University of Nevada, Reno

Dendrochronological Potential of Bermuda Cedar

A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Geography

by

Jehren A. Boehm

Dr. Adam Csank/Thesis Advisor

December, 2019

THE GRADUATE SCHOOL

We recommend that the thesis prepared under our supervision by

Entitled

be accepted in partial fulfillment of the requirements for the degree of

, Advisor

, Committee Member

, Graduate School Representative

David W. Zeh, Ph.D., Dean, Graduate School

i

Abstract

The Bermuda cedar, Juniperus bermudiana, is an endangered species endemic to the

Bermuda Islands. Likely speciating from a common ancestor of mainland and Caribbean junipers, the Bermuda cedar thrives in the limestone soil and breaks the salty Atlantic

wind for less hardy flora. From the time of its establishment on the isolated archipelago

until the 15th century, no mammals treaded beneath the Bermuda cedar canopy. The first

human use for Bermuda cedar was to repair ships that had wrecked on the treacherous

reefs igniting a craze for the valuable lumber. After multiple waves of deforestation and

large shifts in land use, conservation of the Bermuda cedar was always an issue and

eventually was prioritized by the late 20th century. By 1950 between 90-95% of Bermuda

cedars, already competing with multitudes of introduced species, were defoliated and

killed by an outbreak of invasive scale leaf insects that were accidentally introduced.

Roughly 1% of Bermuda cedars that lived in the 1930’s are still growing today.

As a culturally important forestry product since the 17th century an accurate

chronology is vital to tell the story of Churches, historic structures and to reconstruct

weather and climate that has impacted the Bermuda Islands over the last centuries. To

date there has been no successful attempt to create a chronology from this species for

historical timber dating or climate reconstruction. Construction of a regional chronology

for the island of Bermuda was attempted with 110 cores, 1 partial section, and 1 full

section. Using computer assisted cross-dating with independent radiocarbon testing, a

statistically robust regional chronology was not successfully created with the samples

provided. While a faint common signal was detected amongst Bermuda cedar across the ii territory, more compiled cross sections and geochemical analysis are required to produce a statistically robust regional chronology.

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TABLE OF CONTENTS

ABSTRACT ...... i

LIST OF TABLES ...... iv

LIST OF FIGURES: ...... v

INTRODUCTION ...... 1

STUDY GEOGRAPHY ...... 5

METHODS ...... 12

RESULTS ...... 29

DISCUSSION ...... 39

CONCLUSIONS ...... 46

REFERENCES ...... 49

APPENDIX A ...... 52

APPENDIX B ...... 62

iv

LIST OF TABLES

Table 1 ...... 35

Table 2 ...... 65

v

LIST OF FIGURES:

Figure 1 ...... 3

Figure 2 ...... 6

Figure 3 ...... 7

Figure 4 ...... 8

Figure 5 ...... 10

Figure 6 ...... 15

Figure 7 ...... 16

Figure 8 ...... 17

Figure 9 ...... 18

Figure 10 ...... 20

Figure 11 ...... 23

Figure 12 ...... 24

Figure 13 ...... 30

Figure 14 ...... 32

Figure 15 ...... 33

Figure 16 ...... 36

Figure 17 ...... 37

Figure 18 ...... 38

Figure 19 ...... 45

Figure 20 ...... 52

Figure 21 ...... 53

Figure 22 ...... 54 vi

Figure 23 ...... 55

Figure 24 ...... 56

Figure 25 ...... 57

Figure 26 ...... 58

Figure 27 ...... 59

Figure 28 ...... 60

Figure 29 ...... 61

1

Introduction

Motivating science questions

This attempt at creating a chronology of Bermuda cedar began as an offshoot of a dendro-provenancing study looking at the timber trade between Bermuda and Continental

North America in the 18th and 19th centuries (Kirsten Greer et al., 2019). The National

Museum of Bermuda took interest in the ability of dendrochronology to date structural timbers with annual precision and requested a chronology be attempted from the few remaining specimens of Bermuda cedar that still grow in the territory today. Having a master chronology of Bermuda cedar would allow them to date historic structures on

Bermuda that were built from local timber. The Conservation Services of Bermuda also saw value in developing a chronology. From their perspective a chronology of Bermuda cedar would aid them in identifying trees that had survived and recovered from the ecological disaster created when scale leaf insects Lepidosaphes newsteadii, Carulaspis minima, and Diapsis carueli defoliated all but a few Bermuda cedars in the 1940s

(Challinor & Wingate, 1971; Walker, 1998). The accidental introduction of exotic insects that feed on the photosynthesizing scales of Junipers led to a profound decline in the

Bermuda cedar population which had not inherited any resistance from its mainland relatives. A first attempt at reforesting the territory with the related Juniperus virginiana was hopeful to reintroduce a canopy favorable to Bermuda cedar regeneration, but later proved to be a competitive and hybridizing species (Adams & Wingate, 2008). With few true Bermuda cedars remaining and initial reforestation attempts endangering the species’ existence even further through the propagation of hybrids, a chronology could expedite 2

and cheapen the process of correctly identifying the protected Juniperus bermudiana,

which would date to pre-1940, from hybrid subspecies thus avoiding the need for costly

genetic testing (Adams & Wingate, 2008). The benefit of a regional chronology of

Bermuda cedar is apparent but the species’ ability to produce consistent annual ring

boundaries was unknown.

The motivating science questions of this study are as follows:

1. Are traditional visual cross-dating techniques sufficient to create a regional

chronology of Bermuda cedar?

2. Due to the confounding geography and weak seasonal climate of Bermuda, are

apparent ring boundaries in the wood truly annual features?

3. Are Bermuda cedar sensitive to regional long-term climate mechanisms?

Species overview

The surviving trees of the endemic Juniperus bermudiana are but a few living relics

of a once prolific keystone tree species. Related to and likely speciating from a common ancestor of the Eastern Red Cedar (Juniperus virginiana) of mainland North America and

Caribbean species J. silicicola and J. barbadensis, the Bermuda Cedar once blanketed the

Bermuda islands protecting the interior environs from harsh and salty winds (Challinor &

Wingate, 1971). Mature Bermuda cedars can reach diameters of 60 centimeters and heights of 15 meters (Figure 1; Groves, 1955). The extent of the cedar’s sprawling

forests, well adapted to the limestone soil, were only limited by the fluctuations of sea

level throughout the ice ages of the Pleistocene (Glasspool & Sterrer, 2009). 3

Figure 1: Mature Bermuda cedar specimen at Saint James cemetery. Photo: A. Csank.

This small and remote, nearly tropical, archipelago developed very few endemic

species from its time of creation until its discovery by the Spanish in 1503. Of the 17

endemic land plant species of Bermuda, the Bermuda Cedar proved to have the greatest

cultural and commercial value (Groves, 1955). J. bermudiana contains compounds in its

heartwood that resist decay and discourage insect habitation (Schweingruber, 2007;

Verrill, 1902). Along with its pleasant aroma and deep color, it is highly valued in

carpentry for items from jewelry and clothes chests to structural lumber. Its desirable traits for lumber led to multiple events of deforestation until its realized value contributed

to its conservation (Groves, 1955).

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Challenges in Crossdating Junipers

Of the conifers used in dendrochronological studies worldwide, junipers are used

less frequently than pines (Derose et al., 2016). Species in the genus Pinus are commonly

chosen for dendrochronological studies due to their predictable concentric growth that, when selectively sampled based on site characteristics, can be highly sensitive to a specific climate variable (Stokes & Smiley, 1968). Species in the genus Juniperus are

known for their lobate trunks, multiple stems, invasive growth traits, and difficulty in

crossdating (Edmondson, 2010). While junipers are drought tolerant and grow over a vast

expanse of the entire globe at nearly all elevations and may be ideal for streamflow

reconstructions and other climate proxies, co-occurring pines are often used instead for their relative ease in crossdating (Derose et al., 2016).

The anatomical differences and crossdating difficulty between junipers and pines is explained by their contrasting adaptations in water use. As dissected in Willson et al.

(2008), junipers exhibit anisohydric behavior while pines exhibit isohydric behavior. In order for pines to maintain a constant xylem water potential and reduce risk of cell cavitation during drought conditions gas exchange will decrease and radial growth will slow or halt completely while carbon allocation may focus on fine root expansion.

Junipers maintain a constant gas exchange while xylem water potential fluctuates at a greater risk to cell cavitation. This anisohydric adaptation inherent to all junipers results in the lobate growth of the bole as parts of the xylem cavitate under extreme soil water deficits allowing water to be pulled through xylem connected to deeper root structures.

Junipers are a drought adapted genus that facilitate carbon allocation during times

of environmental stress differently than pines. While pines may be easier to crossdate, 5 junipers’ ecophysiology may hold a greater potential to investigate intra-seasonal variability via missing, false, and wedging rings (Derose et al., 2016; Edmondson, 2010).

