Threats to biodiversity continue to increase worldwide and the conservation of biodiversity through in situ and complementary ex situ measures are more important than ever. Here we studied the presence of introduced tree species in New Zealand considered threatened according to the IUCN Red List of Threatened Species. We conducted desktop assessments of tree collections across New Zealand in conjunction with a field assessment of the identity and status of threatened introduced trees in eight regional tree collections, focussing on endangered (EN), critically endangered (CR), and extinct in the wild taxa. A total of 15 CR and 52 EN gymnosperm taxa were recorded for New Zealand representing approximately 38 and 40 % of the world's CR and EN gymnosperms, and a smaller percentage (1 %) of the world's CR and EN angiosperms. Of particular note are the CR Cupressus chengiana var. jiangensis and Widdringtonia whytei, and several EN gymnosperms, including Cupressus guadalupensis var. guadalupensis, Nageia maxima, and Pinus nelsonii, that are considered priority taxa for ex situ conservation by Botanic Gardens Conservation International. The field assessment confirmed the presence of seven CR and 26 EN tree taxa growing in the Canterbury region. Although many of these were present as one or two individual trees, the combined resources of the collections and the presence of several globally rarer and priority taxa indicate a potentially important role of New Zealand's tree collections in ex situ conservation. To fulfill their potential, their protection and health status as well as propagation and rejuvenation should be given urgent attention.

The contribution of exotic plantation forests to the conservation of New Zealand's flora and fauna is a somewhat controversial issue, partly because the establishment of some plantations involved the conversion of indigenous vegetation. Such conversion no longer occurs within the professional forest industry and there is a growing appreciation of the contribution of 'production' land, including plantation forests, to the protection of New Zealand's unique indigenous biodiversity. This paper provides a comprehensive synthesis of information currently available on threatened species known to occur in New Zealand's plantation forests. Based on an evaluation of the published literature, unpublished reports, national threatened species databases, and personal observations we have compiled records of 118 species classified by the Department of Conservation as threatened that occur in plantations. Of these species, 16 are classified as 'Nationally Critical', 17 'Nationally Endangered' and 17 'Nationally Vulnerable', while the majority are classified as either in 'Gradual Decline', 'Sparse' or 'Range Restricted'. We highlight the direct and indirect benefits of plantations to various threatened taxa and draw attention to the missed conservation opportunities that are generated by a lack of understanding and the somewhat 'puritanical' views of New Zealand's mainstream conservation paradigm. We also discuss some of the potential negative consequences of plantations such as their potential function as 'population sinks' and 'ecological traps'. We conclude with a discussion of future research opportunities that aim to improve the conservation value of plantation forests.

The Canterbury Plains have lost most of their pre-Polynesian indigenous vegetation, primarily forest and shrubland. One of the few remaining areas is the 2.3 ha Eyrewell Scientific Reserve which consists mostly of low k (a) over bar nuka (Kunzeo ericoides) forest and a small area of grassland. We assessed the Reserve vegetation using a combination of plots and transect surveys at different times of the year between 2001-2003. For comparison with the Reserve vegetation we also assessed plots in an adjacent grazed k (a) over bar nuka remnant, adjacent cultivated pasture and Eyrewell Forest, a pine plantation. Our study of the Eyrewell Reserve in 2001-2003 found that since an assessment of the Reserve in 1972, 28 indigenous species were no longer present but 14 indigenous species and 48 adventive species were newly recorded. The dramatic invasion of the Reserve is illustrated by the fact that 60% of the 118 species recorded in 2003 were adventives compared to 34% in 1972. Despite this invasion and the loss of indigenous species, Reserve plots still have more than twice as many species as plots in the adjacent pine plantation. The Reserve also included several species of high conservation value such as the "Chronically Threatened" Leptinella serrulata, and the "At Risk" Aciphylla subflabellata, Coprosma intertexta and Pterostylis tristis. Plots in the Reserve grassland and adjacent pasture had the lowest percentage of indigenous species of all habitat types, with the pasture plots having no indigenous vascular plant species. In contrast the understorey of the old pine stands had the highest percentage of indigenous species of any of the habitats and in places was dominated by k (a) over bar nuka up to 4 in tall, indicating that these plantations also have conservation value. Eyrewell Reserve and the few other remaining k (a) over bar nuka remnants in the Canterbury Plains represent an important pool of indigenous species for conservation. Options for the future management of the Reserve are discussed.

The vegetation of Pinus radiata plantation forests in New Zealand was studied to examine how the indigenous flora has responded to this novel habitat. A chronosequence of stands about 5, 16 and 27 years was assessed in each of four different biogeographic regions to test the effects of several stand and site factors on the succession of vascular understorey plant communities. A total of 202 indigenous and 70 adventive vascular plant species were found across all study areas, with considerable geographic variation among forests in species composition, species richness (range 48–135 species), and the percentage of indigenous species (50–86%). Both richness and cover of adventive species decreased significantly over time, whereas richness and cover of indigenous species was highest in the oldest stands, and overall species richness was lowest at mid-rotation. The guild composition changed from dominance of grasses and forbs in young stands to dominance of ferns and understorey trees in mature stands. These temporal changes were accompanied by a decrease in light-demanding pioneer species and an increase in shade tolerant, later seral species adapted to a forest environment. Measurements of the degree of canopy closure in stands with low or high stocking and modelling of temporal changes of canopy closure indicated that these understorey plant dynamics are influenced by changes in light availability as stands age. Despite the successional changes within forests, geographic variation more strongly influenced understorey communities because stands within a forest area were grouped together in DCA and TWINSPAN analyses, along rainfall and temperature gradients. Although the canopy species of such intensively managed plantation forests is an alien element in the New Zealand flora, the sheltered forest environment of older stands allows the establishment of a mostly indigenous forest understorey community with considerable similarities to indigenous forests located nearby.