Croatian Journal of Forest Engineering (Apr 2011)
Vegetation and Structural Features of Norway Spruce Stands (Picea abies Karst.) in the Virgin Forest of Smrčeve Doline in Northen Velebit
Abstract
Detailed research into the virgin forest of Smrčeve Doline, situated in Northern VelebitNational Park, was undertaken in the vegetation period of 2010 (Fig. 1). The virgin forest covers an area of 488 ha, of which spruce forests account for 300 ha, beech forests for 125 ha, while the rest is without any forest vegetation. The altitude ranges between 1,279 m and 1,607 m. The virgin forest mainly extends in the north-south direction. Over half of the spruce stands are distributed in sinkholes, as well as on northern and northwestern slopes ascending towards the tops. In the geomorphological sense, this is an exceptionally richly developed Dinaric karst relief, where the parent material is made of limestone breccias and limestone-dolomite blocks, which often resurface. The soil is organogenic and organomineral calcomelanosol in a mosaic with calcocambisol. The average annual temperature is 3.5 °C and the amount of the average annual precipitation is 1,898mm(meteorological stationVučjak, 1954mabove sea level, period 1961–1990, data of the DHMZ). Phytocoenological research based on the standard Central European method of the Zürich-Montpellier School has shown that stands of Norway spruce are distributed in two forest communities (Table 1): spruce forest with Laserpitium krapfii (Laserpitio krapfii-Piceetum abietisVukelić, Alegro et Šegota 2010) and spruce forest with Hypericum richerii grisebachii (Hyperico grisebachii-Piceetum abietis /Bertović 1975/ Vukelić, Alegro, Šegota et Šapić 2010). The floral composition with their differences justifies their classification into independent associations in relation to other sub-alpine phytocoenoses of the Dinaric region. Compared with them, spruce forests of the sub-alpine belt of northern Velebit are differentiated by the presence and the higher cover of species Campanula velebitica, Melampyrum velebiticum, Hypericum richeri grisebachii, Laserpitium krapfii, Valerianamontana, Euphorbia carniolica, Geranium sylvaticum,Adenostyles alliariae and other, as well as the absence of the species of the Alpine-boreal and the south Balkan region (Vukelić et al. 2010a, Vukelić et al. 2010b). These results are of exceptional importance because, in combination with other research, they will be indispensable for defining forest communities of spruce in the Gorski Kotar area, which, according to preliminary comparisons, show more similarities with the communities of the Dinaric and pre-alpine area of Slovenia. The structural features of the stands were established in two sample plots situated in the most representative part of the virgin forest. In addition to basic site parameters, some possible anthropogenic impacts were also analyzed in square plots of 50 × 50 m. These impacts are relevant for the assessment of the natural status of the stands. To quantify structural parameters in the sample plots, circumferences and heights were measured 1 cm above the diameter at breast height in all the trees, and their life status was determined using the methodology of Maser et al. 1979 (Tables 2 and 3). Standing trees (live and dead) were divided into 9 degradation categories. The quantity and decomposition rates of dead standing and fallen timber were recorded. The decomposition stage of dead fallen timber was classified into 5 decomposition categories. In terms of assessing the natural status of forests, we assumed that it was a primary virgin forest stand, which shows no traces of direct anthropogenic impacts, and as such can be used for all comparative research of spruce ecosystems. The criteria for the assessment of the status are based on similar research of Central European authors, primarily that of Geburek et al. (2010), who systematically constructed biodiversity indices for Austrian forests. Measurements of structural parameters in the two sample plots revealed a very high amount of growing stock, resulting from the absence of management and the presence of exclusively natural factors. In terms of tree number distribution by diameter classes (Fig. 3 and 4), this research indicates bimodal distribution that deviates significantly from the balanced de Liocourt curve (selective form of distribution). This was also confirmed by past research into Central European virgin forests (Lorimer et al. 2001,Westhpall et al. 2006, Diaci et al. 2009). It is expected that the distribution of diameters at breast height of spruce stands in Smrčeva Dolina will gradually assume a reverse sigmoid curve form (reverse S shape). The reason lies in the continuous regeneration process that takes place in newly created canopy gaps and on dead lying timber. The newly-established young generation slowly penetrates into the upper stand layers and fills in the canopy gaps.With canopy gaps occurring continuously over the entire virgin forest area, the development of young generation achieves a specific form of the reverse S shape of tree number distribution. The growing stock in the sample plots is relatively high for these altitudes. It is primarily the result of favorable micro-site conditions, which are conducive to the biological-ecological requirements of spruce. Differences in the two plots emerge from different ecological and particularly from edaphic parameters. The first plot (association Laserpitio krapfii-Piceetum abietis) is situated in the sinkhole itself and on its lower slope, where the soil is very deep and suitable (colluvium), while the second is about 200 m higher, immediately under the top of the slope, where the soil is considerably shallower and rockiness is more distinct (association Hyperico grisebachii- -Piceetum abietis). With reference to the measured parameters of live trees, the quantity and decomposition rate of dead standing and fallen timber, the complete absence of stumps of anthropogenic origin, the distance from roads and mountain trails, the geographic position, inaccessibility and other factors, Smrčeve Doline can be considered a virgin forest with the highest degree of naturalness.
