New urban ecological restoration techniques: Testing the short-term effects of adding deciduous leaf litter and plant residue compost on topsoil quality and native herbaceous plant establishment

摘要

Urban expansion has led to native habitat destruction. Meanwhile, cities produce large quantities of plant residue wastes. To explore the potential to use plant residues to restore native habitats in cities, this thesis compared the short-term effects of deciduous leaf litter and plant residue compost on topsoil quality and seeded native herbaceous plant establishment. To determine if natural plant colonisation alone can restore native plants, the thesis compared the establishment and ecological characteristic and diversity of naturally colonised plant species on the barren surface of modified and unmodified soil. Following three months of repeated measurements after amendment, compost significantly increased soil moisture, organic matter, extractable NPK, and significantly decreased soil pH and bulk density. The decrease in soil pH due to incorporating compost with higher pH than the receiving soil showed that compost may not restore soil pH in a predictable manner. The average number and median shoot lengths of seeded native plants on compost-amended soil were significantly higher than those on control three months after germination. Compost may therefore be used for purposes such as quick establishment of dense tall native plant cover. Conversely, leaf litter did not significantly change the abovementioned soil properties in the short term. However, the average number of seeded native plants on leaf litter-amended soil three months after germination was significantly higher than control and insignificantly different from that on compost-amended soil. At that time, seeded native plants on leaf litter-soil exhibited stunt growth relative to other treatments. Leaf litter might then be used to establishing slow-growth native lawns for urban native landscaping practices. But this technique requires further refinement.Above barren soils across experimental treatments, exotic weeds consisted mostly of the naturally colonised plants. This means natural plant colonisation may not effectively restore native plants. There was no significant difference in the colonising plant average species richness and diversity across treatments. The steepness of the colonising species’ rank-abundance curves were similar between treatments. Thus, natural plant colonisation on amended or un-amended soil could not lead to the establishment of particular plant species. Due to soil nutrient-enrichment, Canada thistles (Cirsium arvense) occupied a greater proportion of colonised species on compost-treated soil than the most dominant colonised species on other types of soil. Thus, compost amendment of soil may not restore plant communities with high species diversity. Moreover, the average number of the colonising weeds above compost-amended soil was significantly higher than control, while that of weeds above leaf litter-amended soil was significantly lower than control three months after site preparation. At that time, weeds on leaf litter-amended soil were significantly shorter than those on compost-amended soil and control. This means leaf litter could impede exotic weeds while compost had the reverse effect. Compost should only be used to establish native plants if exotic weeds are removed or when the site soil seed bank and adjacent land contain few exotics. While this thesis documented the different short-term effects of plant residue compost and deciduous leaf litter on soil and plants, long-term investigations may find potentially different applications for the different types of plant residues in native plant restoration projects with different purposes. Reusing plant residues differentially could mean that composting may not always be necessary in plant waste management and urban ecological restoration may help to reduce waste output from cities.