Cacapon Institute

Deer Exclusion Fencing Experiment

Updated November 22, 2010      Share

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. 

* 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:

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Project Description

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Results Site 1

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Results Site 2

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Cost Comparison

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On Natural Recruitment

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Suggested Revisions to USDA-CREP Tree Planting Protocols in Areas with High Concentrations of White-tailed Deer.

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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 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.  

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 crabapples, hawthornes, 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.  

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.
Below is what the above graph represents in the real world.  The photo at the left is the unfenced area 5 years after the area was planted.  The photo on the right is the NEB fenced area 3 years after fencing. 

 

 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.  Trees selected for this site were a mix of fruit (apple, peach), nut (such as hazelnut), and flowering trees (such as dogwood).  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.  Vegetation got ahead of us in June 2008 and again in 2009, fence voltage down below 3000V.  All of the above issues, plus numerous electrified farm fences in vicinity, led to “training to the fence” inconsistency.  Fully 1/3 of two of the plots had nearly 100% mortality due to high water table.  CI replanted with species appropriate to conditions (buttonbush, alder, willow) in July 2010.

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.

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 in both 4' and 2' tubes.  Good growth was observed in fruit trees (particularly apple trees in 4' tubes) in the eastern Control Block (ECB) as of July 2010.  No growth significantly above tubes was observed in Western Control Block (WCB); 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:

Here is a summary of what we saw have observed through 2010:

bullet If the fence is properly installed, energized, and clear of heavy weed growth, protection within fenced areas can be ~100%.
bullet 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.
bullet There does not appear to be much of an edge effect (if any) where trees near the fenced area are protected. 
bullet Failure to maintain the fence reasonably clear of heavy weed growth results in lowered voltage on the fence and, over time, dramatically reduced success. 
bullet Just as the literature says, voltages in the 2000-2500 voltage range are not terribly effective. 
bullet The fencing sadly doesn’t protect against drought or insects.  

 

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.

 

On Natural Recruitment.

The fence design was initially tested in an informal experiment along the riparian corridor of Skaggs Run (a tributary of the North River, tributary of the Cacapon River).  This site has a long history of excessive deer browsing, with little natural recruitment of trees anywhere on a 54 acre property over the past 20 years.  A variety of fencing configurations were installed, from 4 feet apart to 7 feet apart.  After two years, these are the results:

bullet There have been only two plants slightly browsed (both recently).
bulletEvery tree outside the fence exclosures has been heavily browsed.
bulletThree non-tubed plants were lost overwinter 2008 to vole damage.
bulletA significant amount of natural recruitment has taken place, including: black walnut, witch hazel, hornbeam, hophornbeam, linden, red maple, oak spp, hickory, dogwood, cherry, ash, box elder, tulip poplar, locust.
bulletLack of browse in these areas offers the potential for proper forest structure and biotic community formation below the 6 ft browse line.  Planting riparia is not just about the trees, it's about restoring the forest ecosystem.

 

 

Cacapon Institute

Suggested Revisions to USDA-CREP Tree Planting Protocols

in Areas with High Concentrations of White-tailed Deer.

September 4, 2007  Revised August 18, 2010

PDF of Proposed revisions including layout sketch with bill of materials.

 

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 (CI) surveys show more than 90% can be severely impacted by browse.  We are currently testing a relatively low cost defense using temporary electric fencing materials.  Results are promising.  This approach, or other 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.

 

We suggest the CREP committee consider adopting the following tree planting/protection protocol for implementation in areas with high deer densities, except in areas where the public has regular access to the site and liability issues would be a problem.  The intent of the fence is to protect the planting area for a sufficient time (3-5 years) until the trees have reached a height where deer are not a major threat. 

 

General Guidelines

 

This practice assumes that riparian plantings are the standard 35 foot width.  The literature indicates that deer fence success is reduced as exclosures become larger.

