Assessing Effects of Depredation by Deer 

 on Apple Production 



James A. Parkhurst 



Department of Forestry and Wildlife Management, University of Massachusetts 



Hungiy deer regularly visit apple orchards 

 throughout the Northeast, particularly during winter 

 months when preferred native foods are scarce or 

 unavailable. The extent of damage caused by deer 

 browsing is extremely variable, depending upon or- 

 chard location and local deer population levels; damage 

 in areas of high deer density can be extensive. A need 

 presently exists for a means to assess the impact of deer 

 depredations, but devising an easy and consistent 

 method to predict accurately fruit production losses 

 stemming directly from deer browsing has been diffi- 

 cult. Most previous methods were either too compli- 

 cated to use in the field, or were based upon question- 

 able assumptions. Recently, two researchers at Utah 

 State University devised what they believe to be a reli- 

 able method of estimating apple production loss in the 

 first crop following winter browsing by deer [Austin, D. 

 D. and P. J. Urness. 1989. Evaluating production 

 losses from mule deer depredation in apple orchards. 

 Wildlife Society Bulletin 17(2):161-165]. The following 

 is a summary of their methodology and findings. 



Methods 



Tests were conducted from 1983 to 1986 using 

 semi-dwarf and standard-sized Red Delicious trees 

 ranging in age from 8 to 15 years. Because test plots 

 were located outside the typical summer range of the 

 deer studied, only winter browsing damage was as- 

 sessed. To allow comparisons between browsed and 

 unbrowsed trees, deer browsing pressure within or- 

 chards was regulated through use of 8 ft-high fencing. 

 Data collected and enumerated included: a) number of 

 intact and nipped buds (counted prior to or during the 

 period of bud swelling), b) number of flower clusters, 

 c) number of apples on trees (pre-harvest), d) number 

 of hand-harvested apples, and e) mean weight of 

 apples within and above the browsing zone. Bud 

 counts were made by counting terminal buds on the 

 current year's growth plus all buds and bud spurs 

 greater than 1 cm (2.54 in) in length along the second 

 year or older growth. Counts of flower clusters within 

 and above the browsing zone were made just before 

 opening (during late-pink bud stage) . Researchers also 



examined variation in apple production within trees 

 and between trees. 



Results 



1 . Where whole trees were measured, the number of 

 apples harvested declined as the percentage of buds 

 removed increased. When bud removal exceeded 20%, 

 significant reductions in apple production were noted. 

 For example, at 31% bud removal, apple production 

 over the whole tree declined 49%. 



2. The percentage of apple production lost in the first 

 crop following depredation was approximately propor- 

 tional to the percentage of bud removal due to browsing 

 (i.e., at 30% bud loss, 30% of apple crop within browsing 

 zone was lost). 



3. Production of apples above the browsing zone was 

 not affected by browsing occurring in the lower sec- 

 tions of the tree. 



4. Browsing by deer had no effect on the individual 

 weight of apples produced within the browsing zone 

 (mean weight varied from 182 to 186 g per apple 

 throughout the study). It was determined that weight 

 of harvested fruit is dependent upon the ratio of leaves 

 to fruit rather than upon selective browsing of deer. 



How to Assess Damage 



To determine the potential loss of fruit production 

 in mature orchards (trees 6 years and older that are 

 producing a harvestable crop), the researchers offered 

 the following guidelines (see example provided). This 

 information was condensed from a manual developed 

 as a guide for producers to determine the impacts of 

 depredation on production (Austin, D. and P. J. 

 Urness. 1987. Guidelines for evaluating annual crop 

 losses due to depredating big game. Utah Division of 

 Wildlife Resources, Publication No. 87-5, Salt Lake 

 City, UT. 40pp.). 



1. Determine nipping losses. Just prior to trees 

 breaking dormancy and before leaves and flower clus- 

 ters become noticeable, randomly select 15 representa- 



Fruit Notes, Summer, 1990 



23 



