Some limitations inherent to static indices of plant competition

1993 ◽  
Vol 23 (10) ◽  
pp. 2141-2152 ◽  
Author(s):  
Philip J. Burton
Keyword(s):  
Plant Competition ◽  
Simulation Models ◽  
Stand Development ◽  
Crop Species ◽  
Vegetation Development ◽  
Competitive Intensity ◽  
Vegetation Control ◽  
Fundamental Limitations ◽  
Vegetation Complex ◽  
Intensity Of Competition

Various measurements of the abundance, proximity, and stature of neighbouring plants are utilized as indices of competitive intensity experienced by crop trees. These indices can be useful in assessing the desirability of vegetation control and stand thinnings, and in simulating stand development. Static competition indices, however, have fundamental limitations which should be more widely considered. Competition is usually a constraint to growth, not a determinant of growth, so any measurement of competition alone is fundamentally limited in its ability to predict individual crop tree performance. Differences in the microsite effects of competitors and the autecological responses of crop species result in wide variation in the size of the functional competitive arena, and suggest the need for distinct weightings of competitive intensity for different combinations of species and site. Site differences and weather variation, when coupled with species differences in above- and below-ground allocation, will alter the mode and intensity of competition within a stand and from year to year. The phenology of competitors and focal species will likewise alter interference patterns within a year, making one-time measurements sometimes misleading. Suggested alternatives for determining the importance and intensity of competition include the maintenance of competition-free seedlings ("phytometers") in order to gauge the competitive constraints experienced elsewhere in a plantation. Simulation models of tree growth and stand development also show promise, but they must incorporate the dynamics of noncrop vegetation development. In developing guidelines for the assessment of noncrop interference and the advisability of vegetation control, there is still a need to determine, in a generalizable manner, appropriate survey plot sizes and critical competition thresholds for different combinations of site type, crop species, and vegetation complex.

Ten-year responses of ponderosa pine plantations to repeated vegetation and nutrient control along an environmental gradient

1999 ◽  
Vol 29 (7) ◽  
pp. 1027-1038 ◽  
Author(s):  
Robert F Powers ◽  
Phillip E Reynolds
Keyword(s):  
Pinus Ponderosa ◽  
Ponderosa Pine ◽  
Plant Competition ◽  
Site Index ◽  
Stem Volume ◽  
Growth Responses ◽  
Xylem Water Potential ◽  
Potential Productivity ◽  
Vegetation Control ◽  
Moisture Availability

Factorial combinations of vegetation, nutrient, and insect control treatments were applied repeatedly to three contrasting California plantations of Pinus ponderosa var. ponderosa Dougl. ex Laws. Ten-year findings show that potential productivity is far greater than previously believed. Stem volume gains were linked directly with increases in crown volume. Insect problems were negligible. Vegetation control increased tree growth profoundly on xeric sites but less so on the most mesic. Where soil was both droughty and infertile, growth responses traced primarily to improved soil moisture availability and secondarily to better nutrition. The most fertile site also was droughty, and trees responded only to improved moisture availability. Water was less limiting on the most productive site. There, both fertilizers and herbicides triggered similar, substantive growth increases. Drought from both plant competition and climate reduced stomatal conductance, xylem water potential, and net assimilation rates. Assimilation rates increased linearly with site index, but treatment differences were not apparent once drought had peaked. Fertilization improved water-use efficiency where water stress was not extreme. Advantages in water availability to pines from vegetation control will dissipate as tree crowns close and transpiration rises.

scholarly journals Evaluation of Land Suitability Methods with Reference to Neglected and Underutilised Crop Species: A Scoping Review

Land ◽  
2021 ◽  
Vol 10 (2) ◽  
pp. 125
Author(s):  
Hillary Mugiyo ◽  
Vimbayi G. P. Chimonyo ◽  
Mbulisi Sibanda ◽  
Richard Kunz ◽  
Cecilia R. Masemola ◽  
...  
Keyword(s):  
Machine Learning ◽  
Scoping Review ◽  
Simulation Models ◽  
Land Suitability ◽  
Land Evaluation ◽  
Suitability Analysis ◽  
Crop Species ◽  
Crop Models ◽  
Crop Suitability ◽  
Crop Simulation Models

