Pinus pinea (stone pine) is the 6th most important tree species in Portugal, covering an estimated area of 175,743 ha (2010) of
which 35% are young pure plantations. Pinus pinea forested area had increased 54% compared with 1995 values, the highest
increase recorded among the national forests species (AFN 2010). Portugal has the second largest area after Spain which has
456,600 ha (Ministerio de Agricultura Pesca y Alimentación 2007). Together the Iberian Peninsula accounts for approximately
75% of all stone pine forested area in the world.
The species is well adapted to the high temperatures and drought characteristic of Mediterranean climates (Montero G. et al.
2005). It is less sensitive to pests and diseases than other Mediterranean pines but has a major biotic threat (Leptoglossus
occidentalis) which feeds on Pinus pinea nuts causing serious economic losses. Pinus pinea holds a considerable interest among
landowners in the south Portugal and has been used in afforestation programs as an alternative to Pinus pinaster nematode
affected areas and also in the montados with chronic Quercus suber recruitment problems. Pinus pinea value comes mainly
from its nuts (Mutke et al. 2005a) which are the most important edible product of Mediterranean forests (Calama et al. 2007a).
In 2011, cone/nut production represented 22 million euros in Portugal (Calado 2012). Portuguese production is high? at on
average 193 kg of cones per ha in 2006 (Gabinete de Planeamento e Políticas 2006) compared with 124 kg/ha in Spain
(Ministerio de Agricultura Pesca y Alimentación 2007). The interest in stone pine in Portugal is high due to the possibility of
anticipating cone/nut production through the use of grafted material, a technique that has been used in new plantations in
Portugal since the 80s. The experience gained lead to the publication of a manual outlining grafting techniques (Carneiro et al.
2007). Additionally, mechanical harvesting methods are being study in order to optimize cone collection and reduce harvesting
costs (Gonçalves 2006).
For a particular stone pine stand, cone yields depend on several factors: trees age, site index, health, stand density and management (Montero G., and Canellas, I. 2000). However, Pinus pinea exhibit an extreme interannual variability in cone production often synchronized over large geographical areas (masting) (Camarero et al. 2010). The relation between environmental factors and cone yield is not straightforward and requires a combined analysis of environmental conditions during the 4 years of cone development in the tree. Biotic factors, namely the desynchronization of population pests outbreaks is a possible explanation but climate is more commonly referred (Calama et al. 2007b). For example, the number of flowers in a particular year depends on the previous winter climatic conditions influencing the formation and number of cone buds (Mutke et al. 2005b). Nut weight/cone weight ratios produced in the 3rd year depend upon the precipitation from late Spring to early Summer of that year (Calama et al. 2007b). Although some attempts have been made to disentangle the drivers of cone production, the ecological factors behind cone production remains elusive for Portugal.
Mutke et al. (2007b) have revised the main stand management practices for stone pine cone production. For example,
fertilization has been found to have a positive effect on stem growth (Lerena 2000) and on cone yields (Calama et al. 2007a).
Recent work based on a 4 yearold trial has shown that irrigation with 50 liters per tree per week during June and July yielded
four times more cones than the control (Mutke et al. 2007a, Mutke et al. 2007b). In Portugal, the effects of irrigation and
fertilization in grafted and nongrafted Pinus pinea stands is being addressed in the PINEA Project: Modelling growth and pine
nuts production for Pinus pinea under changing environmental conditions (funded by FCT PTDC/AGRFOR/3804/2012).
Due to the expected increase in new stone pine areas in Portugal, accurate models able to predict Pinus pinea cone
productivities is of major importance for management support systems purposes and decision making in the future.
Spain leads the Pinus pinea cone yield modelling with studies carried out since the 1990s (Calama et al. 2007a) and with the
development of the model PINEA2. This is a single tree, distance independent model, parameterized for different regions in
Spain (Calama et al. 2008a). It was developed for even aged stands and adapted for multiaged ones (Calama et al. 2008b).
In Portugal there are models available (Freire 2009) that needs refinements with data from permanent plots, cone productivity collections, climatic data and competition indexes. Competition is a crucial aspect due to the stone pine light demanding canopies. In fact, optimum growth and cone yield is reached within a specific stand basal area threshold (Freire 2009). Linking ground base measurements (e.g. basal area) with remotely sensed vegetation indexes (e.g. NDVI? LAI) can improve the monitoring process to track stand productivity changes at a higher temporal scale over large regional areas. However, not only intraespecific competition matters. In Portugal, the increase in mixed stands of stone pine and cork oak, particularly in south country, impose new questions regarding the ecological implications of the interspecific mixture, the impacts in nonforest products yields and how to manage these systems in a climate and economic change context.
An estimation based on the increase in stone pine area between the two most recent National Forest Inventories (1995/1996 –
2005/2006) and using 2011 prices, reveals that about 39 million euros have been invested in afforestation of new stone pine
plantations. Nevertheless, little research has been carried out and little information is still available to support the management
of stone pine in Portugal. This projects intends to help fill this gap.