Ecological Archives M082-006-A1

Steven L. Voelker, Paul-Emile Noirot-Cosson, Michael C. Stambaugh, Erin R. McMurry, Frederick C. Meinzer, Barbara Lachenbruch, and Richard P. Guyette. 2012. Spring temperature responses of oaks are synchronous with North Atlantic conditions during the last deglaciation. Ecological Monographs 82:169–187. http://dx.doi.org/10.1890/11-0848.1

Appendix A. Supporting descriptions of methods and results.

Proxy development from wood anatomical data

Vessel formation would clearly be inhibited at 0°C or at some level above 0°C, but the linear relationships predict negative temperature values for lower end vessel sizes sampled (Fig. 5, Table A3). Similarly, spring temperatures occurring during EW formation should have some upper bound. To address this we modified the linear relationships to follow asymptotic trends such that anatomical proxies were restricted to estimating maximum temperature of about 17°C and minimum temperatures of either 2°C or 6°C (Fig. A2). For reference, the maximum and minimum spring temperatures occurring across all sites from 1895–2008 were 14.5°C and 7.0°C (Table 1). In a strict sense these threshold values were arbitrary, but our goal was to allow temperature estimates to approach and occasionally exceed the modern range of temperature values (Tables 1, A1, A2). The 2° minimum value was included largely for reference as we consider the 6° minimum more biologically reasonable. The 6° C minimum for average spring temperature is 1°C lower than that which has been observed at any of the three sites (Table 1) and corresponds to the average temperature associated with treeline limitation of growth whether there are strong or weak seasonal dynamics (Hoch and Körner 2009).

EWAs of modern wood decreased during cold springs and had a strong relationship to temperature (Fig. 5, Table 2). However, the greater EWFS of sub-fossil wood (Fig. 3) and the resulting increases in EWA and EWAs compared to modern wood (Table 3) would predict implausibly warmer temperatures for sub-fossil wood for the entire late Quaternary period. To address this issue, we standardized each EWFS measurement of sub-fossil wood to correspond to the modern wood value for the same EWD (i.e., each EWD measurement was multiplied by the ratio of the modern regression predicted EWFS / sub-fossil regression predicted EWFS for a given EWD; these regression lines werevery nearly the same as the relationships of EWFS vs. EWD shown in Fig. 3). Atmospheric CO2 concentrations are likely the only consistent difference between the modern oaks and the Late Quaternary environmental conditions. By standardizing each EWFS measurement of sub-fossil wood to correspond to the modern wood EWFS for the same EWD we were able to take advantage of the strong temperature signal incorporated by EWAS (Fig. 5), while accounting for the putative CO2 effects on EWFS.

 


TABLE A1. Temperature estimates for sub-fossil wood using different functions for earlywood diameter (EWD) earlywood hydraulic diameter (EWDh), modal EWD and earlywood specific lumen area (EWAs). The range and means represent values calculated for each cambial ages and tree combination. Values for EWAs were corrected to the modern earlywood specific vessel frequency for a given EWDa.

Anatomical variable

Function

Minimum

Mean

Maximum


EWD

Linear

-0.5

6.6

12.5

 

Sigmoid: 17° max, 2° min

2.0

6.1

12.8

 

Sigmoid: 17° max, 6° min

6.0

7.8

12.7

EWDh

Linear

-13.2

4.1

14.5

 

Sigmoid: 17° max, 2° min

2.0

5.0

14.2

 

Sigmoid: 17° max, 6° min

6.0

7.2

14.2

Modal EWD

Linear

-0.4

12.3

22.9

 

Sigmoid: 17° max, 2° min

2.3

12.0

16.5

 

Sigmoid: 17° max, 6° min

6.0

11.6

16.8

EWAs

Linear

4.7

8.8

15.4


 

TABLE A2. Equations used for linear and sigmoidal temperature estimates.

