversified-adaptive and integrative agro-ecological and food-pastoral-systems designs that operate across multiple scales and ‘scapes’ (e.g. thought-, social-, land-, food-, health-, wild-scapes), simultaneously. There needs to be a paradigm shift in pastoral production systems and how grazing herbivores are managed –grazed- within them, derived initially from a change in perception of how they provide wealth. The thoughtscapes will include paradigm shifts where grazers move away from the actual archetype of pastoralism, future landscapes are re-imagined, and regenerative and sustainable management paradigms are put in place to achieve these visions. From this will come a change in collective thinking of how communities and cultures (socialscapes) perceive their relationships with pastoral lands. The landscapes are the biotic and abiotic four-dimensional domains or environments in need of nurture. Landscapes are the tables where humans and herbivores gain their nourishment, i.e. foodscapes. Foodscapes and dietary perceptions, dictate actions and reactions that are changing as developed countries grapple with diseases related to obesity, and people starve in developing countries. Societies are demanding healthscapes and nutraceutical foodscapes, and paradoxically, some are moving away from animal products. While indigenous species of animals, including humans (wildscapes), have been displaced from many of their lands by monotonic pastoralism, multifunctional pastoral systems can be designed in view of dynamic multi-scapes of the future. The purpose of this Research Topic is to influence future mental and practical models of pastoralism in continually evolving multi-scapes. We seek a collection of papers that will cultivate such a shift in thinking towards future models of sustainable multipurpose pastoralism. The contributions will be synthesized to establish how multifunctional pastoral systems can be re-imagined and then designed in view of the integrative dynamics of sustainable future multi-scapes.

Mechanisms and Spatial Patterns of Bark Beetle-associated Mortality Following Variable Density Thinning Treatments in a Sierra Mixed-conifer Forest
Mechanisms and Spatial Patterns of Bark Beetle-associated Mortality Following Variable Density Thinning Treatments in a Sierra Mixed-conifer Forest

Author: Alexis Bernal

Publisher:

Published: 2019

Total Pages: 96

ISBN-13:

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Long-term trends of tree mortality have increased over the last several decades, coinciding with above-average temperatures, high climatic water deficits, and bark beetle outbreaks. With the anticipation that drought and bark beetles may increase with climate change, uncertainty exists over the appropriate treatments that could ensure the future sustainability of forest resources and the ecosystem services that forests provide. Conventional thinning treatments are used to reduce stand density, with the assumption that reductions in competition can alleviate drought stress and enable trees to resist bark beetle attack. Alternative thinning treatments may also reduce stand density, but have a greater focus on increasing spatial heterogeneity. Variable density thinning is a management method intended to mimic the spatial heterogeneity that was present in mixed-conifer forests prior to logging and fire exclusion. Although the added benefits of increasing spatial heterogeneity include biodiversity, wildlife, recreation, and restoration, information is lacking on the effects that these treatments have on tree resistance to disturbances. Since 2012, the Sierra Nevada experienced widespread tree mortality coinciding with severe drought conditions and bark beetle outbreak. This provided a unique opportunity to explore the mechanisms driving bark beetle-associated mortality following variable density thinning treatments in the central Sierra Nevada. Using dendrochronological methods, we modeled the relationship between drought resistance and bark beetle-associated mortality to evaluate if reductions in competition enhance tree resistance to bark beetles. We also determined if structural elements within variable density thinning treatments influenced the level and spatial pattern of bark beetle-associated mortality. By exploring these relationships, our findings could provide a greater understanding on the underlying mechanisms that drive mortality to disturbances and also provide information to help develop prescriptions for enhancing resistance to drought and bark beetles.

Influence of Past Management on Landscape-scale Dynamics of Indigenous Pathogens and Their Conifer Hosts in Sierra Nevada Forests
Influence of Past Management on Landscape-scale Dynamics of Indigenous Pathogens and Their Conifer Hosts in Sierra Nevada Forests

Author: Heather Kathryn Mehl

Publisher:

Published: 2012

Total Pages:

