Species interactions and abiotic effects on stand structure of bristlecone pine (Pinus longaeva) and limber pine (Pinus flexilis)

Selene Arellano1, Anna Douglas2, Neira Ibrahimovic3 , Janette Jin1

1University of California, Berkeley; 2University of California, Santa Cruz; 3University of California, Los Angeles

ABSTRACT

Plants experience a wide range of biotic and abiotic stresses based on their environmental conditions. Demographic stages—recruits, saplings, and adults—may react differently under stress. In this study, we examine how the factors of aspect, substrate, and competition affect the stand structure of Great Basin bristlecone pine (Pinus longaeva) and limber pine (Pinus flexilis), which are among the few trees that can withstand the stressful subalpine environment. We surveyed an even distribution of north and south- facing slopes with both dolomite and granite substrate in the White Mountains of Inyo National Forest, California. We recorded the density of different demographic stages of both tree species and tested how neighboring trees affected the cone production of bristlecones. We found that the effect of aspect and substrate depended on the demographic stage. We also found no evidence of competition between bristlecone and limber. Taken together, our results suggest that abiotic factors are more important than biotic factors in determining bristlecone and limber establishment. Overall, we suggest that abiotic factors are more influential in shaping subalpine plant communities.

Keywords: bristlecone pine, limber pine, competition, abiotic stress, stand structure

INTRODUCTION and have low levels of phosphorus, which is an essential element for plant development Plants may experience extreme stress (Wright and Mooney 1965, Malhotra et al. when they are growing in environments with 2018). Slope aspect is another stress- challenging abiotic or biotic conditions. inducing abiotic factor. South-facing slopes Abiotic stressors can include intense solar in the northern hemisphere have higher radiation, low soil moisture, nutrient solar radiation and drier soils, which limits a deficient substrate, or limited water plant’s water access. Therefore, more availability (Beasley and Klemmedson 1973, vegetative cover is generally associated with Harsch et al. 2009). Substrate is a prominent north-facing slopes regardless of season abiotic factor affecting a plant's growing (Toro Guerrero et al. 2016). Biotic conditions (Wright and Mooney 1965). For interactions, like interspecific competition, example, dolomite-derived soils are alkaline are another form of stress that can inhibit

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plant growth (Godsoe et al. 2017). stressful environments because they are Interspecific competition can impact species better adapted to abiotic subalpine distributions when one species alters the conditions like dolomite substrate. As young growth rates and fitness of another species limbers are establishing themselves into (Abrams 1987, Godsoe et al. 2017). areas formerly occupied by bristlecone, Combinations of biotic and abiotic stress more interactions between bristlecone and are prevalent in the subalpine environment limber are occurring (Millar et al.). of the White Mountains, Inyo National Research on bristlecone and limber has Forest. The two co-dominant tree species in historically focused on dendrochronology, as the White Mountains are Great Basin bristlecone’s slow-growth strategies bristlecone pine (Pinus longaeva, hereafter preserve climate records (Furguson 1968). referred to as bristlecone) and limber pine Few studies have analyzed the stand (Pinus flexilis, hereafter referred to as structure and community dynamics of limber). While most plants cannot grow in forests dominated by bristlecone and limber extremely stressful environments, (Baker 1992). Moreover, there is conflicting bristlecone and limber are adapted to evidence about the relative importance of surviving harsh subalpine conditions abiotic and biotic factors on tree (Mooney et al. 1962). establishment. While some studies have Bristlecones are the oldest non-clonal found abiotic and biotic variables were living organisms on Earth (Furguson 1968). equally important in determining tree stand They are slow-growth trees mainly found in structure, other studies have found abiotic nutrient-poor dolomite substrate (Brown variables played a larger role (Meier et al. and Schoettle, 2008). Bristlecone forests are 2010, Godsoe et al. 2017). characterized by short warm seasons and In this study, we examined how aspect and limited moisture availability (Brunstein and substrate affected the stand structure of Yamaguchi 2018, LaMarche and Stockton bristlecone and limber in the White 1974). Bristlecones have a more restricted Mountains. We predicted there would be elevational range (2200–3700 m) than more trees from all demographic stages on limbers (2290–3350 m) and are usually north-facing slopes due to better growing found in drier parts of the White Mountains conditions (Wright and Mooney 1965). We (Brown and Schoettle 2008). While also predicted there would be overall more bristlecones typically encounter minimal bristlecone on dolomite and more limber on interspecific competition from other plants granite due to previous research reporting due to the harsh abiotic conditions they the same trends (Wright and Mooney 1965). endure in the subalpine (Beasley and Finally, we predicted there would be Klemmedson 1973), they may experience interspecific competition between competition from limbers (Smithers 2017). It bristlecone and limber because limber are is possible bristlecones inhabit harsher known to be a more competitively dominant environments because the presence of species (Windmuller-Campione and Long limber prevents them from living on more 2016). Our study provides implications for nutrient-rich granite soils (Billings and stand structure and community dynamics of Thompson 1957 , Wright and Mooney 1965). old-growth trees in stressful environments. Alternatively, bristlecones may inhabit more

