Black pine (Pinus nigra Arn.) growth divergence along a latitudinal gradient in Western Mediterranean mountains

? Most studies of tree-growth and climate report positive responses to global warming in high latitudes and negative responses at lower ones.

? We analyzed tree-ring width of Pinus nigra Arn. along a 500 km latitudinal transect in the Iberian Peninsula to study the temporal trend and climate forcing in tree radial growth during the last century.

? Tree growth was enhanced by cool summers and moist cold seasons. Increased moisture stress has decreased tree growth rates. However, we present evidence of growth increases in some trees in all sampled populations after 1980’s. Climate change negatively (positively) affected between 72% (5%) of trees in the southern populations and 40% (25%) in the north Trees with positive growth trends were favored by winter temperatures and their abundance was inversely correlated with forest productivity.

? Our findings add evidences of tree growth divergence in the Mediterranean basin and show the gradual transition between forests where positive (temperate and boreal) and negative (Mediterranean) growth trends dominate.

     

Rank reversals in tree growth along tree size, competition and climatic gradients for four forest canopy dominant species in Central Spain

? Interspecific differences in tree growth patterns with respect to biotic and abiotic factors are key for understanding forest structure and dynamics, and predicting potential changes under climate change.

? Repeated observations from the Spanish Forest Inventory (SFI) were used to parameterize maximum likelihood estimators of tree growth as a function of tree size, competition indices and climate for Pinus pinaster, P. sylvestris, Quercus ilex and Q. pyrenaica.

? Significant responses to both biotic and abiotic factors were found, with interspecific differences in species performance along competition, temperature and precipitation gradients. Q. ilex was the species most tolerant to competition while P. pinaster was the species most sensitive to climatic variation. Species relative positions shifted along gradients of these factors with rank reversals in species performance along size, competition and climatic gradients.

? The results based on average growth matched previous forestry classifications and experimental studies on relative growth rate (RGR).

? When examining growth along studied abiotic and biotic gradients, a mismatch was found between species performance ranks as predicted by our models and information derived from previous knowledge. Those discrepancies highlight the relevance of ontogeny and environmental heterogeneity in defining species performance along competition gradients.

     

Intraspecific variation in growth and allocation patterns in seedlings of Pinus pinaster Ait. submitted to contrasting watering regimes: can water availability explain regional variation?

? Interpopulation variation in key functional traits of Pinus pinaster Ait. is well recognized. However, the relative importance of drought tolerance to explain this regional variation in the species remains elusive.

? Here, we raise the question whether water availability constitutes a likely driver of regional variation in biomass allocation, growth and morphological traits of ten populations that cover the distribution range of P. pinaster. We carried out an experiment where seedlings of five families per population were submitted to two contrasting watering treatments.

? The effects of water availability and population were significant for relative diameter and height growth rate, biomass allocation and number of lateral stems and dwarf shoots. Total dry mass significantly differed between watering treatments but it did not among populations. Populations could be clustered into four main groups. Root mass fraction explained most of the variation and significantly correlated to altitude but not to aridity.

? The geographical pattern of genetic variation found in morphology and biomass allocation did not translate into population differences in drought tolerance or phenotypic plasticity to water availability, indicating that water availability is not a likely driver of the regional variation observed in the studied traits of P. pinaster at the seedling stage.

     

Improving models of forest nutrient export with equations that predict the nutrient concentration of tree compartments

? The objective of this study was to explore the distribution of major nutrients (N, P, K, Ca and Mg) in the aboveground compartments of an intensively managed tree species (Pinus pinaster Ait.). A total of 53 trees were cut down in even-aged stands respectively 8, 16, 26, 32 and 40 years old. The nutrient concentrations of the aboveground compartments were analysed.

? Nutrient concentrations of foliage did not vary with any of the variables used, except needle age. Nutrient concentrations of living branches, stem bark, stem sapwood, stem heartwood, stemwood and stem decreased with increasing branch diameter, bark thickness, sapwood thickness and heartwood thickness, respectively. Beyond a certain value of the predictive variable (stem diameter ≈ 15 cm; branch diameter ≈ 2.5 cm), the concentration of all the nutrients stabilised.

? A 50 year-old pine stand was used to obtain a validation dataset for nitrogen concentration. For this nutrient, the regression relationships gave satisfactory estimates for most compartments (mean error = 12–25%) and particularly for the stem.

