Relationships between environmental variables and vegetation across mountain wetland sites,N. Iran

The mountain wetlands studied represent a unique habitat on the southern slopes of the Alborz mountain range, the second largest range in Iran. In comparison with other parts of this range the western section is ecologically and botanically unknown. Floristic and vegetation variation were assessed using diverse environmental variables along a broad altitudinal span (350 m to 3200 m a.s.l.). Using both statistical and ordination analyses floristic variation was assessed on three defined altitudinal belts which were delimited based on Alborz macro-climatic boundaries. The distribution of individual wetland plant species, of phytogeographic elements and of life-forms all differ among altitudinal belts. This result is also shown in both direct and indirect analyses of ordinations. The proportion of geophytes significantly increases with altitude and geophytes are very well represented in the upper altitudinal belt. The number of species of a narrow phytogeographical distribution (e.g. endemics) increases with altitude, soil pH and EC declined with altitude. The first axis of DCA ordination with passively projected environmental variables indicates that, organic matter and concentration of Fe²⁺ are increased toward higher altitude. The second axis of ordination is related to both soil texture and slope inclination. The distribution of species in the CCA species plot is also close to the distribution of those in the DCA ordination. This study indicates that altitude and slope together with other dependent environmental variables (pH, EC, Ca²⁺ and soil texture) are the main ecological factors controlling species distribution across the Western Alborz wetland sites.     

Variations of the germinable soil seed bank along the altitudinal gradient in the northwestern Red Sea region

The variations in the size, composition and diversity of the germinable soil seed bank were studied along an altitudinal gradient in the northwestern Red Sea region. The standing vegetation and the germinable seed bank were studied in 58 stands distributed along the altitudinal range from sea level to coastal mountain peaks. The classification of the germinable seed bank by the two-way indicator species analysis (TWINSPAN) led to the recognition of five groups representing different altitudinal ranges. Detrended correspondence analysis (DCA) shows that these groups are clearly distinguished by the first two DCA axes. The results demonstrate significant associations between the floristic composition of the seed bank and the edaphic factors such as CaCO₃, electrical conductivity, organic carbon and soil texture. Species richness, Shannon index of diversity and the size of the germinable seed bank show a hump-shaped curve along the altitudinal gradient, whereas evenness shows a weak increase with elevation increasing. Beta diversity of the seed bank declines with altitude increasing. The similarity between the standing vegetation and the seed bank approaches a U-shaped pattern along the elevation gradient. About 34.8% of the species that constitute the standing vegetation are vulnerable to elimination from the standing vegetation because they are not represented in the seed bank. Soil seed bank can be used for restoration of the vegetation at some of the degraded sites.     

Diversity of wetland vegetation in the Bulgarian high mountains, main gradients and context-dependence of the pH role

We fill a gap in understanding wetland vegetation diversity and relationship with environmental determinants in Bulgarian high mountains. A total of 615 phytosociological samples were taken from springs, mires, wet meadows and tall-forb habitats throughout Bulgaria, of which 234 relevés are from mire and spring vegetation above timberline. The vegetation was classified by TWINSPAN and the resulting vegetation types were reproduced by the formal definitions using the combination of Cocktail species groups based on phi-coefficient of joint co-occurrence of the species. Nine vegetation types of springs and fens have been clearly delimited above the timberline. All vegetation types include Balkan endemic species, the representation of which varies. Fens generally harbour more Balkan endemics than do springs, with the exception of species-poor high-altitude Drepanocladetum exannulati. The gradient structure of the vegetation was revealed by DCA and by CCA with forward selection of environmental factors. The major determinants of vegetation variation strongly differ above and below the timberline and likewise between springs and fens. The base-richness gradient controls the floristic variation of Bulgarian submontane fens, whereas the complete data set including both submontane and subalpine fens is governed by the altitude gradient from lowland and basin fens to subalpine fens rich in Balkan endemics. When focusing on sites above the timberline only, the first DCA axis separates fens from springs without organic matter. The major species turnover in springs follows the variation in water pH and mineral content in water, whereas fen vegetation variation is primarily controlled by succession gradient of peat accumulation. Altitude remains an important factor in all cases. Weak correlation between water pH and conductivity was found. This correlation was even statistically insignificant in fens above the timberline. Water pH is not influenced by mineral richness in Bulgarian high mountains, since it is buffered by decomposition of organic matter in fens. In springs, pH reaches maximum values due to strong aeration caused by water flow. The plant species richness decreases significantly with increasing altitude. The increase of species richness towards circumneutral pH, often found in mires, was not confirmed in Bulgarian high mountains. The correlation between species richness and pH was significant only when arctic-alpine species and allied European high-mountain species were considered separately. The richness of boreal species was independent on pH. Some of them had their optima shifted to more acidic fens as compared to regions below the timberline. Our results suggest that subalpine spring and fen vegetation should be analysed separately with respect to vegetation-environment correlations. Separate analysis of fens below and above timberline is quite appropriate.     

