Comparative study of
biomechanical properties in
ethnobotanically useful plants.
Francisca D. Herrera and Dr. Curtis Clark
McNair Scholars Program
Biological Sciences Department
California State Polytechnic University, Pomona
background
• biomechanics
– the study of the mechanics of biological
materials and structures
• ethnobotany
– the study of the historical and/or traditional uses
of plants by humans
• medicinal and nutritional
• mechanical
purpose
to explore the usefulness of biomechanics in
investigating the ethnobotany of early
southern California indigenous cultures
overview
Pluchea sericea vs. Salix exigua
- structurally similar
- different uses
Typha sp. vs. Scirpus sp.
- structurally different
- similar uses
Juncus textilis vs. Juncus mexicanus
- structurally similar
- similar uses
sub-study 1 sub-study 2 sub-study 3
objectives
1. analyze the biomechanical performance of
the selected species
2. determine differences between the
compared species
3. predict the biomechanical reasons for a
particular ethnobotanical use
hypothesis
Ho: Regardless of differences in ethnobotanical
use, there are no differences in the
biomechanical properties between compared
organisms in each case study.
study organisms
Pluchea sericea
‘Arrow-weed’
Salix exigua
‘Sandbar Willow’
sub-study 1 sub-study 2 sub-study 3
ethnobotany
P. sericea ‘Arrow-weed’
arrowshafts
S. exigua ‘Sandbar Willow’
frameworks
sub-study 1 sub-study 2 sub-study 3
biomechanicssub-study 1 sub-study 2 sub-study 3
flexibility and breakage point
kg
stemdiameter
15cm
1/2 pt
1.0
m.
study organisms
Juncus textilis Juncus mexicanus
sub-study 1 sub-study 2 sub-study 3
ethnobotany
Juncus spp.
basketry
sub-study 1 sub-study 2 sub-study 3
biomechanics
tensile strength
30cm
stem
diameter
sub-study 1 sub-study 2 sub-study 3
study organisms
Typha sp.
‘Cattail’
Scirpus sp.
‘Bulrush’
sub-study 1 sub-study 2 sub-study 3
ethnobotanysub-study 1 sub-study 2 sub-study 3
Typha sp. ‘Cattail’ Scirpus sp. ‘Bulrush’
mats and thatch
biomechanics
diameter (mm) stemwater drop
sub-study 1 sub-study 2 sub-study 3
hydrophobicity
analyses
1. anatomical comparisons• light microscopy
2. statistical analysis• program: SPSS
• tests: regression & two-factor ANCOVA
- Dependent Variable: biomechanical performance
- Fixed Factors: species and condition (fresh/dry)
- Covariates: height and diameter
resultssub-study 1 sub-study 2 sub-study 3
P. sericea
‘Arrow-weed’
S. exigua
‘Sandbar Willow’
results
flexibility –
arrow-weed is less flexible than willowit takes more weight to deflect arrow-weed to the 15cm point,
holding constant the effect of height and diameter
breakage –
arrow-weed breaks more easily than willow(flexibility is a predictor of breakage)
sub-study 1 sub-study 2 sub-study 3
resultssub-study 1 sub-study 2 sub-study 3
Juncus textilis Juncus mexicanus
results
tensile strength –
Juncus mexicanus is stronger than
Juncus textilis
sub-study 1 sub-study 2 sub-study 3
resultssub-study 1 sub-study 2 sub-study 3
Typha sp.
‘Cattail’
Scirpus sp.
‘Bulrush’
resultssub-study 1 sub-study 2 sub-study 3
tensile strength –
there was no difference between Scirpus and
Typha
hydrophobicity –
there was no difference between Scirpus and
Typha
discussion
arrow-shafts & dwelling frameworks –
Our null hypothesis was rejected.
Dry arrow-weed is stiffer and fresh willow is
more flexible.
Results supported the preference of these
biomechanical properties in their
ethnobotanical use.
sub-study 1 sub-study 2 sub-study 3
discussion
basketry –
Our null hypothesis was rejected.
