„Small habitatS” and their input to flora and veg- etation diverSity on the landScape level
Jerzy Solon
institute of geography and Spatial organisation polish academy of Sciences, 00-818 Warsaw, twarda 51/55
E-mail: j.solon@twarda.pan.pl
introduction and theoretical background
The conservation of floristic and vegetation diversity is one of the main tasks of nature protection, especially in rural, fragmented landscapes.
Biological diversity in the widest sense is measured either by estimating richness (number of types of living system) in an area, or by one or more indices combining richness and relative abundance within an area (Wilson, ed. 1988). The first and most obvious way to evaluate diversity makes reference to „intrinsic” species richness and thus deems an area with higher richness to be of greater importance than one with lower richness. The second way involves attempts to assess the contribution made by any given area to the overall diversity (or species richness) of a given geographic region. It is possible from this perspective that an area with lower intrinsic diversity may actually be more important than others with higher diversity.
Because diversity is a complex and scale-dependent feature it is useful to evaluate its level with the help of the classical approach, proposed by Whittaker (1972). This division distinguishes between: (a) alpha-diversity, which concerns the local diversity within a habitat (site, patch); (b) beta-diversity, which concerns the rates of changes in species composition along habitat gradients; and (c) gamma-diversity, which combines the two aforementioned aspects and is concerned with species richness on the regional scale. Gamma-diversity described for vascular plants corresponds to so-called local floras. From this perspective it is possible to formulate two opposing hypotheses describing the role played of small patches for preserving the species richness on the regional level (compare: Ĺs 1999):
A. Small patches, even having high local (alpha) diversity, are more similar in species composition to neighbouring matrix areas (reduced beta (between-habitats) diversity). Thus, small areas contribute less to the regional (gamma) species richness
Fig. 1. A model of possible input of vegetation types to the total flora richness on the landscape level:
a – small communities are unimportant; b – small communities are very important.
and diversity than do larger areas. This situation is due to invasion of matrix and edge species and reduction of site-specific species. If it is a case, a relationship between the cumulative area (patches ordered from the biggest to the smallest) and cumulative species number may look like it is shown on the fig. 1a.
B. Small patches, even having low local (alpha) diversity, are very distinct in species composition from neighbouring matrix areas (enhanced beta diversity). Thus, small areas contribute relatively more to the regional (gamma) species richness and diversity than do larger areas. This situation is due to the fact that smaller areas harbour more specialised species and habitat differences between small and large areas explain the observed pattern. In this case the relationship may look like it is shown on the fig.
1b.
in reality different intermediate patterns are also possible.
The aim of this study is to check the applicability of the above approach for the evaluation of the input of small habitats to flora richness on the landscape level. In opposition to the classical method (focused on the evaluation of diversity and species richness for separate plots) in this case all plots representing the same vegetation type (with all the species occurring) are taken as the basic units for the analysis.
data and methods of elaboration
two test areas were chosen for the analysis.
The first was located in the Narew River valley near Tykocin (NE Poland).
During the field work 108 phytosociological records were made as well as the detailed map of actual vegetation in the scale of 1:5000. On the area of 9.05 sq. km 49 phytoso- ciological vegetation types were distinguished. Among them two types were connected with ruderal and segetal vegetation. Those were excluded from the analysis. So the
analysis was conducted for the area of 7.82 sq. km, for 995 separate vegetation patches and for 47 vegetation types belonging to 10 groups of types (so called „aggregated types” in the analysis). The Shannon’s diversity index calculated for the whole landscape equals 3.8309 in the case when all 47 vegetation types were taken as basic units, and 2.3188 – when vegetation typology was simplified to 10 groups. Taking into account the number of phytosociological records one may state that on average every tenth patch got the floristic description, and ca. 14 descriptions were made for each sq.
km. On this area 250 species of higher plants were recorded. Among them 139 species were present at least in one vegetation type with the cover higher than 0.5% (so-called
„dominating species” in the analysis). More information about the vegetation of the area as well as about the methodology of field studies one may find in Solon (1997).
The second test area was located in the surroundings of Pińczów town in southern Poland. During the many years of field studies more than 500 phytoso- ciological records were made, of which 378 were utilised in this analysis. The map of actual vegetation was prepared in the scale of 1:25000. In total the area of 92.04 sq.
km was mapped, but because of ruderal and segetal communities as well as because of the presence of vegetation types with poor phytosociological characte-ristics, the vegetation of only 39.33 sq. km was chosen for the analysis. On this area 697 separate vegetation plots were distinguished, covered by 59 phytoso-ciological vegetation types (which later were aggregated to 12 groups). The Shannon’s diversity index calculated for the whole landscape equals 4.4954 in the case when all 59 vegetation types were taken as basic units, and 2.6882 – when vegetation typology was simplified to 12 groups.Taking into account the number of phytosociological records one may state that on average every second patch got the floristic description, and ca. 10 descriptions were made for each sq. km. On this area 797 species of higher plants were recorded. Among them 588 species were „dominating species”. More information about the vegetation of the area as well as about the methodology of field studies one may find in Kostrowicki
& Solon (eds., 1994).
there were two stages of data analysis.
