Benefits of thinning and burning for understory diversity vary with spatial scale and time since treatment

Rossman, Allison K.; Halpern, Charles B.; Harrod, Richy J.; Urgenson, Lauren S.; Peterson, David W.; Bakker, Jonathan D.

doi:10.1016/j.foreco.2018.03.006

Cited by 21 publications

(21 citation statements)

References 77 publications

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“…, Kerns and Day ), while others report sustained richness improvements over unburned stands (Webster and Halpern , Rossman et al. ). Overall, it appears that the impact of MPB outbreak on burning treatments in this study did not modify the understory vegetation compared with the untreated stands, but MPB outbreak did negatively interact with overstory structure and composition in the control and burn‐only treatments by killing many of the ponderosa pines up to 55 cm dbh.…”

Section: Discussionmentioning

confidence: 97%

“…Douglas-fir sapling growth in the post-treatment growth period increased crown fire hazard by reducing the gap between surface and canopy fuels (this study and Crotteau et al 2018b), and if not tended soon, saplings will resist future lowintensity prescribed fire as bark thickens, making future fire-only management strategies more challenging. Compounded growth and MPB outbreak have reduced the relative longevity of the thinned units, but the thin + burn is still sufficiently different because of the combined overstory and understory treatment (similar to studies without MPB outbreak, e.g., Stephens et al 2012, Rossman et al 2018. Given that historical fire return intervals at Lubrecht Experimental Forest ranged up to 14 yr (Grissino-Mayer et al 2006), the same period over which this study reports an overall trend toward convergence, this interval may also be appropriate as a treatment regime return interval to improve long-term resilience in this forest type (Reinhardt et al 2008), though increased fire frequencies with warming climate may require shorter treatment return intervals.…”

Section: Treatment Convergence and Longevitymentioning

confidence: 90%

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Vegetation dynamics following compound disturbance in a dry pine forest: fuel treatment then bark beetle outbreak

Crotteau

Keyes

Hood

et al. 2019

Ecological Applications

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In the western United States, restoration of forests with historically frequent, low‐severity fire regimes often includes fuel reduction that reestablish open, early‐seral conditions while reducing fuel continuity and loading. Between 2001 and 2016, fuel reduction (e.g., thinning, prescribed burning, etc.) was implemented on over 26 million hectares of federal lands alone in the United States, reflecting the urgency to mitigate risk from high‐severity wildfire. However, between 2001 and 2012, nearly 20 million hectares in the United States were impacted by mountain pine beetle (MPB; Dendroctonus ponderosae), compounding restoration effects in wildfire‐hazard‐treated stands. Knowledge of the effects of treatments followed by natural disturbance on long‐term forest structure and communities is needed, especially considering that fuel treatments are increasingly being implemented and warming climate is predicted to exacerbate disturbance frequency and severity. We tested the interacting effects of treatments designed to reduce high‐severity wildfire hazard in stands subsequently challenged by MPB outbreak on vegetation dynamics using a factorial experimental design (control, thin only, burn only, thin + burn) in a ponderosa pine (Pinus ponderosa)‐dominated forest. Stands were treated by 2002, then impacted by MPB outbreak from 2005 to 2012. We assessed change in overstory and understory forest community structure, composition, and diversity over time. There were distinct thinning, burning, and year effects. Thinning immediately reduced overstory density; pine density then declined 4.5 times more in unthinned than thinned treatments due to MPB. Burning immediately reduced graminoid, shrub, and total understory cover by as much as 52%, resulting in greater species evenness than unburned treatments, but differences disappeared by 2016 due to growth and MPB outbreak. Similarly, multivariate analyses indicated forest communities were starkly different after treatment but became more similar over time, though key understory and overstory attributes still distinguish control and thin + burn. This study shows the value of long‐term silvicultural experiments to evaluate treatment longevity and the compounded effects of treatment and natural disturbance. We demonstrate the homogenizing effects of treatment‐induced growth coupled with MPB‐caused tree mortality on management strategies that just treat the overstory (thinning) or understory (burning), showing that only combined treatments can provide the unique structural and compositional outcomes expected of restoration.

