LARGE-SCALE EDGE EFFECTS IN TROPICAL RAINFORESTS AND THEIR IMPLICATIONS FOR CONSERVATION

Transcription

1 LARGE-SCALE EDGE EFFECTS IN TROPICAL RAINFORESTS AND THEIR IMPLICATIONS FOR CONSERVATION SUSAN LAURANCE 1, VALERY GOND 2 & GAEL BRIANT 3 1 JAMES COOK UNIVERSITY, CAIRNS; 2 CIRAD, MONTPELLIER; 3 UNIVERSITE LAVAL, QUÉBEC

2 Conservation Assumptions of Protected Areas Adequate populations Maintain Ecosystem Function

3 Are protected areas large enough to withstand external pressures? Illegal logging Hunting Encroaching fires

4 What is happening to rainforest trees on forest edges?

5 Edge-related changes in tree communities Long term studies of tree communities at the Biological Dynamics of Forest Fragments Project in the Brazilian Amazon Major increases in mortality, damage, and turnover within ca. 1 m of edges Detectable increases in mortality and turnover up to ca. 3 m of edges

6 Increased wood debris CWD production (Mg/ha/year) Y = log X R=.6, P< Distance to edge (m)

7 Increased fire incursion Fire frequency (no./century) Surface fires at Tailândia, Brazil Distance to edge (m) Cochrane & Laurance (22) Journal of Tropical Ecology

8 Large-scale desiccation of rainforest trees in fragmented landscapes Dense rain forest area 74% to 65% % to 2% 67% to 51% 3 Dry forest area

9 Methods Tree canopy moisture measured over dry season (June August) ~ 8 years (2-27) MODIS satellite images 12 x 8-day composites examined pa. Leaf water canopy content measured as SIWSI (Shortwave Infrared Water Stress Index) using spectral bands 2 (NIR: nm) & 6 (SWIR: ) Five edge distances -5m, 5-1km; 1-2km & 2-5 km Relative change in canopy moisture

10 Results - Average dry season canopy desiccation rates of three forest types SIWSI,4 Intact rainforest,35,3,25 Edge rainforest,2,15,1 Dry forests,5 -, juin June juillet July August août

11 1) Landscape fragmentation influences the spatial extent of desiccation Δ SIWSI Δ SIWSI a inf a dét,1 d ,1 -,2 -,3 a inf a dét,1 d ,1 -,2 -,4 -,3 -,5 -,6 -,7 65% Forest cover Zone de São Félix -,4 -,5 2% Zone Forest nord cover a inf a dét Δ SIWSI, ,1 d -,2 Site 1 and 3 edge penetration distance (d) observable desiccation to 1 & 1.5 km from edge; Site 2 up to 2.7 km -,3 -,4 -,5 51% Forest cover Zone sud-ouest

12 2) Landscape fragmentation influences the magnitude of desiccation Δ SIWSI SIWSI Δ SIWSI SIWSI a inf inf a dét dét,1,1 d ,1 -,2 -,3 a inf inf a dét dét,1,1 -,1 -,1 -,2 -,2 d ,4 -,5 -,6 -,7 65% Forest cover Zone de São Félix -,3 -,3 -,4 -,4 -,5 -,5 2% Zone Forest nord cover a inf inf a dét dét Δ SIWSI SIWSI,1,1 -,1 -,1 -,2 -,2 -,3 -,3 -,4 -,4 -,5 -, d Zone sud-ouest 51% Forest cover Steepness of the edge interior gradient: New edges Sites 1 & 3 had steepest gradients, but after 1 km little change; Old edges Site 2 had lower canopy moisture but the gradient longer and flatter with strong differences evident at 5m 1km and 1 2km.

13 3) Landscape fragmentation influences the progression progression of desiccation Δ SIWSI SIWSI,1,1 d ,1 -,2 -,3 -,4 -,5 -,6 65% Zone Forest de São Félix cover -,7 Δ SIWSI SIWSI,1 No d Seuil dthreshold inexistant ,1 -,2 -,3 -,4 -,5 2% Forest cover Zone nord Δ SIWSI SIWSI,1,1 d ,1 -,2 -,3 -,4 -,5 -,6 51% Zone Forest sud-ouest cover Site 1 & 3 showed increased desiccation distance to 3.7 & 1.8 km Site 2 showed no change fragments are saturated by edge effects Variations Variations non.2 non.1 assèchement assèchement humidification humidification

14 Four main effects of deforestation on dry season canopy desiccation 1) Intact forest show no detectable change yet edge forests declined significantly in canopy moisture 2) Penetration distance of canopy desiccation differed among heavily and moderate fragmented landscapes 3) Magnitude of canopy desiccation differed among fragmented landscapes 4) Progression of canopy desiccation occurred in moderate fragmented forest over time but not in heavily fragmented landscapes

15 IMPLICATIONS Intact rainforests in eastern Amazonia exhibit a strong resilience to prolonged dry season (typical of this region) with no detectable changes in canopy water during this study.

16 IMPLICATIONS Once fragmented these forests showed large changes in canopy water that extended deep into the forest. Such patterns of desiccation predispose fragmented forests to fire potentially leading to the loss of millions of hectares of forest.