The Bark Beetles, Fuels, and Fire Bibliography

Do Bark Beetle Outbreaks Increase Wildfire Risks in the Central U.S. Rocky Mountains? Implications from Recent Research

Scott H. Black et al. — Thu, 18 Apr 2013 09:08:52 PDT

ABSTRACT: Appropriate response to recent, widespread bark beetle (Dendroctonus spp.) outbreaks in the western United States has been the subject of much debate in scientific and policy circles. Among the proposed responses have been landscape-level mechanical treatments to prevent the further spread of outbreaks and to reduce the fire risk that is believed to be associated with insect-killed trees. We review the literature on the efficacy of silvicutural practices to control outbreaks and on fire risk following bark beetle outbreaks in several forest types. While research is ongoing and important questions remain unresolved, to date most available evidence indicates that bark beetle outbreaks do not substantially increase the risk of active crown fire in lodgepole pine (Pinus contorta) and spruce (Picea engelman- nii)-fir (Abies spp.) forests under most conditions. Instead, active crown fires in these forest types are primarily contingent on dry conditions rather than variations in stand structure, such as those brought about by outbreaks. Preemptive thinning may reduce susceptibility to small outbreaks but is unlikely to reduce susceptibility to large, landscape-scale epidemics. Once beetle populations reach widespread epidemic levels, silvicultural strategies aimed at stopping them are not likely to reduce forest susceptibility to outbreaks. Furthermore, such silvicultural treatments could have substantial, unintended short- and long-term ecological costs associated with road access and an overall degradation of natural areas.

The Effects of Bark Beetle Outbreaks on Forest Development, Fuel Loads and Potential Fire Behavior in Salvage Logged and Untreated Lodgepole Pine Forests

B J. Collins et al. — Thu, 18 Apr 2013 09:08:50 PDT

Recent mountain pine beetle infestations have resulted in widespread tree mortality and the accumula- tion of dead woody fuels across the Rocky Mountain region, creating concerns over future forest stand conditions and fire behavior. We quantified how salvage logging influenced tree regeneration and fuel loads relative to nearby, uncut stands for 24 lodgepole pine forests in north-central Colorado that had experienced >70% overstory mortality from mountain pine beetles. We used our field measurements to predict changes in fuel loads and potential fire behavior in the forests that develop over the century fol- lowing the outbreak and associated harvesting. Our field measurements and stand development projec- tions suggest that salvage logging will alter the potential for canopy fire behavior in future stands by creating conditions that promote regeneration of lodgepole pine and quaking aspen as opposed to sub- alpine fir. The abundant subalpine fir that has regenerated in untreated, beetle-killed stands is predicted to form a stratum of ladder fuels more likely to allow fires burning on the surface to spread into the forest canopy. Harvesting increased woody surface fuels more than 3-fold compared to untreated stands imme- diately after treatments; however, coarse fuels will increase substantially (by 􏰀55 Mg ha􏰁1) in untreated stands within three decades of the beetle infestation as dead trees topple, and the elevated fuel loads will persist for more than a century. Though salvage logging will treat a small fraction of beetle-infested Col- orado forests, in those areas treatment will affect stand development and fuel loads and will alter poten- tial fire behavior for more than a century.

Mountain pine beetle host-range expansion threatens the boreal forest

Catherine I. Cullingham et al. — Thu, 18 Apr 2013 09:08:48 PDT

Abstract

The current epidemic of the mountain pine beetle (MPB), an indigenous pest of western North American pine, has resulted in significant losses of lodgepole pine. The leading edge has reached Alberta where forest composition shifts from lodgepole to jack pine through a hybrid zone. The susceptibility of jack pine to MPB is a major concern, but there has been no evidence of host-range expansion, in part due to the difficulty in distinguishing the parentals and their hybrids. We tested the utility of a panel of microsatellite loci optimized for both species to classify lodgepole pine, jack pine and their hybrids using simulated data. We were able to accurately classify simulated individuals, and hence applied these markers to identify the ancestry of attacked trees. Here we show for the first time successful MPB attack in natural jack pine stands at the leading edge of the epidemic. This once unsuitable habitat is now a novel environment for MPB to exploit, a potential risk which could be exacerbated by further climate change. The consequences of host-range expansion for the vast boreal ecosystem could be significant.

