Below are links to several background reports and videos that will help you understand the issue of deer overabundance.
1- White-tailed Deer in Northeastern Forests: Understanding and Assessing Impacts by Thomas Rawinski
This 2014 report explains the deer situation and also lists plants they prefer and those they avoid. Lots of good photographs.
2- Two short video clips from a recent conference on The Growing Deer Debate in the Catskills. They set out some of the issues involved in ‘the deer wars’. Tom is one of the 6 speakers.
3--Video of the Dummerston Vermont Conservation Commission’s symposium on the deer situation in southern Vermont, held in fall 2017. This is a longer video (1.5 hours), but enlightening as it focuses on Vermont. The most useful part for me was the 2nd speaker, Nick Fortin, Deer Project Leader of the Vermont Fish and Wildlife Department, who gave an overview of deer biology and history in the state of Vermont. He said deer eat 10# to 15# of vegetation per day!
Monitoring White-tailed Deer Impacts:
The Ten-tallest Method
Thomas J. Rawinski
U.S. Department of
Agriculture, Forest Service
Northeastern Area
State and Private Forestry
11 Campus Boulevard,
Suite 200
Newtown Square, PA
19073
Introduction
Forest ecosystems contain plants, animals, fungi and
microbes interacting with each other and their physical environment in a
complex system of energy and matter exchanges. The purpose of this document is to describe a way to better understand
one aspect of this dynamic, the influence of white-tailed deer (Odocoileus virginianus) herbivory on vegetation (Figure 1).
Figure 1. A white-tailed deer feeding in a meadow. Photo courtesy of
Paul D. Curtis.
White-tailed deer, at high population densities, can alter
ecosystems in ways that diminish forest-related values. Throughout the United States, deer
populations are managed using a variety of often integrated approaches to
achieve population levels compatible with forest health. Common to all approaches is the need
for effective long-term monitoring of the understory vegetation to detect
improving or deteriorating conditions.
Consistent with the principles of integrated pest management (IPM), deer
are judged to be at an acceptable level when plants of many species are able to
reach full growth potential. For
trees, this means that many species are able to grow above the reach of deer to
regenerate a forest.
The ten-tallest method is novel in its simplicity. It follows the growth, browse damage
and reproductive condition of plant populations that serve as indicators of changing
levels of browse impact. Except
with the plotless application of the method, plants are not individually
marked.
The method was developed for landowners, students, citizen
scientists and natural resource professionals. It should be used where deer are obviously impacting the
understory vegetation. It can also
be used in adjacent fenced areas to reveal growth potential in the absence of
browsing. It involves minimal cost
and generates data that are easy to collect and manage.
Small tree saplings are a prime focus, but the method can
also be applied to shrubs and herbs.
It can be used beyond forests, in clearings and scrub.
The prime metric is plant height. Are tree saplings on trajectories to grow above the reach of
deer? Is browse damage increasing
or decreasing? Are understory
shrubs and herbs producing more flowers? Answering these questions takes time – many years of
monitoring.
The ten-tallest method doesn’t address all needs in the
realm of deer impact monitoring or research. For close scrutiny of individual plants or for
community-level inquiries, other methods can and should be used. Every method has its intended purpose.
Plot Selection
Walk through a forest, observing the plant life and the
impacts of deer browsing. Look for
places where deer-preferred trees, shrubs or herbs are most abundant and
suitable for monitoring (Figure 2). Such plants tend to be most abundant where canopy gaps allow
extra sunlight to reach the forest floor or where the more fertile soils exist. Root sprouts of American Beech are an
exception because they are tolerant of shade and can thrive on poor soils. Feel free to monitor non-native species
such as Winged Euonymus because these can serve the purpose as well as native
species.
Which plant species are preferred by deer and which are not? Lists of each are found in the Forest
Service publication, White-tailed Deer in
Northeastern Forests: Understanding and Assessing Impacts.
Figure 2. An understory of browse-suppressed Sugar Maple saplings, an
ideal location for establishing a ten-tallest plot, Chenango County, NY.
Avoid forest edges and places of high human activity where
deer impacts are not representative of those found in forest interiors.
Try to establish plots in different sectors of a forest and
in different habitats. Deer
impacts are never uniform
across the landscape.
Some locations will experience heavier browse pressure than others. And, a plant species may grow better at
some locations than others, owing to differences in light, moisture and soil
fertility. Variability in height
growth and browse impact across the landscape is to be expected, and that is
why multiple plots are sampled.
The observer is left to interpret growth data in terms of browse impact and
other possible contributing factors.
