A forest simulation approach using weighted Voronoi diagrams. An application to Mediterranean fir Abies pinsapo Boiss stands

Abstract

Aim of study: a) To present a new version of the forest simulator Vorest, an individual-based spatially explicit model that uses weighted Voronoi diagrams to simulate the natural dynamics of forest stands with closed canopies. b) To apply the model to the current dynamics of a Grazalema pinsapo stand to identify the nature of its competition regime and the stagnation risks it is currently facing.Area of study: Sierra del Pinar de Grazalema (S Spain) Material and methods: Two large plots representative of Grazalema pinsapo stands were used to fit and validate the model (plus 6 accesory plots to increase the availability of mortality data). Two inventories were carried out in 1998 and 2007 producing tree size and location data. We developed a forest simulator based on three submodels: growth, competition and mortality. The model was fitted, evaluated and validated for Grazalema plots. The simulation outputs were used to infer the expected evolution of structural diversity of forest stands.Main results: Vorest has proved to be a good tool for simulating dynamics of natural closed stands. The application to Grazalema pinsapo stands has allowed assessing the nature of the main processes that are driving its development pathway. We have found that the prevailing size-asymmetric competition dominates the self-thinning process in small-sized trees. At the same time, there is an active tree-size differentiation process.Research highlights:• Vorest has proved to be a good tool for simulating natural stands with closed canopies.• The Grazalema pinsapo stand under consideration is currently undergoing a natural process of differentiation, avoiding longterm stagnation.

Predicting suitability of forest dynamics to future climatic conditions: the likely dominance of Holm oak [Quercus ilex subsp. ballota (Desf.) Samp.] and Aleppo pine (Pinus halepensis Mill.)

“…Abies pinsapo is an endangered relict fir, which in the course of the twentieth century has suffered afforestation in some areas (Álvarez 2013), as the management of stands is leading to a process of mortality (Abellanas et al 2016). Abies pinsapo shares with Q. canariensis both a high demand for water and a restricted distribution, and consequently follows a similar trend to the latter in our LR model, although with more drastic consequences.…”

Regeneración de los pinsapares béticos. Análisis de tendencia interanual y estacional del NDVI

“…En este mismo periodo, se han sucedido años húmedos y años secos, y, de hecho, los últimos años se corresponden con un periodo seco. En el caso de la Sierra de Grazalema, el hecho de que la tendencia no fuera significativa permite inferir que estamos ante un pinsapar muy denso, maduro y estable (Arista, 1995;Abellanas et al, 2016).…”

A Novel Model to evaluate Spatial Structure in Thinned Conifer- Broadleaved Mixed Natural Forests

“…The results of grey correlation analyses of the number of trees adjacent to the central tree and its key in uencing factors showed that the average crown width of conifer-broadleaved mixed forests at each thinning intensity (10%, 15%, 20%, 25%, 30%, 35%) had a greater in uence on the spatial extent of structure units when compared to the control forest plot; the crown length factor had higher in uence than the tree height. It has been shown that the allocation of tree organs is strongly related to spatial partitioning and that tree growth grows with the acquisition of canopy space (Abellanas et al, 2016a;Goudie et al, 2009;Moeur, 1993). Our ndings thus provide a theoretical basis for the scienti c determination of the structure units of nurtured mixed conifer-broadleaved forests.…”

“…Both methods have shortcomings which are compensated for by using the non-spatial structure parameters of the stand as weights. The in uence of the diameter at breast height is strong and is thus used to weight the spatial structure units (Aakala et al, 2013;Li et al, 2015), and this has developed into a weighting analysis using tree height, diameter at breast height, and crown (Abellanas et al, 2016b;. This study modi es this weighting analysis by not only adding the crown length attribute to those of diameter at breast height, height, and crown spacing but also making reasonable usage of the crown and stand spacing factors that are related to stand density based on the characteristics of the species in the mixed forests.…”