Nevertheless, the challenges of crossdating junipers are great and require extensive preparations in the lab and in the field. Common practice when sampling junipers is to sample more cores and cross sections than you would when sampling pines (Edmondson,

2010; Maxwell, Wixom, & Hessl, 2011). Cross sections are vital to identifying missing and false rings shared by all juniper trees in a site (Derose et al., 2016). The ecohydrologic duress of the Bermuda cedar remains unstudied and it is not known how its inherited drought tolerant adaptations are put to use in the calcareous soils of the

Bermuda Islands.

Study Geography

Location

Bermuda is an arcuate cluster of islands that loosely fits the description of an archipelago. A territory of Great Britain, Bermuda is quite far in the Atlantic from any other land (Figure 2; overview map). The closest port to Bermuda is Cape Hatteras, North

Carolina roughly 1,040km to the northwest. At 32 degrees North of the Equator, seasonal solar angles on Bermuda match those seen in Charleston, SC, Montgomery, AL, Tucson,

AZ, and San Diego, CA. As seen on the International Tree Ring Database (ITRB) map, there exists multitudes of tree ring chronologies along this latitude (Figure 3; NCEI,

2016). Bermuda’s longitude, however, places the islands east of the Gulf Stream current 6 in a perpetually warm oceanic climate 2,000 km north of the Caribbean (Figure 2; overview map).

Figure 2: Map of Bermuda. Overview map indicates the Gulf Stream current. Detailed map includes locations of sampled Bermuda cedar. 7

Figure 3: International Tree Ring Data Bank map of chronologies. Green triangles denote tree ring chronologies. Red triangles denote two chronologies of Juniperus virginiana. Climographs presenting minimum and maximum monthly temperatures and precipitation for each chronology site are included. Note their pronounced seasonality in temperature compared to Bermuda.

Geology and hydrology

Bermuda, the northernmost reef complex in the world is a remnant of a volcano that most recently erupted 33 million years ago (Glasspool & Sterrer, 2009). After being

eroded down near to sea level, the substrate of the islands consists of recrystallized

carbonate sand grains likely transported from the African Sahara (Vacher, Hearty, &

Rowe, 1995).The topography of Bermuda has been set by coastal erosion and karst

dissolution balanced by carbonate deposition (Bretz, 1960). The low hills can be

characterized as dunes and the depressions as collapsed caves (Vacher et al., 1995). The

permeability and solubility of the carbonate soil of Bermuda retains a lens of freshwater

on top of brackish water at stasis with sea level (Mylroie, Carew, & Vacher, 1995). 8

Climate

Residing on the warm side of the Gulf Stream current, Bermuda’s humid subtropical

(Cfa) climate remains remarkably mild except for the occasional tropical cyclone or

hurricane. The average annual rainfall of 150cm is distributed evenly throughout the year

with April commonly being the driest month (Glasspool & Sterrer, 2009). Average

annual temperature remains close to 21.6°C with slight variation from 27.5°C in August

to 17.6°C in February (Figure 4). Relative humidity is uniformly above 70% year round

(Glasspool & Sterrer, 2009).

Figure 4: Climograph of Bermuda. Average monthly temperatures follow seasonal shifts albeit, regulated by ocean temperatures. Precipitation is received year-round, but it is possible that April and May are too short of a dry period for Bermuda cedar to shut down growth completely.

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Colonial Contact

The first explorers that sailed past the reefs of Bermuda were deterred from its

shores by rugged reefs and the disturbing calls of the endemic Cahow (Gadfly petrel)

likely nesting on the coastal fringes of dense, vigorous Bermuda Cedar forests (Glasspool

& Sterrer, 2009). The mysticism of the “Isle of Devils” kept away all human visitors until

the entire crew of shipwrecked Sea Venture found salvation on Bermuda’s shores in 1609

(Rueger & von Wallmenich, 1996). Permanent habitation soon followed, and shipping routes shifted to take advantage of Bermuda’s new appeal as a land of many natural resources. Of high value was the timber of the Bermuda cedar with its lightweight strength and natural resistance to insects and ship worm (Pers. Comm. A Csank). As the remote archipelago saw more traffic through the 18th and 19th centuries, invasive species

found their way into niches opened by the industrious deforestation of the shipbuilding

era (Groves, 1955). Some of the most vigorous and old specimens to live on Bermuda in

the past millennium are likely now part of historic churches or sunken ships. Since many

members of the Juniperus genus can grow quite old with J. bermudiana’s closest relative,

J. virginiana, living longer than 700 years, historic lumber could possibly date back to

1000 A.D.(Brown, 1996; Maxwell, Wixom, & Hessl, 2011).

Attempting to recover from centuries of aggressive deforestation and changes in

land use, Bermuda was struck with a devastating defoliation event impacting J.

bermudiana from the mid 1940’s to the mid 1950’s (Walker, 1998). Sometime in the late

1930’s or early 1940’s a host of mites, scale insects and aphids were accidentally

introduced to the isolated territory and later discovered in overwhelming numbers

(Challinor & Wingate, 1971; Walker, 1998). Eradication of the insects proved futile and 10 only a small percentage of trees proved to be resistant to the attack. Less than a decade after the first trees were defoliated, the Bermuda government authorized the Department of Agriculture to remove dead trees and plant ornamental trees within 100 feet of public roads in an attempt to beautify the islands for the tourist economy (Challinor & Wingate,

1971; Groves, 1955).

Figure 5: Mature Bermuda cedar at Fort Scaur. Note the growth affected by the prevailing winds. Trees in the background are not adapted to handle the strong winds common on Bermuda and act as a poor windbreak.

Introduced ornamental trees lack the adaptations of the Bermuda cedar to resist the strong winds and salt spray that pervade, providing insufficient cover for the native understory (Figure 5; Walker, 1998). With the loss of the Bermuda Cedar forest canopy across island, the understory was reduced to the point that tree seedlings could not establish, perpetuating the crisis (Challinor & Wingate, 1971). As found in the paper by 11

Adams & Wingate (2008a), roughly one percent of J. bermudiana survived the blight and

continued producing cones so related species J. virginiana var. virginia and J. virginiana

var. silicicola were introduced to create a windbreak and canopy suitable for germination

of the now endangered species. Unbeknownst to the efforts, J. v. var. silicicola

introduced by J. D. C. Darrell (Darrell’s cedar) can hybridize with J. bermudiana but is

likely infertile with the species. Darrell’s cedar has become prolific on the islands and

shed their pollen at the same as the outnumbered Bermuda cedar. This uninhibited

competition is likely to eventually wipe out the germplasm of the Bermuda cedar entirely.

This study seeks to create the first ever chronology for Bermuda cedar from the

remaining one percent of a once prolific endemic species.

Study Motivations

The struggle for survival of the Bermuda cedar is very real. Its reign as the dominant endemic tree species on the incredibly isolated arcuate cluster of islands is near its end. The adaptations that the Bermuda cedar developed, and its ecosystem functions,

was of little use when humans arrived with industry and their host of introduced species.

Waves of conservation over the centuries brought the population back from the brink

several times, but the accidental introduction of scale insects, mites and aphids has

brought J. bermudiana to its most critical state yet (Adams & Wingate, 2008; Challinor

& Wingate, 1971; Groves, 1955; Walker, 1998). The best attempts at reviving this endemic species has only endangered the waning germplasm even more.

The rich history of colonized Bermuda is, quite literally, framed by Bermuda cedar. The aromatic wood is not only found in fine carpentry, but in the structural 12

skeletons of historic and common buildings alike. The evergreen tree with its wispy

stature and red heartwood has worked its way into the culture of the island, always

present, from ceremonial to ordinary, in just about any aspect of Bermuda life. With the

decimation of 99% of this beloved tree, the window of opportunity is closing to make

scientific use of this dwindling resource.

A chronology is the first step in unlocking data contained within each ring of

Bermuda cedar, dead or alive. Linking together the growth history of all the remaining trees in the territory can eventually connect the chronologies contained within the historical timbers hidden across the islands. The ability to place a date on each ring of a

Bermuda cedar sample allows living trees to be assigned an age and historical accounts to be verified. A successful chronology can also serve to protect existing Bermuda cedars by dating them prior to the leaf blight event and verifying their protected status without costly genetic testing. Dependent upon the Bermuda cedar’s sensitivity to external environmental variables, a chronology could open the door to further research into reconstructing climate or extreme weather events such as hurricanes. With a regional chronology established, isotope dendrochronology could be employed to answer more detailed questions concerning tree physiology and climatology on the seasonal scale.

Methods

Scattered across the archipelago of Bermuda, the remaining 1% of the endemic

and endangered Bermuda cedar were sought after for sampling. Since the Bermuda cedar was the only juniper growing on the islands before the leaf blight, any tree known to be 13 over 70 years old could be safely considered a true Bermuda cedar and not a hybrid.

Attempting the first ever chronology of Bermuda cedar, collection and lab methods were tuned towards creating a datable annual resolution chronology rather than climate reconstruction.