In agriculture, land use and land classification address questions such as “where”, “why” and “when” a particular crop is grown within a particular agroecology. To date, there are several land suitability analysis (LSA) methods, but there is no consensus on the best method for crop suitability analysis. We conducted a scoping review to evaluate methodological strategies for LSA. Secondary to this, we assessed which of these would be suitable for neglected and underutilised crop species (NUS). The review classified LSA methods reported in articles as traditional (26.6%) and modern (63.4%). Modern approaches, including multi-criteria decision-making (MCDM) methods such as analytical hierarchy process (AHP) (14.9%) and fuzzy methods (12.9%); crop simulation models (9.9%) and machine learning related methods (25.7%) are gaining popularity over traditional methods. The MCDM methods, namely AHP and fuzzy, are commonly applied to LSA while crop models and machine learning related methods are gaining popularity. A total of 67 parameters from climatic, hydrology, soil, socio-economic and landscape properties are essential in LSA. Unavailability and the inclusion of categorical datasets from social sources is a challenge. Using big data and Internet of Things (IoT) improves the accuracy and reliability of LSA methods. The review expects to provide researchers and decision-makers with the most robust methods and standard parameters required in developing LSA for NUS. Qualitative and quantitative approaches must be integrated into unique hybrid land evaluation systems to improve LSA.

scholarly journals Competitive intensity and inefficiency in European container ports

2018 ◽  
Vol 3 (2) ◽  
pp. 165-184 ◽  
Author(s):  
Axel Merkel
Keyword(s):  
Technical Efficiency ◽  
The European Union ◽  
Stochastic Production Frontier ◽  
Competitive Intensity ◽  
Content Type ◽  
Negative Effect ◽  
Container Ports ◽  
Stochastic Production ◽  
The Relationship ◽  
Intensity Of Competition

Purpose The purpose of this paper is to empirically examine the relationship between intensity of competition and technical efficiency of large European container ports, accounting for regional diversities and spatial aspects of inter-port competition. Design/methodology/approach The analysis consists of applying a stochastic production frontier approach to a dataset of 77 large European container ports over the period 2002-2012, with inefficiency terms simultaneously modeled as a function of (among other factors) a constructed index of competitive intensity at different spatial levels. Findings The results indicate that there is no significant negative effect of competitive intensity on efficiency. In fact, for competing European ports within a proximity of 300 km, a higher level of competition is found to be associated with a higher level of technical efficiency. Originality/value The originality of the paper stems from its particular focus on European port regions and its novel findings in this context, which have implications for the discussions regarding pro-competitive port policy and regulation in the European Union.

Examining 40-year stand development following vegetation control: white spruce planted in a trembling aspen dominated cutover

2011 ◽  
Vol 41 (4) ◽  
pp. 728-739 ◽  
Author(s):  
Robert L. Fleming ◽  
Allister D. Smith
Keyword(s):  
Populus Tremuloides ◽  
Picea Glauca ◽  
White Spruce ◽  
Growth Patterns ◽  
Stand Development ◽  
Trembling Aspen ◽  
Herbicide Application ◽  
Vegetation Control ◽  
Mechanical Site Preparation ◽  
Age Shift

Many of the major questions regarding stand establishment practices involve implications for longer-term ecosystem development. We examined 41-year treatment effects on stand composition and dynamics using a white spruce ( Picea glauca (Moench) Voss) planting, mechanical site preparation (MSP) – herbicide (2,4-D plus 2,4,5-T) trial in a trembling aspen ( Populus tremuloides Michx.) dominated mixedwood. Both barrel and blade MSP with planting increased total and white spruce year 41 stand-level biomass over that in untreated areas. Year 2 herbicide application reduced year 41 trembling aspen biomass without substantially increasing that of white spruce, resulting in total yields similar to those in untreated areas. Barrel MSP increased year 41 trembling aspen biomass over that of untreated areas whereas blade MSP reduced it. Herbicide-related declines in trembling aspen biomass persisted or increased with time whereas white spruce response to herbicide varied with time and MSP. By accounting for inherent growth patterns, age shift calculations gave more balanced temporal depictions of planted white spruce response than effect size or percentage gain calculations. With barrel MSP, stand composition demonstrated a degree of mixedwood homeostasis whereas with blading, trembling aspen composition declined unilaterally from year 20 to 41.

scholarly journals A polymer electrolyte membrane fuel cell model with multi-species input

2005 ◽  
Vol 219 (4) ◽  
pp. 255-271 ◽  
Author(s):  
P Rama ◽  
R Chen ◽  
R Thring
Keyword(s):  
Carbon Monoxide ◽  
Fuel Cell ◽  
Low Temperature ◽  
Polymer Electrolyte ◽  
Cell Model ◽  
Polymer Electrolyte Membrane ◽  
Simulation Models ◽  
Porous Electrodes ◽  
Electrolyte Membrane ◽  
Fundamental Limitations

