Biodiversity at Linnaeus' birthplace in Stenbrohult, southern Sweden. 4. The vascular plant flora and its changes.
Our study was more thorough than previous ones, which make detailed comparisons to examine changes of the flora difficult. We divided the parish into 124 squares, each of them 1 ´ 1 km (UTM-grid), and almost all of them were searched during several hours at 2–3 visits spread over 15 May–September. For common species only presence were noted, and the number of squares where a species were found in 1970–79 is in the species list above noted directly after the species name. For each species we also add if we consider it likely (L) or possible (L?) that the species was established in Stenbrohult in 1728, when Linnaeus left the parish (cultivated species excluded, but escapes from cultivation included). We call such species linnaean species and estimate that there were about 600 such species in 1728. This estimate includes disappeared species that have never been reported and a few still undiscovered species, possibly at most 35 species. Among the vascular plant species/subsp. known from Stenbrohult about 78 are now considered locally extinct and 48 of these were probably present in 1728 (Table 1). This value of 8% disappeared linnaean species is too low, and we think that more than 10% is a more realistic figure, since some species disappeared before being recorded. Most of the known disappeared species occurred in managed meadows, pastures and cultivated fields (Table 3). During the last 150 years more than 99% of the meadows in Stenbrohult, cut for hay in July or later, have been abandoned and mainly converted to cultivated fields, pastures and forests. Ceased traditional management of meadows, dense spruce Picea abies plantations, artificial fertilisation of pastures and drainage of numerous small wetlands have been especially destructive to the flora.
Many species are at present on the verge of extinction or decreasing (Table 2) and we suggest measures that may save some of them. The most important measure is to expand the area of hay meadows cut after the middle of July, preferably also with grazing by cattle and horses after harvest. These animals are now mainly grazing former fields with a relatively species poor flora due to previous cultivation and fertilization. Grazing of shores of lakes and streams were formerly ubiquitous but are now rare which have effected the flora and caused some extinctions. However, the large Lake Möckeln is only a little polluted and still unregulated, which is positive for many species. Bogs continue to be exploited for peat up to the present time, with mainly negative effects on the flora. The species that have probably decreased and increased in Stenbrohult during the last 100 years are presented in Table 2, and the habitat distribution of the linnean species in Table 3.
During the last 250 years at least 221 species have immigrated to Stenbrohult, mostly still generally expanding species in southern Sweden, and often spread by man. However, at least 30 of these new species are now considered disappeared (Table 1). Some introduced dominating species, e.g. Holcus mollis, Arrhenatherum elatius, Lupinus polyphyllus and Spiraea species, have a negative influence on smaller species. Nitrogen coming with the precipitation add to their effects.
The extinction rate of linnaean species have accelerated over the years in Stenbrohult and since our study mainly was made about 30 years ago, we consider the time ripe for a new study. If it is made with our method a much better estimate of changes of the flora can be made than at present. We have also noted the precise location and sometimes the habitat and number of flowering individuals of less common species, which will facilitate determination of the causes of population changes in the future.
The flora and fauna of Stenbrohult is still very rich, e.g. with about 200 red-listed species recorded in recent times among the organism groups studied until now (Nilsson 2002, unpubl.). We consider the preservation of the linnaean species as a true tribute to the work of Carl Linnaeus, but to do this several urgent measures must be done. We suggest some of them in this flora, including habitat restoration and management.
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