Trees and people: Relationships between tōtara trees and their environment

Abstract

This research addresses significant gaps in the literature concerning Podocarpus totara (tōtara), a foundational taonga species in Aotearoa New Zealand. The study uniquely integrates Western Science techniques alongside Mātauranga Māori (Māori knowledge) to explore the physiology and cultural significance of this key endemic gymnosperm.

The Western Science component involved quantitative measurements of instantaneous leaf gas exchange, photosynthetic response curves to light, CO2, and vapour pressure deficit (VPD), and analysis of the stable carbon isotopic composition of leaf-respired CO2 (δ13CRl). Measurements were conducted on adult tōtara over seven months (August 2024 to March 2025) across two distinct growth environments: individual, fully exposed trees and trees growing in stands of varying densities. Key photosynthetic parameters, including net photosynthetic rate (A), stomatal conductance (gs), and maximum carboxylation rate (Vcmax), were quantified. Physiological results showed that tōtara growing individually exhibited significantly higher net photosynthetic rates than those in stand environments (1.15 μmol CO2 m-2 s-1 versus 0.47 μmol CO2 m-2 s-1), likely due to greater irradiance and reduced competition for light. Overall values were low, consistent with other Podocarpaceae species. Analysis of δ13CRl provided an integrated signal of carbon-water dynamics, revealing a general trend of values becoming less negative from spring to autumn. This trend is consistent with stomatal closure in response to water limitation and increased VPD during the warmer months (summer drought 2024-2025). No statistically significant difference was found between individual and stand trees over the measurement period. Furthermore, a simple model designed to predict A and gs failed to accurately correlate with observed field data, potentially because it was parameterized using data from saplings grown under optimal greenhouse conditions rather than adults subject to field variability.

The Mātauranga Māori component explored tōtara’s significance through a cultural lens. In te ao Māori (the Māori world), tōtara is considered paramount and is connected to humans through whakapapa (ancestry/genealogy) as children of Tāne-Mahuta, the god of the forest; tōtara is considered the tuakana (older sibling) to humans. The species has historically been crucial for crafting waka (canoes) and marae carvings, and its attributes, such as wisdom and generosity, are honored in whakataukī (proverbs). Semi-qualitative techniques were used to respectfully ‘interview’ six adult tōtara, treating each tree as an ‘expert’ to foster a journey of personal and cultural reconnection for the author. This research highlights the fundamental philosophical contrast between the individualistic, objective nature of Western Science and the holistic, entangled perspective of Te Ao Māori, where humans are part of nature. The approach successfully employed techniques and customs from both knowledge systems side by side, aiming to create new insights while ensuring that the distinct ethics and special character of each worldview are maintained and acknowledged. The study advocates for continued research at this interface to enhance understanding of the interface and foster increased communication and respect in practitioners of both worldviews.