Effects Of Feral Pig Rooting On

Vegetation Communities & Rare Endemic

Plants On Santa Cruz Island, California

Structure Of Talk

• Vegetation Monitoring Design

– Community

– Rare Plants

• General Community-level Patterns

– Richness, Diversity & Eveness

– Structure & Species Composition

• Rooting Effects On Vegetation Dynamics

• Rooting Effects On Rare Endemic

• Generality Of Results

Physical Characteristics

• 246 km2 in area

(96 mi2)

• Complex

Topography

(highest elevation

745 m)

• Complex Geology

& Soils

Santa Cruz Island Floristics

• 10-12 Plant

Communities

– 5-6 major ones

• 470 Native Species

• 157 Non-native

Species

• 36 Channel Island

Endemic Species

• 7 Santa Cruz Island

Endemic Species

Goals

• Vegetation

– Evaluate the degree to which feral pig rooting was influencing changes in structure & species composition in the 5 major vegetation communities

• Rare Plants

– Determine which species were being impacted by feral pig rooting

Vegetation Communities

• 5 types– Grassland

– Chaparral/Bishop Pine

– Oak Woodland

– Coastal Scrub

– Fennel

Vegetation Monitoring Protocol

• Stratified (semi) random design

– 100 plots (30 m x 2 m)

• Species-based

– Cover (100 points)

• Point Intercept

• Herbaceous layer, shrub layer, tree layer

– Density (60 m2)

• Belt transect

• Shrubs and trees

• Bare ground, litter, rooting

• Sampling 1991-1995, 1998

Rare Plants

Rare Plant Monitoring Target Species

• Berberis pinnata insularis– Presence/Absence

– 3 populations

• Arabis hoffmannii– Census, height, floral counts

– 3 populations

• Thysanocarpus conchuliferus– Presence/Absence

– 1-11 populations

• Dudleya nesiotica– Density, cover, & floral counts

– Height

– Vegetation community (cover & height)

• Malacothamnus fasciculatus nesioticus– Census, height, floral counts

– 3 populations

General

Patterns For

Vegetation

Communities

Species Diversity

1991 1992 1993 1994 19950

10

20

30

40

50

60

70S

1991 1992 1993 1994 19950

3

6

9

12

15

N2

OWGrassFennelChap/PineCS

Community

1991 1992 1993 1994 19950.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

G

OWGrassFennelChap/PineCS

Community

Shrub Expansion

1991 1992 1993 1994 19951

10

100

Adult S

hru

b D

ensity

(log)

1991 1992 1993 1994 19951

10

100

Shru

b S

eedlin

g D

ensi

ty (

log)

Pine/ChapOWGrassFennelCS

Community

Native Grasses & Forbs

Native Herbaceous Species

1991 1992 1993 1994 19950

10

20

30

40

Specie

s (

%)

Native Herbaceous Species

1991 1992 1993 1994 19950.01

0.10

1.00

10.00

100.00

Cover

(%)

OWGrassFennelChap/PineCS

Community

Alien Grasses & Forbs

Alien Herbaceous Species

1991 1992 1993 1994 19950

10

20

30

40

50

60

70

80

Specie

s (

%)

Alien Herbaceous Species

1991 1992 1993 1994 19950.01

0.10

1.00

10.00

100.00

Cover

(%)

OWGrassFennelChap/PineCS

Community

Rooting Effects On Vegetation

Communities

Magnitude Of Rooting

1991 1992 1993 1994 19950

10

20

30

40

50

60

70

80R

ooting (

%)

Rooting Frequency & Vegetation

Communities

CSChap

Fennel

Grass OW

Pine

Vegetation Community

0

50

100

150

200

Fre

quency

RootedUnrooted

Condition

Rooting Intensity & Vegetation

Communities

CSChap

Fennel

Grass

OWPine

Vegetation Community

0

10

20

30

40

50

60

70

80R

oo

ting

(%

)

Analysis Approach

• Disturbance Regime

– Intensity (% rooted)

– Frequency (cumulative number times)

– Interval (years since last rooted)

• Multiple Regression

– Community Measures

• Total Species Richness (S)

• Species Diversity (N2)

• Evenness (Molinari’s G)

