Abstract
The structure and composition of temperate old-growth oak forests are reviewed based on 108 case studies about 175 stands. The stands were classified as dry, dry-mesic and mesic forest types and the variables (density, basal area, size distribution, dead wood volume) were compared among them.Compared to the global range of this forest type, the United States was overrepresented, while West and Central Asia, Europe and Central America were underrepresented. In mesic oak forests the basal area and density of large trees were higher than in dry stands, while tree density and sapling density were lower. The proportion of oaks in tree and sapling layers were the highest in dry and lowest in mesic forests. The size distribution of trees followed negative exponential or rotated sigmoid types. In dry habitats all size categories are dominated by oaks, while in mesic type, only large ones followed the same trend. The volume of dead wood and the proportion of downed dead wood increased along the humidity gradient. In stands with repeated measurements, basal area and relative density of oaks decreased in the last decades.The understanding of the structure and composition of temperate old-growth oak forests is necessary for their restoration and application of close to nature forestry principles.
Highlights
Earth’s forests have been affected by humans in many ways for thousands of years; most have long been exploited and altered
We considered a forest as an oak forest if the overall relative basal area of the Quercus species reached 25% and (1) relative basal area of oaks is larger than of any other genus, or (2) the total relative basal area of any other genus does not exceed 30%
We found representative data in only 10 papers from Europe (22 stands of 17 forest sites), and three additional papers on oak forest stands of Asia (1–1 stand in China and Japan, respectively)
Summary
Earth’s forests have been affected by humans in many ways for thousands of years; most have long been exploited and altered. The area of forests has reduced, and this human impact on forest ecosystems is still intensifying. The estimated forest cover on Earth about 8000 years ago was at least 6000 million ha (Bryant et al, 1997; de Gouvenain and Silander, 2016), while currently it is 4006 million ha (FAO, 2020). Human land-use does not mereley reduce forest area and changes and influences the structure and composition of forest ecosystems. Long-lasting human impact often simplifies the forest structure, reducing species richness and biodiversity (Badalamenti et al, 2018)
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