? A procedure is proposed to estimate the nutrient exports associated with harvests of Pinus pinaster biomass.

     

Freezing injury in primary and secondary needles of Mediterranean pine species of contrasting ecological niches

? Pine seedlings show a marked ontogenetic difference between primary and secondary needles, the latter prevailing with a different timing among species.

? Using the electrolyte leakage method following an artificial freezing test, we aimed at (1) determining the differences in freezing tolerance between primary and secondary needles in eight pines of contrasting thermal habitats: P. canariensis, P. pinea, P. halepensis, P. brutia, P. pinaster, P. nigra, P. sylvestris and P. radiata, (2) evaluating the relation between freezing tolerance and sclerophylly and (3) relating freezing tolerance with the climate of origin.

? Primary needles were significantly more sensitive to freezing than secondary needles in Pinus halepensis, P. brutia, P. pinaster and P. nigra, whereas no differences were found in P. canariensis, P. pinea and P. radiata. LT50 was uncorrelated with needle sclerophylly but very highly correlated with the mean temperature of the coldest month at the seed source.

? Results support an adaptive role of secondary needles in the mountain Mediterranean pines P. nigra, P. pinaster and P. brutia, while the more complex responses in coastal Mediterranean pines can be interpreted in the light of seedling ontogeny and species’ ecological niches.

     

Has global change induced divergent trends in radial growth of Pinus sylvestris and Pinus halepensis at their bioclimatic limit? The example of the Sainte-Baume forest (south-east France)

? It is agreed that climate (precipitation and temperature) influences the distribution of plant species. Near the margins of a species’ natural range, climate becomes limiting to physiological processes. There, climate change may be expected to have a significant impact on tree growth and the species’ ranges may be altered.

? In order to assess what influence climate change could exert on the distribution of pine species at their margin, radial growth trends in ring-width chronologies over the last century were analysed. In the French Mediterranean area where climate change is characterized by increased temperature, forest plots were selected along an altitudinal transect on the north-facing slope of the Sainte-Baume mountain (Bouches-du-Rhône, France) where the ranges of Pinus sylvestris and Pinus halepensis overlap.

? Two growth patterns were identified. For P. halepensis, radial growth has increased at all altitudes indicating that climate change has improved growth conditions of this species near the margin of its ecological range. For P. sylvestris, radial growth has increased only at low altitudes and even decreased at high altitudes.

? It must be deduced that the growth changes observed cannot be generalised either at the species level or at the geographical level and must be interpreted with great caution.

     

Genetic variation, mating patterns and gene flow in a Pinus pinaster Aiton clonal seed orchard

? Relatedness among parents, variation in clonal fertility and background pollination deviate the realized genetic gain and the gene diversity of open pollinated seed orchard from expectation, in particular in wind pollinated species such as Pinus pinaster Aiton.

? This work investigates the genetic variation, the mating system and the pollen contamination in a P. pinaster clonal seed orchard (CSO), by screening the 60 clones from the CSO and the seeds collected from 21 mother-trees with three nuclear microsatellites.

? The expected diversity was similar, but the observed heterozygosity decreased 20% in the progenies compared with the parental trees. The outcrossing rate was 90.1%, the biparental inbreeding 21.7% computed through a multilocus approach, and the observed selfing 3.9%. The observed gene flow from outside the CSO was 52.4%.

? From the results we concluded that the observed gene flow and the biparental inbreeding were high, and care should be taken in the implementation and management of future CSO, in particular clones should be checked for relatedness and the ramet number could be directly proportional to their breeding value.

     

Effect of salt on ROS homeostasis, lipid peroxidation and antioxidant mechanisms in Pinus pinaster suspension cells

? In the Pinus genus, information on the effectiveness of oxidative defence mechanisms during exposure to salt is lacking. The effect of salt stress imposition on ROS homeostasis was investigated using maritime pine (Pinus pinaster Ait.) suspension cells as a model system.

? Cells were maintained in MS-based medium, exposed to salt (50, 100 and 150 mM NaCl) and analysed for biomass production, evidencing a decreasing growth capacity. Use of 100 mM NaCl imposed severe salt stress without affecting cell viability, being chosen for subsequent studies on the ROS homeostasis of salt shock-treated suspension cells.

