This paper presents an invasive plant species that occur in the forests of Kalnik. It also presents the state of the distribution and their impact on forests of Kalnik. A total of 14 invasive species in the forests of Kalnik and these are – Acer negundo L., Ailanthus altissima (Mill.) Swingle, Ambrosia artemisiifolia L., Amorpha fruticosa L., Asclepias syriaca L., Conyza canadensis (L.) Cronquist, Echinocystis lobata (Michx.) Torr. et Gray, Erigeron annuus (L.) Pers., Impatiens glandulifera Royle, Juncus tenuis Willd.), Phytolacca americana L., Reynoutria japonica Houtt., Robinia pseudoacacia L., Solidago gigantea Aiton. Alochtonous vegetation is not only inevitable, but it also appears to be a constant future challenge in the globalizing world which communicates on all levels with every means possible. Its influence should not by any means be marginalized. Its importance and influence is not completely negative and there are possible benefits and dangers which should be controlled by the preventive measures and physical regulation. The most important species in Kalnik forest vegetation is definitely acacia. It is especially important for private forest lands where acacia tree has become very popular because of its characteristics as a fast growing tree species without any special requirements with relation to growth and it gives fast results concerning timber and firewood. Private lots are usually very small and fragmented. There is a growing need for timber, therefore the trees are grown extensively, from stumps and roots. Other woody species still do not pose a serious threat in economical or biological sense. The impact of herbaceous plants differs in various areas. The most problematic issues for the forestersare thick layers of unwanted specieswhich grow in young forest stands or in forests in the phase of restorationwhere these unwanted speciesinvasively compete with autochthonous species. In biological sense, invasive species pose a constant threat not only to domestic vegetation and biodiversity, but also to human health. We should also mention apiculture, a very important and well developed activity on Kalnik. Above mentioned species are very important and interesting for apiculture as a type of rich bee pasturage. Apiculture in this area depends on acacia pasturage and it is one of very important reasons for growing acacia tree. Other tree species are also valuable for bee pasturage, especially late in autumn when there is no other bee pasturage available and they are mostly species which blossom in autumn and represent a valuable source of pollen (Japanese Knotweed, Prickly cucumber and European goldenrod). Generally speaking, the biggest responsibility for possible consequences of invasive plant species to the vegetation of Kalnik lies on foresters who have to recognize and monitor the appearance of invasive species, especially in state forest lands where they grow and directly influence their composition and state. U radu se navode invazivne biljne vrste koje se javljaju u šumama Kalnika. Također se navodi i stanje njihove rasprostranjenosti u Hrvatskoj i njihov utjecaj na šume Kalnika. Ukupno je zabilježeno 14 invazivnih vrsta koje u šumama Kalnika stvaraju probleme, a to su – Acer negundo L. (negundovac), Ailanthus altissima (Mill.) Swingle (pajasen), Ambrosia artemisiifolia L. (ambrozija), Amorpha fruticosa L. (čivitnjača), Asclepias syriaca L. (cigansko perje), Conyza canadensis (L.) Cronquist (kanadska hudoljetnica), Echinocystis lobata (Michx.) Torr. et Gray (divlji krastavac), Erigeron annuus (L.) Pers. (krasolika), Impatiens glandulifera Royle (žljezdasti nedirak), Juncus tenuis Willd. (nježni sit), Phytolacca americana L. (vinobojka), Reynoutria japonica Houtt. (japanski dvornik), Robinia pseudoacacia L. (bagrem), Solidago gigantea Aiton (velika zlatnica). Najviše problema u šumama Kalnika čini bagrem, i to na svim tipovima staništa i u sastojinama svih starosnih skupina, a posebno su štete značajne u mladim sastojinama te u sastojinama u fazi obnove. Na površinama nakon čistih sječa a prije pošumljavanja, u mladim sastojinama i osunčanim čistinama starih sastojina u fazi obnove, štetu čine i gusti sklopovi krasolike, ambrozije, žljezdastoga nedirka i vinobojke. Ostale navedene vrste za sada nalazimo uz rubove šuma, cesta, vlaka, obalama vodotoka te na šumskim čistinama, gdje dolaze u manjim skupinama ili pojedinačno te za sada ne čine ozbiljne štete, ali su stalna prijetnja autohtonim vrstama, kao i bioraznovrsnosti.