Description Of Vegetation Research Articles

W. S. Cooper As I Knew Him: Teacher, Mentor and Friend

W. S. Cooper As I Knew Him: Teacher, Mentor and Friend

A phytosociology survey and vegetation description of inselbergs in the uKhahlamba-Drakensberg Park World Heritage Site, South Africa

No previous scientific surveys have been conducted on inselbergs in the Drakensberg. The aim of this study was to collect specimens, identify, describe and name the vegetation clusters and assess biogeographical connections with other Afromontane regions. A total of 103 relevés where sampled from six inselbergs. The plant sampling was carried out according to the Braun-Blanquet method with the plant and environmental data entered in TURBOVEG and exported as a Cornell Condensed format file (CC!) into Juice. Classification was completed using TWINSPAN (Two-way Indicator Species Analysis) (modified), resulting in 4 major communities, 11 communities, 13 sub-communities and 18 variants. Ordination (indirect) was carried out using CANOCO (version 4.5) to investigate the relationship between species. The four major communities identified are Rhodohypoxis rubella (wetland grass and forblands), Scirpus ficinioides – Crassula peploides (sheet rock grass and forblands), Pentaschistis exserta (high-altitude alpine grassland), previously undescribed, and Merxmuellera drakensbergensis – Helichrysum trilineatum (high-altitude alpine fynbos grassland), described in other vegetation and floristic studies. Four habitats were identified, namely wetlands, sheet rock shallow soil, highaltitude alpine grassland and deep soil high-altitude fynbos grasslands. Substrate and moisture availability appeared to be the defining micro-climatic conditions determining the different vegetation clusters whilst altitude is the overriding environmental factor influencing all vegetation.Conservation implications: Rising temperatures as a result of carbon dioxide increase is predicted to drastically decrease the number of endemic and near-endemic montane species, whilst altering the composition of vegetation units which comprise the alpine vegetation.

Utilizing Amerindian Hunters' Descriptions to Guide the Production of a Vegetation Map

Describing vegetation types is critical for managing natural resources and assessing ecosystem risk. Vegetation maps are historically produced by “Western experts,” often ignoring local-level groups critical to resource management. Indigenous hunters, as resource managers, have strong connections to their landscapes and their descriptions of vegetation within their homelands can be useful in the map-making process. This project examined the usefulness of vegetation descriptions from Rupununi, Southern Guyana Indigenous hunters in the map-making process and how their descriptions were influenced by biophysical environmental attributes. A Landsat TM and ASTER DEM merged imagery of the Rupununi was classified using Indigenous hunters' vegetation descriptions to train the classification and assess accuracy. Based on the hunters' vegetation descriptions an eleven-class map was produced that covered the main vegetation types they described. Whereas “expert” maps rely on organized forest inventory data, Indigenous hunters' vegetation classifications were influenced by their interactions with the biophysical environment. The final map shows that Indigenous hunters may be important partners in the map-making process and play key roles in tropical forest management decision-making processes.

Potential landscape phytocomplexes of Sudety Mountains

The author presents his own concept of potential landscape phytocomplexes as the structural space units on the level of plant organization higher than an ecosystem (i.e. above biogeocenosis). He also defines the concept of vegetation landscape in a typological sense. Basing on the example of Sudety Mountains and Foreland regions, the author demonstrates a method of distinguishing landscape phytocomplexes and their utilization for regional description of vegetation and geobotanical regionalization.

A Study on Floristic Composition, Chorology and Ecological Structure: A case Study from a Small-scale Forest Reserve, Talesh, Iran

This study, carried out on vegetation of the Gisoum forest reserve with 171 hectares area located 14 km to Resvanshar city, Guilan province, was to examine the structure and composition of the forest vegetation. A first topographic map of the area with the scale of 1:10000 was prepared and the study area was delimited. Transect- quadrate method of sampling was used to record the floristic and phytosociological data necessary for the analysis in about 44 quadrates of 400 m2. Some vegetation parameters viz. density and diameter at breast height (DBH) for trees (over story vegetation) as well as cover-abundance for under story vegetation were recorded, respectively. The life form spectrum of Raunkiaer, the dominant vegetation type of the area, is based on importance value and vegetation structure based on frequency classes, also their chorology caring a central importance in vegetation description were determined. The study of the floristic list showed that 76 species belonging to 66 genera and 45 families existed in the area.The largest families were Asteraceae and Rosaceae with 5 species. Investigation of the geographical distribution of plant species indicated that 44 % belonged to the Europe – Siberian zone. Plant life forms by Raunkiaer method showed that phanerophytes with 35.5 % and hemicryptophytes with 27.6 % were the most frequent life forms. Dominant vegetation type based on importance value index was Buxus hyrcanus-Parrotia persica. Also the evaluation of vegetation structure based on frequency class revealed that abundance-distribution was irregular in under story and regular in upper story vegetation.

