Species Interactions in the Dynamics of Even- and Uneven-Aged Boreal Forests

Abstract

Many boreal tree stands are neither clearly even-aged nor clearly uneven-aged. The stands may undergo a series of stages, during which an even-aged stand is transformed into two-storied mixed stand, and finally to multistoried or uneven-aged stand structure. The species composition often changes during the succession of stand stages. This study developed models for stand dynamics that can be used in different stand structures and species compositions. The model set consists of species-specific individual-tree diameter increment and survival models, and models for ingrowth. Separate models were developed for Scots pine, Norway spruce, and hardwood species. The models were used in a growth simulator, to give illustrative examples on species influences and stand dynamics. Methods to simulate residual variation around diameter increment and ingrowth models are also presented. The results suggest that mixed stands are more productive than one-species stands. Spruce in particular benefits from an admixture of other species. Mixed species improve diameter increment, decrease mortality, and increase ingrowth. Pine is a more beneficial admixture than birch. Simulations showed that uneven-aged management of spruce forests is sustainable and productive, and even-aged conifer stands growing on medium sites can be converted into uneven-aged mixed stands by a series of strong high thinnings.

Stand management optimization – the role of simplifications

“…One simplification was that growth variation around model prediction was not simulated, although it would have an impact on the simulation results (Miina 1993;Pukkala et al 2013). The main influence would be faster differentiation and wider variation of tree size.…”

“…The further development of trees was predicted with the models of Pukkala et al (2013). Their model set consists of individual-tree diameter increment model, individual-tree survival model, and models for ingrowth.…”

Optimal nitrogen fertilization of boreal conifer forest

“…The following relationship was found: After finding this relationship, the growth response was simulated as follows. First, the volume increment of the stand without fertilization was calculated using the model set of Pukkala et al (2013). Second, the additional volume increment obtained from fertilization was predicted using the model of Kukkola and Saramäki (1983).…”

“…The models of Kukkola and Saramäki (1983) give the response separately for different years. In the current study, growth was simulated in 5-years steps because the used models (Pukkala et al 2013) predict 5-year growths. When calculating the response, 3 rd year since fertilization was used for the first 5-year period and 8 th year for the second 5-yeafr period.…”

“…To find the relationship between additional volume increment (obtained from the response model) and additional diameter increment (required in simulation and optimization) the growth of several pine and spruce stands growing on different sites was simulated using individualtree models (Pukkala et al 2013). The obtained results for volume and diameter increment were used to calculate the relationship between volume growth multipliers and diameter growth multipliers.…”