Canopy fuel characteristics and potential crown fire behavior in Aleppo pine (Pinus halepensis Mill.) forests

Canopy fuel characteristics that influence the initiation and spread of crown fires were measured in representative Aleppo pine (Pinus halepensis Mill.) stands in Greece. Vertical distribution profiles of canopy fuel load, canopy base height and canopy bulk density are presented. Aleppo pine canopy fuels are characterized by low canopy base height (3.0–6.5 m), while available canopy fuel load (0.96–1.80 kg/m²) and canopy bulk density (0.09–0.22 kg/m³) values are similar to other conifers worldwide. Crown fire behavior (probability of crown fire initiation, crown fire type, rate of spread, fireline intensity and flame length) in Aleppo pine stands with various understory fuel types was simulated with the most updated crown fire models. The probability of crown fire initiation was high even under moderate burning conditions, mainly due to the low canopy base height and the heavy surface fuel load. Passive crown fires resulted mostly in uneven aged stands, while even aged stands gave high intensity active crown fires. Assessment of canopy fuel characteristics and potential crown fire behavior can be useful in fuel management and fire suppression planning.     

Effects of low night temperature and light on chlorophyll fluorescence of field-grown seedlings of Scots pine (Pinus sylvestris L.)

In vivo chlorophyll fluorescence kinetics was observed in naturally regenerated and planted Scots pine (Pinus sylvestris L.) seedlings growing at two adjacent sites in northern Sweden. Some seedlings were shaded from direct solar radiation and some were protected from frost at night. Air temperature and solar radiation were monitored. In vivo chlorophyll fluorescence kinetics of current-year needles was measured at both room temperature and 77 K. On clear days during August, variable fluorescence of photosystem II of needles from exposed, naturally regenerated seedlings was reduced by night frosts, whereas frost caused little change in fluorescence of needles from shaded seedlings. Overnight frost-protection reduced the inhibition of photosystem II by direct sunlight. Recovery from photoinhibitory damage occurred on cloudy days. In September, the decline of variable fluorescence of photosystem II was more pronounced in unshaded than in shaded seedlings, and coincided with frosts at night. In addition, the reduction in variable fluorescence was larger for planted seedlings than for naturally regenerated seedlings. It is suggested that the inhibition of photosystem II activity was caused by an interaction between low temperatures and light. Natural night frosts are proposed to increase the susceptibility to photoinhibition in the following day(s).     

Estimation of canopy fuel characteristics of Aleppo pine (Pinus halepensis Mill.) forests in Greece based on common stand parameters

Canopy fuel characteristics that influence the initiation and spread of crown fires were measured in forty representative Aleppo pine (Pinus halepensis Mill.) stands in Greece. Aleppo pine canopy fuels are characterized by low canopy base height (CBH) (2.0–6.5 m), while available canopy fuel load (CFL) (0.63–1.82 kg/m²) and canopy bulk density (CBD) (0.07–0.22 kg/m³) values are similar to those of other conifers worldwide. Regression equations for the estimation of canopy fuels were developed based on common stand parameters. Stand basal area was the best-fitted predictor for the estimation of CFL and CBD at stand level, explaining 77 and 74 % of the observed variation, respectively. Regression analysis failed to provide any significant estimates for the CBH. Prediction of canopy fuel characteristics based on stand basal area can be useful in fuel management and fire prevention planning since it and can be easily incorporated into existing forest inventory systems and can be used for the Kyoto protocol requirements of carbon changes in Aleppo pine forests located in Greek sites.     

Cold acclimation of Pinus contorta and Pinus sylvestris assessed by chlorophyll fluorescence

Needle samples of six provenances each of lodgepole pine (Pinus contorta Dougl. var. latifolia) and Scots pine (Pinus sylvestris L.), originating from latitudes 55 to 68 degrees N in western Canada and northern Sweden, were collected during the autumn and subjected to freezing temperatures in the range of -8 to -29 degrees C on three occasions in September and October. Needle injury was assessed by two different methods: visual assessment and chlorophyll a fluorescence. Chlorophyll a fluorescence data showed a highly significant correlation with the visual assessments of injury, indicating that the technique can be used as a simple, non-destructive and objective measure for rapid detection of freezing injury and for ranking of needle materials with respect to development of cold acclimation. The analyses showed that, during the autumn, lodgepole pine needles were more hardy and acclimated to low temperatures earlier than Scots pine needles.     

