**Integrating Wildlife Conservation with Commercial Silviculture — Demography of the Swainson's Warbler (***Limnothlypis swainsonii***), a Migrant Bird of Conservation Concern in Southern Pine Forests, USA**

Donata R. Henry, Darren A. Miller and Thomas W. Sherry

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/61168

#### **Abstract**

Intensively managed pine (*Pinus* spp.) forests encompass over 15.8 million hectares in the southeastern United States and provide an important source of wood products and an economic return to landowners. Given the extent of this landscape and the diversity of management goals and stakeholders, understanding how these forests can also be managed for biological diversity is important. Swainson's warbler (*Limnothlypis swainsonii;* SWWA), a species of high conservation priority, has been documented occupying young, unthinned pine plantations (a novel habitat type), but demographic assessment is lacking. We compared breeding phenology and repro‐ ductive success of SWWA in commercial loblolly pine (*Pinus taeda*) stands versus bottomland hardwood forest (the historical habitat type). Timing of nesting, clutch size, and hatching rates were not significantly different with 59% (n = 32) of eggs hatching in pine versus 69% in bottomland hardwood (n = 52). Mayfield estimates of nesting success were similar in pine (27%) versus hardwoods (32%) within and across years. These results indicate that closed-canopy, short-rotation pine stands can provide suitable breeding habitat for SWWA. We also review the value of intensively managed pine landscapes for avian conservation in general.

**Keywords:** Silviculture, biodiversity, habitat conservation, biodiversity, Swainson's warbler, *Limnothlypis swainsonii*

© 2015 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

### **1. Introduction**

Globally, plantation forests are increasing by an estimated 13 million hectares annually [1], comprising approximately 264 million hectares, and predicted to reach 345 million hectares by 2030 [2]. These forests are critical for meeting global wood supply demands as forests dedicated to wood fiber production produce substantially more volume of wood per hectare than natural forests [2,3]. Although the primary management objective of these forests is to provide commodities, they can simultaneously contribute to conservation of biological diversity [4-7].

For perspective, the southeastern United States has produced more timber than any other country in the world since 1986, yielding more than a million jobs and \$51 billion dollars (USD) to the economy in 2009 [8,9]. Contributing largely to this productivity are intensively managed pine (*Pinus* spp.) forests, which increased in area from nearly none in 1952 to approximately 15.8 million hectares in 2010 [9]. These plantation forests currently comprise about 19% of the forested area in the region, 86% of which are privately owned [9], and are expected to stabilize in area, thus remaining an important component of forests in the southeastern United States [10,11]. Although forested area has remained relatively stable from the early 1900's to 2007, urbanization is increasing and is considered the greatest threat to this forest cover [10,11].

Intensively managed pine forests contribute to the conservation of biological diversity, including habitat conditions for diverse avian communities [12-16], albeit with limitations [13, 17,18]. Conservation value of intensively managed forests depends on the silvicultural regimes, including rotation length, stand establishment methods, stocking density, thinning regimes, and intermediate treatments (e.g., prescribed fire, herbicide application, and fertilizer use); landscape context; physiographic region; resemblance to natural forest structure; landscape scale features such as corridors and edges; and other factors. Given the extent of this silvicultur‐ al landscape, its importance to forest conservation, its economic value, and a diversity of management goals and stakeholders, it is critical to understand how commercial forests can simultaneously be managed to conserve biological diversity, particularly on private land.

Bird communities respond predictably to changes in vegetation structure in different silvicul‐ tural regimes and stand ages. Some species occupy young pine forests following clear-cuts, whereas others prefer more mature stages of succession within these broad classes [12,14,15,19,20]. For example, species of high conservation concern inhabit even-aged, thinned pine plantations in response to prescribed fire and herbicide applications [14]. Migratory bird species typically found in deciduous forests may occupy mature, even-aged pine plantations, primarily in the presence of a well-developed understory. In southeastern US pine plantations these species include Acadian flycatcher (*Empidonax virescens*) [21], red-eyed vireo (*Vireo olivaceus*), wood thrush (*Hylocichla mustelina*), worm-eating warbler (*Helmitheros vermivora*) [22], ovenbird (*Seiurus aurocapillus*), and Swainson's warbler (*Limnothlypis swainsonii*) [12,23,27,37]. Thus, pine plantations are not just occupied by habitat-generalist birds.