Endemic gypsophytes composition delimitated by soil properties and altitude: From calciphytes to halophytes in the south–central Alborz Ranges

Specialized plant species have long served as geobotanical tools for locating mines and ores. Despite their importance, not much research has been dedicated to studying the ecology of endemic specialized plant species, such as those of gypsum or calcareous habitats. Here we describe and analyze the occurence of endemic plant species in gypsum habitats of the south–central Alborz Ranges (Semnan), Iran, in relation to altitude and soil properties. Ecological data and soil samples were collected from 120 plots along along an altitudinal gradient correlated with differences in soil properties. Forty seven plant species, including 6 species endemic to the Semnan area and 20 species endemic to Iran, were identified. The occurrence of the species were analyzed using canonical correspondence (CCA) and detrended correspondence Analysis (DCA), and based on the results the species were categorized as gypsophytes G₁ (1600–2245 m a.s.l.), calciphytes (1500–1700 m a.s.l.), gypsophytes G₂ (1300–1600 m a.s.l.) and halophytes (1100–1300 m a.s.l.). Gypsum content, elevation and salinity (Na content) were identified as the environmental factors having the largest effects on vegetation compositon. Endemic Semnan plant species included Astragalus fridae, Euphorbia gypsicola and Gypsophila mucronifolia at higher altitudes, and Astragalus semnanensis, Centaurea lachnopus and Nepeta eremokosmos at lower altitude gypsic soils. More frequent Iranian endemic plant species included Moltkia gypsaceae at higher altitudes, Echinops nizvanus and Acantholimon cymosum at lower altitude gypsic soils, Astragalus glaucacanthos, A. podolobus and A. microcephalus occurring mainly in calcic carbonate soil, and halophyte species such as Artemisia sieberi dominating at lower altitudes with more saline–alkaline soil.     

Species Diversity and Life-Form Patterns in Steppe Vegetation along a 3000 m Altitudinal Gradient in the Alborz Mountains, Iran

Biodiversity pattern and life-form spectra were studied along a 3,000 m altitudinal gradient from a semi-desert area to the alpine peak of Tochal Mountain. The gradient is located on the southern slopes of Central Alborz with a Mediterranean continental climate. DCA ordination was applied to 1,069 relevés and 7 quantitative variables to discover the relation of diversity and altitude. A biodiversity pattern was obtained by relating values for species richness and Shannon-Wiener’s index to 100-m altitudinal sections. Altitude was determined as the major ecological gradient. Both diversity indices are negatively correlated with altitude and show a decreasing trend beyond a peak in species richness at 1,800–1,900 m a.s.l. towards a very low diversity in the high alpine zone. The biodiversity peak does not match with the potential tree line in the area (2,500–3,000 m a.s.l.). The high diversity in foothills can be related to habitat heterogeneity, longer suitable climatic conditions, and diverse disturbance factors, while unfavorable conditions at high-altitude alpine and low-altitude desert areas reduce the number of species at both extremes. Life-form patterns clearly change along altitudinal gradient. Annuals with decreasing trend, and hemicryptophytes and chamaephytes with increasing trend along the altitudinal gradient are notable patterns of life form in the area. Temperature, soil moisture and nutrients are the main factors that explain the ecological influence of altitude on species diversity and life-form patterns in the semi-arid steppe vegetation of the area.     

