Large mulches and manual release enhance growth of ponderosa pine seedlings

Woody and herbaceous vegetation that captures scarce soil moisture often kills or stunts the growth of conifer seedlings in young plantations in the Sierra Nevada of California. Two methods for excluding this vegetation are to apply large (3-m×3-m), long-lasting (at least 5 years) mulches around the seedlings soon after planting, or to repeatedly grub seedlings of competing vegetation in study plots. Both techniques were tested and proved to be effective, significantly increasing ponderosa pine diameter and height relative to the control and to seedlings surrounded by small paper mulches. The effective treatments were large enough to enable conifer seedlings to capture site resources unimpeded by competing plants. Eight species of shrubs, seventeen forbs, four grasses, and one fern grew naturally on the study site.Results suggest that the forester now has two biologically effective means for controlling unwanted vegetation and for attaining rapid early pine growth in environments similar to the study area. Although more expensive, the large heavy polyester mulches ($9.90 per seedling over 5 years) give the forester an alternative to manual release ($2.05 per seedling over 5 years).     

Predicting survival of planted Douglas-fir and ponderosa pine seedlings on dry,low-elevation sites in southwestern Oregon

Four equations were developed for predicting the probability of Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] and ponderosa pine (Pinus ponderosa Dougl. ex Laws.) survival for the first (0–1) and first to third (1–3) growing seasons after applying mulching, scalping, or artificial shading (shade cards) treatments in plantations in southwestern Oregon, U.S.A. Variables describing conifer size, levels of competing vegetation, presence of silvicultural treatments, site factors, and climate factors were collected from 13 sites ranging from 0 to 6 years after planting and examined as potential predictors of survival. Age, stem diameter, a competition index for shrubs, severity of growing season at time of treatment, average annual precipitation, aspect, and slope angle were predictors of Douglas-fir survival during 0–1 and 1–3 growing seasons after treatment; the presence of silvicultural treatments was also a predictor only during the first growing season after treatment. Age, aspect, and slope angle were predictors of ponderosa pine survival over both 0–1 and 1–3 growing seasons after treatment; height-diameter ratio, competition indices for herbs, shrubs, and hardwoods, silvicultural treatment, severity of growing season at time of treatment, and average annual precipitation were also predictors only during the first growing season after treatment; crown width was a predictor of survival only during 1–3 growing seasons after treatment. When significant in the models, predicted probability of survival increases with treatments, less severe weather conditions, diameter, crown width, age, and precipitation; probability decreases with increasing height-diameter ratio and competition indices for herbs, shrubs, and hardwoods.     

Recruitment of ponderosa pine seedlings in the Cascade Range

Abiotic stresses on seedling regeneration in xeric ecosystems are great, hence recruitment processes can be facilitated by stand factors that ameliorate the germinant-scale microenvironment. An experiment was conducted on the eastern slope of the Cascade Range to test the effects of shrub cover, simulated seed caching, and substrate on the recruitment of Pacific ponderosa pine (Pinus ponderosa var. ponderosa Dougl. ex Laws.) seedlings. Failure rates of seeds sowed in exclosures were large, with less than 30% emerging as germinants in the spring following fall sowing. Simulated seed caching improved emergence rates by more than sevenfold and was responsible for 88% of all spring germinants. Emergence rates were lowest from uncached seeds on litter. Just 16% of the crop survived the summer and fall to the month of November, or less than 5 months after emergence. Shrub cover did not affect emergence rates, but establishment rates were higher: seedlings beneath shrubs succumbed to desiccation at a slower rate than unshaded seedlings. By August there were 2.3 times more survivors at shrub-shaded sites than unshaded sites, and by the end of fall, when seedlings were considered established, more than 78% existed beneath shrubs. This study provides evidence that the natural recruitment of ponderosa pine seedlings is facilitated by the occurrence of the species’ common shrub associates.     