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Section: Discussionmentioning

confidence: 97%

Section: Treatment Convergence and Longevitymentioning

confidence: 90%

Vegetation dynamics following compound disturbance in a dry pine forest: fuel treatment then bark beetle outbreak

Crotteau

Keyes

Hood

et al. 2019

Ecological Applications

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“…), particularly for herbaceous perennials (Rossman et al. ). Lack of long‐term (15 yr) plant responses to a single‐entry burn may be expected in forests that are characterized historically by frequent fire.…”

Section: Discussionmentioning

confidence: 99%

“…, Rossman et al. ) or homogenize plant community patterns. Others point out that these inconsistencies may reflect the fact that species‐specific responses are lost when all taxa are lumped together into very broad categories such as herbaceous plants (Willms et al.…”

Section: Discussionmentioning

confidence: 99%

“…, Rossman et al. ). For example, some studies show an increase in understory richness and abundance 3–5 yr after fire, especially for short‐lived forbs, supporting the notion that use of finer‐scale functional groups can help elucidate plant responses to fire, although responses may still be ephemeral (e.g., Metlen and Fiedler , Strahan et al.…”

Section: Discussionmentioning

confidence: 99%

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Prescribed fire regimes subtly alter ponderosa pine forest plant community structure

Kerns

Day

2018

Ecosphere

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Prescribed fire is an active management tool used to address wildfire hazard and ecological concerns associated with fire exclusion and suppression over the past century. Despite widespread application in the United States, there is considerable inconsistency and lack of information regarding the extent to which specific outcomes are achieved and under what prescribed fire regimes, particularly in regard to ecological goals related to plant community structure. We quantify differences and patterns in plant functional group abundance, species richness and diversity, and other key forest components through time from a unique long‐term (15‐yr) experiment within the Malheur National Forest of Oregon. Treatments included five fire regimes: fall and spring 5‐yr burning, fall and spring single burn, and no burning. Original burns were conducted in the fall of 1997 and spring of 1998, and plant data were collected every five years starting in 2002. Many perennial plant group responses were neutral, subtle, and ephemeral. Total cover increased marginally in response to the first burn, but this response disappeared within a decade. Three 5‐yr reburns did not increase or decrease total plant cover, richness, or diversity. Some plant groups with fire resistant and resilient traits, such as annual forbs, exotic forbs, open bunchgrasses, and rhizomatous and resprouting perennials, showed some short‐term positive responses to initial burning and 1–2 reburns, but not 3. The moderately more severe fall burns generally impacted plant responses more than spring burning, but many patterns were legacies from the original higher severity burns. Burn frequency was more important for less severe spring burning. Overall, we document that most native perennial plant functional groups were able to resist or recover from burning and reburning, but did not necessarily strongly respond. This may be due to the importance of other overriding forcing factors and ecosystem inertia not easily overcome by very low‐severity prescribed burns. Results from our study are important for practitioners using prescribed fire to achieve biodiversity, conservation, and habitat goals that hinge on a vigorous native perennial plant response, as such outcomes are not certain even with frequent burn regimes.

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The effects of forest thinning on understory diversity in China: A meta‐analysis

Zhang

et al. 2020

Land Degrad Dev

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Forest management has been widely used to maintain and improve multiple ecosystem services. However, large‐scale synthesis of the effects of forest management on understory diversity, especially regarding the effects of thinning, has not been well represented in China. Therefore, we synthesized 146 peer‐reviewed publications and conducted a meta‐analysis to evaluate the response of understory diversity (species richness) and seven related variables to forest thinning in China. Overall, forest thinning significantly increased shrub diversity by 28% and herb diversity by 24%. Unthinned diversity and recovery time were the two most important drivers of understory diversity. When the unthinned diversity was low, a decline of understory species richness in managed stands could occur, which may be related to the size of the regional species pool. Rather than the recovery time of 1–2 years after forest thinning, the period of 3–5 years after thinning found the greatest diversity improvement. The northern arid and semiarid ecological domains observed the greatest diversity improvement, which may be due to the specific characteristics in this ecological domain. The coniferous forest was more favorable for understory improvement than in the broadleaved forest. Specific mechanisms on how disturbance (thinning intensity) affect understory diversity need to be further explored. No significant influences of stand stage or sampling quadrat area could be identified. Our study provides a synthetic review of the effects of forest thinning on understory diversity in China and may benefit forest management strategies. Future studies should address changes in compositional or functional diversity after thinning.

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Benefits of thinning and burning for understory diversity vary with spatial scale and time since treatment

Cited by 21 publications

References 77 publications

Vegetation dynamics following compound disturbance in a dry pine forest: fuel treatment then bark beetle outbreak

Vegetation dynamics following compound disturbance in a dry pine forest: fuel treatment then bark beetle outbreak

Prescribed fire regimes subtly alter ponderosa pine forest plant community structure

The effects of forest thinning on understory diversity in China: A meta‐analysis

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