R. Franklin
Preliminary Written Exam
Prepared for C. Millar
(10%)
1. List and briefly describe each type of proxy indicator that a) has been used, and b) could be used for reconstruction of climate and ecosystems in the two geographic regions and for the time period indicated above. For each proxy, indicate strengths, weaknesses and biases relative to construction of climate and ecosystem history. For this question do not describe interpretations from the studies, rather focus on the values and limitations of the proxies themselves.
As in most mountain areas, meterological data are sparse for the treeline ecotone of the northern
Rocky Mountains and the Sierra Nevada, so natural records of climate and vegetation change must be utilized to document these fluctuations (Diaz and Bradley 1997). The more common methods of reconstructing these changes in mountain regions over the last 500 years are:
Historical Documents/Instrumental Records
Instrumental records are accurate records of temperature and precipitation variability over the past 100 – 200 years. It is with these records that we calibrate the measurements of other natural archive methods or reconstructing paleoclimate and paleoecology. The records can range from daily to monthly to yearly temperature and precipitation readings to historical photographs or writings about vegetational patterns and glacier positions. Some limitations associated with instrumental records are changes in the daily timing of the collection of temperature (corrected when noticing large sudden shifts in temperature trends not explainable by climate processes) and spatial and temporal limits on weather stations (low numbers of weather stations at high elevations, spotty records with missing years of data). These data will be biased to lower elevations (where people are) and certain times of the day (when people collect readings), especially instrumental records in the early part of the recording period.
Tree rings (ring width, latewood density, birth/death dates)
Tree ring studies are by far the most prevalent of climate and ecology reconstruction proxies.
These archives can be manipulated in a variety of ways (Fritts 1976) to derive climate information on winter, summer and annual temperature and precipitation by calibrating those separate periods with ring width measurements and latewood density. Examining the distribution of birth and death dates of trees in a spatial context can sort out fluctuations of treeline, maximum extents of glaciers and drought/pluvial periods. The tree-ring record of climate change is strong in its ability to determine, to the date of formation, a ring recording specific climate information such as one single drought year or the exact advance of a glacier.
However, in examining processes as vegetation change there can be significant lags (because of microclimate, topography, and other feedbacks and effects) in the response of a “moving” population of trees- whether it is up, down and around slope or is a change in species composition. Treeline changes may lag shifts in climate by decades to centuries so caution is taken when interpreting these findings. Tree rings also are affected by a combination of factors and it is important to be able to determine to which climate measurement they are in fact responding, for example, to maximum, minimum, or average temperatures, not all of which may be available for calibration purposes (Wilson and Luckman 2003).

R. Franklin
Preliminary Written Exam
Prepared for C. Millar
Lichenometry
Lichenometry has been used to determine ages of surfaces of surfaces affected by climatic change, most noticeably, morainal deposition during the late Holocene. Measurements of lichen diameters taken on these surfaces reveal oftentimes a dominant lichen size peak which is calibrated with growth rates derived from rock of known age of deposition. Lichenometry has an error of approximately 10 – 30 years (Porter 1981) and is a useful tool for dating glacial advances and snow-kill events (cold periods killing a lichen population) (Bull 2003). Many climatic fluctuations of interest to paleoecologists and climatologists occur in the time scales of less than several decades, so lichenometry is usually only used for dating geomorphological events and is rarely used for dating climatic events.
Lake records (diatoms, pollen, varves)
With the use of 210Pb dating of pollen cores it is possible to extract information from lake and bog sediments that can be analyzed on decadal timescales. Presence of cold or warm tolerant diatom types, pollen types indicating vegetation shifts (less prevalent in the literature covering only the past 500 years), and presence or absence of organic-rich sediment in varve layers of high elevation lakes all can shed light on the climatic and vegetative conditions at the time of formation of these annual layers. While diatom and OM presence can shift quickly in response to local patterns, pollen counts can have lags associated with changing treeline and dispersal rates that deposit pollen grains 10s of miles from the pollen source. Diatom assemblages can also be affected by local geology.
Radiocarbon dates
Radiocarbon dates are primarily useful for older samples than those that span the past 500 years but material can be dated in this time period with a +/- 10% accuracy for material over 100 years in age. Usually the ages of material have error bars that exceed the range of timechange of interest but minimum and maximum dates of material that is found in moraines or above or below treeline (indicating pats TL elevation) is useful for establishing upper and lower bounds for fluctuations or for dates of glacial advances.
Tephrochronology
Tephrochronology is rarely used for this time period although Clark and Gillespie (1997) did use a tephra date to put a maximum age on the LIA advance in the Sierra Nevada. The drawback of this method is that it can be only used as a upper or lower boundary date and volcanic eruptions that leave tephra layers are relatively rare in this time period.
Herbchronology
Herbchronology is a method of dating potentially annual rings in long-lived herbs, shrubs and sub-shrub to their year of formation in an attempt to date a surfaces exposure or stability and also periods of climate favorable to plant establishment. This method could be used in these reconstructions but has not yet been reported on in the scientific literature. The drawbacks of this technique is that these plants, not being coupled to the atmosphere but rather subject to soil temperatures and movement, microenvironmental influences and herbivory, have a potentially poor record of regional climate. However the availability of a record of annual ring growth in

