If you appraise something or someone, you consider them carefully and form an opinion about them. [formal] This prompted many employers to appraise their selection and recruitment policies. [VERB noun] Gloria slid an appraising eye over the rest of the rack before reaching for the dress.
(a) Natural ecosystem boundaries occur between a tropical evergreen and riparian forest, and between the riparian forest and the river that it borders. (b) Natural boundaries occur across the gradient from marine to intertidal to foreshore environments near the shore in temperate coastal regions.
First, an ecosystem needs energy to work. Just like the computer you are using to read this, an ecosystem cannot function without energy. In many ecosystems, energy first enters the ecosystem from the sun. You may have heard of solar-powered electricity. Well, many ecosystems are also solar-powered.