Bristlecone Research Articles

Wood Cellular Dendroclimatology: Testing New Proxies in Great Basin Bristlecone Pine.

Dendroclimatic proxies can be generated from the analysis of wood cellular structures, allowing for a more complete understanding of the physiological mechanisms that control the climatic response of tree species. Century-long (1870–2013) time series of anatomical parameters were developed for Great Basin bristlecone pine (Pinus longaeva D.K. Bailey) by capturing strongly contrasted microscopic images through a Confocal Laser Scanning Microscope. Environmental information embedded in wood anatomical series was analyzed in comparison with ring-width series using measures of empirical signal strength. Response functions were calculated against monthly climatic variables to evaluate climate sensitivity of cellular features (e.g., lumen area; lumen diameter) for the period 1950–2013. Calibration-verification tests were used to determine the potential to generate long climate reconstructions from these anatomical proxies. A total of eight tree-ring parameters (two ring-width and six chronologies of xylem anatomical parameters) were analyzed. Synchronous variability among samples varied among tree-ring parameters, usually decreasing from ring-width to anatomical features. Cellular parameters linked to plant hydraulic performance (e.g., tracheid lumen area and radial lumen diameter) showed empirical signal strength similar to ring-width series, while noise was predominant in chronologies of lumen tangential width and cell wall thickness. Climatic signals were different between anatomical and ring-width chronologies, revealing a positive and temporally stable correlation of tracheid size (i.e., lumen and cell diameter) with monthly (i.e., March) and seasonal precipitation. In particular, tracheid lumen diameter emerged as a reliable moisture indicator and was then used to reconstruct total March–August precipitation from 1870 to 2013. Wood anatomy holds great potential to refine and expand dendroclimatic records by allowing estimates of plant physiological adaptations to external stressors. Integrating xylem cellular features with ring-width chronologies can widen our understanding of past climatic variability (including annual extreme events) and improve the evaluation of long-term plant response to drought, especially in connection with future warming scenarios.

Search for Annual 14C Excursions in the Past

AbstractTwo radiocarbon excursions (AD 774–775 and AD 993–994) occurred due to an increase of incoming cosmic rays on a short timescale. The most plausible cause of these events is considered to be extreme solar proton events (SPE). It is possible that there are other annual 14C excursions in the past that have yet to be confirmed. In order to detect more of these events, we measured the 14C contents in bristlecone pine tree-ring samples during the periods when the rate of 14C increase in the IntCal data is large. We analyzed four periods every other year (2479–2455 BC, 4055–4031 BC, 4465–4441 BC, and 4689–4681 BC), and found no anomalous 14C excursions during these periods. This study confirms that it is important to do continuous measurements to find annual cosmic-ray events at other locations in the tree-ring record.

Defense traits in the long-lived Great Basin bristlecone pine and resistance to the native herbivore mountain pine beetle.

Summary Mountain pine beetle (MPB, Dendroctonus ponderosae) is a significant mortality agent of Pinus, and climate‐driven range expansion is occurring. Pinus defenses in recently invaded areas, including high elevations, are predicted to be lower than in areas with longer term MPB presence. MPB was recently observed in high‐elevation forests of the Great Basin (GB) region, North America. Defense and susceptibility in two long‐lived species, GB bristlecone pine (Pinus longaeva) and foxtail pine (P. balfouriana), are unclear, although they are sympatric with a common MPB host, limber pine (P. flexilis).We surveyed stands with sympatric GB bristlecone–limber pine and foxtail–limber pine to determine relative MPB attack susceptibility and constitutive defenses. MPB‐caused mortality was extensive in limber, low in foxtail and absent in GB bristlecone pine. Defense traits, including constitutive monoterpenes, resin ducts and wood density, were higher in GB bristlecone and foxtail than in limber pine. GB bristlecone and foxtail pines have relatively high levels of constitutive defenses which make them less vulnerable to climate‐driven MPB range expansion relative to other high‐elevation pines. Long‐term selective herbivore pressure and exaptation of traits for tree longevity are potential explanations, highlighting the complexity of predicting plant–insect interactions under climate change.

Environmental drivers of cambial phenology in Great Basin bristlecone pine.

