Download 1 In the Lower Mississippi Valley, over 300,000 acres of agricultural

Reforestation Adjacent to Existing Forest Benefits Birds:
Proximity and Vertical Structure are Important
Reforestation of small, isolated tracts will likely
result in mature forests that are "sink” habitats
(Pulliam 1988) for birds. On these sites
reproductive output does not compensate for adult
mortality. This may be due to factors such as:
"edge effects" (e.g., lower rates of reproductive
success associated with proximity to habitat edges),
"area effects" (e.g., minimum area requirements
not being met by smaller tracts), or "isolation
effects" (e.g.,
Small isolated
limitations on
population mixing
forest tracts are
and mating
likely population
opportunities
“sinks” for birds.
because of limited
dispersal among
tracts).
Conversely, reforestation adjacent to existing forest
increases contiguous forest area and thereby builds
interior forest core (i.e., areas buffered from
agricultural or urban habitats).
Because bottomland
Reforestation
reforestation has
historically focused
adjacent to
on planting relatively
existing forest
slow-growing tree
increases
species, particularly
oaks [Quercus],
contiguous
reforested sites are
forest area and
usually dominated by
adds to interior
grasses and forbs for
up to a decade
forest core.
following
reforestation. Thus, grassland birds are the first
birds to colonize reforested sites. However,
because abundance and productivity of grassland
birds decline as woody vegetation increases within
the landscape (Johnson and Temple 1990),
grassland birds may not fair well on reforested sites.
Specifically, abundance and productivity of early
colonizing birds may be reduced on reforested sites
that abut mature forest tracts compared with
isolated reforested tracts.
500
Bird detections/100 ha
In the Lower Mississippi Valley, over 300,000 acres
of agricultural land have been reforested in the last
10 years. Decisions on how and where to reforest
are complex and usually reflect landowner
objectives. However, initial decisions regarding
reforestation markedly influence bird use of
restored sites as young forests mature.
Dick cis s e l
400
Re d-w inge d Black bird
300
200
100
0
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17
Ye as post-pl an ti n g
Grassland birds are first to colonize reforested sites.
As woody vegetation develops on reforested sites,
birds preferring shrub-scrub habitat displace
grassland species (Twedt et al. 2002). Planting
faster-growing trees compresses the time for
colonization by shrub-scrub birds and the vertical
structure of fast-growing trees attracts forest
birds (Twedt and Portwood 1996). Planting next to
existing forest patches has been advocated for
conservation of forest dwelling birds. Hardwood
plantations adjacent to existing forest tracts create
"transitional edges" that mitigate the detrimental
impacts associated with forest-agriculture interfaces
(Lindberg et al. 1998).
cropland. Reforested sites were between 2 and 15
years post-planting and were planted mostly with
oaks and ash. Mature forest tracts contained trees
>50 years old but differed in their silvicultural
management.
Bird detections/100 ha
250
RESULTS
Reforested Sites –
Whit e-eyed V ireo
200
Y ellow-breast ed Chat
Indigo B unt ing
150
Abundance of grassland birds (e.g., Red-winged
Blackbird and Dickcissel) was greater on isolated
reforested tracts. Conversely, abundance of
shrub-scrub birds (e.g., Yellow-breasted Chat and
Indigo Bunting) was greater on reforested sites
adjacent to forest. Nesting success on reforested
sites was similar for each bird species regardless of
their proximity to mature
forest. However,
Isolated tracts
grassland birds tended
harbored more
to have low (<18%) nest
grassland birds
success. Thus, for most
which had poor
grassland birds,
reforested tracts are likely nest success and
likely “sink”
population sinks that
cannot sustain their
populations.
populations without
immigration.
100
50
0
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16 17
Yeas post -plant ing
Shrub-scrub birds displace grassland birds as trees
emerge from herbs and grasses.
We assessed the effect
of different
reforestation strategies
on bird colonization
and productivity in
northeast Louisiana and
west-central Mississippi using reforested sites
within different landscape contexts. We surveyed
birds and determined nest success on both
reforested and mature forest sites within different
landscapes. We surveyed reforested sites that (1)
abutted large tracts of mature bottomland forest, or
(2) were adjacent to agricultural fields that were
distant from large tracts of mature forest. We also
surveyed mature forest stands that (1) were buffered
by reforestation, or (2) were adjacent to agricultural
Bird abundance and nest success
was determined on reforested
sites that (1) abutted mature
forest, or (2) were next cropland
and far from mature forest; and
in mature forest (1) buffered by
reforestation, or (2) adjacent to
cropland.