Forest developmental trajectories in mountain pine beetle disturbed forests of Rocky Mountain National Park, Colorado

Matthew Diskin et al. — Thu, 18 Apr 2013 09:08:46 PDT

Abstract: A mountain pine beetle (Dendroctonus ponderosae Hopkins) epidemic has caused widespread mortality of lodge- pole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) trees across western North America,. We characterized the initial effects of beetle-induced mortality on forest structure and composition in Rocky Mountain National Park, Colorado. In 2008, we surveyed stand structure and tree species composition across lodgepole pine dominated forests in the western portion of the Park. We defined five lodgepole pine forest types to describe variability in pre-epidemic forest conditions. This forested landscape appears to be resilient to the effects of the beetle. Surviving trees, including both canopy trees and saplings, were plentiful in most of the post-epidemic forests, even after accounting for anticipated future mortality. Subalpine fir (Abies lasiocarpa (Hook.) Nutt.), Engelmann spruce (Picea engelmannii Parry ex Engelm.), and aspen (Populus tremu- loides Michx.) had modestly higher relative abundances after the epidemic. Lodgepole pine remained the dominant species on approximately 85% of the landscape. The impact of the outbreak on forest structure and composition varied considerably among the five forest types, suggesting that post-epidemic forest developmental trajectories will vary according to pre- outbreak stand characteristics. Active management efforts to regenerate lodgepole pine forests, e.g., tree planting, will likely not be necessary on this landscape.

Bark beetle effects on fuel profiles across a range of stand structures in Douglas-fir forests of Greater Yellowstone

Daniel C. Donato et al. — Thu, 18 Apr 2013 09:08:45 PDT

Abstract. Consequences of bark beetle outbreaks for forest wildfire potential are receiving heightened attention, but little research has considered ecosystems with mixed-severity fire regimes. Such forests are widespread, variable in stand structure, and often fuel limited, suggesting that beetle outbreaks could substantially alter fire potentials. We studied canopy and surface fuels in interior Douglas-fir (Pseudotsuga menziesii v. glauca) forests in Greater Yellowstone, Wyoming, USA, to determine how fuel characteristics varied with time since outbreak of the Douglas-fir beetle (Dendroctonus pseudotsugae). We sampled five stands in each of four outbreak stages, validated for pre-outbreak similarity: green (undisturbed), red (1–3 yr), gray (4–14 yr), and silver (25–30 yr). General linear models were used to compare variation in fuel profiles associated with outbreak to variation associated with the range of stand structures (dense mesic forest to open xeric parkland) characteristic of interior Douglas- fir forest.

Beetle outbreak killed 38–83% of basal area within stands, generating a mix of live trees and snags over several years. Canopy fuel load and bulk density began declining in the red stage via needle drop and decreased by ;50% by the silver stage. The dead portion of available canopy fuels peaked in the red stage at 41%. After accounting for background variation, there was little effect of beetle outbreak on surface fuels, with differences mainly in herbaceous biomass (50% greater in red stands) and coarse woody fuels (doubled in silver stands). Within- stand spatial heterogeneity of fuels increased with time since outbreak, and surface-to-crown continuity decreased and remained low because of slow/sparse regeneration. Collectively, results suggest reduced fire potentials in post-outbreak stands, particularly for crown fire after the red stage, although abundant coarse fuels in silver stands may increase burn residence time and heat release. Outbreak effects on fuels were comparable to background variation in stand structure. The net effect of beetle outbreak was to shift the structure of mesic closed-canopy stands toward that of parklands, and to shift xeric parklands toward very sparse woodlands. This study highlights the importance of evaluating outbreak effects in the context of the wide structural variation inherent to many forest types in the absence of beetle disturbance.

Fuel loadings 5 years after a bark beetle outbreak in south-western USA ponderosa pine forests

Chad M. Hoffman et al. — Thu, 18 Apr 2013 09:08:43 PDT

Abstract. Landscape-level bark beetle (Coleoptera: Curculionidae, Scolytinae) outbreaks occurred in Arizona ponder- osa pine (Pinus ponderosa Dougl. ex Law.) forests from 2001 to 2003 in response to severe drought and suitable forest conditions. We quantified surface fuel loadings and depths, and calculated canopy fuels based on forest structure attributes in 60 plots established 5 years previously on five national forests. Half of the plots we sampled in 2007 had bark beetle- caused pine mortality and half did not have mortality. Adjusting for differences in pre-outbreak stand density, plots with mortality had higher surface fuel and lower canopy fuel loadings 5 years after the outbreak compared with plots without mortality. Total surface fuels averaged 2.5 times higher and calculated canopy fuels 2 times lower in plots with mortality. Nearly half of the trees killed in the bark beetle outbreak had fallen within 5 years, resulting in loadings of 1000-h woody fuels above recommended ranges for dry coniferous forests in 20% of the mortality plots. We expect 1000-h fuel loadings in other mortality plots to exceed recommended ranges as remaining snags fall to the ground. This study adds to previous work that documents the highly variable and complex effects of bark beetle outbreaks on fuel complexes.

