Evaluating the usefulness of hemispherical photographs as a means to estimate photosynthetic photon flux density during a growing season in the understorey of Nothofagus pumilio forests

Abstract

Old-growth Nothofagus pumilio forests in Chile are managed employing a shelterwood system. A wide range of canopy openings can be found in old-growth and managed forests. Plant survival and growth in the understorey are influenced by the light available. There are limitations (practical and economic) to monitoring the light in the understorey. The aim of this study was to assess the options to estimate the forest understorey photosynthetic photon flux density (PPFD) measured during the growing season (GS) using canopy openness (CO) estimated by means of hemispherical photographs (HP). PPFD was measured using 31 sensors (Li-190SA quantum sensor) over the course of three GSs (October to March). The sensors were installed in an old-growth stand and another subjected to a regeneration felling under a shelterwood system. One HP was taken above each sensor (during the final GS) and the CO estimated. A comparison of the three seasons revealed that the sum of the PPFD during the GSs did not differ significantly. The CO could be used to effectively predict the sum of the PPFD during a GS (R ² = 0.959). These results demonstrate the usefulness of HPs as a means to estimate the sum of the PPFD during a GS.

Keywords:

• Canopy openness
• hemispherical photographs
• light
• Nothofagus pumilio
• photosynthetic photon flux density
• southern Patagonia

Acknowledgements

The authors thank the Chilean Commission for Scientific and Technological Research (Project No. 1000645). They are also grateful to the Programa de Bosques Patagónicos of the University of Chile. The authors thank Marcelo Alvarez (Chilean National Forest Corporation) for his logistical support and assistance in the field. They also thank D. Butler-Manning for comments and proofreading the manuscript.