Acorns are a valuable food resource for many wildlife species.
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Acorns are a valuable food resource for many wildlife Acorns are a valuable food resource for many wildlife speciesspecies
Influence survival and recruitment of many speciesInfluence survival and recruitment of many species
Acorns as a “keystone” resource: Acorns as a “keystone” resource: (Wolff 1996)(Wolff 1996)
* Affect populations of rodent mast consumers, which then…– Affect seed predation and dispersal– Affect populations of their predators;– Affect gypsy moth populations– Affect prevalence of Lyme disease
* Affect deer populations, which then…– Affects regeneration and forest structure
Oak regeneration is dependant first on acorn productionOak regeneration is dependant first on acorn production
Acorn production variesAcorn production varies
• Among years
• Among species
• Among locations
• Among individuals
• … but tends to be synchronized…
NCWRC hard mast Index Data from WNC region, NCWRC hard mast Index Data from WNC region, 1985-20051985-2005
White Oak (Q. alba)
0
1
2
3
4
5
6
7
Scarlet Oak (Q. coccinea)
Avera
ge H
ard
Mast
Index (
Regio
n)
0
1
2
3
4
5
6
7
Chestnut Oak (Q. prinus)
0
1
2
3
4
5
6
7
Northern Red Oak (Q. rubra)
0
1
2
3
4
5
6
7
Black Oak (Q. velutina)
0
1
2
3
4
5
6
7
Wide variation among individual oaks Wide variation among individual oaks thought to be due to:thought to be due to:
• Age
• Size
• Stand density
• Topographic position
• Weather
• GENETICS…
Why do Oaks Mast?Why do Oaks Mast?
• Predator satiation hypothesis – reduce predator populations in “bust” years, then satiate (+ surplus) in “boom” years.
• Wind pollination hypothesis – synchronized flowering & pollination > fertilization and results in synchronized acorn production.
White Oak vs. Red Oak GroupsWhite Oak vs. Red Oak Groups
• White oak subgenus (e.g., white and chestnut oaks) produce flowers (spring) and acorns (fall) during the same year.
• Red oak subgenus (e.g., northern red, scarlet, black oaks) produce flowers in spring, but acorns develop during the fall of the next year.
ObjectivesObjectives
• Describe how acorn production varies among years, species, & individuals
• What identifies “good” acorn producers?
• Potential new method for estimating within-year crop size
Study BackgroundStudy Background
• Begun in 1991 (1993) by Don Beck, BCEF scientist
• “Inherited” in 1995 when Don retired
• Team effort – collections and trap maintenance done by District personnel
• Large-scale study ended in 2000
Study AreasStudy Areas
• Several areas within 3 southern Appalachian National Forests and 3 states:– Cherokee NF (Tennessee)– Pisgah NF (North Carolina)– Chattahoochee NF (north Georgia)
ACORN SAMPLING METHODSACORN SAMPLING METHODS
• 765 individuals of 5 species (northern red oak; scarlet oak; black oak; white oak; chestnut oak)
• Wide range of dbh- and age-classes
• Most trees dominant or codominant
• Range of elevations (850-1180m), topographic conditions
Methods (con’t.)Methods (con’t.)
• Number of traps proportional to BA (2-14 per tree)
• Crown areas computed as an octagon• Acorns collected by District personnel at
approximately 2-week intervals• Acorns counted, classified, weighed green and
dry in lab• Production estimates likely conservative, since
traps don’t measure acorns that removed from tree crowns or traps
How Does Acorn Production Vary How Does Acorn Production Vary Among Species, Space, and Time?Among Species, Space, and Time?
Black Oak
Me
an
(+S
E)
Nu
mb
er
of A
corn
s/ft2 B
A
0
500
1000
1500
Chestnut Oak
0
500
1000
1500
Northern Red Oak
0
500
1000
1500
Scarlet Oak
0
500
1000
1500
White Oak
1993 1994 1995 1996 19970
500
1000
1500
A
B
A
B,C D
A,BA
B
C C
AB
A
C E
AB
A
C
D
A B C
D
E
Variation among oak speciesVariation among oak species
• Production varies within species
• Some synchrony in production among subgenera
• Mix of species often offsets crop failure
• Complete failure 1997
Me
an
(+
SE
) N
um
be
r
0
100
200
300
400
500
600
700
800M
ea
n (
+S
E) G
re
en
Wt
0
1
2
3
4
5
6
SPECIES
BO NRO SCO CO WO
Me
an
(+
SE
) D
ryW
t
0
1
2
A,B
C
A B
D
A
B
C
A
D
AA,B
A,B
C
B
lbs A
co
rn
s/f
t2
BA
lbs A
co
rn
s/f
t2
BA
# A
co
rn
s/f
t2
BA
WO produced the most acorns, but NRO and WO WO produced the most acorns, but NRO and WO produced the highest dry biomass.produced the highest dry biomass.
