Interactions between enrichment planted seedlings and mature trees in
selectively logged lowland dipterocarp forest
Abstract
Old-growth forests in Southeast Asia are dominated by trees of the
Dipterocarpaceae family which are targeted by selective logging. Their
traits (supra-annual mast fruiting, limited dispersal, and recalcitrant
seeds that form no seed bank) mean they can have poor natural
regeneration rates in some selectively logged forests. Enrichment
planting is commonly used to overcome recruitment limitation and
increase restoration success. However, it is still unclear what factors
influence the success rate of planted seedlings, including the
characteristics of the surrounding tree matrix and local neighbourhood.
Here, we examine the growth and survival of 721 enrichment line-planted
seedlings within 24 plots of the selectively logged forest of the Sabah
Biodiversity Experiment, in Malaysian Borneo, in relation to their
species identity and local neighbourhoods. We mapped the spatial
location, size, and identity of nearly 5,000 surrounding matrix trees (≥
10 cm diameter at breast height (DBH)) within a 10 m radius of focal
planted seedlings in 2012 and 2015. We analysed levels of tree
density-dependence, asymmetric competition with naturally occurring
trees, and confamilial density-dependence for each seedling. Survival
and growth rates of enrichment planted seedlings were positively
associated with canopy openness and total basal area of the surrounding
tree matrix. These results were consistent between two planting cohorts.
Increased survival and growth of enrichment planted seedlings in areas
of the Sabah Biodiversity Experiment with higher canopy openness (up to
around 40%) is consistent with understory light as a limiting resource.
The unexpected higher survival and growth of enrichment planted
seedlings in forest areas with higher basal area of unlogged remnant
trees may be explained by the logging-induced creation of patches with
varying local conditions, with those less heavily impacted by logging
containing more naturally occurring trees, greater moderation of extreme
high temperature and low humidity, more established mycorrhiza and
reduced soil compaction.