Relationships between moisture, chemistry, and ignition of Pinus contorta needles during the early stages of mountain pine beetle attack

W. Matt Jolly et al. — Thu, 18 Apr 2013 09:08:41 PDT

Very little is known about how foliar moisture and chemistry change after a mountain pine beetle attack and even less is known about how these intrinsic foliar characteristics alter foliage ignitability. Here, we examine the fuel characteristics and ignition potential of Pinus contorta (lodgepole pine) foliage during the early stages of a mountain pine beetle attack. Foliar samples were taken periodically from multiple trees identified as green (healthy, unattacked), recently attacked, or red (dead). The fuel moisture con- tent, chemical composition, and time to ignition of needles from each attack category were quantified. Foliar moisture contents varied by an order of magnitude between the attack categories and were lowest for red needles (􏰀12% on average), highest for green needles (􏰀109% on average), and most variable for needles of recently attacked trees. Dry matter proportions of fiber in the needles of attacked and red trees were nearly twice that of green needles. Starch and sugar levels were much lower in the needles of attacked and red trees than green trees. Crude fat contents also differed between the attack categories. Time to ignition was strongly related to time since beetle attack. Ignition times varied from as little as 11 s for red needles to 41 s for green needles. A combined model of foliar moisture content, fiber, and crude fat explained 92% of the variation in the foliar time to ignition. Results show that decreased mois- ture contents and changes in foliar chemistry increase the foliar flammability of mountain pine beetle- attacked trees. This suggests that less heat would be required to ignite the foliage of attacked trees and thus crown fire potential may be higher in attacked stands as long as foliage is retained on the tree. Published by Elsevier B.V.

Forest structure altered by mountain pine beetle outbreaks affects subsequent attack in a Wyoming lodgepole pine forest, USA

Daniel M. Kashian et al. — Thu, 18 Apr 2013 09:08:38 PDT

Abstract: Extensive outbreaks of the mountain pine beetle (Dendroctonus ponderosae Hopkins) will alter the structure of many stands that will likely be attacked again before experiencing a stand-replacing fire. We examined a stand of lodgepole pine (Pinus contorta var. latifolia Engelm. ex S. Watson) in Grand Teton National Park currently experiencing a moderate- level outbreak and previously attacked by mountain pine beetle in the 1960s. Consistent with published studies, tree diame- ter was the main predictor of beetle attack on a given tree, large trees were preferentially attacked, and tree vigor, age, and cone production were unimportant variables for beetle attack at epidemic levels. Small trees killed in the stand were killed based mainly on their proximity to large trees and were likely spatially aggregated with large trees as a result of the previous outbreak. We concluded that the driving factors of beetle attack and their spatial patterns are consistent across outbreak se- verities but that stand structure altered by the previous outbreak had implications for the current outbreaks in the same loca- tion. This study should catalyze additional research that examines how beetle-altered stand structure affects future outbreaks — an important priority for predicting their impacts under climate change scenarios that project increases in out- break frequency and extent.

Low-severity fires increase susceptibility of lodgepole pine to mountain pine beetle outbreaks in Colorado

Dominik Kulalowski et al. — Thu, 18 Apr 2013 09:08:36 PDT

Both fire and insect outbreaks are critical components of many forest ecosystems and understanding the two-way interactions between these disturbance types is an important goal for researchers, resource managers, and policy makers. Much recent research has focused on understanding the effects of out- breaks on subsequent fires, but the effects of fires on subsequent outbreaks are also important in shaping ecosystem dynamics.

In the current study we examined how low-severity fires influence susceptibility of lodgepole pine to mountain pine beetle (MPB). We examined 607 lodgepole pine trees in stands that were affected by low- severity fire in 2002 and subsequent MPB outbreak in Routt National Forest, Colorado. For each tree we recorded effect by fire (no visible effect; visible effect – i.e. charring), recent effect by MPB (no visible effect; infestation – i.e. presence of MPB entry or exit holes; or mortality), dbh, and age (based on incre- ment core samples).