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METHODS cold, moist conditions on north-facing slopes (Ferguson 1968). The hillsides are typically 2.1 Study System dominated by granite, dolomite, and quartzite substrates (Wright and Mooney We conducted our study in the White 1965). Average temperatures in the White Mountains of Inyo National Forest, California Mountains range from -14.4°C to 18.3°C, and (37°N, 118°W; 3048–3353 m) from August average precipitation is 1235 mm. 1–6, 2021 (Fig. 1). The rain shadow effect in Bristlecone and limber are two dominant the White Mountains creates a harsh tree species able to withstand the strenuous subalpine habitat characterized by dry, subalpine environment. warm conditions on south-facing slopes, and

Figure 1: Map of White Mountain survey sites. We surveyed a total of 52 900 m2 plots in the White Mountains of California. The red/pink colors represent forests dominated by granite substrate. The indigo/violet colors represent forests dominated by dolomite substrate. The darker shades of red and indigo represent north-facing slopes and the corresponding lighter shades of pink and violet represent south-facing slopes.

2.2 Site Level Surveys substrate, and the remainder were dominated by dolomite substrate. For each To examine how abiotic factors affected set of 26 substrate-specific plots, half of the the stand structure of bristlecone and sites were north-facing slopes and half of the limbers, we surveyed 52 plots. Of these sites were south-facing slopes. Every plot plots, half were dominated by granite

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had an area of 900 m2 that we demarcated number of steps, and then selecting the tree with two 30 m transects laid perpendicularly closest to where we landed. At times when to each other. We laid the transects out there were fewer than two trees of a specific randomly along the mountainside and species in our plot, we only surveyed the surveyed 3–5 plots on the north-facing slope trees present. For every tree we selected, we and 3–5 plots on the south-facing slope counted the number of cones on the tree as before continuing the process at a new site. a measure of reproductive fitness. For large Upon surveying each plot, we counted and trees, cone number was visually estimated recorded the total number of live recruits, by counting the number of cones in one saplings and adults for both bristlecone and section of the tree, then scaling by the limber. All cone-bearing trees were classified number of equivalent sections on the tree. as adults. The non-cone bearing trees were We also measured the circumference of the distinguished by size, with trees less than tree, the distance to the nearest neighboring half a meter being classified as recruits and adult tree, and the circumference of the trees over half a meter being classified as neighboring tree. We noted whether the saplings (Fig. 2). neighboring tree was a bristlecone or limber. Overall, we surveyed 90 bristlecones and 46 limbers, for a total of 136 trees.

2.4 Statistical Analysis

All statistical analyses were conducted using JMP v.16 Pro software. We ran a two- way ANOVA to test whether the interaction between demographic stage and species had an effect on tree density. We also ran two- way ANOVAs to test whether the substrate, Figure 2: Recruit, sapling, and adult demographic stage of bristlecone and limber trees. In order to aspect, and interaction between substrate study stand structure, we recorded the density of and aspect had an effect on the density of bristlecone and limber recruits, saplings, and adult bristlecone recruits, saplings, and adults. The trees in our 52 sites. Adult trees were classified as direction of the differences were detected cone bearing trees. For non-cone bearing trees, we by running Post Hoc Tukey HSD tests. We ran differentiated between recruits (≤ 0.5 m in height) and saplings (> 0.5 m in height). All trees pictured an ANCOVA to determine whether the above are bristlecones. circumference of the neighboring tree, distance to neighboring tree, and species of 2.3 Tree Level Surveys neighboring tree had an effect on the adult bristlecone cone production. We ran a To study the interactions between adult simple linear regression to test if the density bristlecone and adult limber, we surveyed of limber had an effect on the density of up to two trees of each species in each of our bristlecone. 900 m2 plots. We randomly selected the trees at each plot by using a random number generator to determine our direction and

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RESULTS 3.2 Abiotic Effects on Recruits

3.1 Abiotic Effects on Stand Structure All statistical results for this section are found in Fig. 4, Table 1. Substrate had a All statistical results for this section are significant effect on the density of found in Fig. 3, Table 1. Bristlecone adults bristlecone recruits; there were more were most abundant among bristlecone bristlecone recruits present on dolomite. recruits, saplings, and adults. Limber Substrate did not have a significant effect on saplings were most abundant among limber the number of limber recruits. recruits, saplings, and adults. There was no difference between the density of bristlecone recruits and limber recruits. However, there were more limber saplings than bristlecone saplings and there were more bristlecone adults than limber adults.

