Definitions for invasive plants
People use different words for invasive speciesAlien ExoticInvasive Non-indigenousImported WeedyIntroduced Non-nativeImmigrant ColonizerNaturalized
Definitions for invasive plants
LEGAL DEFINITIONSState: 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 2000Noxious 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 asHighly competitive Cause environmental degradationExotic Easily spreadHighly aggressive Are difficult to controlCause economic lossAugment wildfires
• “Species of concern” are species that have potential to cause greatest impact on Nevada’s ecosystem and economic well being
(2) The Nature ConservancyInvasive 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 invaderDispersal: Short Long
Uniqueness: Common Novel Common Novel
Impact: 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 activityCasual 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 humansInvasive 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 accountDarwin 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 sensingSatellite imagery: spectral signatures (from Eric Peterson, NV Natural
Heritage Program, http://heritage.nv.gov/reports.htm)
From a spectral perspective
Fall Winter Spring SummerO N D
J F MA M J
J A S
Pea
k gr
eenn
ess
Min
. gr
eenn
ess
Remote sensing
From a spectral perspective
Fall Winter Spring SummerO N D
J F MA M J
J A S
Pea
k gr
eenn
ess
Min
. gr
eenn
ess
NDVI = greenness index based on chlorophyll reflectance in infrared relative to red.
Remote sensing
From a spectral perspective
Fall Winter Spring SummerO N D
J F MA M J
J A S
Pea
k gr
eenn
ess
Min
. gr
eenn
ess
NDVI = greenness index based on chlorophyll reflectance in infrared relative to red.
Does change in NDVI (ΔNDVI) correspond with Bromus abundance?
Remote sensing
Ground truthed data: 262 training plots
0 20 40 60 80 100
02
04
06
08
01
00
Measured Annual Grass Cover
Est
ima
ted
An
nu
al G
rass
Co
ver
Measured Bromus cover
Rel
ativ
e Δ
ND
VI
Remote sensing
Ground truthed data: 262 training plots plus 75 validation plots9.7% error for validation plots
Remote sensing