Author
Laurel Haavik, Northeastern Area State & Private Forestry, USFSIssues
Three major issues confront forests in the northeastern US: changing environmental conditions, simultaneous vulnerability of many forests to disturbance, and spread of established invasive species along with arrival of new invasive species. Changing environmental conditions can affect forest pest biology directly, or indirectly through impacts on tree physiology (see Insect Disturbance and Climate Change). As a result of extensive timber harvesting and land clearing for farming in the early 1900s, followed by re-establishment of forests often dominated by pioneer tree species, much of the forested landscape in the eastern US has reached or is nearing maturity. It follows that disturbance initiated by climate-induced weather events, and ultimately delivered by insects or pathogens, serving their ecological function of readying the forest for the next cohort(s) of trees, may appear catastrophic if it occurs simultaneously across the landscape in many different forests. Eastern US forests are also threatened and challenged by several non-native invasive insects and pathogens (see “ecology and distribution in US” in table), which can have unpredictable and sometimes catastrophic impacts (e.g., emerald ash borer and beech bark disease) on forest ecology, because of a lack of shared co-evolutionary history with these forest ecosystems. As a changing climate affects vulnerable mature forests that house native and non-native disturbance agents, complex and unpredictable outcomes are likely.Likely Changes
Some of these outcomes have already been observed, modeled, or tested, and some broad predictions can be made for specific pests based on this information and knowledge of pest biology and ecology (see “climate influence” in the individual species section). A few general patterns have emerged. Hotter summers with more dry periods will be particularly problematic for northeastern US forests, because these conditions stress trees, which can increase survival and population growth of pests that specialize on weakened or dying trees. These insects and pathogens, often termed secondary pests, may become more serious pests in the future if more stressed trees appear on the landscape (e.g., bronze birch borer, twolined chestnut borer, Armillaria root disease, and many others). More frequent and intense severe storms may provide host material for insects that are attracted to freshly wounded or broken trees (e.g., engraver beetles, eastern larch beetle). Milder winters may relax range restrictions on insects or pathogens with a distribution currently limited by cold temperatures (e.g., hemlock woolly adelgid, southern pine beetle). Earlier budburst in spring may cause a phenological mismatch between trees and caterpillars that develop on early-season foliage, which may be beneficial or detrimental to insect population growth (e.g., spruce budworm, winter moth). Specific changes, based on current research, are listed by pest below, under the heading “climate influence”.
Predicted changes in climate are understandably enveloped by a degree of uncertainty, which also creates difficulty in predicting how those changes will directly and indirectly influence forest pests. Ultimately, a changing environment will select for species and individuals (trees, insects, and pathogens) that are adapted to new conditions.
Options for management
Sound management practices are key to creating forests that are resistant and resilient to climate change. The current vulnerable state of forests in the northeastern US necessitates management action to maintain the current forest cover types and/or restore areas that have degraded since European settlement. Because trees are long-lived organisms, relative to insects and pathogens, they will likely adapt more slowly to changing environmental conditions, which may place them at a disadvantage. Likewise, silvicultural activities can have lasting effects that extend beyond the existing forest conditions in which they were implemented. Integrated management tactics that target weak points in a pest’s life cycle along with attentive forest management have been successful in the past and will be essential in the future to retain forests that are resilient to changing environmental conditions. Adaptive management, a dynamic approach to silviculture that evaluates and modifies management decisions as conditions change, will also be important.
Silvicultural systems should be modified at the stand level based on existing stand conditions; the underlying edaphic conditions of the site and which species are adapted to grow there; options given future climate and pest scenarios; and desired outcomes. Management guides (e.g., https://www.nrs.fs.fed.us/fmg/nfmg/index.html) exist for most forest cover types in the northeastern US, and information on biology, ecology, impact, and management of some major pests is listed in the comprehensive list below (see “resources”). Forest health technical expertise is available for federal lands through the USDA Forest Service, Forest Health Protection. For State and Private lands, consult your local state forest pest specialist or county extension agent. These tools should be consulted before forest management activities begin, and throughout implementation of a silvicultural system.
Information by Insect
Ecology and distribution in US: non-native, quarantined: eradications in progress (Map)
Hosts: many hardwoods, especially maple (Acer spp.), birch (Betula spp.), buckeye (Aesculus spp.), elm (Ulmus spp.), and willow (Salix spp.)