The timing of wood formation is crucial to determine how environmental factors affect tree growth. The long-lived bristlecone pine (Pinus longaeva D. K. Bailey) is a foundation treeline species in the Great Basin of North America reaching stem ages of about 5000 years. We investigated stem cambial phenology and radial size variability to quantify the relative influence of environmental variables on bristlecone pine growth. Repeated cellular measurements and half-hourly dendrometer records were obtained during 2013 and 2014 for two high-elevation stands included in the Nevada Climate-ecohydrological Assessment Network. Daily time series of stem radial variations showed rehydration and expansion starting in late April-early May, prior to the onset of wood formation at breast height. Formation of new xylem started in June and lasted until mid-September. There were no differences in phenological timing between the two stands, or in the air and soil temperature thresholds for the onset of xylogenesis. A multiple logistic regression model highlighted a separate effect of air and soil temperature on xylogenesis, the relevance of which was modulated by the interaction with vapor pressure and soil water content. While air temperature plays a key role in cambial resumption after winter dormancy, soil thermal conditions coupled with snowpack dynamics also influence the onset of wood formation by regulating plant-soil water exchanges. Our results help build a physiological understanding of climate-growth relationships in P. longaeva, the importance of which for dendroclimatic reconstructions can hardly be overstated. In addition, environmental drivers of xylogenesis at the treeline ecotone, by controlling the growth of dominant species, ultimately determine ecosystem responses to climatic change.

Recruitment patterns and growth of high-elevation pines in response to climatic variability (1883–2013), in the western Great Basin, USA

Over the period 1883–2013, recruitment of subalpine limber pine (Pinus flexilis E. James) and Great Basin bristlecone pine (Pinus longaeva D.K. Bailey) above the upper tree line, below the lower tree line, and across middle-elevation forest borders occurred at localized sites across four mountain ranges in the western Great Basin. A synchronous pulse at all ecotones occurred between 1963 and 2000 (limber pine) and between 1955 and 1978 (bristlecone pine) when pines expanded 225 m beyond forest borders. Little recruitment occurred before this interval or in the 21st century. No obvious environmental factors distinguished recruitment locations from nonrecruitment locations. Where their ranges overlap, limber pine has leapfrogged above bristlecone pine by 300 m. Limber pine tree-ring chronologies, developed to compare radial-growth responses with recruitment, showed dominant pulses of increased growth during the same interval as recruitment. Significant climate correlations of growth and recruitment indicated lead and lag effects as much as 6 years and complex relationships with climate variables, corroborating the importance of cumulative climate effects relative to any single year. Water relations were the most important drivers of growth and recruitment and interacted with growing-season minimum and maximum temperatures. These results underscore the importance of studying ecotones at all margins when evaluating conifer response to climate change.

The world's oldest living tree discovered in Sweden? A critical review

In 2008, there was news that in Sweden a 9550-year-old spruce was discovered which would accordingly be the oldest living tree in the world. The pros and cons of the claim are discussed in this review based on the original publications by the discoverers of the spruce. The findings presented here support the conclusion that spruces in the Swedish mountains may reach 100–600 years of age but not nearly 10,000 years. There is neither evidence of genetic continuity between dead wood remains discovered beneath the allegedly 9550-year-old tree and the living tree itself. Nor is there evidence of a clonal origin of the spruce. On the contrary, it must be assumed that it reproduces sexually. In fact, there are good reasons to endorse the generally accepted view that Great Basin bristlecone pines are the oldest living trees on earth.

Mountain Pine Beetles Use Volatile Cues to Locate Host Limber Pine and Avoid Non-Host Great Basin Bristlecone Pine.

