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Trade-offs in multifunctionality
of road verges and their
delivery of ecosystem services
Hans Martin Hanslin
Dept. Urban greening and environmental engineering
Norwegian institute of bioeconomy research
Litterature review for Norwegian road authorities
Qualitative review, northern conditions
How to integrate multiple functions in verges, focus on
pollinators, plant diversity and soil processes
Narrow down to a focus on some processes
Functions and services
Roadverges contributes to ecological functions and
ESS in the landscape, a.o.
• Habitat function
• Dispersal corridor/stepping stone
• Resources for pollinators etc
• Replacement habitat for grassland species
• Source populations for reestablishment
• Aesthetic aspects
• Noise reduction, trapping pollution,
• Intercept runoff and manage stormwater
Biodiversity key
to high yield of
many ESS
• regulator of
processes
• a final ES
• a valuable good
Key questions
How to establish and maintain biodiversity in the long
term?
Which factors and processes contributes to biodiversity in
road verges?
Set up against management of invasive species
Can you integrate invasion resistance based on biodiversity?
S-N grasslands
Long history of management – depletion of soil nutrients
Species are allowed to complete life cycle
Moderate disturbances - cutting and gap creation
Cutting lowers competition for light – reduces competitive
exclusion
Cutting/brosing and other smallscale disturbances create
gaps and safe-sites for seedling establishment
How relevant are these processes for roadverges?
Similar?
Differs in many aspects, like:
• (higher) nutrient levels
• Timing of cutting
• Higher and more variable cutting height
• Soil physical and chemical conditions
• No/delayed removal of cut material
• Damages to vegetation cover from machinery
• Usually much smaller size and larger border effects
• Garbage accumulation,
• Higher input of weeds and invasive species etc.
• Landscape species pool is lower?
Factors
Abiotic conditions
Landscape
Soil
Nutrients
Water
Species pool
Connectivity
Hydrology
Biotic conditions
Competition
Herbivory
Symbionts
Management
Time/history
Site preparation
Vegetation establishment
Cutting regime
Nutrient management
Management invasives
Seedrain, germination and seedling survival are key
processes for invasion
Competitive ability important for persistence and dominance
Both phases to be targeted by management
Prevent establishment by rapidly establish and keep a
closed vegetation cover of competitive species tolerant of
frequent cutting (mainly grasses)
Shortcuts processes promoting biodiversity
- cuts of possibilities to regenerate from seeds and increases
species turnover
Trade-offs
High biodiversity
Invasive management
Cutting frequency
Low/Moderate
High
Clonal growth
Low-moderate
Strong
Less competitive
Strong competitors
Moderate
Low/absent
Prevent competitive exclusion
Yes
No
Spontaneous establishment
Yes
No
Mosaic management
Yes
No
Low-high
Low
Vegetation composition
Gap frequency
Soil nutrients
What to do?
Split strategy, depending on invasion risk
High risk – Safe solution, grass based,
strong competitors, frequent cutting etc
Low risk – different options based on
landscape context
Intermediate risk – Increase the biotic
resistance of the system based on priority
effects, assembly filters, niche overlaps
and redundancy
Priority effects
Early establishing species get a
disproportionate large benefit
Strong priority effects are common in many
invasive species
Niche management
Theory – invasability reduced if species with similar traits
as invader are present or if available niches are filled.
Difficult: similar traits and function, including phenology (vs.
seedling stage)
Large overlap in function among species – leaving no
available opportunities or resources even when species
are lost or decline in system – ecological redundancy
Assembly filters
A combination of abiotic, biotic and dispersal filters can
be used to reduce establishment of invasive species.
Dispersal filters
• landscape management to reduce
seed rain
Abiotic filter
• lower availability of nutrients and
water
• regular cutting, cutting removal
Biotic filters
• priority effects,
• niche management
• cumulative resistance
• Plant-soil feedbacks
Theoharides & Dukes, 2007
Gaps
Gaps are still needed to maintain BD of
system to allow regeneration and nonclonal species to persist.
Does all this work?
Some examples that it does, context dependent?
Frankly, more targeted research is needed on how this
applies to biodiversity of road verges