Growth and phenology of seedlings of four contrasting slash pine families in ten nitrogen regimes

Seedlings of two fast- and two slow-growing families of slash pine, Pinus elliottii Englm. var. elliottii, were grown in a greenhouse for one growing season in one of 10 nitrogen (N) regimes. Increasing the N concentration in the nutrient solution resulted in both increased growth rates during the exponential growth phase and extended duration of the growing season. The two components of total height, free growth (epicotyl length to the first bud) and summer growth (height growth after the first bud), both increased significantly with increasing N concentrations up to 40-60 mg l(-1) but decreased at N concentrations above 180 mg l(-1). Compared to seedlings grown in the presence of an optimum N concentration, seedlings grown in the presence of trace amounts of N were smaller and had less summer growth as a percentage of total growth, earlier cessation of height growth, fewer flushes, lower shoot/root ratio, higher root fibrosity, and lower N concentrations in all seedling tissues. Compared to slow-growing families, fast-growing families had more summer height growth, more flushes and later growth cessation, higher shoot/root ratios and higher root fibrosity at all N concentrations. In the presence of an optimum or higher concentration of N, the fast-growing families also had higher needle and total N concentrations than the slow-growing families. Strong family by N-treatment interactions occurred for height, phenology and biomass traits because of the extra responsiveness of one family to increasing N concentration. Several seedling traits were identified that appear promising for predicting field performance in slash pine. The results indicated that the nutrient environment greatly influences genetic expression (e.g., family patterns of summer growth were most closely related to field rankings for seedlings in the trace-N treatment).     

Bark beetle community structure under four ponderosa pine forest stand conditions in northern Arizona

We studied the bark beetle guild (Coleoptera: Scolytidae) in the ponderosa pine forests of northern Arizona to explore if the species assemblages and relative abundance differ between managed and unmanaged stands. Four stand conditions were assessed: (1) unmanaged stands with high tree density, (2) thinned stands, (3) thinned and burned (with prescribed fire) stands and (4) stands that had been burned by stand replacing wildfires. The study was conducted in the ponderosa pine forests of the Coconino Plateau, northern Arizona. For several decades this area has been relatively free of bark beetle outbreaks despite the current overstocked condition of many stands. We found that a similar species assemblage composed of Dendroctonus frontalis, D. brevicomis, D. valens, D. approximatus, D. ponderosae, and Ips pini occurred across all four stand conditions over 3 years of study. The population levels of all these species were endemic across all stand conditions. The non-aggressive D. approximatus and D. valens were indicator species for thinned and unmanaged stands, respectively, but this was not consistent among years. The ambrosia beetle Gnathotrichus sp. and the bark beetle predator Enoclerus sp. consistently indicated stands burned by wildfire. In addition to our field experiment, we analyzed the historical pattern of attacks of bark beetles in our area of study. Our findings suggest that the pattern of attack of D. brevicomis (the only Dendroctonus species for which attacks have been reported) and Ips spp. has been through scattered small infestations in groups of 1–10 trees. Whereas small infestations by Ips spp. are increasing, those for D. brevicomis are decreasing. Although we agree that the high density stands in northern Arizona are in an “unhealthy” condition, our results do not show that they were supporting large bark beetle outbreaks. Our results challenge the theoretical assumptions about the relationship between stand structure, tree resistance and bark beetle performance.     

Response of antelope bitterbrush to repeated prescribed burning in Central Oregon ponderosa pine forests