Black Oak
Me
an
# /
ft
2 B
A
0
200
400
600
800
1000
1200
Chestnut Oak
0
200
400
600
800
1000
1200
1400
Northern Red Oak
Year
1993 1994 1995 1996 19970
200
400
600
800
1000
1200
Scarlet Oak
0
200
400
600
800
1000
1200
White Oak
Year
1993 1994 1995 1996 19970
200
400
600
800
1000
1200
Chatahoochee NF (N. Georgia)Cherokee NF (Tennessee)Pisgah NF (North Carolina)
A
B
C
A
B
A
AB A
A
B
A
A,B
A
B
A,B BA
A
2,506+364(B)
C
A,BA
B
B
A A
A B
A
B
B
A,B
A
B
BB
A
AB A
A
A
B A
A,B
A
B
A B B
Me
an
# /
ft
2 B
AM
ea
n #
/ f
t2
BA
Acorn production of each species varied among southern Acorn production of each species varied among southern
Appalachian National ForestsAppalachian National Forests
SpeciesSpecies Other Averages Other Averages Range Range (# / ft(# / ft22 BA) BA)
__________________________________Black Oak 115 – 588Northern Red Oak 444 – 1525Scarlet Oak 38 - 1034Chestnut Oak 240- 259White Oak 112 – 996__________________________________Geography, number of years sampled, which
years sampled, sample size…
Black Oakp=0.0001r2=0.4957
0 1 2 3 4 5 6 7
0
500
1000
1500
2000
2500
3000
Chestnut Oakp=0.0001
r2=0.7328
0 2 4 6 8 10 12
0
500
1000
1500
2000
2500
3000Northern Red Oakp=0.0001r2=0.5152
Basal Area (ft2)
0 2 4 6 8 10 12 14 16
Crow
n A
rea (
ft2 )
0
1000
2000
3000
4000
5000
Scarlet Oakp=0.0001r2=0.7481
0 1 2 3 4 5 6 7
0
500
1000
1500
2000
2500
3000
White Oakp=0.0001r2=0.7122
Basal Area (ft2)
0 2 4 6 8 10
0
1000
2000
3000
4000
Crow
n A
rea (
ft2 )
Crow
n A
rea (
ft2 )
That’s because bigger trees have bigger crowns, hence a That’s because bigger trees have bigger crowns, hence a greater area upon which to produce acorns.greater area upon which to produce acorns.
Black Oakp=0.0003r2=0.14
0 1 2 3 4 5 6 7
0
200
400
600
800
1000
1200
1400
1600
Chestnut Oakp=0.9199
0 2 4 6 8 10 12
0
200
400
600
800
1000
1200
1400
Northern Red Oakp=0.0581r2=0.03
Basal Area (ft2)
0 2 4 6 8 10 12 14 16
0
200
400
600
800
1000
1200
Scarlet Oakp=0.3701
0 1 2 3 4 5 6 7
0
500
1000
1500
2000
2500
3000
White Oakp=0.0098r2=0.04
Basal Area (ft2)
0 2 4 6 8 10
0
500
1000
1500
2000
2500
3000
Me
an
No
. ('9
3-'9
7)
# A
co
rns/f
t2 B
A
Me
an
No
. ('9
3-'9
7)
Me
an
No
. ('9
3-'9
7)
# A
co
rns/f
t2 B
A
But, do larger-diameter trees produce more acorns per unit But, do larger-diameter trees produce more acorns per unit BA than smaller-diameter trees?BA than smaller-diameter trees?
Species
BO NRO SCO CO WO
Mean
(1993-1
997)
(+S
E)
Num
ber
of
Aco
rns/
ft2 B
A
0
100
200
300
400
500
6000-9.9 inches dbh9.9 - 19.7 inches dbh19.8 - 29.9 inches dbh30 - 40 inches dbh
A
B
B
B
A
B
CB,C A
B
B
A,B A
B
C
B,C
Some species (BO, NRO, WO) produce fewer acorns per Some species (BO, NRO, WO) produce fewer acorns per unit BA when they are <10 inches dbh.unit BA when they are <10 inches dbh.
What Characterizes “Good” Acorn What Characterizes “Good” Acorn Producers?Producers?
