The ecological filters in restoration practice

The post provided by Paweł Waryszak

This post refers to the article Best served deep: the seedbank from salvaged topsoil underscores the role of the dispersal filter in restoration practice by Waryszak et al. published in Applied Vegetation Science (https://doi.org/10.1111/avsc.12539).

Vegetation in fire-prone ecosystems has evolved a number of mechanisms to survive in these hot, volatile and harsh environments (Pausas & Bradstock, 2007). One of the mechanisms that enables regeneration of vegetation after fire in such environments is to produce seeds that can stay dormant in the soil (forming a soil seedbank) between the inevitable fire events (often for a very long time) to produce seedlings postfire. If there is a long interval between fires these seeds accumulate in high numbers in topsoil. Rehabilitation of areas after mining has long used soil seedbanks to improve the success of revegetation. In urban areas development of sites for housing and other uses usually requires removal of the natural system, including the vegetation and much of the topsoil. In fire-prone environments, the seedbank in the soil is a valuable resource that can be used to rehabilitate other degraded urban sites in the same way as in mining contexts.

This is exactly the scenario that led to the Banksia Woodland restoration study and Paweł’s PhD research project. Banksia Woodland is a fire-prone ecosystem in the Southwestern Australian floristic region, one of the world’s biodiversity hotspots (Myers et al. 2000). A commercial company that needed land to build a new airport facility agreed to offset the clearing of remnant Banksia Woodland (20 ha) at the development site by transferring topsoil (approximately 750 tonnes per hectare) and the rich seedbank contained therein, to 16 ha of degraded post-agricultural land in an adjacent outer urban area. Establishment of plants on a degraded site can be framed in the context of abiotic and biotic controls that influence the success of plant growth – these can be considered ecological filters. The spread and treatment of transferred topsoil were pre-defined in the framework of manipulating these ecological filters. The aim was to find the most successful restoration method, using transferred topsoil, that could reinstate a diverse ecosystem similar to the one that had been cleared for development. Following manipulation of three ecological filters on the restoration sites (abiotic, biotic and dispersal), we examined seedling emergence and survival, and species and functional group composition. Overall we found almost two times more native species seedlings in the topsoil when compared to species found in the cleared reference Banksia Woodland. There were 90 native species recorded in the original Banksia woodland of which 54 were found emerging from transferred topsoil. You may wonder how we ID-ed the little “baby-seedlings”?

We were lucky to have experts on seedling identification to help with fieldwork, and glasshouses on campus where we could grow any mystery seedlings until they revealed their true identity. See below for a beautiful photo collection by one of our co-authors, Mark Brundrett. Read the paper to learn what had happened to seedlings by the end of the last study season in autumn 2014.

References:

• Myers, N., Mittermeier, R.A., Mittermeier, C.G., Gustavo, A.B.d.F., & Kent, J. (2000). Biodiversity hotspots for conservation priorities. Nature, 403, 853–858. https://doi.org/10.1038/35002501
• Pausas, J.G., & Bradstock, R.A. (2007). Fire persistence traits of plants along a productivity and disturbance gradient in Mediterranean shrublands of south-east Australia. Global Ecology and Biogeography, 16, 330–340. https://doi.org/10.1111/j.1466-8238.2006.00283.x

Brief personal summary: Research of Paweł Waryszak centres around the environmental and data science with a particular focus on plants. Before joining the Blue Carbon Lab (Deakin University, 2018), Paweł received PhD degree from Murdoch University (Western Australia) in 2017 after working on a research project presented in this paper.