EcoVeg: a new approach to vegetation description and classification

A vegetation classification approach is needed that can describe the diversity of terrestrial ecosystems and their transformations over large time frames, span the full range of spatial and geographic scales across the globe, and provide knowledge of reference conditions and current states of ecosystems required to make decisions about conservation and resource management. We summarize the scientific basis for EcoVeg, a physiognomic‐floristic‐ecological classification approach that applies to existing vegetation, both cultural (planted and dominated by human processes) and natural (spontaneously formed and dominated by nonhuman ecological processes). The classification is based on a set of vegetation criteria, including physiognomy (growth forms, structure) and floristics (compositional similarity and characteristic species combinations), in conjunction with ecological characteristics, including site factors, disturbance, bioclimate, and biogeography. For natural vegetation, the rationale for the upper levels (formation types) is based on the relation between global‐scale vegetation patterns and macroclimate, hydrology, and substrate. The rationale for the middle levels is based on scaling from regional formations (divisions) to regional floristic‐physiognomic types (macrogroup and group) that respond to meso‐scale biogeographic, climatic, disturbance, and site factors. Finally, the lower levels (alliance and association) are defined by detailed floristic composition that responds to local to regional topo‐edaphic and disturbance gradients. For cultural vegetation, the rationale is similar, but types are based on distinctive vegetation physiognomy and floristics that reflect human activities. The hierarchy provides a structure that organizes regional/continental vegetation patterns in the context of global patterns. A formal nomenclature is provided, along with a descriptive template that provides the differentiating criteria for each type at all levels of the hierarchy. Formation types have been described for the globe; divisions and macrogroups for North America, Latin America and Africa; groups, alliances and associations for the United States, parts of Canada, Latin America and, in partnership with other classifications that share these levels, many other parts of the globe.

Pollen-based quantitative reconstructions of Holocene regional vegetation cover (plant-functional types and land-cover types) in Europe suitable for climate modelling.

We present quantitative reconstructions of regional vegetation cover in north-western Europe, western Europe north of the Alps, and eastern Europe for five time windows in the Holocene [around 6k, 3k, 0.5k, 0.2k, and 0.05k calendar years before present (bp)] at a 1° × 1° spatial scale with the objective of producing vegetation descriptions suitable for climate modelling. The REVEALS model was applied on 636 pollen records from lakes and bogs to reconstruct the past cover of 25 plant taxa grouped into 10 plant-functional types and three land-cover types [evergreen trees, summer-green (deciduous) trees, and open land]. The model corrects for some of the biases in pollen percentages by using pollen productivity estimates and fall speeds of pollen, and by applying simple but robust models of pollen dispersal and deposition. The emerging patterns of tree migration and deforestation between 6k bp and modern time in the REVEALS estimates agree with our general understanding of the vegetation history of Europe based on pollen percentages. However, the degree of anthropogenic deforestation (i.e. cover of cultivated and grazing land) at 3k, 0.5k, and 0.2k bp is significantly higher than deduced from pollen percentages. This is also the case at 6k in some parts of Europe, in particular Britain and Ireland. Furthermore, the relationship between summer-green and evergreen trees, and between individual tree taxa, differs significantly when expressed as pollen percentages or as REVEALS estimates of tree cover. For instance, when Pinus is dominant over Picea as pollen percentages, Picea is dominant over Pinus as REVEALS estimates. These differences play a major role in the reconstruction of European landscapes and for the study of land cover-climate interactions, biodiversity and human resources.

Характеристика рослинності Полонини-Руни Карпат в умовах антропогенної трансформації

The results of researches the geobotanical description of the polonina Runa Carpathians vegetation. The detailed analysis of anthropogenic factor the trample, the damaging of shoot plant. Key words: natural populations, vegetative groupings, condition of cultivation, anthropogenic factor.