Figure 4: Substrate and aspect interact in their effect on bristlecone recruits and limber recruits. We ran two separate two-way ANOVAs to examine the effect of substrate, aspect, and the interaction between substrate and aspect on bristlecone and limber recruits. We ran a post-hoc Tukey HSD for bristlecone recruit tree density and a post-hoc Tukey HSD for

Figure 3: Stand structure of limber and bristlecone. limber recruit tree density. Levels not connected by Overall, bristlecones had the greatest number of the same letter are significantly different. Letters with adults, and limbers had the greatest number of a ‘prime’ marking are related to each other, and saplings. Additionally, we found no difference letters with no ‘prime’ marking are related to each between the density of bristlecone recruits and other. There was a greater density of bristlecone limber recruits. We found more limber saplings than recruits on dolomite (p substrate for bristlecone < 0.001). bristlecone saplings, and more bristlecone adults There was no effect of substrate on the density of limber recruits (p substrate for limber = 0.1801). Aspect did than limber adults (p spp. = 0.0211, p demographic stage < not have a significant effect on the density of 0.001, pspp, x demographic stages < 0.001). We ran a post-hoc Tukey HSD to determine the differences. Levels not bristlecone recruits (p aspect for bristlecone = 0.1238) or the connected by the same letter are significantly density of limber recruits (p aspect for limber = 0.3064). different. There were more bristlecone recruits on south-facing slopes in dolomite, but no effect of aspect on bristlecone recruit density in granite (p substrate x aspect for bristlecone = 0.0221). There were more limber recruits on north-facing slopes when on granite, but no effect of aspect on limber recruit density in dolomite (p substrate x aspect for limber < 0.001).

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Table 1: Statistics testing effects of aspect, substrate and interaction between aspect and substrate on tree density at different age demographics. Table also depicts effects of limber density on bristlecone density, neighbor tree species, distance to neighboring tree, and circumference of neighboring tree on bristlecone cone production. To standardize cone production between different tree sizes, we saved the residuals from a regression curve plotting tree circumference and number of cones per tree. Asterisks represent p < 0.05.

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Aspect alone did not have a significant saplings on north versus south-facing slopes effect on the number of bristlecone or when on dolomite. limber recruits, but the two-way interaction between substrate and aspect had a significant effect on both bristlecone and limber recruits. There were more bristlecone recruits on south-facing slopes when on dolomite but no difference in the density of bristlecone recruits on north versus south- facing slopes when on granite. There were more limber recruits on north-facing slopes when on granite but no difference in the density of limber recruits on north versus south-facing slopes on dolomite.

3.3 Abiotic Effects on Samplings Figure 5: Substrate and aspect interact in their effect on bristlecone saplings and limber saplings. We ran All statistical results for this section are two separate two-way ANOVAs to examine the effect found in Fig. 5, Table 1. Substrate had a of substrate, aspect, and the interaction between significant effect on the density of substrate and aspect on bristlecone and limber bristlecone saplings; there were more saplings. We ran a post-hoc Tukey HSD for bristlecone bristlecone saplings present on dolomite. sapling tree density and for limber sapling tree density. Levels not connected by the same letter are Substrate also had a significant effect on the significantly different. Letters with a ‘prime’ marking density of limber saplings; there were more are related to each other, and letters with no ‘prime’ limber saplings present on granite. marking are related to each other. More bristlecone Aspect did not have a significant effect on saplings were present on dolomite (p substrate for bristlecone the density of bristlecone saplings. However, = 0.0016), and more limber saplings were present on granite (p substrate for limber = 0.001). There was no aspect did have a significant effect on the difference in aspect on the density of bristlecone density of limber saplings; there were more saplings (p aspect for bristlecone = 0.1444). However, more limber saplings on north-facing slopes. The limber saplings were present on north-facing slopes two-way interaction between substrate and (p aspect for limber = 0.0198). There were more limber aspect had no significant effect on the saplings on north-facing slopes in granite, but aspect did not affect density of limber saplings in dolomite (p density of bristlecone saplings. On both substrate x aspect for limber = 0.0099). The interaction dolomite and granite, there was no between substrate and aspect had no effect on the difference in the density of bristlecone density of bristlecone saplings (p substrate x aspect for saplings on north versus south-facing slopes. bristlecone = 0.5841). However, the two-way interaction between substrate and aspect did have a significant 3.4 Abiotic Effects on Adults effect on the density of limber saplings. All statistical results for this section are There were more limber saplings on north- found in Fig. 6, Table 1. Substrate had a facing slopes when on granite but there was significant effect on the density of no difference in the density of limber bristlecone adults, with more bristlecone adults present on dolomite. Substrate also

