Conceptualising the Global Forest Response to Liana Proliferation

Oliver L. Phillips,Marion Pfeifer,Andrew R. Marshall,Yadvinder Malhi,Robin L. Chazdon,Mason J. Campbell,Hamidu Seki,Philip J. Platts,Robert Marchant,Roy E. Gereau,Jingjing Liang,John Herbohn

doi:10.3389/ffgc.2020.00035

Abstract

Lianas are woody vines, rooted in the soil, and supported physically by trees. Lianas contribute to forest ecosystem functioning globally, but especially in the tropics and subtropics. However, prolific liana growth following heavy disturbance frequently affects subsequent recovery of forest tree diversity, biomass, structure, and function. Understanding this forest liana dynamic, and its sensitivity to climate and anthropogenic forces, is essential for worldwide forest restoration and climate change mitigation. Here, we synthesise the evidence for both positive and negative effects of lianas on forests and propose a framework that outlines the expected global response of forests to disturbance-induced liana proliferation. Emerging evidence suggests that lianas play a major role in both facilitating and delaying forest recovery following disturbance. At low levels of disturbance and/or where environmental conditions favour tree growth, lianas can facilitate forest recovery by protecting trees from extreme weather, fire, weed invasion and herbivory. However, under conditions where lianas proliferate beyond critical thresholds, positive feedbacks are expected to induce and sustain liana-dominated forest states that can endure for decades or even longer. We conceptualise alternative classes of forest recovery response to disturbance and describe measurement and modelling of liana thresholds. We identify four essential challenges for global change science relating to lianas: (1) incorporation of lianas and sapling stems into forest monitoring and tree stand measurements worldwide; (2) long-term experiments to determine variation in liana-tree competition, and potential drivers across forest successional gradients; (3) identification and prediction of liana thresholds and other alternative forest recovery response classes; and (4) dynamic mechanistic modelling of forest recovery to determine regional and global variation within and among different recovery response classes, in relation to variation in potential drivers, liana feedbacks and their interactions. Addressing these challenges will determine the importance of lianas in shaping regional and global forest composition, recovery and dynamics.

Highlights

When ecosystems are disturbed beyond threshold levels for sustaining ecological function, they can lose resilience and undergo abrupt reductions in biological attributes and core processes (Scheffer et al, 2001; Newton and Cantarello, 2015)
Our hypothesis asserts that the impact of disturbance on forest recovery is proportional to disturbance-induced changes in liana competitive success over trees through direct impact on trees and stimulated liana growth. This aligns with previous speculation that lianas can be central to disturbance-induced “feedback” mechanisms (Jakovac et al, 2015; Table 1). We propose that these liana feedbacks play a significant and fundamental role in global forest dynamics
Adapting an existing framework (Bestelmeyer et al, 2011), we propose three data elements that will be central to characterising recovery dynamics of disturbed forest systems in the context of liana thresholds (Figure 6): (1) the biological response; (2) drivers; and (3) response mechanisms (Table 1)

Summary

Introduction

When ecosystems are disturbed beyond threshold levels for sustaining ecological function, they can lose resilience and undergo abrupt reductions in biological attributes and core processes (Scheffer et al, 2001; Newton and Cantarello, 2015). Threshold identification continues to be a major challenge for global change science, relating to human forest disturbance (Reyer et al, 2015; Martin et al, 2017), which has led to worldwide reductions in carbon sequestration (Grace et al, 2014) and biodiversity (Barlow et al, 2016). Tree species richness typically recovers to pre-disturbance levels within just a few years in temperate forests and a few decades in tropical forests (Martin et al, 2013; Meli et al, 2017), varying between 11 and 228 years based on recent neotropical data (median 54 years; Rozendaal et al, 2019). Data limitations have precluded identification of forest recovery thresholds (i.e., critical levels of disturbance preventing tree canopy regeneration), their spatio-temporal variation and mechanisms leading to them (Reyer et al, 2015)

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Conclusion