Frequent wildfires erode tree persistence and alter stand structure and initial composition of a fire‐tolerant sub‐alpine forest

Fairman, Thomas A.; Bennett, Lauren T.; Tupper, Shauna; Nitschke, Craig R.

doi:10.1111/jvs.12575

Cited by 90 publications

(72 citation statements)

References 87 publications

(154 reference statements)

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“…, Fairman et al. ). This threat is evidenced by the 2016 Soberanes fire, which was caused by a human ignition and re‐burned a large portion of the region impacted by the 2008 Basin Complex fires' under a narrow return interval.…”

Section: Discussionmentioning

confidence: 99%

“…Shortened fire intervals may also impact resprouter persistence, reducing resprouters' abilities to recover after aboveground damage (Canadell and Lopez‐Soria , Fairman et al. ). Shifts in the occurrence of resprouters' “persistence niche” may have concrete consequences for resilience, competition, and regeneration in a variety of systems impacted by altered disturbances where resprouters are present (Clarke et al.…”

Section: Introductionmentioning

confidence: 99%

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Novel disturbance interactions between fire and an emerging disease impact survival and growth of resprouting trees

Simler

Metz

Frangioso

et al. 2018

Ecology

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Human-altered ecological disturbances may challenge system resilience and disrupt biological legacies maintaining ecosystem recovery. Yet, the extent to which novel regimes challenge these legacies varies. This may be partially explained by differences in the vulnerability of life history strategies to disturbance characteristics. In the fire-prone, resprouter-dominated coast redwood forests of California, the introduced disease sudden oak death (SOD) alters fuel profiles, fire behavior, and aboveground tree mortality; however, this system is dominated by resprouting trees that are well-adapted to aboveground damage, and belowground survival of individuals may represent the principal biological legacy connecting pre- and post-fire communities. Much of the research exploring altered disturbances and forest recovery has focused on legacies determined by seed dispersal and aboveground survival of adults. In this work, we use pre- and post-fire data from a long-term monitoring network to assess the impacts of novel disturbance interactions between wildfire and SOD on the belowground survival and vegetative reproduction of resprouters. We found that increasing accumulation of coarse woody surface fuels from SOD-killed hosts decreased the likelihood of belowground survival for resprouting tanoak trees, but not for redwoods. Tanoaks' belowground survival was negatively related to substrate burn severity, which increased with the volume of surface fuels from hosts, suggesting heat damage as a possible mechanism influencing altered patterns of resprouter mortality. These impacts increased with decreasing tree size. By contrast, redwood and tanoak trees that survived both disturbances resprouted more vigorously, regardless of post-fire infection by P. ramorum, and generated similar recruitment at the stand level. Our results demonstrate that disease-fire interactions can narrow recruitment filters for resprouters, which could impact long-term population and demographic structure; yet, compounded disturbance may also reduce stand density and disease pressure, allowing competitive release of survivors. Resprouters displayed vulnerabilities to altered disturbance, but our research suggests that legacies maintained by resprouting may be more resilient to certain compounded disturbances, compared to seed-obligate species, because of high rates of individual survival under increasingly severe events. These trends have important implications for conservation of declining tree species in SOD-impacted forests, as well as predictions of human impacts in other disturbance-prone systems where resprouters are present.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Novel disturbance interactions between fire and an emerging disease impact survival and growth of resprouting trees

Simler

Metz

Frangioso

et al. 2018

Ecology

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“…, Fairman et al. ). Aboveground carbon is less affected by a single fire event in forests dominated by tree species that resprout epicormically (Volkova and Weston ), except under extreme conditions that result in high rates of tree mortality (e.g., extreme fire intensity following drought; Bennett et al.…”

Section: Introductionmentioning

confidence: 99%

“…In forests, most aboveground carbon (AGC) is stored in live trees (Hubbard et al 2004, Gordon et al 2018), consequently ecosystem carbon losses during a fire are generally relatively small (Volkova andWeston 2013, Keith et al 2014). Redistribution of carbon from the live to dead pool will depend on fire response syndromes of plant species, with high redistribution occurring in forests dominated by obligate seeder and basal resprouter tree species (Keith et al 2014, Fairman et al 2017). Aboveground carbon is less affected by a single fire event in forests dominated by tree species that resprout epicormically (Volkova and Weston 2013), except under extreme conditions that result in high rates of tree mortality (e.g., extreme fire intensity following drought; Bennett et al 2016).…”

Section: Introductionmentioning

confidence: 99%

Aboveground forest carbon shows different responses to fire frequency in harvested and unharvested forests

