relationsHiPs between develoPment of Plant communities and Habitats in tHe landscaPes
of river valley
Piotr banaszuk
*, agnieszka wysocka
*, beata matowicka
*** department of Protection of soil and land surface, technical university of Białystok, Poland
** division of landscape ecology, technical university of bialystok, Poland
abstract
Relationship between plant communities and habitat conditions in the natural mire valley landscape was examined in the Narew River mire valley, within the borders of the Narew National Park, in the north-eastern part of Poland. In the 37 sampling points in forests, sedge and reed communities, the soil and groundwater samples were taken and the species composition was recorded in 1996 -1997. In every sampling point water table was measured additionally. The Canonical Correspondence Analysis (CCA) was performed, by means of computer program CANOCO, to examine the unimodal relationships between plant species and environmental variables.
Species composition of studied communities is related mainly to natural processes which depends on dynamics of floods, fluctuations of the surface water and groundwater levels, and its nutrient richness. Geochemical processes are mainly affected by hydrological conditions of habitats in various locations in mire valley landscape.
introduction
The wetland ecosystems are very vulnerable and many of them are disturbed. The aims of mires protection consists of the preservation of natural swamps and renaturalisation of changed ones. The protection or reconstruction of specific spatial pattern of habitats in the mire valley landscape is one of the main problem of mire valley preservation.
Since the vegetation in these habitats is influenced by many non-biotic variables it is necessary to detect the patterns and processes that cause or induce changes in habitats (Barendregt, 1993). This can be done with landscape ecology research in the natural mire valleys. The research concerning biogeochemical processes in the natural valleys, an influence of the water supply on the nutrient availability in plant communities (Wassen et al.,1990, 1992), interactions between the hydrological and soil conditions
in fens (de Mars 1996) were carried out in Poland mainly in Biebrza Wetlands. Similar studies related to the biogeochemical processes were carried out in the natural and disturbed Narew River Valley (Banaszuk, Banszuk, Wołosz 1995; Banaszuk, Wysocka 1996), although there are few studies concerning the relation between the vegetation and habitat conditions in the landscapes of swamp valleys.
The aim of this paper is to examine the relationship between plant communities and habitat conditions in the natural mire valley landscapes in the Narew River valley, within the borders of the Narew National Park, in the north-eastern part of Poland.
description of study area
The meridional part of the Narew River Valley, between Suraż and Żółtki, is a melt-out valley type covered with swamps, situated in north-eastern part of Poland (see Fig. 1).
In 1996, the Narew National Park was established here from Suraż to Rzędziany in order to protect the unique landscape, precious plant communities and rare, vanishing plant and animal species. The explicit plant communities distribution, abundance of plant species and exceptional biodiversity of breeding birds and fish as well as mammal species are the result of the specific formation and pattern of one of the least unchanged swamp habitats in Central Europe.
The 98 % of the valley is covered with swamps. The dominant types of mire habitats are fluviogenous, which means that they are subjected to the river floods (Okruszko, 1983a). The 75% of the valley bottom is covered with the telmatic peatland and 5 % is occupied by the limnetic peatland, other habitats like all kinds of marshes or peatlands supplied by the groundwater are also found in the valley (Banaszuk, 1996).
Telmatic peatlands with sedge community Caricetum elatae occur on the peat soils within the range of the long and deep floods. The marshing telmatic peatlands, which are created in marshing process, occupy mainly territories where the main river-bed
Fig. 1. Location of the Narew mire valley.
is deeply cut into the valley bottom with gradually reducing but still present flooding (Okruszko, 1983b). At less advanced stage of this process the sedge community Caricetum gracilis typicum occupies periodically overdried peat soils, whereas the territories with more overdried habitats with moderate peat muck soils are occupied by Caricetum gracilis with Agropyro—Rumicion and also by Glycerietum maximae (Banaszuk 1996). The limnetic peatland also occur in the valley, within the range of permanent flooding, on the peat soils with reed community (Phragmitetum communis).
The woods occupy only 5% of the valley and they are mainly alder forest.
Forests with features characteristic to the riverside carrs occupy only small areas on the valleys edges, whereas within the borders of the Park the alder forest is found in three sub-associations: Carici elongatae-Alnetum typicum, Carici elongatae-Alnetum ribetosum and Carici elongatae-Alnetum sphagnetosum (Matowicka 1994).