Tree diameter (dbh) was the most important factor in determining susceptibility to MPB such that lar- ger trees were more susceptible to MPB. But once dbh was taken into account, trees that were charred were more likely to have been attacked and killed by MPB. Previous work has found that stand-replacing fires reduce susceptibility of lodgepole pine stands to MPB in these ecosystems. The current results high- light the fact that fires that are below a high threshold of severity and instead injure or otherwise weaken trees, may increase susceptibility to MPB. Fire-affected lodgepole may act as vectors for the spread of out- breaks during moderate outbreak conditions or as refuges during endemic population phases. It is impor- tant to consider how low-severity fires, including prescribed burns, may increase forest susceptibility to outbreaks at local to landscape scales.

Modeling wind fields and fire propagation following bark beetle outbreaks in spatially-heterogeneous pinyon-juniper woodland fuel complexes

Rodman R. Linn et al. — Thu, 18 Apr 2013 09:08:34 PDT

We used a physics-based model, HIGRAD/FIRETEC, to explore changes in within-stand wind behav- ior and fire propagation associated with three time periods in pinyon-juniper woodlands following a drought-induced bark beetle outbreak and subsequent tree mortality. Pinyon-juniper woodland fuel complexes are highly heterogeneous. Trees often are clumped, with sparse patches of herbaceous veg- etation scattered between clumps. Extensive stands of dead pinyon trees intermixed with live junipers raised concerns about increased fire hazard, especially immediately after the trees died and dead needles remained in the trees, and later when the needles had dropped to the ground. Studying fire behavior in such conditions requires accounting for the impacts of the evolving heterogeneous nature of the wood- lands and its influence on winds that drive fires. For this reason we used a coupled atmosphere/fire model, HIGRAD/FIRETEC, to examine the evolving stand structure effects on wind penetration through the stand and subsequent fire propagation in these highly heterogeneous woodlands. Specifically, we studied how these interactions changed in woodlands without tree mortality, in the first year when dried needles clung to the dead trees, and when the needles dropped to the ground under two ambient wind speeds. Our simulations suggest that low wind speeds of 2.5 m/s at 7.5-m height were not sufficient to carry the fire through the discontinuous woodland stands without mortality, but 4.5 m/s winds at 7.5-m height were sufficient to carry the fire. Fire propagation speed increased two-fold at these low wind speeds when dead needles were on the trees compared to live woodlands. When dead needles fell to the ground, fine fuel loadings were increased and ambient wind penetration was increased enough to sustain burn- ing even at low wind speeds. At the higher ambient wind speeds, fire propagation in woodlands with dead needles on the trees also increased by a factor of ∼2 over propagation in live woodlands. These simulations indicate that sparse fuels in these heterogeneous woodlands can be overcome in three ways: by decreasing fuel moisture content of the needles with the death of the trees, by moving canopy dead needles to the ground and thus allowing greater wind penetration and turbulent flow into the woodland canopy, and increasing above-canopy wind speeds. 2012 Elsevier B.V. All Rights Reserved

Ecology Comments & Reply: Do mountain pine beetle outbreaks change the probability of active crown fire in lodgepole pine forests?

Christopher J. Moran et al. — Thu, 18 Apr 2013 09:08:32 PDT

Wildfire provides refuge from local extinction but is an unlikely driver of outbreaks by mountain pine beetle

Erinn N. Powell et al. — Thu, 18 Apr 2013 09:08:31 PDT

Abstract. Bark beetle outbreaks and wildfire are important disturbances in conifer ecosystems, yet their interactions are not well understood. We evaluated whether fire injury increased susceptibility of lodgepole pines (Pinus contorta) to mountain pine beetle (Dendroctonus ponderosae Hopkins), how it influenced beetle reproductive success, and whether beetle population phase altered this interaction. Eight sites that experienced wildfire and eight unburned sites were examined in the Greater Yellowstone Ecosystem (USA). Half were in areas where D. ponderosae was undergoing outbreaks, and half were in areas with low populations. We examined 2056 trees one year after fire for burn injury and beetle attack. We quantified beetle reproductive success in a random sample of 106 trees, and measured gallery areas of D. ponderosae and competing subcortical herbivores in 79 additional trees. Baited flight traps sampled stand-level populations of subcortical herbivores and predators.