Anatomical variable

Equation form for
temperature (T)

a

b

x0

y0


EWD

T = ax+b

0.0464

-5.1731

EWDh

T = ax+b

0.1086

-20.547

Modal EWD

T = ax+b

0.0834

-8.7502

EWAs Linear

T = ax+b

41.322

-2.2727

EWD, 2° min

T = y0+a/(1+((x/x0)^b))

15.1515

-5.092

318.0105

2

EWDh, 2° min

T = y0+a/(1+((x/x0)^b))

14.9303

-9.3561

275.7743

2

Modal EWD, 2° min

T = y0+a/(1+((x/x0)^b))

15.7254

-4.7545

224.2319

2

EWD, 6° min

T = y0+a/(1+((x/x0)^b))

11.3981

-5.8523

357.9158

6

EWDh, 6° min

T = y0+a/(1+((x/x0)^b))

11.019

-11.0428

293.4685

6

Modal EWD 6° min

T = y0+a/(1+((x/x0)^b))

11.6014

-6.6674

255.4677

6


 

TABLE A3. Results of pair-wise comparisons using SMATR software to test scaling relationships of EWFs and EWDa. Significance is indicated by * = p < 0.05, ** = P < 0.01, *** = P < 0.001. Other results abbreviations: NS = non-significant, NT = comparison not tested, NCS = no common slope among pairs necessary for test. Category abbreviations: MO = Missouri, WI = Wisconsin, SD = South Dakota, PB = Pre-Boreal, YD = Younger-Dryas, BA = Bolling-Allerod, SF = all sub-fossil wood, MOD = all modern wood.

   

MO

WI

SD

PB

YD

BA

SF

MOD

Elevation
shift
among
common
slope

MO

-

 

 

 

 

 

 

 

WI

**

-

 

 

 

 

 

 

SD

*

NS

-

 

 

 

 

 

PB

NCS

NCS

NCS

-

 

 

 

 

YD

NCS

NCS

NCS

NS

-

 

 

 

 

BA

NCS

NCS

NCS

*

NS

-

 

 

 

SF

***

***

***

NT

NT

NT

-

 

 

MOD

NT

NT

NT

***

***

***

***

-

                   

Shift
along
common
slope

MO

-

 

 

 

 

 

 

 

WI

***

-

 

 

 

 

 

 

SD

***

***

-

 

 

 

 

 

PB

NCS

NCS

NCS

-

 

 

 

 

 

YD

NCS

NCS

NCS

NS

-

 

 

 

 

BA

NCS

NCS

NCS

NS

NS

-

 

 

 

SF

***

***

NS

NT

NT

NT

-

 

 

MOD

NT

NT

NT

NS

NS

NS

NS

-


 

FigA1
 

   FIG. A1. Light microscopy images of transverse sections of sub-fossil bur oak wood, containing of normal-shaped vessels, moderately collapsed wood, and severely collapsed wood. Image (a) is sample MED 681: cambial age = 111 years, EW diameter estimate = 238.9 um, EW diameter corrected for collapse = 226.5 um. Image (b) is the same image as (a), highlighting examples of measurements conducted on a single tree-ring. The earlywood (EW) and latewood (LW) areas outlined, labeled and highlighted and separated by a dashed line. Examples of EW vessels areas measured are filled black. Note that small vessels, of approximately 70 µm diameter or less that were within the EW area were not measured on any sample. Image (c) shows MED 257: cambial age: 91 years, EW diameter estimate = 196.1 um, diameter corrected for collapse = 214.4 um. Image (d) shows MED 634: cambial age = 44 years, EW diameter estimate = 177.5 um, diameter corrected for collapse = 227.5 um.


 

FigA2
 

   FIG. A2. Examples of sigmoidal transfer functions used to estimate spring temperature from earlywood vessel diameter (EWD) modal EWD, and earlywood vessel hydraulic diameter (EWDh). The sigmoidal relationships approximate the linear trends (Fig. 6) across the temperature range covered by our sampling (shaded gray area) while constraining the maximum and minimum spring temperatures that might be recorded by earlywood vessel sizes.


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