Lifting and storing bareroot blue oak (Quercus douglasii) seedlings

In California today, several species of native oaks are not regenerating adequately. Artificial regeneration is a means of ensuring sufficient recruitment to replace trees that die or are harvested, and restoring areas where trees have been cleared. Until recently, however, no bareroot oak seedlings were being produced in the state and there was little information to guide nursery operators. This study evaluated the potential of bareroot blue oak seedlings to survive and grow after outplanting. Results indicated that 1-0 nursery stock performed well in the field as long as seedlings were planted early enough in the season to take advantage of a favorable growing environment. Late lifting and long storage resulted in planting at a time when soils were already becoming dry and temperatures were hot. As a result, seedlings grew slowly or even died. Seedlings lifted early in the season (December) grew best. Either one or two months of storage had little effect on seedlings lifted at this time of year. However, seedlings lifted in January, February, and even early March performed adequately as long as they were in the ground by early March. In this study, root growth capacity was not a good predictor of subsequent field performance.     

Patterns of stomatal conductance among blue oak (Quercus douglasii) size classes and populations: implications for seedling establishment

Quercus douglasii Hook. & Arn. (blue oak) is a deciduous white oak that is currently failing to regenerate throughout much of its range in California, USA. Patterns of water use were observed in adult trees, saplings and seedlings to determine if ontogenetic changes in water use occur, which might be important in the establishment of this long-lived perennial species in a Mediterranean-type system. Seasonal and diurnal stomatal conductance (g(s)), late-season predawn xylem water potentials (Psi(pre)), carbon isotopic ratio (delta(13)C) and soil water status were compared among the three size classes at three sites differing in mean precipitation and soil water characteristics. Comparisons were also made between microsites with and without regeneration (defined by the presence or absence of saplings). Overall patterns of water use were consistent among the three sites, except that, at the site with the highest rainfall, Q. douglasii plants had higher g(s) and more positive Psi(pre) values. Although no differences in water use patterns were found between regeneration and non-regeneration microsites, the observed ontogenetic differences in water use may have important implications for Q. douglasii establishment. Compared with adult trees and saplings, seedlings had higher gas exchange rates during periods of high soil water content (early in the season and in the morning). Seedling g(s) was correlated with percent extractable soil water (ESW) throughout the season; adult tree and sapling g(s) was correlated with ESW between June and September. Despite experiencing greater water stress (indicated by more negative Psi(pre) values) than older trees, seedlings had more negative delta(13)C values, implying lower water-use efficiencies.     

Seasonal trends in photosynthetic parameters and stomatal conductance of blue oak (Quercus douglasii) under prolonged summer drought and high temperature

Understanding seasonal changes in photosynthetic parameters and stomatal conductance is crucial for modeling long-term carbon uptake and energy fluxes of ecosystems. Gas exchange measurements of CO2 and light response curves on blue oak leaves (Quercus douglasii H. & A.) were conducted weekly throughout the growing season to study the seasonality of photosynthetic capacity (Vcmax) and Ball-Berry slope (m) under prolonged summer drought and high temperature. A leaf photosynthetic model was used to determine Vcmax. There was a pronounced seasonal pattern in Vcmax. The maximum value of Vcmax, 127 micromol m(-2) s(-1), was reached shortly after leaf expansion in early summer, when air temperature was moderate and soil water availability was high. Thereafter, Vcmax declined as the soil water profile became depleted and the trees experienced extreme air temperatures, exceeding 40 degrees C. The decline in Vcmax was gradual in midsummer, however, despite extremely low predawn leaf water potentials (Psipd, approximately -4.0 MPa). Overall, temporal changes in Vcmax were well correlated with changes in leaf nitrogen content. During spring leaf development, high rates of leaf dark respiration (Rd, 5-6 micromol m(-2) s(-1)) were observed. Once a leaf reached maturity, Rd remained low, around 0.5 micromol m(-2) s(-1). In contrast to the strong seasonality of Vcmax, m and marginal water cost per unit carbon gain (partial partial differential E/ partial partial differential A) were relatively constant over the season, even when leaf Psipd dropped to -6.8 MPa. The constancy of partial partial differential E/ partial partial differential A suggests that stomata behaved optimally under severe water-stress conditions. We discuss the implications of our findings in the context of modeling carbon and water vapor exchange between ecosystems and the atmosphere.     