Recently, Swainson's warblers (SWWA), a species of conservation concern [24], have been documented occupying intensively managed pine stands in the southeastern United States [25-27]. SWWA are attracted to high stem densities and thicket-like conditions within unthin‐ ned pine plantations, which are similar structurally to switch cane (*Arundinaria gigantica*) thickets in bottomland hardwood forests [25-27], the habitat complex in which this species was first documented and remains best studied. However, understanding effects of forest man‐ agement on avian species such as SWWA necessitates understanding treatment impacts on demographic parameters, and not just abundance [28,29]. To better understand use of a novel habitat condition by a conservation priority bird species, we compared breeding phenology and reproductive success of SWWA between intensively managed loblolly pine stands versus cane thickets within bottomland hardwood forests. Given abundant evidence that SWWA use pine plantations in Louisiana [25-27] we tested the hypothesis that the species experiences demographic success (based on abundance and nesting characteristics) in pine stands com‐ parable to that in bottomland hardwoods. We discuss our results in the context of how contemporary silvicultural practices in southeastern pine plantations are likely to impact species of conservation concern such as SWWA.

### **2. Methods**

FIGURES

**1. Introduction**

218 Precious Forests - Precious Earth

diversity [4-7].

Globally, plantation forests are increasing by an estimated 13 million hectares annually [1], comprising approximately 264 million hectares, and predicted to reach 345 million hectares by 2030 [2]. These forests are critical for meeting global wood supply demands as forests dedicated to wood fiber production produce substantially more volume of wood per hectare than natural forests [2,3]. Although the primary management objective of these forests is to provide commodities, they can simultaneously contribute to conservation of biological

For perspective, the southeastern United States has produced more timber than any other country in the world since 1986, yielding more than a million jobs and \$51 billion dollars (USD) to the economy in 2009 [8,9]. Contributing largely to this productivity are intensively managed pine (*Pinus* spp.) forests, which increased in area from nearly none in 1952 to approximately 15.8 million hectares in 2010 [9]. These plantation forests currently comprise about 19% of the forested area in the region, 86% of which are privately owned [9], and are expected to stabilize in area, thus remaining an important component of forests in the southeastern United States [10,11]. Although forested area has remained relatively stable from the early 1900's to 2007, urbanization is increasing and is considered the greatest threat to this forest cover [10,11].

Intensively managed pine forests contribute to the conservation of biological diversity, including habitat conditions for diverse avian communities [12-16], albeit with limitations [13, 17,18]. Conservation value of intensively managed forests depends on the silvicultural regimes, including rotation length, stand establishment methods, stocking density, thinning regimes, and intermediate treatments (e.g., prescribed fire, herbicide application, and fertilizer use); landscape context; physiographic region; resemblance to natural forest structure; landscape scale features such as corridors and edges; and other factors. Given the extent of this silvicultur‐ al landscape, its importance to forest conservation, its economic value, and a diversity of management goals and stakeholders, it is critical to understand how commercial forests can simultaneously be managed to conserve biological diversity, particularly on private land.

