Cacapon Institute
Deer Exclusion
Fencing Experiment
Updated July 4, 2008
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It
is not the number of trees we plant but the number of
trees we grow that will restore our forests and protect
our waters.
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* August
2008.
Cacapon
Institute (CI)
receives $48,683
grant from the National Fish and Wildlife Foundation Chesapeake Bay
Small Watershed Grants Program. The project is titled: “Failure is Not
an Option: Investigating a Cost-Effective Approach to Reducing Deer
Damage in Reforestation Programs.” Read press release
here.
Overabundant deer
are a problem for forest health and agricultural viability
throughout the Northeast. The standard approach to deer
exclusion fencing, in areas larger than backyard gardens, uses
permanent fencing installed as a physical barrier to deer. Whether
electric, woven wire or plastic, these fences are quite expensive.
We are testing an approach that does not create a physical barrier.
Rather, it uses inexpensive temporary electric fencing materials to create
an area where it is simply uncomfortable for deer to be.
On this page:
Project Description.
Two riparian
plantings test sites in areas with high deer density were selected.
Two "official" control and experimental subplots were delineated
within each study site (official is in quotes because the entire
area of each site that is not enclosed in wires will serve as
control). Each test block is 100 feet long; the width varies
between sites (see site pictures below). The experimental subplots
have a double or triple perimeter of single strand, temporary
electric fencing that enclose the area to be protected. The wires
are from 24” to 30” above the ground.
| Site 1, near Yellow
Springs, WV. This is a WV Potomac Tributary Strategy
Riparian Buffer Demonstration Project site, described in
detail here. The site
has a multi-year history of failed plantings indicating a severe problem with
deer browsing (it was replanted in April 2005). Test blocks are 100 feet long and ~60
feet wide. There are three perimeter wires, with the
distance outer two being four feet apart and the inner pair
eight feet apart. Fence is charged using a solar
charger. |
Site 2, a USDA-CREP
(Conservation Reserve and Enhancement Program) site near
Baker, WV. Forest condition in the area and the
landowner indicate a deer problem exists in this area.
This area was planted and a high tensile, electric cattle
fence installed in the spring of 2007. Test blocks are
100 feet long and ~35 feet wide, the standard buffer width
in WV. There are two perimeter wires spaced four feet
apart. Fence is powered via a tap from the high
tensile fencing. |
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Data collected includes deer browse and tree vigor on previously planted
trees, grid mapping of tree recruitment by position and species,
proximity effects of electric wires (single and enclosures), signs
of deer within each subplot, and maintenance required to keep the
fence clear and functioning.
If successful, this
method could be used to economically increase success of riparian
plantings in high deer density areas. It would also allow no cost
natural recruitment of trees from seed or roots to occur, and allow
the use of much shorter tubes (for rodent protection) or no tubes at
all, thereby reducing a major cost element of these plantings.
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Site 1: The following
graphs present data collected at the
WVPTS Riparian
Forest Demonstration Project at Yellow Spring, WV between June 2007
and June 2008.
Three site categories are included: control no wire – no electric
wire along long axis of study area; control w/wire – one electric
wire along long axis of study area; and experimental – 100’ x 60’
study plot enclosed with a triple perimeter of single strand,
temporary electric fencing (spaced 4 and 8 feet apart).
Data for August 2007 shows
significant browse damage in one of the experimental blocks,
with no further damage in later months. This damage was
probably due to heavy weed growth that reduced voltage on
the electric fence to less than 2500V during the night and
early morning hours when the weeds were covered with dew.
This condition was also the case in July, but training deer
to the fence that occurred during the previous months when
the fence voltage was much higher may have been sufficient
to keep them out for a time. The literature on using
electric fencing to dissuade deer is pretty clear on the
need for 4500V or more to be effective. Weeds were cleared
from the fence in August after the problem was detected, and
voltages were restored to >5000 volts at all times
(typically >6000 volts). No browsing damage has been
observed since that time, although some fence repair was
needed in November 2007. No winter browsing was
observed in any block. The only trees that have
gotten ahead of the deer in the unprotected areas are a few
scraggly hawthornes and one
buttonbush. |
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Graph
on left
is a 100% stacked bar graph shows
only living plants with leaves above tube that are
susceptible to browse damage. |
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Graph at left shows the height of the highest intact leaf
above the top of the tree tube. Growth well
above the tube is occurring in both experimental blocks, and
not occurring in control blocks. |
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Site
2 – Baker CREP Site Results
Two site categories are shown in the graph
below: two control blocks (with one wire along long axis)
and two experimental blocks (with 2 wires around perimeter
as noted above). The following conditions pertain to the
site. This was a new planting when we installed the
fence, and the vast majority of trees were fully contained
within their tree tubes at the start. Early results were much less clear than at the Yellow
Spring site, with a certain amount of browse damage to
plants occurring within the treatment area. We were
concerned that the farm border fence that was supplying the
electricity for the study area fence might not be on consistently, as
it was powered through a ground fault interrupter circuit
that shut down on occasion. We installed a solar
charger at the site on July 20, 2007, but a certain
amount of browsing continued in August 2007. We purchased a digital fence
voltage meter and determined that a short in the fence was
dropping the voltage down to near 2200V, which was also the
voltage of the farm’s perimeter fence. Once the short was
found, and weeds cleared, the voltage rose to > 5000V.
