plain formed of sediments deposited by meltwater at the terminus of a glacier, are covered by forests. The highest point of the city lies at a height of on the Pietrasze Forest. The lowest point lies at a height of on the river valley of the Biała. Forests are an important part of the city character, they currently occupy approximately (18% of the administrative area of the city) which places it as the fifth most "wooded" city in Poland; behind Katowice (38%), Bydgoszcz (30%), Toruń (22.9%) and Gdańsk (17.6%). Part of Knyszyn Forest is preserved within the city limits by two nature reserves—a total area of . The Zwierzyniecki Forest Nature Reserve (), which is contained within the city limits, is a fragment, , of the riparian forest with a dominant assemblage of oak and hornbeam. The Antoniuk Nature Reserve () is a park in the city that preserves the natural state of a forest fragment characteristic of the Białystok Upland, with a dominant mixed forest of hazel and spruce. The of forests lying in the vicinity of the Dojlidy Ponds are administered by the Białystok Central Sports and Recreation Center( – BOSiR). The Dojlidy Ponds recreation area includes a public beach, walking trails, birdwatching and fishing. Climate The city has a warm-summer continental or hemiboreal climate (Dfb) according to the Köppen climate classification system under the isotherm for the average temperature of the coldest month, or an oceanic climate (Cfb) if the isotherm is used. The city would have been classified as being in the Dfb zone regardless of the accepted isotherm for climatological normals as recent as 1981–2010, but as a consequence of climate change, the winters have warmed up so that the climate in the city may be classified as oceanic. Białystok is one of the coldest cities in Poland by annual temperature and one with the climate having the most continental characteristics, as is the case for much of north-eastern Poland, with the mean yearly temperature of and the length of the growing season amounting to 205 days, shorter than elsewhere in Poland. While winters are rather mild compared to other cities on the similar latitude, such as Samara, Barnaul, or Edmonton, they are colder than in Western Europe (in cities like Bremen and Dublin). Winters usually have little sunshine, with weather patterns changing from those influenced by the low-pressure systems generated by the Icelandic Low