Site selection and sampling

A traditional approach of sampling a population of trees across all ages at multiple sites was attempted as outlined by Stokes and Smiley (1968). Such a sampling design would have also allowed for the collection of numerous full disc sections of dead trees as is often necessary for studies focused on trees in the Cypress family (Derose et al., 2016; Edmondson, 2010; Maxwell, Hessl, Cook, & Buckley, 2012; Maxwell et al.,

2011). Upon arrival in the field, the sheer difficulty in locating Bermuda cedars made the traditional sampling method described by Stokes and Smiley (1968) an impossibility.

Since Bermuda is nearly homogenous in soil type and topography is quite benign across its 52 square kilometers, the entire territory was reconsidered as one site (Figure 2; overview map). The revised sampling plan became an opportunistic collection of two cores from all mature trees that survived the leaf blight (in which permission to sample was granted by private landowners) using a 5 mm diameter increment borer. Many of these specimens were located in cemeteries or church yards where they had been spared development and some written evidence of the tree’s age could be obtained. Cores were collected from two plantation sites in which Eastern red cedars were planted after the leaf blight. Three large diameter cores from three standing dead trees killed by the insect blight in the late 1940’s were collected using a 12mm increment borer. Owing to 14

Bermuda cedar’s status as an endangered tree obtaining whole disks was difficult. We

were able to obtain two sections from fallen deadwood that were sampled using a

chainsaw, and pieces from historical structures were sampled with a handsaw. Sawn off samples from historical structures were not used in this attempt to create a chronology,

however, future work may attempt to tie them into the chronology.

Using the increment borer on mature trees, much attention was given to sampling

away from strip bark and upon the lobes or buttresses of the trunks to avoid erroneous

growth patterns or indecipherable ring compression (Figure 6; Schweingruber, 2007).

Most trees had two cores taken from different sides, however, many trees with strip bark permitted only one core to be taken. Plantation trees of Eastern Red cedar (J. virginiana) were sampled in hopes of capturing post blight growing conditions from trees that were planted after the great defoliation event and investigating if rings were annual or not.

Two dead and decayed trees that were brought down from Hurricane Fabian in 2003 were

sampled by chainsaw to serve as the only cross sections to inspect multiple radii along

the circumference. One of the two cross sections was reduced in size for ease of

transport. In total: 70 trees were sampled producing 110 cores, one full section, and one

partial section for processing and analysis. 15

Figure 6: Sampling of a mature Bermuda cedar at Saint Marks cemetery. Photo: A. Csank

Physical sample preparation

Once the samples were brought back to the lab, procedures from Stokes and

Smiley (1968) were followed to mount and sand the cores. Trees with minimal false rings and clearly defined ring boundaries were selected for skeleton plotting as described in

Stokes and Smiley (1968). Poor results from skeleton plotting necessitated movement to an alternative computer assisted cross-dating technique described later.

Initial inspection of cores that received spot sanding revealed extensive problematic rings and inconsistent ring widths between cores taken from the same trees.

Multiple failed attempts at cross-dating A and B cores from several trees using the 16 skeleton method as described by Stokes and Smiley (1968) directed efforts towards using computer software to experiment with ways to deal with problematic rings in a more time-efficient and systematic manner. In order to create high quality scans, all cores were re-sanding using an improvised, inverted, sanding technique described below.

To eliminate longitudinal thicknesses or waves along the length of the cores, a belt sander with a 400-grit belt was used (Figure 7). Cores were passed over the belt at a consistent speed and pressure 45 degrees to the rotation of the belt, not an atypical application of mechanical sanding in dendrochronology (Csank & Strachan pers. Comm;

Figure 8). This motion was repeated in both directions of the length of the core to minimize left/right handed pressure bias. The high speed of the belt sander causes heat to build up and centrifugal force adds unwanted pressure into the surface of the core limiting the effectiveness of finer grit belts. Since the speed of the belt sander available could not be adjusted lower, a finer grit belt introduced surface scratches equivalent to the 400-grit belt. Hand sanding was subsequently implemented to complete the process.

Figure 7: Core preparation with longitudinal thicknesses, or waves, taken into account. Sample A will lay flush to a scanning bed producing an image with minimal distortion. The improved surface of sample B will not lay flush to a scanning bed and may introduce distortion of actual ring widths into the scanned image.

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Figure 8: Belt sander scars left behind when sanded parallel to the rotation of the belt. This parallel orientation allows the core to roll along its long axis leaving deep scratches where finer grit sandpaper cannot remove them.

Inverted sanding method

Traditional hand sanding techniques were improved upon during the course of

this project, in order to obtain the finest surface possible for flatbed scanning in a

problematic species. The final technique used for surface finishing can be termed an

“inverted sanding method.”

Step 1: Sandpaper preparation While the surface of sandpaper is denser than wood, it eventually breaks down

and degrades. A brand-new sheet of sandpaper will cut deeper into the surface of wood than an old sheet of the same grit. During the sanding process of the 110 cores in this study, sheets of used sandpaper were not thrown away but kept and shifted down the spectrum of cutting depth. To initiate this differentiation between three sheets of 18 sandpaper of the same grit without first sanding multitudes of cores, two sheets of sandpaper can be rubbed together to knock down the most aggressive abrasive particles.

Attention must be given to apply even pressure across the entire sheet. Sandpaper ANSI grits 320 and two 400 grit sheets at different stages of use were adhered to a 45 x 90cm bathroom tile using packing tape (Figure 9).

Figure 9: Inverted sanding technique. Perpendicular angles between different sheets of sandpaper allow stereoscopic inspection to easily identify regions along cores in which scratches from the previous sheet were not removed and need further sanding.

Step 2: Planing the cores Mounted cores were inverted and pushed and pulled across each surface. To decrease the risk of a rogue sand particle detaching from the sandpaper and deeply scratching the improved surface, samples were oriented roughly at a 45-degree angle to the path of motion. Moving the sample from one sheet of sandpaper to another, the angle that the sample was held was changed by 90 degrees (Figure 9). If samples were longer than sheet of sandpaper, the sample would be rotated 180 degrees as many times as necessary to keep the plane of the improved surface level. Samples were not brought to a 19 finer grit nor the angle changed until sandpaper grain imprinted in the wood from the previous rougher grit sandpaper was replaced by the grain of the current sheet. All samples were quickly inspected under a stereoscope to confirm that the sanding grain indeed replaced the previous orientation and grit. High powered optical inspection ensured that the surface of the sample was flat and true enough for the next finer grit sandpaper to effectively remove the grain of the rougher grit sandpaper. For the duration of time spent on each grit of sandpaper, pressure was gradually reduced so cutting was directed at the “peaks” of the grain rather than the “valleys”. Sawdust accumulation in the sandpaper was removed with a shop vacuum to maintain consistent sanding across samples.

Step 3: Polishing For the final stage of sanding, the oldest and smoothest 400-grit sheet was used before a 600-grit sheet. These two sheets were not affixed to the tile but were placed on top of a 4mm rubber mat on top of the tile (Figure 9). In this polishing stage, using the old and smooth 400-grit sandpaper, pressure was gently and gradually increased so that the rubber mat could rebound pressure into minor pockets that remained along the plane of the core. The 400-grit sheet was replaced by a 600-grit sheet for the final polish where a decent amount of pressure was again used.

Due to the common occurrence of problematic rings, explained in depth below, in

Bermuda cedar and the lack of full cross sections to survey their full circumferential extent, the improved surface of all cores had to be maximized in width (Figure 10). This inverted sanding technique allowed the entire improved surface of the core to be brought 20 down to the full interior diameter of the increment borer at a controlled speed. The angle of the sanding motion not only allows rogue particles to be ejected from the improved surface before damaging multiple rings but also prevents the core from rolling on its axis and rounding the edge of the improved surface, maximizing surface area on the focal plane to be inspected, scanned, or photographed.

Figure 10: Width profiles of different stages of core sanding. Sample C has not been sanded enough to expose the full width of the core for analysis. Sample A is sanded enough to expose the full width of the core. Sample B has been too much by hand, rounding the edges and reducing visibility of cells at the edge of the core.

Optical inspection and imaging

Polished cores were examined under a stereoscope to identify potential rings that may not be clearly visible on a scanned image. These potential rings include very dense latewood boundaries indicative of a “wedged” missing ring, or very faint areas of latewood similar to false rings found in other mid-latitude tree species. Suspect possible ring boundaries were marked on the core mount so they could be seen in a scanned image and given extra attention.

Cores were then organized by site and scanned at the highest resolution possible per length of the longest core in each site. To avoid confusion with digitally labelling cores, cores were always organized in ascending and alphabetical order and a sticky note 21

label was always included in the scan. An Epson perfection V600 Photo scanner was

used with all image enhancement settings unchecked and the lid up. Cores that could not

fit along the length of the scanner were rotated diagonally so the improved surface stayed

flush with the glass of the scanner. DPI (dots per inch) was adjusted so that the longest

core in every scan equaled 70,000 pixels along the y-axis of the scanner. Resolution

values ranged from 2500 – 4000 DPI.

