Literature review

Pinus pinea, or stone pine, in terms of forest cover, is the 6th most important forest tree species in Portugal, having in 2006 an estimated area of 83,900 ha. It is a native tree species of Portugal and is socially important, in particular in the region of the Sado river valley, where there is a long tradition of its culture, which creates local employment (ANSUB 2005). In addition, of the most important Portuguese forest tree species, Pinus pinea had the largest increase in planted area (Autoridade Florestal Nacional 2010) since 1995. Internationally Portugal has the second largest area of Pinus pinea forests of any country, after Spain which has an estimated area of 456,600 ha (Ministerio de Agricultura Pesca y Alimentación 2007). Together the countries of the Iberian Peninsula account for approximately 75% of all stone pine stands.

Environmentally the species is very well adapted to the high temperatures and drought (Montero et al. 2004) characteristic of the Mediterranean climate. It is less sensitive to diseases and pests than other Mediterranean pines. Pinus pinea has been shown to be resistant to a major pest for Pinus pinaster in Portugal, the pine wilt nematode Bursaphelenchus xylophilus, which was identified in 1999 and from 2008 has been declared to be affecting the whole country. This resistance is increasing the interest in Pinus pinea for afforestation in areas where Pinus pinaster is seriously affected by the pine wilt nematode.

A considerable number of birds, mammals, insects, reptiles and amphibians are dependent on stone pine stands (Montoya 1990). The harvesting of the edible pine nuts – a non-wood forest product (NWFP) – is considered to have fewer negative impacts on forest ecosystems than timber harvesting and can provide an array of social and economic benefits (UNECE/FAO 2006). Pinus pinea stands also offer protection against wind erosion on the sandy soils where the species tends to grow (Calama et al. 2007b). Economically, as stone pine is not a fast growing species and its timber is not very valuable, the highest income source from stone pine stands is the pine nuts (Mutke et al. 2005a). These are considered to be the most important edible fruit from Mediterranean forests (Calama et al. 2007b). Stone pine in Portugal is highly productive, producing in 2006 an average of 193 kg of cones per ha (Gabinete de Planeamento e Políticas 2006). In Spain, in the same year, yields were only 124 kg/ha (Ministerio de Agricultura Pesca y Alimentación 2007). Mechanical harvesting of cones has modernized cone collection and increased economic interest (Gonçalves 2006).

For a particular stone pine stand cone yields depend on several factors including the age of the trees, site index, health, number of tress per hectare, pruning, thinning, etc. (Montero and Canellas 2000). There is have large annual variation in cone yields and it has been demonstrated that this is to a large extent caused by climatic factors, with the most limiting being water stress (Mutke et al. 2005b). The number of flowers in a particular year depends on conditions in , the winter of the previous year, which will have direct effects on the number of buds formed and on their development. Therefore a good cone initiation year is linked with a previous good rainfall year. The size of the cones produced in the 3rd year, the year when they are harvested, as well as the nut weight/cone weight ratio, are related to the precipitation in late spring and early summer of that year. Extreme temperatures or serious droughts(Calama et al. 2007a) at any time in this cycle will reduce the economic yield of pine nuts.  

Mutke et al. (2007a) have reviewed the main stand management practices for stone pine cone production. Fertilization has been found to have a positive effect on stem growth (Lerena et al. 2000) and on cone yield (Calama et al. 2007b). A study on irrigation carried out in Valladolid did not show a response in a stand of 75 years old (Enriquez 2000). However, recent work based on a trial with 4 years trees has shown that weekly irrigation with, 50 liter per tree during June and July, yielded four times more cones than the control (Mutke et al. 2007a; Mutke et al. 2007b). In addition, in Portugal, a positive effect from irrigation and fertilization of this species has been noted from empirical observations in golf courses, where stone pine trees have much higher cone yields than trees in neighboring stands.

Most modelling work on Pinus pinea, including work concerning cone yields, has been done in Spain. It was started mainly in the 1990’s(Calama et al. 2007c). Current work has used the model PINEA2. This is a single tree, distance independent model, parameterized for different regions in Spain (Calama et al. 2008b). It was developed for even-aged stands and adapted for multi-aged structures (Calama et al. 2008a). In Portugal there are also already models to predict the existence of cones in a tree and to predict cone green weight based on traditional forest measurements (Freire 2009). However up to now there is no process based model calibrated and validated for Pinus pinea. Therefore, there is no model able to evaluate how Pinus pinea will respond to changes in climate. Because of the importance of climate on Pinus pinea cone yields (Calama et al. 2007a; Mutke et al. 2005b) this is crucial. In addition, process-based models have the ability to deal with aspects such as decisions on fertilization, selection of land for the establishment of new plantations and strategic scenarios (e.g. long-term wood supply planning), which have been difficult for traditional forest empirical models. Of the currently available process-based models the 3-PG model has been parameterized for a large number of species including Eucalyptus globulus, E. grandis x urophylla, E. grandis x camaldulensis, E. grandis, Pinus taeda, Pinus ponderosa, Pseudotsuga menziesii, Pinus patula, Picea sitchensis, Corymbia. maculata, Araucaria cunninghamii, E. pilularis, E. delagatensis, Picea abies, Pinus radiata and P. elliottii (Fontes et al. 2006). The results based from such extensive work confirm that the principles underlying the model are sound and hold for a wide range of evergreen forests (Landsberg et al. 2005).

