Current Condition of Pannonic Salt Steppes at Their Distribution Limit: What Do Indicator Species Reveal about Habitat Quality?

Abstract

Little is known about the suite of ecological conditions under which characteristic species may continue to develop under the pressure of recent habitat deterioration. We aimed to determine the niche of three indicator species of the priority habitat Pannonic salt steppes and to find out how their vegetation composition, land use, and soil chemistry mirror the current condition of their typical habitat. A plot-based vegetation survey was conducted in degraded and in pristine (reference) inland salt steppes in East-Central Europe. We confirmed decreased habitat quality at their northern geographical limit. Most of the sites there showed a strong prevalence of generalists (e.g., Elytrigia repens) and lack of specialists, both resulting from lowered habitat extremity and inappropriate land use (abandonment). A small proportion of plots (19%) were in the same good condition as the reference vegetation in the central area. Soil analyses revealed that the studied halophytes are able to persist on desalinized soils if the land use is suitable. The occurrence of the annual Camphorosma annua (Amaranthaceae) was driven largely by abiotic stress; grazing alone is insufficient for its long-term persistence, while the perennial Artemisia santonicum (Asteraceae) and Tripolium pannonicum (Asteraceae) have higher survival chances as they are able to coexist with generalists. Overall habitat quality can be reliably determined from the analyzed ecological conditions of indicator species. The outcomes of the presented work are relevant for conservation practice and can serve as a quick tool for assessing the current stage of other grassland habitats.

Keywords: alkali soils; electrical conductivity; extreme edaphic conditions; habitat naturalness; indicator species; organic carbon; sodium adsorption ratio; total nitrogen.

Figure 1

Map of the study area (Pannonian Basin) with three core areas of target habitat (Pannonic salt steppes): A—Podunajská nížina lowland—vegetation plots in several stages of habitat degradation, B—Hortobágy, and C—Kiskunság—vegetation plots (reference) in preserved salt steppes. Vegetation plots have three different symbols, one for each indicator species of Pannonic salt steppes: Blue diamond—Camphorosa annua, yellow square—Artemisia santonicum subsp. patens, and red circle—Tripolium pannonicum subsp. pannonicum.

Figure 2

(a) Data attribute plot of vegetation naturalness for indicator species Artemisia santonicum subsp. patens based on the LOESS visualization method and displaying Borhidi indicator values [51] as vectors. Detrended correspondence analyses (DCA) ordination diagram projects 51 records/plots classified according to vegetation naturalness groups 1 to 5: (black circle ●—group 1 in Hungary, black square ■—group 1 in Slovakia, grey square ■—group 2, grey diamond ♦—group 3, grey star ✦—group 4, grey circle ●—group 5) and six species: Artesan—Artemisia santonicum, Elymrep—Elytrigia repens, Festpse—Festuca pseudovina, Limogme—Limonium gmelinii, Planmar—Plantago maritima, and Poaang—Poa angustifolia. Displayed vectors: T—temperature; L—light; SR—soil reaction; N—nutrients; M—moisture; LU—land use. Ordination scores of the displayed species (species weight range) are more than 0.10. Axis eigenvalues: 0.534 and 0.349; DCA 1 axis length: 3.091; DCA2 axis length: 2.963. (b). Pair-plot (boxplots of species number and land use intensity) in five groups of naturalness (1–5) with connected median points for Artemisia santonicum subsp. patens. The upper letters (a, b) indicate homogeneous groups according to Tukey’s post-hoc test (α = 0.05).

Figure 3

(a) Data attribute plot of vegetation naturalness for indicator species Camphorosma annua based on the LOESS visualization method and displaying Borhidi indicator values as vectors. DCA ordination diagram projects 39 records classified according to vegetation naturalness (black circle ●—group 1 in Hungary, black square ■—group 1 in Slovakia, grey square ■—group 2, grey diamond ♦—group 3, grey star ✦—group 4, grey circle ●—group 5) and six species: Artesan—Artemisia santonicum, Campann—Camphorosma annua, Festpse—Festuca pseudovina, Planmar—Plantago maritima and Puccdis—Puccinellia distans agg. Displayed vectors: T—temperature; L—light; SR—soil reaction; N—nutrients; M—moisture; LU—land use. Ordination scores of the displayed species (species weight range) are more than 0.10. Axis eigenvalues: 0.467 and 0.136; DCA 1 axis length: 2.413; DCA2 axis length: 1.511. (b). Pair-plot (boxplots of species number and land use intensity) in five groups of naturalness (1–5) with connected median points for indicator species Camphorosma annua. The upper letters (a, b, c) indicate homogeneous groups according to Tukey’s post-hoc test (α = 0.05).

Figure 4

(a) Data attribute plot of vegetation naturalness for indicator species Tripolium pannonicum subsp. pannonicum based on the LOESS visualization method and displaying Borhidi indicator values as vectors. DCA ordination diagram projects 44 records classified according to vegetation naturalness (black circle ●—group 1 in Hungary, black square ■—group 1 in Slovakia, grey square ■—group 2, grey diamond ♦—group 3, grey star ✦—group 4, grey circle ●—group 5) and six species: Astetri—Tripolium pannonicum, Elymrep—Elytrigia repens, Festpse—Festuca pseudovina, and Puccdis—Puccinellia distans agg. Displayed vectors: T—temperature; L—light; SR—soil reaction; N—nutrients; M—moisture; LU—land use. Ordination scores of the displayed species (species weight range) are more than 0.10. Axis eigenvalues: 0.551 and 0.415; DCA 1 axis length: 3.262; DCA2 axis length: 2.789. (b). Pair-plot (boxplots of species number and land use intensity) in five groups of naturalness (1–5) with connected median points for Tripolium pannonicum subsp. pannonicum. The upper letters (a, b) indicate homogeneous groups according to Tukey’s post-hoc test (α = 0.05).

Figure 4

(a) Data attribute plot of vegetation naturalness for indicator species Tripolium pannonicum subsp. pannonicum based on the LOESS visualization method and displaying Borhidi indicator values as vectors. DCA ordination diagram projects 44 records classified according to vegetation naturalness (black circle ●—group 1 in Hungary, black square ■—group 1 in Slovakia, grey square ■—group 2, grey diamond ♦—group 3, grey star ✦—group 4, grey circle ●—group 5) and six species: Astetri—Tripolium pannonicum, Elymrep—Elytrigia repens, Festpse—Festuca pseudovina, and Puccdis—Puccinellia distans agg. Displayed vectors: T—temperature; L—light; SR—soil reaction; N—nutrients; M—moisture; LU—land use. Ordination scores of the displayed species (species weight range) are more than 0.10. Axis eigenvalues: 0.551 and 0.415; DCA 1 axis length: 3.262; DCA2 axis length: 2.789. (b). Pair-plot (boxplots of species number and land use intensity) in five groups of naturalness (1–5) with connected median points for Tripolium pannonicum subsp. pannonicum. The upper letters (a, b) indicate homogeneous groups according to Tukey’s post-hoc test (α = 0.05).

Figure 5

Minimum, maximum, and mean values of soil chemical properties measured on 77 vegetation plots.

Figure 6

Significant soil properties for three indicator species (ART, CAM, and TRI) at different groups of naturalness (1–5): Na_exch—exchangeable sodium; pH—soil reaction; Cox—organic carbon; Ntot—total Nitrogen. Boxplots show median (red squares), interquartile range (boxes), non-outlier range (whiskers), outliers (empty circles), and extreme values (asterisk). Statistical significance by ANOVA.