Wildfire predisposed trees to D. ponderosae attack, but nonlinearly, with moderately injured trees being most preferred. This tree-level interaction was influenced by stand-level beetle population size, in that both healthy and fire-injured trees of all classes were attacked where populations were high, but no healthy trees, and only low and moderately injured trees were killed where populations were low. The number of adult brood produced per female was likewise curvilinear, being highest in moderately injured trees. This reflected an apparent trade-off, with high intraspecific competition arising from the large number of beetles needed to overcome defenses in healthy trees, vs. high interspecific competition and low substrate quality in more injured trees.

These results suggest that fire-injured trees can provide a reservoir for D. ponderosae during periods when populations are too low to overcome defenses of healthy trees, and might otherwise face localized extinction. However, the likelihood of populations increasing from endemic to outbreak levels in response to increased susceptibility is offset by the opposing constraints of lower substrate quality and higher competitor load in severely injured hosts, and the relative scarcity of moderately injured trees. Wildfire may confer some reproductive increases to populations already outbreaking. We present a conceptual model of how these disturbances and inherent feedbacks interact to affect beetle population dynamics.

Effects of Mountain Pine Beetle on Fuels and Expected Fire Behavior in Lodgepole Pine Forests, Colorado, USA

Tania Schoennagel et al. — Thu, 18 Apr 2013 09:08:29 PDT

In Colorado and southern Wyoming, mountain pine beetle (MPB) has affected over 1.6 million ha of predominantly lodgepole pine forests, raising concerns about effects of MPB-caused mortality on subsequent wildfire risk and behavior. Using empirical data we modeled potential fire behavior across a gradient of wind speeds and moisture scenarios in Green stands compared three stages since MPB attack (Red [1–3 yrs], Grey [4–10 yrs], and Old-MPB [,30 yrs]). MPB killed 50% of the trees and 70% of the basal area in Red and Grey stages. Across moisture scenarios, canopy fuel moisture was one-third lower in Red and Grey stages compared to the Green stage, making active crown fire possible at lower wind speeds and less extreme moisture conditions. More-open canopies and high loads of large surface fuels due to treefall in Grey and Old-MPB stages significantly increased surface fireline intensities, facilitating active crown fire at lower wind speeds (.30–55 km/hr) across all moisture scenarios. Not accounting for low foliar moistures in Red and Grey stages, and large surface fuels in Grey and Old-MPB stages, underestimates the occurrence of active crown fire. Under extreme burning conditions, minimum wind speeds for active crown fire were 25–35 km/hr lower for Red, Grey and Old-MPB stands compared to Green. However, if transition to crown fire occurs (outside the stand, or within the stand via ladder fuels or wind gusts .65 km/hr), active crown fire would be sustained at similar wind speeds, suggesting observed fire behavior may not be qualitatively different among MPB stages under extreme burning conditions. Overall, the risk (probability) of active crown fire appears elevated in MPB-affected stands, but the predominant fire hazard (crown fire) is similar across MPB stages and is characteristic of lodgepole pine forests where extremely dry, gusty weather conditions are key factors in determining fire behavior.

What explains landscape patterns of tree mortality caused by bark beetle outbreaks in Greater Yellowstone?

Martin Simard et al. — Thu, 18 Apr 2013 09:08:27 PDT

ABSTRACT

Aim Bark beetle outbreaks have recently affected extensive areas of western North American forests, and factors explaining landscape patterns of tree mortality are poorly understood. The objective of this study was to determine the relative impor- tance of stand structure, topography, soil characteristics, landscape context (the characteristics of the landscape surrounding the focal stand) and beetle pressure (the abundance of local beetle population eruptions around the focal stand a few years before the outbreak) to explain landscape patterns of tree mortality during outbreaks of three species: the mountain pine beetle, which attacks lodgepole pine and whitebark pine; the spruce beetle, which feeds on Engelmann spruce; and the Douglas-fir beetle, which attacks Douglas-fir. A second objective was to identify common variables that explain tree mortality among beetle–tree host pairings during outbreaks.

Location Greater Yellowstone ecosystem, Wyoming, USA.