Upper Palaeolithic archaeobotany of Ghar-e Boof cave, Iran: a case study in site disturbance and methodology

The excavation of Ghar-e Boof, a cave in the Zagros Mountains, places the site not only at the center of discussion on the transition to and development of its regional lithic tradition: the Rostamian (37,000–31,000 BP), but also in differentiating between plants used by humans or mere traces of the surrounding vegetation. The large pulses of Lathyrus or Vicia sp. recovered from this shallow cave in the southwest of Iran may, for instance, represent food collected from wild stands already in the early Upper Palaeolithic. The seeds of barley (Hordeum sp.), although not all clearly domesticated, are without doubt signs of disturbance or bioturbation since the historic era. Analysis of cave deposits over 30,000 years old raise a number of methodological and interpretive challenges. Human, taphonomic, or biomechanical disturbances impact the deposition of plant remains, as well as affect the composition of the assemblages, undermining spatial and ecological examination of the data set. Comprehension of provenance of the samples, site genesis, and matrix development, through detailed micromorphological and stratigraphical studies, is thus suggested in conjunction with the archaeobotanical analyses, to identify disturbances, define their cause, and treat them appropriately. Numerical studies and ecological interpretations of climate, vegetation composition, or indications of human activity therefore follow specific criteria discussed here. Despite signs of disturbance in the plant assemblages, archaeobotanic research can lead to recognition of environmental conditions, plausible human subsistence, site use and seasonality, and sound vegetation description.

Regional climate model simulations for Europe at 6 and 0.2 k BP: sensitivity to changes in anthropogenic deforestation

Abstract. This study aims to evaluate the direct effects of anthropogenic deforestation on simulated climate at two contrasting periods in the Holocene, ~6 and ~0.2 k BP in Europe. We apply We apply the Rossby Centre regional climate model RCA3, a regional climate model with 50 km spatial resolution, for both time periods, considering three alternative descriptions of the past vegetation: (i) potential natural vegetation (V) simulated by the dynamic vegetation model LPJ-GUESS, (ii) potential vegetation with anthropogenic land use (deforestation) from the HYDE3.1 (History Database of the Global Environment) scenario (V + H3.1), and (iii) potential vegetation with anthropogenic land use from the KK10 scenario (V + KK10). The climate model results show that the simulated effects of deforestation depend on both local/regional climate and vegetation characteristics. At ~6 k BP the extent of simulated deforestation in Europe is generally small, but there are areas where deforestation is large enough to produce significant differences in summer temperatures of 0.5–1 °C. At ~0.2 k BP, extensive deforestation, particularly according to the KK10 model, leads to significant temperature differences in large parts of Europe in both winter and summer. In winter, deforestation leads to lower temperatures because of the differences in albedo between forested and unforested areas, particularly in the snow-covered regions. In summer, deforestation leads to higher temperatures in central and eastern Europe because evapotranspiration from unforested areas is lower than from forests. Summer evaporation is already limited in the southernmost parts of Europe under potential vegetation conditions and, therefore, cannot become much lower. Accordingly, the albedo effect dominates in southern Europe also in summer, which implies that deforestation causes a decrease in temperatures. Differences in summer temperature due to deforestation range from −1 °C in south-western Europe to +1 °C in eastern Europe. The choice of anthropogenic land-cover scenario has a significant influence on the simulated climate, but uncertainties in palaeoclimate proxy data for the two time periods do not allow for a definitive discrimination among climate model results.