According to Matowicka (1996), typical alder forest of Carici elongatae- Alnetum typicum occupies the areas with big fluctuations of groundwater levels. In the early spring, water level is 10 – 20 cm above the ground, whereas in the early autumn it decreases rapidly to 50 cm below the ground. The longest floods remain there for 6 months. The forest is developed on the slight peat-muck soils with 6 cm of muck layer.
Carici elongatae-Alnetum sphagnetosum is related to territories with slight peat-muck soils, but the muck layer is deeper (10 cm), although the pattern of flooding is similar to those characteristic for typical alder forest. In the Carici elongatae-Alnetum ribetosum the fluctuations of the water levels are smaller, the water level during the flood which remains only for 3 months, is only 5 cm above the ground.
The willow shrubs Salicetum pentandro-cinerea occupies the zones between the alder forests and the unforested mire. This association develops on the peat soils or mucking peat soils. The flooding remains up to 8 months (Matowicka, 1996).
methods
Groundwater, soil and vegetation sampling
The studies were carried out at 37 sampling sites located in the Narew National Park. The sampling sites were chosen on the basis of the real vegetation map of the Narew National Park in such a manner that the most common reed and sedge plant communities as well as forests were studied. At every site, 1 - 3 piezometers with filters at different depth were located depending on variation of habitats and deposits of the stratigraphy. The groundwater samples were taken from the depth of 20 - 40 cm which directly influences the trophism of habitats as well as from a peat layer and from underlying mineral deposits. Within eight hours, Electro Conductivity (converted to 250C; EC25) and pH were measured in groundwater samples as well as HCO3- was assayed by titration. The Fe2+/3+, NH4+, PO43- (molybdate reactive phosphorus), NO3-, SO42- and Cl- were assayed with Shimadzu spectrophotometer, whereas Na+ and K+ with flame photometer, Ca2+ and Mg2+ were assayed by titration.
At every site, the soil sample was taken from the roots zone (30 cm of depth). In these samples the pH (in H2O and in KCl) were measured. The Na+ and K+ concentrations were determined with flame photometer and concentrations of Ca2+ and Mg2+ were measured by titration, whereas the concentration of N+ was determined with
Shimadzu spectrophotometer.
Plant species were recorded at sampling sites. The vegetation was recorded following Braun-Blanquet approach.
statistics
Data obtained from chemical analyses of soil samples and the shallow groundwater samples were analysed statistically. Soil and groundwater variables were standardised to zero mean and unit variance and log-transformed. The unimodal relationship between species and environmental variables was revealed with Canonical Correspondence Analysis (CCA) performed by means of computer program CANOCO (ter Braak, 1988). This analysis is the combination of ordination and multiple regression for relating the composition of species communities to their environment. CCA constructs the linear combinations of the environmental variables, along which the species distribution is maximally separated. Separation is measured by the eigenvalues calculated by CCA. The results are shown on the ordination diagrams, where the species or sample sites are represented by points and the environmental variables are represented by arrows. Arrows point the direction of changes of the environmental variables and their length is proportional to the rate of change (ter Braak, 1988).
Ordination diagram is the 2-dimentional picture of the 3-dimentional CCA axes.
Data set consisting of species abundance, soil and groundwater chemistry and flooding were analysed with CCA technique. The cover-abundance scale was transformed into ordinal scale values (Kaźmierczak, van den Maarel, Noest 1979) as follows: r, +›2, 1›3, 2›5, 3›7, 4›8, 5›9. Chemistry data set was log-transformed.
The flood variable was defined in three classes (1- slight short flood, 2 - strong long term flood, 3 - strong whole year flood). Four of the soil and groundwater chemistry variables (Mg, HCO3-, Ca, Fe, Ca in soil and soil pH) were not used included into analysis, because were strongly correlated with some of other remaining variables.
The Monte Carlo Permutation Test as a significance test of four axes and an overall test of the environmental variable effect on the vegetation was carried out. The relation between environmental variables and vegetation was considered as statistically significant at P<0.01.
results
The most important in the explanation of the correlation between the environmental variables and vegetation is the first axis, (eigenvalue 0.523), and the second axis (eigenvalue 0.315), while the contribution of the third axis is very small, the eigenvalue is equal to 0.202 (see Tab. I). The fourth axis is not statistically significant and therefore it was excluded from the interpretation. The Monte Carlo permutation test shows that the three axes give significant (p<0.01) picture of the relations between the environmental variables and the species composition of several plant communities.
