Early Stages Of Establishment Research Articles

An ecophysiological basis for understanding plantation establishment

Forest plantations in the early stages of establishment are considered as hierarchical biological systems, and some implications for the design of research projects and the education of regeneration foresters and scientists are discussed. Since less than optimum environmental conditions convey stress to seedlings, seedlings will in turn exhibit a strain response at either the biochemical, physiological, or morphological level. Environmental conditions in a clear-cut are contrasted with other regeneration niches, and implications for the performance of different plantation species are discussed. The important physiological and biochemical limitations on the absorption of water, nitrogen, and carbon by seedlings during their establishment phase are described. Methods of quantifying stress at the plantation site, including simple ways to separate seedling growth into its different physiological components, are shown. An example of an eastern white pine (Pinusstrobus L.) plantation grown under different levels of soil temperature, fertilization, and brush control is presented to illustrate the concepts. An approach to silvicultural research is proposed that determines the effects of silvicultural treatment on the seedling environment and then relates these environmental conditions to seedling biochemistry, physiology, and growth.

Effects of nutrients on the growth and survival ofin vitro Artocarpus heterophyllusLam. plantlets after transfer toex vitroconditions in the glasshouse

SummaryThe effects of nutrients in the planting substrate on the growth and survival of in vitro jackfruit (Artocarpus heterophyllus Lam.) plantlets under ex vitro conditions was investigated. A low level or absence of nutrients in the substrate for at least 20 days resulted in significantly more growth and survival of plantlets. Nutrient feeding after 20 days improved the further growth and survival. Nitrogen, particularly in the ammonium form, was shown to be the most inhibitory nutrient during the early stages of establishment.

Palynological Light on Tropical Rainforest Dynamics

Although there are more than a hundred Quaternary pollen diagrams from the non-arid tropics, very few are from strictly lowland ever-wet rainforest. Nevertheless, those from more upland or seasonal sites imply major changes of size and location of all tropical forests which must have had repercussions on the composition of and niche realization in the lowland ever-wet forest. Among the ecologically most important implications are that these features of the forest have been constantly changing at varying rates for at least a million years and still are changing. While it is no longer possible necessarily to associate diversity with changelessness, the alternative extreme view that diversity is the outcome of Quaternary environmental change has yet to be demonstrated palynologically. The courses of expansions of some trees in the early stages of establishment of an Australian rainforest in the Holocene are fitted to standard population growth curves and the significance of fine resolution pollen analysis for the study of rainforest ecology is demonstrated.

Palynological light on tropical rainforest dynamics

Although there are more than a hundred Quaternary pollen diagrams from the non-arid tropics, very few are from strictly lowland ever-wet rainforest. Nevertheless, those from more upland or seasonal sites imply major changes of size and location of all tropical forests which must have had repercussions on the composition of and niche realization in the lowland ever-wet forest. Among the ecologically most important implications are that these features of the forest have been constantly changing at varying rates for at least a million years and still are changing. While it is no longer possible necessarily to associate diversity with changelessness, the alternative extreme view that diversity is the outcome of Quaternary environmental change has yet to be demonstrated palynologically. The courses of expansions of some trees in the early stages of establishment of an Australian rainforest in the Holocene are fitted to standard population growth curves and the significance of fine resolution pollen analysis for the study of rainforest ecology is demonstrated.

Early adjustment of patterns of metaphase association in the evolution of a polyploid species

Evidence is presented for the adjustment of chromosomal association at metaphase in the very early stages of establishment of a new level of polyploidy. The species concerned is S. cambrensis Rossner, the hexaploid hybrid between S. squalidus L. (2n=20) and S. vulgaris (2n=40). It is suggested that the perfect bivalent pairing of S. vulgaris is the basis for the success of S. cambrensis.

Potentiation of a nucleolytic activity in Bacillus subtilis.

In several strains of Bacillus subtilis extensive breakdown of chromosomal DNA may be potentiated by osmotic lysis of protoplasts. At its most severe, in strains originating from Farmer & Rothman's thymine auxotroph, the rate of DNA breakdown was greater than 50% per hour at 40 degrees C. The rate of DNA breakdown in most other strains tested was approximately 5% per hour except for SP beta- strains, in which the rate of DNA breakdown was only 0.3%. DNA degradation was attributed to relaxation of control of a nuclease specified by the prophage of SP beta or a related phage. The most potent nuclease in lysates was an ATP-activated protein of Mr 280 000. Derivatives of Farmer and Rothman's strain containing integrated plasmids had the highest rate of DNA degradation. Although the chromosome was completely destroyed, covalently closed circular plasmids were generated from the integrated sequence. These showed massive deletions of the B. subtilis part of the integrated plasmid but the vector sequence remained intact. The nucleolytic activity therefore appears to recognize specific sequences in B. subtilis DNA. We suggest that activation of SP beta genes during development of competence may be a cause of deletion of cloned genes in the early stages of establishment of cloned sequences.