Growth and visible responses of Scots pine (Pinus sylvestris L.) seedlings to simulated summer frost

Scots pine seedlings, 20–30 days old, were exposed to simulated summer frost in controlled environment growth chambers. The responses observed showed extreme variation between individual seedlings; seedlings suffering from needle-necrosis, healthy-looking, and dead seedlings were found in the same treatment. Four days exposure to temperatures below –4.5°C caused multiple-leaders maximally in 7.7 % of the pine seedlings and resulted in decreased shoot and root dry weight and shoot length.     

No difference in frost hardiness between high and low altitude Pinus sylvestris (L.) offspring

Seedlings representing offspring from 46 Swedish natural stands of Pinus sylvestris (L.) from latitude 63° to 68° and altitude 75 to 675 m were artifically frost hardened and tested for autumn frost hardiness using artifical freeze testing in a programmable freezing chamber. A clinal variation in frost hardiness was observed over latitude. Altitude had no effect on the frost hardiness. The results are discussed in relation to the reproduction‐ and migration biology of P. sylvestris.     

Aftereffects of maternal environment on autumn frost hardiness in Pinus sylvestris seedlings in relation to cultivation techniques

Full-sib families of Pinus sylvestris (L.) from genetically identical parent clones, grown at three geographic locations (64, 59.5, and 56 degrees N), were tested for autumn frost hardiness. At one of the locations (64 degrees N), maternal clones were grown in plots subjected to different site treatments. Progenies raised in a heated greenhouse with additional artificial light were induced to undergo two shoot elongation periods, separated by a period with long nights and non-hardening temperatures, followed by a hardening period. Frost hardiness was tested by exposing seedlings to -17, -19, or -21 degrees C during the hardening period. Progenies produced at the northernmost locality (64 degrees N) were the most hardy. The hardiness ranking among localities and the magnitude of differences in hardiness were in accordance with earlier results obtained from the same crosses that had undergone only one shoot elongation period. Effects of maternal site treatments were significant but small compared with family differences. The growth regimes used in the present study did not eliminate maternal effects induced by geographic location, but maternal effects related to site treatment decreased substantially in relation to family variation when compared with seedlings that had undergone only a single shoot elongation period. The results are discussed in relation to other studies of the same crosses raised under different growth conditions.     

The effect of late summer fertilization on the frost hardening of second-year Scots pine seedlings

In this study the effect of summer fertilization on the initiation of frost hardening of containerized second-year Scots pine (Pinus sylvestris L.) seedlings is studied. During the second growing season three different fertilization programs (water soluble NPK with micronutrients) determined by electrical conductivity of peat water extract (0.2, 0.5 and 1.2 mS cm^-1) were initiated. The growth and nutrient concentrations of needles were monitored during the fertilization period. The frost hardiness of seedlings was assessed on four separate occasions at two week intervals from August 7 to September 18. This assessment was based on artificial freezing tests and visual damage scoring of tissue browning on current-year needles. Clear differences in foliar N, P and K concentrations were observed between the fertilization treatments. Fertilization prolonged the growing period of needles and increased root collar diameter. In all the tests, the highest fertilization level resulted in the highest level of frost hardiness. The difference between the fertilization treatments ranged from 1 °C to 2.2 °C. Frost hardiness increased with an increase in foliar nitrogen concentration and slightly less consistently with increases in foliar phosphorus and potassium concentrations.     

施肥对黎蒴栲幼苗叶绿素含量的影响

为了探讨苗期施肥对黎蒴栲叶片叶绿素含量的影响,采用均匀设计对黎蒴栲实生幼苗进行不同梯度的配比施肥试验。结果表明:施肥处理T_4(N 0.112 5 g/株、K_2O 0.050 0 g/株)、T_5(N 0.075 0 g/株、P_2O_5 0.350 0 g/株)均较有利于黎蒴栲幼苗的生长。施氮肥处理的黎蒴栲苗木叶片叶绿素a、叶绿素b、总叶绿素含量均高于未施氮肥处理(T_3,P_2O_5 0.175 0 g/株、K_2O 0.100 0 g/株)和对照的,施氮肥有利于黎蒴栲幼苗叶片叶绿素的积累。黎蒴栲叶片叶绿素含量在施肥前期,与氮肥施用量呈正相关;后期生长阶段,叶片叶绿素含量与其生长状况密切相关。可通过叶片叶绿素含量了解植物对氮肥的需求情况。     

Effect of water stress conditioning on morphology,physiology and field performance of Pinus halepensis Mill. seedlings