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had a significant effect on the density of aspect had a significant effect on the density limber adults, with more limber adults of bristlecone adults. On dolomite, there present on granite. were more bristlecone adults on north- facing slopes. On granite, there was no difference in the density of bristlecone adults on north versus south facing slopes. The two-way interaction between substrate and aspect also had a significant effect on the density of limber adults (Figure 6, Table 1). On granite, there were more limber adults on north-facing slopes. On dolomite, there was no difference in the density of limber adults on north versus south-facing slopes.

3.5 Species Interaction Between Bristlecone Figure 6: Substrate and aspect interact in their effect and Limber on bristlecone adults and limber adults. We ran two separate two-way ANOVAs to examine the effect of There was no relationship between the substrate, aspect, and the interaction between density of limbers and the density of substrate and aspect on bristlecone and limber bristlecone (Table 1). The neighbor tree saplings. We ran a post-hoc Tukey HSD for bristlecone type, circumference of neighbor, and sapling tree density and a post-hoc Tukey HSD for limber sapling tree density. Levels not connected by distance to neighbor had no effect on the the same letter are significantly different. Letters with focal tree's cone production (Table 1). a ‘prime’ marking are related to each other, and letters with no ‘prime’ marking are related to each DISCUSSION other. More bristlecone adults were present on dolomite (p substrate for bristlecone <0.001). More limber 4.1 Abiotic Effects on Stand Structure adults were present on granite (p substrate for limber <0.001). More bristlecone adults and limber adults We found support for our prediction that were found on north-facing slopes (p aspect for bristlecone bristlecone grows primarily on dolomite and <0.001, p aspect for limber = 0.0033). There were more bristlecone adults on north-facing slopes on dolomite limber grows primarily on granite (Beasley and no difference in bristlecone adult density on and Klemmedson 1973, Wright and Mooney north versus south facing slopes on granite (p substrate x 1965). This relationship is likely due to aspect for bristlecone = 0.0014). There were more limber bristlecone having higher stress tolerance adults on north-facing slopes on granite and no difference in limber adult density on north versus than limber, which it needs to grow on harsh south facing slopes on dolomite (p substrate x aspect for limber alkaline dolomite substrate (Wright and = 0.0024). Mooney 1965, Beasley and Klemmedson 1973). Aspect had a significant effect on both the Among the three demographic stages of density of bristlecone adults and limber limber, we found that limber saplings were adults, with more bristlecone adults and most abundant. Saplings may be able to limber adults on north-facing slopes. The withstand a relatively wide range of two-way interaction between substrate and environmental stressors compared to