Effects of thinning on soil and tree water relations, transpiration and growth in an oak forest (Quercus petraea (Matt.) Liebl.)

To quantify the effects of crown thinning on the water balance and growth of the stand and to analyze the ecophysiological modifications induced by canopy opening on individual tree water relations, we conducted a thinning experiment in a 43-year-old Quercus petraea stand by removing trees from the upper canopy level. Soil water content, rainfall interception, sap flow, leaf water potential and stomatal conductance were monitored for two seasons following thinning. Seasonal time courses of leaf area index (LAI) and girth increment were also measured. Predawn leaf water potential was significantly higher in trees in the thinned stand than in the closed stand, as a consequence of higher relative extractable water in the soil. The improvement in water availability in the thinned stand resulted from decreases in both interception and transpiration. From Year 1 to Year 2, an increase in transpiration was observed in the thinned stand without any modification in LAI, whereas changes in transpiration in the closed stand were accompanied by variations in LAI. The different behaviors of the closed and open canopies were interpreted in terms of coupling to the atmosphere. Thinning increased inter-tree variability in sap flow density, which was closely related to a leaf area competition index. Stomatal conductance varied little inside the crown and differences in stomatal conductance between the treatments appeared only during a water shortage and affected mainly the closed stand. Thinning enhanced tree growth as a result of a longer growing period due to the absence of summer drought and higher rates of growth. Suppressed and dominant trees benefited more from thinning than trees in the codominant classes.     

Response of Scots pine (Pinus sylvestris L.) and pubescent oak (Quercus pubescens Willd.) to soil and atmospheric water deficits under Mediterranean mountain climate

The physiological responses to water deficits of Scots pine (Pinus sylvestris L.) and pubescent oak (Quercus pubescens Willd.) were studied under Mediterranean mountain climate. Minimum leaf water potentials were ?3.2 MPa for oak and ?2.1 MPa for pine, with higher predawn values for pubescent oak. Relative sap flow declined in both species when vapour pressure deficit (D) went above ca. 1.2 kPa, but stomatal control was stronger for pine during the 2003 summer drought. P. sylvestris plant hydraulic conductance on a half-total leaf area basis (k _L,s?1) was 1.2–2.6 times higher than the values shown by Q. pubescens, and it showed a considerably steeper decrease during summer. Leaf-level gas exchange was positively related to k _L,s?1 in both species. Scots pine was more vulnerable to xylem embolism and closed stomata to prevent substantial conductivity losses. The results of this study confirm that pubescent oak is more resistant to extreme drought events.     

Sensitivity of red oak (Quercus rubra L.) and American beech (Fagus grandifolia Ehrh.) seedlings to sodium salts in solution culture

Sodium salt sensitivity of red oak (Quercus rubra L.) and American beech (Fagus grandifolia Ehrh.) was evaluated in solution culture. Both species showed symptoms of salt injury when grown in the presence of less than 10 mM Na. In red oak, leaf symptoms first appeared at a sodium concentration of 6.0 mM and leaf weight was significantly reduced at 7.5 mM Na. Leaf, stem and root dry weights of American beech were significantly reduced in the presence of 4.0 mM sodium. In both species, browning of leaf margins and necrosis were evident in the Na-treated plants. The observed symptoms were associated with high concentrations of sodium in the tissues. Neither species appears to have control over sodium uptake and translocation.     

Development of cork oak (Quercus suber L.) seedlings in response to tree shelters and mulching in northwestern Tunisia

The need for reforestation in cork oak (Quercus suber L.) areas is challenged by difficulties. Principal among these is herbivory of young plants, vegetative competition, and slow growth rates of cork oak seedlings. We evaluated the early development of cork oak seedlings treated using tree shelters and mulching in northwestern Tunisia. We tested three tree shelter treatments (non-vented, vented, and control) to shield seedlings from animal damage and five mulch types to control competing vegetation (Italian Stone Pine, Lentisk, combination of Italian Stone Pine and Lentisk (organic mulches), gravel (inorganic mulch) and no mulch). At the end of the two-year experiment, sheltered seedlings were 89-99% taller than unshelteredseedlings and had higher numbers and lengths of shoot growth flushes. In contrast, both stem diameter growth and dry weight biomass (from samples extracted after two years) were significantly reduced inside tree shelters. Root-to-shoot ratio was not significantly different in sheltered vs. unsheltered seedlings, suggesting that tree shelters do not adversely affect this parameter. Mulching alone did not favour growth, but could be beneficial when combined with tree shelters. The combination of vented tree shelters and gravel mulch was the most effective treatment for promoting diameter, height and stem volume growth.     