Bird communities respond predictably to changes in vegetation structure in different silvicul‐ tural regimes and stand ages. Some species occupy young pine forests following clear-cuts, whereas others prefer more mature stages of succession within these broad classes [12,14,15,19,20]. For example, species of high conservation concern inhabit even-aged, thinned pine plantations in response to prescribed fire and herbicide applications [14]. Migratory bird species typically found in deciduous forests may occupy mature, even-aged pine plantations, primarily in the presence of a well-developed understory. In southeastern US pine plantations these species include Acadian flycatcher (*Empidonax virescens*) [21], red-eyed vireo (*Vireo olivaceus*), wood thrush (*Hylocichla mustelina*), worm-eating warbler (*Helmitheros vermivora*) [22], ovenbird (*Seiurus aurocapillus*), and Swainson's warbler (*Limnothlypis swainsonii*)

[12,23,27,37]. Thus, pine plantations are not just occupied by habitat-generalist birds.

Recently, Swainson's warblers (SWWA), a species of conservation concern [24], have been documented occupying intensively managed pine stands in the southeastern United States [25-27]. SWWA are attracted to high stem densities and thicket-like conditions within unthin‐ ned pine plantations, which are similar structurally to switch cane (*Arundinaria gigantica*)

*Study areas* – We conducted this study during five breeding seasons, 1999-2003, in southeastern Louisiana, United States in five of the Florida Parishes (counties) north of Lake Pontchartrain (Figure 1). In this region, lower elevations associated with river systems and drainages supported both extensively forested and highly fragmented tracts of bottomland hardwood forest. More upland areas, once dominated by longleaf pine (*Pinus palustris*) savannahs, have been converted to agriculture, towns, and suburbs, and over 80,000 ha of loblolly pine plantations. Elevation above sea level did not exceed 150 m in any of the study sites. Henry et al., Draft Chapter for: *Forestry*, InTech

 FIGURE 1. Map of Louisiana, USA showing Parishes (cross-hatching) **Figure 1.** Map of Louisiana, USA showing Parishes (cross-hatching) where study sites were located (black circles).

FIGURE 2. Bottomland hardwood (a) and commercial loblolly pine (b) forests where Swainson's warbler nests were located in St. Tammany Parish and Washington Parish, respectively, southeast Louisiana, USA.

where study sites were located (black circles).

(a) (b)

Photographs by Donata R. Henry.

Henry et al., Draft Chapter for: *Forestry*, InTech

Our bottomland hardwood site was located in the Honey Island Swamp unit of the Pearl River Wildlife Management Area (PRWMA) in St. Tammany Parish (30˚23'N, 89˚43'W; managed by the Louisiana Department of Wildlife and Fisheries; Figure 2a). Honey Island Swamp is a floodplain that was extensively logged in the 1940-1950s, and strip-type thinned in 1987-88 for a more selective harvest of specific tree species. During our study, most of this area was mature second growth with canopy trees of water oak (*Quercus nigra*), basket oak (*Q. michauxii*), laurel oak (*Q. laurifolia*), sweetgum (*Liquidambar styraciflua*), black gum (*Nyssa sylvatica*), bald cypress (*Taxodium distichum*), hickories (*Carya* spp.), and magnolias (*Magnolia* spp.). Midstory trees included red maple (*Acer rubrum*), ironwood (*Carpinus caroliniana*), swamp dogwood (*Cornus foemina*), hollies (*Ilex* spp.), buttonbush (*Cephalanthus occidentalis*), and silverbell (*Halesia diptera*). The understory was interspersed with southern switchcane, arrowwood (*Viburnum dentatum*), wax myrtle (*Myrica cerifera*), Chinese privet (*Ligustrum sinense*), dwarf palmetto (*Sabal minor*), blackberry (*Rubus* sp.) thickets, and occasionally dense stands of water oak and/ or other hardwood saplings. Numerous bayous and smaller drainages (often containing cypress and gums) dissected the study area, and flooded most frequently during spring and summer. We surveyed over 25 km of roads, trails, and drainages within approximately 2,300 ha. We considered Honey Island Swamp to be high-quality breeding habitat for SWWAs due to its higher density of breeding pairs compared to other large tracts of hardwood forests that we surveyed (including Bogue Chitto National Wildlife Refuge contiguous with PRWMA and Sherburne WMA in the Atchafalaya River Basin). FIGURES FIGURE 1. Map of Louisiana, USA showing Parishes (cross-hatching) where study sites were located (black circles). ####### # # # # # ######## # # # ## New Orleans Baton Rouge

