Cultural Landscape as Both a Threat and an Opportunity to Preserve a High Conservation Value of Vascular Flora: A Case Study

Abstract

This study aimed to show the influence of cultural landscape structure on species richnessand the conservation value of vascular flora.The analyses are based on 3201 original floristic lists (relevés) and 83,875 floristic data collected since 1994 within Gopło Millennium Park (Nadgoplański Park Tysiąclecia) in a rural area in central Poland. Descriptions of landscape composition in grid cells (0.5 km × 0.5 km) include land use structure, mean deviation of uneven proportions of various land use types, and Shannon index of diversity (H’). Vascular plant diversity was described using total species richness and contributions of groups of native and alien species. Assessment of floristic conservation value was based on qualitative and quantitative floristic index (Wfj and Wfi), mean coefficient of conservatism (C), and floristic quality index (FQI). Floristic analyses were conducted in relation to the whole study area and within grid cells, basing on numbers of species and number of floristic data. The results suggest that species richness in grid cells depends more strongly on diversity and evenness of contributions of land use types, irrespective of which land use types were present. Species richness is strongly dependent on land use structure. Larger contributions of arable fields and built-up areas are linked with a decrease in species richness of nonsynanthropic native plants and species of floristic conservation value. Regularity in this respect is very well illustrated by indices excluding the influence of species richness on floristic value (quantitative floristic index Wfi and mean coefficient of conservatism C). According to the algorithm of FQI, the most valuable floras are characterized by a large number of species with a high contribution of conservative ones. In the study area, this condition was met by floras of surface waters and wetlands.

1. Introduction

At early stages of civilization, all forms of human impact on the natural environment were selective, spatially limited, and did not affect its potential for regeneration. Currently, however, the use of natural resources is a decisive factor influencing landscape structure and determining the possibility of existence of plant species and communities [1]. Changes in land use structure, generating transformations of landscape elements, will be key factors of global biodiversity change by the year 2100 [2].

Relations concerning landscape structure, habitat preferences, and species richness have been studied by many researchers [3]. So far, studies have concerned, primarily, effects of farming on patterns of plant species richness in relation to a broad spectrum of patchy rural cultural landscape [4,5,6,7,8] or some of its elements, e.g., meadows and pastures [9,10,11,12], linear marginal habitats or forest islands in the agricultural landscape [13,14,15,16], and aquatic habitats located between fields [17]. The spatial scope of analyses varies widely: from the continental scale [18] to a local one, limited to small areas [19,20,21]. In some studies, special attention was paid to relations between alien species richness and structure of land use (land cover) [22,23,24]. Attempts were also made to predict species richness changes in time and space in relation to landscape structure metrics [24,25]. In addition, dynamic progress has been made in studies aimed to quantify biodiversity in relation to function, i.e., indicate the value and range of those features of species that affect ecosystem function [1,26,27,28,29,30,31].

In accordance with the Council of Europe Landscape Convention [32], Poland (similar toother EU countries) has undertaken integrated actions to protect landscape [33,34]. This applies primarily to protected areas, including landscape parks, where landscape (also cultural landscape) is protected with its biodiversity and cultural heritage [35]. Gopło Millennium Park is one of the first landscape parks in Poland where the influence of the landscape mosaic on vascular flora has been investigated. The conducted field and laboratory research aimed (1) to analyse land use structure and flora of vascular plants in relation to the whole park and the grid cells, (2) to define relations between landscape structure and the overall plant species richness and species richness of groups differing in origin status, and (3) to diagnose the influence of land use types on the conservation value of flora.

2. Materials and Methods

2.1. Study Area

The study area is located in central Poland, in the mesoregion of Gniezno Lakeland (PojezierzeGnieźnieńskie) [36], within landscape park Gopło Millennium Park (Nadgoplański Park Tysiąclecia, 52°32′–52°36′ N, 18°19′–18°22′ E), which protects Lake Gopło and the neighbouring ecosystems (covers about 130.5 km²). The lake and the upper section of the river Noteć are the major hydrological parts of a postglacial tunnel valley.

