Forest migration northward. Though "Fagus" and "Picea" populations did not expand directionally, they have grown in the Scandinavian range. The movement of "Picea" species in the past 1000 years has shown a strong connection to climate change through a model comparison. In the more recent past, there has been documentation of elevation shifts in distribution of many core forest tree species of Catalonia. The populations of two tree species (European Beech, "Fagus sylvatica"; and Holm Oak, "Quercus ilex") were evaluated in their dynamics over elevations through time. Generally, Holm Oak reside lower on mountain slopes than does European Beech. In the past
Nyssa sylvatica long stalk and a rich source or nectar for bees. They are often dioecious so a male and female tree in proximity is required to set seed, however, many trees are also polygamo-dioecious, which means they have both male and female flowers on the same tree. The fruit is a black-blue, ovoid stone fruit, about 10 mm long with a thin, oily, bitter-to-sour tasting flesh and very popular with small bird species. There are from one to three fruits together on a long slender stalk. They are a valuable energy food for birds, especially the American robin. "Nyssa sylvatica" forms