Canopy openness and lai estimates in two seasonally deciduous forests on limestone outcrops in central Brazil using hemispherical photographs

André Rosalvo Terra Nascimento,Jeanine Maria Felfili Fagg,Christopher William Fagg

doi:10.1590/s0100-67622007000100019

André Rosalvo Terra Nascimento, Jeanine Maria Felfili Fagg + Show 1 more

Open Access

https://doi.org/10.1590/s0100-67622007000100019

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Abstract

Patches of seasonally dry tropical forests occur on limestone outcrops in Central Brazil surrounded by the dominant savanna vegetation. They contain valuable timber species but are threatened by farming and mining activities. The objective of this study was to describe canopy opening and light relations in two seasonally deciduous dry forests on slopes and limestone outcrops, in the Paranã valley at the northeastern region of the Goiás state, Brazil. The studied forests were in the Fazenda Sabonete in Iaciara-Go and Fazenda Forquilha in Guarani-GO. Woody plants were sampled in 25 (20 x 20 m) plots in each forest. In the Sabonete forest 40 species, 705 ind./ha-1 with a basal area of 15.78 m²/ha-1 were found, while in Forquilha there were 55 species, 956 ind./ha-1 with a basal area of 24.76 m²/ha-1. Using hemispherical photographic techniques, 25 black and white photographs were taken at each site, during the dry season, totaling 50 photographs. These were taken at the beginning of each vegetation-sampling plot. The photographs were scanned in grey tones and saved as 'Bitmap'. The canopy opening and leaf area index (LAI) were calculated using the software Winphot. The mean canopy opening was 54.0% (±9.36) for Fazenda Sabonete and 64.6% (±11.8) in Fazenda Forquilha, with both sites presenting significant differences in the opening estimates (P < 0.05). Their floristic richness and structure also differed with the more open canopy forest, Forquilha, being richer and denser, suggesting the need for further studies on species-environment relationships in these forests.

Highlights

Structural variation in tropical forest canopies influences light availability and distribution
Sabonete and Forquilha forests, with canopy openness above 50% and leaf area index (LAI) under 1 m2/m2 at most points, were within the range found in most seasonal forests for these variables (Table 2) and agreed with the ranges quoted by Gerhardt (1996) and Baldochi et al (1984) that found canopy openness above 50% and LAI under 2 m2/m2 in the dry season
Even if belonging to similar type of forest, they presented significant differences for the mean values of canopy opening (P < 0.05) and leaf area index (P < 0.05), showing the largest structural variation found in these forests

Summary

Introduction

Structural variation in tropical forest canopies influences light availability and distribution. Light is the main factor that limits the growth and survival of many species, and many times its distribution affects the regeneration pattern of the stand (NICOTRA et al, 1999). In seasonal forests, the changing environmental conditions between the dry and rainy seasons, cause different reactions in the regenerating seedlings. Tropical plants grouped into categories such as shade tolerant or gap colonizers (BUDOWSKI, 1970; MARTÍNEZ-RAMOS, 1994) show distinct responses to the varied micro-climatic conditions. With respect to changing micro environmental conditions in gaps, some studies have demonstrated differences in the ecophysiological response of plants, especially in photosynthetic rates (CHAZDON e FLETCHER, 1984; LIBERMAN et al, 1989, AVALOS e MULKEY, 1999)

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