Documented traces of prehistoric human presence near Lake Gopło date back to the Neolithic period. At that time, human settlements were located mostly on already deforested, fertile soils, known now as ‘Kuyavian black earths’ [37,38]. In the late Middle Ages, Gopło was naturally connected with the Vistula and Warta, and its water level was 6m higher than currently [39]. Regulation works carried out in the upper Noteć valley in the 19th century contributed to substantial changes in morphometric features of the lake, decline of wetlands, drying of meadows, and even their transformation into arable fields. In large spaces, farming practices have accelerated the processes of peat decomposition and erosion [40].

Despite human impact since the Neolithic period, valuable ecosystems have been preserved near Lake Gopło. They are protected as a landscape protection area, a nature reserve, a landscape park, and Natura 2000 sites (SOO and OSO). The landscape park (and, earlier, the landscape reserve) was created to protect natural breeding sites of birds, historical values linked with beginnings of the Polish State as well as the natural and cultural landscape of Kuyavia.

Gopło Millennium Park is a good testing ground for research on biodiversity in relation to land use structure. The cultural landscape historically shaped since the beginning of the Piast dynasty (in the 10th century), with its natural richness and monuments of material culture, has been protected since 1967. Very fertile plains of so-called Black Kuyavia (Czarne Kujawy), with ‘black earths’ developed from exposed lake sediments of Lake Gopło, are the basis for commercial farming. In contrast, in the southern part of the park (shaped by the Vistulian glaciation and characterized by more varied relief and poorer, leached brown soils) subsistence farming prevails. The flora of the park is wellstudied, with a rich database on anthropogenic conditions [41,42,43].

Gopło Millennium Park was divided into grid cells (0.5 km × 0.5 km) to analyse both land use structure and flora in each grid cell (Figure 1). Within, arable fields dominate. Smaller proportions of its area are covered by surface waters and wetlands as well as by meadows and pastures. Forests occupy a very small proportion (

Table 1. Land use structure (original data).

Land Use Type	Covered Area [ha]	Proportion of Total Area [%]
Forests (1)	1035.9	7.4
Surface waters and wetlands (2)	2283.2	16.3
Meadows and pastures (3)	1418.1	10.1
Arable fields (4)	8026.3	57.3
Built-up areas, orchards, and private gardens (5) Marginal habitats (6)	699.3	5.0
	537.2	3.8
Total	14,000.0	100.0

, Figure 1). Arable fields dominate also in most (65.3%) grid cells, i.e., they cover at least 50% of their area (mean 57.2%) (

Table 2. Selected parameters of land use within the grid of grid cells.

Land Use Type	Mean Area Covered		Maximum Area Covered		Number (%) of Grid Cells Where This Land Use Type Covers ≥50% of Cell Area
	[ha]	[%]	[ha]	[%]
Forests (1)	1.8	7.2	24.9	99.5	16 (2.9%)
Surface waters and wetlands (2)	4.1	16.4	24.9	99.5	110 (19.6%)
Meadows and pastures (3)	2.5	10.0	18.6	74.5	12 (2.1%)
Arable fields (4)	14.3	57.2	25.0	100.0	351 (62.7%)
Built-up areas, orchards, and private gardens (5) Marginal habitats (6)	1.2	4.8	24.2	96.8	7 (1.3%)
	1.0	4.0	20.5	82.0	0 (0.0%)

, Figure 2).

2.2. Floristic Classifications and Indices

To describe the conservation value of flora, usually, contributions of rare and threatened species or habitat specialists are used. There are also some known examples of synthetic use of several characteristics of species to determine the floristic value of a study area [44,45]. One possibility is the concept of multivariate evaluation (valorization). It assumes that natural and anthropogenic factors influence, e.g., frequency of occurrence, spectrum of occupied habitats, distribution range, and threat status of species. Thus, each species carries partial information about the conservation value of the flora of the study area, reflected, e.g., in contributions of habitat specialists or species that are very rare, threatened at the regional or national scale, or reach their range limit [46]. This approach takes into account the origin status, frequency, threat category, chorological aspect, and significance of local species resources. Species conservation value (w) was calculated by summing up the partial results (valorization indices) presented in

Table 3. Principles of assessment of species conservation value (w), after Chmiel (2006) [46].

