In the Świętokrzyski National Park, 29 plant communities have been discovered, including 23 regarded as plant associations. Such an appreciable diversity results from the natural variability of habitats in the region.
Upland fir mixed coniferous forest. The biggest areas covered by this forest association occur in the Łysogóry range, the Klonowski range, and the Wilkowska valley. In the ŚNP, it is not a homogeneous community. Owing to ecological and floral differences, three variants of it have been designated: the typical variant, the ferny variant (with Dryopteris dilatata), the variant with the blackberry Rubus hirtus
- Carpathian beech forest. The biggest areas of this association are located on the northern and southern slopes of the Łysogóry range, and in the following forest districts: Św. Krzyż, Jastrzębi Dół, Św. Katarzyna, and Chełmowa Góra. The Carpathian beech forest develops usually in flat parts of slopes, and in watercourse valleys, where mineral and organic flows are accumulated, causing local fertilisation of the habitat
- Central-Polish mixed forest is the third forest association found in the ŚNP. It grows in the Wilkowska valley; on the mountains: Psarska, Miejska, and Chełmowa; in the forest enclave called uroczysko Serwis; in the forest districts: Dąbrowa, and Św. Katarzyna. It covers flat or slightly raised areas, with groundwater located deeply beneath the surface. There are brown soils and Luvisols in these habitats.
Local rowan association (zespół jarzębiny świętokrzyskiej) develops on the fringes of the bigger boulder fields (gołoborza) of the Łysogóry range. Between the quartzite blocks, at least 0.5 m above the mineral substratum, there accumulates the suspended humus, very acid and poor in minerals. On such humus there germinates the European rowan, also known as mountain ash (Sorbus aucuparia), together with spruce, fir, and sometimes deciduous trees. In such ecological conditions only the rowan root system manages to cross the free space, and reach the mineral substratum. Other trees die, mainly of water shortage, when their root systems reach the free space.
Other forest associations found in the ŚNP include: ash-alder riparian forest (Circaeo-Alnetum Oberd 1953), subcontinental oak-hornbeam forest (Tilio-Carpinetum Traczyk 1962), marshy coniferous forest (Vaccinio uli-ginosi-Pinetum Kleist 1929, Kobebendza 1933), and marshy small-reed coniferous forest (Cala-magrostio villosae-Pinetum Staszkiewicz 1958)
Willow scrubs (Salici-Franguletum Malc. 1929, Tx. 1937) develop in wet and humid meadows (e.g. in Czarna Woda valley). Not numerous reed beds include: reedy rushes (Scirpo-Phragmitetum Koch 1926), water horsetails (Equisetetum limosi Steffen 1931), bottle sedges (Caricetum rostratae Rubel 1912), blister sedges (Caricetum vesicariae Br.-Bl. et Denis 1926), slim sedges (Caricetum gracilis (Graebn. et Hueck 1931) R. Tx. 1937), and reed canary grass associations (Phalaridetum arundinaceae Libb. 1931).
Among wet and fresh meadows there are: Junco-Molinietum Prsg. 1951; Cirsietum rivularis Ralski 1931; Arrhenatheretum medioeuropaeum (Br.-Bl. 1919) Oberd. 1952; Lolio-Cynosuretum R. Tx. 1937.
Nardo-Juncetum squarrosi (Nordh. 1920) Buk 1942, dominated by matgrass, is an anthropogenic plant community found in the Park.