ISBN-13: 9781267400604

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The effects of forest management on pathogen dynamics in Sierra Nevada forests are examined in two distinct systems in this thesis. The first chapter focuses on the causes of forest canopy gaps in Yosemite Valley, where the frequency of disease centers initiated by two native root disease fungi (Heterobasidion irregulare and Armillaria mellea) have increased as an unintended consequence of land management practices implemented decades to over a century ago. Ground surveys were conducted in 1999 and 2011, and photographs from 1972 were used to examine long-term changes in gap causes, frequencies, and sizes. Native root diseases, in conjunction with pine bark beetles, were the most frequent agents of gap initiation. Other gap initiating agents included additional species of bark beetles and heart and butt rotting fungi. Specific mortality agents did not affect the forest in the same way; organisms differed in their influences on gap size, selectivity of tree species removed from the forest, and their response to altered stand conditions. Over the past thirty-nine years, the number and sizes of canopy gaps in the Valley have continually increased, resulting in the loss of roughly one-third of the forest canopy in the west end of Yosemite Valley by 2011, largely as a consequence of the persistence and expansion of root disease-associated gaps over time. This study demonstrates how previous land management (e.g., tree removal, fire suppression) can impact vegetation dynamics over extended time scales, and highlights the importance of considering land-use legacies when interpreting current landscape patterns and processes, and planning future conservation and management objectives. The study presented in the second chapter examines forests dominated by true fir (Abies spp.) infected with dwarf mistletoes (Arceuthobium spp.) throughout the Sierra Nevada. Often, when fir stands are managed for timber, understory trees are left on site following harvest for stand re-stocking. With this type of management, dwarf mistletoe infection on residual firs is a frequent concern. This study examined the effects of dwarf mistletoe infection on developing red (A. magnifica) and white (A. concolor) fir and the efficacy of pre-commercial thinning for reducing losses associated with dwarf mistletoe infection. Radial growth and dwarf mistletoe infection severity were monitored for 20 years, and mortality for 25 years. Fir survival and radial growth decreased with increasing dwarf mistletoe infection severity, and thinning increased survival times and radial growth rates. However, the intensification of dwarf mistletoe on individual trees and spread to previously uninfected trees was greater in thinned than unthinned stands. The results of this study suggest that pre-commercial thinning may help compensate for growth and mortality losses; however, the impact of dwarf mistletoe infection on true firs has been minimal over the course of this study, and so the benefits of thinning may not justify the expense of applying treatments for dwarf mistletoe control in these stands.

Distribution of Bark Beetle Attacks on Ponderosa Pine Trees in Montana
Distribution of Bark Beetle Attacks on Ponderosa Pine Trees in Montana

Author: Philip Cornwell Johnson

Publisher:

Published: 1967

Total Pages: 8

ISBN-13:

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The boles of 71 mature ponderosa pine trees killed by Dendroctonus brevicomis LeConte (Coleoptera: Scolytidae) were analyzed to determine the distribution of the attacks by endemic populations of this bark beetle and those of several phloem -feeding associates. The longitudinal -circumferential distribution of the attacks fitted dia- grammatically into four distinguishable bole infestation patterns. The characteristics of the patterns and similarities with comparable ‍?attacks of D. brevicomis in northeastern California are discussed.

Plant Community Response to Thinning and Repeated Fire in a Sierra Nevada Mixed-conifer Forest Understory
Plant Community Response to Thinning and Repeated Fire in a Sierra Nevada Mixed-conifer Forest Understory

Author: Maxwell Odland

Publisher:

Published: 2020

Total Pages: 0

ISBN-13:

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Fire suppression in the western United States has significantly altered forest composition and structure, resulting in higher risk from fire and large-scale drought and bark beetle events. Mechanical thinning and prescribed fire are common treatments designed to reduce high-severity fire risk, but few studies have tracked long-term understory plant community response with repeated fire application that emulates historic fire regimes. We evaluate changes in understory plant community diversity and composition and environmental characteristics over two decades following a factorial field experiment that crosses thinning and two applications of prescribed fire at the Teakettle Experimental Forest (TEF) in the southern Sierra Nevada. We compare experimental fuels treatments against nearby old-growth, mixed-conifer forests with frequent, low severity fire regimes in Yosemite and Kings Canyon National Parks. This study points to key differences in how thinning and prescribed fire treatments affect plant understory diversity. Although local understory plant richness initially increased most following thinning combined with prescribed fire, this treatment did not generate understory communities similar to those in reference forests; Intense shrub growth resulted in low understory evenness and beta diversity over time, which a secondary burn treatment did not alter. Burning without thinning retained a more heterogeneous understory over time and, at least in the two years following the second burn treatment, with high understory richness and evenness similar to reference forest understories. Our results suggest management treatments may need to focus on creating heterogeneity in burn effects and environmental conditions to foster diverse forest understories and limit post-treatment shrub cover.