Extensive Tree Mortality Research Articles

US Forest Service Bark Beetle Research in the Western United States: Looking Toward the Future

Abstract Bark beetles cause extensive tree mortality in coniferous forests of western North America and play an important role in the disturbance ecology of these ecosystems. Recently, elevated populations of bark beetles have been observed in all conifer forest types across the western United States. This has heightened public awareness of the issue and triggered legislation for increased funding for state and federal agencies to address issues associated with bark beetle outbreaks. Recently, US Forest Service, Research and Development entomologists from the western research stations met with US Forest Service, State and Private Forestry, Forest Health Protection entomologists, our primary stakeholder, to identify bark beetle research priorities. These include vegetation management; ecological, economic, and social consequences of outbreaks; fire and bark beetle interactions; effects of climate change on bark beetle populations; and chemical ecology.

Ant predation on red oak borer confirmed by field observation and molecular gut‐content analysis

Abstract1 Populations of an indigenous longhorn beetle, the red oak borer Enaphalodes rufulus (Haldeman) (Coleoptera: Cerambycidae), recently reached epidemic levels in the Ozark National Forests of Arkansas and Missouri, resulting in extensive tree mortality.2 The factors regulating E. rufulus populations are largely unknown. Ants appear to be the most abundant potential predators in the Ozarks and have been shown to play a role in regulating populations of other forest insects.3 The main objective of the present study was to determine whether ants are predators of early E. rufulus life stages by direct observation of E. rufulus eggs artificially placed on tree trunks and by development of molecular tools to detect E. rufulus DNA within ant gut contents.4 Three hundred and eighty E. rufulus eggs were applied to ten northern red oaks. Ants ate or carried away 72% of the eggs within 1 h. Camponotus pennsylvanicus (De Geer) and Aphaenogaster tennesseensis (Mayr) were identified as the two primary ant species observed in the study.5 A portion of the mitochondrial 16S rRNA gene of E. rufulus was sequenced and polymerase chain reaction primers were developed to detect E. rufulus DNA in the guts of C. pennsylvanicus. Enaphalodes rufulus DNA persisted in ant gut contents for at least 24 h after ingestion under laboratory conditions, and E. rufulus DNA was detected in field‐collected ant populations, suggesting the natural occurrence of ant predation on this insect.

Change in the forested and developed landscape of the Lake Tahoe basin, California and Nevada, USA, 1940–2002

The current ecological state of the Lake Tahoe basin has been shaped by significant landscape-altering human activity and management practices since the mid-1850s; first through widespread timber harvesting from the 1850s to 1920s followed by urban development from the 1950s to the present. Consequences of landscape change, both from development and forest management practices including fire suppression, have prompted rising levels of concern for the ecological integrity of the region. The impacts from these activities include decreased water quality, degraded biotic communities, and increased fire hazard. To establish an understanding of the Lake Tahoe basin's landscape change in the context of forest management and development we mapped, quantified, and described the spatial and temporal distribution and variability of historical changes in land use and land cover in the southern Lake Tahoe basin (279 km 2) from 1940 to 2002. Our assessment relied on post-classification change detection of multi-temporal land-use/cover and impervious-surface-area data that were derived through manual interpretation, image processing, and GIS data integration for four dates of imagery: 1940, 1969, 1987, and 2002. The most significant land conversion during the 62-year study period was an increase in developed lands with a corresponding decrease in forests, wetlands, and shrublands. Forest stand densities increased throughout the 62-year study period, and modern thinning efforts resulted in localized stand density decreases in the latter part of the study period. Additionally forests were gained from succession, and towards the end of the study period extensive tree mortality occurred. The highest rates of change occurred between 1940 and 1969, corresponding with dramatic development, then rates declined through 2002 for all observed landscape changes except forest density decrease and tree mortality. Causes of landscape change included regional population growth, tourism demands, timber harvest for local use, fire suppression, bark beetle attack, and fuels reduction activities. Results from this study offer land managers within the Lake Tahoe basin and in similar regions a basis for making better informed land-use and management decisions to potentially minimize detrimental ecological impacts of landscape change. The perspective to be gained is based on quantitative retrospection of the effects of human-driven changes and the impacts of management action or inaction to the forested landscape.