Criterion and Group		Value of Valorization Index
Origin status (defined in Table 4)	Nn	10
	Ns	8
	Ap	6
	Ar	4
	Kn	0
	D	0
Frequency class (defined in Table 5)	I	8
	II	7
	III	6
	IV	5
	V	4
	VI	3
	VII	2
	VIII	1
Local threat category (defined in Table 6)	CR	10
	EN	8
	VU	6
	NT	4
	LC	2
Significance of local resources (defined in Table 7)	in Wielkopolska and Kujawy region	5
Chorological aspect (defined in Table 8)	isolated localities; absolute or regional limit of distribution within or close to study area	5

.

The floristic value of individual grid cells was determined in 2 ways, using the following formulas:

Wfj = Σ w/N and Wfi = Σ (w · n)/N_n

where Wfj—floristic value of the area calculated on the basis of species richness; Wfi—floristic value of the area calculated on the basis of the structure of records; w—species value; n—sum of records of the species in the grid cell; N—number of species in the grid cell; N_n—total number of the floristic data (i.e., records of individual species)collected in the study area.

To describe the conservation value of flora, also, the concept of Floristic Quality Assessment (FQA) was used [47,48]. Its essence is an expert evaluation of the coefficient of conservatism (c), i.e., association of the species with habitats that were not transformed by human impact, on a scale of 1–10. By summing up c values of species present in the given area and dividing it by species number (n), the mean coefficient of conservatism (C) for the flora of the study area was estimated:

C = ∑ c/n

Floristic quality index (FQI) was calculated by multiplying the mean value (C) by the grid cell root of the number of species (√n).

FQI = C × √n

The concept of FQA has been widely applied in North America [49,50,51,52,53,54,55,56,57,58,59,60]. The criteria and groups listed in Table 1, used to describe the conservation value of the total flora and floras of individual grid cells, are defined in

Table 4. Classification and definitions of groups of species differing in origin status and naturalization, after Chmiel (2006) [46], Jackowiak (1990) [61], and Thellung (1915) [62].

Floristic Group Based on Origin Status	Short Description
Native species: Nonsynanthropic native species (Nn)	native species growing exclusively or nearly exclusively in natural, undisturbed habitats
SSemi-synanthropic native species (Ns)	native species growing also in semi-natural and rarely in anthropogenic habitats
Synanthropic native species (apophytes) (Ap)	native species growing exclusively or nearly exclusively in semi-natural and anthropogenic habitats
Alien species:
Archaeophytes (Ar)	species that, thanks to human impact, appeared spontaneously in Central Europe before discovery of America (in 1492)
Kenophytes (Kn)	species that, thanks to human impact, appeared spontaneously in Central Europe after discovery of America
Diaphytes (D)	alien species appearing spontaneously only in some periods or temporarily escaping from cultivation

,

Table 5. Frequency classes of species, after Chmiel (2006) [46].

Frequency Class	Class Description	% of Occupied Grid Cells	Number of Occupied Grid Cells
I	very rare	<0.51	<3
II	rare	0.51–2.00	3–11
III	infrequent	2.01–5.00	12–28
IV	widely distributed	5.01–10.00	29–56
V	moderately frequent	10.01–20.00	57–112
VI	frequent	20.01–35.00	113–196
VII	common	35.01–50.00	197–280
VIII	very common	>50.00	>280

,

Table 6. Classification and definition of local threat categories, after IUCN 2021 [63].

Threat Category	Short Description
Critically endangered (CR)	extremely high risk of extinction (species characterized by a narrow scale of habitats and plant communities; a low number of small, declining populations)
Endangered (EN)	not close to extinction, but very likely to become critically endangered in near future
Vulnerable (VU)	not classified as CR or EN, although its resources are deteriorating (range fragmentation, isolation of populations, decreasing size and number of populations)
Near threatened (NT)	not threatened, but considering changes in its resources and environment in situ, it is likely to be threatened in near future
Least concern (LC)	size of its range and its resources in study area relatively stable; may be of interest because of its decline in neighbouring regions

,

Table 7. Significance of local resources of individual species, after Chmiel (2006) [46]; diagnoses based on the Atlas of Distribution of Vascular Plants in Poland [64] and expert knowledge.

Local Resources	Short Description
Significant in study area	density of localities of a given species within study area distinguished from its distribution in Wielkopolska (W) and Cuyavia (K)

and

Table 8. Chorological aspect, after Chmiel (2006) [46]; diagnoses based on the Atlas of Distribution of Vascular Plants in Poland [64] and expert knowledge.