博斯腾湖湖滨湿地植被数量分类与排序

应用双向指示种分析(TWINSPAN)方法对湿地植物群落进行分类,采用除趋势对应分析(DCA)、典范对应分析(CCA)对群落进行排序,以明确博斯腾湖湖滨湿地的主要植物群落类型及影响植被类型变化和分布的主要环境因子。结果表明,博斯腾湖湖滨湿地植被可分为7个主要群丛,分别为长苞香蒲(Ass.Typha angustata)、芦苇+长苞香蒲(Ass.Phragmites australis+Ty.angustata)、芦苇+水烛(Ass.P.australis+Ty.Angustifolia)、多枝柽柳-芦苇(Ass.Tamarix ramosissima-P.australis)、胡杨-多枝柽柳(Ass.Populus euphratica-Ta.ramosissima)、旱柳-多枝柽柳(Ass.Salix matsudana-Ta.ramosissima)和多枝柽柳(Ass.Ta.ramosissima),它们分布于湖滨浅水带、湖滨沼泽带、湖岸乔灌林带和旱生灌丛带;TWINSPAN分类产生的7个主要群丛在DCA排序图上被很好地反映出来。CCA排序与DCA排序结果基本一致,说明土壤含水量和土壤总含盐量是决定该地区植被分布格局的主要环境因子。博斯腾湖湖滨湿地植被种类单一,生态结构简单,水盐动态及其相互作用是影响该地区植被分布的主要因素之一。因此,在对博斯腾湖湖滨湿地进行植被保护与重建过程中,需重点考虑土壤含水量和土壤总含盐量这2个主要环境因子的影响,合理开发、利用水资源,防止土壤盐渍化的发生。     

Coastal plant and soil relationships along the southwestern coast of South Korea

We studied how plant species distribution was regulated by the relationships between vegetation and soil factors on the southwestern coast of South Korea. Vegetation was classified using two-way indicator species analysis (TWINSPAN), thereby producing four vegetation groups that were linked to three habitat types. Two ordination techniques —; detrended correspondence analysis (DCA) and canonical correspondence analysis (CCA) —; were applied to examine the relationships between vegetation and 12 edaphic factors, including soil pH, water and osmotic potentials, moisture content, electrical conductivity, Cl and Na⁺ contents, total Kjeldahl nitrogen, and contents of organic matter, sand, silt, and clay. Results were similar for both types of evaluations. According to DCA and CCA, the 23 communities tended to cluster into three types: salt swamp, salt marsh, and sand dune. The first two canonical axes accounted for 14.9% of the community-soil factor relationship among communities. As identified via CCA, the main gradients were soil-water relations and soil texture.     

旅游干扰下滇西北高原湖滨湿地植被及土壤变化特征

研究了旅游干扰下滇西北高原碧塔海和属都湖湖滨湿地植被和土壤变化特征. 结果表明： 采用TWINSPAN分类方法将22个典型湿地样点划分为原生湿地、轻度退化、中度退化和重度退化4个类型.沿退化梯度,碧塔海和属都湖湿地植物群落的密度、盖度、物种数、Shannon多样性指数增大,植被高度下降,碧塔海湿地植物群落的Whittaker多样性指数增大;碧塔海湿地植物物种数、土壤有机质、全氮、孔隙度、速效氮、速效磷、速效钾含量低于属都湖湿地,群落密度、高度、土壤全钾、pH值变化规律则相反.利用42种植物的重要值和11个土壤理化指标进行典范对应分析,发现土壤有机质、全钾、全氮等养分含量是影响旅游干扰下碧塔海和属都湖湖滨湿地植物物种分布的关键因素. TWINSPAN分类和植被-土壤变化特征分析表明,旅游干扰对碧塔海湿地的影响比属都湖湖滨湿地更大.     

Environmental factors and vegetation composition, Lefka Ori massif, Crete, S. Aegean

Aim The aim of this study was to explore the environmental factors that determine the spatial distribution of oro‐mediterranean and alti‐mediterranean plant communities in Crete. Location The paper provides a quantitative analysis of vegetation–environment relationships for two study areas within the Lefka Ori massif Crete, a proposed Natura 2000 site. Methods Eleven environmental variables were recorded: altitude, slope, aspect, percentage of bare rock, percentage of unvegetated ground, soil depth, pH, organic matter content and percentages of sand, silt and clay content. Classification of the vegetation was based on twinspan , while detrended correspondence analysis (DCA) and canonical correspondence analysis (CCA) were used to identify environmental gradients linked to community distribution. Results One hundred and twenty‐five species were recorded from 120 plots located within the two study areas. Forty‐seven of the recorded species are endemic, belonging to 35 families. Hemicryptophytes and chamaephytes were the most frequent, suggesting a typical oro‐mediterranean life form spectrum. The samples were classified into five main community types and one transitional. The main gradients, identified by CCA, were altitude and surface cover type in the North‐west site, while in the Central site the gradients were soil formation‐development and surface cover type. Main conclusions The use of classification in combination with ordination techniques resulted in a good discrimination between plant communities and a greater understanding of controlling environmental factors. The methodology adopted can be employed for improving baseline information on plant community ecology and distribution in Mediterranean mountain zones.     

