Sean Sloan and his team examined the spatial relationships of rainforest regrowth relative to the size and proximity of remnant rainforest cover over a pastoral region in Australia’s Wet Tropics. They analysed the relationship between the extent and distribution of secondary rainforest regrowth to soil agricultural potential, land-cover history, terrain slope, distance to primary rainforest, and size of primary rainforest.
European impact on the rainforests of the Atherton Tableland commenced with logging in the 1870s, progressing to broad-scale deforestation by the 1920s for dairy farms. Small forest patches remained in inaccessible areas. Pasture abandonment commenced in the 1940s, with larger transitions occurring from the 1980s onwards as economic realities forced dairy farmers out of the industry.
In the paper Sean and his team identified 2491 patches of secondary rainforest covering a total area of 11,158ha across the Atherton Tableland. A major finding was that secondary rainforests displayed a strong spatial affinity with primary rainforest. They found that across their study area 68% of the total area of secondary rainforest occurs within 500m of primary forests, 85% within 1.0km, and 91% within 1.5km of primary rainforest.
They found that rainforest regrowth was dominated by smaller patch size classes as the distance from primary rainforest increased. They also found that at a given distance from a given primary rainforest fragment, the proportional area of secondary rainforest was greater where the corresponding primary rainforest fragment was larger.
Another interesting finding was that as distance from primary rainforest increased there was also an increase in the temporal lag between land abandonment and the secondary rainforest achieving 70% canopy closure.
Natural regeneration of rainforest relies on seed dispersal by animals and wind to re-establish native plants. Therefore, for naturalregeneration to be successful it relies on an abundant and diverse source of rainforest seeds nearby. The findings from this study suggest that natural rainforest regeneration is most suited to edge expansion of remnant rainforest patches or stimulating regeneration close to existing rainforest stands.
Their findings underline the need to conserve even modest rainforest patches as seed reservoirs to enable regeneration.
The authors conclude by suggesting that the conservation value of secondary regrowth should be considered more important than previously thought. They go on to suggest promoting and managing secondary regrowth in relation to ecosystem services, biodiversity and climate change.