Chorological Aspect	Short Description
Location in relation to continuous range of distribution	localities of species within study area either situated in isolated localities (I) or reaching an absolute/regional limit of distribution within study area (or close to it) (N, NE, E, SE, S, SW, W, or NW)

.

2.3. Indices of Landscape Heterogeneity

In spatial analyses, six major land use types in the cultural landscape were taken into account: (1) forests; (2) surface waters and wetlands; (3) meadows and pastures; (4) marginal habitats: roadsides, grassy field borders, and small mid-field woodlots; (5) arable fields; and (6) built-up areas, orchards, and private gardens. Land use type takes into account only marginal habitats that are not used for agriculture and are landscape components located in a mosaic of arable fields or meadows. They are either linear (grassy field borders, ditches and small water courses, roadsides, etc.) or non-linear (small wooded patches, water bodies and marshes, covering less than 0.2 hectare). This land use type excludes similar landscape components located within extensive woodlands, also forest edges.

They were digitized on the basis of orthophotomaps (https://geoserwis.gdos.gov.pl/mapy/) using QGIS 2.0 Dufour software (accessed on 15 November 2020). The covered area and proportion of the total area were determined in relation to the whole study area and each grid cell (0.5 km × 0.5 km).

In every grid cell, landscape heterogeneity was quantified using the Shannon diversity index (H’) [65].

Landscape heterogeneity in individual grid cells was also described using mean deviation of proportions of land use types (d), calculated as follows:

d = (x − y)/N

where x—area covered by one land use type; y—arithmetic mean of areas covered by all land use types (i.e., 16.67% of grid cell area here); N—number of distinguished land use types. In relation to an analysed grid cell, proportions of land use types would be even if all the analysed types covered equal parts of the grid cell, i.e., 4.16 ha each (1/6 = 16.67% of grid cell area), because six land use types were distinguished. Then, the value of (d) would be 0.

2.4. Floristic Database

Basic field research, consisting of complex mapping of vascular flora, was conducted in 1994–1997. In the next 25 years, the area was monitored, and maps of distribution were updated for the most unstable elements of its flora: threatened and invasive species. Floristic diversity and species richness was documented with floristic lists (relevés). Each time, location of the study plots on the grid of 560 grid cells (0.5 km × 0.5 km) was recorded and land use types were defined. Consequently, the total study area covered 140 km². Floristic analyses were made in two ways: in relation to the number of species and in relation to sums of floristic data concerning individual species and groups of species in different land use types. In the whole study period, 3201 floristic lists and 83,875 floristic data (records of individual species) were collected. The dominance of arable fields in the study area was reflected in the largest numbers offloristic lists (1296, i.e., 40.5% of the total number) and floristic data (22,103, i.e., 26.4% of the total number) collected during mapping of the flora of this land use type. Particularly noteworthy, however, is therelatively high number floristic data (

Table 9. Distribution of floristic lists and floristic data collected within various land use types.

Land Use Type	Number of Relevés	%	Number of Floristic Data	%
Forests (1)	207	6.5	6554	7.8
Surface waters and wetlands (2)	427	13.3	12,144	14.5
Meadows and pastures (3)	371	11.6	13,523	16.1
Arable fields (4)	1296	40.5	22,103	26.4
Built-up areas, orchards, and private gardens (5)	205	6,4	6761	8.1
Marginal habitats (6)	583	18.2	18,924	22.6
Others (7)	112	3.5	3866	4.6
Total	3201	100.0	83,875	100.0

) for marginal habitats in comparison with the small proportion of the total area covered by them (see Table 1).

Scientific names of vascular plants in Appendix A follow Mirek et al. (2020) [66]. Information on properties (status) of these species, provided there, is based on my article [46] and my expert knowledge.

In the series of statistical analyses, regression analysis was used. This option is an integral part of Microsoft Excel version 365. The p-value index was calculated in the Statistica 13 program.