Susceptibility of ponderosa pine, Pinus ponderosa (Dougl. ex Laws.), to mountain pine beetle, Dendroctonus ponderosae Hopkins, attack in uneven-aged stands in the Black Hills of South Dakota and Wyoming USA

Mountain pine beetle, Dendroctonus ponderosae Hopkins can cause extensive tree mortality in ponderosa pine, Pinus ponderosa Dougl. ex Laws., forests in the Black Hills of South Dakota and Wyoming. Most studies that have examined stand susceptibility to mountain pine beetle have been conducted in even-aged stands. Land managers increasingly practice uneven-aged management. We established 84 clusters of four plots, one where bark beetle-caused mortality was present and three uninfested plots. For all plot trees we recorded species, tree diameter, and crown position and for ponderosa pine whether they were killed or infested by mountain pine beetle. Elevation, slope, and aspect were also recorded. We used classification trees to model the likelihood of bark beetle attack based on plot and site variables. The probability of individual tree attack within the infested plots was estimated using logistic regression. Basal area of ponderosa pine in trees ≥25.4 cm in diameter at breast height (dbh) and ponderosa pine stand density index were correlated with mountain pine beetle attack. Regression trees and linear regression indicated that the amount of observed tree mortality was associated with initial ponderosa pine basal area and ponderosa pine stand density index. Infested stands had higher total and ponderosa pine basal area, total and ponderosa pine stand density index, and ponderosa pine basal area in trees ≥25.4 cm dbh. The probability of individual tree attack within infested plots was positively correlated with tree diameter with ponderosa pine stand density index modifying the relationship. A tree of a given size was more likely to be attacked in a denser stand. We conclude that stands with higher ponderosa pine basal area in trees >25.4 cm and ponderosa pine stand density index are correlated with an increased likelihood of mountain pine beetle bark beetle attack. Information form this study will help forest managers in the identification of uneven-aged stands with a higher likelihood of bark beetle attack and expected levels of tree mortality.

The influence of disturbance events on pileated woodpeckers in Northeastern Oregon

The pileated woodpecker ( Dryocopus pileatus) is a species of conservation concern and an indicator of mature and old forest habitat conditions in the Pacific Northwest. The effects of natural and human-caused disturbance on density of nesting pairs, reproductive success, and traditional home ranges were compared over 30 years in two areas and over 15 years in five additional areas. In one study area, density of nesting pairs of pileated woodpeckers decreased from five to one after extensive regeneration cuts eliminated most of the stands of mature and old-growth grand fir ( Abies grandis) and reduced the density of nest and roost trees and foraging substrate since 1990. Density of nesting pairs, reproductive success, and home range location remained fairly consistent over 30 years in a second study area with extensive tree mortality resulting from insect outbreaks but without regeneration harvests. The amount of unharvested stands and closed canopy stands in home ranges were positively correlated with reproductive success, and the amount of area in harvested stands was negatively correlated with reproductive success in 2003–05. High tree mortality and subsequent loss of canopy closure in stands of grand fir and Douglas-fir from insect outbreaks did not appear to be detrimental to pileated woodpeckers provided that dead trees and logs were abundant and that stands were not harvested.

Insect-induced tree dieback and mortality gaps in high-altitude balsam fir forests of northern New England and adjacent areas

:In recent decades, high-altitude balsam fir (Abies balsamea) forests of northern New England and adjacent areas have been fragmented by canopy openings associated with several stand disturbances. To document the causes of extensive tree dieback and mortality and the source of canopy gaps, we studied the tree growth patterns of live balsam fir from five stands in four sites in the northeastern United States (NUS): Whiteface Mtn. in New York state and Mt. Moosilauke (two stands), Mt. Blue, and Mt. Lafayette in New Hampshire. Additionally, tree-ring patterns of dead fir were documented at two sites, Whiteface Mtn. and Mt. Mégantic (southern Québec). Organic horizons from four of the five NUS stands were analyzed for identification of insect remains and plant macrofossils in 11 and seven soil cores, respectively. Four of the five balsam fir tree-ring chronologies from the NUS stands showed a major growth decline in the 1970s, which was also apparent in the two chronologies from dead trees at Whiteface Mtn. and Mt. Mégantic. At the NUS stands, spruce budworm (Choristoneura fumiferana) head capsules were found in all 11 soil cores from forest and open stands. In spite of large variations in the number of head capsules among levels (range: 1–34; mean: 9.5 ± 8.8 for 71 levels analyzed), their occurrence at all the levels analyzed indicates that the insect had sustained activity through time. Macrofossil remains from the organic horizons included plant assemblages similar to the aboveground forest vegetation. Rubus idaeus, an intolerant species, indicated that gap conditions prevailed sometime in the past. Our tree-ring and macrofossil data along with insect surveys from northern New England provide evidence for the major role played by spruce budworm in tree dieback and mortality during infestations and subsequent gap formation in high-altitude fir forests. The impact of other stand disturbance factors is discussed.

