Conifer forests dominate much of the landscape of Thásos but olive groves Olea europaea are the most abundant broadleaf woodland habitat, covering 7,400 hectares (21%) of the island. Although obviously planted and an important part of the local agriculture, these pasture woodlands support a rich variety of wildlife. Many groves are clearly very ancient and consist of hollow trees that provide niches for dead wood invertebrates, birds, reptiles and (presumably) bats.
They vary much in their significance as a result of past and current land use and this is reflected in their ground layer. Neglected groves, which are declining in abundance, have an understorey of tall shrubs, known as shibylak (see Scrub). They contain a diverse range of scrub species, supporting a rich invertebrate fauna, and probably constitute the most significant habitat on the island for breeding birds. Most groves are grazed to a greater or lesser extent by goats or sheep and beneath the olive canopy the ground layer is often composed of flower-rich grassland (though parched by early summer), representing some of the best examples of lowland grassland habitat on the island. Olive groves are widely distributed around the coast and all are worthy of exploration. Particular concentrations of important olive groves can be found on the western outskirts of Thassos Town, on the floodplain of the Skala Potamia basin, around Kinira, on the Aliki isthmus, east of Potos, and along the coast between Skala Maries and Limenaria.
Other broadleaved woodland habitat types are very localised on Thásos. Behind the beach at Skala Potamia is a fringe of sallow Salix spp. and mature poplar Populus alba but this is limited in extent and threatened by tourist development. Dense poplar woodland, much of it quite young, occurs to the south-east of Thassos Town but wet woods are naturally scarce on the island and should be conserved wherever possible. Deciduous tree species such as oriental hornbeam Carpinus orientalis and various oaks Quercus spp. occur widely as scattered components of maquis but the only other significant broadleaf woodland species are oriental plane Platanus orientalis and sweet chestnut Castanea sativa. Magnificent ancient planes occur as planted specimens in many of the towns and villages but natural plane woodland is confined to the banks of streams and rivers. In the floodplain of the Maries river there is a narrow band of plane woodland stretching for several kilometres but the best example I have seen on the island is in the valley of the main river above Thassos Town. Here there are concentrations of venerable plane trees extending up to the marble quarries and one tributary in particular supports more than fifty superb trees in a woodland setting that is more reminiscent of central and northern Europe than the Aegean. These trees are clad with tree lungwort Lobaria pulmonaria and most are hollow, suggesting that this is an ancient remnant woodland and probably of great importance for the conservation of 'old woodland' organisms on Thásos. This is probably one of the island's oldest examples of the phytosociological community known as Plantanion orientalis, which is reported to occur as a distinctive representative on Thásos and is typical of shaded stream banks. Other good examples of this habitat are along the banks of the main gorge at Mikros Kazaviti and in the valley above Potamia that is the route of the mountain track up to Ipsarion, where numerous old planes occur.
Sweet chestnuts are also planted for their produce, chiefly around the mountain village of Panagia. Just above the village, growing amongst mixed conifer scrub and Kermes oak maquis, there are a hundred or so ancient sweet chestnut trees that must be at least 300 years old. Most of the trees grow adjacent to the forest track and were presumably planted several centuries ago for the autumn harvest of nuts, but they may represent a relict of native chestnut woodland. The health of the trees varies but most have abundant dead wood in the canopy and a high proportion are damaged by the extensive larval workings of saproxylic beetles, which riddle the heartwood of trunks and major limbs. The main species concerned is the impressive longhorn Cerambyx welensii, whilst scarabaeid larvae, possibly Gnorimus variabilis, are also frequently seen under bark on the trunks of the biggest trees. This relatively small area of woodland is exceptional on Thásos and should be regarded as a high priority for conservation and management. Planting of new generations of chestnuts are required and efforts to stop the removal of fallen timber for firewood would be welcome. There are reports of typical Mediterranean chestnut woods, with Cornelian cherry understorey around the villages of Mikro and Megalo Kazaviti which obviously need investigation. Above Mikros Kazaviti is an extremely interesting area of neglected terraces which supports pedunculate oak Quercus robur and sweet chestnut wood pasture. The oaks are relatively young but the chestnuts, whilst not as old as those at Panagia, are probably 2-300 years old.
The map displays locations of the more significant broadleaved woodlands on the island.