Climate Change and the Phenology and Distribution of Native Orchids in Aotearoa New Zealand

<p><strong>In this thesis, phenological and distribution changes are investigated in 21 orchid species in Aotearoa New Zealand. This thesis was the first attempt to detect past phenological changes and to use Species Distribution Models (SDMs) to predict future changes of plants in Aotearoa New Zealand. In Chapter 2, herbarium specimens and photo observations from iNaturalist, the New Zealand Plant Conservation Network (NZPCN), and New Zealand Native Orchid Journal (NZNOJ) were used to create a dataset of records up to 104 years old for each species. Generalised Additive Models (GAMs) were used to test for the effect of year on flowering date, which would imply changing flowering times. Analyses showed that flowering times of 13 species (61.90% of the 21 study species) were occurring earlier in 2024 than in 1920 or the earliest year on record. In Chapter 3, the same dataset was combined with a mixed method of background and target-background pseudo-absence records, to construct SDM models to predict changes in 2081-2100, under four Shared Socio-economic Pathways (SSPs). The suitable habitats of four species (19.05%) were predicted to increase, while the remainder were predicted to decrease: eight species (38.10%) of which were montane, alpine, or subantarctic species; three species (14.29%) were from humid environments; and five species (23.81%) had unexplained declines, possibly caused by modelling limitations. Both of these findings suggest that there has or will be an impact on orchid populations, which may risk their long-term persistence. A decline in distribution due to reduced habitat suitability will results in small and fragmented populations, with wider impacts on biodiversity. Concurrent distribution and phenological changes could result in mismatches between some orchid species and their pollinators, threatening reproductive success. Finally, a number of initiatives are suggested that could improve the resilience of populations to the impacts of climate change, including habitat modification and assisted migration. The results of this study have improved the understanding of climate change impacts on the flora of Aotearoa New Zealand, although further research is needed.</strong></p>