OK...that's a very difficult one to explain
😕 damn it
It's something that is intuitive to many artists, and therefore unless you've had a formal art education it's not something most give much tangible thought to, let alone try to describe.
But a quick trawl of the interweb and I came up with the definition below...
Tension, a balance maintained in an artistic work between opposing forces or elements; a controlled dramatic or dynamic quality.
Tension is very important for an object to be beautiful. Tension is created in architecture when hard, vertical stretches of columns are placed against delicately curving columns. Tension is created in music when harsh, loud sounds compete with gentle, soft ones. And tension is created in dance when hard, jerky movements that take effort are combined with, or opposed to, gentle, flowing movements that seem effortless.
I guess the tension in your scape is created by the juxtaposition of the gnarly root in the left third of the scape and the flowing line of the less gnarly root stretching out through the other two thirds of the scape. Opposing forces which together create visual interest and energy without unbalancing the overall design.
In the fist version, for me the bit of root sticking up very proud on the left gave the scape a little too much tension and unbalanced the whole. In other words it was too dominant and my eye was continually drawn to it at the expense of rest of the scape, or the less dominant focal points.
Hope that makes sense
🙂