The tree-killing mountain pine beetle (Dendroctonus ponderosae Hopkins) is an important disturbance agent of western North American forests and recent outbreaks have affected tens of millions of hectares of trees. Most western North American pines (Pinus spp.) are hosts and are successfully attacked by mountain pine beetles whereas a handful of pine species are not suitable hosts and are rarely attacked. How pioneering females locate host trees is not well understood, with prevailing theory involving random landings and/or visual cues. Here we show that female mountain pine beetles orient toward volatile organic compounds (VOCs) from host limber pine (Pinus flexilis James) and away from VOCs of non-host Great Basin bristlecone pine (Pinus longaeva Bailey) in a Y-tube olfactometer. When presented with VOCs of both trees, females overwhelmingly choose limber pine over Great Basin bristlecone pine. Analysis of VOCs collected from co-occurring limber and Great Basin bristlecone pine trees revealed only a few quantitative differences. Noticeable differences included the monoterpenes 3-carene and D-limonene which were produced in greater amounts by host limber pine. We found no evidence that 3-carene is important for beetles when selecting trees, it was not attractive alone and its addition to Great Basin bristlecone pine VOCs did not alter female selection. However, addition of D-limonene to Great Basin bristlecone pine VOCs disrupted the ability of beetles to distinguish between tree species. When presented alone, D-limonene did not affect behavior, suggesting that the response is mediated by multiple compounds. A better understanding of host selection by mountain pine beetles could improve strategies for managing this important forest insect. Moreover, elucidating how Great Basin bristlecone pine escapes attack by mountain pine beetles could provide insight into mechanisms underlying the incredible longevity of this tree species.

Evidence of a higher late-Holocene treeline along the Continental Divide in central Colorado

Using a combination of 23 radiocarbon ages and annual ring counts from 18 Rocky Mountain bristlecone pine ( Pinus aristata) remnants above the local present-day limits, a period of higher treeline has been determined for two sites near the Continental Divide in central Colorado. The highest remnants were found about 30 m above live bristlecone pines of similar size. The majority of the remnants, consisting of standing snags, large logs, and smaller remains, are highly eroded, such that the innermost annual rings of all but one are missing. The radiocarbon ages obtained from the oldest wood recovered from each remnant indicate that the majority were established above the present-day limit of bristlecone pine from prior to 2700 cal. yr BP to no later than about 1200 cal. yr BP. These radiocarbon ages combined with the annual ring count from the corresponding remnant indicate that the majority of the sampled remnants grew above the present-day limit of bristlecone pine from sometime before 2700 cal. yr BP to about 800 cal. yr BP. Evidence of recent climatic warming is demonstrated at one of the sites by young bristlecone pine saplings growing next to the highest remnants; the saplings were established after AD 1965 and represent the highest advance of treeline in at least 1200 years.

A revised age of ad 667–699 for the latest major eruption at Rabaul

The most recent major eruption at Rabaul was one of the largest known volcanic events at this complex system, having a volcanic explosivity index (VEI) rating of 6. The eruption generated widespread pumice lapilli and ash fall deposits and ignimbrites of different types. The total volume of pyroclastic material produced in the eruption exceeded 11 km3 and led to a new phase of collapse within Rabaul Caldera. Initial 14C dating of the event yielded an age of about 1400 years bp, and the eruption became known as the “1400 bp” eruption. Previous analyses of the timing of the eruption have sought to link it to events in ad 536 and ad 639. However, we have re-evaluated the age of the eruption using the Bayesian wiggle-match radiocarbon dating method, and the eruption is now thought to have occurred in the interval ad 667–699. The only significant equatorial eruptions recorded in both Greenland and Antarctic ice during this interval are at ad 681 and ad 684, dates that coincide with frost rings in bristlecone pines of western USA in the same years. Definitively linking the Rabaul eruption to this narrow age range will require identification of Rabaul tephra in the ice records. However, it is proposed that a new working hypothesis for the timing of the most recent major eruption at Rabaul is that it occurred in the interval ad 681–684.

Tree Lines

This collaboration of ink drawings and texts examines the high altitude landscape and forests of the White Mountains, in Eastern California, in particular the bristlecone pine, and a neighboring species, the limber pine and western juniper, and their environs. It is the premise of the writer and artist that drawing and writing about these species and this place fosters a valuable kind of local knowledge, while producing striking works of art and craft.

Shelter provided by wood, facilitation, and density-dependent herbivory influence Great Basin bristlecone pine seedling survival

