With the exception of trees which maybe too large for easy replacement, most landscape plantings are valued/appraised at replacement cost. For shrubs, that means size and age are not necessarily determining factors - in fact, a very mature age may have a devaluing effect on the appraisal.......plants do have a life expectancy. Replacement cost would include the purchase of a similar plant of decent size, removal of the damaged plant and planting of the replacement specimen. By "decent size", I mean a similar species of plant offered for sale by a retail nursery at a standard larger nursery size. For most shrubs, that will be a 5-10 gallon size.

For trees of significant size, there is a formula that is a modification of replacement cost that factors in species, base cost, cross section area, condition and location. Market value is seldom ever considered unless there is a cut timber value or if the tree in question is a particularly unique specimen.

It is an unfortunate fact of life that when an established landscape is damaged by negligence (construction, car accident, vandalism) you are not going to be recompensed for the time and effort involved at attaining that matured establishment.

ps. I am a certified horticulturist and practicing landscape designer that has worked in association with several larger Seattle nurseries and I have done a number of landscape appraisals. I am pretty familiar with the process.