FIGURE 2. Bottomland hardwood (a) and commercial loblolly pine (b) forests where Swainson's warbler nests were located in St. Tammany Parish and Washington Parish, respectively, southeast Louisiana, USA. Photographs by Donata R. Henry. **Figure 2.** Bottomland hardwood (a) and commercial loblolly pine (b) forests where Swainson's warbler nests were lo‐ cated in St. Tammany Parish and Washington Parish, respectively, southeast Louisiana, USA. Photographs by Donata R. Henry.

We surveyed pine plantations (n = 35) located in Washington (30˚46'N, 90˚12'W), Livingston (30˚24'N, 90˚47'W), St. Helena (30˚40'N, 90˚48'W), Tangipahoa (30˚42'N, 90˚27' W), and St. Tammany (30˚28'N 90˚ 02'W) Parishes of Louisiana on land owned and managed by Weyer‐ haeuser Company for pine sawtimber production (Figure 2b). Pine stand size ranged from 50 to 200 ha. Typical management of these stands included clear-cut harvest of existing stands followed by mechanical and chemical site preparation, planting of loblolly pine seedlings at approximately 1,700 seedlings/ha, herbicide release treatment, thinning, and then final harvest at 25-35 years of age. Pine stand canopies were composed of loblolly pine, with hardwood species in the midstory including crab apple (*Malus* spp.), red maple, and sweetgum. Typical understory shrubs included yaupon (*Ilex vomitoria*), wax myrtle (*Myrica cerifera*), and huckle‐ berry (*Gaylussacia* spp.). Sites in Livingston Parish also contained abundant dwarf palmetto in the understory.

Our bottomland hardwood site was located in the Honey Island Swamp unit of the Pearl River Wildlife Management Area (PRWMA) in St. Tammany Parish (30˚23'N, 89˚43'W; managed by the Louisiana Department of Wildlife and Fisheries; Figure 2a). Honey Island Swamp is a floodplain that was extensively logged in the 1940-1950s, and strip-type thinned in 1987-88 for a more selective harvest of specific tree species. During our study, most of this area was mature second growth with canopy trees of water oak (*Quercus nigra*), basket oak (*Q. michauxii*), laurel oak (*Q. laurifolia*), sweetgum (*Liquidambar styraciflua*), black gum (*Nyssa sylvatica*), bald cypress (*Taxodium distichum*), hickories (*Carya* spp.), and magnolias (*Magnolia* spp.). Midstory trees included red maple (*Acer rubrum*), ironwood (*Carpinus caroliniana*), swamp dogwood (*Cornus foemina*), hollies (*Ilex* spp.), buttonbush (*Cephalanthus occidentalis*), and silverbell (*Halesia diptera*). The understory was interspersed with southern switchcane, arrowwood (*Viburnum dentatum*), wax myrtle (*Myrica cerifera*), Chinese privet (*Ligustrum sinense*), dwarf palmetto (*Sabal minor*), blackberry (*Rubus* sp.) thickets, and occasionally dense stands of water oak and/ or other hardwood saplings. Numerous bayous and smaller drainages (often containing cypress and gums) dissected the study area, and flooded most frequently during spring and summer. We surveyed over 25 km of roads, trails, and drainages within approximately 2,300 ha. We considered Honey Island Swamp to be high-quality breeding habitat for SWWAs due to its higher density of breeding pairs compared to other large tracts of hardwood forests that we surveyed (including Bogue Chitto National Wildlife Refuge contiguous with PRWMA and

FIGURE 1. Map of Louisiana, USA showing Parishes (cross-hatching) where study sites

Baton Rouge

#######

New Orleans

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