Rapid and sometimes extensive mortality and decline of oak, principally Quercus suber and Q. ilex, has occurred in parts of southern Spain and Portugal in recent decades. We report here isolation of the aggressive root pathogen Phytophthora cinnamomi from roots of diseased oaks or from soil at eleven out of thirteen decline foci examined. It is proposed that the introduction and spread of 7*. cinnamomim&y be a major factor in the Iberian oak decline, interacting with drought and other site factors, and leading to stress-related attacks by insects and other fungi. By analogy, it may also be involved in the similar oak declines occurring elsewhere on the Mediterranean.

This study proposes a discrete optimal control model to obtain harvest strategies that maximize the net present value (NPV) of the timber harvested from uneven-aged Pinus nigra stands located in the Spanish Iberian System, between two stable positions. The model was constructed using an objective function that integrates financial data on the harvesting operations with a matrix model describing the population dynamics. The initial and final states are given by the stable diameter distribution of the stand, and the planning horizon is 70 years. The scenario analysis corresponding to the optimal solutions revealed that the stand diameter distribution does not deviate substantially from the equilibrium position over time and that the NPV for the optimal harvesting schedule was always greater than the NPV for the "sustainable/stable" harvesting strategy. The NPV increase for the different scenarios is between 5.36% and 14.43%, showing a greater increase in higher site index scenarios and higher recruitments.

This study analyzes the stability of De Liocourt's distribution, investigating the influence of factors such as site index, recruitment, and basal area. It is proved that De Liocourt's distribution is not stable, and some simple models providing better fit to the stable diameter distribution of the stand than De Liocourt's are introduced. The stable diameter distributions obtained were characterized by a decrease in stem density in relation to the corresponding De Liocourt's distributions for low-and high-diameter classes and an increase for intermediate-diameter classes. Despite their instability, De Liocourt's distributions have shown a high degree of fit to the corresponding stable diameter distributions. The goodness of fit between both distributions was better for high recruitment, high site quality, and low basal area. FOR. SCI. 58 (1) 2009). These models are defined by the finite difference linear system of equations N(t ϩ 1) ϭ AN(t), where N(t) and N(t ϩ 1) are column vectors that contain the number of stems/ha within each diameter class at time t and t ϩ 1, respectively, and A is a square primitive matrix that contains, for each time step, the transition probabilities between adjacent classes and individual recruitments. The population growth rate is the dominant eigenvalue 0 of matrix A. By asymptotic analysis (long-term behavior), we know that, independent of the initial conditions, when 0 Ͼ 1, the total number of stems/ha of the tree population increases exponentially over time (unless harvests are conducted), when 0 Ͻ 1, the population is decaying until extinction, and when 0 ϭ 1, a stable distribution proportional to the right eigenvector W 0 of A corresponding to 0 is obtained. Gotelli (2001) refers to this special case of stable distribution when 0 ϭ 1 as the "stationary distribution," and this is also the case that we are referring to here.In general, the concept of stability is closely associated with the concept of perturbation: a system is considered stable if it always returns to a reference position (equilibrium) after small perturbations (otherwise, the system is said to be unstable). In the case of these projection matrix models, this stability property is stronger, because the stable distribution (stationary distribution) is reached independently of the initial conditions. Applied to tree populations, the stable diameter distribution of a stand is reached when it neither increases in size nor changes in structure; that is, the number of stems/ha within each diameter class remains constant after each time step. These stable diameter distributions are closely dependent on recruitment, removal, and stem migration throughout the diameter classes over time (Schütz 2006). A method to obtain these distributions, closely related to the right eigenvector W 0 of the transition matrix A corresponding to the dominant eigenvalue 0 , the stand basal area G, and the global amount of recruitment R, was introduced in López et al.

The life cycle of Tetrastichus turionum, a pupal endoparasitoid of the European pine shoot moth Rhyacionia buoliana, was studied in Spain in the field, prior to its use as a potential biological control agent of this pest in Chile. T. turionum showed two generations acting on the same host generation. Adults from the overwintering generation emerged and dispersed from mid-to late spring and gave rise to a fast developing, current year generation. Adults of this generation emerged and oviposited in early to mid-summer, producing progeny that overwintered as fourth instar larvae inside their host. Both generations appeared highly synchronized to the presence of pupae in the host population. The role of decreasing day length in the induction of diapause is also discussed. Laboratory bioassays showed that T. turionum did not oviposit on R. buoliana larvae already parasitized by Orgilus obscurator, a major larval parasitoid, already introduced in Chile. The results reinforce the suitability of T. turionum as a promising parasitoid that would complement O. obscurator in the biological control of European pine shoot moth.

Aim of study: The aim of this work is to test the positive effect of a substantially developed resin sector on rural demographic evolution. This work shows how in the period between 1970 and 2010 the demographic decline in the interior regions of Spain was more pronounced in areas characterized by the importance of resin-producing forest stands compared to other nearby rural municipalities where this natural resource is not present.Area of study: The study area consists of a set of rural municipalities in Central Spain, both resin and non-resin producing, in the provinces of Segovia, Avila, Valladolid, Burgos, Soria, Cuenca and Guadalajara.Material and methods: The relationship between resin production and population in resin and non-resin producing municipalities was modeled by means of linear regression analysis.Main results: Generally speaking, between 1950 and 1970 the production of resin halted demographic decline in the regions where this activity was substantially developed. However, when the resin sector entered into crisis in the 1970s, and the economic repercussions of this activity gradually ceased to be felt, the demographic decline in the regions which had been involved in resin production was much more acute than in other non-resin-producing rural areas.Research highlights: This work shows the relationship between resin extraction activity and population evolution in rural municipalities. Sustainable resin exploitation can contribute to the maintenance and development of rural communities, and should be used as a tool for generating employment in rural areas.