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
	Results
	Cost Comparison
	Suggested Revisions to USDA-CREP Tree Planting Protocols in Areas with High Concentrations of White-tailed Deer.
	Why It Matters.

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 20^th,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.