Table 1. Abundance (territories / 100 ha), nest success (%), and predicted
habitat condition on reforested sites adjacent to and isolated from mature
forest tracts. Average nesting success of all species did not differ between
landscape locations (16.5%; CI90% = 15.2% – 17.7%)
Abundance
Isolated
Adjacent
Nest
success
Habitat
condition
Mourning Dove
12
7
16.8
SINK
Dickcissel
106
61
17.6
SINK
Red-winged Blackbird
146
63
14.2
SINK
Yellow-breasted Chat
13
31
36.6
SINK
Yellow-billed Cuckoo
6
7
27.9
SOURCE
Orchard Oriole
11
10
34.1
SOURCE
Northern Cardinal
11
15
25.3
SOURCE
Indigo Bunting
13
34
31.2
SOURCE
1
SOURCE habitats have greater productivity than mortality; SINK habitats
have greater mortality than productivity. Determination based on observed
nest success and adult and juvenile survival estimates obtained from
published literature.
2
Parasitism of nests of
forest breeding birds
by Brown-headed
Cowbirds varied
markedly among
years of study.
Although parasitism
Female Brown-headed
Cowbird lays eggs in nests
did not appear to be
of other forest birds.
related to
reforestation, cowbirds were more abundant in
agricultural landscapes and parasitism rates
declined with increasing distance of nests from
forest edge. Because parasitism of Indigo
Bunting nests declined with increasing distance
from a forest edge, reforestation adjacent to
existing forests will increase productivity of
buntings.
On the other
Reforestation near
hand, shrubmature forest attracted
scrub birds
more shrub-scrub birds
had nesting
success >25%. which had better nest
Nesting
success and were likely
success for
“source” populations.
most these
species was sufficient to maintain their
populations on these sites. Thus, reforested
tracts are likely population sources for shrubscrub birds.
Mature Forest Sites –
On mature forest tracts the amount of young
reforestation in the landscape positively
impacted nest survival of Acadian Flycatchers.
When reforestation was widespread in the
landscape, nest survival did not vary with
distance to forest edge, but when little
reforestation was
nearby, nests further
Reforestation
from the forest edge
acts as a
survived better.
buffer to
Thus, reforestation
appears to act as a
mitigate edge
buffer to mitigate
effects.
detrimental edge
effects. More developed reforestation tracts
(i.e., older or taller) appear to be more effective
as buffers than are tracts dominated by grasses
and forbs.
1
Parasitism Risk
0.8
0.6
0.4
0.2
0
0-100
100-200
200-300
300-400
Distance from Edge (m)
Cowbird parasitism of Indigo Bunting nests
declines with distance from forest edge.
WHERE TO REFOREST –
Daily Nest Survival
1.00
Because reforestation appears to buffer detrimental
edge effects, we recommend restoration adjacent
to existing forests. Similarly, because parasitism
appears to decrease
with distance from
Reforestation near
forest edge,
large forest tracts
placement of
is more beneficial
reforestation near
large forest tracts
than restoration
is more beneficial
near small forest
than restoration
0.98
0.96
Low LS2
Low
Average
Mean
LS2
High LS2
High
0.94
0.92
0.90
0-100
100-200
200-300
300-400
Distance from Edge (m)
Acadian Flycatchers have increased nest survial
near forest edges when a greater propoprtion
(average – high) of the landscape is reforested.
patches.
3
near small forest patches.
However, because recruitment of naturally invading
woody plants is greatest near woody edges (Twedt
2004), planting trees within 100 meters of an
existing forest is likely not required to promote
forest restoration.
priority to less flood-prone sites such that their
restoration does not increase existing forest
fragmentation. The forest bird decision support
model established quantitative reforestation
priorities for all areas within the Mississippi
Alluvial Valley. An ArcView shapefile of the
model output can be viewed and downloaded at
http://www.lmvjv.org/cpa_volume1.htm.
Planting trees
within 100
meters of
existing forest is
not required to
promote
reforestation.