? Increased total ROS levels were evident on the second day of salt exposure, but a superoxide ion transient burst was immediately noticeable. Additionally, lipid peroxide formation seemed to correlate with superoxide ion breakdown. In-gel superoxide dismutase activity evidenced a FeSOD homodimer with strongly increasing activity between hours 12–48 of salt stress imposition. Subsequently, P. pinaster Fe-Sod1 and csApx1 genes were isolated from a cDNA library and expression was shown to increase within 12–24 h.

? Results show that severe salt treatment generates oxidative stress in P. pinaster cells despite the induction of antioxidant systems, and suggest a putative involvement of ROS in salt stress signalling.

     

Effects of organic residue management and legume cover on growth of pine seedlings, nutrient leaching and soil properties

? The short-term effect of organic residue management on the growth and nutrition of Pinus pinaster Ait. seedlings, and on nutrient leaching and chemical properties of an acid soil was assessed through a lysimeter experiment. Treatments included absence, placement on the soil surface, and incorporation into the soil (with and without legume cover cropping) of organic residues (forest floor litter or forest floor litter plus harvest residues).

? Residues placed on the soil surface enhanced seedling growth. Organic residues reduced nutrient losses (NO ₃ ^? , Ca and Mg) and resulted in nutrient accumulation in the soil. Harvest residues positively affected K seedling nutrition status and enhanced K soil accumulation.

? Legume cover cropping reduced soil nutrient losses (N, Ca, Mg and K) during the early stage of seedling growth; it also improved seedling nutrition status (N and P), but without any effect on growth.

? Harvest residues plus forest floor litter placed on the soil surface was the most appropriate management to both reduce nutrient losses through leaching and increase height of seedlings at the end of the experimental period (two years).

     

Photosynthetic temperature adaptation of Pinus cembra within the timberline ecotone of the Central Austrian Alps

? Temperature is suggested to determine the upper limit of tree life. Therefore, future climate warming may be of importance for tree distribution within the European Alps, where low temperatures limit carbon metabolism.

? We focused on the effects of air and soil temperature on net photosynthesis (P _n) of Pinus cembra an evergreen climax species of the timberline ecotone of the Central Austrian Alps. Light response and temperature response curves were estimated along an altitudinal gradient ranging from the forest limit up to the krummholz limit in both summer and fall.

? In general, P _n was significantly lower in fall as compared to summer. Nevertheless, independent from season mean P _n values tended to increase with elevation and were positively correlated with root zone temperatures. The specific leaf area by contrast declined with increasing elevation. Furthermore, the temperature optimum of net photosynthesis declined with increasing elevation and was positively correlated with the mean maximum air temperature of the 10 days prior the date of measurement.

? Thus, our findings appear to reflect a long-term adaptation of the photosynthetic apparatus of Pinus cembra to the general temperature conditions with respect to elevation combined with a short term acclimation to the prevailing temperature regime.

     

Root elongation in tropical Eucalyptus plantations: effect of soil water content

? Sustainability of Eucalyptus plantations is often questioned in resource-limited environments, especially in areas characterized by soils with poor nutrient and water holding capacities. Yet, field-based observations of fine root dynamics in relation with the seasonality of rainfall are lacking.

? This study was undertaken on two Eucalyptus stands planted in the Kouilou Region (south-western Congo), which is characterized by a four-month-long dry season. Fine root (less than 2 mm in diameter) dynamics were studied using rhizotron observations of root elongation in the field.

? Fine root elongation rates displayed a seasonal variation in the two stands, with higher elongation rates during the rainy season than during the dry season. Positive and significant correlations were found between fine root elongation rates and soil water content at all depths, but a better correlation was found with soil water content in the deep soil horizon than in the superficial horizons.

? These results suggest that the temporal variations in fine root elongation were related to the seasonality of rainfall, and they were probably associated with seasonal changes in tree water status, carbon assimilation and belowground allocation.

     

Forest floor contribution to phosphorus nutrition: experimental data

? Although accumulation of decomposing litter temporarily removes nutrients from active circulation, it creates a medium that is more suitable for nutrient uptake where soil conditions are unfavorable.

? A pot experiment was conducted using labeling of isotopically exchangeable phosphate ions of the soil and applying the dilution principle to accurately assess the contribution of the forest floor to P nutrition of maritime pine seedlings (Pinus pinaster Aït.). Three-week-old maritime pine seedlings were planted in pots containing either mineral soil (MS) or mineral soil covered with a forest floor layer (MS+FF).

