Implications of Riparian Willow Invasion to Instream Community Structure and Function;

Implications of riparian willow invasion to instream community structure and function; a synthesis using causal criteria analysis

Biological Invasions

Paul J. McInerney*1, 2, Gavin N. Rees1,3, Ben Gawne1, 4 and Phil Suter2

Murray-Darling Freshwater Research Centre, PO BOX 991, Wodonga, VIC 3689, Australia
La Trobe University, P.O. Box 991, Wodonga, VIC 3689, Australia
CSIRO Land and Water, P.O. Box 991, Wodonga, VIC 3689, Australia
University of Canberra, Locked Bag 1, Canberra, ACT 2601, Australia

* Corresponding author

Email address:

Telephone: +61 2 6024 9649

Fax: +61 2 6059 7531

Online Resource 1: Weights applied to analysis from Eco Evidence

Study design type / Weight
BACI or BARI MBACI or Beyond MBACI / 4
Gradient response model / 3
Before v. after (no reference/control) / 2
Reference/control vs. impact (no before) / 2
After impact only / 1
Number of independent control locations / Weight
No control locations / 0
One control location / 2
More than one control location / 3
Number of independent impact locations / Weight
One impacted location / 0
Two impacted locations / 2
More than two impacted locations / 3
Number of locations for gradient response model / Weight
3 independent locations / 0
4 independent locations / 2
5 independent locations / 4
More than 5 independent locations / 6

Online Resource 2: Individual study weights relating to each cause-effect linkage exported from Eco Evidence