Antelope bitterbrush is a dominant shrub in many interior ponderosa pine forests in the western United States. How it responds to prescribed fire is not well understood, yet is of considerable concern to wildlife and fire managers alike given its importance as a browse species and as a ladder fuel in these fire-prone forests. We quantified bitterbrush cover, density, and biomass in response to repeated burning in thinned ponderosa pine forests. Low- to moderate-intensity spring burning killed the majority of bitterbrush plants on replicate plots. Moderately rapid recovery of bitterbrush density and cover resulted from seedling recruitment plus limited basal sprouting. Repeated burning after 11 years impeded the recovery of the bitterbrush community. Post-fire seed germination following the repeated burns was 3–14-fold lower compared to the germination rate after the initial burns, while basal sprouting remained fairly minor. After 15 years, bitterbrush cover was 75–92% lower on repeated-burned compared to unburned plots. Only where localized tree mortality resulted in an open stand was bitterbrush recovery robust. By controlling bitterbrush abundance, repeated burning eliminated the potential for wildfire spread when simulated using a customized fire behavior model. The results suggest that repeated burning is a successful method to reduce the long-term fire risk imposed by bitterbrush as an understory ladder fuel in thinned pine stands. Balancing the need to limit fire risk yet provide adequate bitterbrush habitat for wildlife browse will likely require a mosaic pattern of burning at the landscape scale or a burning frequency well beyond 11 years to allow a bitterbrush seed crop to develop.     

Effectiveness of freezer storage in fulfilling the chilling requirement of fall-lifted ponderosa pine seedlings

The degree to which freezer storage fulfilled the chilling requirement of ponderosa pine (Pinus ponderosa Dougl. ex Laws.) seedlings of two sources was determined by monitoring their development after potting or planting. The seedlings were lifted in September, October, November, or March and subjected to storage before outplanting. The fulfillment of chilling was assessed by measuring days to budbreak, cumulative percentage of seedlings flushing, foliated shoot length, and rate of bud abortion. The effect of freezer storage depended on stage of seedling development at lifting, length of storage, and seed source. Storage did not totally replace winter conditions, especially for seedlings lifted in September and October. Those from a high-elevation seed source flushed sooner than those from a low-elevation source. Delayed budbreak after planting of early lifted seedlings from the high-elevation source disappeared in the second year, but those from the low-elevation source continued to show effects. Seedlings lifted and stored in November had patterns of budbreak that were similar to those of seedlings that had overwintered in beds.     

不同土壤水分胁迫格局对印度沙漠中的黄檀种苗营养吸收和生物量的影响

1998年7月,利用非称重式蒸渗池种植单一种源的一年生黄檀种苗,研究在印度沙漠地区培养黄檀种苗的合理灌水技术参数。当各处理（W1、W2、W3、W4）的土壤水分含量分别降低到7.56%、5.79%、4.44%和3.23%时,通过灌溉使苗木生长保持在一定的土壤的水分状况,如36.2mm（W1）、26.5mm（W2）、20.2mm（W3）和18.1mm（W4）。结果表明,在36.2mm（W1）水平时,种苗的株高、冠径、叶数和叶面积达到最大值（p〈0.01）。在W1和W2处理中,虽然上述参数没有明显差异,但在W2处理中,种苗的每升水分利用率的生物量最大。在W3、W4和W5灌溉水平下,不利于提高种苗的株高、生物量和营养积累。在W2水平以下（5.79%）,土壤水分有效率能提高根系生物量占总生物量的百分比。但在W3和W4处理中,叶干生物量百分比下降,同时在W5处理中,茎干生物量百分比下降。在W5处理中,土壤水势达到-196Mpa,种苗才可以成活。在W3和W4处理中,土壤水分有效率的限额影响黄檀种苗的生长和生物量。在W2处理中,土壤水分有效利用率最高,种苗的生长和生物量达到最高值。因此,在壤砂土条件下,通过灌溉维持幼苗土壤水分含量在5.79%以上时,可获得较好的黄檀种苗的生长和生物量产量。     

Stock quality and field performance of Pinus patula seedlings produced under two nursery growing regimes during seven different nursery production periods

