Esteban Chirino

Perspectives in dryland restoration: approaches for climate change adaptation

Reforestation efforts in dryland ecosystems frequently encounter drought and limited soil productivity, although both factors usually interact synergistically to worsen water stress for outplanted seedlings. Land degradation in drylands (e.g. desertification) usually reduces soil productivity and, especially, soil water availability. In dry sub-humid regions, forest fires constitute a major disturbance affecting ecosystem dynamics and reforestation planning. Climate change projections indicate an increase of drought and more severe fire regime in many dryland regions of the world. In this context, the main target of plantation technology development is to overcome transplant shock and likely adverse periods, and in drylands this is mostly related to water limitations. In this paper, we discuss some selected steps that we consider critical for improving success in outplanting woody plants, both under current and projected climate change conditions including: (1) Plant species selection, (2) Improved nursery techniques, and (3) Improved planting techniques. The number of plant species used in reforestation is increasing rapidly, moving from a reduced set of well-known, easy-to-grow, widely used species, to a large variety of promising native species. Available technologies allow for reintroducing native plants and recovering critical ecosystem functions for many degraded drylands. However, climate change projections introduce large uncertainties about the sustainability of current reforestation practices. To cope with these uncertainties, adaptive restoration approaches are suggested, on the basis of improved plant quality, improved techniques for optimizing rain use efficiency in plantations, and exploring native plant species, including provenances and genotypes, for their resilience to fire and water use efficiency.

Effect of different vegetation type cover on the soil water balance in semi-arid areas of South Eastern Spain

Abstract The simulated soil water balances under five vegetation types, using a developed model for the purpose, shows that the interception by plants represents 22 % to 35 % of annual rainfall (553 mm), in dry grasses and pine with grasses respectively. Eta is the main outflow from the soil; being more than 80 % of net precipitation in pine plus shrub vegetation type. The bare soils and dry grasses show the highest deep drainage values (208 and 142 mm, respectively), however, is difficult to estimate what portion of this infiltrated water results in aquifer recharge. During the studied year one large rainfall event (134.6 mm) produced the main infiltration flow under all vegetation types, with a significant observed change in the aquifer piezometric level. A second simulation without this event, shows that the annual drainage in all types of cover was reduced. The soil water content evolution under each vegetation type, shows that the bare soils and dry grasses present the highest values. The most complex vegetation type, with high shrub biomass and pinus presents the highest consumption. Coefficients of determination for the regression of predicted daily soil water content on observed values were 0.65, 0.87, 0.90 and 0.93 for the pine reforestation with shrub understory; pine reforestation with dry grass understory; shrubland and dry grassland, respectively.

Xylem Cavitation and Embolism in Plants Living in Water-Limited Ecosystems

Water deficit is considered the main limiting factor for the establishment, survival, and growth of plants mainly in water-limited ecosystems. Plants have evolved a wide range of morphologic and functional mechanisms to adapt to arid environments. However, if the tension in the xylem conduits becomes too high, thus xylem cavitation can occur i.e., water column breakage. This results in the hydraulic disconnection of leaves and above-ground parts from roots because xylem conduits are filled with air and water vapor, and this phenomenon is called embolism. Therefore, the resistance of the xylem to cavitation and embolism is of paramount importance for plant functioning. In this chapter, we will review the role of plant hydraulics and xylem cavitation in the context of water-limited ecosystems and their relationship with other plant functional traits and with survival capacity. These topics will be analyzed and discussed on the basis of current knowledge and our research experiences.

Comparative performance of soil water balance models in computing semi-arid aquifer recharge

Abstract Estimating groundwater recharge is essential to ensure the sustainable use of groundwater resources, particularly in arid and semi-arid regions. Soil water balances have been frequently advocated as valuable tools to estimate groundwater recharge. This article compares the performance of three soil water balance models (Hydrobal, Visual Balan v2.0 and Thornthwaite) in the Ventós-Castellar aquifer, Spain. The models were used to simulate wet and dry years. Recharge estimates were transformed into water table fluctuations by means of a lumped groundwater model. These, in turn, were calibrated against piezometric data. Overall, the Hydrobal model shows the best fit between observed and calculated levels (r2 = 0.84), highlighting the role of soil moisture and vegetation in recharge processes. Editor D. Koutsoyiannis; Associate editor X. Chen Citation Touhami, I., et al., 2014. Comparative performance of soil water balance models in computing semi-arid aquifer recharge. Hydrological Sciences Journal, 59 (1), 193–203.