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recruits, since they have more established 4.2 Abiotic Effects on Recruits roots. Additionally, while limber adults grow predominantly on granite, limber saplings The density of recruits for both bristlecone are less confined to one substrate (Smithers and limber differed significantly depending et al. 2018). Therefore, it is reasonable that on the substrate and aspect of the sites we found the highest density of limber surveyed. There were generally more saplings when surveying both substrates. bristlecone recruits on dolomite than Among the three demographic stages of granite. Bristlecone predominantly inhabits bristlecone, we found that bristlecone adults dolomite because few other plant species were most abundant. This is likely because are able to survive in this harsh substrate bristlecones have high mortality at early (Wright and Mooney 1965). Furthermore, stages of life, but up to 99% survive when we likely found more bristlecone recruits in they are five years old or older (Barber 2013, the substrate more densely populated by Conlisk et al. 2017, Elliott 2012). Thus, the bristlecone adults because there would be a abundance of adult bristlecones we see higher production of seeds. In contrast, we relative to recruits and saplings may be a found no difference in the density of limber result of thousands of years of accumulation. recruits on dolomite and granite, which When analyzing overall stand structure, contradicts our prediction. This result we also found more limber saplings than follows another tree recruitment study that bristlecone saplings across all aspects and also found a high abundance of limber substrates (Figure 1, Table 1). Although we recruitment on dolomitic soils (Millar et al. did not record the age of the sapling trees we 2015). The increasing presence of limbers on surveyed, it is reasonable to assume that dolomite may indicate a shift in limber most of the saplings we surveyed are older range, as climate change pushes the treeline than five years since both limber and upward (Smithers et al. 2017, Smithers bristlecone are slow-growth tree species. 2017). As bristlecone moves to higher Thus, it is likely we will see higher limber elevations, limber recruits may be taking density and lower bristlecone density when over dolomite sites that were previously the trees reach their adult stage. If this trend dominated by bristlecone (Delos Santos et continues, we would expect to see a future al. 2018). Future studies could investigate shift from bristlecone dominance to limber how climate change impacts limber dominance in the White Mountains which recruitment in areas once dominated by could be further intensified by the impacts of bristlecone. climate change. However, it is important to In the interaction between substrate and note that the stand structure of slow-growth aspect, there were more bristlecone recruits species provides better evidence for on dolomite south-facing slopes. This episodic climatic events in history (climatic contradicts our prediction that bristlecones changes are reflected in the growth rings of would prefer north-facing dolomite slopes slow-growth trees) than future across all demographic stages. Even with establishment of a species (Baker 1992, more solar radiation and limited moisture, Beasley and Klemmedson 1973, Curry 1965). south-facing slopes may be the optimal place for recruits to establish in dolomite (National Avalanche Center, 2017). Higher

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solar radiation on south-facing slopes may determine how stresses like climate change allow recruits to maximize photosynthetic may impact their distribution. output, giving them a stronger start to life (Barnard et al. 2017). However, there was no 4.3 Abiotic Effects on Saplings difference in bristlecone recruit density on north or south-facing granite slopes. We The density of saplings depended on suspect no difference was detected due to substrate and aspect type. Overall, there the lack of bristlecone recruits in granite, as were more bristlecone saplings on dolomite opposed to aspect significantly impacting and more limber saplings on granite, which recruit tree density. supports our prediction. This finding Contrary to our results with bristlecone highlights an interesting relationship recruits, there were more limber recruits on between limber recruit and sapling stages. north-facing granite slopes. There was no Although we found no difference of limber difference in aspect for limber recruits on recruit density on dolomite and granite, we dolomite (Figure 5). North-facing slopes are found more limber saplings on granite. To usually optimal growing habitats, since they explain this pattern, we suggest limber have less intense sunlight and more recruits may experience high mortality when moisture availability (National Avalanche establishing on dolomite. Therefore, there is Center, 2017). While granite has higher likely a low probability of limber sapling nutrient availability and is generally a better establishment on dolomite, even though the growing habitat for plants, it has poor water shifting treeline moves limber recruits into retention in comparison to dolomite (Wright an area dominated by bristlecone. and Mooney 1965). Dolomite, being light On both dolomite and granite, there was grey or white, reflects a greater percentage no difference in the density of bristlecone of incoming solar radiation than darker saplings on north and south-facing slopes. granite (Wright and Mooney 1965). We suggest aspect had an effect on Therefore, lower soil temperatures in bristlecone recruits in dolomite, but not on dolomite leads to greater moisture retention bristlecone saplings. This may be because from less evaporation. Limber recruits may recruits are at a more vulnerable stage in life establish on north-facing granite slopes due compared to saplings. Therefore, recruit to the greater availability of water. More reliance on more immediate needs like water availability may be necessary to make sunlight may have skewed their preference up for low water retention in granite soils, towards south-facing slopes. especially when recruits are trying to On granite, there were more limber establish their roots. Furthermore, since we saplings on north-facing slopes. This follows found no difference in aspect when limber the pattern of more limber recruits on recruits were on dolomite, it is possible that granitic north-facing slopes. The implication limber recruits are not as dependent on solar may be that limber recruits do well on radiation as bristlecone recruits (Bidartondo granitic north-facing slopes, as the 2001, Beasley and Klemmedson 1980), thus proportion of limber recruits making it to the making them a more resilient species. Future sapling stage is high. North-facing slopes and studies could investigate the needs of granite soils are known to have more bristlecone and limber recruits in order to optimal growing conditions, so it is

