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$\partial^{13}\mathrm{C}$ as an Indicator of Edge Effects in Tropical Rainforest Reserves

V. Kapos, G. Ganade, E. Matsui and R. L. Victoria
Journal of Ecology
Vol. 81, No. 3 (Sep., 1993), pp. 425-432
DOI: 10.2307/2261521
Stable URL: http://www.jstor.org/stable/2261521
Page Count: 8
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$\partial^{13}\mathrm{C}$ as an Indicator of Edge Effects in Tropical Rainforest Reserves
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Abstract

1. The effects of proximity to an exposed forest edge on plants in Amazonian lowland rainforest were assessed by examining carbon isotopic composition ($\partial^{13}$C) of canopy leaves and of understorey leaves and air. 2. Exposed canopy leaves of Licania heteromorpha and Scleronema micranthum, were collected (a) in continuous forest, (b) within 100 m of a 5-year-old edge, and (c) in isolated 1-ha forest fragments. Leaves of the understorey species, Duguetia aff. flagellaris and Astrocaryum sociale, were sampled at intervals along transects from a 5-year-old edge towards the forest interior and in control areas. Leaves of D. flagellaris were also collected from young gaps, gap edges, old gaps, undisturbed understorey and from secondary vegetation. $\partial^{13}C$ and $\mathrm{CO}_2$ concentration of understorey air were measured along the study transects. The proportion of the transect area occupied by gaps was estimated. 3. The isotopic composition of the carbon in canopy leaves did not differ among the three types of sampling areas. However, D. flagellaris had significantly higher $\partial^{13}C$ within 60 m of the edge than in undisturbed control areas. $\partial^{13}C$ of understorey air was elevated up to 40 m from the forest edge (-9.3% cf. -10.5% in control areas). This difference accounted for 87% of the elevation of foliar $\partial^{13}C$ in D. flagellaris near the edge. 4. Gaps occupied almost 90% of the transect area within 60 m of the edge as compared to c. 14% in the control areas. Foliar $\partial^{13}C$ of D. flagellaris growing in gaps was significantly less negative than in undisturbed understorey, old gaps and gap edges, which had similar values. 5. The frequency of gaps near the edge is probably responsible for the extent of the elevation in foliar $\partial^{13}C$. While the exact nature of edge effects in tropical forest remains complex, it is clear that at least the outer 60 m of a forest patch must be considered `edge-affected'.

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