Two types of containerized P. patula seedlings, referred to as hard and soft seedlings, were raised by droughting and different fertilizer applications. Hard seedlings were raised by applying half the water and a quarter of the fertilizer (0.01 g per seedling 21%N:7.1%P:14.2%K) applied to the soft seedlings. At the end of the nursery cultural treatments the two types of seedlings were morphologically distinct. Hard seedlings had lower heights, height to root collar diameter ratios and seedling dry masses than soft seedlings, but mortality was similar for both seedling types when planted during seven different production periods within the planting season on three sites which differed climatically and geologically. Correlations between mortality and height to root collar diameter ratio (r = 0.76), root to shoot ratio (r = 0.83) and root growth potential (r = --0.69) were obtained indicating that grading of seedlings on these parameters may improve survival. However, it was evident that survival could be significantly improved by identifying the best time of year and conditions for planting, as well as improving stock quality.     

Initial moisture stress,budbreak and two-year field performance of three morphological grades of slash pine seedlings

This study examined the relationship between root collar diameter, plant moisture stress and budbreak in three morphological grades of bareroot 1+0 slash pine (Pinus elliottii Engelm.) nursery seedlings and assessed the role of these parameters in predicting field performance potential under operational conditions. Two months after outplanting seedlings with small (3.2 mm) diameters exhibited greater signs of moisture stress than those with the largest (4.7 mm) diameters, as determined by lower xylem pressure potential values. Intermediate and large-sized seedlings (diameter >3.2 mm) showed earlier budbreak than smaller seedlings with more rapid shoot elongation after planting and had significantly greater survival rates for two years after planting on both a moist flatwoods and a dry sandhill planting site. However, after two years on the more favorable moist site, height and diameter measurements of seedlings with significantly smaller diameters initially did not differ from those of intermediate sized seedlings (diameter >3.2 and <4.7 mm). Large seedlings had greater second-year leader and diameter increments and attained greater total height and diameter after two years on both sites. Decreasing the proportion of smaller seedlings included in the field performance analyses increased overall mean plantation survival while increasing the proportion of large seedlings increased mean two-year total height and diameter as well as annual growth increments.     

The productivity of Tipuana tipu under three cutting regimes in southeast Queensland

The tree legume Tipuana tipu, which has potential as a browse species in sub-tropical regions, was subjected to three cutting frequency regimes of 6, 8 and 12 week intervals at a cutting height of 1 m. Cutting at 12 week intervals gave a total leaf yield of 4.02 t/ha/year which was significantly higher than the other two treatments. There was 100% survival of all plants in all treatments over 2 years and the implications of the results for the management of Tipuana tipu in a hedgerow system for folder production are discussed.     

Survival of tanoak (Lithocarpus densiflorus) and Pacific madrone (Arbutus menziesii) seedlings in forests of southwestern Oregon

Survival of tanoak (Lithocarpus densiflorus) and Pacific madrone (Arbutus menziesii) seedlings was studied in order to interpret succession in conifer hardwood forests and to determine ways to suppress establishment of these species. Seed protected from rodents and birds, and unprotected seed was sown in clearcuts and in conifer stands 40 to 200+ years old. Second-year survival rates of tanoak seedlings were high (50–70%) in exposed clearcuts and conifer stands. Seed predators appear to be of prime importance in limiting tanoak establishment. Survival rates of Pacific madrone seedlings on the same sites as the tanoak were low (0–8%), and many factors caused mortality. Seedlings of both species grew slowly; after 3 years, average tanoak height was only 6.0 to 14.0 cm, average madrone height 2.0 to 6.0 cm.     

Effect of shoot size on the gas exchange and growth of containerized Picea mariana seedlings under different watering regimes

Containerized black spruce (Picea mariana [Mill.] B.S.P.) seedlings of three different sizes (small, medium, and large) were planted in raised sand beds maintained under wet, moderately dry or dry watering regimes during the growing season. The small seedlings were of a conventional stock type. The two larger sizes were novel stock types grown in larger containers. Physiological measurements during the summer showed that the small and medium seedlings maintained nearly similar levels of gas exchanges and water status, but that the large seedlings had reduced net photosynthesis and stomatal conductance under all watering regimes. Analysis of dry masses showed comparable relative growth rates in the small and medium seedlings, but a small to null growth in the large seedlings. Examination of root relative growth rate under wet conditions revealed significant root growth in small and medium seedlings, but negligible growth in the large seedlings. It was concluded that increasing the shoot size of containerized seedlings can be achieved without increasing the susceptibility of the seedlings to water stress, as long as the vigour of the root system is maintained.     