Jpeg images were then adjusted in Photoshop to be measured in CooRecorder

9.3.1. by Cybis. Adjustment in Photoshop consisted of rotating and cropping images as

necessary and adjusting curve limits to exclude color values outside the range of color

scanned from the cores. This curve limiting enhanced the contrast between the thin

latewood boundaries and earlywood with minimal editing of the photo. This adjustment

also made faint false rings easier to identify at the lower zoom level used in

CooRecorder, where they went unnoticed under the high magnification of the stereoscope. Text labels for each core were also added.

Visual cross dating

Polished cores were organized by site and tree to begin crossdating under

stereoscopic inspection. Copious ring growth anomalies such as false and wedging rings

compiled with large ring width variation to produce low confidence in ring year assignment. Computer software was employed to aid in visual cross dating using

statistical inference of normalized values to categorize annual ring boundaries from false

ring boundaries. Assignment and measurement of ring boundaries in the software 22 program CooRecorder 9.3.1 by Cybis was performed with the physical sample alongside under stereoscopic inspection.

Image analysis, ring identification, and statistical crossdating

Using CooRecorder 9.3.1, visual assignment of ring boundaries was qualitatively and manually assigned. Copious missing rings, suspect locally absent rings, fading rings, and wedging rings were marked, given a note referring to their category, and then disabled. CooRecorder measures the pixels in between each enabled point and produces a raw ring width series and a proportion to last two years growth normalized series that is continually updated as points are added, subtracted, or modified. Cores that exhibited most of its rings to be anomalous were not measured and excluded from the chronology.

Points within CooRecorder that marked definitive ring boundaries were setup to be green in color whereas disabled points marking ring anomalies and their categorized note were setup to be red in color (Figure 11). Once enough ring boundaries were marked to create a normalized ring width index (RWI), the series could be visually compared against another series. Within CooRecorder, default cross dating tools correlate raw ring width values across the entire length of the series and by 20-year blocks against a chosen series. 23

Figure 11: False rings. Green crosses denote ring boundaries assigned as annual rings. Red crosses denote areas where latewood forms but does not create a sharp clear boundary with adjacent earlywood.

For lack of sufficient full cross sections, locally absent or missing rings had to be

isolated by comparing ring width series amongst cores from the same tree or trees from

the local site. Qualitatively assigning a disabled ring boundary point focused on ring size,

latewood thickness and density, sharpness of latewood boundary, and presence of other false rings (Figure 11). Possible rings that were disabled were re-enabled where statistical

inference or 20-year block correlation coefficient indicated a better match with another ring present. If raw ring width values were not alike, normalized values were used to 24

identify missing or “ghost” rings to match two cores within a tree. The wedging and

lobing of all members of the Cupressacea family means that even within a single tree,

raw ring width values may vary by several standard deviations (Figure 12;

Schweingruber, 2007). These radial inconsistencies can invert the ring width relationships of neighboring rings, decreasing the correlation amongst other cores within the chronology. This method across numerous cores helps to differentiate between false, wedging, fading, or missing rings that are not locally present in the core or may look identical to a true annual ring boundary.

Figure 12: Variability in ring width relationships. Between transect A and transect B, the relationships between rings W,X,Y, and Z can change or reverse. As seen in this photo, lobes of the stem can change position over time and cannot be seen before coring.

25

Chronology building

After cores were cross-dated amongst A&B cores in CooRecorder with the

highest visual and statistical confidence possible, collections for each site were created in

the program CDendro by Cybis for correlation analysis. The best correlated pairs were

identified and then reexamined in CooRecorder to identify problematic blocks where

specific rings required further study under the stereoscope using the original core. Poorly correlated pairs that could not be resolved were excluded as mean site chronologies were

constructed.

Mean site chronologies were used as a secondary check against cores that cross

dated poorly before excluding them completely from the regional chronology. Three site

chronologies were created corresponding to the three trees sampled for radiocarbon

dating. The three site chronologies were correlated against each other before attempting

to create a regional chronology named “C14”.

From the remaining useable cores, an experimental island-wide chronology was constructed, named “Experimental”, using the control regional chronology as a master.

Any ring that exhibited wedging, fading, or false characteristics were disabled. Ring width series were loaded into a collection in Cdendro where cross correlations were calculated for all the cores and a threshold of .10 for Pearson’s R correlation coefficient and a t-test of 1 was used to eliminate cores to create a mean sample and .rwl file for

detrending in R using the package DplR (Bunn, 2008). Detrending was done using the

Friedman’s super smoother spline to control for the extreme variability in growth

between A & B cores as well as individual trees. The Friedman’s super smoother spline, 26

commonly used in studies where ecological disturbance is high, is very flexible in short

timespans and effectively eliminates long term variations in growth.

To address the motivating science question 2, referring to false rings, both the

C14 and Experimental chronologies were re-measured in CooRecorder to include any false ring or anomalous ring as annual rings. These chronologies were titled C14x and

EXBx respectively before being run through the program COFECHA to assess the viability of resolving cross-dating errors.

Amongst all the chronologies measured in CooRecorder and compiled in

CDendro, the program COFECHA was used to identify the best matching cores as reference cores to create a final chronology from. In this final chronology, all the accumulated time qualitatively inspecting ring boundaries under stereoscope magnification was guided by the mean ring width series of the reference cores where statistical inference determined if areas of latewood production were annual boundaries.

Only the highest quality cores exhibiting defined ring boundaries and lacking wedging

rings were used for the final chronology. Cores were re-measured in CooRecorder

comparing normalized and raw values with the reference curve during the measuring

process to identify possible missing or false rings as they arose. The program COFECHA

was used to assess the series inter-correlation of all chronologies as an assessment of success or failure.

Climate sensitivity assessment

Temperature and precipitation records from the Bermuda meteorological division

were obtained from the HGIS project of the Empire Timber blog and formatted into 27 monthly averages using the AVERAGEIF equation in Microsoft Excel (Kristen Greer et al., n.d.). Two gaps in temperature data were identified and filled with high resolution .5 degree gridded data from the Climatic Research Unit (CRU) of the University of East

Anglia. The downloaded gridded data was organized in a 13 column format and the required years were extracted and rotated before being inserted into the existing four column Bermuda meteorological dataset. The inserted data was highlighted and labeled as CRU data.

To assess if Bermuda cedars are sensitive to climate, the seascorr function in the

R package treeclim was used (Zang & Biondi, 2015). The function seascorr requires an uninterrupted record of at least 50 years of two average monthly climate variables in a four-column format including year, month, variable 1, and variable 2. With an appropriately filled and formatted dataset, seascorr compares the ring width value of each year to the preceding months’ climate variables and outputs a graph detailing the correlation of each month to ring width. Parameters such as the end of the growing season and size of multiple month blocks to be analyzed can be adjusted. Using the seascorr function, climate sensitivity was assessed from monthly temperature and precipitation in 1,2,3,4,5, and 6-month blocks.

Radiocarbon dating

To include an independent check of cross dating accuracy, radiocarbon dating was performed on four rings in three cores. Radiocarbon dating is common for assigning approximate dates to organic material. The predictable radioactive decay of the rare isotope Carbon 14 causes it to become lighter with time and its current weight can 28

determine how many years prior it was created. Accuracy of dating decreases as Carbon

14 has undergone multiple half-lives of radioactive decay. Approximate dates can be further narrowed down when sampling multiple annual rings from tree cores (Kai-Mei &

Fan, 1986). The values of the isotope Carbon 14 contained in each sample can be plotted against a well-documented and calibrated curve of atmospheric C14 concentrations after above ground nuclear testing was halted (Quarta, D’Elia, Valzano, & Calcagnile, 2005).

This method can also be applied to tropical trees with indistinct annual ring boundaries

(Worbes & Junk, 1989). Applying radiocarbon dating to tree rings produced post nuclear testing, accuracy of dating is much higher than that of tree rings produced pre-nuclear testing.

Before sampling rings from cores for C14 analysis, cores were soaked in water to release them from their mounts. Water soluble glue is pertinent in traditional dendrochronological techniques so later analyses can remove the core from the mount.

Wood glue is not water soluble and therefore should not be used if disassembly may ever be required. Remaining glue adhered to the bottoms of the cores were gently and persistently peeled and scraped away from rings to be sampled. A second soak in water for 10 minutes allowed for more precise massaging of wood grains to coerce remaining glue out of the wood. Special care was given for each sample to contain the maximum amount of latewood in each ring to ensure that Carbon within that ring was from that growing season and not stored in the tree from the previous growing season. Samples were reduced down to Alpha cellulose using the modified sodium chlorite oxidation method of Leavitt & Danzer (1993). A radiocarbon “dead” and a modern sample blank were processed along with the Bermuda cedar samples to ensure no contamination was 29

introduced during cellulose processing. Each ring sample was stored in separate vials and

labeled in code so the independent lab testing was blind to the predicted year of each sample. Samples were sent off to Lalonde AMS lab at the University of Ottawa, Canada

for analysis and dating.