Table I contains the canonical coefficients and Table II shows the inter-set correlation between the environmental variables and axis. The first axis (Axis 1) of CCA calculated as linear combinations of environmental variables is determined mainly by floods. However, K+, NO3- in groundwater and mineral parts content in soil
Table I. Canonical coefficient for standardised variable Axis 1 Axis 2 Axis 3
Eigenvalues 0.523 0.315 0.202
pH -0.10 -0.43 -0.07
EC25 0.30 0.60 -0.53
Na -0,15 -0.28 -0.18
K 0.33* 0.02 0.30
NO3- 0.26 0.28 0.07
NH4+ -0.01 0.24 0.05
PO43- -0.17 0.14 0.25
SO42- -0.05 -0.99 0.99
Cl- -0.20 0.77 -0.14
floods 0.99 -0.24 0.01
mineral parts content 0.26 0.06 -0.19
Mgs 0.19 -0.06 0.73
Ks -0.04 0.13 0.09
* Figures in bold are the canonical coefficients of those variables which are correlated with the CCA axes.
table ii. inter-set correlations of environmental variables with cca axes
* Figures in bold indicate the most extreme values for each axis
Axis 1 Axis 2 Axis 3 Fraction extracted 0,091 0,092 0,059
pH -0,100 0,003 -0,498
EC25 -0,055 0,209 0,008
Na -0,226 0,003 -0,104
K 0,085 0,255 0,081
NO3- -0,088 -0,027 0,120
NH4+ -0,106 0,489 0,041
PO43- 0,117 0,486 0,220
SO42- -0,312 -0,423 0,500
Cl- -0,248 0,200 0,304
Floods 0,873* -0,151 -0,013
Mineral parts content -0,211 0,028 -0,092
Mgs 0,214 0,605 0,206
Ks 0,253 0,043 0,210
also affect the first axis, their contribution to explanation of axis is negligible. The electro-conductivity of groundwater, Cl- and NO3- in levels groundwater are correlated with the second axis (Axis 2). The third axis (Axis 3) is mainly determined by SO42- and Mg2+ in the soil as well as K+ in the groundwater.
The inter-set correlation of environmental variables with CCA axis are rather moderate, although the fraction of total variance in environmental data extracted by the each axis are low. Floods has the largest correlation with the first axis, whereas the concentration of magnesium in the soil (Mgs) is strongly correlated with second axis.
Both chlorides and pH of groundwater are strongly correlated with the third axis (Tab.
II).
interpretation of ordination diagram
The whole variety of plant communities can be divided mainly by the first axis into two groups: reed and sedge communities on the right side of the diagram, and typical alder forests, periodically overdried alder forests, river-side forests on the left side of the diagram. On the strong, long lasting floods side (the right side of the diagram) the group of reed and sedge communities of Phragmitetea Cl. occur (see Fig. 2). Reed communities are located far away from the diagram centre, close to an arrow representing flood variable, while Caricetum elatae communities are placed closer to the centre, but the distance to an arrow are various - from very close to very distant. Caricetum gracilis does not fit any pattern which can be a result of small number of relevés. These results are conformable to conclusions given by Oświt (1991). According to his paper Phragmitetum communis has the highest frequency of floods from 80 to 100% with the depth of floods about 130 cm. It is located close to the river and is mainly supplied by the flooding water from river. Next plant community Caricetum gracilis typicum is characterised by frequency of floods from 40% to 70%, with depth of flood 50 – 60 cm, maximum 100 cm. This plant community occurs or close to the river or just behind the reed communities. The association Caricetum elatae has frequency of floods equal to 18% to 58%. The depth of floods is similar to those in Caricetum gracilis typicum. The community Caricetum elatae occurs on the whole width of the valley, behind two described before communities (Okruszko, Oświt 1973).