* Fruiting Frequency * Fruiting Frequency* Density of Acorns* Density of Acorns
SPECIES
BO NRO SCO CO WO
% o
f T
rees P
roducin
g A
corn
s in 0
-5 Y
ears
(1993-1
997)
0
5
10
15
20
25
30
35
40
45
500 YEARS1 YEAR2 YEARS3 YEARS4 YEARS5 YEARS
N=86
N=155
N=124 N=161N=111
Most oaks don’t produce acorns every year.Most oaks don’t produce acorns every year.
Ranked Trees as Poor, Moderate, or Ranked Trees as Poor, Moderate, or Good Producers (Healy et al. 1999)Good Producers (Healy et al. 1999)
• Good producers produce, on average, > the 5-year mean for the species;
• Moderate producers produce 60 – 100% of the species’ 5-year mean;
• Poor producers produce < 60% of the species’ 5-year mean
N=135
Species
BO NRO SCO CO WO
Pe
rce
nta
ge
of
Ind
ivid
ua
ls
0
10
20
30
40
50
60
70
80Poor ProducerModerate ProducerGood Producer
N=162
N=111
N=124 N=155
A small % of individuals are “good” producersA small % of individuals are “good” producers
SPECIES
BO NRO SCO CO WO
Me
an
(+
SE
) %
of
Pro
du
ctiv
e Y
ea
rs (
19
93
-19
97
)
0
10
20
30
40
50
60
70
80
90
100
Poor ProducersModerate ProducersGood Producers
A
B
BB
A,B
AA
BB
A
BB
A
A,BB
Good producers produce acorns during more years…Good producers produce acorns during more years…
Chestnut Oak
0
5000
10000
15000
20000
25000
Northern Red Oak
Year
0
2000
4000
6000
8000
10000
12000
Scarlet Oak
1993 1994 1995 1996 19970
5000
10000
15000
20000
25000
White Oak
Year
1993 1994 1995 1996 19970
5000
10000
15000
20000
25000
30000
35000
40000
45000
50000
Black Oak
0
2000
4000
6000
8000
10000
12000
14000
16000
Poor ProducersModerate ProducersGood Producers
A
B
C
A
B
C
AA
B
A
A
B
A
B
C
A
B
C
A
B
B
AA
B
A
B
B
AAB
AB
B
A
B
C
Me
an
(+S
E) N
o.
Aco
rn
s/m
2 B
A/F
ru
itin
g T
re
e
AA,B
B
AA
BB
AA A
B
C
Good producers have a greater density of acorns Good producers have a greater density of acorns when they fruit.when they fruit.
0
2000
4000
6000
8000
10000
12000
14000
16000
CHESTNUT OAK
Me
an
(+
SE
) N
um
be
r o
f A
co
rn
s/m
2 B
A
0
5000
10000
15000
20000
25000
Poor ProducersModerate ProducersGood Producers
NORTHERN RED OAK
Year
0
2000
4000
6000
8000
10000
12000
SCARLET OAK
Year
1993 1994 1995 1996 19970
5000
10000
15000
20000
25000
WHITE OAK
1993 1994 1995 1996 19970
10000
20000
30000
40000
50000
BLACK OAK
Good GoodPoor PoorModerate Poor PoorModerate Good Poor
Good Moderate Good Poor Poor Poor Moderate Poor Good Poor
Good Moderate Good Poor Poor
Despite low representation, good producers Despite low representation, good producers outperform, especially during good crop years.outperform, especially during good crop years.
Black Oak
0
20
40
60
80
100
120
Chestnut Oak
0
20
40
60
80
100
120
Northern Red Oak
Pe
rce
nta
ge
of
Fru
itin
g I
nd
ivid
ua
ls
0
20
40
60
80
100
120
Poor ProducersModerate ProducersGood ProducersPopulation
Scarlet Oak
Year
1993 1994 1995 1996 19970
20
40
60
80
100
120
White Oak
Year
1993 1994 1995 1996 19970
20
40
60
80
100
120
Good Good Poor PoorModerate
ModerateGood Good Poor Poor Poor Moderate Poor Good Poor
PoorGoodPoor Moderate PoorGood Poor Good Moderate Poor
Hard to identify good producers, because good, moderate, Hard to identify good producers, because good, moderate, and poor producers represented equally each year.and poor producers represented equally each year.