Results

The outcome of the attempt to create a regional chronology of Bermuda cedar

from visual and statistical cross dating has produced no clear result. Lack of cross sections to resolve circumferential persistence of anomalous ring growth resulted in large standard deviations of growth for long periods of times within each chronology. While a faint signal was present amongst three chronologies, series inter-correlations within each chronology do not reach proper thresholds for rigorous statistical significance.

Site Selection and Sampling

Improvised site selection and sampling produced 114 cores from 73 trees. Of the

73 trees sampled, 52 were J. bermudiana, 18 were J. virginiana, and 1 was Elaeodendron

laneanum. Of the 73 standing trees sampled 70 trees produced 102 cores with the

outmost ring connected to the 2014 and early 2015 sampling campaigns. Two sections of fallen dead J. bermudiana were provided by the Conservation Services of Bermuda with known death dates from recent hurricanes. Three 12mm cores were taken from three

standing dead trees on Nonsuch Island nature preserve with death dates estimated to be in

conjunction with the leaf blight on the late 1940’s (Table B2). 30

Physical sample preparation

All 114 cores were prepared using the inverted sanding method described earlier.

Improved surfaces were found to be flat across the length and width of all cores (Figure

7&10). Magnified optical inspection under the stereoscope found improved surfaces to be nearly free of scratches without additional (non-inverted) hand sanding. While some scratches were still present, the majority of surface of all cores were polished well enough to identify ring and cell wall boundaries as well as anomalous ring growth

(Figure 13).

Figure 13: Examples of wedging and fading rings. Both images are from the same core DP_2A. Arrow indicates direction of growth. While some scratches are present, ring boundaries and cell walls are visible.

31

Optical inspection and imaging

Before polished cores were scanned, core mounts were inspected under a stereoscope and marked in positions of faint or anomalous rings that could possibly be missed in a scanned image (Figure 14). This stage illuminated the sheer quantity of weak latewood boundaries or false rings. The great quantities of these ring anomalies exposed varying differences between true ring boundaries, wedging rings and false rings. During the analysis, new categories of “reverse latewood”, “ghost rings”, “fading rings”, “offset rings”, and “seasonal banding” were created to qualitatively categorize cores that could possibly be cross-dated or not (Figure 15). Attempts to cross-date samples using the skeleton plotting and list methods were abandoned as the extreme variability of ring growth in between A & B cores could not be overcome with traditional visual techniques alone. 32

Figure 14: Image comparison between magnification and high-resolution scanning. Image on the left was taken using a Nikon microscope camera. Image on the right is a crop from a scan at a resolution of 2500 DPI (dots per inch).

Regardless of any core’s ability to be cross-dated, all cores were scanned using the methods described in the methods section. Aside from the restrictive length of the scanner for some cores, the greatest struggle presented itself in sawdust particles continually obscuring scans. Compressed air in a well-ventilated area is recommended to remove stubborn sawdust from cores before scanning. A collection of 20 images totaling

2GB was created for image analysis and measuring in Cybis CooRecorder 9.3.1. 33

Figure 15: A cross section illuminates ring anomalies outside the confines of a 5mm core. Different transects would create different ring width series. Transect A may falsely include ring W but exclude ring X. Transect B would miss both ring W and X. Rings Y and Z represent possible seasonal false rings.

Image analysis and ring identification

Software assisted crossdating was backed up with optical assessment using a

Nikon SMZ10 4x stereoscope with 10x eyepieces. Even with resolutions up to 4000 Dpi

on some scans, resolution was still unsatisfactory for deciding upon ring boundary

designations for especially problematic areas (Figure 14). The variable and seemingly random nature of these ring anomalies became apparent upon inspection of the two cross sections (Figure 12). As is standard for most chronologies of Juniperus, numerous full cross sections are inspected around the full circumference of each ring to identify locally absent or missing rings (Edmondson, 2010). With the incredible variability of ring growth exhibited amongst the samples of Bermuda cedar provided, two sections were not 34 enough to isolate missing rings but were enough to provide a glimpse into the difficulties posed by Bermuda cedar ring anomalies.

Examining rings around the circumference of the full and partial section, many uncertainties arose concerning the distinguishing factors between missing rings and false rings. Rings that fit the description of an annual ring (latewood cell wall thickening towards the ring boundary followed by large earlywood growth to the outside of the ring boundary) can sometimes disappear along its circumference before reappearing again

(Figure 15). The reverse is also true where very weak false rings, when followed around their circumference, can appear to have all the characteristics of a true annual ring boundary. This varying radial ring growth behavior becomes tricky in building a chronology when false and annual rings become confounded in the confines of a 5mm core (Figure 12).

The large number of cores collected for this study allowed for many samples to be excluded from cross-dating and chronology building. Many cores did exhibit reasonable annual growth rings that weakly correlated to other cores when measured. Of the 114 cores prepared for analysis, 50 were measured in CooRecorder (Table B2).

CooRecorder’s instantaneous correlation statistics between series allowed for qualitative assessments of ring boundaries on the screen and under the stereoscope to be backed up with statistical inference. The overall low correlations sought after to identify a matching core or matching block within a series brought great significance to using the stereoscope on any core in question to conclude if a ring boundary is indeed annual.

35

Chronology building

Of the 50 cores measured, 36 were used to build two independent chronologies.

17 cores were used in the first chronology (C14 chronology) where members were

selected based on their proximity to three trees chosen to be sampled for C14 dating in a

previous study design. Series inter-correlation of .231 was produced for the un-trended

raw ring-width series using the program COFECHA. Using COFECHA with the default

smoothing spline with rigidity of 32 years lowered the series inter-correlation to .153

(Table 1).

COFECHA results Chronology Detrending option # Length # Rings Series Inter- Mean # Flags name Series Yrs correlation Sensitivity C14x none 20 213 2174 0.084 0.797 144 EXBx none 23 225 2776 0.167 0.684 182 C14 none 17 151 1605 0.231 0.693 104 C14 33% Smoothing 17 151 1605 .157 0.695 65 Spline Experimental none 16 197 1577 0.287 0.5 100 Experimental 33% Smoothing 16 197 1577 .159 .5 53 Spline Final none 31 180 3205 0.278 0.502 299 Final Friedman Super 31 180 3205 0.214 0.493 199 Smoother Final 33% Smoothing 31 180 3205 0.116 0.502 54 Spline Reference none 14 180 1822 0.213 0.487 119 Best 4 none 4 177 497 0.293 0.439 30

Table 1: Table of COFECHA results for all chronologies produced. Note how detrending lowered the number of flags but also decreased series inter-correlation.

For the second chronology (Experimental chronology) 16 cores from the entire territory of Bermuda were used excluding the cores used in the C14 chronology. Series inter-correlation of .287 was produced from the un-trended raw ring-width series using 36

the program COFECHA (Table 1). Using COFECHA with the default smoothing spline

with rigidity of 32 years lowered the series inter-correlation to .153 (Table 1).

Comparing the chronologies C14 and Experimental together in the program

CDendro, a Pearson’s R correlation coefficient of .46 and a t-test value of 6.3 was calculated (Figure 16).

Figure 16: Comparison of C14 and Experimental chronologies within the program CDendro. The raw ring width Experimental chronology is dark blue, while the raw ring width C14 chronology is green. The red line represents the heavily detrended C14 chronology while the black line represents the heavily detrended Experimental chronology. The two series correlate at .46 with a TTest of 6.3

A third chronology (Final chronology) was created from 33 of the 36 measured cores. A series inter-correlation of .278 was produced from the un-trended raw ring-width series using the program COFECHA (Table 1). The series was then run through the program COFECHA to calculate series inter-correlation when de-trended using the

Friedman Super smoother de-trending method applied in the R program DplR was found to be lower at .214 (Table 1). Default COFECHA settings using a smoothing spline with rigidity of 32 years further lowered the series inter-correlation to .116 (Table 1). All

COFECHA summary statistic outputs and block segment correlations are provided in the appendix (Figures 20-29) The C14, Experimental, and Final chronologies were plotted in

R using the DplR package (Figure 17). 37

The chronologies including false rings and other ring anomalies as annual ring

boundaries produced very low series inter-correlations. The C14x raw ring-width chronology produced and series inter-correlation of .084 and the EXBx raw ring-width chronology produced a series inter-correlation of .167 using the program COFECHA.

Figure 17: C14 (top left), Experimental (bottom left), and Final (top right) chronologies. The Friedman super smoother detrended Final series is also presented (bottom right). Black line denotes ring width index (RWI), red line denotes smoothing spline, and grey area represents sample depth.

