Species wood density and the location of planted seedlings drive early-stage seedling survival during tropical forest restoration

Abstract

The success of restoration projects is known to vary widely, with outcomes relating to numerous biotic and abiotic factors. Though many studies have examined the factors associated with long-term restoration success, few have examined which factors impact the establishment of restoration plantings. In Australia's Wet Tropics, we used a large replicated restoration experiment to assess seedling survival for 24 native rainforest species commonly used in local restoration efforts. The experiment allowed for a rigorous assessment of the effects of species functional traits, planting conditions, and landscape- and local-scale biotic and abiotic factors on seedling survival. This study reports on seedling survival between three different time periods of 0–4, 4–9 and 9–31 months post planting. The probability of seedling survival was influenced by multiple factors, varying in importance over time. Across the whole study period, seedlings with high wood density and which were planted closer to intact forest consistently displayed the highest probabilities of survival. Transient factors affecting seedling survival across the three time periods included plot aspect (0–4 months only), the identity of the planter and slope (4–9 and 9–31 months). Overall, species survival did not differ between the low (6 species) and high (24 species) diversity treatments, but was significantly lower in monocultures of Flindersia brayleyana by the end of the study. We demonstrate that early-stage seedling survival depends on species wood density and planting location. Our results support the use of species with more conservative growth strategies when limited funds are available for follow-up plantings. High wood density species had significantly higher survival than lower wood density, early successional species typically used in rainforest restoration plantings. Synthesis and applications. Our study highlights the importance of wood density and landscape structure to the initial survival of rainforest plantings. Factors influencing seedling survival shifted over time but, most importantly, our results highlight that, when planting into abandoned pastures, it may be preferable to select species with higher wood densities to maximize survival during the crucial early stages of establishment and growth.