R. Franklin
Preliminary Written Exam
Prepared for C. Millar areas not colonized by arboreal species (i.e. above treeline) has potential for ecological studies of population dynamics and species composition and diversity.
(35%)
2. A) Develop time maps or time lines for each proxy, indicating climatic and ecosystem interpretations from as many (all, if only a few exist) or key studies over the last 500 years.
The goal is to display and compare climate and ecosystem interpretations from different proxies for this time period. As appropriate develop different sets of time maps for the RM and
SN. Indicate the temporal range of each study/proxy that you include. You may choose to develop these maps graphically (actual lines with time indicated and information about the various proxy studies and interpretations aligned with date ranges), in table format (column for each proxy/interpretation), or text.
See attached scan of graphical timelines.
(20%)
B) After outlining and describing the climatic and ecosystem interpretations from individual
proxies and studies, include a summary line/text/column that indicates any coherent climate zones and coherent ecosystem zones that emerged from this comparative analysis. Indicate
major research gaps (time periods, proxy weaknesses) in record reconstruction for each region. Give as much detail about climate for each delineated zone as you think the proxies allow (e.g. not just “warm period”, but seasonal emphasis, climate mechanisms, such as winter storm patterns and origins, role and source of monsoon). Where appropriate, discuss physical mechanisms that might explain the changes in observed climate periods.
Northern Rocky Mountains :
Four main cohesive climatic events seem to characterize the Northern Rocky Mountains (NRM).
In order from the oldest to the most recent, the first climatic/ecological zone extends from time prior to the last 500 years to ~AD1600. It is a moderately variable period according to the different proxies, as there are some minor moraine building episodes and tree growth decline, indicating cold periods but the main trend is that of average temperatures with colonization above present treeline.
The second period straddles the 18 th
/19 th
century boundary and is characterized by major glacial advances along the NRM, severe cold summers, tree mortality and the beginning of a trend towards cool wet summers. Both cold summers and wet spring/winters facilitate glacier advance which is synchronous along the NRM. Although the cool wet period extends through the 1700s, with cool summers and a strong pluvial regime straddling the 19 th
/20 th
century boundary, the third distinct event is in the 19 th
century when glaciers reach their maximum extent for the 500year period. The 19 th century is not as cold as the late 1600s/early 1700s but the increased precipitation leads to the maximal advance of glaciers at this time.
The fourth distinct event of the period comes at the end of the Little Ice Age advance and is the highly variable period covering the 20 th
century. Strong summer warming coupled with drought conditions (1917 – 1941 is the most severe drought of the 500-year period) and low snowpack
(+PDO phase) accelerate glacial retreat during the first part of the century, a negative PDO phase