Study on community structure and self-sustaining mechanism of broad-leaved/Korean pine forests in northeast China

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Growth and survival of seedlings of various picea species under northern climatic conditions

The main purpose of these studies was to investigate the adaptation of young seedlings of various seed lots of Picea abies (L.) Karst., P. glauca (Moench) Voss, P. x lutzii Little and P. sitchensis (Bong.) Carr. to northern climatic conditions. Effects of temperature and photoperiod on elongation growth and growth cessation were studied under controlled conditions in a phytotron. In addition, growth and survival of the seedlings outdoors at 69°39’ N lat. were followed for two years. Seed lots of /’. abies originated from northern Norway (66° N lat.), those of the other species were from Alaska (between 57°.and 66° N lat.). The critical photoperiod for budset was 19–20 h for seed lots of P. abies. In general, the critical photoperiod for budset increased with increasing latitude of the seed source, but the results indicated a significantly shorter cirtical photoperiod for seed lots from about 60° N lat., <120 m a.s.l. of P. sitchensis (between 12 and 16 h) than for comparable seed lots of P x lutzii (17–18 h) or P. glauca (18 h). The time course of budset under natural light conditions, both in the phytotron and outdoors, generally followed the pattern predicted from the critical photoperiod. However, in P. glauca the budset occurred earlier than in P. abies although the latter had a longer critical photoperiod. Due to the short critical photoperiod and consequently delayed growth cessation and hardening, all seed lots of P. sitchensis (from 58° to 60° N lat.) were severely damaged during winter. Some damage was also observed in P. x lutzii and in P. abies. The optimum temperature for elongation growth was higher for P. sitchensis than for the other species. In the phytotron experiments, seedlings of P. sitchensis grew best at temperatures between 12 and 21°C, but at 9°C the best growth was obtained in some seed lots of P. abies. After two growth seasons outdoors, all seed lots of P. abies were taller than any seed lot of the other species. Also P. glauca seed lots and one seed lot of P. x lutzii showed good growth, and their growth rhythm seemed to be well adapted to the northern conditions.     

Herbicides and planting date affect early performance of container-grown and bare-root loblolly pine seedlings in Alabama

The survival of bare-root and container-grown loblolly pine (Pinus taeda L.) seedlings exceeded 90% when outplanted in March at two sites in Lee County, Alabama. At both sites, soil moisture and seedling survival were greater in March than in May. A March herbicide application reduced weed biomass by 75–80% at both sites. At the moist site, herbicide application did not affect survival. However, at the drier site, a reduction in weed biomass increased both the percent soil moisture and the survival of May-planted bare-root seedlings. When soil moisture at planting time was less than 13% on a dry weight basis container-grown seedlings survived better than bare-root seedlings. At both sites, reduced weed competition resulted in greater seedling heights and diameters.Alabama Experiment Station Journal Series No. 9-85802.     

Frost tolerance of two-year-old Picea glauca seedlings grown under different irrigation regimes in a forest nursery

Abstract

This study examined the impact of increased irrigation efficiency on the hardening and frost tolerance of 2-year-old containerized white spruce seedlings in the context of groundwater protection, irrigation management and the maintenance of seedling quality in northern climates. The seedlings were grown under three different irrigation regimes (IR =30%, 40% and 55% v/v; cm³ H₂O/cm³ substrate) and were hardened under conditions of natural photoperiod and temperature. After being subjected to artificial frost tests on four sampling dates during autumn, the seedlings were compared for bud development and frost tolerance. IR had no influence on frost tolerance as determined by measurements of physiological (electrolyte leakage, root water loss) and morphological (shoot damage, root initiation) variables. At the end of the second growing season, there was no significant difference between IRs in seedling height, root collar diameter, shoot dry mass and root dry mass. The results indicate that the amount of water applied to large-dimension 2-year-old white spruce seedlings during the growing season can be significantly decreased without prematurely impeding their growth or hindering their acquisition of frost tolerance.     