Five-month-old Pinus halepensis Mill. seedlings were subjected to 4 irrigation treatments for 8 weeks. After the treatments, morphological and physiologicalattributes assessed included height, diameter, dry weight, water relations parameters, and determination of N, P, K, soluble carbohydrates, and starch concentrations. The remaining seedlings were field planted. Survival and height growth were recorded forfour growing seasons after planting. The mostsignificant effect of irrigation was onmorphology. Increased irrigation lead toseedlings with significantly higher height,root collar diameter and shoot and rootbiomass. Starch and soluble carbohydrateconcentrations were also affected byirrigation. However, parameters derived frompressure-volume curves were not significantlydifferent among treatments, nor were N, P, andK concentrations. There were no differencesamong treatments for survival in the field,which was highly related to summer rainfall. Incomparison, absolute and relative heightgrowth showed some significant but minordifferences among treatments.     

Influence of photoperiod and temperature on frost hardiness and free amino acid concentrations in black spruce seedlings

We investigated the effects of a 4-week exposure to an 8-h or 18-h photoperiod at 5 or 25 degrees C on the development of hardiness to -20 degrees C and the accumulation of proline (Pro), arginine (Arg) and tryptophan (Trp) in shoots of black spruce (Picea mariana (Mill.) B.S.P.) seedlings. The greatest degree of hardening to -20 degrees C occurred in seedlings exposed to an 8-h photoperiod at 25 degrees C, and some hardening occurred in seedlings exposed to 5 degrees C in either an 8-h or 18-h photoperiod. Proline accumulated in shoots in response to 5 degrees C and either an 8-h or 18-h photoperiod, whereas Trp accumulated in response to an 8-h photoperiod at either temperature, and Arg only accumulated in shoots in the 5 degrees C + 8-h photoperiod treatment. Only the accumulation of Trp was significantly related to the degree of hardiness to -20 degrees C.     

Effects of serpentine soil factors on Virginia pine (Pinus virginiana) seedlings

Effects of simulated serpentine soil conditions (elevated Mg:Ca ratio and Ni concentration) on seedlings from populations of Virginia pine (Pinus virginiana Mill.) from serpentine and non-serpentine sites were evaluated in sand culture. We determined (1) how seedlings are affected by elevated Mg:Ca ratio and Ni concentrations, (2) if there are interactive effects between Mg:Ca ratio and Ni concentrations on seedling growth, needle pigment concentrations, and nutrition, and (3) if Virginia pine populations from serpentine areas are edaphic ecotypes. A Mg:Ca ratio of 5 and 50 microM Ni both reduced seedling growth compared with control seedlings grown in the presence of the standard Mg:Ca ratio of 0.5 and no Ni. Interactive effects between Mg:Ca ratio and Ni concentrations were highly significant for growth, foliar pigments, and needle and root elemental concentrations. Nickel-mediated reductions in growth and foliar pigment concentrations were less at the serpentine Mg:Ca ratio of 5 than at the standard (non-serpentine) Mg:Ca ratio of 0.5. Foliar N was reduced by Ni concentrations as low as 10 microM, and foliar and root K, Ca and P concentrations were significantly reduced by Ni concentrations above 25 microM, with greater reductions at a Mg:Ca ratio of 0.5 than at a Mg:Ca ratio of 5. There were no population x serpentine soil factor interactions for seedling growth, foliar pigment concentrations, or nutrition, suggesting that seedlings from trees growing on serpentine soils are not edaphic ecotypes. We conclude that serpentine conditions present at the site of seed collection have not resulted in the selection of edaphic ecotypes of Virginia pine with respect to Mg:Ca ratio and Ni concentration.     

Effects of pre-commercial thinning on growth and reproduction in post-fire regeneration of Pinus halepensis Mill

Context

Excessive recruitment in post-fire regeneration of Pinus halepensis can require pre-commercial thinning. The 1994 Moratalla fire (Spain) and the thinning applied there since 2004 provided good conditions for testing pre-commercial thinning effectiveness.

Aims

To analyse pre-commercial thinning effects on tree size, reproductive potential, stem biomass and annual growth in 15-year-old saplings.

Methods

Twenty nine circular plots (5 m radius) were established based on (1) years since thinning and (2) aspect. Non-thinned plots were included as controls. Sapling variables were measured and pine cones were counted and classified according to maturity. Three saplings per plot were felled, five sample disks were extracted from each and tree rings were analysed with Windendro® software.

Results

Sapling size, annual growth and stem biomass were higher in thinned plots than in control plots 2–4 years after thinning. Annual growth declined five years after thinning. Cone counts were higher 2–5 years after thinning, depending on the cone type. Aspect influenced some variables.

