Old-growth forests arę natural biocoenoses, which developed and function without apparent impacts of human activity, which are adjusted to their habitats and remain in perfect biocoenotic equilibrium. In a forest environment there occurs a high diversity of seminal and cryptogamic plants and fungi, including lichenized fungi (lichens). The disappearance of old-growth forests affected by human activity or their strong fragmentation and isolation are the greatest danger for numerous typically forest lichens. On the basis of selected lichens - indicators of old-growth forests we undertook an attempt at detecting well-preserved lowland areas, which are at present biocentres of typically forest species. The most important features of indicatory species were considered the following: they are native species growing exclusively in forest communities; they are permanent components of forest biocoenoses, while their biological-ecological properties are adjusted to the phytoclimate and biotopes of forest environment; they inhabit specific forest habitats; they are typical epiphytes and epixylites inhabiting old live trees and dead wood of various stages of decomposition; they do not grow in managed forests. A total of 71 species that will serve the function of obligatory indicators (IND) of old-growth forests were selected for Poland's natural lowland forests (see Table 1). 53 of these species are presently strongly threatened, possessing the status of the Red List Categories (CR, EN and VU). The following 10 forest areas were evaluated: Białowieża National Park (58 IND), the reserves of Budzisk (34 IND), and Starożyn (29 IND) in North-Eastern Poland, reserves of Borki (29 IND), Las Warmiński (17 IND) and Krutynia (18 IND) in Northern Poland, and the reserves of Spała (15 IND), Zagożdżon (13 IND), Białe Ługi (10 IND) and Żyznów (4 IND) in Central Poland (Table 2). The highest number of old-growth forests occur in the Białowieża National Park (84%). This value indicates that the Białowieża Ntional Park may now be considered a model comparitive object, the biocentre of epiphytic and epixylic forest species of old-growth forests representing the total ecological amplitude of biodiversity and occupied habitats. In all the 10 biocentres there occur 66 indicatory species of old-growth forests, the highest number of which, ca 88%, occur in the Białowieża National Park, while 51.5% in the Budzisk reserve in the Knyszyńska Forest.
Porosty – wskaźniki niżowych lasów puszczańskich w Polsce [Lichens – indicators of lowland old-growth forests in Poland]