Radiocarbon sampling

To test the real-world application of these chronologies, three cores were sampled

for C14 radiocarbon AMS dating as detailed in the methods section above. Rings were 38

sampled ten years apart upon initial counting to frame the bomb spike and assigned dates

were updated for each individual chronology. Per mil values of samples from cores DP 1 and SP 1 were received and plotted in Excel against the calibrated bomb spike from zone

2 in the northern hemisphere (Hua, Barbetti, & Rakowski, 2013; Kaimei, Youneng, &

Fan, 1992; Worbes & Junk, 1989). Original dates assigned to samples were off by 1-4

years from adjusted years. Revised years assigned to samples were off by 1-6 years from

adjusted years. Revised years for core SP were all shifted positively in the correct direction of the bomb spike where revised years for the core DP were not all shifted in the same direction in respect to the original assigned years and decreased in accuracy

(Figure 18).

Radiocarbon Bomb Spike Curve Comparison 950 DP Original 850 DP Revised DP Adjusted 750 SP Original 650 SP Revised SP Adjusted 550 NH Zone 2

450

350

250

150

50

-501950 1955 1960 1965 1970 1975 1980 1985 1990 1995

Figure 18: Radiocarbon results plotted against Northern Hemisphere zone 2 bomb spike curve.

39

Discussion

Site selection and sampling

The mysteries behind the annual and seasonal growth patterns of Bermuda cedar

leave large gaps in knowledge that are necessary for the chronology building process.

The unfortunate decline of the Bermuda cedar in the 1940’s left the sampling plan for this

study with few ideal specimens. The traditional practice of collecting cores from young

trees to clarify the youngest dates of the chronology as described by Stokes and Smiley

(1968) was not useful for this study. Because wedging and false rings tend to be most

common in younger Junipers as the apical meristem is incredibly sensitive to external

factors and the Eastern Red cedar samples included in this study were no exception

(Schweingruber, 2007). It is still undetermined if the Eastern Red cedars that were

planted in the 1950’s will mirror the growth patterns of Bermuda cedar.

The land cover of Bermuda is largely urbanized. With a population of 60,000

contained in less than 53 square kilometers, very few natural settings with Bermuda cedar

exist. Many of the old trees used in the chronologies came from cemeteries in which

permission to sample was easily obtained, but the natural setting questionable (Figure 6).

Non-porous surfaces, atmospheric pollutants, and agricultural nutrients all exist within

close proximity to the species in question. What effects agriculture, urbanization, and

introduced species have had on annual growth of Bermuda cedar remains in question. It

is clear, however, that the complexity of the Bermuda cedar story does not allow a

useable chronology to be developed simply using cores collected on site but will require a

more focused and instrumented study design.

40

Image analysis and ring identification

Throughout the visual cross-dating process, potential annual growth rings could not be strictly categorized by their visual qualities. Concerning motivating science question 2, ring anomalies and annual ring boundaries cannot be clearly distinguished in

cores. While many aspects of the climate of Bermuda raise the possibility of Bermuda

cedar adding biomass as a tropical tree species would, the xylem anatomy and latitude in

which they grow suggest that most specimens clearly shut down growth for the winter

and resume in the spring, possibly in conjunction with the timing of pollination (Adams

& Wingate, 2008). However, over half the collected samples had inconsistencies in ring

formation that made them unsuitable for further crossdating attempts and raise questions

about their annual growth patterns. Without numerous full cross sections, it remains

impossible to identify annual ring boundaries with certainty.

The buttressing or lobing of J. bermudiana focuses radial growth in some areas

creating very large rings while leaving other areas with extremely small rings. While the

largest lobes commonly provide the best radius to measure, position of lobes around the

circumference of the trunk either migrate or are abandoned and eventually grown over

(Schweingruber, 2007). When coring any member of the Cupressaceae family, it is best

practice to core into a lobe and not the space between lobes, however, in the case of

Bermuda cedar, it is purely chance that a useable radius will be withdrawn (Maxwell et

al., 2011). Most cores in this study exhibited regular growth for a portion of its length

until rings became many standard deviations larger and ring boundaries became less

defined with proximity to the pith. Rarely did any cores from the same tree correlate well

with each other suggesting that cores alone are incapable of capturing the required best 41 measurable radius of Bermuda cedar. Attempting to build a new chronology from cores alone proved very inaccurate relying mainly on qualitative assessment guided by loose statistical inference. This is confirmed by examining the radiocarbon results (Figure 18) in which initial crossdating was close, but false rings and wedging rings are likely present in the tree but not identifiable using the cores alone. Even when statistical inference from the final chronology was used to resolve the radial inconsistencies and correctly assign dates to rings, accuracy did not improve in both sampled cores. Using cross sections for chronology building is vital to reduce the random growth variability of J. bermudiana along the chosen measured radius (Worbes, 2002).

The protected endangered status of Bermuda cedar has proven a great difficulty in procuring full cross sections. Its highly desired wood is not commonly left to decay and is quickly harvested (Pers. Comm. A. Csank). To make room for ornamental trees in public areas, even the root balls of trees were removed (Groves, 1955). If a second attempt at creating a regional chronology of Bermuda cedar is undertaken, tree mortality events, such as tropical storms or hurricanes, need to be taken advantage of. If a local entity could compile a large collection of Bermuda cedar full cross sections with known death dates over many years, another attempt at a chronology would have a greater chance of success.

Ring anomalies

Wedging rings pose great uncertainty in all chronologies (Worbes, 2002). For most instances of wedging rings found in precipitation limited environments, it can be assumed that radial growth was confined to a small area of the stem and was absent 42

elsewhere around the circumference (Derose et al., 2016). For a Juniperus species growing in a subtropical environment, are wedging rings indicative of locally absent rings or concentrated sub-annual growth? With a wide array of examples of wedging rings found in the samples of this study, more questions are raised than answered. More research is needed into the occurrence of wedging rings in Bermuda cedar and if it is

explained by anisohydric growth behavior related to drought stress as seen in mainland

junipers.

Revisiting motivating science question 2, using the statistical results produced by

C14x and EXBx compared to those from the C14 and Experimental chronologies, all that

can be stated is that not all false and wedging rings can be considered annual rings but

not all can be excluded. A concentrated tour of the two sections included in this study

exposes many variations of wedging rings that may reappear, fade away, or blend into a

false ring. Clearly, a strict threshold for qualitatively assigning annual ring boundaries to

wedging rings is not appropriate. According to Worbes (2002), wedging rings must be

assessed through the use of full cross sections.

False rings present a great challenge in cross-dating cores from Bermuda cedar.

Some trees exhibited more false rings than defined boundaries while others seemed to

grow in a clearly annual pattern with very few false rings. Depending on the tree, a ring

may appear false in one area while the same ring may appear very defined in another.

Trying to distinguish a true-false ring from a false-true ring from 5mm cores of Bermuda

cedar nears the realm of guessing. Full cross sections may aid in the identification of false

or locally absent rings but too little is still unknown about the annual growth of this

species. Radiocarbon results conclude that while the ring formed in 1966 was not 43

correctly identified through crossdating, the same per-mil ratio was found in both cores

(Figure 18). This is strong evidence that Bermuda cedar does undergo an annual growth

cycle. However, sampling design for radiocarbon was focused on correctly identifying

the year of growth for clearly defined rings and not comparing per mil values between

neighboring false rings. Regardless, an in-depth and focused study of the xylogensis of

Bermuda cedar is necessary to truly distinguish where, why and when false rings are

formed.

Missing or locally absent rings are a common occurrence in Juniperus of North

America. They are most commonly associated with wedging rings when radial growth is

concentrated. If J. bermudiana produces missing or locally absent rings in its subtropical

habitat was not concluded in this study. While a few missing rings were assigned to

match statistical inference in the Final chronology, the weak series inter-correlation

cannot conclude if a ring was truly missing or not.

Some cores exhibited false rings that often appeared quite dark, roughly one third the distance to the next clearly defined ring boundary (Figure 15). This could indicate a seasonal response to a climate variable suggesting the need for more research into their climatic sensitivity. Other studies have been performed using the false rings from

Juniperus to reconstruct sub-seasonal weather events such as Edmonson (2010). While the chronologies of Bermuda cedar presented in this study are not statistically robust,

Seascorr analysis did point to certain seasonal correlations. With Bermuda cedars pollenating in May, sensitivity to rainfall in the preceding two months and the last two months of the previous growing season would make sense (Adams & Wingate, 2008). A direct link to climate sensitivity cannot be made with the data presented, but it does 44

suggest that Bermuda cedars may grow in accordance with each other based on climatic

variables aside from their individual variability. Narrowing down alternative climate

variables is essential to understanding Bermuda Cedar’s viability for climate

reconstruction.

Chronologies & Crossdating Error

Regarding motivating science question 1, although the series inter-correlations of the presented chronologies neared the lower boundary of those found for some species of

Eastern North America, the non-result must be taken as a first step towards more directed studies of the Bermuda cedar. Improvements in series inter-correlations from the all- inclusive C14x and EXBx chronologies to the remaining three C14, Experimental, and

Final chronologies suggest that a faint signal exists amongst many Bermuda cedar (Table

1). The reproducibility of series inter-correlations of the three chronologies, in which great care was taken to make qualitative assessments backed up by statistical inference, suggests that higher correlations could be achieved with more cross sections. Although the series inter-correlations were low across the entire length of the chronologies, several

periods in time exhibited higher correlations with smaller standard deviations (Figure 16).