Focus the sampling on two or three preferred species that
are most abundant in a forest, but also monitor some of the less common or less
preferred species if those species show browse damage.
How many plots per forest? There’s no set rule, but the more plots the better, especially
when the growth data are to be analyzed statistically using such tests as repeated
measures ANOVA. Some forests will have
many places suitable for sampling while other forests far fewer, e.g., where
low-preference species such as Black Huckleberry or Hay-scented Fern dominate the
understory (Figure 3).
Available time often dictates the number of plots that can
be established and monitored. At the
1,039 acre Rheinstrom Hill Audubon Sanctuary, for example, two people spend two
days each year re-sampling 55 species populations at 25 stake locations (Figure
4).
Figure 4.
Ten-tallest plot locations at Rheinstrom Hill Audubon Sanctuary in
Columbia County, NY.
Plot Sampling
A plot must contain at least ten individuals of a plant
species of interest within an area of 1,076 square feet (100 square meters),
which equates to a circle with an 18.5 feet (5.64 meters) radius. Confident that a place is suitable for
a plot, drive a central stake into the ground. A section of ¾ inch diameter PVC pipe, 2.5 feet long, works
well. Use a permanent marker or
some other method to number the stake.
Given a choice as to whereto place the stake, consider the proximity of landmarks that
could be helpful in relocating the stake.
A tape measure is pivoted around the central stake to mark the edge of the plot circle. Eight wire stake flags placed along the periphery of the plot are usually sufficient to eyeball the plot area. When uncertain whether a plant of interest is inside or outside the plot, run the tape measure to it. Leaving the wire flags in place saves time when re-sampling the plots, but if desired, the wire flags can be retrieved and reestablished with each sampling.
Record site name, location, plot number, date and observer
information on the form. Each plot number has to be unique. Plot number consists of site name,
stake number and species name, e.g., “Beaver Meadow 2 Sugar Maple”. At large properties, one might add a
subsite name into the plot number, e.g., “Montezuma NWR, Main Pool Forest 1
Buckthorn”. Estimate the total number of individuals
of the monitored species in the plot.
If a shrub or herbaceous species is being monitored, count and record
the total number of reproductive individuals in the plot, i.e., those with flower
buds, flowers or fruit.
With a yardstick or a small tape measure, measure the height
of the ten tallest individuals to the nearest half inch. Measure directly below the highest leaf
blade of the plant. If sampled
during the dormant season, measure to the top of the tallest living bud. Stems originating outside the plot but
leaning into the plot are not measured.
Examine the measured stems for any evidence of browse damage and indicate
Yes (Y) or No (N) on the form (Figure 5).
Use a question mark (?) when uncertain about the cause of plant damage.
Where deer and moose coexist, browse damage from the two may
be indistinguishable. Record such
uncertainty in the Notes section. Drape
a section of flagging tape over each plant that gets measured and evaluated.
Once ten plants have been measured, see if there are any
plants in the plot that are taller than the shortest one measured. If such a plant is found, that shortest
measurement gets crossed out and replaced by the new taller measurement. Continue this procedure, looking to
“beat” the next shortest measurement until you are confident that the ten tallest
have been measured.
Do not measure stems of woody plants that are greater than five
feet tall, but indicate in the Notes section of the form that a certain number
of these taller individuals exist in the plot. Record other observations in the Notes section, e.g.,
“White Ash saplings deformed by chronic browsing”, or “three Red-berried Elder
plants in plot measuring 9, 12 and 16 inches tall”.
Multiple species may be sampled at a stake location. This is accomplished by removing the
flagging draped across the first species and repeating the procedure for the
next. Use a separate form,
identifying this plot as “Beaver Meadow 2 White Ash”, for example. As defined here, a plot is really a
species population monitored at a stake location.
The sampling goes quicker if two or more people are
involved. Take photographs of the
plots for future reference (Figure 6).
When all species populations have been measured, collect the
draped flagging tape and proceed to the next stake location. The central stake stays in the ground,
as will the wire flags, if so desired.
Re-sample the plots in future years near the date when first
sampled. Because none of the
plants are individually marked, the ten tallest individuals measured in one
year may not be same individuals measured the next year. This is fine, and to be expected; the
method monitors attributes of plant
populations, not individual plants. Returning each year near the same date
is especially important if herbaceous plants are being monitored to ensure that
the plants are in the same stage of development.
Figure 6. Measuring a Red Oak sapling at stake no.16 at Rheinstrom Hill Audubon Sanctuary, Columbia County, NY. The strip of flagging tape will be draped across the sapling once it has been measured and evaluated for browse damage.
