Positive effects of liana cutting on seedlings are reduced during El Niño‐induced drought

Abstract

Liana cutting is a management practice currently applied to encourage seedling regeneration and tree growth in some logged tropical forests. However, there is limited empirical evidence of its effects on forest demographic rates in Southeast Asia. We used 22 four‐hectare plots in the Sabah Biodiversity Experiment (a reduced impact logging site) enrichment line planted with 16 dipterocarp species to assess the effects of complete liana cutting on tree growth and survival. We compared plots where lianas were only cut along planting lines (standard enrichment line planting) with those with one (2014) or two rounds (2011 and 2014) of complete liana cutting. We found increased seedling growth following the first complete liana cut in 2011 relative to the enrichment line planting, consistent with previous studies. The response after 3 years to the cutting in 2014 depended on whether lianas had been previously cut or not: in twice‐cut plots, seedling growth was not significantly different from the standard enrichment planting controls, whereas growth in plots with only one complete cut in 2014 was significantly slower. Seedling survival decreased through time for both once‐ and twice‐cut liana treatments but remained stable in controls. Sapling growth after the 2014 liana cutting showed a similar pattern to seedling growth, while tree growth following the 2014 liana cutting was significantly lower than controls regardless of whether lianas were cut twice (2011 and 2014) or once (2014). Differences in response between the two rounds of liana cutting were likely due to changes in precipitation—2011 was followed by consistent rainfall while 2014 was followed by two severe droughts within 2 years. Synthesis and applications. Our results generally support the widely reported positive effects of liana cutting on tree growth and survival. However, reduced growth and survival after the 2015/2016 El Niño suggests that drought may temporarily undermine the benefits of liana cutting in logged tropical forests. Managers of similar areas in SE Asia should consider halting liana cutting during El Niño events. In other tropical areas, seedling survival should be monitored to assess to what extent results from SE Asia are transferable.

Detection of Spatial and Temporal Patterns of Liana Infestation Using Satellite-Derived Imagery

“…The area surrounding the DVCA has been selectively logged at varying intensities between 1972 and 1993 [38]. The vegetation within the primary forest is dominated by Dipterocarps [39], whereas the logged forest has received targeted removal of larger Dipterocarps and now has a higher proportion of fast-growing, early successional species [40]. The climate is typical of the aseasonal tropics with a mean annual temperature of 26.7 • C and an average yearly rainfall of 2900 mm [40].…”

“…The vegetation within the primary forest is dominated by Dipterocarps [39], whereas the logged forest has received targeted removal of larger Dipterocarps and now has a higher proportion of fast-growing, early successional species [40]. The climate is typical of the aseasonal tropics with a mean annual temperature of 26.7 • C and an average yearly rainfall of 2900 mm [40]. Daily rainfall, temperature and solar radiation have been recorded at the Danum Valley Field Centre and are freely available for download from the South-East Asian Rainforest Research Partnership (www.searrp.org/scientists/available-data/).…”

Conceptualising the Global Forest Response to Liana Proliferation

“…Therefore, besides removal of exotics, liana cutting is only appropriate for excessively abundant, parasitoid species in heavily disturbed areas, where they are most likely to arrest succession (Schnitzer and Carson, 2001;César et al, 2016). Recent mixed success of liana cutting for improving tree growth and survival in Malaysia also suggests inconsistent applicability, including reduced effect during drought (O'Brien et al, 2019). Research is urgently needed to evaluate the broader applicability of liana cutting to avoid its misuse in forest management, and to determine its potential for recovering the global carbon sink.…”

Upscaling tropical restoration to deliver environmental benefits and socially equitable outcomes

“…For example, carbon sequestration within young secondary forest is $60% higher in the western versus eastern Amazon 99 . Meanwhile, following the 2015-16 El Nin ˜o drought in heavily logged landscapes of Malaysian Borneo, forest regrowth was slower on hilltops and close to oil palm plantations, where exposure and edge effects are strongest 100 , while positive effects of liana-cutting on regeneration were reversed due to intense sunlight in the understorey 101 . Understanding such variation offers opportunities for climate-smart restoration that avoids climate-mediated setbacks.…”