Biomass and diversity of dry alpine plant communities along altitudinal gradients in the Himalayas

A non-linear relationship between phytodiversity and altitude has widely been reported, but the relationship between phytomass and altitude remains little understood. We examined the phytomass and diversity of vascular plants along altitudinal gradients on the dry alpine rangelands of Ladakh, western Himalaya. We used generalized linear and generalized additive models to assess the relationship between these vegetation parameters and altitude. We found a hump-shaped relationship between aboveground phytomass and altitude. We suspect that this is engendered by low rainfall and trampling/excessive grazing at lower slopes by domestic livestock, and low temperature and low nutrient levels at higher slopes. We also found a unimodal relationship between plant species-richness and altitude at a single mountain as well as at the scale of entire Ladakh. The species-richness at the single mountain peaked between 5,000 and 5,200 m, while it peaked between 3,500 and 4,000 m at entire Ladakh level. Perhaps biotic factors such as grazing and precipitation are, respectively, important in generating this pattern at the single mountain and entire Ladakh.     

荒漠啮齿动物群落与植物群落的对应分析

动物与其生存环境变量之间的关系一直是生态学家们广泛关注的问题.啮齿动物作为荒漠生态系统中重要的功能群,其数量大小和生态功能对生态系统的平衡和稳定具有重要意义.生境中的植被为啮齿动物提供赖以生存的食物资源和栖息地,了解啮齿动物群落与植被特征之间的关系对于理解动物群落变动规律具有重要意义.不同植被条件下啮齿动物群落的结构不同,Hernández等(2005)研究发现北美Chihuahuan荒漠的灌木生境中啮齿动物密度高于草地生境.     

Quantitative analysis of endangered Acanthopanax senticosus communities in Dongling Mountain of Beijing

Based on the survey of community plots, a quantitative analysis of endangered Acanthopanax senti-cosus communities in Dongling Mountain was performed with two way indicator species analysis (TWINSPAN), detrended correspondence analysis (DCA) and canonical correspondence analysis (CCA). The communities of A. senticosus were classified into 9 types by TWINSPAN and the results were validated by DCA. On the DCA graph, the first axis reflected the gradient of altitude and the second axis reflected the aspect and slope. Most of A. senticosus were distributed in the thick forests at a high altitude with little light. With the exception of being a dominant species of shrub layers in a few communities, A. senticosus has a relatively scarce distribution. In accordance with DCA, the results of CCA also show the trend that the distribution of A. senticosus communities varied along with the gradient change of environmental factors. Altitude and light are the main factors affecting A. senticosus growth.     

云南大围山种子植物区系海拔梯度格局分析

 海拔梯度包含了多种环境因子的梯度效应,因而研究山地植物区系的海拔梯度格局对揭示植物区系的环境梯度变化规律、了解生物适应性和生物多样性沿海拔梯度的变化趋势等具有重要意义。为了探讨山地植物区系构成特征及其海拔梯度的生态意义,该文根据对大围山国家级自然保护区植被线路调查和垂直样带调查,并结合文献研究等获得的植物区系资料,分析了该保护区种子植物区系构成的基本特征及其随海拔梯度的变化趋势;利用系统聚类的方法寻找和研究大围山植物区系沿海拔梯度变化的断点位置。研究结果表明：1)大围山大多数热带成分分布的上限位于海拔1 500 m左右,以此为界划分热带雨林和常绿阔叶林是合理的。 2)湿润雨林分布于海拔700 m以下;山地雨林分布于海拔700～1 500 m;季风常绿阔叶林分布于海拔1 300～1 800 m;山地苔藓常绿阔叶林分布于海拔1 800 m以上;在海拔2 100 m以上的迎风坡面、土层瘠薄的地段分布有不甚典型的山地苔藓矮林。     