The results of statistical analysis, which proved that alder forests and willow shrub communities occured on the short and small inundation side of the diagram (left side) are resembling the results of investigations carried out by Kulczyński (1940). According to these results, the alder forests and willow shrubs can occur as the secondary communities on the sedge peat under the conditions of strong drainage caused by the river erosion. In this case they are paludified by the seasonal floods and periodically they overdry in the time of low groundwater and river water level. The second type of alder forest and willow shrubs occur on the edge of the valleys and is paludified by groundwater. In the conditions of long lasting inundation the root system of tree is constantly flooded and the plant cannot develop in anaerobic conditions, therefor development of forest and shrub communities is limited to two zones
Fig. 2. Ordination diagram based on the canonical correspondence analysis of vegetation data with respect to 13 environmental variables.
mentioned above: periodically overdrying peatlands and edges of valley. The frequency and depth of floods in forests is smal from 8 months, with water level from 10 cm to 20 cm above the ground in habitats with Salicetum pentandro-Cinerea to 3 months of flooding with water level 5 cm above the ground in habitats with Carici elongatae- Alnetum ribetosum (Matowicka 1994).
The only one sedge community is found on the short flood side of the diagram.
This is Caricetum appropiquate, which belongs to the fourth group of communities from Phragmitetea Cl., which is characterised by the shortest and most shallow floods (26 - 37%). This plant community is located on the edge of intensive floods zone, often
close to plant communities from Scheucherio-Caricetea fuscae Cl. supplied mainly by the groundwater (Oświt 1991).
As it was described, the range and depth of floods mainly determine differentiation of communities into forest associations and low vegetation. The development of different plant communities is mainly determined by the hydrological conditions of habitats. In addition, various chemistry of groundwater and soil was also observed in those different habitats.
The sedge and reed communities are limited to habitats with potassium and nitrates brought in with inundation. The mean value of nitrates and potassium concentration in groundwater in sedge and reed communities are 1.38 mg dm-3 and 1.49 mg dm-3. The nourishment of habitats with these two elements by flooding was observed in the natural mire in the Narew River valley. Long floods in spring and short in summer bring in the high amount of dissolved mineral and organic-mineral suspension, which is decomposed in the overdried part of soils during the low water levels. Potassium, nitrogen and phosphorus brought in one of the three most important hydrochemical processes occurring in the Narew mire valley (Banaszuk, Banaszuk, Wołosz 1995).
Whereas the low vegetation is related to potassium and nitrate content in groundwater and occupies the long flooded habitats located close to the river bank, the alder forests occur on the edge of the valley. Typical alder forests are associate to habitats with high electro-conductivity (mean value of EC25 814 µS cm-1) related to high calcium content (160.92 mg dm-3) and bicarbonates (619.98 mg dm-3) in groundwater.
These habitats are mainly supplied with groundwater from surrounding uplands.
Process of supplying the valley with calcium- and bicarbonate-rich groundwater with high EC25 values is the most important hydrochemical process occurring in the natural valley (Banaszuk, Banaszuk, Wołosz 1995). Chemistry of alder forest located on the edge of the valley can be modified by pollutants from arable land placed on uplands. Higher concentration of chlorides, sulphates, magnesium and potassium in groundwater is considered as an indication of its antropogenic pollution. Supply of the valley with groundwater polluted by the agriculture was observed mostly in the disturbed part of valley, but also it occurs in the natural mire valley, although only in the edges (Banaszuk, Banaszuk Wołosz 1995; Banaszuk, Wysocka 1995). The willow shrubs occupy a zone between the sedge vegetation and alder forests and are supplied by groundwater with discharges from uplands. Chemistry of groundwater in willow shrub habitats is similar to chemistry of groundwater in alder forest.
The riverside carrs occupy habitats similar to those which are occupied by alder forests and therefore are supplied in similar way. These habitats are characterised by a high concentration of magnesium in soil and high concentration of sulphates in groundwater. Chemistry of groundwater in reed communities is alike to riverside carrs with higher content of potassium, but reed communities are supplied mainly by floods, while riverside carrs are supplied by groundwater.
conclusions
Main environmental variable which differentiates distribution of communities in the
mire valley is frequency and duration of flooding. The sedge and reed communities are correlated with strong perennial floods, which supply the habitats with nitrogen and potassium. In landscape of Narew mire valley reed and sedge communities can be put in the ecological series from closest to the river-bed Phragmitetum communis with longest floods, tall vegetation and high biomass production, through Caricetum gracilis typicum, which occurs close to the river-bed or behind the reed community to Caricetum elatae.
The alder forests and willow shrubs are plant communities with shorter floods and lower water level during inundation. They are mostly supplied by the calcium, magnesium and bicarbonate rich groundwater from the moraine. The riverside carrs occupy magnesium rich soils. Although the differences between alder forests and riverside carrs were noticed, more detailed differentiation needs further complex investigations.
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