Microsites created by live plants and non-living structures can be important for plant establishment where abiotic stress is high. The activity of herbivores and resulting pattern of seedling survival also affects plant distributions. We investigated factors thought to influence survival of bristlecone pine (Pinus longaeva Bailey) seedlings in the White Mountains, California, USA, with two field experiments in which microsite and exposure to herbivory were manipulated. In the microsite experiment, we planted seedlings underneath wooden shade structures, underneath sagebrush plants, and in exposed locations. In the herbivory experiment, we tested the effects of herbivore exclusion in three different habitat types. We planted seedlings in full wire cages (herbivores excluded), in half cages (herbivores allowed while enabling assessment of possible non-herbivore effects of cages on seedling survival), or with no cage (herbivores allowed), and repeated these treatments in three habitats: below, within, and above a bristlecone woodland. Over three growing seasons, seedlings planted under wooden shade structures had higher survival (28.9%) than seedlings growing under sagebrush (10%) or in exposed areas (3.3%). We found a significant treatment by habitat interaction in the herbivory experiment (χ2=12.056, P=0.017), driven by a clear pattern of high herbivory inside the bristlecone woodland, but not above or below it. Our results suggest that biologically-derived microsites (shelter from dead wood and live shrubs), as well as herbivore-mediated density-dependent mortality, are important determinants of bristlecone pine seedling survival.

Impacts of simulated herbivory on volatile organic compound emission profiles from coniferous plants

Abstract. The largest global source of volatile organic compounds (VOCs) in the atmosphere is from biogenic emissions. Plant stressors associated with a changing environment can alter both the quantity and composition of the compounds that are emitted. This study investigated the effects of one global change stressor, increased herbivory, on plant emissions from five different coniferous species: bristlecone pine (Pinus aristata), blue spruce (Picea pungens), western redcedar (Thuja plicata), grand fir (Abies grandis), and Douglas-fir (Pseudotsuga menziesii). Herbivory was simulated in the laboratory via exogenous application of methyl jasmonate (MeJA), a herbivory proxy. Gas-phase species were measured continuously with a gas chromatograph coupled to a mass spectrometer and flame ionization detector (GC–MS–FID). Stress responses varied between the different plant types and even between experiments using the same set of saplings. The compounds most frequently impacted by the stress treatment were alpha-pinene, beta-pinene, 1,8-cineol, beta-myrcene, terpinolene, limonene, and the cymene isomers. Individual compounds within a single experiment often exhibited a different response to the treatment from one another.

Tree ring effects and ice core acidities clarify the volcanic record of the first millennium

Abstract. In 2012 Plummer et al., in presenting the volcanic chronology of the Antarctic Law Dome ice core, chose to list connections to acid layers in other ice cores and also possible chronological coincidences between ice acid dates and the precise dates of frost damage, and/or reduced growth in North American bristlecone pines. We disagree with the chronological links indicated by Plummer et al. for the period before AD 700, and in this paper we show that a case can be made that better linkages between ice acid and tree ring effects occur for this period if the ice chronologies are systematically moved forward by around 7 years, consistent with a hypothesis published by Baillie in 2008. In the paper we seek to explore the proposition that frost damage rings in North American bristlecone pines are a very useful indicator of the dates of certain large explosive volcanic eruptions; the dating of major eruptions being critical for any clear understanding of volcanic forcing. This paper cannot prove that there is an error in the Greenland Ice Core Chronology 2005 (GICC05), and in equivalent ice chronologies from the Antarctic, however, it does provide a coherent argument for an apparent ice dating offset. If the suggested offset were to prove correct it would be necessary to locate where the error occurs in the ice chronologies and in this regard the dating of the increasingly controversial Icelandic Eldgjá eruption in the AD 930s, and the China/Korean Millennium eruption which occurs some 7 years after Eldgjá, may well be critical. In addition, if the offset were to be substantiated it would have implications for the alleged identification of tephra at 429.3 m in the Greenland GRIP core, currently attributed to the Italian volcano Vesuvius and used as a critical zero error point in the GICC05 chronology.

Changing climate response in near-treeline bristlecone pine with elevation and aspect

In the White Mountains of California, eight bristlecone pine (Pinus longaeva) tree-ring width chronologies were developed from trees at upper treeline and just below upper treeline along North- and South-facing elevational transects from treeline to ~90 m below. There is evidence for a climate-response threshold between approximately 60–80 vertical m below treeline, above which trees have shown a positive growth-response to temperature and below which they do not. Chronologies from 80 m or more below treeline show a change in climate response and do not correlate strongly with temperature-sensitive chronologies developed from trees growing at upper treeline. Rather, they more closely resemble lower elevation precipitation-sensitive chronologies. At the highest sites, trees on South-facing slopes grow faster than trees on North-facing slopes. High growth rates in the treeline South-facing trees have declined since the mid-1990s. This suggests the possibility that the climate-response of the highest South-facing trees may have changed and that temperature may no longer be the main limiting factor for growth on the South aspect. These results indicate that increasing warmth may lead to a divergence between tree growth and temperature at previously temperature-limited sites.