Productivity of mixed versus pure stands of oak (Quercus petraea (Matt.) Liebl. and Quercus robur L.) and European beech (Fagus sylvatica L.) along an ecological gradient

The mixture of beech (Fagus sylvatica L.) and oak (sessile oak, Quercus petraea (Matt.) Liebl., and pedunculate oak, Q. robur L.) is of considerable importance in Europe and will probably become even more important under climate change. Therefore, the performance of oak and beech in mixture was compared with the species’ growth in pure stands. Data from 37 long-term mixing experiments in Poland, Germany and Switzerland were pooled for analysis of mixing effects on stand productivity and possible interrelationships with mixing portions or site conditions. We found that on average, mixed stands of oak and beech exceeded biomass productivity in pure stands by 30 % or 1.7 t ha^?1 year^?1, as the growth of both species was benefitted by the mixture. However, that the interaction actually ranged from facilitation and overyielding on poor sites to underyielding on fertile sites triggered by competition. An empirically derived interaction model showed volume and dry mass growth changing in mixed stands from gains of 50 % to losses of 10 % depending on site conditions. It is concluded that the analysed mixture grows in accordance with the stress-gradient hypothesis and that our results suggest a site-specific relationship between species mixture and biomass productivity. As a consequence, an adequate species mix should result in increased productivity under steady state as well as climate change.     

Morphological indicators of stock quality and field performance of red oak (Quercus rubra L.) seedlings underplanted in a central Ontario shelterwood

The value of initial stem diameter near the root collar, shoot length and number of first-order lateral roots (FOLR) as morphological indicators of stock quality and field performance was examined for bareroot (1+0, undercut) red oak (Quercus rubra L.) underplanted in a shelterwood in central Ontario. These three attributes were measured on more than 400 seedlings prior to planting, and their relationship with height and basal diameter growth two years after planting was determined using correlation and regression analysis. Initial diameter, shoot length and number of FOLR were positively and significantly correlated with second-year height and diameter. These relationships were strongest for diameter, but this variable explained less than 25% of the total variation in growth. Of the three indicators, diameter was also the best predictor of several physical characteristics of root systems two years after planting. Initial diameter was significantly correlated with root volume, root area and lateral root, taproot and total root dry mass. Weaker relationships existed between initial shoot length and number of FOLR and second-year root system features. Stem diameter two years after planting was more strongly related to root volume, area and dry mass than was initial diameter, the probable result of adjustment in root-shoot balance of planting stock to the shelterwood environment.     

Effect of fire severity on physical and biochemical soil properties in Zagros oak(Quercus brantii Lindl.) forests in Iran

Fire affects the physical and chemical properties and soil biological activity of natural ecosystems. This study was conducted in the Miyan Tang region, Ilam Province in western Iran. The study site was 110 hectares,where we sampled soils in areas that were classified by fire severity: low(LS), high(HS) and medium severity(MS),and unburned(UB), which served as the control. In each severity class, 25 transect points were randomly selected for measurement. Around each transect plot center, 3 soil samples were selected randomly and soils collected from the 0 to 20 cm depth were combined into a composite sample that was used in laboratory analysis to represent conditions at that point. Plots in the UB and LS fire classes had similar soil conditions and had higher values of factors such as saturated moisture, organic carbon, carbon dioxide,and silt and clay content. In contrast, plots in the HS and MS fire severity classes were clustered in the positive direction along the first axis that represented gradients in soil acidity, electrical conductivity, cation exchangecapacity, accessible phosphorus, accessible potassium,bulk density, and sand. Soil attributes were similar in areas of HS and MS fire severity classes, whereas soil conditions in the LS class and UB controls were most similar. Fire in the LS areas either did not significantly alter the physical–chemical soil properties and microbial basal respiration, or soils were able to recover quickly after being burned.     

