No. 1099

Title:

Fine-scale synchronicity in the growth chronology of an Abies sachalinensis population and its links to forest patch dynamics – novel applications of time-series and spatial analyses

Author(s):

Shimatani, Ichiro K (The Institute of Statistical Mathematics);
Kubota, Yasuhiro (University of the Ryukyus)

Key words:

dendroecology, disturbance, gap, Kalman filter, patch mosaic, smoothing, state-space model

Abstract:

    As a result of small-scale disturbance, spatio-temporal synchronicity and variability in tree growth chronology play a central role in producing the fine-scale patch-mosaic structure of an old-growth forest. This paper examines forest patch dynamics using dendroecology in a long-term forest monitoring plot in a coniferous/deciduous mixed forest, in northern Japan. Increment cores were taken from all Abies sachalinensis trees in the plot that were taller than 2 m. We applied a time-series smoothing technique (the Kalman filter) to 386 A. sachalinensis ring series. The smoothing process eliminated short term fluctuations and highlighted growth trends over the mid-term (5 to 30 years), which allowed us to identify release events and to conduct fine-scale spatial analyses. Primarily based on cluster analysis, we first specified a scale of 10 m as the diameter of gaps created by single tree-falls, the smallest gap unit. Then we classified released A. sachalinensis trees into spatially separated groups which we interpreted as representing old gaps in the canopy. We calculated the number of gaps and the distribution of gap diameters. On average, 1.12 gaps were created per ha per year, and their diameters were skewed to the smallest size, namely 10 m. The most extensive disturbance during the last five decades resulted in the creation of 10.7 gaps per ha over five years, with a maximum diameter of 50 m. Out of 87 gaps, 82 contained more non-released than released A. sachalinensis trees, implying imperfect synchronization. Two detailed descriptions of the processes underlying the formation of A. sachalinensis patches demonstrated that the 20-30 m diameter patches examined were actually made up of smaller patches associated with different disturbances and different responses by understory trees. The variation in disturbances and in the responses of understory trees contributed to the creation of the variable patch-mosaic structure. Quantifying such stochastic uncertainty through statistical modeling is crucial for advancing the understanding of forest dynamics.