Maria Regina Chambel

Divergence among species and populations of Mediterranean pines in biomass allocation of seedlings grown under two watering regimes

Seedlings of four populations each of Pinus pinaster, P. halepensis, P. canariensis and P. pinea were grown in controlled conditions to evaluate both inter- and intra-specific differences in response to watering. We submitted half of the plants to a moderate water stress and after 22 weeks, we recorded height, stem diameter and root, stem and leaves dry weight. Patterns and amounts of phenotypic changes, including changes in biomass allocation, were analysed. We found a scant response in P. canariensis, P. pinaster and P. halepensis presented high population divergence for phenotypic changes, and P. pinea showed marked allocational shifts and no population divergence. The phenotypic changes observed within species are interpreted as a plastic response. The variation encountered within P. halepensis and P. pinaster may be indicative of specialisation to either resource-rich or resource-poor habitats, being populations from favourable sites more plastic. P. pinea exhibited a very uniform plastic response, indicating generalist behaviour.RésuméDes semis de quatre populations de Pinus pinaster, de P. halepensis, de P. canariensis, et de P. pinea ont été élevés en conditions contrôlées pour évaluer au niveau inter- et intra-spécifique les différences de réponse au régime d’alimentation hydrique. Nous avons soumis la moitié des plants à un stress hydrique modéré et après 22 semaines nous avons mesuré leur hauteur, le diamètre de la tige et des racines, le poids sec de la tige et des feuilles. Les modèles et l’importance des changements phénotypiques, incluant les variations d’allocation de biomasse ont été analysés. Nous avons trouvé une faible réponse pour P. canariensis; P. pinaster et P. halepensis ont présenté une importante divergence des populations au plan des changements phénotypiques, et P. pinea a montré une modification sensible au plan de l’allocation de biomasse sans divergence de population. Les changements phénotypiques observés chez les espèces ont été interprétés comme une réponse en terme de plasticité. Les variations rencontrées chez P. halepensis et P. pinaster peuvent être l’indice d’une spécialisation pour des habitats riches ou pauvres en terme de ressources. P. pinea a présenté une plasticité uniforme de réponse, révélant un comportement généraliste.

Climate-related variability in carbon and oxygen stable isotopes among populations of Aleppo pine grown in common-garden tests

The Aleppo pine (Pinus halepensis Mill.) is found in the Mediterranean under a broad range of moisture and thermal conditions. Differences in severity and duration of water stress among native habitats may act as selective forces shaping the populations’ genetic make-up in terms of contrasting drought strategies. We hypothesised that these strategies should translate into intraspecific variation in carbon isotope composition (δ13C, surrogate of intrinsic water-use efficiency, WUEi) of wood holocellulose, and such variation might be linked to changes in oxygen isotope composition (δ18O, proxy of stomatal conductance) and to some climatic features at origin. Thus, we evaluated δ13C, δ18O, growth and survival for 25 Aleppo pine populations covering its geographic range and grown in two common-garden tests. We found intraspecific variability for δ13C and growth, with high-WUEi populations (which showed 18O-enriched holocellulose) having low growth. These results suggest stomatal regulation as common control for δ13C and productivity. We also detected sizeable relationships between δ13C and climate factors related to the magnitude and timing of drought such as the ratio of summer to annual rainfall. The main climate variable associated with δ18O was minimum temperature, but only in the coldest trial, suggesting differences in growth rhythms among sources. Overall, slow growing populations from highly-seasonal dry areas of the western Mediterranean exhibited a conservative water-use, as opposed to fast growing sources from the northernmost distribution range. The particular behaviour of the Mediterranean Aleppo pine as compared with other conifers demonstrates different selective roles of climate variables in determining intraspecific fitness.

Population divergence for heteroblasty in the canary island pine (Pinus canariensis, Pinaceae)

A heteroblastic (or vegetative phase) change is an abrupt manifestation in the general heteroblastic development during the ontogeny of plants. The Canary Island pine undergoes an especially marked and delayed heteroblastic change, including both the formation of secondary needles on dwarf shoots and the onset of preformed growth. To assess genetic and environmental effects on the heteroblastic change in this species, we followed plants from 19 populations at a dry site and a wetter site. Comparing juvenile and adult needles from the same individuals, the adult had a significantly lower rate of water loss and higher leaf mass per area. Pooling data from all seed sources, the heteroblastic change took place when plants reached a critical height, on average, at 4 years of age at the dry site and 1 year earlier at the wet site. Within a subsample of individuals of equal size, mortality was significantly higher in juvenile plants than in mature plants. However, the juvenile phase was longer in plants from dry regions when compared to plants from highly productive, wet regions. This apparent contradiction might be explained through differential resource allocation and the cost of sclerophylly and resprouting ability. Considering the life strategy of the Canary Island pine, we interpret the prolonged juvenile phase as an unavoidable trade-off for the high tolerance of adults to harsh environments.