Black Oak
10
20
30
40
50
60
70
80
90
100
0
200
400
600
800
1000
1200
1400
1600
Chestnut Oak
0
10
20
30
40
50
60
70
80
90
100
0
200
400
600
800
1000
1200
1400
1600
Northern Red Oak
0
10
20
30
40
50
60
70
80
90
100
0
200
400
600
800
1000
1200
1400
1600
Scarlet Oak
Year
1993 1994 1995 1996 19970
10
20
30
40
50
60
70
80
90
100
0
200
400
600
800
1000
1200
1400
1600
White Oak
Year
1993 1994 1995 1996 19970
10
20
30
40
50
60
70
80
90
100
0
200
400
600
800
1000
1200
1400
1600
1800
Me
an
(+
SE
) #
/ f
t2
BA
of
Fru
itin
g T
re
es
% o
f T
re
es B
ea
rin
g A
co
rn
s (
-------)
A
B
A
BB
A
B
C
D D
A
B
A
C C
A,BA
A
C
B
A
B
A,C
D
C
Good GoodMod Poor Poor
Good GoodMod Poor Poor
Good Good ModPoor Poor GoodPoor Mod Poor Poor
GoodMod PoorPoor Poor
Acorn production is not synchronous within species. Good Acorn production is not synchronous within species. Good crop years are characterized by more trees producing crop years are characterized by more trees producing acorns acorns andand by more acorns per producing tree. by more acorns per producing tree.
Chestnut Oak
0 10 20 30 40 50 60 70 80 90 1003
4
5
6
7
8
9
Northern Red Oak
0 10 20 30 40 50 60 70 80 90 1004
5
6
7
8
9
% of Trees Bearing Acorns
0 10 20 30 40 50 60 70 80 90 1003
4
5
6
7
8
9
10
White Oak
0 10 20 30 40 50 60 70 80 90 1000
2
4
6
8
10
12
% of Trees Bearing Acorns
Ln M
ean #
Acorns/m
2 B
ALn M
ean #
Acorns/m
2 B
ABlack Oak
20 30 40 50 60 70 80 90 1005
6
7
8
9
Ln M
ean #
Acorns/m
2 B
A
This relationship may allow a new method for estimating crop size, This relationship may allow a new method for estimating crop size, simply by quantifying the % of trees (by species) producing each year.simply by quantifying the % of trees (by species) producing each year.
Tested if there are more acorns per fruiting oak during Tested if there are more acorns per fruiting oak during years when more oaks are fruiting using NCWRC hard years when more oaks are fruiting using NCWRC hard
mast index data (1985-2005)mast index data (1985-2005)
All OaksRegionr = 0.99831P < 0.0001
% Trees Bearing Acorns
0 20 40 60 80 100
Me
an P
erc
ent
Cro
wn
with
Aco
rns
0
20
40
60
80
Then tested whether the proportion of trees bearing acorns Then tested whether the proportion of trees bearing acorns could be used to predict Hard Mast Index (NCWRC data)could be used to predict Hard Mast Index (NCWRC data)
Quercus albaRegion
0
2
4
6
8
Quercus coccineaRegion
Har
d M
ast
Inde
x (H
MI)
0
2
4
6
8
Quercus prinusRegion
0
2
4
6
8
Quercus rubraRegion
0
2
4
6
8
Quercus velutinaRegion
% Trees Bearing Acorns (PBA)0 20 40 60 80 100
0
2
4
6
8
Quercus albaArea
0
2
4
6
8
Quercus coccineaArea
0
2
4
6
8
Quercus prinusArea
0
2
4
6
8
Quercus rubraArea
0
2
4
6
8
Quercus velutinaArea
% Trees Bearing Acorns (PBA)0 20 40 60 80 100
0
2
4
6
8
(a) (f)
(b)
(c)
(e)
(d)
(g)
(h)
(j)
(i)
• The % of trees bearing acorns is a good predictor of HMI
• Developed predictive equations for all species, the red and white oak “groups”, and all oaks
• Need to sample a lot of trees
The required sample size varies with the crop year, and The required sample size varies with the crop year, and with the desired confidence level with the desired confidence level
• Confidence Level• _________________• PBA 80% 90% 95%• ____________________________• 10% 60 98 139• 20% 106 174 246• 30% 139 228 323• 40% 158 260 369• 50% 165 271 384• 60% 158 260 369• 70% 139 228 323• 80% 106 174 246• 90% 60 98 139• _____________________________
Summary of Acorn Study ResultsSummary of Acorn Study Results• Acorn production varies among years & species.
• Production not synchronous (3-29% vs 70-90%).
• Good crop = more trees with acorns + more acorns/tree
• Acorn density correlated with the % of fruiting trees.
• Good producers produce more acorns more frequently.
• Good producers constitute <50% of population, but produce the majority of the crop.
• A similar % of good & poor producers produce in all years.
• The % of trees bearing acorns predictor of crop size and hard mast index
• Must sample a lot of trees to get good estimates
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