During the first stage of elaboration all phytosociological records were put into tables – one table for each phytosociological type of vegetation. This was done twice:
firstly – for basic types, secondly – for aggregated groups of types. Then all species occurring in all records for a given vegetation type were combined into one (basic) list.
In the next step the lists were narrowed by elimination of species with the maximum cover no higher than 0.5% (dominating species list). At the same time areas occupied by all vegetation types were calculated from numeric maps of actual vegetation, which had been elaborated in ArcView 3.0.
During the second stage all vegetation types were put in descending order according to their area. Then vegetation types were systematically combined and cumulative numbers of species as well as cumulative areas were calculated.
Pińczów Tykocin
number of types 59 47
Mean number of species 94.69 23.64
Median number of species 95 21
Minimum number of species 3 4
Maximum number of species 216 62
standard deviation 56.63 12.83
Table 1. Mean floristic richness of vegetation types
Fig. 2. The area occupied by vegetation types versus the number of plant species - a scatterplot:
a – Pińczów test area; b – Tykocin test area.
results
Floristic richness of vegetation types.
On both test areas the distinguished vegetation types differ strongly from the point of view of the plant species present. In the floristically richest types one may find up to 62 plant species (in Tykocin) or up to 216 species (in Pińczów). The short characteristics of floristic richness are presented in Table 1.
Detailed analysis showed that on both test areas there is not any statistically significant correlation between the number of species occurring in a given vegetation type and the area occupied by this type (fig. 2a and fig. 2b). One may only state that vegetation types occupying small areas are rather poor in species.
Input of small habitats to floristic gamma diversity
On the fig. 3a and 3b are presented cumulative curves showing the relationship between the area and the number of species for all species and all vegetation types on
Fig. 3. The relationship between the cumulative area and the cumulative number of species for all species and all vegetation types: a – Pińczów test area; b – Tykocin test area.
Fig. 4. The relationship between the cumulative area and the cumulative number of species for dominant species and aggregated vegetation types: a – Pińczów test area; b – Tykocin test area.
both test areas. As it is visible from the figures in both cases c. 50% of vegetation types (30 types in Pińczów and 23 types in Tykocin) cover 95% of the area. But the remaining 5% of the area host as much as one third (in Tykocin) or c. 15% (in Pińczów) of the regional species number.
The shapes of cumulative curves for both test areas are very similar, with the correlation coefficient of 0.94. But one may observe that in Pińczów plant communities occupying greater part of the total area (in fact also bigger in absolute values) are relatively richer in species in comparison to the Tykocin area. On the other hand communities which are locally of the medium size are floristically richer in Tykocin.
It should also be stated that the input of the group of the smallest communities (occupying 5% of areas) to the floristic gamma diversity is strongly emphasised on Tykocin test area.
A similar pattern could be observed when only dominant species and aggregated vegetation types are taken into account (fig.4a and 4b). In both cases the “last” 4 % of the area is occupied by 4 types of vegetation which still exclusively hold c. 6% of the total flora of Pińczów surroundings and c. 11% of Tykocin test area.
conclusions
On both analysed areas small habitats are characterised by rather low intrinsic floristic richness, but they play an important role on the landscape level, firstly because of their influence on the typological richness of the whole landscape, secondly because of their considerably high input to regional (gamma) floristic richness.
The above results do not depend on the way of distinguishing vegetation types: the same pattern was described for narrowly understood phytosociological types of vegetation (associations and subassociations) as well as for wider groups, corresponding to physionomic formations.
Small differences between areas observed in shapes of cumulative curves can be easily explained on the basis of the differences in the land use. On the Tykocin area prevailed are cultivated and heavily utilized meadows, while in Pińczów surroundings seminatural meadows and forest are dominating.
Taking into account what was said above, it is also possible to conclude that the more natural vegetation of the area the smaller the role played by small habitats in maintaining and preserving plant species richness on the landscape level.
references
Ĺs, S. (1999): Invasion of matrix species in small habitat patches. Conservation Ecology [online] 3(1): 1. Available from the Internet. URL: http://www.consecol.
org/vol3/iss1/art1.
Kostrowicki a.S., Solon J. (ed.) (1994): Studium geobotaniczno-krajobrazowe okolic Pińczowa. Dok. Geograf., 1-2.
Solon J. (1997): Antropogeniczne zmiany różnorodności biologicznej w krajobrazie roślinnym (na przykładzie fragmentu doliny Narwi w okolicach Tykocina), Prob.
Ekol. Krajobrazu, 1, 129-139.
Whittaker, r. h. (1972): Evolution and measurements of species diversity. Taxon 2, :213-251.
Wilson e.o. (ed.) (1988): Biodiversity. Natl. Acad. Press, Washington D.C.