Collins

Bradstock

Ximenes

et al. 2018

Ecological Applications

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Sequestration of carbon in forest ecosystems has been identified as an effective strategy to help mitigate the effects of global climate change. Prescribed burning and timber harvesting are two common, co‐occurring, forest management practices that may alter forest carbon pools. Prescribed burning for forest management, such as wildfire risk reduction, may shorten inter‐fire intervals and potentially reduce carbon stocks. Timber harvesting may further increase the susceptibility of forest carbon to losses in response to frequent burning regimes by redistributing carbon stocks from the live pools into the dead pools, causing mechanical damage to retained trees and shifting the demography of tree communities. We used a 27‐yr experiment in a temperate eucalypt forest to examine the effect of prescribed burning frequency and timber harvesting on aboveground carbon (AGC). Total AGC was reduced by ~23% on harvested plots when fire frequency increased from zero to seven fires, but was not affected by fire frequency on unharvested plots. The reduction in total AGC associated with increasing fire frequency on harvested plots was driven by declines in large coarse woody debris (≥10 cm diameter) and large trees (≥20 cm diameter). Small tree (<20 cm DBH) AGC increased with fire frequency on harvested plots, but decreased on unharvested plots. Carbon in dead standing trees decreased with increasing fire frequency on unharvested plots, but was unaffected on harvested plots. Small coarse woody debris (<10 cm diameter) was largely unaffected by fire frequency and harvesting. Total AGC on harvested plots was between 67% and 82% of that on unharvested plots, depending on burning treatment. Our results suggest that AGC in historically harvested forests may be susceptible to declines in response to increases in prescribed burning frequency. Consideration of historic harvesting will be important in understanding the effect of prescribed burning programs on forest carbon budgets.

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“…), more frequent disturbance (Fairman et al. ), drought (Worrall et al. ), and emergence of new diseases (Rizzo and Garbolotto , Simler‐Williamson et al.…”

Section: Introductionmentioning

confidence: 99%

Compound disease and wildfire disturbances alter opportunities for seedling regeneration in resprouter‐dominated forests

et al. 2019

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Human‐altered disturbance regimes and changing climatic conditions can reduce seed availability and suitable microsites, limiting seedling regeneration in recovering forest systems. Thus, resprouting plants, which can persist in situ, are expected to expand in dominance in many disturbance‐prone forests. However, resprouters may also be challenged by changing regimes, and the mechanisms determining facultative seedling recruitment by resprouting species, which will determine both the future spread and current persistence of these populations, are poorly understood. In the resprouter‐dominated forests of coastal California, interactions between wildfire and an emerging disease, sudden oak death (SOD), alter disturbance severity and tree mortality, which may shift forest regeneration trajectories. We examine this set of compound disturbances to (1) assess the influence of seed limitation, biotic competition, and abiotic conditions on seedling regeneration in resprouting populations; (2) investigate whether disease‐fire interactions alter postfire seedling regeneration, which have implications for future disease dynamics and shifts in forest composition. Following a wildfire that impacted a preexisting plot network in SOD‐affected forests, we monitored seedling abundances and survival over eight years. With pre‐ and postfire data, we assessed relationships between regeneration dynamics and disturbance severity, biotic, and abiotic variables, using Bayesian generalized linear models and mixed models. Our results indicate that postfire seedling regeneration by resprouting species was shaped by contrasting mechanisms reflecting seed limitation and competitive release. Seedling abundances declined with decreasing postfire survival of mature, conspecific stems, while belowground survival of resprouting genets had no effect. However, where seed sources persisted, seedling abundances and survival generally increased with the prefire severity of disease impacts, suggesting that decreased competition with adults may enhance seedling recruitment in this resprouter‐dominated system. Species’ regeneration responses varied with their relative susceptibility to SOD and suggest compositional shifts, which will determine future disease management and forest restoration actions. These results additionally highlight that mechanisms related to biotic competition, seed limitation, and opportunities for seedling recruitment beneath mature canopies may determine possible shifts in the occurrence of resprouting traits. This result has broad applications to other systems impacted by human‐altered regimes where asexual persistence may be predicted to be a beneficial life history strategy.

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Frequent wildfires erode tree persistence and alter stand structure and initial composition of a fire‐tolerant sub‐alpine forest

Cited by 90 publications

References 87 publications

Novel disturbance interactions between fire and an emerging disease impact survival and growth of resprouting trees

Novel disturbance interactions between fire and an emerging disease impact survival and growth of resprouting trees

Aboveground forest carbon shows different responses to fire frequency in harvested and unharvested forests

Compound disease and wildfire disturbances alter opportunities for seedling regeneration in resprouter‐dominated forests

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