Vertical heartwood variation patterns and prediction of heartwood volume in Pinus canariensis Sm.

Heartwood and sapwood distribution along the stem were assayed in 26 Canary Island pines growing along the natural range of the species at the Canary Archipelago. Trees were sampled at breast height and approximately every 2 m up to the lowest section without heartwood. Heartwood and sapwood thickness, together with age and radial growth traits were measured in each section. Heartwood tapered towards the top of the tree and disappeared at a certain height. Sapwood distribution was more variable among individuals; sapwood width was almost constant in some individuals but tapered slightly or with a curvilinear variation in others. Two general patterns of heartwood and sapwood variation were defined, one characterised by a constant decrease in heartwood percentage and subsequently a slight sapwood variation along the stem (uniform pattern) and another one with a peak in heartwood percentage at a height between 4 and 8 m (irregular pattern). The relative crown height to total tree height was significantly higher in the second group, averaging 49% versus 32% in the uniform group. A mechanical‐physiological hypothesis is given to explain this result in the light of similar results in other species. A model including heartwood radius at breast and tree height as predicting variables was able to explain 90% of heartwood radius at a given height in the stem. A similar model with sapwood width at breast height explained 80% of sapwood width variation along the stem. Heartwood volume was predicted by means of log‐linear regression models including heartwood diameter at breast height and tree height ðr 2 ¼ 97:5%Þ. Sapwood volume was better predicted through stem diameter at breast height and tree height ðr 2 ¼ 92:7%Þ.

Intraspecific variation in the use of water sources by the circum-Mediterranean conifer Pinus halepensis

The relevance of interspecific variation in the use of plant water sources has been recognized in drought-prone environments. By contrast, the characterization of intraspecific differences in water uptake patterns remains elusive, although preferential access to particular soil layers may be an important adaptive response for species along aridity gradients. Stable water isotopes were analysed in soil and xylem samples of 56 populations of the drought-avoidant conifer Pinus halepensis grown in a common garden test. We found that most populations reverted to deep soil layers as the main plant water source during seasonal summer droughts. More specifically, we detected a clear geographical differentiation among populations in water uptake patterns even under relatively mild drought conditions (early autumn), with populations originating from more arid regions taking up more water from deep soil layers. However, the preferential access to deep soil water was largely independent of aboveground growth. Our findings highlight the high plasticity and adaptive relevance of the differential access to soil water pools among Aleppo pine populations. The observed ecotypic patterns point to the adaptive relevance of resource investment in deep roots as a strategy towards securing a source of water in dry environments for P. halepensis.

Mediterranean Pines (Pinus halepensis Mill. and brutia Ten.)

Aleppo pine (Pinus halepensis Mill.) and Brutia pine (P. brutia Ten.) are two native species of the Mediterranean basin, the first widespread mostly in its western part and the second widespread mostly in its eastern part. Together, they cover more than 7 million ha and play major ecological and economical roles in low to mid elevation Mediterranean forests. Both species are well adapted to dry summer conditions and colonize successfully abandoned arable lands and burned areas.

Resin-tapped pine forests in Spain: Ecological diversity and economic valuation

Abstract Since ancient times, Mediterranean pine forests have been habitat for human activity, providing a wide range of goods such as timber, seeds, resin and derived products. Among them, tar and resin have played an historical role on the interaction between human activity and forests. In Spain, the resin played an important role in the economic and social development in rural areas during 20th century. But after 1980, resin production plummeted and the virtual disappearance of resin tapping caused the abandonment of traditional forest activities and the subsequently losses of ecosystem forest services (provision, regulation and cultural). This paper deals with some of the ecosystem services provided by resin tapped pine forests and shows how the abandonment of this traditional forestry activity would lead to a loss of social welfare beyond the economic activity. Among these ecosystem services, special attention is paid to the biodiversity of the pine forests. For that purpose, a stratified vegetation sampling was conducted in the leading resin-tapping Spanish region. Ecological analysis was therefore compared with the social preferences for several attributes associated to resin-tapped pine forests in Spain, including the biodiversity of flora.