Seedling survival and growth of Aquilaria malaccensis in different microclimatic conditions of northeast India

We studied seedling survival and growth of Aquilaria malaccensis in three different environmental conditions(homegardens,green house and in different canopy conditions) of northeast India.Results show that mean seasonal survival was highest in green house(95.53%±2.33),followed by homegardens(89.3%±1.89) and different canopy conditions(77.62%±6.73);the highest values were found during February to April for both the homegardens(96%±1.68) and green house(98% ± 0.88) and lowest during November to January(78%±2.99) in homegardens and May to July(90%±4.53) in green house.In case of transplanted seedlings in different canopy conditions,mean seasonal survival was highest during May to July(98%±1.92) and lowest during August to October(66%±12.81).However,mean seasonal growth of collar diameter was highest in different canopy conditions(23.99%±1.76) compared to green house(21.52%±2.70) and homegardens(12.44%±1.33) and it was highest during rainy season(May to July) and lowest during dry winter(November to January) in all the three experimental sites.These variations may be due to the different microclimatic conditions as well as nutrient status of the soil in all the three experimental sites.Although,seedling quality plays a great role in their survival and growth,based on the result of green house experiment,it can be concluded that maintenance of seedlings in green house conditions during their early growth period may improve both the survival and growth for large scale plantation of the species.Thus,the species can be reintroduced in its natural forest range to compensate the loss of natural population of this precious species in northeast India.     

Fate of N-labelled nitrate in a wet summer under different residue management regimes in young hoop pine plantations

A field study was conducted to investigate the fate of ¹⁵N-labelled nitrate applied at 20 kg N ha⁻¹ in a wet summer to microplots installed in areas under different residue management regimes in second-rotation hoop pine (Araucaria cunninghamii) plantations aged 1–3 years in south-east Queensland, Australia. PVC microplots of 235 mm diameter and 300 mm long were driven into 250 mm soil. There were three replications of each of eight treatments. These were areas just under and between 1-year-old windrows (ca. 2–3 m in width) of harvesting residues spaced 15 m apart, and with and without incorporated foliage residues (20 t DM ha⁻¹); the areas just under and between 2- or 3-year-old windrows spaced 10 m apart. Only 7–29% of the added ¹⁵N was recovered from the top 750 mm of the soil profile with the leaching loss estimated to be 70–86% over the 34-day period. The ¹⁵N loss via denitrification was 3.7–6.3% by directly measuring the ¹⁵N gases emitted. The microplots with the incorporated residues at the 1-year-old site had the highest ¹⁵N loss (6.3%) as compared with the other treatments. The ¹⁵N mass balance method together with the use of bromide (Br) tracer applied at 100 kg Br ha⁻¹ failed to obtain a reliable estimate of the denitrification loss. The microplots at the 1-year-old site had higher ¹⁵N immobilisation rate (7.5–24.7%) compared with those at 2- and 3-year-old sites (2.1–3.6%). Incorporating the residues resulted in an increase in ¹⁵N immobilisation rate (24.5–24.7%) compared with the control without the incorporated residues (8.4–14.3%). These findings suggest that climatic conditions played important roles in controlling the ¹⁵N transformations in the wet summer season and that the residue management regimes could also significantly influence the ¹⁵N transformations. Most of the ¹⁵N loss occurred through leaching, but a considerable amount of the ¹⁵N was lost through denitrification. Bromide proved to be an unsuitable tracer for monitoring the ¹⁵N leaching and movement under the wet summer conditions.