Succession, climate and neighbourhood dynamics influence tree growth over time: an 87-year record of change in a Pinus resinosa -dominated forest, Minnesota, USA
Question: Resource availability and its influence on tree-to-tree interactions are expected to change over the course of forest stand development, but the rar- ity of long-term data sets has limited examinations of neighbourhood crowding over extended time periods. How do a history of neighbourhood interactions and population-level dynamics, including demographic transition, impact long- term tree growth?
Location: Natural mature Pinus resinosa-dominated forest in northern Min- nesota, USA.
Methods: Using a spatially explicit data set of repeated diameter measurements recorded over an 87-yr period, we modelled the influence of tree-to-tree inter- actions on growth as it varied over time. We also applied maximum likelihood estimation and simulated annealing to examine how inter- and intraspecific competition and the relative importance of neighbour size and distance varied over time and with different climatic conditions.
Results: Crowding had a consistent negative influence on growth, but crowding intensity and importance were dynamic over time and differed between trees that survived the entire study period compared to those that ultimately died. The scaling of neighbour diameter, neighbour distance, and neighbour species (inter- vs intraspecific competition) also varied as demo- graphic transition occurred and longer-lived species assumed greater dominance.
Conclusions: Given observed relationships with moisture stress (based on pre- cipitation: potential evapotranspiration) and maximum temperature, crowding intensity and importance may increase if temperatures rise in the future and water become more limiting. Long-term data sets, such as the record examined in this study, have immense value for testing assumptions about stand dynam- ics, particularly as forests respond to projected shifts in climate and disturbance regimes.