Planting Trees and Shrubs Will Help Bring Woodland Birds Back to Farms, Study Finds

Oftentimes, where there are trees, there are birds, whether the landscape is woodland, forest, an urban park or rural farmland. In Australia, farmland is being revegetated to attract woodland bird species, a team of researchers wrote in The Conversation. Trees bordering paddocks are being planted, and stands of trees and shrubs that run beside creeks are being replenished.

The research team included four researchers from La Trobe University in Melbourne, Australia — professor of ecology Andrew F. Bennett; research fellow Angie Haslem; associate research fellow Greg Holland; principal research fellow with the Research Centre for Future Landscapes Jim Radford — as well as the director of the Monash Drone Discovery Platform and senior lecturer in ecology at Monash University Rohan Clarke. Their new study showed how the replanting of trees and shrubs on farmland is helping woodland birds to return.

The researchers’ findings, “Restoration promotes recovery of woodland birds in agricultural environments: A comparison of ‘revegetation’ and ‘remnant’ landscapes,” were published in the Journal of Applied Ecology.

After comparing communities of birds living on farmland that had varying numbers of trees, the researchers said in The Conversation that increasing the amount of vegetation on open farmland from one to ten percent led to twice the number of species of woodland birds.

“This is important, because populations of woodland birds have been steeply declining in southern Australia, with species such as the southern whiteface, brown treecreeper and white-browed babbler now of conservation concern. The collective efforts of landholders can help reverse these declines by attracting species back into otherwise-cleared farmland,” said the researchers.

In many rural areas of Australia, more than 90 percent of native woodland vegetation that was once home to many species of woodland birds has been cleared and replaced with intensive farmland.

“Birds are a visible and often colourful part of Australia’s wildlife; most mammals, for example, are nocturnal and harder to see. In general, farmers, landholders and the community like to see wildlife, they’re part of our identity as Australians and they contribute to the aesthetics of the landscape and give much pleasure,” Bennett, who was lead author of the research, told EcoWatch in an email. “From a conservation perspective, we need to maintain species throughout their range. With so much land cleared, maintaining them through farmland regions is an important part of conservation.”

According to the scientists in The Conversation, there are a range of bird species that live among native farmland vegetation.

“Some species typically occur primarily in regions heavily cleared for farming, such as the ‘sheep-wheat’ belt, rather than, for example, the forested ranges where there are more national parks. Birds have a range of ecological roles in farm landscapes,” Bennett told EcoWatch.

Instead of sampling single “patches” of land like most studies that are conducted on the value of revegetation, the researchers looked at whole landscapes of about three square miles in size that spanned from one to three southwestern Victoria farms, the researchers wrote in The Conversation.

The study areas were divided into three types of landscapes comprising one to 18 percent tree cover on each. One group had tree cover from revegetation, while another had vegetation leftover after the land had been cleared, called “remnant native vegetation.” A third group was a mixture of both.

The researchers found that woodland bird species increased when more of the land was revegetated. 

“For example, in landscapes with only 1% revegetation cover, most birds were open-country species such as galah, red-rumped parrot and willie wagtail, with only 11 woodland species on average. On the other hand, landscapes with 15% revegetation cover had 25 woodland species, on average, as part of the bird community,” the scientists wrote in The Conversation.

Landscapes that had been revegetated were found to support fewer and different types of woodland birds than native landscapes with mature trees.

“It takes many decades for trees to grow and mature and develop resources associated with older trees. The revegetation plots were up to about 20-45 years old, whereas a mature tree may be 100+ (and up to 250) yrs old. Some of the main differences in species between the two types of landscapes were that bird species associated with mature trees were less common or scarce in revegetation. This includes trunk and bark foragers (e.g. tree creepers), those that forage in canopy foliage (e.g. some honeyeaters, thornbills, pardalotes), and some aerial insectivores that like to forage around and perch on open canopy branches (e.g. dusky woodswallow, tree martin),” Bennett told EcoWatch.

Bennett added that revegetation is usually achieved through the planting of trees and shrubs, without ground-layer plants.