3. Results

3.1. Species Richness in Relation to Land Use Types

Flora of the park included 867 vascular plant species. Most of them were recorded in marginal habitats (603 species, 69.6% of the total species number). A slightly lower numbers of species was found in meadows and pastures (520, 60.0%), forests (473, 54.6%), as well as surface waters and wetlands (466, 53.7%). The lowest numbers of species were recorded in arable fields (261, 30.1%) and in built-up areas, orchards, and private gardens (392, 45.2%). Only 90 species were shared by all the land use types. Numbers of species shared by two, three, four, and five land use types were as follows: 138, 141, 162, and 125, respectively. However, as many as 211 species were habitat specialists, recorded in only one type of land use. Species richness within individual grid cells increased with growingdiversity of land use types (Figure 3).

Species richness tends to be higher in squares with even proportions of various land use types. This condition would be optimally fulfilled if all the analysed land use types covered equal parts of a square, i.e., 4.16 ha each (16.67%). The analysis shows that species richness is negatively correlated with growing values of mean deviation, i.e., increasing areal disproportions of various land use types in grid cells(Figure 4).

In addition, the Shannon index of diversity (H’) indicates a dependence of species richness on landscape composition. Growing H’ values increase the chance of higher species richness in grid cells (Figure 5), but this relationship is weaker (R² = 0.19) than for mean deviation of uneven proportions of various land use types (R² = 0.37).

Maximum proportions of individual land use types (resulting from the situation when one type clearly dominates) always had a negative influence on floristic richness in grid cells (Figure 6).

3.2. Variation in Percentage Contributions of Species Groups Differing in Origin Status and Naturalization in Relation to Land Use

The flora of Gopło Millennium Park is dominated by native species (645 species, i.e., 74.4% of the total number), while alien plants are represented by 222 species. Very similar proportions are observed in numbers of records: native species account for 74.6% of the total number of floristic data. Among native taxa, species avoiding human impact prevail (Nn and Ns). However, they were recorded less frequently than apophytes (Ap), which are able to colonize anthropogenic habitats (

Table 10. Proportions of groups differing in origin status in the total flora, expressed as numbers of species and floristic data.

Land Use Type	Number of Floristic Lists	%	Number of Floristic Data	%
Non/semi-synanthropic native species (Nn, Ns)	374	43.1	20.178	24.1
Apophytes (Ap)	271	31.3	42,990	51.3
Archaeophytes (Ar)	93	10.7	16.796	20.0
Kenophytes (Kn)	60	6.9	3381	4.0
Diaphytes (D)	69	8.0	530	0.6
Total	867	100.0	83,875	100.0

).

Nonsynanthropic and semi-synanthropic native species were the most numerous and most frequent (

Table 11. Geographical-historical structure of floras of the distinguished land use types, expressed as percentage contributions to the total number of species (A) and to the total number of floristic data (B).

Land Use Type	Origin Status of Species
	Non/Semi-Synanthropic Native Species		Apophytes		Alien Species
	A [%]	B [%]	A [%]	B [%]	A [%]	B [%]
Forests (1)	50.7	58.8	37.5	37.0	11.8	4.2
Surface waters and wetlands (2)	53.2	71.9	39.1	25.5	7.7	2.6
Meadows and pastures (3)	40.0	28.3	43.8	67.3	16.2	4.3
Arable fields (4)	14.6	0,4	44.8	34.4	40.6	65.2
Built-up areas, orchards, and private gardens (5)	15.8	5.8	44.9	52.2	39.3	42.0
Marginal habitats (6)	36.2	14.5	40.6	73.5	23.2	12.0

) in aquatic/wetland ecosystems and in forests.

Their contributions to the floras of grid cellsare usually markedly higher when the proportion of aquatic/wetland ecosystems is high (R² = 0.48) (Figure 7(2A)). Increased proportions of forests, marginal habitats, as well as meadows and pastures also positively affect native species richness, although less strongly (Figure 7(3A)). Increased proportions of arable fields (R² = 0.61) (Figure 7(4A))and, to a lesser extent, of built-up areas, orchards, and gardens (R² = 0.02) limit the shares of native species within grid cells (Figure 7(5A)). Species richness and the number of records of apophytes only slightly depend on land use structure (Figure 7(1B–6B)).

Alien species were the most numerous and frequent in arable fields as well as in built-up areas, orchards, and gardens (Table 11). Their contribution to the floras of grid cellstends to increase primarily with growing areal contributions of arable fields (R² = 0.53) (Figure 7(4C)).