Mistletoe ( Viscum album) in the fir forest of Mount Parnis, Greece

In the fir forest of Mount Parnis 67.67% of the overstorey trees were found infected by the mistletoe ( Viscum album). The “6-class” rating system was used to quantify the degree of tree infection. The most intensive mistletoe infection was observed on old age trees. Extensive tree mortality was observed during the years 2000–2002. Low precipitation in two consecutive years (2000–2001) was an important parameter that affected tree mortality. Fir trees were attacked by the bark beetles Phaenops knoteki (Buprestidae) and Pityokteines spinidens (Scolytidae). Mistletoe is an important factor that reduces tree vigour and predisposes trees to beetle attacks during periods of low precipitation. Tree mortality was correlated with the degree of mistletoe infection. During a 5-year-period (1998–2002), mortality of trees with heavy and medium mistletoe infection was 44.44%, while mortality of trees with light infection was 9.5% and that of the non-infected trees 4.66%.

The Western Pine Beetle and Forest Health: Historical Approaches and Contemporary Consequences

During the 20th century, forest entomologists developed a knowledge base about the impact of various insects on tree species, most often with an eye toward controlling those that caused the greatest damage to forest resources. Based in part on extensive tree mortality attributable to insect activity and identified by forest entomologists, contemporary forest managers have concluded that parts of America’s forests are undergoing a health crisis (Brooks 1996); however, concerns about forest health are not novel to recent decades, but can be traced to the beginning of the 20th century. In the early decades of the past century, forest entomologists used terms that centered on the metaphor of health in their research on the biology, ecology, and control of forest insects. Researchers focused on tree growth as one of the best ways to assess the impact of insects on the forest; and this, in turn, served as a basis for decisions about control measures. Trees with reduced vigor are more vulnerable to insect damage; and tree mortality, when it occurs on a large enough scale, lowers the overall productivity of the forest. The control methods devised to protect forest resources from insect damage reflected the focus and emphasis on tree vigor or part of what contemporary forest managers would include under the broader umbrella of “forest health.” Forest entomologists helped to develop control methods, such as sanitation logging, to improve the overall health of a given stand. In this article, I focus on bark beetles and the western pine beetle, Dendcroctonus The Western Pine Beetle and Forest Health: Historical Approaches and Contemporary Consequences

Structural differences between forests regenerating following spruce budworm defoliation and clear-cut harvesting: implications for marten

American marten (Martes americana Turton) avoid recent clearcuts when establishing territories but do not avoid similarly aged stands with a history of extensive tree mortality caused by the eastern spruce budworm (Choristoneura fumiferana Clem.). We quantified differences in overstory vegetation, understory vegetation, and coarse woody debris between stands that were clear-cut or defoliated by spruce budworms 10-20 years prior to our study. Our objectives were to identify habitat features with functional significance for marten that were lacking in managed stands and to propose goals for silvicultural practices that more closely resemble a natural disturbance (insect defoliation), thus improving habitat quality for marten. In contrast to regenerating clearcuts, defoliated stands had greater volumes of snags, downed logs, and root masses and included taller trees. Although live-tree basal area was similar between stand types, our results suggest that vertical structure provided by large snags can offset limited availability of live trees for marten, particularly where coarse woody debris and understory vegetation are plentiful. In stands under even-aged management, habitat quality for marten may be enhanced by retention of >18 m2/ha cull trees and snags. Uneven-aged silvicultural systems, which more closely mimic natural disturbance by defoliating insects, may have particular promise for maintaining marten habitat.

Wildfire in Russian Boreal Forests—Potential Impacts of Fire Regime Characteristics on Emissions and Global Carbon Balance Estimates

Most of the research about the effects of the release of carbon and other chemicals to the atmosphere during forest fires focuses on emissions from crown fires or slash fires in which a high percentage of the fine fuels are burned. However, in many temperate and boreal conifer ecosystems, surface fires of varying intensities and severities are an important part of the fire regime. In Russia a large percentage of the area burned in a typical year is in surface fires, which will result in lower carbon emissions than crown fires because of lower fuel consumption. In Russian boreal forest, different distribution patterns of fire severity across the landscape could produce fourfold differences in carbon release. Furthermore, tree mortality after surface fires is often quite extensive, leading to a pulse in carbon release as needles and other fine fuels fall to the ground and decompose. With extensive tree mortality, a decrease in carbon sequestration is expected for several years, until stand level photosynthesis returns to prefire levels. Perhaps the largest potential source of error in estimates of carbon release from biomass fires in Russia is inaccuracy in estimates of burned area. Many published estimates of annual burned area in Russia may be extremely low. On the basis of information on fire return intervals and area of boreal forest, 12 million ha per year may be a reasonable conservative estimate of burned area until better data are available. Based on this estimate, direct and indirect fire-generated carbon emissions from boreal forests worldwide may exceed 20% of the estimated global emissions from biomass burning, making them an important component in understanding global atmospheric chemistry. In considering effects of fire on global atmospheric chemistry, it is important to include the effects of fire severity, postfire mortality, decomposition of fine fuels, and changing postfire vegetation structure as components of fire-induced changes in ecosystem- level carbon flux. But the most important factor may be accurate information on the annual area burned. Levels of carbon storage are likely to be highly sensitive to changes in fire return intervals that result from direct human activities and from climatic changes, making accurate assessments of burned areas and fire severity critical. Strong fire management programs will be key to managing future fire regimes and carbon cycling in Russia’s boreal forest.