“Often there is a fairly dense shrub layer – which favours some species for foraging and shelter (e.g. New Holland honeyeater, superb fairy-wren) and hence also contributes to differences in species,” Bennett said.

Bennett added that the rows often used when revegetating an area don’t mimic native vegetation’s “natural patchy structure.”

“Remnant native vegetation is inherently patchy, with trees and shrubs spaced somewhat randomly, sometimes in clumps, sometimes with gaps; whereas revegetation is often planted in rows and more evenly spaced. Over time, the pattern of revegetation will change as some trees die, some fall, some natural regeneration may occur,” Bennett told EcoWatch.

Birds that use the trunks, large branches and canopy foliage of older trees, like the varied sitella, white-throated treecreeper, white-naped honeyeater and spotted pardalote, weren’t found as often on revegetated land, the scientists wrote in The Conversation.

“With regard to age, as revegetation gets older it develops a greater range of resources – for example, as trees get older there’s more likely to be a larger canopy, dead limbs (for perching), limbs that fall to the ground as logs, the development of tree hollows in trunk[s] and large limbs, and also with larger trunks and branches (with age) there’s a greater surface area for bark-foraging species,” Bennett told EcoWatch.

The research showed that revegetation was most successful when it was mixed with remnant vegetation, the scientists wrote in The Conversation. The combination drew types and numbers of birds akin to remnant landscapes. Diversity of types of trees and shrubs planted was also important, as was proximity to native vegetation.

“The diversity of resources (from different plant species and varied physical structure) leads to a greater range of opportunities for species – for foraging, shelter, refuge and nesting. Having a mix of both remnants and revegetation means that there will be a greater range of resources than when there’s revegetation alone – and hence more likely to support the full range of species,” Bennett wrote.

Trees scattered about the landscape are also helpful for birds too, as they “act as stepping stones,” the researchers wrote in The Conversation.

Bennet said that birds have numerous roles in the ecosystems in which they live, such as being “part of natural food webs and thus inter-related with other parts of the ecosystem (ground layer, shrubs, canopy trees and foliage etc); pest control – feeding on insects and other invertebrates that may be detrimental when abundant (e.g. defoliators associated with tree dieback); [and] pollinators for some flowering plants.”

Bennett added that, if there is a diverse community of birds, it can indicate a healthy ecosystem. 

The researchers wrote in The Conversation that a long-term goal of at least ten to 30 percent of wooded vegetation cover was important to ensure enough habitat to support healthy populations of numerous woodland bird species. Of the 60 species the researchers recorded, at least 11 were not found in the revegetated landscapes.

“Natural vegetation has a greater range of species and life-forms than are typically present in revegetation. Planting for revegetation typically involves only trees and shrubs, but sometimes only trees in woodlots. It rarely/never includes planting lifeforms such as native grasses, sedges, ground-layer herbs and lilies. Further, remnant native vegetation is more likely to have components such as microbial communities (bacteria, fungi) and soil/litter invertebrates already present,” Bennett told EcoWatch. “However, I should note that much of the remnant native vegetation in this study area is far from pristine – it has a history of disturbance from grazing by stock and grass/weed invasion, so most are quite disturbed stands.”

Bennett said that revegetating land that had been used for farming comes with its own unique issues.

“Where revegetation occurs in former farmland, it is likely to have higher levels of nutrients (e.g. nitrogen, phosphorous) in the soil than in remnant vegetation, and this can contribute to greater persistence of pasture grasses and weeds.”

And revegetation isn’t just for the birds, the researchers said.

“Of course, it’s not just for woodland birds — revegetating farms has a number of benefits. Planting along creeks helps stabilise stream banks and improve aquatic environments, trees store more carbon as they grow and age, and tree lines (shelterbelts) and shade benefit livestock and farm production,” the researchers wrote in The Conversation.

The climate crisis presents distinct considerations for land managers.

“It raises questions about what the climate and environment will be like in the future (e.g. 20, 50, 100 years from now), bearing in mind that trees are long-lived. So, some are asking whether, when selecting trees and shrubs to plant, we should be selecting species that may be better able to cope with what the future climate will be like in 50 or 100 years,” Bennett told EcoWatch.