R. Franklin
Preliminary Written Exam
Prepared for C. Millar counteracts retreat in the mid 20 th
century and from the 1940s onward retreat accelerates as a higher rate than at the termination of the LIA.
Sierra Nevada :
The SN had a monotonic decrease in temperature that was punctuated by what I saw as three ecological/climate events. At the turn of the 17 th century there was a combined wet and cold (low summertime temperatures) period that culminated in the mid-Matthes advance (corresponding to the Maunder sunspot minima) at the end of the 1600s. The second cohesive event initiated at the turn of the 19 th
century and lasted through the end of the 1800s. This time was characterized by periods of low summer temperatures, lowering treelines and higher precipitation. Treelines were responding to temperature and not precipitation.
The third period is characterized by higher variability as it has one of the most severe droughts in the early (1916 – 1934) century and high precipitation in the mid century (1936 – 1986) with a trend of seedling establishment above treeline with establishment episodes during the first part of the high precipitation period and from 1986 onward.
(20%)
C) Indicate any obvious differences in climate and major ecosystem responses between the two geographic regions (N RM vs SN). Describe possible reasons for the differences.
Trends over the past 500 years in the NRM seem to be controlled by the combination of temperatures (which affect treeline movement and tree establishment and mortality) and precipitation events. These precipitation events are correlated with the activity of the northern
Pacific Ocean, notably the Pacific Decadal Oscillation. The PDO modulates temperature effects on the NRM to produce the general trends we see in figure1. The NRM had an inverse correlation between winter precipitation and ENSO (dry conditions during warm phases) during the first and last parts of the 20 th
century. There was no strong correlation during middle 20 th century (Brunelle et al 2005).
In the Sierra Nevada the trend is more monotonic it seems, with less of an influence from the
Pacific Ocean, as the high Sierra crest blocks incoming precipitation. This is especially apparent when we compare the broad trend of treeline activity and glacial advance and retreat with the
NRM which are more strongly influenced by the PDO. Treeline activity in the early period for the SN is linked, not to precipitation, as these high elevation forest and treeline are not affected by drought so much as temperature change. Later treeline variation is still influence by minimum temperatures but with some influence also from the PDO. There has been a monotonic temperature decrease in the SN over the past millennium with two cold periods at the turn of the
19 th century (low summer temperatures and the LIA maximum) and during the first half of the
1600s (lowest summer temperature period for the past millennium). The more advanced glacial positions at the end of the 19 th
century are a result of the temperature combined with slightly wetter conditions.
Overall, the NRM seem to be exhibiting a more straightforward, cohesive and “strong” response to temperature and precipitation combined over the period of interest. Although in the SN the

R. Franklin
Preliminary Written Exam
Prepared for C. Millar record is not as straightforward and more “monotonic” in trend, there is still the effect of temperature modulated by precipitation phases of the PDO.
(15%)
D) Discuss which proxies were most valuable in your reconstruction. Indicate those proxies or studies that yielded information discordant with the other studies, thus rendering interpretation for that time period unclear. Conclude with your analysis of the value of outlining and displaying historic data in a time mapping format. When this approach (actual time line table or text) is not taken in research papers, authors may choose to select only pertinent literature that backs their own interpretation, thus sliding over conflicting proxy interpretations, or developing a more coherent picture of climate history than complete data would actually permit. Can you identify published studies where you believe this has happened?
The proxy methods that yielded the most information about the past 500 years in quantity and also with the highest resolution are the tree-ring data. These reconstructions yield information about temperature and precipitation by season, dates of glacial expansion and retreat and treeline movement. This method however could tell conflicting stories when looked at across a whole region, like the NRM, as in the case of an anomalous cool period in the 1930s – 1950s recorded by tree rings in Luckman 1997 or at the beginning of the 1700s (Luckman 1993). These discrepancies can be explained by the nature of tree ring records to potentially be influenced by local micrositesite conditions, topography or environmental effects. For the whole of this period tree rings were the ubiquitous proxy revealing climate and ecological information on many different time scales.
Moraine formation dates at times yielded information discordant with other proxies. This is because glaciers while acting broadly synchronous over a whole region, are sometimes affected by local climate and topography, i.e. residing on a northfacing slope, etc. Treeline fluctuations are not discordant but appear at some times to react to precipitation and at others to react to temperature changes.
During the time periods between the two pulses of “LIA activity” in the NRM there were predominantly tree ring records of cool wet summers but also summertime drought in Alberta.
As this time period does not have a clear signal as the two LIA times, perhaps there were local site and microclimate forces were affecting the tree ring record at that time. This might be a time frame which a regional gradient could be developed to see where exactly changes in precipitation regime were occurring.
As I am a more visual learner and can assimilate information when it is in a graphical form the time-line method of presenting data appeals to me. However aside from my personal preferences
I do believe that discrepancies and patterns are much more apparent when outlined in this form.
Adding a spatial scale, in addition to the temporal one, to this mapping project would yield even more information and would be a worthy endeavor for a comprehensive review of recent (past
500 yr) climate and ecological change.

R. Franklin
Preliminary Written Exam
Prepared for C. Millar
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