Abstract. Generalized additive models (GAMs) are a non‐parametric extension of generalized linear models (GLMs). They are introduced here as an exploratory tool in the analysis of species distributions with respect to climate. An important result is that the long‐debated question of whether a response curve, in one dimension, is actually symmetric and bell‐shaped or not, can be tested using GAMs. GAMs and GLMs are discussed and are illustrated by three examples using binary data. A grey‐scale plot of one of the fits is constructed to indicate which areas on a map seem climatically suitable for that species. This is useful for species introductions. Further applications are mentioned.

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▪ Abstract  Conservation in New Zealand is failing to halt an ongoing decline in biodiversity. Classical problems of ecosystem loss and fragmentation have largely been countered in some regions by reservation of 30% of total land area. Unsustainable harvesting of native biodiversity has stopped; indeed harvesting of terrestrial species is rare. In contrast, marine reserves do not cover even 1% of the managed area, and harvest of native species, some of it unsustainable, are a major industry. Introduced pests, especially mammals, are the overwhelming conservation problem. Legislation, management, and considerable public opinion is based on preservationist ideals that demand the sanctity of native land biodiversity. Considerable success in threatened species management, island eradications, and mainland control of pests is increasing opportunities for restoration. New legislation is increasingly built on concepts of sustainability and offers the opportunity for integrating conservation, use, and development. Realization of these opportunities requires greater understanding of the relative merits of preservation versus sustainability, the dynamics and costs of pest control, the need for ecosystem processes in addition to individual species, and the involvement of people, especially the rights of indigenous Maori. Understanding marine environments and linking attitudes to land and sea is also a challenge.

Soil compaction can affect seedling root development by decreasing oxygen availability and increasing soil strength. However, little quantitative information is available on the compaction tolerances of non-crop native species. We investigated the effects of soil compaction on establishment and development of two New Zealand native species commonly used in restoration programmes; Cordyline australis (Agavaceae) (cabbage tree) a fleshy rooted species, and Leptospermum scoparium (Myrtaceae) (manuka) a very finely rooted species. Seedlings were grown in a range of soil compaction levels in growth cabinet experiments. Low levels of soil compaction (0.6 MPa) reduced both the number and speed of C. australis seedlings penetrating the soil surface. In contrast, L. scoparium seedlings showed improved establishment at an intermediate compaction level. Root and shoot growth of both species decreased with increasing soil strength, with L. scoparium seedlings tolerating higher soil strengths than did C. australis. Despite these results, soil strength accounted for only a small amount of variation in root length (R 2 < 0.25), due to greater variability in growth at low soil strengths. Soil strengths of 0.6 MPa are likely to pose a barrier to C. australis regeneration. This is consistent with adaptation to organic and/or soft, waterlogged soils. Active intervention may be necessary to establish C. australis from seed on many sites previously in farmland.

Abstract. A quantitative study of relationships between forest pattern and environment in the central North Island, New Zealand, is based on forest composition data from ca. 2000 existing plots distributed throughout the forests of the region. Estimates of mean annual temperature, rainfall, and solar radiation are derived for each plot from mathematical surfaces fitted to climate station data. Estimates of the depth of the last major rhyolitic eruption, (Taupo Pumice, ca. 130 AD) are derived from isopach maps. A classification procedure is used to identify broad compositional groups. Generalised linear models are used to examine relationships between major species and climatic and other physical factors. Significant relationships are identified between the distributions of both plot groups and species, and climate, vulcanism, topography and drainage. Among these factors, temperature and/or solar radiation are indicated as major determinants of the regional forest pattern, with rainfall, topography, and drainage acting at a secondary level. The role of the Taupo Pumice eruption is more difficult to interpret, and its effects seem to have been greatly influenced by topography. Deep extensive deposits of tephra on flat‐to‐rolling sites close to the eruption centre have probably favoured the current dominance of these sites by more rapidly dispersing conifers. In contrast, on adjacent steep sites where forest destruction was likely to be less severe, slow‐dispersing Nothofagus species are largely dominant. Further work is needed to understand the factors favouring conifer dominance of the central basins and the degree to which Nothofagus species might expand their range in the future.