Species richness of all groups of plants, irrespective of their origin status, is positively affected by a diversity of land use types in grid cells (Figure 8A–C). This dependence is the most conspicuous among apophytes. Species of this group are generally eurytopic, so they can colonize also areas with a diversity of land use types.

3.3. Floristic Conservation Value of Sites Covered by Various Land Use Types

A comparison of floristic conservation value of forests, waters and wetlands, meadows and pastures, as well as marginal habitats, if based only on species composition, indicates small differences between them (Figure 9A–C). The least valuable floras were observed on ruderal sites (built-up areas) and segetal ones (arable fields). Differences between them are more noticeable when FQI is applied. The exclusion of alien species from its algorithm implies lower FQI values (according to methodological rules) because aliens account for considerable proportions of segetal and ruderal floras.

When, in the evaluation, floristic data are taken into account, differences in floristic conservation value are more noticeable. All three indices unanimously show that aquatic/wetland flora is characterized by the highest conservation value (Figure 10A–C). When numbers of floristic data are considered, the influence of casual species on final results of floristic conservation value assessment is minimized. Similarly, the influence of rare habitat specialists associated with the evaluated ecosystem is also smaller.

4. Discussion

4.1. Species Richness in Relation to Land Use

More and more attention has been paid recently to protection of cultural landscapes and their biodiversity [67,68].To emphasize the great value of mutual relations between culture and biodiversity, the term biocultural diversity was coined in 2005 [69].

Vascular plant species richness in the study area is unevenly distributed between individual land use types. The largest number of species was recorded in marginal habitats, although they cover the smallest proportion of the study area. The smallest number was recorded in arable fields, which are dominant components of the landscapes surrounding Lake Gopło.

Nevertheless, it would be wrong to conclude that marginal habitats intrinsically contribute to a high floristic richness in the analysed grid cells, because a large number of plant species found there originate from the neighbouring ecosystems. Admittedly, in homogeneous cultural landscapes, especially in farmlands, they can become localrefugia and ecological corridors facilitating migration (also of segetal species, typical of arable fields). The latter possibility is confirmed by results of research conducted in Sweden, which concerned the influence of linear marginal habitats on floristic richness of research plots [14]. The presence of marginal habitats can slow down the loss of plant species originating from other ecosystems. This effect is enhanced if the area covered by marginal habitats is larger [14]. Similar results have been reported from southern France, where the role of marginal habitats among vineyards and olive groves was studied [70]. The biodiversity of cultural landscape can be strongly affected by even small remaining patches of semi-natural vegetation, scattered among cultivated patches [71]. However, this role of marginal habitats may be less effective if intensive farming is conducted in their immediate vicinity [72]. The negative impact of highly commercial agriculture on biodiversity has already been reported [73,74].

It is commonly believed that commercial forests play a minor role in shaping biodiversity, as compared with natural forests [75]. However, research conducted in artificial forests or plantations shows that species richness of some groups of organisms, also plants, can be greater there than in natural forests [76,77]. Results of this study indicate that expression of species richness in the grid of grid cells is positively influenced by landscape heterogeneity, expressed here as the high number and evenness of proportions of various land use types. The heterogeneity of landscape components ensures a diversity of suitable niches, affecting biotic processes [25], and increases the chances of occurrence of habitat specialists. In Gopło Millennium Park, two processes are equally harmful to biodiversity: extensive farming methods are gradually abandoned, whereas land use is intensified. This phenomenon, observed earlier in West Europe, is currently common also in countries of Central and Eastern Europe [78]. Some authors suggestthat stopping agricultural activity can be a chance for ecosystem restoration or new landscape functions [79].

Out of the two alternative measures of landscape heterogeneity in grid cells, the mean deviation of uneven proportions of land use types (d) more precisely described the dependence of species richness on the landscape mosaic on the grid of cells. Landscape diversity expressed as the Shannon index less precisely reflects the relationship between species richness and landscape heterogeneity.

The influence of land use structure on species richness within individual grid cellsdepends more on the number of land use types than on which land use types are present. In all grid cells, an increasing dominance of any land use type was linked with a decrease in species richness. Such a dominance lowers landscape heterogeneity and thus reduces the availability of suitable habitats. This applies particularly to the dominance of arable fields [80]. In comparison with them, built-up areas, especially cities and towns, seem to be enclaves of local plant species richness [81]. Similar analyses in Europe and the USA indicate that plant species—in contrast to animals—react more strongly to local environmental conditions at the site of their occurrence than to landscape composition [73].