东灵山濒危植物刺五加生存群落的数量分析

在样方调查的基础上,分别采用双向指示种分类法(TWINSPAN)、除趋势对应分析法(DCA)和典范对应分析(CCA)对东灵山地区濒危植物刺五加的生存群落进行数量分析。TWINSPAN分类将刺五加生存群落分为9类,分类结果在DCA二维排序图上得到了较好的验证,其中第一轴反映的是海拔梯度,第二轴反映了坡向、坡度的变化。刺五加多分布在位于海拔较高、光照较少的杂木林中,除在少数群落中成为灌木层的优势种外,相对分布较少。CCA排序结果与DCA的排序结果基本一致,反映出植物群落分布随环境因子梯度变化的趋势,揭示了海拔和光照是限制刺五加生长的主要环境因子。     

Changes in plant form and function across altitudinal and wetness gradients in the wetlands of the Maloti-Drakensberg,South Africa

A survey of 93 wetlands in six catchments across the Maloti-Drakensberg is used to assess the distribution of plant functional types across altitudinal and wetness gradients. Altitudes range from 1,000 to 3,200 m a.s.l. Within each catchment, the wetlands were selected to cover the complete range in altitude and wetland types. In each of the selected wetlands, vegetation was sampled in 3 by 3 m quadrats covering the entire range of wetness represented in the wetland, from temporarily wet to permanently inundated soils. Plant species were allocated to one of 11 different functional types (examples are C₃ grasses, C₄ sedges, rosette plants, and shrubs), and the proportion of the vegetation in each sample occupied by each functional type was calculated from the species’ abundances. Canonical Correspondence Analysis shows that “wetness” clearly has the highest impact on the distribution of functional types, followed by altitude. The most important plant functional types in wetlands are grasses and sedges, however, at higher altitudes, forbs (especially rosette plants) and bulbous plants become a more prominent feature in the wetlands. The total amount of graminoids gradually decreases with altitude. The general trend is that sedges tend to increase with increasing wetness and C₃ plants (grasses and sedges) increase with increasing altitude, but these effects are not independent. The distributions of C₄ sedges and C₄ grasses along an altitudinal gradient are quite different, and C₄ grasses grow abundantly at much higher altitudes than C₄ sedges. C₄ sedges are very scarce at the altitudes represented in the Maloti-Drakensberg area, whereas C₃ grasses occur in the permanently wet parts of the wetlands, especially at higher altitudes (normally mostly occupied by sedges). Shrubs are rare in wetlands and tend to be an indication of disturbance. This study complements previous studies on the distribution of grasses and sedges at the lower altitudes within KwaZulu-Natal, which found that at altitudes below 1,000 m a.s.l. C₄ sedges were much more prominent, while forbs and rosette plants were largely absent. This confirms that C₄ as an adaptation to hotter and warmer climates is sometimes a less favorable metabolism in wet high altitude areas. At high altitudes, rosette plants and bulbous plants become more competitive in wetlands, probably because grasses and sedges present at these altitudes generally grow smaller than they do in low altitude wetlands.     

Vegetation structure along the altitudinal gradient at the treeline of Mount Paektu,North Korea

Vegetation structure of the treeline was studied on the southeastern slope of Mount Paektu (North Korea). Fifteen temporary plots (20m×20m) were situated along the altitudinal transect. Seven square samples (phytosociological relevés 5 m×5 m) were analyzed in each plot. Although the character of the vegetation was rather continuous altitudinally, five similar groups of vegetation samples were distinguished by the TWINSPAN procedure. The distribution of samples in the classification showed not only the effect of altitude but also the effect of competition between the tree and the shrub layers and other factors. In the canonical correspondence analysis (CCA) ordination several environmental variables were used (such as altitude of each plot, distance of each plot from the forest edge and the cover percentage of tree, shrub, herb and moss/lichen layers). The variable ‘cover of tree layer’ had the strongest relation to the species data. Continuous changes of species richness along the altitude were confirmed. Species richness decreased significantly with altitude.     