 

Tree tubes are not installed to protect trees from deer browse.  Protection may be necessary to prevent rodent damage, particularly if the planting area is not routinely mowed by the landowner.  CI suggests the use of 1-2’ tree tubes, with inexpensive ˝” x 4’ bamboo stakes used to both support the tube and mark the location of each plant.

 

Temporary electric fencing should be installed, according to CI’s 2-wire perimeter design (see below), the New Hampshire 3 wire offset fence, or a similar design.  Unless the landowner is interested in maintaining a permanent fence (as will be necessary for development of a natural understory and natural tree recruitment), this fence should be installed using temporary fencing supplies to reduce costs.

 

The voltage on the competed fence, clear of weeds, properly installed without shorts to ground, must exceed 5000 volts.  If it does not, first try installing additional ground rods per the energizer manufacturer’s instructions.  If that does not work, consider breaking the fence into several sections that are independently energized.

 

A low wire (6”-12” high) may be installed for the purpose of improving the path to ground and increasing the likelihood that deer will be shocked.  However, if installed, this wire will be a maintenance problem both in terms of weed control and collecting flood debris.

 

When the fence is first installed, training the deer to the fence using peanut butter on aluminum foil wrapped around the hot wire will certainly not hurt prospects for success. 

 

The fence wires must never be up without being energized.

 

Long fence installations (500’ and greater) must incorporate gaps in the fenced exclosure that allow deer shock free passage across the width of the buffer.  These gaps should be situated at locations where deer trails are observed.  If there is an area with numerous deer trails, the fence designer may consider initially building a more robust fence in that area, with two hot wires (at ~20” and 30”), a ground wire at 6”-12”, and fence baiting to ensure that deer are quickly conditioned to avoid the new condition on the ground.

 

If the fence is installed in the vicinity of other electric fence(s), expect the deer to be more acclimated to being shocked and more difficult to control. Additional wires (vertical and/or horizontal) may be needed to accomplish an acceptable level of control.

 

Do not use a farm’s perimeter fence as the source of electricity unless: a) the voltage on that fence always exceeds 5000 V; b) the fence is known to be well maintained clear of weeds and shorts.  Insufficient voltage will insure failure.

 

If a source of 120 volt AC power is readily available, consider buying a plug-in energizer instead of a solar energizer.  They are less expensive, and able to put a higher voltage on the fence.

 

Take voltage measurements in the morning when dew is still on the grass.  This is the time of day when any shorts will have the greatest effect on fence voltage, and the best indicator of the voltage that will likely be on the fence during the nighttime.  Always use a digital voltage meter to test the fence.

 

If the area is known to flood frequently, the fence energizer should be installed above the typical observed flood elevation.

 

If the area is known to flood frequently, the landowner might consider respooling the fence wires before a likely flood event, and reinstalling the wire after the flood waters recede.  That will reduce the issue of either cleaning flood debris from the fence, or removing that wire and installing new wire. 

 

The costs of every planting should include the labor to check the fence periodically for breaks (especially in the first few weeks after installation), and to clear the fence of weeds as needed during the growing season.  It is much easier to clear a fence before the weeds and grass are high enough to be a problem; one person can weed-eat a 600 foot long exclosure in about two hours under optimal conditions.  We suggest setting a three month clearing schedule, starting in middle to late June, and sticking to it.  Three visits should be sufficient in all but the wettest years.  Certain plants, like jewelweed, can grow very quickly in wet areas and may require additional attention.

 

The cost of this fence maintenance for 5 years should be considered a component cost of installation.  Maintenance could be performed either by the landowner as part of their match or by the contractor.  The planting is not complete until the trees grow, and maintenance is necessary for that to happen.

 

 

 

Why does it matter?

     Forested riparian buffers are wide strips of trees located along river and stream corridors.  They provide many important benefits, including shade to keep river water cool and wildlife habitat.  They also dramatically reduce the flow of pollution from the land into our rivers by filtering nutrients, sediments and other pollutants from runoff as well as removing nutrients from groundwater, allowing cleaner water to flow through to the stream. 