EcoVeg: a new approach to vegetation description and classification

EcoVeg: a new approach to vegetation description and classification

Vegetation of the Okavango river valley in Kavango West, Namibia

The vegetation of the Okavango River Valley has previously only been described in general terms along the gradient from base of the valley to the top of the sand plateau, without the clear definition of different vegetation types or distinct vegetation compo- sition. Yet the valley bottom supports a large part of the population within the region, who are dependent on ecosystem services pro- vided by the vegetation. A Braun-Blanquet type survey was conducted to describe the vegetation of the Okavango River Valley in the Kavango West Region of Namibia, with special emphasis on the floodplain vegetation. The survey followed the guidelines set out for the Vegetation Survey of Namibia project. The data was classified using the modified TWINSPAN procedure in Juice, resulting in four higher-order syntaxa and 11 vegetation associations. We described these associations informally according to diagnostic species, species richness and environmental variables. In the case of floodplain and wetland associations, information regarding the flooding regime (depth, duration and probability of flooding) is provided. Although the higher-order groupings within this association come out very clearly, only the wetlands could be related to similar higher-order syntaxa described for the oshana wetlands in the Cuvelai delta. The placement and validity of the other three higher-order syntaxa is unclear at this stage, and needs to be addressed in a synopsis of all existing vegetation descriptions for the greater Kalahari ecoregion. The various vegetation associations can very clearly be associat- ed with distinct positions in the landscape. The degree of flooding at the one extreme, and the sandiness of the soil on the other ex- treme, defines the vegetation type and composition. The Acacia erioloba—Schinziophyton rautanenii association (7) has been cleared and ploughed to at least 90%, with only small patches of this vegetation remaining. Expansion of fields into the sands of the terrace embankment is worrisome, leading to fears of further soil degradation and ultimately desertification. Although signs of overgrazing are visible within the floodplains, this cannot be distinctly quantified as yet. Overgrazing in the wetlands will lead to the destruction of fish spawning and breeding habitats, damaging the other major food source of the people of the region.

Wild boar’s (Sus scrofa) role in the vegetation dynamics of water bodies of Oksky state reserve

Wild boar (Sus scrofa) is a native inhabitant of the southeastern Meshchera lowland. However, as a result of human activity, biotic communities evolved for a long time in the absence this species. When, after a long absence, wild boars reappeared in the Oksky reserve nearly 50 years ago and began to restore its population quickly, the activity of these animals became a new factor of disturbances. Rooting by wild boar can strongly affect wetland and aquatic vegetation, although the effect of wild boar on freshwater ecosystems has seldom been studied. We characterized the use of different types of water bodies by wild boars and assessed long-term and short-term changes in vegetation of water reservoirs under the influence of a wild boar by the example of the Oksky Reserve. Sagittaria sagittifolia was a species that was most attractive for wild boars of any water and wetland vegetation. Vegetation is most intensely disturbed by the animal at floodplain water bodies without significant muddy sediments and at the Pra and Oka rivers. However, the vegetation dynamics begins to be influenced by wild boar activity only in the waters of the high floodplain that are not regularly flooded by spring waters. This influence is expressed as a reduction and thinning of Sagittaria sagittifolia patches, an increase in heterogeneity and patchiness of vegetation on disturbed plots, and formation of naked sites lacking vegetation (in wallows made by the animals). Comparison of our data with initial descriptions of vegetation in ten oxbows of the Pra that were made before wild boar introduction showed an increase in the occurrence of Sagittaria sagittifolia at the level of plant associations and water bodies. This is probably due to the fact that a disturbance of dense thickets of dominant plants of the coastal zone by boars provides favorable conditions for the invasion of species such as Sagittaria sagittifolia.

Use of Pollen and Ancient DNA as Conservation Baselines for Offshore Islands in New Zealand

Islands play a key role globally in the conservation of endemic species. Many island reserves have been highly modified since human colonization, and their restoration and management usually occur without knowledge of their prehuman state. However, conservation paleoecology is increasingly being recognized as a tool that can help to inform both restoration and conservation of island reserves by providing prehuman vegetation baselines. Many of New Zealand's mammal-free offshore islands are foci for biological diversity conservation and, like many islands in the Polynesian region, were deforested following initial human settlement. Therefore, their current restoration, replanting, and management are guided either by historic vegetation descriptions or the occurrence of species on forested islands. We analyzed pollen and ancient DNA in soil cores from an offshore island in northern New Zealand. The result was a 2000-year record of vegetation change that began >1200 years before human settlement and spanned 550 years of human occupation and 180 years of forest succession since human occupation ceased. Between prehuman and contemporary forests there was nearly a complete species turnover including the extirpation of a dominant conifer and a palm tree. The podocarp-dominated forests were replaced by a native but novel angiosperm-dominated forest. There is no modern analog of the prehuman forests on any northern New Zealand island, and those islands that are forested are dominated by angiosperms which are assumed to be climax forests. The pollen and DNA evidence for conifer- and palm-rich forests in the prehuman era challenge this climax forest assumption. Prehuman vegetation records can thus help to inform future restoration of degraded offshore islands by informing the likely rate and direction of successional change; helping to determine whether natural rates of succession are preferable to more costly replanting programs; and providing past species lists if restoration replanting is desired.

