The document discusses using a GIS-based approach to analyze patterns in the spread of introduced plant species along river networks. It proposes analyzing how species traits relate to associations with rivers, examining historical spread patterns along stream order over time, and distinguishing the roles of water dispersal, contiguous habitat, and environmental conditions in facilitating introductions. The goal is to better understand if and how rivers generally facilitate the naturalization and invasion of non-native plants.

1. Understanding the spread of introduced plant
species in river networks: A GIS-based
landscape approach
Emily Rollinson
05/14/12

2. Rivers and riverbanks are ecologically important
rivers
Map from Naiman et al. 2005, Riparia
highways
Very diverse because conditions
change drastically across small River networks act as
spatial scales biodiversity hotlines, connecting
distant areas

3. Non-native species are common along rivers. Why?
Continuous linear habitat Floods remove existing
through landscape is corridor for vegetation and create space for

4. What makes a plant species invasive?
Introduced Naturalized Invasive
Plants are The plants The plants spread from
transported to a survive and the site of introduction
new place outside establish a and establish new
their native range population at the populations across the
introduction site landscape

5. Do rivers facilitate naturalization or invasion?
There are three reasons why they migh
1) Water dispersal
2) Linear, contiguous habitat
across long distances

6. How do rivers spread introduced plants?
There are three reasons why they migh
3) Favorable environmental conditions

7. The GIS-based landscape approach
Many previous studies have directly shown that
rivers facilitate the spread of one or two
introduced species
But: there is no way to know from these case
studies if rivers play a general role in spreading
many introduced species, or if it is species-
specific.
With GIS, databases of introduced species
locations, along with models of river systems,
can be used to look address this question for
many species across a broad spatial scale

8. Proposal objectives
1. Evaluate the degree to which introduced
species are currently associated with riparian
zones.
2. Assess trait-based patterns in the current
association of groups of introduced species
with riparian zones.
3. Assess historical evidence for the spread of
introduced species along river corridors.
4. Use the above patterns to distinguish
among the effects of water dispersal,
habitat linearity, and favorable
environmental conditions in facilitating
introduced species in riparian zones.

9. Available invasive species databases
There are hundreds of
regional invasive species
databases that contain
location data.
I will use two:
Invasive Plant Atlas of New
England (IPANE)
Early Detection and
Distribution Mapping
System (EDDMapS)

10. EDDMapS
• Early detection and
distribution mapping
system
• Presence of invasive Many species with fewer records
species in the 650 species At least 100 records
continental USA
• Database contains
258 species At least 1000 records
2261 plant species
• Most records in the Fewer species with many records
past decade 50 species 5000 records

11. IPANE
• Records of invasive
species
presence/absence
in New England
• Collates historical
herbarium records
that document
recorded locations
of introduced
species over the
past century

12. Available rivers data
• USGS: National
hydrography
dataset
– Digital vector
dataset for GIS that
contains water
features
(lakes, ponds, river
s…)
– Contains
information on flow
direction

13. 1: Broad patterns of association with rivers
• If rivers play some role in the success of introduced
species, then those species should be found near rivers
more often than would expected if they were distributed
randomly across the landscape.
• Approach: Compare the distances from rivers for
introduced species against the distances from rivers for
random points distributed across the landscape.
– Use ArcGIS to calculate the distance of each of these points
from the nearest river in the National Hydrography Dataset
– Create frequency distributions for the distance from the
nearest river for all points for each species
– Produce an overall frequency distribution for introduced
species
– Use ArcGIS to distribute random points across the entire study
area (contiguous United States); produce an overall frequency
distribution for the distance to the nearest river for these
random points

14. 1: Predictions
Introduced species
Number of points
Random landscape points
Distance from nearest river

15. 2: Trait-based patterns
The role rivers play in the spread of an introduced species
may depend on certain traits of that species.
Pysek and Prach (1993): Used historical records to
reconstruct the spread of four invasive plants along rivers in
the Czech Republic
Ornamental Giant hogweed Japanese knotweed Giant knotweed
jewelweed
Pysek and Prach 1993 Journal of Biogeography

16. 2: Species differ in degree of association with rivers
Ornamental Japanese knotweed
jewelweed
Giant knotweed Giant hogweed
Pysek and Prach 1993 Journal of Biogeography

17. 2: Role of dispersal and growth traits
Prediction Dispersal type
High association
with riparian zones
Vegetative
Fast-maturing seeds
(annual)
Slow-maturing seeds
Low association (perennial)
with riparian zones

18. 2: Role of dispersal and growth traits
Dispersal unit Dispersal type Life span Growth form
Vegetative Water Annual Herbaceous
Seed/fruit Animal Biennial Shrub
Wind Perennial Tree
Unassisted

19. 2: Predictions
Vegetative propagules
Number of points
Seeds
Distance from nearest river

20. 2: Predictions
Annual/biennial
Number of points
Perennial
Distance from nearest river

21. 2: Predictions
Water-dispersed seeds
Other dispersal
Number of points
mechanisms
Distance from nearest river

22. 3: Historical patterns of spread
• Use historical records
from IPANE upstream
• Extract stream order
information from NHD
maps
• Do patterns in
association with rivers
change over time?
• Do patterns in
association with
stream order change downstream
over time?

23. 3: Predictions
Average distance from river
Introduced species are initially
spread by rivers, but slowly
spread in other directions
Introduced species
remain associated with
rivers because of
favorable habitat
Time

24. 3: Predictions
downstream
Introduced species
are increasingly
common in
Stream order
downstream areas
over time – suggests
water dispersal
upstream
Time

25. 4: Relative roles of dispersal and habitat conditions
Environmental
Water dispersal Linear habitat
conditions
Historical patterns
Stream order
over time
Proximity to
rivers over
time
Current patterns
Disturbance-
Dispersal
Water, vegetative Animal, vegetative adapted
traits
(vegetative)
Disturbance-
Growth traits Annual No pattern
adapted (annual)