Biodiversity, biosolids and bioindicators in Pinus radiata D. Don planted forests
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
The global issue of biodiversity was addressed at a local level in this thesis, which examined the effects of a biosolids application programme on the diversity of soil and litter arthropods in Pinus radiata D. Don planted forests in mid Canterbury, New Zealand. A taxonomic inventory of selected sites not only added to the sparse records of entomological data for similar habitats across New Zealand, but also enabled the development of a predictive model for comparison and validation in forward research. Evidence was sought for biosolids-mediated effects in the field on (i) the functional diversity of the arthropod assemblage, (ii) Shannon-Wiener diversity (H') and (iii) an ecologically relevant, invertebrate bioindicator. This novel bioindicator, the larval cranefly Leptotarsus spp. (Diptera:Tipulidae) was further used in a laboratory manipulation in an attempt to quantify the ecological relationship between the genus and soil physical properties. It was then subject to chronic toxicology tests to explore the histological effects of dietary uptake of Cu and Zn. Damage to the gut tissues and a differential effect on the architecture of the fat bodies was shown by histochemistry and light micrography. This evidence providing Support for the "scope for growth" hypothesis, which suggests the allocation of energy to detoxification may impact on an organism's energy reserves, thus affecting growth and development. The larval cranefly Leptotarsus spp. is recommended as a pliable and responsive organism for chronic metal toxicity testing. No support was found for the general hypothesis of a biosolid-mediated effect on arthropod functional diversity at the community level or on the diversity (H') of species. However, there was unequivocal evidence of a significant negative effect on the abundance of the larval cranefly Leptotarsus spp. in the field where dewatered biosolids are applied at rates beyond 400 kg N/ha. It was predicted that cranefly species with a brachypterous female would most likely be affected in forests receiving biosolids applications above 400 kg N/ha. The four cranefly species identified from the study sites were the sale representatives of the myceto/geophagic functional group. Although biosolids applications are likely to constrain both the local diversity and abundance of craneflies, the species redundancy hypothesis predicts ecological processes are unlikely to be affected. Laboratory manipulations failed to show linkage between cranefly larval abundance and their contribution to the generation of porous space in the soil, although these larvae are expected to mediate other soil-related processes, such as the redistribution of fungal inoculants. Arthropod diversity under P. radiata is dominated by generalist species. Greater than 50% of the arthropods trapped were indigenous. The sampled forests clearly provide a refuge within the agricultural mosaic and contribute to the retention of local biodiversity. The trophic structure of the arthropod assemblage was dominated by predatory species. A positive relationship between species diversity (H') and the stage of development of a stand was best described by a logarithmic curve, indicating diversity (H') increased most rapidly during the first (approx.) 10 years of forest establishment. The suites of indicator species identified as significantly indicative of the P. radiata habitat are expected to simplify future assessment at the long-term monitoring sites by offering an investigative tool for the non-specialist. This thesis provides information on the community structure of a highly modified habitat which is of interest to both entomologists and forest managers. As well as giving information on seasonal abundances in relation to trapping methodologies, it provides baseline data and predictive models useful for comparing long-term effects and suggests appropriate bioindicator species as tools for straightforward and cost-effective monitoring in the future. In practice, the main results demonstrated that although biosolids-mediated effects in the Pinus habitat were effectively quantified at the level of genus, forest managers can have a high level of confidence that a significant biosolids-mediated effect on invertebrate biodiversity at the community level is unlikely, at least in the short term, at advised rates of application.