Conclusion

Thinning accelerated stand maturity but positive effects were indiscernible until 2–5 years later. Serotinous cones, which are fundamental to regeneration after fire, increased in number after 5 years. The effects of aspect were inconclusive due to interactions with years since thinning.     

Isolation,characterization and effect of plant-growth-promoting rhizobacteria on pine seedlings(Pinus pseudostrobus Lindl.)

In this study,10 bacterial strains were isolated from the rhizosphere of coniferous trees on Mount Tla′loc in Mexico.The strains were characterized by their capacity to produce auxins,solubilize phosphates and stimulate mycelial growth of the ectomycorrhizal fungus Suillus sp.All isolates were identified at the molecular level.Moreover,an experiment was established to evaluate the response of Pinus pseudostrobus seedlings to inoculation with the rhizobacteria strains.The isolated strains belonged to the species Cupriavidus basilensis,Rhodococcus qingshengii,R.erythropolis,Pseudomonas spp.,P.gessardii,Stenotrophomonas rhizophila and Cohnella sp.All of the strains produced auxins;the best producer was R.erythropolis CPT9(76.4 lg mL^-1).P.gessardii CPT6 solubilized phosphate at a significant level(443 lg mL^-1).The strain S.rhizophila CPT8 significantly increased the radial growth of the ectomycorrhizal fungus Suillus sp.by 18.8%.Five strains increased the dry mass of the shoots;R.qingshengii CPT4 and R.erythropolis CPT9 increased growth the most,by more than 20%.Inoculation with plant-growth-promoting rhizobacteria can be a very useful practice in a forest nursery to produce healthy,vigorous plants.     

Regulation of organic and inorganic nitrogen uptake in Scots pine (Pinus sylvestris) seedlings

Plants possess regulatory mechanisms that enhance nitrogen (N) uptake under conditions of spatial and temporal variation in N availability. Study of regulatory mechanisms has focused almost exclusively on the uptake of inorganic N sources (i.e., ammonium (NH4+), nitrate (NO3-). Several lines of evidence, however, suggest that amino acids may constitute a potential source of N for a number of plant species, including conifers. In the present study, we investigated the uptake of amino acids and inorganic N in Scots pine (Pinus sylvestris L.) seedlings grown at different N concentrations. We compared the uptake rate of the individual N sources using U-[13C2], [15N]-glycine, U-[13C6], [15N4]-arginine, 15NH4, or 15NO3, and tested the short-term effect of N supply on the uptake rate of glycine, arginine and in field-grown Scots pine seedlings. Our data indicate that Scots pine seedlings can absorb substantial amounts of N in the form of intact arginine and glycine molecules. The data also suggest that Scots pine seedlings down-regulate their uptake of NH4+-N and arginine-N, but not of glycine-N in response to increased endogenous N concentrations.     

Timing of cold temperature exposure affects root and shoot frost hardiness of Picea Mariana container seedlings

Seventeen‐week‐old black spruce seedlings were hardened under short daylengths and one of three short day length environments, which were either warm (24/16°C, day/night) throughout a 10 week hardening period (WW), cool (10/5°C) throughout hardening (CC), or warm for three weeks followed by seven weeks of cool temperatures (WC). Greatest root and shoot frost hardiness resulted from the exposure of seedlings to three weeks of warm followed by seven weeks of cool temperatures. Seedlings receiving warm temperatures throughout hardening increased in root and shoot frost hardiness, but to a lesser extent than seedlings exposed to cool temperatures. The frost hardiness of woody roots was generally greater than that of fine roots, but the extent of the difference in frost hardiness depended on the time since bud initiation and on the hardening treatment.     

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.

     

Influence of nutrient supply on spring frost hardiness and time of bud break in Norway spruce (Picea abies (L.) Karst.) seedlings

When spring frosts occur on recently planted forest sites, severe damage may occur to the seedlings. The aim of the present study was to test how different low levels of nutrient concentrations in Norway spruce (Picea abies (L.) Karst.) seedlings affected spring frost hardiness and time of bud break. Seedlings were grown in a greenhouse for one season and supplied with fertiliser containing 22, 43 and 72 mg N l^–1, respectively. The treatments resulted in needle nitrogen concentrations ranging from 0.9 to 1.8% in autumn. After winter storage at 0 °C, bud break was recorded on seedlings growing in the greenhouse, outdoors and in growth chambers at 12 °C and at 17 °C. Freezing tests were performed on seedlings directly removed from winter storage and following one week growth in the greenhouse. Seedlings receiving fertiliser with 43 mg N l^–1 had less freezing injury than the two other fertilisation treatments in the present study. The earliest bud break occurred in seedlings receiving 72 mg N l^–1.     