– Guilds/Vegetation Structure

• Shrub Species Richness, Cover, Density

• Shrub Seedling Density

• Non-native and Native Forb Cover and Species Richness

– Annual & Perennial

• Non-native and Native Grass Cover and Species Richness

Rooting/Community Measures Correlations

Statistic Intensity Frequency

Return

Interval

S Positive Positive

N2 Negative

G Negative

Rooting/Vegetation Structure Correlations

Guild Intensity Frequency Return

Shrub Species Negative Positive

Shrub Cover Negative Negative Positive

Shrub Seedlings Negative Negative Positive

Native Annual

Forb Species

Positive

Alien Annual

Forb Species

Positive

Alien Annual

Forb Cover

Positive

Alien Grass

Cover

Positive

Ordination of Plots

-1.0 1.0

-1.0

1.0

ELEVATION

SLOPE

ASPECT

INTENSITY

FREQUENCY

ENV. VARIABLES

SAMPLES

Chaparral/Pine Coastal Scrub Oak Wooldand Fennel Grassland

Ordination of All Species

-1.0 1.0

-0.8

0.8

achmil

adefas

amsint

arcins

artcal

atrsem

avebaravefat

bacpil

bacplu

branigbrocar brodia

bromol

brorub

ceaarb

ceameg

cenmel

cerglo

checal

claper

dicpul

eriarb

erigra

erobot

erocic

eromos

filcal

foevul

galang

galapa

gnamic

hapsqu

hetarb

horgen

hypgla

lamaur

latlae

lolmul

lotden

lupbic

luzsub

marmacmarvul

medpol

miccal

mimfle

mimlon

pinmur

pittri

quedum

quepar

rhuint

rhuova

sanarg

silgal sonasp

stemed

stilep

stipul

vioped

vulmyuzigfre

ELEVATION

SLOPE

ASPECT

INTENSITY

FREQUENCY

SPECIES

Alien Annual Forb Alien Perennial Forb Alien Annual Grass Native Perennial Grass Native Perennial Forb Ferns Shrubs Trees

Native Annual Forb

ENV. VARIABLES

Ordination of Rarer Species

-1.0 1.0

-0.8

0.8

adijor

agrdie

anaarv

antnut

arctom

ascfas

astgam

calalb

calcatcardra

casaff

cashol

cenexa

chemur

chlpom

comdiv

conbon

delpar

disspi

dodcle

epicil

ericon

erifol

eromac

filari

frasal

galporgilach

gnalut

helsco

hemfas

horcal

jepmal

lacser

lepfra

lilhum

lindia

lomcar

lomutr

michet

mircal

oenhoo

oxaalb

peremo

phamin

poaann

poasca

polare

polcalpteaqu

queagr

quechr

quetom

rhapirruburs

sillac

silmarstabul

symmoltrialb

tricil

trigra

trimic2vencar

vicsat

ELEVATION

SLOPE

ASPECT

INTENSITY

FREQUENCY

SPECIES

Alien Annual Forb Alien Perennial Forb Alien Annual Grass Native Perennial Grass Native Perennial Forb Ferns Shrubs Trees

Native Annual Forb

ENV. VARIABLES

Summary & Interpretation For Vegetation

• As much as 10% of the island can be rooted in years with high pig density

• Most rooting occurs in grassland, fennel and oak woodland communities

• High intensity of rooting reduces overall species diversity, but species richness increases in plots with frequent, low intensity rooting

• Recruitment and cover of woody species are reduced with increasing intensity of rooting

• Increase in species richness is outcome of native and non-native annual forbs replacing woody species

• Rarer species potentially reduced by higher intensity and frequency of rooting

• Rooting mediates community structure, patch dynamics and probably succession patterns

Feral Pig Impacts On Rare Plants

• Thysanocarpus conchuliferus– 11 of 14 known populations

found in 1991with individuals present

– 3 populations found in 1992 with individuals present (3 populations rooted)

– 1 population found in 1993-1998 with individuals present (2 additional populations rooted)

– N=56 in remaining population (1998)

– 5 populations rooted by pigs; remaining ones heavy cover alien grass

Feral Pig Impacts On Rare Plants

• Arabis hoffmannii

– Centinela Population

• Pigs reduced stem density from 32 in 1992 to 19 in 1993. Population rebounded 78-110 stems 1994-98.

– Platt’s Harbor Population

• Pigs destroyed population in 1995 (N=15 stems)

– Albert’s Road Population

• Discovered 1995

• No impacts

• Stem density 11-81 from 1995-1998

Generality Of Results

• Likely To Be Representative Of

Effects In Many Similar

Ecosystems With

Mediterranean-climate

• Mediation Of Shrub Invasion

Into Grasslands Has

Conservation Importance

– Type conversion

• Rare Species Impacts!