The original pampa had virtually no trees; some imported species like the American sycamore or eucalyptus are present along roads or in towns and country estates (''estancias''). The only tree-like plant native to the pampa is the evergreen Ombú. The surface soils of the pampa are a deep black color, primarily mollisols, known commonly as ''humus''. This makes the region one of the most agriculturally productive on Earth; however, this is also responsible for decimating much of the original ecosystem, to make way for commercial agriculture. The western pampas receive less rainfall, this ''dry pampa'' is a plain of short grasses or steppe.