Online appendix 1:Guidelines for phytosociological classifications and descriptions of vegetation in southern Africa

Changes in the environment are first observed in changes in the vegetation. Vegetation survey, classification and mapping form the basis on which informed and scientifically defendable decisions on the environment can be taken. The classification and mapping of vegetation is one of the most widely used tools for interpreting complex ecosystems. By identifying different plant communities we are essentially identifying different ecosystems at a particular hierarchical level. Phytosociologists in Europe have been involved in such studies following, in particular, the Braun-Blanquet approach since the early 1900s. In South Africa, such studies were undertaken on a limited basis from the early 1970s and have since then steadily increased. The surveying of the enormous diversity of South African vegetation is one of the objectives of phytosociological studies. The demand for such data has steadily increased over the past few years to guide conservation policies, biodiversity studies and ecosystem management. In South Africa, numerous publications on the vegetation of conservation and other areas in the different biomes have been produced over the last few decades. However, vegetation scientists in South Africa experience unique problems. The purpose of this article is therefore to provide an overview of the history and the specific focus of phytosociological studies in South Africa and to recommend minimum requirements and methods to be followed when conducting such studies. It is believed that the incorporation of these requirements will result in scientifically justifiable research of high quality by phytosociologists in South Africa.Conservation implications: Effective conservation cannot be obtained without a thorough knowledge of the ecosystems present in an area. Consistent vegetation classifications and descriptions form the basis of conservation and monitoring exercises to maintain biodiversity. The incorporation of these guidelines and requirements will facilitate quality phytosociological research in South Africa.

Online appendix 2:Guidelines for phytosociological classifications and descriptions of vegetation in southern Africa

Changes in the environment are first observed in changes in the vegetation. Vegetation survey, classification and mapping form the basis on which informed and scientifically defendable decisions on the environment can be taken. The classification and mapping of vegetation is one of the most widely used tools for interpreting complex ecosystems. By identifying different plant communities we are essentially identifying different ecosystems at a particular hierarchical level. Phytosociologists in Europe have been involved in such studies following, in particular, the Braun-Blanquet approach since the early 1900s. In South Africa, such studies were undertaken on a limited basis from the early 1970s and have since then steadily increased. The surveying of the enormous diversity of South African vegetation is one of the objectives of phytosociological studies. The demand for such data has steadily increased over the past few years to guide conservation policies, biodiversity studies and ecosystem management. In South Africa, numerous publications on the vegetation of conservation and other areas in the different biomes have been produced over the last few decades. However, vegetation scientists in South Africa experience unique problems. The purpose of this article is therefore to provide an overview of the history and the specific focus of phytosociological studies in South Africa and to recommend minimum requirements and methods to be followed when conducting such studies. It is believed that the incorporation of these requirements will result in scientifically justifiable research of high quality by phytosociologists in South Africa.Conservation implications: Effective conservation cannot be obtained without a thorough knowledge of the ecosystems present in an area. Consistent vegetation classifications and descriptions form the basis of conservation and monitoring exercises to maintain biodiversity. The incorporation of these guidelines and requirements will facilitate quality phytosociological research in South Africa.

USING FULL WAVEFORM DATA IN URBAN AREAS

Abstract. In this paper, the use of waveform data in urban areas is studied. Full waveform is generally used in non-urban areas, where it can provide better vertical structure description of vegetation compared to discrete return systems. However, waveform could be potentially useful for classification in urban areas, where classification methods can be extended to include parameters derived from waveform analysis. Besides common properties, also sensed by multi-echo systems (intensity, number of returns), the shape of the waveform also depends on physical properties of the reflecting surface, such as material, angle of incidence, etc. The main goal of this investigation is to identify relevant parameters, derived from waveform that are related to surface material or object class. This paper uses two waveform parameterization approaches: Gaussian shape fitting and discrete wavelet transformation. The two classification methods tested are: supervised Bayes classification and unsupervised Self-Organizing Map (SOM) classification. The results of these methods were compared to each other and to manual classification. The initial conclusion is that, though waveform data contains classification information, the waveform shape by itself is not enough to perform classification in urban regions, and, consequently, it should be combined with the point cloud geometry.

