In the early nineteenth century, alexander von humboldt observed that the distribution of plants up a mountainside mirrors the distribution of plants at increasing latitude. explain the observed shift of the plants to lower elevations by doing each of the following;
(i)a number of modern studies have reinforced the idea that as the global climate warms, plant species are becoming redistributed to higher elevations or latitudes.
(ii) however, in a separate large-scale study comparing historical (1930–1935) plant distributions with modern (2000–2005) distributions in the western united states, researchers observed that 72% of identified plant species shifted to lower elevations despite an associated increase in average temperature.

As explained below.

Explanation:

As Alexander von Humboldt surveyed and observed the far and distant lands of the South American continent he found that the species of plants and animals to be well distributed in higher latitudes and this shift in the plant species was caused by the rise of temperatures in lakes and seas. Thus the species that became extinct were ones that could not adapt and find a suitable habitat for the development and growth and thus found distributed at greater altitudes. After the study came in 1935 and the showed the distribution of plants and animals til 2005, the western united states had most of the plants i.e 72% distributed in lower altitudes as these plants species adapted to the low lying areas as due to the desert and dry conditions that developed in that year.