4.2. Percentage Contributions of Species Groups Differing in Origin Status and Naturalization in Relation to Land Use

Similarly to earlier reports [22,23], this study shows that species richness of native and alien plants increases with increasing landscape heterogeneity. However, the rate of species richness growth in those groups in response to growing diversity of land use types is different. In the cultural landscape of Gopło Millennium Park, the species richness of nonsynanthropic native plants tends to increase mostly in response to growing contributions of surface waters and wetlands to landscape structure. A significant influence of river ecosystems on native species richness is confirmed, for example, by results of research conducted near Dessau (Germany) [22]. A weaker but also positive relationship is noticeable when the proportion of meadows and pastures is growing. In comparison with marginal habitats, the proportion of forests in grid cells does not affect remarkably the species richness of nonsynanthropic native plants. Only scanty forests have been preserved in the study area: they usually form small patches, sometimes surrounded by farmlands and are susceptible to the impact of external factors. Some of the smallest wooded patches, composed of a group of trees and/or shrubs surrounded by fields, were classified as marginal habitats.

As expected, and in accordance with earlier research results [22], species richness of nonsynanthropic native plants was declining markedly with increasing contributions of built-up areas, but mostly of arable fields to land use structure within grid cells.

In contrast, for apophytes, it is difficult to notice any unambiguous relationships between plant species richness and landscape structure. Apophytes can be numerously represented within any land use type, also in grid cells with a simplified landscape structure. However, as shown by values of the Shannon index, the increase in apophyte species richness in relation to growing landscape heterogeneity is greater than for nonsynanthropic native species and anthropophytes. This indicates that apophytes more easily colonize a broad range of ecological niches created by the growing diversity of landscape structure. Nonsynanthropic native species and, somewhat unexpectedly, also anthropophytes considerably less efficiently make use of the mosaic of habitats. Anthropophytes include many species that can be classified as habitat specialists, e.g., some segetal and ruderal species.

4.3. Indices of Floristic Conservation Value

This study provides evidence that plant species richness does not correspond to the conservation value of floras of the selected landscape components. Thus, we should not overestimate the usefulness of plant species richness for assessment of floristic conservation value and determination of priorities of environmental protection. This measure is an important component of plant cover description, but only in combination with its other parameters [82].

All the three applied measures of floristic conservation value (Wfi, C, and FQI) from the marginal habitats, which are refugia of the largest number of plant species, are less valuable floristically than surface waters and wetlands, meadows and pastures, and even forests. Indices of floristic conservation value of ruderal and segetal floras were markedly lower. These differences are more conspicuous when FQI is applied. The exclusion of alien species from its algorithm implies lower FQI values, because aliens account for large proportions of segetal and ruderal floras. The mean coefficient of conservatism (C), even in patches of numerous occurrences of species with high coefficients of conservatism (c), can be masked by large numbers of adventive species or native species with low coefficients of conservatism (c). According to [83], when species richness is high, FQI is a more precise measure of floristic conservation value.

Differences in floristic conservation value are more noticeable when numbers of floristic data are taken into account. Then, the primary role of flora of aquatic/wetland habitats in the ranking of conservation value is the most conspicuous. When analyses are based on sums of floristic data, the influence of casual species on final results of floristic conservation value assessment is minimized. However, it similarly diminishes the influence of habitat specialists associated with the evaluated ecosystem, which are usually very rare.

Research on plant species richness and floristic conservation value in relation to components of cultural landscape can be a useful tool for spatial planning and management taking into account environmental, social, and economic aspects [77,84,85,86,87].

5. Conclusions

In the cultural landscape dominated by farmlands, plant species richness is determined mostly by the number of various land use types and evenness of their contributions. The contribution of alien species to floras of grid cells is positively related to contributions of agricultural areas and built-up areas to the mosaic of landscape. In contrast, nonsynanthropic native species maximize their contribution in the grid cells where surface waters and wetlands prevail.

All the three applied measures of floristic conservation value indicate that the most valuable plant species are found in landscapes dominated by surface waters and wetlands or meadows and pastures.