CONSERVATION ADVISORY SCIENCE NOTES No. 46 NITROGEN CONTENT OF SOILS, CALLUNA VULGARIS, AND SOME NATIVE PLANTS IN TONGARIRO NATIONAL PARK, (1992-1993). (Short Answers in Conservation Science)

Nitrogen levels in soils, shoots of Calluna vulgaris, and a few native plants were measured from areas in Tongariro National Park (T.N.P.). The Calluna was measured in winter and in summer. Associations between soil nitrogen level and plant nitrogen are weak. Comparisons between native plant and Calluna nitrogen levels indicate Calluna is high in nitrogen. Abundance of Phytophagous insects, and insect diversities are positively correlated with nitrogen levels in Calluna but not with soil level. INTRODUCTION. Nitrogen plays a vital role in all protein based living systems; nitrogen containing compounds are essential components of diets of most heterotrophic organisms. Invertebrates are no exception; for herbivorous invertebrates nitrogen is a vital governing factor ruling their growth rates, ultimate size, fecundity, productivity and hence population size and success (Brunsting & Heil 1985, McNeil & Southwood 1978). Correlations between insect abundance or diversity and food plant nitrogen levels have been shown by researchers (McNeil & Prestidge 1982, Prestidge & McNeil 1981, van Der Meijden et al. 1984). These studies, though, considers ' host' plant nitrogen levels affecting insects geared for feeding on those plants and not general insect abundance and diversity in a habitat that may contain much nitrogen, but not, of necessity, many ' host' plants! The approach to studing nitrogen influences in a community may be on a micro or macro scale, depending on the resolution required. Ofen a single plant (single bush effect) and the immediate concentration of nutrients and minerals in the adjacent soil influencing its individual nitrogen content, has a very different bearing on the community (structure and operation) than an ecosystem approach where the total nitrogen of an area or a plant species is held responsible for particular communitity structures (ecosystem effect). I believe that in Tongariro National Park where Calluna has invaded extensively areas of native vegetation ( eg. tussock/herb fields around Pukeonake to Chateau region) the ecosystem may still contain much nitrogen but little as host plant sources, and that single bush characteristics play a more important role, and predict a different structure than the ecosystems. The information gained is compared to English (European) heath systems, with special reference to the effects nitrogen levels have on population growth of Lochmaea suturalis, the proposed biocontrol agent and principle defoliator of Calluna.