A forest bird decision support model is
available to aid in determining the impact
of placement of reforestation on forest
breeding bird conservation.
http://www.lmvjv.org/cpa_volume1.htm
WHAT TO PLANT –
Because grassland birds appear to be unproductive
on reforested sites, it behooves managers to
encourage succession away from colonizing
grassland birds towards shrub and forest breeding
birds. Restoration near existing forest stimulates
colonization by shrub-scrub birds, but
development of vertical forest structure within
reforested sites is essential for attracting forest
birds. Therefore, including a high proportion (30%
– 50%) of fast-growing, early successional tree
species, along with the traditional mix of slowgrowing, heavy-seeded species will encourage
colonization by high priority forest birds. This
Density of naturally invading trees decreases with distance
form forest edge.
A forest bird decision support model was
constructed to aid in decision making regarding
placement of reforestation sites within the
landscape (Twedt et al. in review). This spatial
model endeavored to provide contiguous forest
blocks with interior core habitat of 2000 ha (~5000
acres) and 5000 ha (~12000 acres). Secondary
emphasis was on increasing the area of existing
forest core, regardless of its’ size and on increasing
Trees suitable (when compatible with soils and
hydrology) for planting along with heavy-seeded
oaks and pecan. Many additional species are also
suitable for planting.
Faster-growing trees
Soft-mast trees/shrubs
Eastern cottonwood
Red mulberry
Honey locust
Hawthorn spp.
Black willow
Dogwood spp.
Sweetgum
Possumhaw
American sycamore
Plum spp.
Tulip popular
American snowbell
the proportion of forest within local (10 km)
landscapes. Additionally, this model gave higher
4
Black locust
American beautyberry
Plant ≥10 tree species at a density of
302 seedlings/acre with no more than
80 seedlings/acre of any one species.
Forest Breeding Bird Decisio
forest restoration within the M
depicted in warm colors (redrestoration, cool colors (white
Water is dark blue and existin
5
Conservation: A Spatially Explicit Decision Support
Model. Conservation Ecology (in review).
is particularly important when restoration sites are
distant from existing mature forests. Additionally,
at least one species should be planted for soft-mast.
Heavy-seeded oaks and pecans should be limited to
25 – 40% percent of planted seedlings. We
Additional information is available from:
recommend planting at least ten tree species at a
combined density of 302 seedlings/acre (750
seedlings/ha) with no more than 80 seedlings/acre
(200 seedlings/ha) of any single species (Twedt and
Best 2004).
Dr. Daniel Twedt
USGS Patuxent Wildlife Research Center
2524 South Frontage Road
Vicksburg, MS 39180
[email protected]
REFERENCES
Johnson, R. G. and S. A. Temple. 1990. Nest predation
and brood parasitism of tallgrass prairie birds.
Journal of Wildlife Management 54 (1):106-111.
Lindberg, J.E., V.R Tolbert, A. Schiller, and J.
Hanowski. 1998. Determining biomass crop
management strategies to enhance habitat value for
wildlife. p. 1322-1332. Bioenergy98, Madison, WI,
October 4-8, 1998.
Pulliam, H. R. 1988. Sources, sinks, and population
regulation. American Naturalist 132:652-661.
USGS Patuxent Wildlife Research Cen
12100 Beech Forest Road, Laurel, Maryla
301-497-5500
The mission of Patuxent Wildlife Research Center is to e
providing the information needed to better manage the na
Twedt, D. J. 2004. Stand Development on Reforested
Bottomlands in the Mississippi Alluvial Valley.
Plant Ecology (in press).
The U.S. Department of Agriculture (USDA) prohibits discrimination in all its
origin, sex, religion, age, disability, political beliefs, sexual orientation, and m
programs.) Persons with disabilities who require alternative means for commu
etc.) should contact USDA's TARGET Center at 202-720-2600 (voice and TD
Twedt, D. J. and C. Best. 2004. Restoration of
floodplain forests for the conservation of migratory
landbirds. Ecological Restoration (in press).
To file a complaint of discrimination write USDA, Director, Office of Civil R
Avenue, SW, Washington, DC 20250-9410 or call 202-720-5964 (voice or TD
Twedt, D. J., R. R. Wilson, J. L. Henne-Kerr, and D. A.
Grosshuesch. 2002. Avian response to bottomland
hardwood reforestation: The first 10 years.
Restoration Ecology 10(4):645-655.
Twedt, D. J. and J. Portwood. 1997. Bottomland
hardwood reforestation for Neotropical migratory
birds: Are we missing the forest for the trees?
Wildlife Society Bulletin 25(3):647-652.
Twedt, D. J., W. B. Uihlein, and A. B. Elliott. (in
review). Habitat Restoration for Forest Bird
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