<i>Harungana madagascariensis</i> (Hypericaceae) is a key phorophyte for native epiphytes and lianas during ecological restoration: case study on an oceanic island

Human activities generate multiple pressures on ecosystems, driving rapid biodiversity loss globally. Oceanic islands and tropical forests are most affected by this situation and within them, epiphytes and lianas are among the most threatened floristic components. Yet, they are often understudied and neglected particularly in restoration projects which instead typically favour planting trees and often overlook ecosystem dynamics and functional interactions. We compared native epiphytes and lianas growing on native pioneer trees (<i>Harungana madagascariensis</i> (Hypericaceae)) with those growing on other native trees of (1) similar trunk diameter; and (2) similar age, in wet native forests undergoing restoration after invasive alien plant control, on the volcanic oceanic island of Mauritius. We also investigated whether the different phorophytes had any differential influence on the reproductive status of epiphytes and their size. We studied <i>H. madagascariensis</i> because it is the dominant native pioneer tree of the island's wet native vegetation and also because, since decades, it is often controlled by conservation managers. <i>Harungana madagascariensis</i> hosted more native epiphyte and liana species than native trees of similar age, but no difference was found with trees of similar diameter. Similarly, there was a higher abundance of epiphyte and liana on <i>H. madagascariensis</i> compared to other trees of similar age, but no difference with other trees of similar diameter. Twice more epiphyte/liana species were closely associated with <i>H. madagascariensis</i> (multipatt analysis, IndVal 0.31-0.92; <i>p</i> < 0.05) compared to other phorophytes of similar diameter, and none were closely associated with other phorophytes of similar age. Finally, <i>Harungana madagascariensis</i> hosted more reproductive orchids than phorophytes of similar age and size, but the sizes of epiphytes and lianas did not differ significantly across phorophytes. <i>Harungana madagascariensis</i> therefore benefits native epiphytes and lianas, promoting their colonisation after invasive alien plants are controlled, in contrast with other native phorophytes. This contrast is in fact even larger because the cut <i>H. madagascariensis</i> are often many meters tall, often already hosting epiphytes, in contrast to seedlings that are planted in their place. On an oceanic island where native biodiversity is acutely threatened and where the benefits of cutting native pioneer trees like <i>H. madagascariensis</i> in biodiversity conservation projects remain unproven, our study provides new evidence that the detrimental effects of this management extend beyond the destruction of the native pioneer trees, to also severely hinder the restoration of native epiphyte and liana species. Furthermore, our study underscores how native pioneer trees can help foster the conservation of typically neglected native plant guilds, and the improbable need for stressing that evidence, and not hypotheses, should drive conservation policy.