Methods We used field surveys to quantify stand structure, soil characteristics and topography at the plot level in susceptible stands of each forest type showing different severities of infestation (0–98% mortality; n = 129 plots). We then used forest cover and beetle infestation maps derived from remote sensing to develop landscape context and beetle pressure metrics at different spatial scales. Plot-level and landscape-level variables were used to explain outbreak severity.

Results Engelmann spruce and Douglas-fir mortality were best predicted using landscape-level variables alone. Lodgepole pine mortality was best predicted by both landscape-level and plot-level variables. Whitebark pine mortality was best – although poorly – predicted by plot-level variables. Models including landscape context and beetle pressure were much better at predicting outbreak severity than models that only included plot-level measures, except for whitebark pine.

Main conclusions Landscape-level variables, particularly beetle pressure, were the most consistent predictors of subsequent outbreak severity within susceptible stands of all four host species. These results may help forest managers identify vulnerable locations during ongoing outbreaks.

Seed release in serotinous lodgepole pine forests after mountain pine beetle outbreak

Francois P. Teste et al. — Thu, 18 Apr 2013 09:08:25 PDT

Abstract. There are concerns that large-scale stand mortality due to mountain pine beetle (MPB) could greatly reduce natural regeneration of serotinous Rocky Mountain (RM) lodgepole pine (Pinus contorta var. latifolia) because the closed cones are held in place without the fire cue for cone opening. We selected 20 stands (five stands each of live [control], 3 years since MPB [3-yr-MPB], 6 years since MPB [6-yr-MPB], and 9 years since MPB [9-yr-MPB] mortality) in north central British Columbia, Canada. The goal was to determine partial loss of serotiny due to fall of crown-stored cones via breakage of branches and in situ opening of canopy cones throughout the 2008 and 2009 growing seasons. We also quantified seed release by the opening of forest-floor cones, loss of seed from rodent predation, and cone burial. Trees killed by MPB three years earlier dropped ;3.5 times more cones via branch breakage compared to live stands. After six years, MPB-killed stands had released 45% of their canopy seed bank through cone opening, cone fall due to breakage, and squirrel predation. Further losses of canopy seed banks are expected with time since we found 9-yr-MPB stands had 38% more open canopy cones. This was countered by the development of a modest forest-floor seed bank (6% of the original canopy seed bank) from burial of cones; this seed bank may be ecologically important if a fire or anthropogenic disturbance reexposes these cones. If adequate levels of regeneration are to occur, disturbances to create seedbeds must occur shortly after tree mortality, before the seed banks are lost. Our findings also suggest that the sustained seed rain (over at least nine years) after MPB outbreak may be beneficial for population growth of ground-foraging vertebrates. Our study adds insight to the seed ecology of serotinous pines under a potentially continental-wide insect outbreak, threatening vast forests adapted to regeneration after fire.

Viability of Forest Floor and Canopy Seed Banks in Pinus contorta var. latifoia (Pinaceas) Forests After a Mountain Pine Beetle Outbreak

Francois P. Teste et al. — Thu, 18 Apr 2013 09:08:23 PDT

Premise of the study: Seed banks are important for the natural regeneration of many forest species. Most of the seed bank of serotinous lodgepole pine is found in the canopy, but after an outbreak of mountain pine beetle (MPB), a considerable forest- floor seed bank develops through the falling of canopy cones. After large-scale mortality of pine stands from MPB, however, the viability of seeds in both the canopy and the forest-floor cone bank is uncertain.
Methods: We sampled cones in five stands 3 yr after MPB (3y-MPB); five stands 6 yr after MPB (6y-MPB); and 10 stands 9 yr after MPB (9y-MPB), in central British Columbia, Canada. Seeds were extracted and viability tested using germination techniques.
Key results: Forest-floor cones had seed with high germination capacity (GC): 82% for embedded (partly buried) closed cones vs. 45% for buried partly open cones. For canopy cones, GC steeply declined about 15 yr after cone maturation and by 25 yr, GC was 50%, compared with 98% in the first year. In the 3y- and 6y-MPB stands, seeds from cones that were 7 to 9 yr old had similar GC on dead and living trees; however, seeds from the dead trees had lower vigor than seeds from living trees.
Conclusions: We demonstrate for the first time that a serotinous pine can form a viable soil seed bank by cone burial, which may facilitate natural regeneration if a secondary disturbance occurs. Seeds contained in 15-yr-old cones showed a steep decline in viability, which could limit regeneration if there is a long delay before a secondary disturbance.