Forest type: urban, most hardwood forests (likely)
Climate influence: weather that stresses/weakens host, especially drought, could positively affect survival or population growth (1)
Resources:
FS Fact Sheet
Biology, ecology, and management
Risk of invasion in the US
Ecology and distribution in US: Native ( Map)
Hosts: Birch (Betula spp.), especially B. papyrifera
Forest type: Urban, paper birch, northern hardwoods, mixed hardwoods
Climate influence: weather that stresses/weakens host (warmer temperatures, drought) expected to result in more frequent/intense outbreaks (2,3)
Resources:
FS Fact Sheet
Biology, ecology, and management
Ecology and distribution in US: Native
Hosts: Larch (Larix spp.), Tamarack L. laricina
Forest type: Tamarack, lowland conifer
Climate influence:
- weather that stresses/weakens host can result in population growth and outbreaks (4)
- increased population growth possible with longer, warmer, growing seasons (5)
- fire, flooding, drought, defoliation can result in population growth (6)
Resources:
FS Fact Sheet
History of outbreaks
Ecology and distribution in US: Non-native, expanding rapidly
Hosts: Ash (Fraxinus spp.); white fringe tree Chionanthus virginicus; olive Olea europea
Forest type: Urban, bottomland hardwood, mixed hardwood, northern hardwoods
Climate influence:
- weather that stresses/weakens host can improve survival or population growth (7)
- drought stress increases pest survival and growth, reduces ash growth (8)
- pest may have limited survival in cold climates (northern MN, ND) (9)
Resources:
FS Fact Sheet
Biology, ecology, and management
Phenology
News
Ecology and distribution in US: Native
Hosts: Hardwoods, especially sugar maple (Acer saccharum); aspen (Populus spp.); and oaks (Quercus spp.)
Forest type: Urban, oak-hickory, oak-pine, sugar maple, aspen, mixed hardwoods, northern hardwoods
Climate influence:
- changes in timing and duration of growing season could cause asynchrony with host budburst, which may reduce survival, population growth, and fewer outbreaks; alternatively, warmer spring and summer temperatures could result in increased survival, population growth, and more outbreaks (10)
Resources:
FS Fact Sheet
Biology, ecology, and management
Ecology and distribution in US: Non-native, spreading west and south. (Map)
Hosts: Over 300 hosts, mostly hardwoods, especially oak (Quercus spp.); basswood (Tilia spp.); and aspen (Populus spp.)
Forest type: Urban, oak-hickory, oak-pine, northern hardwoods, mixed hardwoods, bottomland hardwoods, aspen
Climate influence:
- weather that stresses/weakens host, especially drought, could positively affect survival or population growth (11)
- increases in temperature predicted to result in greater area of suitable habitats at higher altitudes and latitudes (12, 13)
- increases both in temperature and precipitation predicted to result in increased area defoliation (14
- the natural enemy, Entomophaga miamiaga, can cause increased levels of gypsy moth mortality during cool, moist springs (15
Resources:
FS Fact Sheet
Biology, ecology, and management
More biology, ecology, and management
Slow-the-spread management program
Impact in the U.S. vs. Europe
Ecology and distribution in US: Non-native, spreading north and west. (Map)
Hosts: All hemlock (Tsuga spp.); eastern and Carolina hemlock (T. canadensis and T caroliniana) are especially vulnerable.
Forest type: Hemlock
Climate influence:
- warmer winters predicted to relax northern limits on range expansion, and could contribute to increased survival and population growth throughout its range (16, 17)
- warmer summer temperatures may reduce survival in southern areas of its range (12, 18)
- warmer winters may have already altered phenology; and development rate (19
Resources:
FS Fact Sheet
Biology, ecology, and management
Biological control program
Ecology and distribution in US: Native
Hosts: Mostly jack pine(Pinus banksiana); sometimes other pines, occasionally spruce, larch, and fir.
Forest type: Jack pine
Climate influence:
- weather that stresses/weakens host, especially drought, could positively affect survival or population growth (20)
Resources:
FS Fact Sheet
Biology, ecology, and management
Population dynamics
Ecology and distribution in US: Non-native (Map)
Hosts: Larch (Larix spp.), especially tamarack (L. laricina)
Forest type: Tamarack, lowland conifer
Climate influence:
- warmer winters may positively affect overwintering survival, which can increase population growth and outbreaks (21)
Resources:
FS Fact Sheet
Biological control in the western U.S.
Ecology and distribution in US: Native
Hosts: All pines (Pinus spp.)
Forest type: Urban, red pine, jack pine, eastern white pine, pitch pine, loblolly pine, oak-pine
Climate influence:
- weather that stresses/weakens host, especially drought, could positively affect survival or population growth (22)
- windthrow or ice breakage from storms or management activity positively affects survival and population growth (23)
Resources:
FS Fact Sheet
Biology and ecology
Management
More management
Ecology and distribution in US: Native
Hosts: Oaks (Quercus spp.), especially red oaks (Q. rubra, Q. velutina, Q. coccinea)
Forest type: Urban, oak-hickory, oak-pine, northern hardwoods, mixed hardwood
Climate influence:
- weather that stresses/weakens host, especially drought, could positively affect survival or population growth (24, 25)
Resources:
FS Fact Sheet
Biology, ecology, and management
Changing role in oak decline
Ecology and distribution in US: Native
Hosts: All pines(Pinus spp.)
Forest type: Urban, red pine, jack pine, eastern white pine, pitch pine, loblolly pine, oak-pine
Climate influence:
- weather that stresses/weakens host, especially drought, could positively affect survival or population growth (26)
Resources:
FS Fact Sheet
Biology, ecology, and management
More management
Ecology and distribution in US: Native, expanding north (Map)
Hosts: Most pines(Pinus spp.)
