Definitions for invasive plants
People use different words for invasive species
Alien
Exotic
Invasive
Non-indigenous
Imported
Weedy
Introduced
Non-native
Immigrant
Colonizer
Naturalized
Definitions for invasive plants
LEGAL DEFINITIONS
State: NRS 555
“Noxious weed” means any species of plant which is, or is likely to be,
detrimental or destructive and difficult to control or eradicate.
Federal: Plant Protection Act of 2000
Noxious weed means any plant or plant product that can directly or
indirectly injure or cause damage to crops (including nursery stock or
plant products), livestock, poultry, or other interests of agriculture,
irrigation, navigation, the natural resources of the United States, the
public health, or the environment.
Federal: Executive Order 13112
(a) “Alien species” means, with respect to a particular ecosystem, any
species … that is not native to that ecosystem
(e) “Introduction” means intentional or unintentional escape, release…of
a species…as a result of human activity
(f) “Invasive species” means an alien species whose introduction does
or is likely to do harm to public health
Definitions for invasive plants
ECOLOGICAL DEFINITIONS
(1) Nevada’s Coordinated Invasive Weed Strategy
• Noxious weeds are “species of plants that cause disease or are
injurious to crops, livestock or land, and thus are detrimental to
agriculture, commerce or public health”
• Invasive weeds often share characteristics such as
Highly competitive
Cause environmental degradation
Exotic
Easily spread
Highly aggressive
Are difficult to control
Cause economic loss
Augment wildfires
• “Species of concern” are species that have potential to cause greatest
impact on Nevada’s ecosystem and economic well being
(2) The Nature Conservancy
Invasive species are:
• Spread from human settings into wild
• Once wild, continue to reproduce
• Displace native species; reduces biodiversity
• Usually non-native
Definitions for invasive plants
ECOLOGICAL DEFINITIONS
(3) Davis & Thompson (2000)
• 8 ways to be a colonizer, but only 2 ways to be an invader
Dispersal:
Short
Long
Uniqueness:
Impact:
Common
Novel
Common
Novel
Small Great Small Great Small Great Small Great
SC
SC NNC NIC SC
SC NNC NIC
Definitions for invasive plants
ECOLOGICAL DEFINITIONS
( (4) Richardson et al. (2000)
Alien plants = plant taxa in a given area whose presence is due to
intentional or accidental introduction as a result of human activity
Casual alien plants = alien plants that flourish but do not form self-replacing
populations. Continued presence depends on re-introductions.
Naturalized plants = alien plants that reproduce consistently and sustain
populations over many life cycles without direct intervention by humans
Invasive plants = naturalized plants that produce reproductive offspring
(often in large numbers) at considerable distance from parent plants
>100m & <50 years for seed dispersing species
>6 m & >3 years for vegetatively reproducing species
Weeds = plants that grow in sites where they are not wanted; usually have
economic or environmental effects
Transformers = subset of invasive plants that change ecosystems
How are they located?
Eyewitness account
Darwin in 1833 during trip through the Argentinean pampas
“… very many (probably several hundred) square miles are
covered by one mass of these prickly [variegated thistle]
plants, and are impenetrable to man or beast. Over the
undulating plains, where these great beds grow, nothing else
can now live.”
Remote sensing
Satellite imagery: spectral signatures (from Eric Peterson, NV Natural
Heritage Program, http://heritage.nv.gov/reports.htm)
Remote sensing
Bromus tectorum greens up early
Remote sensing
Bromus tectorum greens up early, and also senesces early compared
to native species
Remote sensing
From a spectral perspective
Fall
O
Winter
N
D
J
F
Spring
M
A
M
Summer
J
J
A
S
Remote sensing
From a spectral perspective
N
D
J
F
Spring
M
A
M
Summer
J
Min. greenness
O
Winter
Peak greenness
Fall
J
A
S
Remote sensing
From a spectral perspective
N
D
J
F
Spring
M
A
M
Summer
J
Min. greenness
O
Winter
Peak greenness
Fall
J
A
S
NDVI = greenness index based
on chlorophyll reflectance in
infrared relative to red.
Remote sensing
From a spectral perspective
N
D
J
F
Spring
M
A
M
Summer
J
Min. greenness
O
Winter
Peak greenness
Fall
J
A
S
NDVI = greenness index based
on chlorophyll reflectance in
infrared relative to red.
Does change in NDVI (ΔNDVI)
correspond with Bromus
abundance?
Remote sensing
Imagery from Landsat 5; 8 scenes over Owyhee Uplands from 2 times
during year
Remote sensing
But also need ground truthed data
Remote sensing
60
40
20
0
Relative
ΔNDVI
Estimated Annual
Grass Cover
80
100
Ground truthed data: 262 training plots
0
20
40
60
Measured
Annual Grass Cover
Measured
Bromus
cover
80
100
Remote sensing
Ground truthed data: 262 training plots plus 75 validation plots
9.7% error for validation plots
Remote sensing
Map of Bromus tectorum
abundance in Owyhee
Uplands
Remote sensing
Invasive annual grasses
across entire state