Crown Plasticity and Competition for Canopy Space: A New Spatially Implicit Model Parameterized for 250 North American Tree Species

BACKGROUND: Canopy structure, which can be defined as the sum of the sizes, shapes and relative placements of the tree crowns in a forest stand, is central to all aspects of forest ecology. But there is no accepted method for deriving canopy structure from the sizes, species and biomechanical properties of the individual trees in a stand. Any such method must capture the fact that trees are highly plastic in their growth, forming tessellating crown shapes that fill all or most of the canopy space. METHODOLOGY/PRINCIPAL FINDINGS: We introduce a new, simple and rapidly-implemented model--the Ideal Tree Distribution, ITD--with tree form (height allometry and crown shape), growth plasticity, and space-filling, at its core. The ITD predicts the canopy status (in or out of canopy), crown depth, and total and exposed crown area of the trees in a stand, given their species, sizes and potential crown shapes. We use maximum likelihood methods, in conjunction with data from over 100,000 trees taken from forests across the coterminous US, to estimate ITD model parameters for 250 North American tree species. With only two free parameters per species--one aggregate parameter to describe crown shape, and one parameter to set the so-called depth bias--the model captures between-species patterns in average canopy status, crown radius, and crown depth, and within-species means of these metrics vs stem diameter. The model also predicts much of the variation in these metrics for a tree of a given species and size, resulting solely from deterministic responses to variation in stand structure. CONCLUSIONS/SIGNIFICANCE: This new model, with parameters for US tree species, opens up new possibilities for understanding and modeling forest dynamics at local and regional scales, and may provide a new way to interpret remote sensing data of forest canopies, including LIDAR and aerial photography

Connective tissue disorders and smooth muscle disorders in cardiology

The hereditary disorders of connective tissue encompass a spectrum of clinically and genetically heterogeneous conditions caused by genetic defects in structural connective tissue proteins, such as collagen, fibrillin, and elastin. Clinical manifestations of these disorders are variable, and include musculoskeletal, skin, ocular, cardiovascular, and other visceral pathologies. Substantial overlap in clinical features between different disorders of connective tissue is present. Many connective tissue disorders constitute a risk of aneurysm formation and dissection of the aorta and/or other arteries, due to a defect of connective tissue within the vessel wall. Marfan syndrome is the most common syndromic presentation of ascending aortic aneurysm, but other syndromes including vascular Ehlers-Danlos syndrome and Loeys-Dietz syndrome also show ascending aortic aneurysms and the associated risk of aortic dissection and rupture. Familial segregation of the risk for ascending aortic aneurysm can also occur in the absence of associated systemic findings of connective tissue abnormalities in patients with familial Thoracic Aortic Aneurysms and aortic Dissections (TAAD), with or without structural heart defects such as bicuspid aortic valve, aortic coarctation, or patent ductus arteriosus