Low-Cost Fence Designs to Limit Deer Impacts in Woodlands and Sugarbushes

The  white-tailed  deer  (Odocoileus  virginianus)  can  significantly  influence  the  diversity,  longevity  and  sustainability  of  rural  woodlands,  forests  and  maple  syrup  sugarbushes.  As  selective  browsers,  deer  will  eat  some  plants  more  readily  than  they  eat  other  plants.  Many  of  the  tree  species  deer  prefer  to  consume  are  valued  by  owners  as  sources  of  timber,  maple  syrup,  or  as  food-producing  trees  for  wildlife,  such  as  oak  and  maple.  Deer also eat many native wildflower and understory plants.

The effects of deer browsing on woodlands and sugar-bushes can have long-lasting effects (called “legacy” effects) that persist for decades after deer impacts are reduced.  In  areas  with  a  history  of  deer  overabundance,  the  failure  to  establish  and  grow  new,  young  trees is having a detrimental effect on woodlands and the potential to keep these areas healthy and diverse.

Browse impact of deer on stump sprouts.

Under  high  deer  impact,  deer  eat  the  plants  that  are  used  to  assess  if  there  is  a  problem.  As  deer  impact  increases,  the  evidence  for  deer  impact  de-creases.  To  an  untrained  eye,  a  heavily  browsed  woods  may  appear,  open,  park-like  and  picturesque   rather   than   degraded   and   impoverished. In woodlands, the evidence for the over-abundance of deer include one or more of these features:

• Park-like appearance in the woods
• An understory dominated by invasive shrubs
• An understory dominated by ferns
• An understory  dominated  by  non-palatable  woody brush
• A browse line of the lower tree canopy
• Cropped or “Bonsai” tree seedlings
• Absence of, or stunted,  wildflowers  such  as  Trillium,  Indian  cucumber,  or  Jack-in-the-pulpit.

In  most  cases,  recreational  hunting  is  insufficient  to  control  the  impact  that  deer  have  on  native  vegetation. Depending   on   landscape   pattern,   deer   population  size,  and  food  availability  approximately  40%  to  60%  of  a  deer  herd  must  die  or  be  culled  each  year  to  stabilize  the  population.  Reducing the population requires even greater mortality.  As  the  hunter  demographic   becomes   older   and   less   effective,  and  land  is  less  accessible  for  hunting,  the  management  impact  of  recreational  hunting  is  increasingly  limited.  In  some  cases  recreational  hunting  may  be  able  to  help  augment  other  deer  management  strategies  and  reduce  the  impacts  of  deer.

Protection  of  isolated  trees  is  possible  with  wire  cages  or  tree  tubes.  Several tree tube designs are available. Tree  tubes  should  be  at  least  5  ft  tall  and  with  ventilation  ports  to  allow  air  circulation.  Tree  tubes  need  to  be  securely  staked  to  the  ground,  and  checked  annually  to  ensure  the  tube  is  functional and the bottom in full contact with the soil. Tree cages made from  2”  x  4”  welded  wire  or  poultry  wire  should  be  5  ft  tall  and  well  staked.  Some  nut  trees  and  conifers  may  do  better  in  larger  diameter cages  than  in  tubes.  Weed  management  around  the  tube  or  cage  is  necessary  to  improve  seedling  growth,  and  will  limit  habitat  for  rodents  that  might  girdle  the  seedling.

Examples of four tube types, both cylindrical and flat designs, the latter being assembled into a cylinder. All are 5 ft tall. Not presence of air-ventilation holes to reduce accumulation of hot air.

For larger areas, fencing is a more efficient and  cost-effective option than tubes or cages. Typical fencing designs include clearing an access trail, driving posts where needed, and the use of large machinery to transport 8 ft woven wire fence spools. Some newer designs use 8 ft plastic mesh fence that allows for the use of small and less expensive fence posts.  No  fence  perfectly  excludes  deer,  and  all  fences  require  inspection  and  some amount of maintenance. The most expensive fences, but most effective, are made of woven wire with driven fence posts. Installation costs are typically $2.50 to almost $4 or more per running foot.

Research  by  Cornell  Cooperative  Extension  and  Cornell   University   Department   of   Natural   Re-sources  staff  is  assessing  the  costs  and  efficacy  of  two  fencing  designs  to  prevent  or  limit  deer  im-pacts. The objective is to identify low cost options that  adequately  exclude  deer  until  tree  seedlings  grow  above  the  reach  of  deer.  The  two  methods  use  either  plastic  mesh  or  high  tensile  wire  as  the  fencing material. These designs are being tested in 0.5 to 2 acre areas that have been managed through thinning or harvesting to increase sunlight and accelerate the establishment and growth of wood-land regeneration.  In some cases, herbicides were used to control interfering understory plants.  The  fencing  designs  are  also  being  tested  in  sugarbushes  to  protect  young  maples  and  promote  regeneration  and  sugarbush sustainability.

