Slide 19: Environmental Variables
Environmental variables are often direct variables, such as precipitation (typically mean annual rainfall and seasonal rainfall averages), temperature (mean annual temperature, maximum and minimum averaged over a long period, and even specific data such as the mean minimum temperature in June). Soil conditions include pH, texture, organic carbon and fertility, but these measures are often difficult to obtain on an appropriate scale, since there can be considerable variation even within an area). In general, it is a good idea to avoid indirect measures of a variable, which is obviously a challenge since much of a country is not monitored, and many such measures are not easily taken. Features such as slope and altitude allow some degree of projection into the future, since the lapse rate (extent to which temperature changes with increasing altitude) may closely parallel changing climatic conditions.
Solar radiation and wind, which are essential for plant growth responses and dispersal are both particularly challenging to obtain accurate measures of.