What constrains life in the rainforest? Here we see plants growing upon plants growing upon plants – nearly every part of this tree trunk is covered with another organism. Ecosystems appear in miniature the closer one looks. So what prevents a baroque elaboration of this arrangement to infinite numbers of infinitely small plants? Resource limitation.…

Broadway Boulevard – a paved multi-lane road, cutting a straight path across fifteen miles of desert, bringing the city uncomfortably close to the Rincon and Tucson mountains. This is progress, of a sort. Sixty years ago, the city would have been scarcely visible, with none of these highways or towers yet constructed. There would have…

Look in the mountains to the west of Tucson and your eye will be drawn to a set of shimmering rectangles that dominate the valley floor. These are not solar panels, nor parking lots, nor any nefarious construction. They are immense pools of water, part of the Central Arizona Project. Tucson’s need for water has…

Late afternoon sun reflects from deeply incised bedrock. How large is this scene – are we looking at a canyon hundreds of feet deep, or instead at a small rivulet? The stream here is nearly one foot wide. You probably guessed that correctly, but how? The mind is adept at picking up on small cues…