What are the specific ecological settings in a novel, invasive landscape that permit native avian succession?

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Varughese Jobin, CP Harikrishnan and VV Robin, IISER Tirupati, India, Ritobroto Chanda and Swapna Lawrence, IISc, Bangalore, India, Devcharan Jathanna, Wildlife Conservation Society - India, Bangalore, India

Background/Question/Methods
Invasive landscapes negatively impact the richness and abundance of native biodiversity. On the other hand, studies also show their potential for native faunal colonisation. Given the rapid depletion of natural forests, it becomes a prerogative to look for the conservational aspects of such landscapes. Our study examines the ecological settings within invasive habitats that permit the establishment of forest fauna.
Birds are a helpful taxon to assess the impacts of invasive landscapes, as their ecology and distribution are relatively well-studied. Few studies have studied the positive effects of invasive plant species on bird distribution, particularly habitat-specialist species. Our research focuses on understory birds known to be the slowest recovering guild in secondary forests.
The heavily modified landscape of Western Ghats sky-islands provides us with an excellent system to study this phenomenon. Timber management has created a complex wooded landscape of Shola forests and plantations of Acacia, Eucalyptus and Pine, with varying intensity of understory of regenerating forest trees and invasive acacia and pine. Several threatened endemic, understory birds inhabit these novel invasive woodland habitats. The reasons and drivers of succession are, however, unclear.
This study assesses the impact of the structural and landscape characteristics associated with the invaded habitats on avian succession.
We ask the following questions: • How do the structural attributes of overstory in invasive stands affect the occupancy and abundance of understory birds?
• How does the structural and compositional attributes of the understory impact the occupancy and abundance of understory birds?
• How do the landscape variables of invasive habitats impact the occupancy and abundance of the target species?

We conducted sampling of birds and vegetation in 0.5% of the largest Shola Sky Islands (>1400m MSL) of Anamalai-Palani hills and Nilgiri hills gridded into nested cells of area, 1ha and 4ha. We used playback of target species in four temporal replicates to record their presences and abundances. We also quantified vegetation and landscape variables.
Results/Conclusions
We surveyed 250 cells and found that understorey structure and altitude determine the presence of most study species. Basal area of native tree species and canopy-cover impact their abundances positively.
This study indicates that a novel habitat of exotic timber plants can form suitable habitats for endemic, endangered, understory birds when supported by appropriate vegetation structure. Such succession will promote connectivity and gene flow across hitherto unconnected habitat islands and have major consequences for conservation.