Cause / Trajectory / Effect / Trajectory / Supports linkage? / Study details / Weight / Citation
vegetation (exotic invasion) → ↓ algae
Willow invasion / No trajectory / No difference in chlorophyll-a concentration between open and infested sites despite significantly more shading at infested sites / No change / No / Reference/control vs. impact (no before)
3(control); 3(impacted) / 8 / Lester, P.J.; Mitchell, S.F; Scott, D(1994)
Willow infestation / No trajectory / Reduced amounts of chlorophyll-a on tiles in willow infested and artificially shaded reaches compared to open reaches. / Decrease / Yes / Reference/control vs. impact (no before)
2(control); 2(impacted) / 7 / Lester, PJ; Mitchell, SF; Scott, D(1996)
Willow infestation / No trajectory / Decrease in filamentous algal growth / Decrease / Yes / Reference/control vs. impact (no before)
3(control); 3(impacted) / 8 / Glova, Gordon J; Sagar, Paul M(1994)
Willow infestation / No trajectory / Salix fragilis leaves support decreased algal biofilms in comparison to eucalyptus / Decrease / Yes / Gradient response model
4(independent) / 5 / McInerney, P.J; Rees, G,N; Gawne, B; Suter, P(2015)
Willow infestation / No trajectory / Leaf biofilms at Salix spp. sites with reduced density and diversity of diatoms / Decrease / Yes / Gradient response model
4(independent) / 5 / Schulze, DJ.; Walker, KF.(1997)
vegetation (exotic invasion) → ∆ biota (trophic structure)
Willow invasion / No trajectory / No change in proportions of functional feeding groups of macroinvertebrates between infested and open sites / No change / No / Reference/control vs. impact (no before)
3(control); 3(impacted) / 8 / Lester, P.J.; Mitchell, S.F; Scott, D(1994)
Willow infestation / No trajectory / Changes to habitat caused by willow infestation alter the functional organisation of macroinvertebrates / Change / Yes / Reference/control vs. impact (no before)
3(control); 3(impacted) / 8 / Jayawardana, J.M.C.K. Westbrooke, Martin(2010)
Willow infestation / No trajectory / In willow infested reaches a higher proportion of macroinvertebrate diet is derived from terrestrial (allochthonous) sources than non-infested reaches / Change / Yes / Reference/control vs. impact (no before)
2(control); 2(impacted) / 7 / Lester, P. J; Mitchell, S. F; Scott, D; Lyon, G. L.(1995)
Willow infestation / No trajectory / Invasive Salix spp. affected abundance of different functional feeding groups / Change / Yes / Reference/control vs. impact (no before)
3(control); 3(impacted) / 8 / Serra, María Noel; Albariño, Ricardo; Díaz Villanueva, Verónica(2013)
Willow infestation / No trajectory / Increase in the proportion of collector gatherers and filter feeding taxa in infested reaches, while shredders more dominant in native reaches / Change / Yes / Reference/control vs. impact (no before)
2(control); 2(impacted) / 7 / Miserendino M. L. and Pizzolon L. A.(2004)
Willow infestation / No trajectory / Lower proportion of scrapers at infested sites in summer, though not significant (p=0.067) / Change / Yes / Reference/control vs. impact (no before)
9(control); 9(impacted) / 8 / Read, Martin G; Barmuta, Leon(1999)
vegetation (exotic invasion) → ↓ ecosystem (primary production)
Willow infestation / No trajectory / No change in primary production by algae grown on tiles at willow infested, artificially shaded and open sites. / No change / No / Reference/control vs. impact (no before)
2(control); 2(impacted) / 7 / Lester, PJ; Mitchell, SF; Scott, D(1996)
Willow infestation / No trajectory / Salix fragilis biofilms display decreased rates of primary production to endemic eucalypt leaves / Decrease / Yes / Gradient response model
4(independent) / 5 / McInerney, P.J; Rees, G,N; Gawne, B; Suter, P(2015)
vegetation (exotic invasion) → ↑ ecosystem (respiration)
Willow infestation / No trajectory / Reduced leaf breakdown rates compared to endemic species / Decrease / No / Reference/control vs. impact (no before)
3(control); 3(impacted) / 8 / Serra, María Noel; Albariño, Ricardo; Díaz Villanueva, Verónica(2013)
Willow infestation / No trajectory / Increased rates of decomposition in rivers in comparison to eucalypts / Increase / Yes / Gradient response model
4(independent) / 5 / Janssen, M.A; Walker, K.F(1999)
Willow infestation / No trajectory / Salix fragilis display greater rates of decomposition per leaf mass / Increase / Yes / Gradient response model
4(independent) / 5 / McInerney, P.J; Rees, G,N; Gawne, B; Suter, P(2015)
Willow infestation / No trajectory / Increased processing rates of allochthonous carbon / Increase / Yes / Gradient response model
17(independent) / 9 / Esslemont, Graeme; Maher, William; Ford, Phillip; Lawrence, Ian(2007)
Willow infestation / No trajectory / Increased rates of decomposition in comparison to eucalypts / Increase / Yes / Gradient response model
6(independent) / 9 / Pidgeon, R. W. J; Cairns, S.C(1981)
Willow infestation / No trajectory / Increased decomposition rates of Salix spp. leaves in comparison to eucalyptus leaves / Increase / Yes / Gradient response model
4(independent) / 5 / Schulze, DJ.; Walker, KF.(1997)