Effects of different concentrations of nitrogen and phosphorus on chlorophyll biosynthesis, chlorophyll a fluorescence, and photosynthesis in Larix olgensis seedlings

In our experiments, one-year-old Larix olgensis seedlings were cultivated in sand, and supplied with solutions with different concentrations of nitrate or phosphate. The effects of nitrogen and phosphorus supply on chlorophyll biosynthesis, total nitrogen content, and photosynthetic rate were studied. The experimental results are listed below: 1) 5-aminolevulinic acid (ALA) synthetic rate increased as nitrate concentrations supplied to larch seedlings increased from 1 to 8 mmol/L. But the rate decreased by 17% when nitrate concentration increased to 16 mmol/L, in contrast to the control. Under phosphate treatments, ALA synthetic rates were similar to those under nitrate treatments. The activities of porphobilinogen (PBG) synthase reached a maximum when larch seedlings were supplied with 8 mmol/L of nitrate or 1 mmol/L of phosphate. 2) when larch seedlings were supplied with 8 mmol/L of nitrate and 0.5 mmol/L of phosphate, the contents of chlorophyll a, chlorophyll b, total chlorophyll, and carotenoids reached a maximum. The total nitrogen contents in leaves increased as nitrate concentrations increased. 3) When phosphate concentrations increased from 0.125 to 1 mmol/L, the total nitrogen contents in leaves slightly increased; however, continuous increase of phosphate concentrations resulted in the decrease in total nitrogen contents in leaves. When nitrate concentrations increased from 1 to 8 mmol/L, soluble protein contents in leaves increased in general, and continuous increase of nitrate concentrations induced a decrease in soluble protein contents in leaves. Under treatment of 0.25 mmol/L of phosphate, the soluble protein contents reached a maximum. 4) In general, F _v/F _m increased as nitrate concentrations increased from 1 to 8 mmol/L, and continuous increase of nitrate concentration resulted in decrease in F _v/F _m. The similar changes occurred under phosphate treatments. As nitrate concentrations increased from 1 to 8 mmol/L, photosynthetic rates gradually increased, but when nitrate concentrations increased to 16 mmol/L, photosynthetic rate reduced by 16%, in contrast to the control. Photosynthetic rates reached a maximum when seedlings were supplied with 1 mmol/L, and an oversupply of phosphate (2 mmol/L) resulted in decrease in photosynthetic rates. The results suggested that supply levels of nitrogen affected ALA biosynthetic rates, activities of PBG synthase, and affected contents of chlorophyll and carotenoids. Moreover, nitrogen supply levels affected contents of total nitrogen and soluble proteins in leaves, and net photosynthetic rates. ALA biosynthesis rates and activities of PBG synthase were affected by phosphate supply, but contents of chlorophyll and carotenoids were not affected. And net photosynthetic rates were affected little by phosphate supply. __________ Translated from Scientia Silvae Sinicae, 2005, 41(4) [译自:林业科学, 2005, 41(4)]     

Large-scale genetic structure and drought-induced effects on European Scots pine (Pinus sylvestris L.) seedlings

Seedlings of ten provenances of Scots pine (Pinus sylvestris L.) from the southwestern to the central part of the species distribution range were investigated in a greenhouse experiment under dry conditions compared to a well-watered control. We conducted an isozyme study and recorded phenology as well as growth traits during the first year of growth. Genetic variability and genetic diversity increased from the westernmost provenances to those central to the distribution. Provenances from the Apennines and Spain revealed the strongest genetic differentiation compared to all others, whereas populations from Germany, Poland and Bulgaria were found to belong to the same gene pool. Seedling development and bud set were faster in northern populations. Shoot length was highest for Polish and German provenances within both regimes, populations from France and Spain had the longest roots. Reduced soil moisture slowed later development stages and delayed bud set for all provenances by about 5 days. Shoot growth decreased considerably under the dry regime for all provenances. German provenances were the most sensitive to drought, whereas Spanish provenances showed adaptation to drought conditions indicated by the lowest reduction in shoot growth relative to optimum conditions. The results of this pilot study show that under more pronounced drought conditions with repeated drought events, the so far established superiority of northeastern provenances compared to southwestern ones could diminish in the future.