The data can be used to plan tree spacings and to calculate basal area. Sycamore ( Acer pseudoplatanus) has the most consistent crown to stem ratio while it grows.Unlike walnut however, as its stem size increases, the ratio with its crown diameter decreases rapidly to the point after 35cm in diameter, when it has the smallest crown diameter for any of the nine tree species assessed. Sweet chestnut ( Castanea sativa), like walnut, has a very large crown while it is young (with a small stem size).if they plant their walnut trees 5m apart, their crowns will not compete until their stem diameter is 15 cm (which will take about 15 years from planting in the UK). Foresters can use that knowledge to design walnut plantations: e.g. When a walnut stem is 15 cm in diameter its crown can be estimated to be 5m wide. Common walnut ( Juglans regia) has the largest crown diameter at any given stage in its stem size.The graph highlights some very interesting growth patterns and difference between different species: The z ratio (y axis) is crown diameter divided by stem diameter the dbh (x axis) is stem diameter at breast height (measured at 1.3m). Crown diameters for different tree species Crown diameter: stem diameter relationship for nine broadleaved tree species. You can see the result on the graph below for nine common European broadleaved trees. We then plotted this z ratio against stem size. We decided to explore this further by calculating the ratio between the two, we called it the z ratio (= crown diameter ÷ stem diameter). It was fascinating to discover that statistically there was a very good relationship (scientists would refer to a correlation from a regression analysis) between stem diameter and crown diameter. Out of my 60 or so publications, it has been one of the most popular among forest scientists ( e.g. I co-authored an academic paper in 2005 that summarised research undertaken to explore the relationship between a tree’s stem diameter and its crown (or canopy) diameter 1.
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