? After 130 d, P uptake was still insignificant in the MS treatment while the P content of the seedlings in the MS+FF treatment increased tenfold with respect to the initial P content. In the latter treatment, the forest floor contributed 99.1% of the P supply to pine seedlings.

? The higher P uptake from the forest floor than from the mineral soil may be explained by its lower ability to retain inorganic P, which enabled a higher concentration of inorganic P to be maintained in solution.

     

Fall fertilization of Pinus resinosa seedlings: nutrient uptake, cold hardiness, and morphological development

? Fall fertilization may increase plant nutrient reserves, yet associated impacts on seedling cold hardiness are relatively unexplored.

? Bareroot red pine (Pinus resinosa Ait.) seedlings in north-central Minnesota, USA were fall fertilized at the end of the first growing season with ammonium nitrate (NH₄NO₃) at 0, 11, 22, 44, or 89 kg N ha^?1. Seedling morphology and cold hardiness [assessed by freeze induced electrolyte leakage (FIEL)] were evaluated six weeks after fertilization and following the second growing season.

? Seedling height and number of needle primordia increased with fertilizer rate for both sampling years. Seedlings fertilized with 44 and 89 kg N ha^?1 attained target height (15 cm) after the second growing season. Shoot and root N concentration increased after the first growing season in fall fertilized seedlings compared to controls. Fall fertilized seedlings had lower FIEL (i.e., increased cold hardiness) compared to controls when tested at ?40 °C after the first growing season, but no significant differences in FIEL of control and fertilized seedlings were observed after the second growing season.

? Results suggest that fall fertilization of red pine seedlings can help render desired target height in the nursery, while maintaining or increasing cold hardiness levels.

     

Effects of climate variables on intra-annual stem radial increment in Pinus cembra (L.) along the alpine treeline ecotone

? Within the alpine treeline ecotone tree growth is increasingly restricted by extreme climate conditions. Although intra-annual stem growth recorded by dendrometers can be linked to climate, stem diameter increments in slow-growing subalpine trees are masked by changes in tree water status.

? We tested the hypothesis that intra-annual radial stem growth in Pinus cembra is influenced by different climate variables along the treeline ecotone in the Austrian Alps. Dendrometer traces were compared with dynamics of xylem cell development to date onset of cambial activity and radial stem growth in spring.

? Daily fluctuations in stem radius reflected changes in tree water status throughout the treeline ecotone. Extracted daily radial increments were significantly correlated with air temperature at the timberline and treeline only, where budburst, cambial activity and enlargement of first tracheids also occurred quite similarly. A close relationship was detected between radial increment and number of enlarging tracheids throughout the treeline ecotone.

? We conclude that (i) the relationship between climate and radial stem growth within the treeline ecotone is dependent on a close coupling to atmospheric climate conditions and (ii) initiation of cambial activity and radial growth in spring can be distinguished from stem re-hydration by histological analysis.

     

Effects of atmospheric and climate change at the timberline of the Central European Alps

? This review considers potential effects of atmospheric change and climate warming within the timberline ecotone of the Central European Alps. After focusing on the impacts of ozone (O₃) and rising atmospheric CO₂ concentration, effects of climate warming on the carbon and water balance of timberline trees and forests will be outlined towards conclusions about changes in tree growth and treeline dynamics.

? Presently, ambient ground-level O₃ concentrations do not exert crucial stress on adult conifers at the timberline of the Central European Alps. In response to elevated atmospheric CO₂ Larix decidua showed growth increase, whereas no such response was found in Pinus uncinata. Overall climate warming appears as the factor responsible for the observed growth stimulation of timberline trees.

? Increased seedling re-establishment in the Central European Alps however, resulted from invasion into potential habitats rather than upward migration due to climate change, although seedlings will only reach tree size upon successful coupling with the atmosphere and thus loosing the beneficial microclimate of low stature vegetation.

? In conclusion, future climate extremes are more likely than the gradual temperature increase to control treeline dynamics in the Central European Alps.

     

Frost damage in Pinus sylvestris L. stems assessed by chlorophyll fluorescence in cortical bark chlorenchyma

? Several techniques were used to investigate the threshold minimum temperature inducing severe frost damage during winter in Scots pine (Pinus sylvestris L.) needles and stems from southern provenances in the Iberian Peninsula.