Errors in ring assignment compounded together as rings were assigned from outside of the core inwards. These errors in ring assignment were masked by the wide variability of ring width, especially with proximity to the pith. The cross-dating suggestions from the program COFECHA indicated that blocks may correlate highly at random, far out of time frames where the series could possibly have grown. All three chronologies varied slightly

amongst each other indicating that blocks of series may correlate better when randomly 45 matched rather than correctly aligned. This may also mean that the qualitative ring assignment process is less informed than it needs to be through circumferential ring assessment.

Figure 19: Example of ring width variability. Measurements of transect A vs transect B will have alternate ring width relationships for rings X and Y. This variability lowers series intercorrelation and prompts flags within the cross-dating program COFECHA.

The great variability in ring size to neighboring rings is a factor that cannot be controlled when using cores alone. Continuing to use traditional visual techniques, the ability to choose radii for measurement based on circumferential inspection for growth anomalies is the only remaining option to increase the statistical strength of a Bermuda cedar regional chronology. As evidenced in Figure 19, ring width variability can invert 46

the relationship of neighboring ring widths found in other cores. Examples such as this

can create many crossdating flags in COFECHA, lower the series inter-correlation of the entire chronology, and aid in incorrect ring assignments on other cores. This type of crossdating error is not limited to Bermuda cedar and must be mitigated in every dendrochronological study with confirmation rooted in the physical samples rather than theoretical statistics. While only a few clear examples of this was found in the measured cores for this study, it is likely that multitudes more exist just outside of the confines of the 5mm cores or somewhere else around the circumference of the tree in which sampling did not occur. Averaging ring widths from multiple radii of many cross sections could reduce the random variability found in cores while creating a reference chronology that cores could be matched to with more confidence.

Conclusions

Future work

In light of the attempts made to create a chronology of Bermuda cedar from

strictly cores using visual techniques, a different research design may yield a more

informed analysis. Ideally, nearly a third to a half of samples collected would be full

cross sections. Unfortunately, the unique circumstances surrounding the protected status

of the Bermuda cedar prevents the ability to destructively sample full cross sections of

living trees as is commonly done with tropical dendrochronology (Speer, Orvis, Grissino-

Mayer, Kennedy, & Horn, 2004; Trouet, Coppin, & Beeckman, 2006; Worbes, 2002). A

cooperative effort of local agencies is required to acquire full disc cross sections with 47

known death dates and identify new specimens of J. bermudiana that were not sampled

in the 2014 and 2015 campaigns. If a return sampling mission were to be conducted, the

research design and sampling should be undertaken by whomever will be analyzing the

wood. Traditional dendrochronology in semi-arid regions allows multiple cross-daters to

replicate findings; however, the mysterious nature of Bermuda cedar rings may require

the analyst to have first-hand experience of each specimen along with multi-year growth

metrics compiled from instrumentation of radial growth by band dendrometers and xylem

activity from sap-flow sensors.

This study calls for more cross sections for analysis to refine the chronologies

produced so that motivating science question 3 can be addressed. However, a xylogenesis

or annual growth study would increase the relevance of future findings. Vigorous living

specimens need a multi-year instrumented study of growth patterns by band-

dendrometers and sap-flow sensors. The problematic nature of false and wedging rings

needs to be analyzed with high resolution isotope chronology to separate and isolate

seasonal water uptake with respective ring anomaly boundaries.

Final Thoughts

In light of this attempt at producing a regional chronology of Bermuda cedar from

cores alone, there are several lessons to be taken away. Signals recorded in natural systems can be hidden underneath many layers of noise. While there are many examples of faithful proxy records in the world, they are unique in their ability to highlight an environmental signal above the noise inherent in all natural systems. Successful studies that uncover proxy records usually have some regulation in sampling design to control 48 for variables that need to be highlighted or muted. In the wake of the devastating scale leaf insect blight on the population of Bermuda cedar, the sampling design of this study had no leverage to minimize noise or to maximize a common growth signal. It is an unfortunate situation of hindsight, in which unlocking the usefulness of Bermuda cedar as a dendrochronological tool will require a much more sophisticated study design than likely would have been needed if this study had been conducted in the early 1940s when far more specimens blanketed the isolated cluster of islands.

Even with innumerable specimens to sample, it is merely conjecture to assume that Bermuda cedar do indeed share a common growth signal and visual dendrochronological techniques alone could provide a definitive result. After examining the cores of 52 Bermuda cedar trees that survived the scale leaf insect blight, geochemical isotope analysis is the best tool available to make sense of the opportunistic growth exhibited by J. bermudiana. However, two cross sections are still insufficient for further study of the Bermuda cedar to inform the analysis of the collected cores regardless of the techniques employed.

Dendrochronology is part qualitative and part quantitative. Its use in decoding tree rings as a proxy record of environmental conditions cannot be divorced from potential human influence or errors. Using an independent analyst for samples taken by another dendrochronologist is the best way to mitigate human influence from personal connection to the study, however, in the case of the Bermuda cedar replication of results is not attainable using the cores sampled in 2014 and 2015.

49

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52

Appendix A

Figure 20: COFECHA results for chronology EXBx. This chronology of remaining cores not used in chronology C14x included all ring anomalies as annual ring boundaries. At the top is correlations by 30- year blocks lagged by 15 years. At the bottom is summary statistics for the entire chronology. Series inter- correlation of 0.167 suggests ring assignments to be completely random with no unifying signal.

53

Figure 21: COFECHA results for chronology C14. At the top is correlations by 30-year blocks lagged by 15 years. At the bottom is summary statistics for the entire chronology. Series inter-correlation of 0.231 is too low to be considered statistically robust.

54

Figure 22 COFECHA results for Experimental chronology. At the top is correlations by 30-year blocks lagged by 15 years. At the bottom is summary statistics for the entire chronology. Series inter-correlation of 0.287 is approaching the lower threshold of an acceptable value for Eastern CONUS forests but is still too low to be considered robust.

55

Figure 23: COFECHA results for chronology C14x.This chronology included all false and ring anomalies as annual rings. At the top is correlations by 30-year blocks lagged by 15 years. At the bottom is summary statistics for the entire chronology. Series inter-correlation of 0.084 suggests ring assignments to be completely random with no unifying signal.

56

Figure 24: COFECHA results for chronology EXBx. This chronology of remaining cores not used in chronology C14x included all ring anomalies as annual ring boundaries. . At the top is correlations by 30-year blocks lagged by 15 years. At the bottom is summary statistics for the entire chronology. Series inter-correlation of 0.167 suggests ring assignments to be completely random with no unifying signal.

57

Figure 25: COFECHA results for chronology C14. At the top is correlations by 30-year blocks lagged by 15 years. At the bottom is summary statistics for the entire chronology. Series inter-correlation of 0.231 is too low to be considered statistically robust.

58

Figure 26: COFECHA results for Experimental chronology. At the top is correlations by 30-year blocks lagged by 15 years. At the bottom is summary statistics for the entire chronology. Series inter-correlation of 0.287 is approaching the lower threshold of an acceptable value for Eastern CONUS forests, but is still too low to be considered robust

59

Figure 27: COFECHA results for Final chronology. At the top is correlations by 30 year blocks lagged by 15 years. At the bottom is summary statistics for the entire chronology. Series inter-correlation of 0.278 is approaching the lower threshold of an acceptable value for Eastern CONUS forests, but is still too low to be considered robust. Highlighted series are the best series to be used in refined reference chronology to illuminate possible cross dating errors.

60

Figure 28: COFECHA results from Reference chronology with the best series whittled down from Final chronology. At the top is correlations by 30 year blocks lagged by 15 years. At the bottom is summary statistics for the entire chronology. Series inter-correlation of 0.213 is lower than Final chronology; the opposite desired effect of removing series thought to be contributing noise to the signal. Highlighted series were used in a final attempt to illuminate a common signal between multiple trees to resolve crossdating errors (Figure 21).

