Acorns are a valuable food resource for many wildlife species

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…

Does Bigger Mean Better?Does Bigger Mean Better?

• In general, bigger trees produce more acorns…

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

Management for Acorn Production:Management for Acorn Production:

• Retain a mix of oak species

• Oak size may be relatively unimportant

• Retain good producers if possible