Sims, A., Kangur, A., Hordo, M., Kiviste, A., Jõgiste, K and Gadow, K.v. 2009. Tracking Disturbance-induced Changes in Stand Development at Irregular Measurement Intervals in the Järvselja Forest Experiments.   Baltic Forestry, 15 (2): 151-160

Long-term sample plots have been used to study pathways of succession, and its mechanisms and causes. These observations are relevant not only to communities protected from human interference, but also to managed forests, where the objective is to explain response patterns following specific harvesting operations. The establishment and maintenance of a series of permanent plots requires a firm commitment beyond short-term economic fluctuations and political changes; nevertheless, such long-term experiments may be abandoned prematurely because of a lack of funding or changing policies. One aspect which has received little attention in the past is the “revival” of previously abandoned field plots. This paper analyses data from the Järvselja long-term forest experimental field plots which were abandoned in 1959 and “revived” in 1995 and 2004. This study distinguishes between two kinds of disturbance: natural and anthropogenic. The impacts of both kinds of disturbance are evaluated in terms of weight (quantity of biomass) and type (relative size of outgoing trees). Finally, the study evaluates density-dependent mortality or self-thinning using Reineke’s limiting line and Nilson’s stand sparsity. Our analysis found Nilson’s approach better suited for interpreting the limiting relationship in mixed forests and for estimating maximum density for different stand and site types; therefore, this topic will be pursued in future studies based on the extensive database of the Estonian Forest Research Plots Network.

Key words: long-term forest experiments, measurement gap, Reineke’s limiting line, Nilson’s stand sparsity