A silviculture-oriented spatio-temporal model for germination in Pinus pinea L. in the Spanish Northern Plateau based on
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ORIGINAL PAPER
A silviculture-oriented spatio-temporal model for germination in Pinus pinea L. in the Spanish Northern Plateau based on a direct seeding experiment Rube´n Manso • Rafael Calama • Guillermo Madrigal Marta Pardos
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Received: 5 March 2012 / Revised: 3 July 2013 / Accepted: 5 August 2013 / Published online: 25 August 2013 Ó Springer-Verlag Berlin Heidelberg 2013
Abstract Natural regeneration in Pinus pinea stands commonly fails throughout the Spanish Northern Plateau under current intensive regeneration treatments. As a result, extensive direct seeding is commonly conducted to guarantee regeneration occurrence. In a period of rationalization of the resources devoted to forest management, this kind of techniques may become unaffordable. Given that the climatic and stand factors driving germination remain unknown, tools are required to understand the process and temper the use of direct seeding. In this study, the spatio-temporal pattern of germination of P. pinea was modelled with those purposes. The resulting findings will allow us to (1) determine the main ecological variables involved in germination in the species and (2) infer adequate silvicultural alternatives. The modelling approach focuses on covariates which are readily available to forest managers. A two-step nonlinear mixed model was fitted to predict germination occurrence and abundance in P. pinea under varying climatic, environmental and stand conditions, based on a germination data set covering a 5-year period. The results obtained reveal that the process is primarily driven by climate variables. Favourable conditions for germination commonly occur in fall although the optimum window is often narrow and may not occur at all
Communicated by M. Meincken. R. Manso Laboratoire d’Etude des Ressources Foreˆt-Bois, INRA Centre de Nancy, 54280 Champenoux, France R. Manso (&) R. Calama G. Madrigal M. Pardos Departamento de Selvicultura y Gestio´n de Sistemas Forestales, CIFOR-INIA, Carretera de La Corun˜a km 7.5, 28040 Madrid, Spain e-mail: [email protected]; [email protected]
in some years. At spatial level, it would appear that germination is facilitated by high stand densities, suggesting that current felling intensity should be reduced. In accordance with other studies on P. pinea dispersal, it seems that denser stands during the regeneration period will reduce the present dependence on direct seeding. Keywords Empirical modelling Two-step regression Regeneration Stone pine
Introduction Pinus pinea is an essential species in Mediterranean ecosystems, its timber and edible seed production generating important economic benefits to the local population. In addition, the species plays a valuable ecological role since it frequently occupies sites with challenging climatic and edaphic conditions (Mediterranean climate and highly sandy soils) where few arboreal species persist. Such conditions are common throughout the Spanish Northern Plateau (Prada et al. 1997), where there are more than 50.000 ha of managed P. pinea f
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