The impact of liana proliferation on recovery of biomass in secondary tropical forests

The world's tropical forests are essential carbon sinks and home to the majority of terrestrial biodiversity. Over half of the world's remaining forests are categorised as degraded or secondary forests and deforestation continues; between 1990 and 2015 there was a net loss of 129 million ha of forest, with the largest forest losses occurring in the tropics [1]. The rate of deforestation and timber extraction in Southeast Asia exceeds that of most other tropical regions [2,3]. Timber exports from Borneo alone surpass those from all of tropical Africa and Latin America combined [4]. The majority of the remaining undisturbed forest in Southeast Asia is classified as production forest [5] and therefore is open to selective logging.

In dipterocarp forests of Southeast Asia virtually all large trees have high timber value with direct implications for the impacts of selective logging. On the first logging rotation typically all marketable stems are removed, leaving only small stems and less desirable timber species. After the first logging rotation, the forest may be logged again, frequently less than 20 years later [6]. This process leaves behind a highly degraded forest with altered structure and composition; logged forests tend to have low, open canopies, high liana densities and reduced abundance of late-successional tree species [7].

It is widely accepted that selectively logged forests have greater conservation value than other degraded forest habitats [7]. A recent review indicated that selectively logged forests typically retain most of their biodiversity and associated ecosystem functions [8].
However, most studies have investigated the diversity and composition of animal species not trees, which



may be more severely impacted by direct extraction and physical damage than the animal species that depend on them. In addition, selective logging may have, as yet unseen, impacts on tree regeneration that limits the sustainability of these forests in the long term. First, removal of high value timber trees reduces potential seed sources limiting seedling recruitment of high-wood density species and potentially shifting future composition of adult trees in the long term [9]. Second, physical damage to the residual forest stand and changes in forest structure post-logging can result in the proliferation of lianas. Recent studies have shown that liana abundance can significantly impact forest dynamics and aboveground biomass [AGB; 10,11]. However no studies have investigated how selective logging may impact future forest composition, and the role that lianas play in shaping the forest communities that regenerate after selective logging.

This project aims to investigate
1. The mechanisms that determine recruitment into the tree community in selectively logged compared to undisturbed forests
2. The role of lianas in shaping community dynamics
3. The long-term sustainability of logged forests in Southeast Asia.