A silviculture-oriented spatio-temporal model for germination in Pinus pinea L. in the Spanish Northern Plateau based on a direct seeding experiment

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 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.

‘Climatic factors control rodent seed predation in Pinus pinea L. stands in Central Spain’

“…In the case of P. pinea, the 'safe' period resulting from this strategy and the time where germination is possible (early fall) overlap (Manso et al 2013a, b). However, germination conditions are highly strict and their timing may vary every year (Manso et al 2013b). As a result, predation may seriously limit subsequent establishment in years of late germination.…”

“…However, although seed harvesting restrictions are imposed to favour seed rain, natural regeneration rarely succeeds (Calama and Montero 2006). This failure may be explained by the following: masting habit and lack of synchrony with regeneration fellings (Calama et al 2011;Manso et al 2012); the species' gravity-based seed dispersal strategy, resulting in patchy seed distribution in managed, open stands ; and a narrow range of adequate climatic conditions for germination, which determines a low probability for seedling establishment in the long term (Manso et al 2013b). However, the impact of plant-animal interactions on regeneration remains unknown.…”

Natural regeneration in Iberian pines: A review of dynamic processes and proposals for management

“…Large interannual variability in germination rates, conditioned to the occurrence of this optimal conditions, is observed. Over a 4 years study, germination rates varied between 9% and 90%, with two years showing autumn germination Ruano et al (2009) events, one year with spring germination events, and one year with almost no germination at all (Manso et al, 2013a). Moreover, extremely poor overstory cover leads to low probabilities of germination.…”

Alternative approaches to assessing the natural regeneration of Scots pine in a Mediterranean forest

“…Natural forest regeneration is a key process in ensuring forest sustainability (Lucas-Borja 2014). However, in the Mediterranean basin, natural regeneration is hampered by the summer drought, high summer temperatures, long intervals between good seed crops, the presence of livestock and the existence of a too dense herb and litter layer (Barbeito et al 2011;Calama and Montero 2007;Manso et al 2013;Pardos et al 2007). Therefore, understanding the dynamics, patterns and factors involved in the success or failure of regeneration and interactions at the seedling level can provide foresters with the fundamental knowledge required for decisionmaking in forest management (Lucas-Borja 2014).…”

“…Explanatory spatial covariates that influence recruitment patterns have also been incorporated into different types of recruitment models, as explanatory variables. The covariates most used are soil nutrients and/or soil moisture (Barbeito et al 2009), light availability (Adili et al 2013;Fyllas et al 2008), environmental conditions (Rathbun and Fei 2006) and stand structure (Manso et al 2013). Vertical and horizontal forest structures determine light availability and, therefore, regeneration dynamics (Catovsky and Bazzaz 2002;Montgomery 2004) and the development of the stand (Boyden et al 2005;.…”