Cacapon Institute
Deer Exclusion
Fencing Experiment
|
It
is not the number of trees planted but the number of
trees we grow that will restore our forests and protect
our waters.
|
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
at all. It uses inexpensive temporary 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. |
 |
 |
Data collected will
include recording 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.
|
Site 1: The following
graph present the first four months of data collected at the
WVPTS Riparian
Forest Demonstration Project at Yellow Spring, WV on June 18, 2007.
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 shows
significant browse damage in one of the experimental blocks,
with no further damage in September. 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.
The only trees that have
gotten ahead of the deer in the unprotected areas are a few
hawthornes and, to a lesser extent, some crabapples and one
buttonbush. |
|
 |
Graph
on left
is a 100% stacked bar graph shows
only living plants with leaves above tube that are
susceptible to browse damage. |
|
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 decided to install a solar
charger at the site, on July 20th, but a certain
amount of browsing continued in August. 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.
Since that time practically no browsing occurred within the
treatment areas (see September), while regular browsing outside the treatment
blocks was widespread.
 |
|
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. |
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: |
|
Here is a summary of what
we’ve seen in the first few growing season:
 |
If the fence is properly
installed, energized, and clear of heavy weed growth,
protection within fenced areas is ~100%. |
 |
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. |
 |
There does not appear to
be much of an edge effect (if any) where trees near the
fenced area are protected. |
 |
Failure to maintain the
fence reasonably clear of heavy weed growth results in
lowered voltage on the fence and, over time,
dramatically reduced success. |
 |
Just as the literature
says, voltages in the 2000-2500 voltage range are not
terribly effective. |
 |
The fencing sadly doesn’t
protect against drought or insects, both of which have
been a problem this year. |
|
|
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).
|
|
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 |
|
|
|
|
|
|
| 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
|
|
|
|
| Grounding kit - 3 rods, clamps, cable |
$30.00
|
1 |
$30.00 |
|
|
|
| |
|
SUBTOTAL |
$290.00 |
|
|
|
| 200 ft control and experimental block each |
|
|
|
|
|
|
| Galv T-Posts for Corners |
$3.50 |
8 |
$28.00 |
|
|
|
| Step-in posts |
$1.80 |
146 |
$262.80 |
|
|
|
| Insulators for corner T-posts |
$2.00
|
8 |
$16.00 |
|
|
|
| 14 gauge aluminum wire (at 31 per 1/4 mile) |
$0.02 |
2950 |
$70.80 |
|
|
|
| |
|
SUBTOTAL |
$377.60 |
|
|
|
| |
|
One acre |
$667.60 |
4 |
15 |
$60.00 |
| |
|
Two acres |
$1,045.20 |
8 |
15 |
$120.00 |
| |
|
Three acres |
$1,422.80 |
12 |
15 |
$180.00 |
| |
|
Four acres |
$1,800.40 |
16 |
15 |
$240.00 |
| |
|
|
|
|
|
|
| Tree Tube Planting Materials |
Installation |
| Cost Category |
Unit Price |
Qty |
Extended |
Man Hours |
Rate |
Extended |
| 4' Tree tubes |
3.29 |
200 |
$658.00 |
|
|
|
| Stakes |
0.5 |
200 |
$100.00 |
|
|
|
| |
|
Sum |
$758.00 |
|
|
|
| |
|
One acre |
$758.00 |
6 |
15 |
$90.00 |
| |
|
Two acres |
$1,516.00 |
12 |
15 |
$180.00 |
| |
|
Three acres |
$2,274.00 |
18 |
15 |
$270.00 |
| |
|
Four acres |
$3,032.00 |
24 |
15 |
$360.00 |
|
Note: |
|
1. assume weed mats used for each setting |
|
2. Retail prices for materials |
|
3. Tree tube stakes are estimated, probably
cost more. |
|
|
Cacapon Institute
Suggested
Revisions to USDA-CREP Tree Planting Protocols
in Areas with High Concentrations of White-tailed Deer.
September 4, 2007
Forested riparian buffers are tree lined corridors alongside
streams and rivers that reduce the flow of pollution moving
from the land into the water. People are planting thousands
of miles of buffers to protect the Chesapeake Bay and its
rivers and streams, many of these miles with funding through
the USDA-CREP program. However, it is not the number of
trees planted but the number of trees we grow
that will restore our forests and protect our waters.
Unfortunately, where deer are abundant young trees are often
damaged by deer browsing; Cacapon Institute’s surveys show
more than 90%. We are
currently testing a relatively low cost defense using
temporary electric fencing materials. Early results are
very promising. This approach, or other more standard
electric fence approaches such as the 3 wire offset fence,
have the potential to dramatically increase survival of
riparian plantings in high deer-density areas – at a
reasonable cost.
The standard approach to CREP (and other) tree plantings
uses tree tubes and weed mats. We suggest that the
following points about tree tubes are generally true:
 |
The
literature indicates that trees in tubes grow vertically
more quickly than trees not in tubes. However, it also
indicates that girth significantly lags vertical growth,
with the result that trees exiting tubes are often very
weak and spindly. The literature indicates that the
initial vertical growth enhancement caused by the
growing environment in tree tubes is lost after a few
years above the tubes. |
 |
The growing
environment in tree tubes may be harmful to seedlings,
particularly at the end of the growing season and due to
creating a favorable environment for fungal growth.
Trees that require more than a year or two to exit the
tubes, if they exit at all, may be damaged. |
 |
Tree tubes
are expensive to install, and require maintenance over
the 6-8 years the State of Maryland suggests are
required to allow weak emerging trees to become
sufficiently strong to be self-supporting. The
literature indicates that plantings with tree tubes
rarely receive the regular maintenance they require in
practice. |
 |
Tree tubes in
flood prone (i.e.: riparian) areas can be damaged or
carried away by high water. |
 |
Tree tubes
are used primarily to protect trees from deer browsing. |
 |
Most agency
people involved in plantings that we know really
don’t like using tree tubes, but see no alternative to
protect saplings from deer. |
 |
CI's
observations indicate that tree tubes simply don’t
protect saplings from deer where deer are abundant. Two
foot tubes provide a nice convenient height for nibbling
the growing tips. Four foot tubes aren’t much, if any,
better at deterring browse damage. | | | |