ANSUB 2005. Conclusões e Recomendações das I Jornadas do Pinheiro Manso da ANSUB. In I Jornadas do Pinheiro Manso da ANSUB. Edited by ANSUB, Alcacer do Sal.
Autoridade Florestal Nacional. 2010. Inventário florestal nacional : Portugal continental : IFN 5, 2005-2006. Autoridade Florestal Nacional.
Calama, R., Barbeito, I., Pardos, M., del Rio, M., and Montero, G. 2008a. Adapting a model for even-aged Pinus pinea L. stands to complex multi-aged structures. Forest Ecology and Management 256(6): 1390-1399.
Calama, R., Garriga, E., Bachller, A., Gordo, J., Finat, L., and Montero, G. 2007a. PINEA2: un modelo integrado para la gestión de las masas regulares de Pinus pinea L. en la meseta norte. Cuadernos SECF 23: 127-132.
Calama, R., Gordo, F.J., Mutke, S., and Montero, G. 2008b. An empirical ecological-type model for predicting stone pine (Pinus pinea L.) cone production in the Northern Plateau (Spain). FOREST ECOLOGY AND MANAGEMENT 255(3-4): 660-673.
Calama, R., Madrigal, G., Candela, J.A., and Montero, G. 2007b. Effects of fertilization on the production of an edible forest fruit: stone pine (Pinus pinea L.) nuts in south-west Andalusia. Investigacion Agraria-Sistemas Y Recursos Forestales 16(3): 241-252.
Calama, R., Sanchez-Gonzalez, M., and Montero, G. 2007c. Management oriented growth models for multifuncional Mediterranean forests: The case of the stone pine (Pinus pinea L.). Scientific Tools and Research Needs for Multifunctional Mediterranean Forest Ecosystem Management(56): 57-69.
Enriquez, V.P. 2000. El pino pinonero, arbol frutal. In 1er Simposio del Pino Pinonero , Pinus pinea L. Junta de Castilla y Leon, Valladolid.
Fontes, L., Landsberg, J., Tome, J., Tome, M., Pacheco, C.A., Soares, P., and Araujo, C. 2006. Calibration and testing of a generalized process-based model for use in Portuguese eucalyptus plantations. Canadian Journal of Forest Research-Revue Canadienne De Recherche Forestiere 36(12): 3209-3221.
Freire, J. 2009. Modelação do Crerscimento e da Produção de Pinha no Pinheiro Manso. In Departamento de Engenharia Florestal. Instituto Superior de Agronomia, Universidade Técnica de Lisboa, Lisboa.
Gabinete de Planeamento e Políticas. 2006. Anuário Vegetal 2006. Ministério da Agricultura, do Desenvolvimento Rural e das Pescas.
Gonçalves, A.C. 2006. Colheita mecânica da pinha e sua influência na estrutura do povoamento. In Seminário 'Projecto AGRO 451 : Optimização do melhoramento e gestão de povoamento de Pinheiro manso para a produção de pinha e pinhão' Ponte de Sôr.
Landsberg, J., Makela, A., Sievanen, R., and Kukkola, M. 2005. Analysis of biomass accumulation and stem size distributions over long periods in managed stands of Pinus sylvestris in Finland using the 3-PG model. Tree Physiology 25(7): 781-792.
Lerena, S.D., Oliet, J., Ruiz, P., Carrasco, I., Penuelas, J.L., and Serrada, R. 2000. Influencia de la relacion N-P-K en el desarrollo en vivero y en campo de planta de  Pinus pinea. In 1er Simposio del Pino Pinonero , Pinus pinea L. Junta de Castilla y Leon, Valladolid.
Ministerio de Agricultura Pesca y Alimentación. 2007. Anuario de Estadística Agroalimentaria Y Pesquera. Gobierno de Espana.
Montero, G., and Canellas, I. 2000. Selvicultura de Pinus pinea L. estado actual de los conocimientos en Espana. In 1er Simposio del Pino Pinonero , Pinus pinea L. Junta de Castilla y Leon, Valladolid.
Montero, G., Martinez, F., Alia, R., Candela, J.A., Ruiz-Peinado, R., Canellas, I., Mutke, S., and Calama, R. 2004. Generalidades de Pinus pinea L. In El pino pinonero (Pinus pinea L.) en Andalucia. Ecologia, distribucion y selvicultura. Edited by G. Montero, J. A. Candela, and A. Rodriguez. Consejeria de Medio Ambiente, Junta de Andalucia, Sevilla.
Montoya, J.M. 1990. El pino piñonero. Agroguías Mundi-Prensa, Madrid.
Mutke, S., Calama, R., Gordo, J., Álvarez, D., and Gil, L. 2007a. Stone pine orchards for nut production: which, where, how? FAO.
Mutke, S., Calama, R., Gordo, J., and Gil, L. 2007b. El uso del pino piñonero como especie frutal en sistemas agroforestales de secano. Cuadernos SECF 22: 137-142.
Mutke, S., Gordo, J., and Gil, L. 2005a. Cone yield characterization of a stone pine (Pinus pinea L.) clone bank. Silvae Genetica 54(4-5): 189-197.
Mutke, S., Gordo, J., and Gil, L. 2005b. Variability of Mediterranean Stone pine cone production: Yield loss as response to climate change. Agricultural and Forest Meteorology 132(3-4): 263-272.
UNECE/FAO. 2006. Forest Products Annual Market Review, 2005-2006. UNECE/FAO. Geneva Timber and Forest Study Paper 21.