? Chlorophyll (Chl) fluorescence, electrolyte leakage (EL), visual scoring (VS), and the normalized difference vegetation index (NDVI) were compared.

? Chl fluorescence, and in particular the maximum potential photosystem II (PSII) efficiency — estimated through the dark-acclimated F_V/F_M ratio-, was found to be a simple, non-destructive indicator of freezing tolerance in needles, as expected.

? Moreover, the existence of a Chl-containing tissue, the cortical bark chlorenchyma, allowed us the use of Chl fluorescence as a new non-destructive indicator of frost damage in live tissues of Pinus sylvestris L. stems.

? Freezing tolerance values of southern provenances are compared with those found by other authors in the northern distribution limit of the species.

     

Influence of annual weather on growth of pedunculate oak in southern Sweden

? A network of oak (Quercus robur L.) chronologies containing 49 sites and 635 single trees was analysed to identify weather variables affecting annual tree-ring increment dynamics in southern Sweden during 1860–2000.

? We analysed (1) the growth response of oak to non-extreme weather, and (2) the temporal and spatial patterns of regional growth anomalies (pointer years) and associated climatic extremes resolved on a monthly scale.

? Growth was controlled by precipitation in the current (June–July) and the previous growing season (August) in 48% and 22% of all sites, respectively. Temperature during July of the current year and August of the previous year was negatively correlated with growth in 29% and 43% of the sites, respectively. Growth was positively correlated with temperature in October of the previous season in 72% of the sites. The most extensive growth anomaly occurred in 1965 and was probably caused by intrusion of cold Arctic air masses into the region at the end of March that year.

? During climatically non-extreme years, oak growth is driven mostly by the dynamics of summer precipitation. Many of the negative growth anomalies, however, were associated with temperature extremes. Southern Swedish oak pointer years tend not to coincide with the pan-European oak pointer years.

     

Relationships of climate and cell features in stems and roots of black spruce and balsam fir

? The anatomical differences of mature black spruces and balsam firs were examined at stem and root level in order to characterize their wood properties at cellular level and link these differences to climate.

? Anatomical variability of these species was evaluated in relation to climate data gathered from 2001 to 2004 during the cell enlargement (CE) and wall thickening and lignification (WTL) phases. Lumen area, single cell wall thickness and total tracheid radial diameter were analyzed and regrouped into earlywood and latewood.

? Results from a principal component analysis (PCA) indicated that both first eigenvectors account for 82% and 90% of total variance for CE and WTL respectively. These component factors revealed that precipitation, humidity and number of days with precipitation significantly influence the lumen area (p = 0.0168) and radial cell diameter (p = 0.0222) in earlywood. Significant differences were registered between species and tree parts (stem and root) for the lumen area, radial cell diameter and cell wall thickness in both earlywood and latewood.

? In our study, black spruce exhibited smaller tracheid size in both stem and roots compared to balsam fir. Furthermore, the lower amount of tracheids produced during the growing season and higher proportion of latewood ensure a higher wood density of black spruce. The influence of temperature on earlywood formation is significant, whereas no influence was observed on latewood.

     

Which factors most influence heartwood distribution and radial growth in plantation teak?

? To investigate the effect of climate on radial growth in young plantation grown teak (Tectona grandis L.), growth ring width was measured in 105 trees and correlated to precipitation and temperature data.

? The social status of trees within the stand was also determined and cross-sectional area (CSA) for the trunk correlated to the proportion of heartwood (HW) within the tree. HW develops asymmetrically in leaning stems of some conifer species, but it is not known if this phenomenon also occurs in broadleaf species. Therefore, we measured HW proportion in leaning and straight stems, along with the number of growth rings in the HW.

? Annual ring width depended strongly on mean monthly temperature during the rainy season and the most significant relationships were found corresponding to the months of June and July. With regard to the weaker relationship between precipitation and radial growth, correlations were highest during the period of bud-break at the beginning of the rainy season.

? The very high stand density affected radial growth, particularly in suppressed trees, which responded little to thinning operations. HW formation was greatest in dominant trees, and was highly regressed with stem CSA.

? Therefore, rapid growth of young stands should be encouraged by reducing stand density. Asymmetric HW formation occurred in both leaning and straight trees, and was significantly greater along the upper sides of leaning stems. It is probable that this eccentric HW formation is linked to mechanical loading on the tree.