5. Floristic and ecological changes in the forest floor vegetation in 1998-2003

Jerzy Solon

Photo 3. St John's wort (Hypericum perforatum L.) - perennial herbaceous plant - Radziwiłów Forest District - by Jerzy Wawrzoniak

Changes in species richness and diversity

During the last five years, the forest floor vegetation in the monitored observation plots underwent insignificant changes reflected both in the changing number of registered species, different values of the forest floor diversity index, as well as in the similarity of species composition.

Changes in the number of plant species were not significant and concerned only two species on 58 POPs and not less than seven species on 30 POPs. Changes in the abundance of a given species were markedly greater on POPs. This was reflected in the high values of the species composition similarity index. Only on 28 plots, the similarity index value was below 60%, while on 86 was higher than 70%.

Table 3. Changes in the number of species and similarity of species composition of the herbaceous layer by natural-forest regions - a comparison in the years 1998-1999 and 2003 

Particular types of plant communities and natural-forest regions did not statistically differ in the amplitude range and mean values of the species composition similarity index. For a majority of them, no differences in species dynamics were found, either. The only statistically differences were found between the Carpathian natural-forest region where the number of vascular plant species on POPs considerably increased and the Mazury-Podlasie natural-forest region where a significant decline in number of species on POPs was noted (Table. 3).

Further analysis of differences in species composition in the years 1998 and 2003 pointed out to the lack of statistically significant relationships between dependent variables: (a) changes in the number of the forest floor species and (b) degree of similarity of species composition and independent variables: geographical longitude, geographical latitude, as well as longitude and latitude jointly. Lack of such relationships was related to all POPs taken together, as well as POPs grouped in phytosociological types. The exception was the fresh coniferous forest type (Leucobryo-Pinetum and Peucedano-Pinetum) and the mixed coniferous forest type (Querco-Pinetum), where relationship was found between the degree of changes in the forest floor vegetation and geographical longitude (correlation at the level of ca 0.3) however it was of weak statistical significance. Besides, the analysis of spatial autocorrelation did not reveal any regular pattern in distribution of differences in species composition.

The changes in forest floor diversity index were of somehow different nature. Likewise the changes in the number of species and degree of species similarity there were no significant, differences in the direction and dynamics of changes in the index values between the phytosociological types and natural-forest regions (except for insignificant difference on the plots representing Querco roboris-Pinetum community, where on average more distinct increase in forest floor diversity was noted). However, other process depending on averaging the values of the forest floor diversity index was observed. It appeared that for POPs with high index values in 1998, those values in 2003 were lower, while for POPs revealing low species diversity in 1998, the index values increased. This phenomenon was most noticeable with regard to biological diversity (Fig. 5), less distinct for species diversity and the least distinct, but statistically significant, for syntaxonomic diversity.

Changes in the of synanthropisation level of the forest floor vegetation

Changes in synanthropisation level of the forest floor vegetation took in the number of species and their area coverage noting that the changes in species coverage were more distinct. The greatest changes in the percentage share of area occupied by plant species were found for nitrophylous species (ranging from a c. 50% decline to a c. 30% rise on some POPs). The range of quantitative changes for species from ruderal communities (from a 10 % decline to a 40 % rise) and species representing ruderal and stress-tolerant strategy of development (from a 30% decline to a 15% rise) was slightly lower. The range of changes in species coverage (from a minimal decline to about 8% rise) concerned euhemerobes and polyhemerobes and was less significant. It should be emphasised that the changes in the aforementioned aspects of the synanthropisation process were not correlated.

The distribution of changes was similar in all monitored groups of plant communities and did not depend on the index values for 1998.

No distinct correlation was found between changes in synanthropisation level and geographical distribution. Nonetheless, a decrease in the coverage share of nitrophylous species was noted on many POPs in north-eastern and eastern Poland and a significant increase at the foreland of the Carpathians and Sudetes. Besides, an increase in the share of species representing ruderal and stress strategy types was found in southern and eastern Poland (Fig. 6). However, these changes were only poorly reflected in the mean values for individual natural-forest regions, however, in the Mazury-Podlasie region the decline in the nitrophylous species was the greatest among the regions and significantly different than the changes noted in the Baltic region (Table 4).

Changes of the ecological character of the forest floor vegetation

The ecological character of the forest floor vegetation underwent varied changes. In a synthetic approach, changes in vegetation requirements regarding the continentality of climate (index K_śr),

mean temperatures (index T_śr), soil moisture (index F_śr) and nitrogen content  (index N_śr) on all the monitored POPs point out to a fluctuational character of changes and frequency histograms of individual classes of changes to symmetrical normal distribution (Fig. 7). Changes in the forest floor vegetation requirements regarding light availability (index L_śr) and soil pH (index R_śr) were of evidently different nature. A marked decrease in the value L_śr noted on 59 plots might have accounted for an increased shading, while the changes in the R_śr index on 72 plots indicated negligible yet significant increase in the level of soil acidity (Fig. 8).

The aforementioned changes proceeded in a similar way in all types of plant communities, no significant differences were found in the distribution of changes of bioindication indices for the groups of plant communities.

On the other hand, the observed spatial character of changes in the values of individual indices was different (Table 5).

An increased shading of the forest floor was recorded on many POPs throughout Poland, but it was most distinct in the Mazowsze-Podlasie natural-forest region which largely differed in this respect from the remaining regions (Table 5).

The changes in the F_śr index indicate a considerable decrease in moisture level in the Małopolska natural-forest region and slightly less distinct decrease in the Baltic and Wielkopolska-Pomerania natural-forest regions, as well as an increase in moisture level in the Sudeten natural-forest region (Table 5).

Also a decrease in the mean level of nitrogen content in the soil in the Sudeten natural-forest region (particularly its southern part) was significantly greater than in other natural-forest regions.

A decline in the R_śr index value (increase of pH) occurred on a number of POPs across Poland, but it was impossible to distinguish neither a clear centre of this phenomenon nor the trend in area changes.

Changes of the number of protected species

In 2003, stations of seven species subjected to complete protection (Aquilegia vulgaris, Dianthus arenarius, Lonicera periclymenum, Prunus fruticosa, Pulsatilla pratensis, Rubus chamaemorus, Sorbus intermedia) were not found on the monitored plots. The number of stations of 14 species decreased (including 11 species under strict protection), while the number of stations of 10 species increased (5 species under strict protection). Substantial changes were found in the geographical distribution of species subjected to strict protection. In 1998, they occurred on 31 POPs, and in 2003 on 23 POPs. In both measurement years, species under strict protection occurred only on 19 POPs (Table 6).