With the emerging realization that low temperature, low pressure polymer electrolyte membrane fuel cell (PEMFC) technologies can realistically serve for power-generation of any scale, the value of comprehensive simulation models becomes equally evident. Many models have been successfully developed over the last two decades. One of the fundamental limitations among these models is that up to only three constituent species have been considered in the dry pre-humidified anode and cathode inlet gases, namely oxygen and nitrogen for the cathode and hydrogen, carbon dioxide, and carbon monoxide for the anode. In order to extend the potential of theoretical study and to bring the simulation closer towards reality, in this research, a 1D steady-state, low temperature, isothermal, isobaric PEMFC model has been developed. The model accommodates multi-component diffusion in the porous electrodes and therefore offers the potential to further investigate the effects of contaminants such as carbon monoxide on cell performance. The simulated model polarizations agree well with published experimental data. It opens a wider scope to address the remaining limitations in the future with further developments.

scholarly journals Determinants of competitive intensity: substitutability and pricing policy

2021 ◽  
Vol 14 (1) ◽  
pp. 5-16
Author(s):  
Paul Cocioc
Keyword(s):  
Production Capacity ◽  
Critical Perspective ◽  
Pricing Policy ◽  
Competitive Intensity ◽  
Pricing Policies ◽  
Intensity Of Competition

The article offer a critical perspective of several elements and some associated indicators used in characterizing and estimating the intensity of competition (i.e., the extent to which the mutual pressure of rivals is exerted on the market). We focus on the pricing policies of the firms and its impact and expected responses from competitors. Influences of substitutes and overall production capacity surplus are also analyzed.

Effect of vegetation control, harvest intensity, and soil disturbance on 20-year jack pine stand development

2018 ◽  
Vol 48 (4) ◽  
pp. 371-387 ◽  
Author(s):  
R.L. Fleming ◽  
J.-D. Leblanc ◽  
T. Weldon ◽  
P.W. Hazlett ◽  
D.S. Mossa ◽  
...  
Keyword(s):  
Natural Regeneration ◽  
Jack Pine ◽  
Soil Disturbance ◽  
Stand Development ◽  
Vegetation Control ◽  
Harvest Intensity ◽  
Stand Productivity ◽  
Size Inequality ◽  
Planted Tree ◽  
Whole Tree

Currently, there are uncertainties regarding the impacts and (or) efficacy of biomass harvesting and silvicultural practices on stand production on coarse-textured boreal soils. Replicated factorial field experiments examining effects of complete vegetation control (repeated glyphosate application) following operational stem-only harvest with disc trenching (SOT), operational whole-tree harvest with (WTT) and without (WT) disc trenching, and whole-tree harvest with complete forest floor removal by blading (WTB) and blading followed by compaction (WTBC) were installed on four sandy northern Ontario jack pine (Pinus banksiana Lamb.) sites. Over 20 years, WTB improved planted-tree survival but decreased longer term stand productivity in comparison with other harvest intensity – soil disturbance treatments. Vegetation control improved tree growth and stand productivity initially, but over time, benefits declined substantially. SOT and WTT had similar impacts on stand production. Disc trenching improved initial planted-tree growth (WTT vs. WT), particularly without vegetation control. Jack pine natural regeneration was greatest with SOT, accounting for 25% of stand biomass at year 20. Stand structure effects included increased size inequality of naturals with WTB and reduced size inequality and asymmetry of naturals with vegetation control. Overall, impacts of forest floor removal and natural regeneration on stand development have become increasingly important over time compared with those of vegetation control.

Simulation Models in Forest Management and Harvesting

1968 ◽  
Vol 44 (1) ◽  
pp. 7-13 ◽  
Author(s):  
R. M. Newnham
Keyword(s):  
Forest Management ◽  
Simulation Model ◽  
Stand Structure ◽  
Simulation Models ◽  
Stand Development ◽  
Operating Characteristics ◽  
Individual Tree ◽  
Harvesting Time ◽  
Advantages And Disadvantages

The advantages and disadvantages of simulation models are described and examples are given of their use in forestry. Stand models and a simulation model for pulpwood harvesting machines are described in some detail. Stand models simulate the growth of a stand on an individual tree basis and can be used for testing the effect of different silvicultural operations on subsequent stand development. The harvesting simulation models imitate the passage of a harvesting machine through a stand of pulpwood. They can be used to test the effect on harvesting time of using machines of different sizes and operating characteristics. The effect of stand structure on harvesting time can also be tested.

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