As described below, the designs are affordable for private woodland owners, and continued research is evaluating the long-term effectiveness of the designs at excluding deer. Fences will need to be maintained until seedlings of desirable species are at least 5 feet tall. In the early years, vegetation inside the fence will look similar to vegetation outside the fence  and  offer  little  incentive  for  deer  to  test  the  fence.  In later years, deer may recognize that the vegetation is actually “greener on the other side of the fence” and be more likely to challenge the fence.

The fence designs shown in this fact sheet are being tested using the AVID field monitoring protocol (www.AVIDdeer.com).  After one growing season,  seedlings  inside  the  exclosures  were  significantly  taller  than  seedlings  outside  the  exclosure.  If  fences  remain  effective,  then  a  significantly  higher  percentage of seedlings may grow beyond the susceptible  browsing  height  in  a  shortened  time  frame.  An  appropriate  number  and  height  of  seedlings  is  necessary  to  consider  a  woodland  opening  to  have  sufficient  stocking,  or  seedling  density.  Depending  on  seedling height at the time of fencing, past deer pressure,  soil  quality,  and  amount  of  sunlight,  seedlings  may need 5 to 10 years of protection before they have grown  beyond  the  typical  height  of  deer  browsing.  This  fact  sheet  will  be  updated  as  new  data  become  available  on  the  effectiveness  of  these  fence  designs.

The cost savings is through the use of low-value trees as living fence posts, and avoids the purchase and installation costs of fence posts.  However,  rather than attaching fencing directly to the tree, a bat-ten strip made of pressure treated wood is attached to the tree with a nail and fender washer. At most one or two nails per tree are used. On fence corners the trees should be 7” – 8” dbh (diameter at breast height), but trees  as  small  as  3”  dbh  will  suffice  on  straight  runs  of  the  fence.  As the tree grows, it pushes against the batten strip, which pushes against the fender washer, which floats the nail. The design prevents the typical situation where the tree grows around the fence material. If after 5 to 10 years the seedlings may be  at  a  safe  height,  and  the  fence  can  be  removed.

Woven wire fence 8 ft tall and suspended on installed posts is a proven method of limiting deer access to forest regeneration. (photo courtesy of Dr. Gary Alt)

Plastic Mesh Fencing

Plastic  mesh  fencing  involves  higher  material  costs  but  less  time  invested  in  labor  for  installation.  Plastic mesh fencing is available on the Internet through numerous suppliers using a search for “poly mesh deer fence.” Mesh size used in this project is approximately  2”  x  2”,  but  other  sizes  might  be  equally  effective.  Current  designs  started  with  a  10  ft  x  330  ft  roll  of  mesh  fence  on  a  cardboard  spindle,  cut  in  half with a chainsaw. The fence height was 5 ft. Some  vendors  offer  7  ft  fencing  which  is  likely  to  be  more  effective  at  excluding  deer  by  al-lowing  for  a  lower  apron  at  ground  level  and  taller  height,  but  with  added  costs  of  labor  to  install.

Materials

• Plastic mesh fence 5’ to 7’ high. Ten-foot long spools can be cut in half. Prices vary from $0.48 to $0.68/foot on the full-length spool.
• 12 gauge high tensile wire, single strand
• Wire tensioner and splicing clips
• Batten strips of pressure treated lumber, approximately 10-inch pieces of 2×4 or 5/4 x 6 deck boards. One per tree.
• Plastic electric fence insulators
• Rust proof (e.g., galvanized) 3” to 3.5” nails
• Deck screws or galvanized joist hanger nails
• 25” to 1.5” fender washers
• Hog rings and hog ring pliers to secure mesh to wire
• Brightly colored synthetic baling twine