vegetation (exotic invasion) → ∆ ecosystem (dissolved organic matter)
Willow infestation / No trajectory / Increased rates of leaching by S. fragilisin comparison to endemic leaves / Change / Yes / Reference/control vs. impact (no before)
3(control); 3(impacted) / 8 / Serra, María Noel; Albariño, Ricardo; Díaz Villanueva, Verónica(2013)
Willow infestation / No trajectory / Willow leaves exhibit increased rates of initial leaching in comparison to eucalypts / Change / Yes / Gradient response model
4(independent) / 5 / Janssen, M.A; Walker, K.F(1999)
Willow infestation / No trajectory / Salix fragilis leaves have increased rates of leaching after submersion in comparison to endemic leaves / Change / Yes / Gradient response model
4(independent) / 5 / McInerney, P.J; Rees, G,N; Gawne, B; Suter, P(2015)
Willow infestation / No trajectory / Rapid weight loss of leaves after submersion compared to Eucalyptus spp. leaves - increased rate in comparison / Change / Yes / Gradient response model
6(independent) / 9 / Pidgeon, R. W. J; Cairns, S.C(1981)
Willow infestation / No trajectory / Higher rates of leaf leaching after submersion in water in comparison to endemic and other introduced leaf types - 25% after 24 hrs / Change / Yes / Gradient response model
4(independent) / 5 / Parkyn, S.M; Winterbourn, M, J(1997)
Willow infestation / No trajectory / Rapid weight loss of Salix babylonica leaves upon submersion - 19% of initial dry weight after 7 days and 31% after 18 days / Increase / Yes / Gradient response model
5(independent) / 7 / Collier, KJ; Winterbourn, MJ(1986)
Willow infestation / No trajectory / Evidence of rapid leaching, total carbohydrate concentration of leaves decreased from 75% AFDW to 25% in the first week. / Increase / Yes / Gradient response model
3(independent) / 3 / Lester, P. J; Mitchell, S. F; Scott, D(1994)
Willow infestation / No trajectory / Increased rates of initial leaching (soluble components) of Salix spp. leaves in comparison to eucalyptus leaves / Change / Yes / Gradient response model
4(independent) / 5 / Schulze, DJ.; Walker, KF.(1997)
vegetation (exotic invasion) → ∆ invertebrates (assemblage)
Willow infestation / No trajectory / Changes to habitat caused by willow infestation alter the functional organisation of macroinvertebrates / Change / Yes / Reference/control vs. impact (no before)
3(control); 3(impacted) / 8 / Jayawardana, J.M.C.K. Westbrooke, Martin(2010)
Willow infestation / No trajectory / Invasive Salix spp. affected invertebrate composition / Change / Yes / Reference/control vs. impact (no before)
3(control); 3(impacted) / 8 / Serra, María Noel; Albariño, Ricardo; Díaz Villanueva, Verónica(2013)
Willow infestation / No trajectory / Increase in the proportion of collector gatherers and filter feeding taxa in infested reaches, while shredders more dominant in native reaches / Change / Yes / Reference/control vs. impact (no before)
2(control); 2(impacted) / 7 / Miserendino M. L. and Pizzolon L. A.(2004)
Willow infestation / No trajectory / Decreased site to site variability of macroinvertebrate assemblage at willow and willow removal sites in comparison to reference (native) sites / Change / Yes / Reference/control vs. impact (no before)
6(control); 6(impacted) / 8 / Becker, A; Robson, B. J(2009)
Willow infestation / No trajectory / Distinct groupings of canopy arthropods in willow riparian zones than in native riparian zones / Change / Yes / Reference/control vs. impact (no before)
3(control); 3(impacted) / 8 / Greenwood, H; O'Dowd, D.J; Lake, P.S(2004)
Willow infestation / No trajectory / Habitat structure had a significant effect on macroinvertebrate assemblage / Change / Yes / Reference/control vs. impact (no before)
3(control); 3(impacted) / 8 / Jayawardana, J. M. C; K Westbrooke; M Wilson; M Hurst, C(2006)
Willow infestation / No trajectory / Minor differences in composition and diversity of invertebrates at willow invaded sites, and different assemblages in willow and redgum leaf packs. / Change / Yes / Reference/control vs. impact (no before)
3(control); 3(impacted) / 8 / Schulze, DJ.; Walker, KF.(1997)
vegetation (exotic invasion) → ↓ invertebrates (abundance)
Willow invasion / No trajectory / Decrease in macroinvertebrate density in autumn winter and summer / Decrease / Yes / Reference/control vs. impact (no before)
3(control); 3(impacted) / 8 / Lester, P.J.; Mitchell, S.F; Scott, D(1994)
Willow infestation / No trajectory / Decreased abundance of macroinvertebrates at infested sites / Decrease / Yes / Reference/control vs. impact (no before)
2(control); 2(impacted) / 7 / Lester, PJ; Mitchell, SF; Scott, D(1996)
Willow infestation / No trajectory / Abundance similar / No change / No / Reference/control vs. impact (no before)
3(control); 3(impacted) / 8 / Serra, María Noel; Albariño, Ricardo; Díaz Villanueva, Verónica(2013)
Willow infestation / No trajectory / Density similar / No change / No / Reference/control vs. impact (no before)
2(control); 2(impacted) / 7 / Miserendino M. L. and Pizzolon L. A.(2004)
Willow infestation / No trajectory / Decreased abundance in summer / Decrease / Yes / Reference/control vs. impact (no before)