Modeling Subalpine and Upper Montane Forest-Climate Interactions in Colorado

The correlation of the distribution of five subalpine and montane tree species with precipitation and temperature were modeled using GIS. The results were compared with data presented by Thompson et al. (2000). Distributions of subalpine fir (Abies concolor), Engelmann spruce (Picea engelmannii), lodgepole pine (Pinus contorta), limber pine (Pinus flexilis) and bristlecone pine (Pinus aristata) were compared to estimated precipitation and temperature fields that had been constructed from the Parameter-elevation Regressions on Independent Slopes Model (PRISM), National Climatic Data Center (NCDC) station data, and Snowpack Telemetry (SNOTEL) system data. Plant distribution maps from Little (1971) and CoGAP (2001) were used to determine the temperature and precipitation associated with the selected tree species. The estimates from this study were compared to those of Thompson, Anderson & Bartlein (2000). In many cases precipitation and temperatures values were higher than those of Thompson, Anderson & Bartlein (2000). Suggestions are made to improve the predictive power of GIS analysis for mapping climate and plant variability.

Mechanisms of species range shift at treeline in bristlecone pine forests

Mechanisms of species range shift at treeline in bristlecone pine forests

Brilliant Green: The Surprising History and Science of Plant Intelligence by Stefano Mancuso and Alessandra Viola (review)

Reviewed by: Brilliant Green: The Surprising History and Science of Plant Intelligence by Stefano Mancuso and Alessandra Viola Franklin G. Miller Brilliant Green: The Surprising History and Science of Plant Intelligence By Stefano Mancuso and Alessandra Viola. Washington, DC: Island Press, 2015. Pp. 192. $20 (cloth). Plants comprise over 99% of the biomass of the earth, and without them there would be no animal life on the planet. Moreover, the thriving of trees and other plants will be necessary for life on earth to survive, and continue to cope with, the negative consequences of human-induced climate change. The importance of plants is not just biological. Imagine the impoverishment of life in great cities like London, Paris, and New York without the green spaces and flowers of Hyde Park, the Tuileries Garden, and Central Park. Metropolitan Washington, DC—my home environment—is graced by the presence of Rock Creek Park, an expansive woodland resource in the center of the city. In the first spring of my retirement, I have been walking the trails adjacent to the creek, admiring and transported by the profusion and beauty of plant life. A recent sojourn in the park brought to mind Wordsworth’s “Tintern Abbey” (1798), in which he relates that he is A lover of the meadows and the woods,And mountains; and of all that we beholdFrom this green earth; [End Page 569] … well pleased to recognizeIn nature and the language of the sense,The anchor of my purest thoughts, the nurse,The guide, the guardian of my heart, and soul. … (ll. 105–12) Wordsworth here and elsewhere suggests a spiritual connection between the plant world and the human psyche. In his famous poem about encountering daffodils “dancing in the breeze,” he exclaims that “A poet could not but be gay, / In such a jocund company” (“I wandered lonely as a cloud” [1815], ll. 6, 15–16). Indeed, the memory of the daffodils fills his heart with pleasure when at later times, “In vacant or in pensive mood,” he thinks of them (l. 20). One doesn’t have to be a Romantic poet to feel a deep connection with plants. Walking many years ago in a quiet and remote mountainous grove of bristlecone pines, breathing the thin air and experiencing the sight of these ancient dwarfs had an effect on my atheistic self that I wouldn’t hesitate to call spiritual. It would be a sacrilege for someone to willfully damage them. To be sure, some are indifferent to the greenness of the earth; indeed, the existentialist philosopher and writer, Jean-Paul Sartre, according to his companion Simone de Beauvoir, was “allergic to chlorophyll” (Barnes 1959, 391). But this is unusual, and virtually anyone can appreciate what plants have to offer. Readers of Brilliant Green will have that appreciation greatly enhanced. This short book is written by a professor at the University of Florence and director of the International Laboratory of Plant Neurobiology in Italy (Mancuso), and a science journalist (Viola). The authors pose the central question of their book in the first paragraph: “Are plants intelligent? Do they solve problems and communicate with their surroundings—with other plants, insects, and higher animals? Or are they passive, unfeeling organisms without a trace of individual or social behavior?” (1). In an entertaining and thought-provoking way, they endeavor to answer to this question by making the case for plants being intelligent, and even sentient. They proceed by describing and characterizing the behaviors—including the relationships between plant and animals—that plants rely on for reproduction, defense against predators, and even in some cases for nourishment. Under the impact of Darwinian biology over the past 150 years, humans have embraced, or at least been forced to recognize, the continuity between their mental abilities and those of animals. The authors demonstrate that when the impressive abilities of plants are contemplated, the many similarities between plants and animals come into view. Plants, of course, are not inert like rocks; they not only grow and reproduce, but they respond to stimuli. Mancuso and Viola relate that “plants use their senses to orient themselves in the world, interacting with other plant organisms, insects, and animals, communicating...