Relationships between aquatic plants and environmental factors along a steep Himalayan altitudinal gradient

We examined the relationships of aquatic plants with physical–chemical characteristics among 28 lakes within a steep altitudinal gradient ranging from tropical (77 m) to high alpine (4750 m) in the Himalayas of Nepal. Species richness and diversity showed an approximately linear decrease with increasing altitude. The study region exhibits a relatively high proportion of monocotyledonous helophytes, as is typical of aquatic plants on the Indian subcontinent. A canonical correspondence analysis of the entire altitudinal gradient (CCA-1) suggested that the strongest abiotic influences on the distribution of aquatic plants are associated with water temperature, substrate quality, altitude, pH, transparency and conductivity. Two more-restricted CCA analyses examined a shorter altitudinal gradient of 70–1500 m. The CCA-2 analysis (all aquatic plants) and CCA-3 (only euhydrophytes) found that the most important abiotic influences were associated with temperature, lake surface area, suspended solids, bicarbonate and dissolved phosphorus. These results suggest that relatively local influences are different from those that have a regional basis, but that climate-related influences are key along altitudinal gradients. The temperature gradient in the CCA distinguished montane and alpine Arcto-tertiary floristic elements of the highest altitudinal regions from the more widely distributed temperate and tropical species of the lower regions.     

广佛地区典型湿地类型植物多样性与土壤因子的关系

为了解土壤影响湿地植物多样性的主要因子,在广佛地区9大湿地类型选取18个样地作为研究对象,通过样方调查以及内业试验获得湿地群落物种组成分布、植物多样性、土壤状况等数据,运用方差分析、典范冗余分析(RDA)、典范对应分析(CCA)对群落分布、植物多样性与土壤因子之间的相关性进行分析。经实地调查,统计出湿地植物312种,隶属90科198属,以禾本科(Gramineae)、莎草科(Cyperaceae)、菊科(Compositae)等为优势科。草本植物占绝对优势,占79.17%。主成分评价结果表明, 近海及海岸湿地土壤养分水平较高。RDA排序分析结果表明土壤因子对植物多样性影响较大的指标是土壤有机质、全氮、全磷、全钾、碱解氮;CCA排序结果表明土壤环境因子对湿地草本植物群落分布主要影响因子为pH、速效钾、有效磷。各研究结果表明,湿地生态系统比陆地生态系统更为复杂和脆弱,植物群落与土壤环境因子之间的关系也更为复杂,湿地植被的分布格局、群落多样性、群落结构和土壤条件及其相互关系受到人为干扰的类型和强度影响更加明显。     

A combination of fuzzy set ordination with detrended correspondence analysis: One way to combine multi-environmental variables with vegetation data

This paper examines one possible way of Fuzzy Set Ordination by using multi-environmental variables. FSO's function is improved through combination with Detrended Correspondence Analysis which is used to summarize environmental information. It can be used to analyse the relationships between vegetation and environment no matter how many environmental variables are involved. An example with vegetation and environmental data collected from upland grasslands in Northern Snowdonia, Wales, is presented. Its results are consistent with that of CCA and DCCA.Abbreviations FSO Fuzzy set ordination - DCA Detrended correspondence analysis - CCA Canonical correspondence analysis - DCCA Detrended canonical correspondence analysis     

Detection of Climate-Sensitive Zones and Identification of Climate Change Indicators: A Case Study from the Bavarian Forest National Park

We determined the climate-sensitive zones along an altitudinal gradient in a low mountain range forest, the Bavarian Forest National Park in south-eastern Germany, and studied which vascular plant species are likely to respond to climate change. Plants were recorded on 273 plots along four straight transects. The composition of the plant species and their environmental correlates were detected using unconstrained correspondence analysis (DCA) with post-hoc correlation of axes against site variables. We tested the effect of site variables on species composition using maximally selected rank statistics, which allow the simultaneous identification of a threshold and assessment of its significance. Species turnover within the vascular plant community along the altitudinal gradient was assessed using the same method on the basis of the DCA sample scores. Using geostatistical models of local temperature and Bayesian methods with binomial errors that account for spatial structure, we tested the influence of temperature on selected single vascular plant species and assessed the suitability of the species as climate change indicators. Temperature was the most important factor explaining the variability in vascular plant community composition, which changed discretely along the altitudinal gradient, with a climate-sensitive zone found between 1,100 and 1,200 m a.s.l. The distribution of ten species with their lower or upper altitudinal limit in this zone was significantly driven by temperature. To track vegetation responses to climate change effectively, we suggest a three-level monitoring program, flexible with regard to the volume of required sampling effort.