How Does Himalayan Blackberry
Impact Breeding Bird Diversity?
A Case Study of the Lower Mainland of BC
Presented to: Invasive Plant Council Research Forum
Presented by: Caroline Astley, M.Sc., R.P.Bio., EP
October 2011
Background
 Recognized need for more research
 Potential for bird habitat, but is it harming
more that it’s providing?
 What is the real impact, either positive or
negative?
 Study through Royal Roads Master’s of
Environment and Management Program
(MEM - M.Sc.)
Background
 Popular opinion: invasives are bad!
 But how bad are they?
 Quantified based on economics
 Mostly based on obvious changes to native
ecosystems
 Impacts not measured against baseline
 Is it possible to measure the impact they
have on biodiversity?
Background



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Chose Himalayan blackberry (R. armeniacus)
Very visible
Contentious
Potential for bird and wildlife habitat
Aggressively taking over
Ubiquitous on landscape
 Many don’t know that it’s invasive
 Socially accepted – berry picking
Himalayan blackberry
 Native to
Caucasus region
 Introduced in
1880’s as
cultivated crop
 Escaped into
PNW by 1945
 Common
colonizer of
disturbed areas
www1.american.edu
Himalayan blackberry
 Very aggressive
 Can produce 7,000 – 13,000 seeds per
square meter that can remain viable for
several years
 Spreads by root and stem fragments, seeds,
and runners
 Creates dense thickets
Study
 How to determine if there is an impact?
 Measure biodiversity
 Breeding birds easily identified and located
 Easily replicated
 Provincial standards exist
 Location important
 Areas where management is active
 Areas with potential for variety of breeding
birds
 Mostly urbanized
Jericho Park
 Easy access
 Large standalone
blackberry
patch
 Young forest
 Heavily used
 Traffic noise
 No canopy over
blackberries
Jericho Park
Maplewood Flats
 Easy access
 Good bird
diversity
 Blackberry in
understorey
 Potential for
transitory
migrating species
Maplewood Flats
PCS MW004
PCS MW008
Stanley Park
 Easy access
 On-going IAP
management
 Heavily used
 Narrow patches
Stanley Park
PCS SP003
PCS SP004
Study Design
 Followed RISC standards
 Variable radius point count
 Five-minute listening periods
 Ran from April 1 to July 2, 2009
 One visit per week minimum
 Beaufort 2 maximum wind (light breeze)
 No/light precipitation (drizzle)
 Min. temp. between 0-7°C
 Started just after sunrise
 Restricted to trails esp. at Maplewood Flats
Study Design
 Used Terrestrial Ecosystem Mapping plot
cards
 “Blackberry” plots >80% R. armeniacus
coverage
 “Control” plots <20% R. armeniacus coverage
 Competed RISC “bullseye” data recording
sheets
 No nest surveys – outside of scope of
project
Study Design
N
YEWA
NWCR
AMRO
BCCH
BCCH
BCCH
5
10 15 20 25 30m
BCCH
SPTO
MCWA
RUHU
(♀)
Results
Location
Jericho
Plot Type Blackberry Control
Stanley Park
Maplewood Flats
Blackberry Control
Blackberry Control
Total Ind.
165
281
48
91
141
231
Total Sp.
12
22
11
24
17
28
Analysis
 Simpson’s Indices (Reciprocal and Index
of Diversity)
Blackberry
Control
Jericho
6.6291
7.7319
Maplewood
5.861
11.7596
Stanley Park
7.1847
15.1107
Jericho
0.8492
0.8707
Maplewood
0.8294
0.915
Stanley Park
0.8608
0.9338
Reciprocal Index (1/D)
Index of Diversity (1-D)
What Does It Mean?
 Judging by these preliminary results,
blackberry has an impact!
 Reduction in number of birds and species in
blackberry dominated areas
 Stand alone thickets are not statistically
different from young forest
 Some birds are using blackberry
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Anna’s and Rufous Hummingbird
Song Sparrow
Spotted Towhee
American Robin
Fox Sparrow (Possible at Jericho)
Breeding Period
Species Feb
March April May
June July
AMRO*
SOSP
SPTO
RUHU*
ANHU*
*Confirmed nesting (observed nests/behaviour)
Adapted from Bell, K. (undated) and BNA On-line (2010)
Aug
Sept
Other Issues
 Increased predator access to nests
 Nest success?
 Further study needed
 Human disturbance during berry picking
 Potential shift away from more diverse
food sources
Management Recommendations
 Management vs. removal
 Removal is best for forested ecosystems
 Replant densely with multiple canopy layers
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Thimbleberry
Salmonberry
Snowberry
Black twinberry
 Removal during breeding season performed
with care
 Can leave some behind
Next Steps
 Need at least one other season of data
collection for rigour
 Re-assess study design to remove excess
statistical “noise”
 Potential future research
 Why is there an impact?
 What factors are causing birds to avoid or
select?
 Is blackberry becoming a preferred forage
species?
Acknowledgements
 Dr. David Clements – TWU
 AY Chapter P.E.O.
 Field Assistants
 BCIT
 Courtney, Petra, Pascal, and Britta
 Hemmera
 Ashleigh, Barry, Eileen, and Charlie
 Hemmera
 Brian Yates and Scott Weston