Excursions in the 14C record at A.D. 774–775 in tree rings from Russia and America

AbstractThe calibration of radiocarbon dates by means of a master calibration curve has been invaluable to Earth, environmental and archeological sciences, but the fundamental reason for calibration is that atmospheric radiocarbon content varies because of changes in upper atmosphere production and global carbon cycling. Improved instrumentation has contributed to high‐resolution (interannual) radiocarbon activity measurements, which have revealed sudden and anomalous activity shifts previously not observed at the common resolution of 5–10 years of most of the calibration scale. One such spike has been recently reported from tree rings from Japan and then again in Europe at A.D. 774–775, for which we report here our efforts to both replicate its existence and determine its spatial extent using tree rings from larch at high latitude (northern Siberia) and bristlecone pine from lower latitude (the White Mountains of California). Our results confirm an abrupt ~ 15‰ 14C activity increase from A.D. 774 to 776, the size and now the hemispheric extent of which suggest that an extraterrestrial influence on radiocarbon production is most likely responsible.

A quiescent path to plant longevity

The giant sequoia and the bristlecone pine trees are capable of living up to several hundreds or even thousands of years. Plants achieve this longevity by regenerating stem cells capable of giving rise to all differentiated cells. Plant stem cells reside in specific niches with high mitotic activity that are known as meristems. Remarkably, at the center of the root stem cell niche (SCN) resides a group of mitotically inactive cells known as the quiescent center (QC). Recent studies suggest that stress-related phytohormones and DNA damage can initiate QC cell division, resulting in the replenishment of stem cells surrounding the QC. We therefore propose that the QC represents a pool of backup cells that serve to replace damaged stem cells, thereby contributing to plant longevity.

A north-south moisture dipole at multi-century scales in the Central and Southern Rocky Mountains, U.S.A., during the late Holocene

Lake-level changes since ca. 3.6 kilo-annum (ka) at Emerald Lake in the Upper Arkansas River Basin of west-central Colorado coincide in time with changes of the opposite direction at Lake of the Woods in northwestern Wyoming. The contrast provides evidence of a multi-centennial moisture dipole across the Southern and Central Rocky Mountains' region similar to one associated with the effects of the El Nino Southern Oscillation (ENSO) on annual to decadal time scales today. Cores and ground penetrating radar (GPR) profiles from Emerald Lake show that deep-water muds accumulated as extensively across the lake basin as today at ca. 3.6–3.0 and 1.4–0.8 ka, and nearly as extensively at 2.5–1.9 ka. The extensive muds indicate episodes of high water at Emerald Lake and date to times when Lake of the Woods was low. Nearshore sand layers at Emerald Lake indicate that water levels fell during the intervening centuries, including when bristlecone pine chronologies have documented repeated multi-decadal droughts in the Upper Arkansas River Basin. Water levels were also low, based on the absence of nearshore mud accumulation, before ca. 3.6 ka, and dramatically lower (>2 m in the currently 4.5-m deep lake) before a sharp rise in water levels by ca. 5.7 ka. A basin-wide change in sediment accumulation patterns, consistent with an expansion and deepening of the lake at ca. 5.7 ka, correlates with regional cooling and similar evidence of increased effective moisture at Lake of the Woods and other sites throughout central North America. The step increase in moisture availability may relate to a global-scale reorganization of climatic patterns, which developed as the mid- and high-latitudes cooled in response to a decline in summer insolation.