Within orchard spatial distribution of mature avocado trees mortality

The growth and development of mature, fruit bearing, avocado trees in Menashe Heights region of Israel was retarded from the late-2000s. As time passed the trees decayed gradually, leaves dropped off and eventually the trees died. This process usually spanned 2 to 4 years. The objectives of the study were to: (i) map the spatial distribution of symptomatic avocado trees, (ii) evaluate the potential role of topography in contributing to tree mortality, and (iii) estimate the extent of the tree mortality phenomena in the orchards. On April 2020 we mapped eight sub-units of avocado orchards. In each sub-unit we recorded the state of each tree. We estimated the topographic elevation of each tree using a digital elevation model (DEM). The relationship between the topographic elevation of the trees and the incidence of damaged trees were calculated using a logistic regression. Analysis of the spatial distribution of declining and dying trees reveled that they were not randomly distributed in the orchard and were more abundant in the lower zones of the orchards. Close observations of these zones revealed that the soil in these areas was soaked with water during the winter. Accordingly, we hypothesize that due to limited oxygen supply, root growth and water uptake were impaired, resulting in a negative feedback loop that increases soil water content, reduces aeration, and impairs roots’ ability to absorb oxygen. Such conditions could make the roots more susceptible to soil-borne fungi that had damaged the roots of trees, causing them to deteriorate and eventually die.