Forested riparian buffers are an important component of every Bay state's Tributary Strategy.  According to the Chesapeake Bay Program, between 1996 and August 2005 Bay Program partners planted 4,606 miles of riparian forest buffers throughout the watershed, with a short-term goal of 10,000 miles restored by 2010.  (http://www.chesapeakebay.net/newsriparian121205.htm )

The considerable expense of riparian plantings (over $1000 per acre) is justified by the goals of improving water quality and restoring ecosystem functions.  Planting the trees is not enough. The planted trees must actually survive if the goal of improving water quality will be achieved.  In addition, planting failures may in fact do actual harm by demoralizing the volunteer community that plants many sites, and may serve as a negative demonstration for farmers who witness plantings on their property fail.

The challenges to survival are many, and include drought, weed competition, insects, rodents, deer, and mechanical damage from mowers or vandalism.

Tree tubes from two to four feet tall are used to reduce damage from deer and rodents.  Weed mats reduce weed competition and newer designs help conserve moisture at ground level.  However much these technologies help, they do not represent a silver bullet.  Rodents may hide under weed mats and use them as cover while they gird a sapling.  And, if small seedlings are planted in tree tubes the trees that finally emerge from the tubes are very spindly and weak.  Maryland recommends leaving the tubes on for 5-8 years to give the resulting tree a chance to strengthen.  But the stakes that hold the tubes upright do not last that long, and must be replaced.     

The state of Maryland evaluated 130 buffer planting sites in 2000.  The sites were planted between 1997 and 1999.  They reported that: 82% met acceptable stocking levels; survival of planting seedlings averaged 60%; and volunteer seedlings made up a third (36%) of the seedlings. They identified weed competition as the "most common stressor for the young seedlings, with drought, deer, machinery such as mowers, and insects also being noted with lesser frequency."  (Pannill et al, 2001)

As a member of the West Virginia Potomac Tributary Strategy Implementation Team (WVPTS), CI is assessing survival and browse damage at three forested riparian buffer demonstration projects, one on the Cacapon, one on the South Branch, and one on Tuscarora Creek near Martinsburg. 

The first WVPTS demonstration site planted was along the banks of the Cacapon River near Yellow Spring, in April 2005.  Each tree was planted with a weed mat and in a tree tube for protection from deer browsing.  Overall survival, as indicated by living leaves seen on a plant, was down to 68% by September 2006.  Living trees and shrubs that rose above the tops of tubes (trees in 4' tubes and shrubs and smaller trees in 2' tubes) were assessed for signs of recent deer browse.  56% exhibited browse damage three months after being planted in 2005, and 91% in September 2006.  Many of the living plants that were not recently browsed were stunted, many severely, and many of these showed signs of browse and dieback from the previous year.

The second demonstration planting site, along the South Branch of the Potomac River, had a mixture of tube and no-tube plantings.  The tube plantings fared about the same as at Yellow Spring.  Plants without tubes (weed mats only) fared more poorly, with 48% survival three months after being planted in 2005 and 41% survival (of those that could be found) in June 2006.  Browse damage was nearly universal and severe on surviving plants in 2005, with the few existing leaves very small in comparison to the same plants in tubes.  As of June 2006, the browse rate was not as severe, with 61% of available plants browsed.

The Tuscarora Creek planting is doing well, with no apparent deer browsing.  However, deer browsing at the other two sites is a serious problem.  In addition, unlike the Maryland report above, the WV sites with high deer pressure have had no significant recruitment of native trees despite the lack of any livestock pressure for more than a decade.  That doesn't mean that no native tree seedlings germinate; they do in abundance.  It means they do not survive the deer browse.

CI’s deer exclusion fencing experiment is designed to test an innovative and relatively low cost method to protect riparian forest plantings from destructive or even catastrophic damage from deer browsing activities.  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.  

 

The first year of this project was funded by the  WV Division of Environmental Protection.  

 

 

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