Differences in morphology, gas exchange and root hydraulic conductance before planting in Pinus canariensis seedlings growing under different fertilization and light regimes

As the main forestry species in the Canary Islands (Spain), Pinus canariensis is frequently used in afforestation programs. Several nursery techniques are commonly employed to modify its morphology and physiology with the aim of improving post-planting survival and growth. In this work, we studied how fertilization and light regime treatments applied during the nursery period modify biomass allocation patterns and produce effects in gas exchange and root hydraulic conductance. Seedlings were grown for a 6-month period in the nursery under two light regimes (full sunlight and 40% PAR reduction), and three fertilization levels were applied in each light regime. Morphology, biomass allocation patterns, leaf gas exchange and hydraulic conductance of the whole root system were evaluated. Fertilization treatments produced significant changes in biomass allocation, gas exchange and root hydraulic conductance under both light regimes. In contrast, no differences were found between full sunlight and shade, except for a slight variation in the root:shoot ratio. Photosynthesis rate and WUE increased with fertilization in both light regimes, while E and gs maintained the same values. An opposite trend was observed for root hydraulic conductance, which showed lower values with high fertilization regimes. The results obtained indicate that fertilization is more important, determining high photosynthetic capacity than high hydraulic conductance rates before planting in Pinus canariensis containerized seedlings.

Physiological Keys for Natural and Artificial Regeneration of Oaks

Oak forests can naturally regenerate from seed or from sprouts. Both strategies result in the establishment of a tree layer, but they involve a crucial difference: i.e. regeneration from seeds affects population genetics while sprouting assures the recovery of biomass after a disturbance but it does not involve sexual reproduction. In addition the two regeneration mechanisms differ in their complexity and are affected by different constraints: i.e. regeneration from seed is a more intricate pathway with several potential bottlenecks (e.g. seed and micro-sites availability, predation, seedling-saplings conflicts) while sprouting is a much more straightforward process benefiting from the presence of an already established root system and more independent from environmental stochasticity. Ultimately, regeneration from seeds or sprouts will result in contrasting forest structures (respectively, high-forests and coppices) with a different functioning and dynamics and requiring particular forestry practices. When natural regeneration is not possible, oak forest restoration must be done using artificial regeneration by seeding or planting (traditionally, both methods have been recommended), provided that acorn predators are controlled. Although similar results have been obtained with regard to survival, under Mediterranean conditions, shoot growth patterns clearly differ for both methods. Indeed, one-year seedlings often discontinue their shoot elongation shortly after transplanting, especially under drought or competition. At this time, a new taproot and fine lateral roots are formed. This observation suggests that the seeding and planting techniques may bear different consequences with regard to root system development, which may ultimately affect seedling establishment. Survival and growth planted seedlings depends on morphological and physiological attributes (Burdett in Can J For Res 20:415–427, 1990; Villar-Salvador et al. in New For 43:755–770, 2012; Grossnickle in New For 43:711–738, 2012). Cultivation techniques strongly determine the functional attributes of seedlings by manipulating the amount of resources (water, mineral nutrients, light, space) and the conditions (temperature, growing medium pH, photoperiod) for seedling growth. Consequently, how seedlings are cultivated impacts on the performance of forest plantations. Cultivation practices improve the ‘‘seedling physiological potential’’, increasing the chances of survival immediately after field planting. Each of these has an influence and interacts with the others (Ketchum and Rose in Interaction of initial seedling size, fertilization and vegetation control. Redding, CA, pp 63–69, 2000), which should be taken into consideration when evaluating a reforestation proposal; otherwise, artificial forest regeneration often results in unacceptably poor seedling performance. Planting date and site preparation, since they increase water availability, have been shown to be the factors most relevant to the survival of Mediterranean species. However, in less restrictive conditions, the use of less intensive soil preparation, on dates more favorable to the initial growth of the seedlings in the field, might be more efficient. Similarly, the use of tree shelters in oaks plantations is under debate, as its effects are species and environmental dependent. A better understanding of the ecophysiological seedling response under the microenvironment of the tree shelter is needed to improve the management of this protection tool. On the other side, the effects of cultivation practices can be linked closely to newly established seedlings (the post-planting phenological cycle), and such benefits are ephemeral in nature; thus, the effects of cultivation practices have their greatest importance during the initial growing seasons (1–2 years), diminishing with time.