Little browsing occurred within the
treatment areas in September 2007 and May 2008, while regular browsing outside the treatment
blocks was widespread. Browsing occurred in both
treatment blocks in June 2008, likely due to excessive weed
growth that was reducing voltage on fence.
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Figure notes:
1. This graph
includes a "below tube top" category, for trees with
leaves that did not reach to the top of the tree
tube.
2. The large number of browse-able trees (leaves
above top of tube) showing early in the control area
were mostly in two foot high tubes in the west
control block. These were all hazelnuts that
sprouted above the tubes quickly - and were just as
quickly browsed to the top. This despite
increasingly heavy thistle growth that made
surveying this area quite unpleasant; the deer did
not seem to care. |
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| Graph above shows the height of the highest
intact leaf above the top of the tree tube.
Growth well above the tube is occurring in
both experimental blocks. Good growth was
observed in fruit trees (in 4' tubes) in the eastern
Control Block as of June 2008. No growth
significantly above tubes was observed in Western
Control Block; this area was primarily planted with
Hazelnuts in 2' tubes. |
The difference between treatment and
control in terms of growth above tubes could not be more
dramatic. See if you can figure out which plants in the
table below are protected: |
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Here is a summary of what
we’ve seen between June 2007 and June 2008:
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If the fence is properly
installed, energized, and clear of heavy weed growth,
protection within fenced areas can be ~100%. |
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In the first few weeks
after installation, you need to check the fence for
damage as the deer get very upset when they first get in
it. The inner wire is more likely to be broken than the
outer wire. |
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There does not appear to
be much of an edge effect (if any) where trees near the
fenced area are protected. |
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Failure to maintain the
fence reasonably clear of heavy weed growth results in
lowered voltage on the fence and, over time,
dramatically reduced success. |
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Just as the literature
says, voltages in the 2000-2500 voltage range are not
terribly effective. |
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The fencing sadly doesn’t
protect against drought or insects.
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Cost Comparison
The following cost comparison is based on retail material
costs, and ballpark labor estimates. It assumes that
either tubes (with stakes) or fence are used to protect the
plantings from deer browse. Everything else about the
planting is assumed to be the same. Not shown are
yearly maintenance costs, for which materials would be
negligible and labor for maintaining fence and cutting weeds
of fence would probably amount to ten hours per acre ($150
at $15/ hour).
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Material Cost
Comparison Tree Tube plantings vs Electric
Fence (CI Design) |
| Fencing Material Budget |
Installation |
| Cost Category |
Unit Price |
Qty |
Extended |
Man Hours |
Rate |
Extended |
| Fence Charger materials |
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| Low impedance solar electric fence battery
charger |
$250.00 |
1 |
$250.00 |
1.5 |
15 |
$22.50 |
| Wood post to mount charger |
$10.00 |
1 |
$10.00
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| Grounding kit - 3 rods, clamps, cable |
$30.00
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1 |
$30.00 |
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SUBTOTAL |
$290.00 |
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| 200 ft control and experimental block each |
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| Galv T-Posts for Corners |
$3.50 |
8 |
$28.00 |
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| Step-in posts |
$1.80 |
146 |
$262.80 |
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| Insulators for corner T-posts |
$2.00
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8 |
$16.00 |
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| 14 gauge aluminum wire (at 31 per 1/4 mile) |
$0.02 |
2950 |
$70.80 |
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SUBTOTAL |
$377.60 |
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One acre |
$667.60 |
4 |
15 |
$60.00 |
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Two acres |
$1,045.20 |
8 |
15 |
$120.00 |
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Three acres |
$1,422.80 |
12 |
15 |
$180.00 |
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Four acres |
$1,800.40 |
16 |
15 |
$240.00 |
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| Tree Tube Planting Materials |
Installation |
| Cost Category |
Unit Price |
Qty |
Extended |
Man Hours |
Rate |
Extended |
| 4' Tree tubes |
3.29 |
200 |
$658.00 |
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| Stakes |
0.5 |
200 |
$100.00 |
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Sum |
$758.00 |
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One acre |
$758.00 |
6 |
15 |
$90.00 |
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Two acres |
$1,516.00 |
12 |
15 |
$180.00 |
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Three acres |
$2,274.00 |
18 |
15 |
$270.00 |
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Four acres |
$3,032.00 |
24 |
15 |
$360.00 |
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Note: |
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1. assume weed mats used for each setting |
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2. Retail prices for materials |
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3. Tree tube stakes are estimated, probably
cost more. |
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