Māori practitioner knowledge indicates a shift in forest fruit biomass and phenology over 75 years

Rapid alterations in plant and animal phenology driven by global climate change and rising temperatures can have far-reaching consequences for cultural and ecological systems. We documented changes, and mechanisms behind the changes, in fruit biomass and phenology in mixed podocarp-hardwood forests in the central North Island of New Zealand since the 1950s using the traditional knowledge (herein referred to as mātauranga) of Indigenous Māori (Tūhoe Tuawhenua and Ngāti Whare) forest practitioners. We also explored the likely cascading consequences of alterations in fruiting systems for forest frugivores, below-ground subsystems, local livelihoods, and language. Practitioners reported that the frequency of fruiting, crop size, and individual fruit size and quality declined significantly over the last 75 years, with the timing of fruit ripening often delayed by three months. A general warming trend, combined with less frequent and later frosts, and increased weather variability such as strong wind events, were identified as mechanisms that have impacted fruiting. Alterations in fruit biomass and phenology have also adversely impacted the body condition, breeding rates, and abundance of kererū | New Zealand pigeon (Hemiphaga novaeseelandiae) and feral pigs (Sus scrofa), two important food species for the community in the forest. Practitioner estimates of historic fruit inputs suggest that there were substantial nitrogen (N) returns to the below-ground subsystem from fruit that were 1–2 orders of magnitude higher than those reported from forest fruit fall elsewhere, and which are now severely reduced. The reduction in nutrient inputs and simple carbohydrates (e.g. sugars) in the fruit pulp to the soil is likely to have greatly impaired forest soil microbial activity, earthworm densities, and soil decomposition processes and rates, and ultimately the supply of soil nutrients for trees. Retention of mātauranga and nomenclature related to fruit are important for comprehension of past ecological states, and for future customary management goal setting and decision-making.