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
70 15
60 12 50
40 9
S
N2 30 6 Community 20 CS 3 Chap/Pine 10 Fennel Grass 0 0 OW 1991 1992 1993 1994 1995 1991 1992 1993 1994 1995
0.7
0.6
0.5
0.4
G 0.3 Community 0.2 CS Chap/Pine 0.1 Fennel Grass 0.0 OW 1991 1992 1993 1994 1995 Shrub Expansion
100 100
10 Community 10 CS Fennel
Adult Shrub Density Adult(log) Density Shrub
Shrub Seedling Density (log) Seedling Density Shrub Grass OW 1 1 Pine/Chap 1991 1992 1993 1994 1995 1991 1992 1993 1994 1995 Native Grasses & Forbs
Native Herbaceous Species Native Herbaceous Species
40 100.00
30 10.00
20 1.00
Cover (%)Cover Community
Species (%)Species
10 CS 0.10 Chap/Pine Fennel Grass 0 0.01 OW 1991 1992 1993 1994 1995 1991 1992 1993 1994 1995 Alien Grasses & Forbs
Alien Herbaceous Species Alien Herbaceous Species
80 100.00 70
60 10.00 50
40 1.00
30 (%)Cover Community
Species (%)Species
20 CS 0.10 Chap/Pine 10 Fennel Grass 0 0.01 OW 1991 1992 1993 1994 1995 1991 1992 1993 1994 1995 Rooting Effects On Vegetation Communities Magnitude Of Rooting
80
70
60
50
40
Rooting (%) 30
20
10
0 1991 1992 1993 1994 1995 Rooting Frequency & Vegetation Communities
200
150
100
Frequency
50 Condition Unrooted 0 Rooted
CS OW Pine Chap Fennel Grass Vegetation Community Rooting Intensity & Vegetation Communities
80
70
60
50
40
Rooting (%) 30
20
10
0
CS OW Pine Chap Fennel Grass Vegetation Community 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
Return Statistic Intensity Frequency 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 Positive Forb Species Alien Annual Positive Forb Species Alien Annual Positive Forb Cover Alien Grass Positive Cover Ordination of Plots
1.0
ASPECT
SLOPE
-1.0 1.0
ELEVATION INTENSITY
FREQUENCY
-1.0
ENV. VARIABLES
SAMPLES
Chaparral/Pine Coastal Scrub Oak Wooldand Fennel Grassland Ordination of All Species
0.8
rhuint
ceameg lotden stilep ASPECT rhuova artcal
SLOPE eriarb filcal luzsub
adefas pittri erobot galang mimlon miccal brorub atrsem lolmul bacplu pinmur erigra arcins mimfle hapsqu lamaur zigfre achmil stipul gnamic vulmyu dicpul quepar erocic avefat -1.0 marvul avebar 1.0 marmac silgal sonasp quedum hetarb sanarg hypgla bromol latlae amsint eromos ceaarb medpol cenmel claper lupbic brocar brodia cerglo branig bacpil horgen ELEVATION checal stemed foevul INTENSITY galapa
vioped
FREQUENCY
-0.8
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
0.8 peremo
oxaalb
poaann ASPECT helsco mircal dodcle SLOPE rhapir filari ruburs tricil quetom queagr cenexa disspi ericon astgam lindia agrdie cashol sillac hemfas oenhoo antnut ascfas quechr trigra
symmol trialb poasca epicil michet erifol comdiv frasal lepfra horcal -1.0 gilach galpor lilhum 1.0 arctom adijor phamin delpar jepmal lomutr casaff vencar calcat trimic2 cardra pteaqu polcal vicsat
calalb lacser ELEVATION stabul silmar anaarv INTENSITY conbon chemur eromac chlpom
polare lomcar
FREQUENCY gnalut
-0.8
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!