9(control); 9(impacted) / 8 / Read, Martin G; Barmuta, Leon(1999)
Willow infestation / No trajectory / No significant difference in abundance between treatments / No change / No / Reference/control vs. impact (no before)
6(control); 6(impacted) / 8 / Becker, A; Robson, B. J(2009)
Willow infestation / No trajectory / Decreased abundance of canopy arthropods in willow riparian zones than in native riparian zones / Decrease / Yes / Reference/control vs. impact (no before)
3(control); 3(impacted) / 8 / Greenwood, H; O'Dowd, D.J; Lake, P.S(2004)
Willow infestation / No trajectory / Macroinvertebrate abundance significantly lower at densely infested sites than non–infested sites (however, only in one stream, no densely infested sites at the other two test streams) / Decrease / Yes / Reference/control vs. impact (no before)
3(control); 1(impacted) / 5 / Glova, Gordon J; Sagar, Paul M(1994)
Willow infestation / No trajectory / Increased macroinvertebrate abundance associated with willow infestation, mostly of an invasive snail / Increase / No / Reference/control vs. impact (no before)
2(control); 2(impacted) / 7 / Wahizatul, A.A; Jennings, J(2013)
Willow infestation / No trajectory / Abundance and biomass of invertebrates effected by level willow infestation, but not consistent / Change / No / Reference/control vs. impact (no before)
3(control); 3(impacted) / 8 / Sagar, P. M. Glova, G. J.(1995)
vegetation (exotic invasion) → NC invertebrates (diversity)
Willow infestation / No trajectory / Taxa richness similar / No change / Yes / Reference/control vs. impact (no before)
3(control); 3(impacted) / 8 / Serra, María Noel; Albariño, Ricardo; Díaz Villanueva, Verónica(2013)
Willow infestation / No trajectory / Diversity similar / No change / Yes / Reference/control vs. impact (no before)
2(control); 2(impacted) / 7 / Miserendino M. L. and Pizzolon L. A.(2004)
Willow infestation / No trajectory / Decreased taxa richness in summer / Decrease / No / Reference/control vs. impact (no before)
9(control); 9(impacted) / 8 / Read, Martin G; Barmuta, Leon(1999)
Willow infestation / No trajectory / No significant difference in taxa richness between treatments / No change / Yes / Reference/control vs. impact (no before)
6(control); 6(impacted) / 8 / Becker, A; Robson, B. J(2009)
willow invasion / No trajectory / Decreased morphospecies richness of canopy arthropods in willow riparian zones than in native riparian zones / Decrease / No / Reference/control vs. impact (no before)
3(control); 3(impacted) / 8 / Greenwood, H; O'Dowd, D.J; Lake, P.S(2004)
Willow infestation / No trajectory / Macroinvertebrate diversity greater in willow reaches / Increase / No / Reference/control vs. impact (no before)
3(control); 1(impacted) / 5 / Glova, Gordon J; Sagar, Paul M(1994)
Willow infestation / No trajectory / Decreased macroinvertebrate diversity associated with willow infestation / Decrease / No / Reference/control vs. impact (no before)
1(control); 1(impacted) / 4 / Wahizatul, A.A; Jennings, J(2013)
Willow infestation / No trajectory / No significant difference in diversity / No change / Yes / Reference/control vs. impact (no before)
3(control); 3(impacted) / 8 / Schulze, DJ.; Walker, KF.(1997)
vegetation (exotic invasion) → ∆ invertebrates (growth)
Willow infestation / No trajectory / 56 day old aged willow leaves may provide a preferred food source for some macroinvertebrates in place of periphyton / Change / Yes / Gradient response model
3(independent) / 3 / Lester, P. J; Mitchell, S. F; Scott, D(1994)
Willow infestation / No trajectory / Increased growth rates of invertebrates feeding on green willow leaves compared green eucalyptus leaves and senescent leaves of willow and eucalyptus. Speculate that willows may provide a preferred food source, but that it will be available for less time. / Increase / Yes / Gradient response model
10(independent) / 9 / Yeates, L.V; Barmuta, L.A(2009)
vegetation (exotic invasion) → ∆ water quality (nutrients)
Willow infestation / No trajectory / Increased nitrogen, phosphorous and biologically reactive carbon entering Australian Rivers / Increase / Yes / Gradient response model
17(independent) / 9 / Esslemont, Graeme; Maher, William; Ford, Phillip; Lawrence, Ian(2007)
vegetation (exotic invasion) → ↑ physical habitat
Willow invasion / No trajectory / Increased shading - incident stream illumination decreased by 80% due to willows, although comparison made with tussock grass riparian zone, not forest / Increase / Yes / Reference/control vs. impact (no before)
3(control); 3(impacted) / 8 / Lester, P.J.; Mitchell, S.F; Scott, D(1994)
Willow infestation / No trajectory / Increased shading / Increase / Yes / Reference/control vs. impact (no before)
2(control); 2(impacted) / 7 / Lester, PJ; Mitchell, SF; Scott, D(1996)
Willow infestation / No trajectory / Increased shading / Increase / Yes / Reference/control vs. impact (no before)
3(control); 1(impacted) / 5 / Glova, Gordon J; Sagar, Paul M(1994)
vegetation (exotic invasion) → ∆ ecosystem (nutrient processing)
No evidence items were included for this linkage