Changes in root growth and relationships between plant organs and root hydraulic traits in American elm （Ulmus americana L.） and red oak （Quercus rubra L.） seedlings due to elevated CO2 level

The relationships between plant organs and root hydrological traits are not well known and the question arises whether elevated CO2 changes these relationships. This study attempted to answer this question. A pseudo-replicated experiment was conducted with two times 24 American elm(Ulmus americana L.) and 23 and 24 red oak(Quercus rubra L.) seedlings growing in ambient CO2(around 360 μmol·L-1) and 540 ± 7.95 μmol·L-1 CO2 in a greenhouse. After 71 days of treatment for American elm and 77 days for red oak,14...     

Changes in root growth and relationships between plant organs and root hydraulic traits in American elm (Ulmus americana L.) and red oak (Quercus rubra L.) seedlings due to elevated CO2 level

The relationships between plant organs and root hydrological traits are not well known and the question arises whether elevated CO2 changes these relationships. This study attempted to answer this question. A pseudo-replicated experiment was conducted with two times 24 American elm (Ulmus americana L.) and 23 and 24 red oak (Quercus rubra L.) seedlings growing in ambient CO2 (around 360 μmol·L–1) and 540 ± 7.95 μmol·L–1 CO₂ in a greenhouse. After 71 days of treatment for American elm and 77 days for red oak, 14 American elm and 12 red oak seedlings from each of the two CO2 levels were randomly selected in order to examine the flow rate of root xylem sap, root hydraulic conductance, total root hydraulic conductivity, fine root and coarse root hydraulic conductivity. All seedlings were harvested to investigate total plant biomass, stem biomass and leaf biomass, leaf area, height, basal diameter, total root biomass, coarse root biomass and fine root biomass. The following conclusions are reached: 1) plant organs respond to the elevated CO2 level earlier than hydraulic traits of roots and may gradually lead to changes in hydraulic traits; 2) plant organs have different relationships with hydraulic traits of roots and elevated CO2 changes these relationships; the changes may be of importance for plants as means to acclimatize to changing environments; 3) biomass of coarse roots increased rather more than that of fine roots; 4) Lorentzian and Caussian models are better in estimating the biomass of seedlings than single-variable models.     

Ectomycorrhizal inoculation with Pisolithus tinctorius increases the performance of Quercus suber L. (cork oak) nursery and field seedlings

Mediterranean ecosystems are characterized by large arid areas where the patchy distribution of trees offers little protection against harsh climate conditions for seedling establishment. Climate change is predicted to result in an increase in these arid regions, with pronounced effects on vegetation. Production of seedlings with developed ectomycorrhizas is a promising strategy for minimizing the initial transplant shock, thereby increasing plant survival and growth during the first, most critical years of a plantation. One important species in the Mediterranean basin is Quercus suber (cork oak), which occurs, together with other evergreen oak species, in an agro-silvo-pastoral system that represents an example of sustainable land use in Europe. In this study, a Pisolithus tinctorius isolate was used for ectomycorrhizal colonization of cork oak nursery seedlings, and the effects on aboveground plant growth and leaf structural and physiological parameters were investigated. Ectomycorrhizal development resulted in a significant increase in leaf area, dry weight, nitrogen content, and photosynthetic pigments, and mycorrhizal plants showed a higher photosynthetic capacity and water use efficiency. Nursery-inoculated plants established in the field showed increased survival and growth during the first year after transplant. These results indicate a potential for further enhancing the use of mycorrhizal inoculation as a cultivation practice in forest nurseries. Considering the difficulty of soil restoration under limiting environmental conditions, nursery inoculation with ectomycorrhizal fungi can be an important advantage for improving the quality of seedling stock and its performance after out-planting in the field, benefiting the regeneration of arid regions and the reintroduction of inocula of ectomycorrhizal fungi into these areas.     