While there are structural differences,
J. mexicanus is the stronger species.
The wet/dry condition is not a good predictor of
tensile strength.
Results neither denied nor confirmed the
desirability of tensile strength in basketry.
sub-study 1 sub-study 2 sub-study 3
discussion
mats & thatching –
Our null hypothesis was not rejected.
No difference may account for overlap in use between the species.
Results indicate that tensile strength and hydrophobicity may have been desirable
properties in mats and thatching
sub-study 1 sub-study 2 sub-study 3
acknowledgements
• Dr. Curtis J. Clark, Professor of Biology
• McNair Scholars Program, Cal Poly Pomona
• BioTrek
• Tongva/Gabrielino of San Gabriel
• Lorene Sisquoc, Apache/Cahuilla
• Dr. Pfeiffer and UC Davis
Species were selected based on the following criteria:
• native southern California plants
• historical ethnobotanical use by southern California indigenous
cultures
• availability of biological material from a common garden
• structural similarities among compared organisms
• feasibility of biomechanical property being measured
Selection of Study Organisms
Regressions performed:
• height vs diameter – to look at usefulness as covariates
• height and/or diameter vs biomechanical property – to look at relationship between covariates and dependent variables
Other analyses:
• species vs condition interaction – to determine a difference in the way species respond mechanically in fresh and dry conditions
• ANCOVA – to test for difference in mechanical performance between species
Development of Statistical Model
Regression Analyses
Arrow-weed & sandbar willow comparison:
height vs diameter
breakage vs deflection
height/diameter vs deflection
height/diameter vs breakage
Comparison of rushes:
height vs diameter
height/diameter vs tensile strength
Bulrush & cattail comparison:
height vs diameter
height/diameter vs tensile strength
ANCOVA Results
Tests of Betw een-Subjects Effects
Dependent Variable: weight in kg to 15cm deflection pt
98.118a 5 19.624 48.670 .000
17.725 1 17.725 43.962 .000
1.772 1 1.772 4.395 .044
40.409 1 40.409 100.222 .000
2.267 1 2.267 5.623 .024
11.715 1 11.715 29.055 .000
5.256 1 5.256 13.036 .001
13.709 34 .403
220.233 40
111.827 39
Source
Corrected Model
Intercept
stem_ht
stem_d
species
condn
species * condn
Error
Total
Corrected Total
Type III Sum
of Squares df Mean Square F Sig.
R Squared = .877 (Adjusted R Squared = .859)a.
arrow-weed vs sandbar willow:
Tests of Betw een-Subjects Effects
Dependent Variable: weight in kg to break stem
195.629a 4 48.907 10.125 .000
12.571 1 12.571 2.603 .116
23.864 1 23.864 4.941 .033
.979 1 .979 .203 .655
11.651 1 11.651 2.412 .129
59.505 1 59.505 12.319 .001
169.061 35 4.830
2616.190 40
364.690 39
Source
Corrected Model
Intercept
species
condn
stem_ht
avg_d
Error
Total
Corrected Total
Type III Sum
of Squares df Mean Square F Sig.
R Squared = .536 (Adjusted R Squared = .483)a.
ANCOVA Results
J. mexicanus vs J. textilis:
ANCOVA Results
Tests of Betw een-Subjects Effects
Dependent Variable: tensile strength
327.318a 2 163.659 34.320 .000
6.193 1 6.193 1.299 .270
9.617 1 9.617 2.017 .174
46.818 1 46.818 9.818 .006
81.067 17 4.769
2265.050 20
408.385 19
Source
Corrected Model
Intercept
species
avg_d
Error
Total
Corrected Total
Type III Sum
of Squares df Mean Square F Sig.
R Squared = .801 (Adjusted R Squared = .778)a.
cattail vs bulrush:
Type III Tests of Fixed Effectsa
1 58 3703.571 .000
1 58 .403 .528
Source
Intercept
species
Numerator df
Denominator
df F Sig.
Dependent Variable: H2O_diam.a.
ANCOVA Results
cattail vs bulrush (cont’d):