61

Figure 29: COFECHA results from the 4 best series chosen for visual confidence in ring assignment and statistical correlation to each other. At the top is correlations by 30 year blocks lagged by 15 years. At the bottom is summary statistics for the entire chronology. Average segment correlation amongst the best 4 series is still abysmally low. Series inter-correlation still did not rise above 0.3

62

Appendix B

Site Tree Core M U date Start Date End assigned #P # Rings # rings # Wedging # Core Type Scan of DPI Species seability False rings False L easured oints oints arge rings

AH 1 A y great 1833 2014 202 186 21 1 0 5mm 2600 J. bermudiana AH 2 A y poor 1854 2014 202 160 20 7 3 5mm 2600 J. bermudiana AH 2 B y great 1842 2014 183 172 8 4 0 5mm 2600 J. bermudiana BH 1 A y good 1901 2014 121 113 6 1 2 5mm 2600 J. bermudiana BP 2 A y great 1867 2014 165 147 15 4 10 5mm 3000 J. bermudiana DH 3 B y great 1878 2014 146 136 9 5 2 5mm 2600 J. bermudiana DP 1 A y weak 1864 2014 178 150 22 1 1 5mm 2500 J. bermudiana DP 1 B y poor 1876 2014 155 138 18 2 4 5mm 2500 J. bermudiana DP 2 A y ok 1936 2014 84 78 4 4 0 5mm 2500 J. bermudiana DP 2 B y good 1897 2014 120 117 3 2 0 5mm 1200 J. bermudiana DP 3 A y good 1912 2014 132 102 28 3 1 5mm 2500 J. bermudiana DP 3 B y good 1947 2014 71 67 3 2 1 5mm 2500 J. bermudiana DP 4 A y good 1952 2014 63 62 0 1 1 5mm 2500 J. bermudiana DP 5 B y good 1937 2014 80 77 0 2 3 5mm 2500 J. bermudiana FS 2 B y weak 1943 2014 83 71 14 6 6 5mm 2600 J. bermudiana FS 3 B y great 1924 2014 114 90 24 2 4 5mm 2600 J. bermudiana FS 4 A y weak 1951 2014 63 63 2 2 1 5mm 2600 J. bermudiana Hartle 1 A y good 1963 2014 54 51 2 0 3 5mm 3200 J. y bermudiana HB 2 A y good 1951 2014 61 63 4 3 1 5mm 2600 J. bermudiana HB 4 B y great 1918 2014 98 96 2 1 0 5mm 2600 J. bermudiana MB 1 C y great 1956 2014 64 58 6 2 1 5mm 3000 J. bermudiana MP 1 A y great 1881 2014 144 133 12 4 0 5mm 3000 J. bermudiana MP 1 B y good 1920 2014 101 94 11 5 0 5mm 3000 J. bermudiana PL 1 B y poor 1873 2014 194 141 51 12 4 5mm 2600 J. bermudiana PL 2 A y weak 1816 2014 185 198 31 9 2 5mm 2600 J. bermudiana PL 2 B y poor 1929 2014 103 85 16 2 0 5mm 2600 J. bermudiana PP 1 A y good 1834 2014 200 180 20 3 1 5mm 2600 J. bermudiana 63

PP 2 A y weak 1817 2014 226 197 27 12 2 5mm 2600 J. bermudiana PP 3 A y poor 1847 2014 215 167 32 7 4 5mm 2600 J. bermudiana PP 3 B y great 1859 2014 179 155 20 5 2 5mm 2600 J. bermudiana PP 4 A y weak 1938 2014 80 76 4 3 0 5mm 2600 J. bermudiana PR 1 A y good 1929 2014 91 85 6 1 1 5mm 3000 J. bermudiana PR 1 B y good 1921 2014 100 93 5 2 0 5mm 3000 J. bermudiana SP 1 A y weak 1910 2014 110 104 7 3 0 5mm 2600 J. bermudiana SP 1 B y good 1866 2014 203 148 40 10 3 5mm 2600 J. bermudiana SP 2 A y good 1884 2014 174 130 24 4 1 5mm 2600 J. bermudiana SP 2 B y poor 1870 2014 230 144 41 9 2 5mm 2600 J. bermudiana STM 1 A y good 1933 2014 90 81 6 3 0 5mm 2600 J. bermudiana STM 1 B y weak 1944 2014 78 70 7 4 2 5mm 2600 J. bermudiana STM 2 A y good 1931 2014 108 83 16 6 1 5mm 2600 J. bermudiana STM 2 B y poor 1977 2014 47 37 9 0 1 5mm 2600 J. bermudiana STP 1 A y weak 1943 2014 83 71 11 3 1 5mm 2600 J. bermudiana STP 1 B y poor 1900 2014 139 114 13 1 2 5mm 2600 J. bermudiana STP 2 A y weak 1954 2014 70 60 7 3 0 5mm 2600 J. bermudiana NI 1 A y weak 1834 1923 94 89 6 4 0 12mm 4000 J. bermudiana NI 2 A y good 1882 1932 57 50 8 6 2 12mm 4000 J. bermudiana NI 3 A y poor 1804 1916 125 112 31 4 1 12mm 4000 J. bermudiana Sectio 1 n/ y poor 1840 2004 212 164 n/ n/ n/ sectio 3200 J. n a a a a n bermudiana Sectio 2 n/ y good 1801 1997 232 196 33 20 0 sectio 2500 J. n a n bermudiana BP 1 A no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 3000 J. a a a bermudiana DH 1 A no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 2600 J. a a a bermudiana DH 1 B no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 2600 J. a a a bermudiana DH 2 A no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 2600 J. a a a bermudiana DH 2 B no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 2600 J. a a a bermudiana DH 3 A no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 2600 J. a a a bermudiana DH 5 A no n/a n/a n/a n/a n/a n/ n/ n/ 5mm 2600 J. a a a bermudiana DP 4 B no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 2500 J. a a a bermudiana DP 5 A no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 2500 J. a a a bermudiana FS 2 A no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 2600 J. a a a bermudiana FS 3 A no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 2600 J. a a a bermudiana 64

FS 4 B no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 2600 J. a a a bermudiana FS 5 A no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 2600 J. a a a bermudiana FS 5 B no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 2600 J. a a a bermudiana GM 1 A no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 3200 J. virginiana a a a GM 2 A no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 3200 J. virginiana a a a GM 3 A no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 3200 J. virginiana a a a HB 1 A no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 2600 J. a a a bermudiana HB 1 B no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 2600 J. a a a bermudiana HB 3 A no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 2600 J. a a a bermudiana HB 3 B no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 2600 J. a a a bermudiana HB 4 A no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 2600 J. a a a bermudiana HB 5 A no n/a n/a n/a n/a n/a n/ n/ n/ 5mm 2600 J. a a a bermudiana LBR 1 A no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 2600 J. a a a bermudiana MB 1 B no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 3000 J. a a a bermudiana MP 2 A no n/a n/a n/a n/a n/a n/ n/ n/ 5mm 3000 J. a a a bermudiana NI 1 A no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 2600 J. virginiana a a a NI 3 A no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 2600 J. virginiana a a a NI n/ A no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 2600 J. virginiana a a a a NI 4 A no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 2600 J. virginiana a a a NI n/ A no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 2600 J. virginiana a a a a NI 6 A no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 2600 J. virginiana a a a NI 7 A no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 2600 J. virginiana a a a NI n/ A no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 2600 J. virginiana a a a a Olive 1 A no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 2600 O. europaea a a a Peters 1 A no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 2600 J. virginiana a a a PL 1 C no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 2600 J. a a a bermudiana PP 1 B no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 2600 J. a a a bermudiana PP 2 B no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 2600 J. a a a bermudiana PP 4 A no n/a n/a n/a n/a n/a n/ n/ n/ 5mm 2600 J. a a a bermudiana PP 4 B no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 2600 J. a a a bermudiana PR 1 C no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 3000 J. a a a bermudiana SH 1 A no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 2600 J. a a a bermudiana SPJ 1 B no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 2600 J. a a a bermudiana 65

STJ 1 A no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 2600 J. a a a bermudiana STJ 2 A no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 2600 J. a a a bermudiana STJ 2 B no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 2600 J. a a a bermudiana STJ 3 A no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 2600 J. a a a bermudiana STJ 3 B no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 2600 J. a a a bermudiana STJ 3 B no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 2600 J. a a a bermudiana STJ 4 A no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 2600 J. a a a bermudiana STJ 4 B no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 2600 J. a a a bermudiana STM 2 B no n/a n/a n/a n/a n/a n/ n/ n/ 5mm 2600 J. a a a bermudiana STM 3 B no n/a n/a n/a n/a n/a n/ n/ n/ 5mm 2600 J. a a a bermudiana Stokes 1 no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 3200 J. virginiana a a a Stokes no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 3200 J. virginiana a a a Stokes 2 A no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 3200 J. virginiana a a a Stokes 2 B no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 3200 J. virginiana a a a Stokes 3 A no n/a n/a n/a n/a n/a n/ n/ n/ 5mm 3200 J. virginiana a a a Stokes 3 B no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 3200 J. virginiana a a a STP 2 B no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 2600 J. a a a bermudiana STP 3 A no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 2600 J. a a a bermudiana STP 3 B no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 2600 J. a a a bermudiana STP 4 A no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 2600 J. a a a bermudiana STP 4 B no n/a n/a 2014 n/a n/a n/ n/ n/ 5mm 2600 J. a a a bermudiana VHD 3 B no n/a n/a n/a n/a n/a n/ n/ n/ 5mm 2600 J.

a a a bermudiana

Table 2: Descriptive statistics of all cores provided for this study. Useability refers to the clarity and distinctness of possible annual ring boundaries along the length of the core. DPI of scans refers to dots per inch of the image of the scanned core.