Figure 6. Measuring a Red Oak sapling at stake no.16 at Rheinstrom Hill Audubon Sanctuary, Columbia County, NY. The strip of flagging tape will be draped across the sapling once it has been measured and evaluated for browse damage.
A list of equipment needed follows.
·
A map and/or aerial photograph of the
area.
·
Clip board with blank forms and writing
implement.
·
GPS unit or phone with GPS capability.
·
Camera or phone for taking photographs.
·
¾ inch diameter PVC pipe stakes, 2.5
feet long, or other such stakes for permanent marking of plot centers.
·
Permanent marker or numbered tags for
numbering plot stakes.
·
A hammer, for driving stakes into the
ground.
·
Large tape measure, for establishing
plot edges.
·
A supply of wire stake flags for
marking plot edges.
·
Small tape measure or yard stick, for
measuring plant heights.
·
Strips of flagging tape, about one foot
long, to drape across measured plants.
·
Numbered metal tags for use in the
plotless application.
Plotless Application of the Method
The plotless application is especially suited to situations
where deer have radically altered the understory, or where low preference
species dominate. With little to
monitor via the plot-based approach, the focus turns to the sprouts arising
from the base of such species as Witch Hazel, Spicebush, Winterberry, Azalea
and Musclewood (Figure 8). When
heavily browsed, those sprouts may not be able to grow above the reach of deer
to replace the older stems. Sprout
growth, or lack thereof, can provide an early indication of diminishing or increasing
deer impact.
Locate an area where the shrubs or trees of interest are
fairly abundant. One may have to
travel alongside a small brook, for example, to find ten suitable Spicebush
plants. Affix a numbered tag to
one of the mature stems of each plant and measure the tallest basal
sprout. Return at about the same
time of year to re-measure the tallest sprout at each individually identified
plant. Use the standard form for
entering the height data, but indicate in the Notes that such measurements were
from the plotless application of the method.
Data Entry and Storage:
The Excel document, “Ten-tallest Form 2018”, serves as the
template for entering data collected in the field. It is a workbook containing 11 worksheets. Upon entering data, the document should
be saved as a new document, e.g., “Beaver Meadow Ten-tallest Data”. Make as many copies of the blank worksheet
as necessary to accommodate all plots sampled at a site (right click the last
blank worksheet tab, select Copy, Move to End, and click the box for Create a Copy). Rename the worksheet tabs by right-clicking
the tab and selecting Rename. To print all worksheets, right-click
any tab and click Select All Sheets
before hitting Print.
After entering information on the first worksheet, much of
that information, such as site name, location, observer and date, can be copied
and pasted onto the next worksheets. When all data have been entered, you may wish to generate a
map of the stake locations using the GPS coordinates.
Each form accommodates five measuring events. Begin a new Excel document after these
five measurements have been entered.
Notice that average height is calculated automatically, which, over
time, provides some instant insight into growth trends.
Ten-tallest data can be tabulated, graphed or analyzed
statistically to reveal height growth over time within and among species (Table
1, Figure 9). It may take several years
to judge whether height growth trends are positive, negative or static (Figures
10 and 11).
The standardized form allows a species’ growth data from one
site to be compared with that from another to judge which has greater deer
impact. Beech sprout height growth
has been commonly used for this purpose.
When does monitoring stop? When enough of the tree saplings have grown above the reach
of deer, i.e., five feet tall.
Such occurred in a plot on Long Island where nine of the ten tallest American
Beech sprouts exceeded five feet tall after five growing seasons.
When shrubs or herbs are being monitored, one can judge improvement
by taller plants or by increased flowering, but a clear stopping point usually
doesn’t exist.
Monitoring herbaceous plants such as White Trillium can be
challenging because the deer feed on them continuously. During warm springs, the trilliums
flower earlier than during cool springs, so relying on a single date for
re-sampling can lead to varying results.
A revealing example is shown from ten trillium plots monitored from 2009
to 2017 (Figure 12). In 2009 and
2010, the trillium flowers were counted on May 7. Spring came early in 2010, so the numbers were low. In 2011 and 2012, the sampling took
place twice during the spring, about ten days apart. The trillium numbers were about halved during that short period
of time. Despite these challenges,
Figure 12 shows that the trilliums increased during the period of 2013 to 2016,
but declined in 2017. It all
suggests that browse pressure can wax and wane over time and not necessarily
follow a linear projection model.
In conclusion, the ten-tallest method can provide useful information
about plant-herbivore dynamics in forest ecosystems. With relative ease,
managers can collect, curate and analyze this information and use it to inform
management decisions.