Stomatal patchiness in the Mediterranean holm oak (Quercus ilex L.) under water stress in the nursery and in the forest

The evergreen holm oak Quercus ilex L. is the most representative tree in Mediterranean forests. Accurate estimation of the limiting factors of photosynthesis for Q. ilex and the prediction of ecosystem water-use efficiency by mechanistic models can be achieved only by establishing whether this species shows heterogenic stomatal aperture, and, if so, the circumstances in which this occurs. Here, we collected gas-exchange and chlorophyll fluorescence data in Q. ilex leaves from a nursery to measure the effects of stomatal oscillations on PSII quantum yield (Φ(PSII)) under water stress. Stomatal conductance (g(s)) was used as an integrative indicator of the degree of water stress. Images of chlorophyll fluorescence showed heterogeneous Φ(PSII) when g(s) was <50 mmol H(2)O m(-2) s(-1), representative of severe drought and corresponding to a container capacity <45%. Stomatal patchiness was related to a coefficient of variation (CV) of Φ(PSII) values >2.5%. A parallel study in the forest confirmed heterogeneous Φ(PSII) values in leaves in response to declining water availability. Three kinds of Q. ilex individuals were distinguished: those resprouting after a clear-cut (resprouts, R); intact individuals growing in the same clear-cut area as resprouts (controls, C); and intact individuals in a nearby, undisturbed area (forest controls, CF). Patchiness increased in C and CF in response to increasing drought from early May to late July, whereas in R, Φ(PSII) values were maintained as a result of their improved water relations since the pre-existing roots were associated with a smaller aerial biomass. Patchiness was related to a % CV of Φ(PSII) values >4 and associated in the summer with mean g(s) values of 30 mmol H(2)O m(-2) s(-1). Under milder drought in spring, Φ(PSII) patchiness was less strictly related to g(s) variations, pointing to biochemical limitants of photosynthesis. The occurrence of heterogenic photosynthesis caused by patchy stomatal closure in Q. ilex during severe drought should be taken into account in ecosystem modelling in which harsher water stress conditions associated with climate change are predicted.     

Root characteristics and growth potential of container and bare-root seedlings of red oak (<Emphasis Type="Italic">Quercus rubra</Emphasis> L.) in Ontario,Canada

Root characteristics and field performance of container and bare-root seedlings of red oak (Quercus rubra L.) were compared during the first growing season after planting. Sixty seedlings of each stock type were planted on a clearfell and weed-free site near Restoule, Ontario. Twenty-four additional seedlings from each stock type were compared at the start of the study in terms of shoot and root parameters. Measurement of root and shoot parameters were repeated at three dates during the first growing season in the field. The root systems of container stock had a larger number of first order lateral long roots and were significantly more fibrous than bare-root stock. These differences were sustained throughout the first growing season. In terms of field performance, container seedlings had 100% survival and achieved significant increases in both biomass and shoot extension. Bare-root seedlings suffered 25% mortality, significant shoot dieback and more variable growth. The mean relative growth rate (RGR) of container seedlings increased throughout the study period to a maximum of 30 mg/g/day, whereas the mean RGR of bare-root stock remained close to or below zero. Overall, the container seedlings proved less prone to transplanting shock than the bare-root seedlings, most likely due to favourable root architecture and the pattern of root development. Further work may be warranted in container design, growing regimes and root architecture to fully realise the potential of container systems for the production of high quality red oak seedlings across a range of site conditions.     

Performance and nutrient dynamics of holm oak (<Emphasis Type="Italic">Quercus ilex</Emphasis> L.) seedlings in relation to nursery nutrient loading and post-transplant fertility

Holm oak (Quercus ilex L.) seedlings were exponentially (E) nutrient loaded using incremental increases in fertilizer addition or conventionally (C) fertilized using a constant fertilizer rate during nursery culture. The fertility treatments (mg N plant⁻¹) were control (0), 25E, 100E, and 100C. Subsequently, 1-year-old plants were transplanted under simulated soil fertility gradients in a greenhouse to evaluate effects of nutrient loading and post-transplant fertility on seedling performance. Post-transplant fertility consisted of fertilizing plants at two rates (0 vs. 200 mg N plant⁻¹). A water-soluble fertilizer 20-20-20 was supplied in both nursery and post-transplant experiments. Nutrient loading increased plant N content by 73% in 100E and by 75% in 100C relative to controls, although no significant differences were detected between constant and exponential fertilization regimes at the 100 mg N plant⁻¹ rate. When transplanted, nutrient loading promoted post-transplant root growth relative to shoot, implicating potential to confer competitive advantage to loaded holm oak seedlings after trans-planting. In contrast, post-transplant fertility increased new shoot dry mass by 140% as well as N, P and K content relative to controls. Results suggest that holm oak seedlings can be successfully nutrient loaded in the nursery at higher fertility rates, improving its potential to extend new roots, but alternative fertilization regimes and schedules that better fit nutrient availability to the growth rhythm and conservative strategy of this species must be tested.     