Forest type: Urban, all pine types
Climate influence:
- warming winters predicted to facilitate range expansion north (27)
- warmer springs, in particular, may increase outbreak severity (28)
- cool winters in northern part of range may synchronize flight of adults in spring, which may lead to more frequent outbreaks (29)
Resources:
FS Fact Sheet
Biology, ecology, and management
Range expansion
More management
Management history
Ecology and distribution in US: Native (Distribution map)
Hosts: Balsam fir (Abies balsamea), white (Picea glauca), red (P. rubens), occasionally black spruce (P. mariana), tamarack, pine, and hemlock
Forest type: Balsam fir, eastern spruce-fir, black spruce
Climate influence:
- intensity and duration of outbreaks predicted to increase with a warmer and drier climate (30)
- warmer winters and longer growing season hypothesized to increase intensity and duration of outbreaks, and impact to boreal black spruce (31)
Resources:
FS Fact Sheet
Biology and ecology
Management
Management (Lake States)
Ecology and distribution in US: Native (Map)
Hosts: Oaks (Quercus spp,)
Forest type: Urban, oak-hickory, oak-pine, northern hardwoods
Climate influence:
- weather that stresses/weakens host, especially drought, could positively affect survival or population growth (32)
Resources:
FS Fact Sheet
Biology and ecology
Additional biology and ecology
Ecology and distribution in US: Non-native, spreading (Map)
Hosts: Many hardwoods, especially oak (Quercus spp.), maple (Acer spp.), apple (Malus spp.), birch (Betula spp.), and blueberry (Vaccinium spp.)
Forest type: Urban, oak-hickory, oak-pine, cherry-maple, mixed hardwoods, bottomland hardwoods
Climate influence:
- warm springs may cause eggs to hatch before oak leaves burst, which may kill caterpillars (33)
- warming climate may cause upward altitudinal shifts in outbreaks (34)
Resources:
FS Fact Sheet
Biology, ecology, and biological control program
Information by disease
Ecology and distribution in US: Non-native, spreading Map
Hosts: American beech (Fagus grandifolia) and European beech (F. sylvatica)
Forest type: Northern hardwoods, bottomland hardwoods, mixed hardwoods
Climate influence:
- mild winters and dry autumn weather may favor establishment and infestation of the scale (35)
- more winter days above freezing may increase fungal infection (36)
Resources:
FS Fact Sheet
Biology, ecology, spread, and impact
Management
Ecology and distribution in US: Unknown, spreading
Hosts: Bur oak (Quercus macrocarpa), especially var. oliviformis
Forest type: Urban, upland oak-hickory, oak-pine
Climate influence:
- models predict decreased tree mortality from this pest under future climate scenarios (CMIP3, A1B) (37)
- above average spring rain may increase the incidence and severity of this disease (38)
Resources:
FS Fact Sheet
Biology, ecology, and management
Ecology and distribution in US: Non-native, spreading Distribution Map
Hosts: Elms (Ulmus spp.), U. americana is especially vulnerable
Forest type: Urban, northern hardwoods, mixed hardwoods, bottomland hardwoods
Climate influence:
- weather that stresses/weakens host may attract elm bark beetles (39)
- warmer temperatures may increase defoliation caused by the disease in Ulmus procera (40)
- warmer temperatures may increase the severity of stem infection (41)
Resources:
FS Fact Sheet: Dutch Elm Disease
FS Fact Sheet: Elm Bark Beetles
History and ecology
Identification, biology, and management
Ecology and distribution in US: Likely non-native, spreading Distribution Map
Hosts: Oaks (Quercus spp.), especially red oaks (subgenus Erythrobalanus)
Forest type: Urban, oak-hickory, oak-pine, bottomland hardwood
Climate influence:
- severe storms or any activity that creates fresh wounds that leak sap, especially in spring and early summer, will attract the vector and spread the disease (FS Fact Sheet
Symptoms, disease cycle, and management
Additional resource on symptoms, disease cycle, and management
Ecology and distribution in US: Diplodia origin unknown; Sirococcus native
Hosts: Several pines (Pinus spp.), especially red pine (P. resinosa), Austrian pine (P. nigra), and Scots pine (P. sylvestris)
Forest type: Urban, red pine, mixed pine
Climate influence:
- warmer winter temperatures and increased summer rainfall are positively correlated with disease incidence (42)
- disease caused by Diplodia can develop rapidly after hail storms and other weather events that cause branch damage (43)
Resources:
FS Fact Sheet, Diplodia pinea
FS Fact Sheet, Sirococcus conigenus
Ecology and distribution in US: Native
Hosts: Many tree species
Forest type: Many forest types
Climate influence:
- higher temperatures, more frequent and severe drought, increased insect defoliation, or events/agents that stress/weaken trees are predicted to increase disease incidence and severity (44)
Resources:
FS Fact Sheet
Ecology and distribution in US: Non-native, spreading (Map)
Hosts: White pines (Pinus spp.), especially P. strobus in the eastern US; alternate host: currant and gooseberry (Ribes spp.)
Forest type: Many forest types
Climate influence:
- models predict decreased tree mortality from this pest in the eastern US under future climate scenarios (CMIP3, A1B) (45)
Resources:
FS Fact Sheet
Disease cycle and management
History, impact, and tree resistance