Forest floor light conditions in a secondary tropical rain forest after artificial gap creation in northern Borneo

Abstract

Forest floor light conditions were monitored in a field experiment regarding alternative approaches to canopy gap creation. To establish gaps, three pioneer canopy treatments (canopy tree felling, girdling and untreated control) were combined with two sub-canopy treatments (slashing or untreated control). The canopy treatments were performed within sub-plot circles (radius 5 m) while the sub-canopy treatment was confined to the central parts (2.5 m radius). Pioneer canopy felling and girdling (stripping of the bark) treatments affected 31% (mean value) of the initial mean standing basal area (39 m 2 ha −1). Relative photosynthetic photon flux densities (PPFD R) and canopy openness were measured (1.5 m above the forest floor) in the sub-plots before and immediately after treatment and at subsequent intervals of 6, 18 and 30 months. During the study period all treatments resulted in increased PPFD R and canopy openness compared to pre-treatment mean values (PPFD R: 1.8–2.3%, canopy openness: 8.8–10.7%). Felling selected pioneer canopy trees provided distinct but transient shade reduction; mean PPFD R values were 12.5% after 6 months and 8.5% 30 months after initial treatment, while canopy openness averaged 14.2 and 11.8% after 6 and 30 months, respectively. Girdling effects were less drastic but after 30 months forest floor openness and PPFD R averaged values similar to, or slightly higher than the felling treatment. Sub-canopy slashing resulted in 2.4–5.1% higher PPFD R and 2.0–2.4% higher canopy openness compared to the untreated control plots and this effect persisted throughout the study period.