Plastic Mesh Fencing Installation

1. Determine your perimeter and flag low-value trees to serve as living fence posts. Try to locate a tree every 40-50 feet (avoid spans greater than 60 feet). If possible, select trees to be on the “inside” of the fence. Avoid abrupt corners on the fence. Best results occur if trees are selected before any harvesting occurs, and those trees must be protected from damage or removal during the harvest.
2. To simplify access, clear significant brush from fence line. It may be less expensive to re-position the fence than to clear the brush.
3. Attach one plastic insulator to each 10” batten strip using deck screws or joist hanger nails. Pre-drill holes for fender washers and nails to limit splitting of the board. Attach batten strips to trees so that the insulator is approximately 54 to 58 inches above ground.
4. Thread 12 gauge wire through insulators, and tighten using wire tensioner and splicing clips.
5. Unroll and position fence to suspend from the wire.
6. Use hog rings on 18 – 24” intervals to attach the plastic mesh fence to the wire.
7. Gates are created by severing the fence vertically, and attaching an apron of fence that extends approximately 4 ft on either side of the opening.
8. If ground topography leaves gaps under fence, pile brush or slash to prevent deer from crawling under the fence. A continuous windrow of brush or slash on the outside edge of the fence will enhance the effectiveness of the fence, and obviate the need for baling twine in the next step.
9. Install baling twine approximately 30” offset from fence and 30” off ground. Height is important, but distance from fence can vary from 1 ft to 4 ft. Wrap twine around saplings, around wooden stakes, or use fiberglass rods with clips.

On abrupt corners, double batten boards may be necessary to protect the tree. Abrupt corners increase resistance when pulling wire around perimeter.

The fence should be inspected two to three times per year, and after storms.
Total Cost: With labor estimated at $15/hour and materials the total project cost averages $0.59/running foot.

A modification of this mesh design that is likely to be more effective includes the use of 7 ft mesh fence and an additional strand of wire approximately 12 inches off the ground. The vertical section of the fence is approximately 6 ft to 6.5 ft, allowing for an apron plus the low wire to restrict deer moving under the fence. The cost for materials would be marginally higher, but labor costs would be as much as double because of the extra effort to install another wire, handling a 7 ft vs. 5 ft spoon, and using a ladder to hog-ring the fence to the top wire. The 7ft and 5 ft designs have been co-located and will be compared for effectiveness through ongoing research.

High Tensile Fencing

High tensile fencing involves lower material costs but almost twice as much time and thus increased labor costs. It involves the use of standard 12 gauge high-tensile galvanized wire that is secured to trees that form the perimeter of the fenced area.

High Tensile Fencing Materials

• 12 gauge high tensile galvanized wire: Available at farm stores for approximately
• $100 for 4,000 feet of wire, approximately $0.03 per foot
• 8 foot long pressure treated deck boards 1 ¼ inch thick x 5 ½ inch wide,
• or pressure treated 2x4s (approximately $3.67/board)
• Wire tensioners and splicing clips (and appropriate tools)
• Electric fence plastic insulators
• Deck screws or galvanized joist hanger nails
• Rust proof (e.g., galvanized) 3” to 3.5” nails
• 25” to 1.5” fender washers

High Tensile Fencing Installation

1. Determine your perimeter and flag low-value trees to serve as living fence posts. Try to locate a tree every 40-50 feet (avoid spans greater than 60 feet). If possible, select trees to be on the “inside” of the fence. Avoid abrupt corners on the fence. Best results occur if trees are selected before any harvesting occurs, and those trees must be protected from damage or removal during the harvest.
2. To simplify access, clear significant brush from fence line. It may be less expensive to re-position the fence than to clear the brush.
3. Attach plastic insulator to batten strips using deck screws or joist hanger nails. Attach insulators from bottom of batten at approximately 10”, 20”, 30”, 40”, 54”, 68”, 82”, and 96”.
4. Position batten strips at selected trees. Before nailing board to tree, thread the top wire in the uppermost insulator of each board.
5. Attach batten strip with a nail and fender washer near ground line and one additional nail and washer at any location along the batten that will secure the board.
6. Thread 12 gauge wire through insulators, and tighten using wire tensioner and splicing clips. Thread and tighten one wire at a time to avoid intertwining wires. Tightening the wire helps secure the boards to the tree.
7. If ground topography leaves gaps under fence, pile brush or slash to prevent deer from crawling under the fence. A continuous windrow of brush or slash on the outside edge of the fence will enhance the effectiveness of the fence, and obviate the need for baling twine in step #9.
8. Use trees that are sufficient in diameter and firmness at angled points in the fence because they will be under significant side strain.
9. Install baling twine approximately 30” offset from fence and 30” off ground. Height is important, but distance from fence can vary from 1 ft to 4 ft. Wrap twine around saplings, around wooden stakes, or use fiberglass rods with clips.

The fence should be inspected two to three times per year, and after storms.
Total Cost: With labor estimated at $15/hour and materials the total project cost average was $0.51/running foot.

For additional information on woodland management go to:
www.ForestConnect.com
www.CornellForestConnect.ning.com
This article was originally published in Cornell University Agricultural Experiment Station’s and Cornell Cooperative Extension’s Supporting Sustainable Management of Private Woodands publication.