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reasonable to postulate that tree retention When examining the effect of substrate will be higher on slopes inducing less and aspect on adult bristlecone and limber, environmental stress on trees (Wright and we found two exceptions to the patterns Mooney 1965). On dolomite, there was no noted above. First, there was no difference difference in the density of limber saplings in the density of adult limbers on north and on north and south-facing slopes, which south-facing granite slopes. Secondly, there follows the same pattern we observed for was no difference in the density of adult limber recruits. It is possible that limber bristlecones on north and south-facing recruits and saplings are more adapted to dolomite slopes. We suggest there was no growing on the north-facing slope on granite preference for adult trees on north-facing because they have been established on slopes due to the overall lack of adult limbers granitic substrate longer than on dolomitic on dolomite soil, and adult bristlecones on substrate. Therefore, there has been more granite soil. The absence of limber in time for adaptations favoring north-facing dolomite and bristlecone in granite was slopes to evolve. In contrast, the expansion likely why aspect had no effect on tree of limber onto dolomitic soils may be a density, rather than showing an indication of relatively recent phenomenon imposed by preferential growing conditions. the effects of climate change shifting treelines upward (Smithers 2017). Thus, the 4.5 Species Interaction Between Bristlecone preference for north-facing slopes on and Limber dolomite may have not yet evolved. Future studies could look into the patterns of Overall, we found no evidence of substrate and aspect preference over time. interspecific competition between bristlecone and limber, which contradicts 4.4 Abiotic Effects on Adults our prediction. It is possible that species growing in extreme stress do not have the We found more adult bristlecones on resources to invest in competition, which is dolomite and more adult limbers on granite. supported by The Stress Gradient This supports our predictions and follows the Hypothesis (He et al.). To further explore the pattern we observed for bristlecone and effects of competition, an experimental limber saplings. Since saplings have a high study could control where limber and chance of survival to the adult stage, it is bristlecone are grown. Controlling where reasonable that we observed the same limber and bristlecone are grown would trends in substrate preference for adults provide clearer evidence for how the species that we did for saplings. Additionally, we affect each other when there are no found a greater abundance of both confounding factors present. bristlecone adults and limber adults on north-facing slopes regardless of substrate, 4.6 Conclusion which supports previous studies showing north-facing slopes have more favorable Although we found no evidence of growing conditions (Wright and Mooney interspecific competition between 1965). bristlecone and limber, aspect and substrate strongly affected stand structure. Thus, we

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can conclude that abiotic factors were more trees in stands of bristlecone pine (Pinus longaeva). influential than biotic factors when Economic Botany 27:141–146. determining the distribution of bristlecone Beasley, R. S., and J. O. Klemmedson. 1980. Ecological and limber. Our findings provide support for relationships of bristlecone pine. The American previous studies arguing abiotic factors are Midland Naturalist 104:242–252. stronger predictors of species distributions in subalpine environments (Meier et al. Bidartondo, M. I., H. Ek, H. Wallander, and B. Söderström. 2001. Do nutrient additions alter 2010). Overall, abiotic and biotic stress plays carbon sink strength of ectomycorrhizal fungi? New a key role in structuring plant communities. Phytologist 151:543–550. While some plants cannot grow in any stressful environment, bristlecone and Billings, W. D., and J. H. Thompson. 1957. limber trees have adapted to extreme stress. Composition of a stand of old bristlecone pines in the White Mountains of California. Ecology 38:158– Understanding how abiotic and biotic stress 160. relatively affects plant communities may provide important implications for subalpine Brown, P. M., and A. W. Schoettle. 2008. Fire and species distribution in the future, especially stand history in two limber pine (Pinus flexilis) and as anthropogenic environmental stress Rocky Mountain bristlecone pine (Pinus aristata) stands in Colorado. International Journal of intensifies. Wildland Fire 17:339–347.

ACKNOWLEDGMENTS Brunstein, F. C., and D. K. Yamaguchi. 1992. The oldest known Rocky Mountain bristlecone pines (Pinus We thank Dr. Krikor Andonian, Dr. Tim aristata Engelm.). Arctic and Alpine Research Miller, Dr. Renske Kirchholtes, and John 24:253–256. Parsons for their guidance and support. This Conlisk, E., C. Castanha, M. J. Germino, T. T. Veblen, J. work was performed at the University of M. Smith, and L. M. Kueppers. 2017. Declines in California’s White Mountain Research low-elevation subalpine tree populations outpace Center at Crooked Creek Field Station, doi: growth in high-elevation populations with 10.21973/N3KM2J. warming. Journal of Ecology 105:1347–1357.

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