Guidelines for phytosociological classifications and descriptions of vegetation in southern Africa

Changes in the environment are first observed in changes in the vegetation. Vegetation survey, classification and mapping form the basis on which informed and scientifically defendable decisions on the environment can be taken. The classification and mapping of vegetation is one of the most widely used tools for interpreting complex ecosystems. By identifying different plant communities we are essentially identifying different ecosystems at a particular hierarchical level. Phytosociologists in Europe have been involved in such studies following, in particular, the Braun-Blanquet approach since the early 1900s. In South Africa, such studies were undertaken on a limited basis from the early 1970s and have since then steadily increased. The surveying of the enormous diversity of South African vegetation is one of the objectives of phytosociological studies. The demand for such data has steadily increased over the past few years to guide conservation policies, biodiversity studies and ecosystem management. In South Africa, numerous publications on the vegetation of conservation and other areas in the different biomes have been produced over the last few decades. However, vegetation scientists in South Africa experience unique problems. The purpose of this article is therefore to provide an overview of the history and the specific focus of phytosociological studies in South Africa and to recommend minimum requirements and methods to be followed when conducting such studies. It is believed that the incorporation of these requirements will result in scientifically justifiable research of high quality by phytosociologists in South Africa.Conservation implications: Effective conservation cannot be obtained without a thorough knowledge of the ecosystems present in an area. Consistent vegetation classifications and descriptions form the basis of conservation and monitoring exercises to maintain biodiversity. The incorporation of these guidelines and requirements will facilitate quality phytosociological research in South Africa.

Крупномасштабная карта растительности ключевого участка в лесотундре Кольского полуострова: методические особенности составления и анализ

Large-scale vegetation mapping of key area of 1400 km2 in forest-tundra zone in the middle flow of Teriberkariver (Kola Peninsula) was conducted on the base of satellite images, topographic maps and field geobotanical investigations. Study of Landsat TM images local spectral characteristics and syntaxonomical analysis of vegetation demonstrated that satellite images with 30 m spatial resolution and 6-bands spectral resolution alone can't be used for automatical large-scale classification of forest-tundra zone vegetation. Map of vegetation in scale 1:50 000 resulted from manual processing of both hypsometry and spectral characteristic, on the base of field work points with description of vegetation. Legend of mapped units contains 2 types for tundra, 5 ones for mountain birch forest and 4 ones for wetlands. Quality and correctness of the map were verified by satellite image of extra high spatial resolution Quick Bird (0,65 m/pixel) and aerial photograph for this territory. The map illustrated that distribution of vegetation is primarily caused by unevenness of relief. Timberline lies at 220-240 m a.s.l., altitudinal distances across mountain birch forest and tundra zones are about 40-60 m, tundra vegetation occurs on moraine hills and bedrocks slopes and summits. Pounikkos flark-and-mounds, tuft-and-fen bog complexes occur from 170 to 240 m.s.l. in depressions and valleys. Proportion of tundra vegetation is about 40%, mountain birch forest – 30%, wetlands – 20%, lakes, rivers and springs take 10% of area investigated.

Assessing and modeling moose (Alces alces) habitats with airborne laser scanning data

In the analysis of forest resources, the use of ALS (airborne laser scanning) enables detailed three dimensional (3D) descriptions of forests and their vegetation. Simultaneously, ecologists have recognized that 3D information on vegetation is highly important in analyzing the habitat suitability of a given site. Recently, animals’ habitat preferences have been analyzed, for example, with GPS-collared animals. This has resulted in detailed knowledge about the animals’ movements both spatially and temporally. This study combines 3D information on vegetation obtained from ALS data with information about animal locations from GPS data. The aim was to map and analyze the habitat preferences of moose. The study area was located on the west coast of Finland. The data consisted of 18 GPS-collared moose (monitored from 2009 to 2010) and ALS data collected in 2010. We investigated how habitat structure changes as a function of distance to observed moose locations and how observed moose locations differ from randomly selected locations in terms of 3D structure. We also created a model-based habitat suitability map and tested it against moose occurrences. The results suggested that there are clear differences between the areas occupied and not occupied by moose and that these differences can be detected from ALS data. More importantly, ALS proved its potential in linking 3D descriptions of vegetation directly to observed moose locations without any proxy variables. These observations strongly support future studies.