New Zealand forest dynamics: a review of past and present vegetation responses to disturbance, and development of conceptual forest models.
New Zealand forests have been and are shaped by a suite of disturbance types that vary in both their spatial extent and frequency of recurrence. Post-disturbance forest dynamics can be complex, non-linear, and involve multiple potential pathways depending on the nature of a perturbation, site conditions, and history. To capture the full range of spatial and temporal dynamics that shape forest ecosystems in a given area, we need to use and synthesise data sources that collectively capture all the relevant space-time scales. Here we integrate palaeoecological data with contemporary ecological evidence to build conceptual models describing post-disturbance dynamics in New Zealand (NZ) forests, encompassing large temporal and spatial scales. We review NZ forest disturbance regimes, focussing primarily on geological and geomorphic disturbances and weather-related disturbances but also considering the role of anthropogenic disturbance in shaping present-day NZ forests. Combining information from 58 studies of post-disturbance forest succession, we derive conceptual models and describe forest communities and forest change for conifer-angiosperm (including kauri forest), and beech forests (pure and mixed). The methods used in these studies included chronosequences, assessments of stand dynamics, longitudinal studies, palaeoecological reconstructions, and comparisons with historical observations; the temporal range of the studies extended from 15 years to millennia (c. 14 000 years BP). Our models capture the generalities of NZ forest dynamics, and can be used to support modelling and help guide decision-making in areas such as ecosystem restoration. However, this generality limits model resolution, meaning the models do not always portray the specific features of individual sites and successional pathways. There is, therefore, scope for more detailed, site-specific development and refinement of these frameworks. Finally, our models capture successional pathways and native plant communities from the past and present; invasive species, climate change, and exotic plant pathogens are likely to alter future forest dynamics in novel and unpredictable ways. These models, however, provide us with baselines against which to interpret and assess the impacts of such effects on forest composition and processes.