EFFECTS OF TEMPERATURE, LEVELS OF NITRATE SUPPLY AND DURATION OF LIGHT AND GROWTH ON NITRATE REDUCTASE ACTIVITY IN AGEOSTIS TENUIS AND AGROSTIS STOLONIFERA

SUMMARYNitrate reductase activity (NRA) was assessed at several moments within the day during the early stages of establishment of tiller generated plants and seedling swards of Agrostis tenuis and A. stolonifera grown at different temperatures and levels of nitrate supply. Agrostis tennis consistently exhibited higher NRA values than A. stolonifera at initial developmental stages or low nitrate availability. The reverse situation was found to occur at high nitrate availability or in longer established plants and seedling swards. This emphasizes the difficulties in establishing consistent differences between species in NRA. Both species showed increased NRA with increased nitrate availability, increased night temperature or decreased day temperature. Agrostis stolonifera increased its NRA to a greater extent than A. tenuis as nitrate availability increased. The importance of daily and developmental variation in NRA in establishing differences between these species is discussed.

Effect of spring wild fires on Iseilema (Flinders grass) populations in the Mitchell grass region of north-western Queensland

The effect of spring wildfires and consequent ashbeds on the emergence and survival of the annual Iseilema spp. (Flinders grass) was studied in field and pot experiments during favourable growing conditions between December 1976 and April 1977. Emergence of Iseilema seedlings was lower on burnt than unburnt treatments when the amount of litter present at burning was 100 g m-2 or more. Litter had a major influence on emergence in unburnt areas. Initially there was a rapid increase in emergence with increasing litter followed by decreased emergence with a further increase in litter. Microtopography had no effect on emergence in unburnt treatments but there were significantly more seedlings in depressions (750 m-2) than on flats or rises (240 m-2) in burnt areas. The number of tillers per plant was greater in burnt areas than in unburnt areas at the same density, especially when the density was lower than 500 m-2. At higher densities, the number of tillers per plant decreased in both treatments. Seedling survival was greater in burnt areas in the early stages of establishment but, by maturity, survival was highest in the unburnt areas.

II. Correlates of career motivation and satisfaction

Sources of career motivation and satisfaction were studied among a national sample of dietitians in the early establishment stage of their careers. Thirty-two items were rated on importance and satisfaction. Seven importance factor scores were developed to describe aspects of career motivation: prestige, monetary reward, independence/self-sufficiency, professional challenge, self-realization, social service, and social stimulation. Professional challenge and self-realization were the factors rated highest by the young dietitians (less than 30 years old), and prestige and social stimulation were lowest in importance. Satisfaction dimensions were: professional challenge, service to others, financial, professional power, and professional stimulation. Professional challenge provided the greatest source of satisfaction, whereas financial reward was least satisfying.

Factors Important to Yellow Birch Establishment in Upper Michigan

Increasing the proportion of yellow birch (Betula alleghaniensis Britton) in the northern hardwood type should also increase the economic return from management. Under current market prices the stumpage value of yellow birch is about double that of sugar maple (Acer saccharum Marsh.), the next most valuable species in the type. The use of yellow birch for veneer accounts for most of its high value. In upper Michigan about 30% of the net volume of this species is sold as veneer compared to only 7% of the volume of sugar maple. The proportion of yellow birch stems in the old-growth northern hardwood stands is seldom over 12% (Lake States 1935). In this type it is most commonly found as single trees on the edge of small openings or occasionally in small groups where the more tolerant species have died out or been destroyed by a catastrophic type of disturbance. Yellow birch seldom occurs as a pure stand except on relatively small areas that have been opened and mineral soil exposed, such as by windthrow, light burns, or abandoned clearings. However, in the hemlock-yellow birch sub-type (Soc. Amer. Foresters 1954), which occurs on mesophytic sites, yellow birch commonly makes up 25% or more of the stand basal area. In secondgrowth stands the percentage is usually less, the amount seeming to vary with the soil moisture conditions and species association. Some regeneration studies have been made in the north central and northeastern portions of the botanical range of yellow birch, but very little work has been reported in the Lake States, which are in the western portion. Although the general silvical requirements of this species are fairly well known, particularly as the tree reaches the larger size classes, little information is available on the early stages of establishment and growth in the Upper Peninsula of Michigan. The reasons for the lack of sufficient yellow birch reproduction after cutting in other regions are generally considered to be the relative intolerance of the species (Baker 1949, Graham 1941), browsing by animals, and more specific seedbed requirements than its competitors. A study was begun in the Upper Peninsula of Michigan in the fall of 1952 to determine (1) the influence of seedbed conditions on the regeneration of yellow birch, and (2) the relative importance of physical and biotic factors on the establishment and early growth of yellow birch seedlings. In the area selected for study, all seedbearing trees except yellow birch and a few white pine and hemlock were cut during the winter of 1952-53, and the area was disked in the fall of 1953. This paper summarizes the changes that occurred during four growing seasons after disking and discusses results of special studies on the factors affecting the early growth of yellow birch.