Quantifying soil, microbial, and plant community changes following wetland restoration on private land

Abstract

<p>Extensive global and national wetland loss has reduced ecosystem services to people and undermines the sustainability of ecosystems. Restoration projects aim to regain the biophysical conditions of remnant wetlands that produce an abundance of ecosystem services. Ecological restoration practices manipulate community succession to enhance ecological functions, and these different successional stages may be reflected in the soil physio-chemical characteristics, plants, and soil microbes, which in turn produce a variety of ecosystem services. Considerable potential for wetland restoration on private property exists in New Zealand, but it remains unknown how successful restoration is when undertaken through a landholder’s own prerogative. Relative to restoration of public land, private restoration projects are often small scale, personally funded and preference driven. In this thesis, I quantify the outcomes of small-scale private wetland restoration projects by measuring changes in plant and soil microbial communities, and soil physiochemical characteristics. I explore the relationships among variation in plant, soil and microbial datasets and test for causes of this variation. Using a paired sampling design, I sampled 18 restored wetlands and 18 unrestored wetlands on private property in the Wairarapa region. I used a Whitaker plot design to sample wetland plant communities at multiple scales and took soil samples that I analysed for physio-chemical properties. Additionally, I quantified the biomass and community composition of the microbes in the soil samples using phospholipid fatty acid analysis. In my second chapter, I use linear mixed-effect models, principal components analysis, and non-metric multidimensional scaling to ask: How does wetland restoration alter the plant community, soil physio-chemical characteristics, and the soil microbial community? In my third chapter, I employ Procrustes analysis to look at the association of variation in plants, microbes, and soil characteristics to explore whether successional processes of these attributes are concurrent within wetlands. I then use hierarchical cluster analysis to determine which of the wetlands are at similar successional stages and identified site contexts and restoration treatments that were in common among similar wetlands. These analyses provide insight to the conditions that advance successional processes in restored wetlands. Specifically, I ask 1) How do plant, microbial, and soil characteristics co-vary during wetland restoration? 2) How do indicators of wetland succession respond to restoration? 3) Are different restoration practices and site contexts influencing wetland outcomes during restoration? Private wetland restoration enhanced succession in plant, soil, and microbial properties towards those more similar to undisturbed wetland conditions. Specifically, restoration added ~13 native plant species, increased totalfungal and arbuscular mycorrhizal biomass, and total microbial biomass by 25%. Restoration increased soil moisture by 93%, soil organic carbon by 20%, and saturated hydraulic conductivity by 27%. It also reduced bulk density by 0.19 g-1 cm3 and plant available phosphorus (Olsen P) by 23%. Procrustes analysis revealed a lack of congruence in the recovery of plant, microbial, and soil indicators of succession, signifying that the plant community succeeded faster than the microbial community and soil characteristics. Variation in soil and microbial properties separated restored wetlands into two groups of early and later succession wetlands, which was independent of the number of years since restoration began at the sites but corresponded to elements of wetland hydrology. Soil and microbial characteristics in hydrologically connected wetlands recovered more quickly following restoration than hydrologically isolated wetlands. Private restoration increased spatial heterogeneity of outcomes at the plot scale, which depended on site factors. My data suggests that private wetland restoration is effective in increasing plant, soil, and microbial characteristics that produce ecosystem services. Additionally, wetland restoration increased environmental heterogeneity and the capacity for ecosystem service delivery, which may contribute to increased resilience of the Wairarapa landscape.</p>