Influence of the soil water holding capacity on the potential distribution of forest species. A case study: the potential distribution of cork oak (<Emphasis Type="Italic">Quercus suber</Emphasis> L.) in central-western Spain

This study reports a parametric approach to the climatic and edaphoclimatic potential distribution of the cork oak (Quercus suber L.) in central-western Spain together with an analysis of the influence of the maximum soil water holding capacity (WHC) on such potential distribution. To these ends, we employed 12 climatic and 2 edaphoclimatic parameters of eco-physiological influence derived from the current distribution of cork oaks. The climatic and edaphoclimatic parameters elaborated for two extreme WHC values (50 and 250 mm) are calculated for the whole study area and are mapped by means of a digital elevation model and a geographic information system. The results point to an important climatic potential area for high soil WHC values but there is also a remarkable dependence on this latter parameter, mainly in the Duero basin, since the limits of the climatic potential area are reduced strongly as WHC decreases. We deduce certain other conclusions as regards the importance of this variable in the potential distribution of species and in forestation and reforestation projects using this species.     

Revisiting the use of soil water budget assessment to predict site productivity of sessile oak (<Emphasis Type="Italic">Quercus petraea</Emphasis> Liebl.) in the perspective of climate change

Climate change is expected to increase the frequency and severity of drought events over the next few decades in Western Europe. Consequently, there is a crucial need for an efficient tool for field water budget diagnosis to enable forest managers to estimate tree survival and productivity. Robust estimates of water budget using soil and topography were compared for their ability to predict site yield of Quercus petraea (Matt.) Liebl. Site yield was estimated using site index at 100 years. Ninety-nine even-aged high-forest stands located in northern France were investigated. Water budget was estimated by topographic position and soil water capacity (SWC) calculated for different soil depths down to a maximum 2.0 m. (1) Site index predictions improved when calculating SWC for increasing depths until 1.0 m. (2) Site index predictions did not improve when calculating SWC at depths below 1.0 m, thus confirming that the water contained in deep soil layers is not used for tree growth but probably contributes to tree fitness or survival by maintaining a not too negative in-tree water potential. (3) Topographic position was also a predictor of site index in addition to SWC. Practical recommendations for estimating extractable soil water content are given.     

Effect of fire severity on physical and biochemical soil properties in Zagros oak (<Emphasis Type="Italic">Quercus brantii</Emphasis> Lindl.) forests in Iran

Fire affects the physical and chemical properties and soil biological activity of natural ecosystems. This study was conducted in the Miyan Tang region, Ilam Province in western Iran. The study site was 110 hectares, where we sampled soils in areas that were classified by fire severity: low (LS), high (HS) and medium severity (MS), and unburned (UB), which served as the control. In each severity class, 25 transect points were randomly selected for measurement. Around each transect plot center, 3 soil samples were selected randomly and soils collected from the 0 to 20 cm depth were combined into a composite sample that was used in laboratory analysis to represent conditions at that point. Plots in the UB and LS fire classes had similar soil conditions and had higher values of factors such as saturated moisture, organic carbon, carbon dioxide, and silt and clay content. In contrast, plots in the HS and MS fire severity classes were clustered in the positive direction along the first axis that represented gradients in soil acidity, electrical conductivity, cation exchange capacity, accessible phosphorus, accessible potassium, bulk density, and sand. Soil attributes were similar in areas of HS and MS fire severity classes, whereas soil conditions in the LS class and UB controls were most similar. Fire in the LS areas either did not significantly alter the physical–chemical soil properties and microbial basal respiration, or soils were able to recover quickly after being burned.