Intervention monitoring: Revegetation improves habitat for streamside birds - but it takes time

A study that monitored riparian revegetation in the Yarra catchment has found that bird numbers and species diversity can be improved, to something close to a natural state, where willow is removed and revegetation is given time to mature. 

Willow removal and revegetation
Willow removal and revegetation

Birdlife Australia has been monitoring key revegetation sites for Melbourne Water to determine how long it takes to detect an improvement in streamside bird community after willow removal works have taken place.  

Removing invasive species and revegetating with native species has been a focus for waterway managers for many years.  However, few monitoring programs have been in place to determine how long it takes for wildlife, such as birds, to reappear after willows have been removed. An analysis of long-term monitoring data from sites located in the Yarra catchment is providing some insights on this question.  

Rural sites along the Plenty River, Arthurs Creek and Running Creek are monitored at regular intervals after willow removal works have been completed and bird numbers and species present are assessed. Four different treatments were compared: 

  • Willow‐infested (no willow control) 
  • Willows removed and revegetation carried out within the last 18 years 
  • Willows removed and revegetation carried out more than 18 years ago 
  • Remnant native vegetation  

Mean bird abundance across treatments in the Arthurs Creek and Plenty River catchment

Mean bird abundance across treatments in the Arthurs Creek and Plenty River catchment
Mean abundance of riparian birds per 0.5 ha for revegetation works of different ages in the Plenty and Arthurs Creek catchment. Error bars indicate +/- 1 Standard Error. Number of replicate plots vary from 2 to 4 per treatment with a minimum of 48 surveys being undertaken at each plot.

 

Mean bird species richness across treatments in the Arthurs Creek and Plenty River catchment

Mean bird species richness across treatments in the Arthurs Creek and Plenty River catchment
Mean species richness of riparian birds per 0.5 ha for revegetation works of different ages in the Plenty and Arthurs Creek catchment. Error bars indicate +/- 1 Standard Error. Number of replicate plots vary from 2 to 4 per treatment with a minimum of 48 surveys being undertaken at each plot.

Bird diversity and overall numbers were lowest in willow infested sites demonstrating that willow infestations do not support healthy riparian bird populations. 

Both the overall number of birds and the variety of different bird species present showed a positive response to willow removal that improves with time. In this analysis, revegetation needs to be at least 18 years old for bird density and diversity to be similar to mature native vegetation and to have a measurable improvement over willow infested sites.  

Other similar studies indicate that as revegetation sites age, improving the habitat complexity by infill planting with understory and mid-storey shrubs and grasses is helpful for supporting a wide variety of riparian bird species.