Eastern Towhee Numbers Increase Following Defoliation by Gypsy Moths

-Bird populations and habitat were monitored each year before (1984 to 1986), during (1987 to 1988), and after (1989 to 1996) a major gypsy moth (Lymanltria dispar) outbreak in the eastern panhandle of West Virginia. Extensive tree mortality caused by repeated defoliations by gypsy moths resulted in the release of understory vegetation. Densities of Eastern Towhees (Pipilo erythrophthalmus) were significantly higher in the period following the gypsy moth outbreak. Both before and after the outbreak, Eastern Towhee densities were higher in areas of the forest with less overstory (particularly high canopy) and lower densities of live trees (particularly small trees). This indicates that not all forms of successional habitat, specifically areas with a high density of small-diameter trees, are suitable for species deemed as early successional. Although the gypsy moth outbreak resulted in an increase in the number of saplings, it also opened up the canopy and created a dense layer of shrubs in many areas. Because Eastern Towhees forage and nest on the ground and in shrubs, the outbreak increased the amount of suitable habitat for this species. Given that densities of Eastern Towhee are declining in the state, it is useful to document habitat features that are important for sustaining towhee populations. Received 13 January 1997, accepted

The pine wood nematode Bursaphelenchus xylophilus (Steiner and Buhrer) Nickle (= B. lignicolus Mamiya and Kiyohara): an assessment of the current position

Summary Pine wood nematode, Bursaphelenchus xylophilus (Steiner and Buhrer) Nickle, is the casual organism of pine wilt disease, a major tree killer in the Far East. This paper describes the biology of B. xylophilus, particularly its inter-relationships with vector insects in the genus Monochamus (Coleoptera: Cerambycidae), tree species and environmental conditions. The principal method of transmission, and hence of international plant health significance, is introduction of nematodes to susceptible dying or dead trees during female oviposition. This occurs in all countries where the nematode occurs but is the only significant method of transmission and survival of B. xylophilus in North America. Extensive tree mortality in Japan and China is associated with presence of highly susceptible tree species, suitable vector species and high summer temperatures. Pest risk assessments have been carried out to determine the risks to Europe; it is concluded that the nematode would undoubtedly survive in Europe but that tree mortality is likely only in the warmer southern countries. Methods to prevent transfer of nematodes to Europe are discussed in relation to European Union legislation.

Tectonic influences on tree growth in northern Patagonia, Argentina: the roles of substrate stability and climatic variation

In northern Patagonia, Argentina, we examined the influences of climatic variation and inter-site variation in substrate stability on the dendroecological effects of earthquakes. In association with the great earthquake in 1960 centered off the coast of nearby Valdivia, Chile, extensive tree mortality occurred in northern Patagonia in Nothofagusdombeyi–Austrocedruschilensis stands on unstable debris fans. To examine the effects of the 1960 and earlier earthquakes on tree growth, we developed tree-ring chronologies from samples of the surviving A. chilensis on unstable debris fan sites and at adjacent nonfan sites of more stable substrates. For controlling the effects of regional climatic variation, we also produced a tree-ring chronology from this species in a more distant and undisturbed stand. Strong variations in tree-growth patterns on fan sites were associated with the historically documented major seismic events of south central Chile that occurred in 1737, 1751, 1837, and 1960. Tree-ring chronologies from nonfan sites (i.e., sites of greater substrate stability) showed much less response to these earthquakes. On the fan sites, strong growth suppressions were associated with the former three earthquakes, whereas strong releases followed the 1960 earthquake. The difference in response is explained by the occurrence of the 1960 earthquake during a period of drought, which in combination with the violent shaking of the ground, resulted in extensive tree mortality followed by growth releases of the survivors. However, severe droughts in the absence of earthquakes also can produce tree mortality and subsequent release of the survivors. Consequently, the synergistic effects of climatic variation and earthquake events must be carefully considered in developing records of both climatic variation and earthquakes.

Did climatic warming trigger the onset and development of yellow‐cedar decline in southeast Alaska*

AbstractYellow cedar (Chamaecyparis nootkatensis) is a valuable tree species that is experiencing an extensive forest decline on over 200000 ha of unmanaged forest in southeast Alaska. Biotic factors appear secondary and some abiotic factor is probably the primary cause of this naturally occurring decline. A warming climate, which coincided with the onset of extensive tree mortality about 100 years ago, may have triggered one of the possible abiotic causes such as freezing damage and/or soil toxicity.

Seedling responses to forest canopy disturbance following a spruce budworm outbreak in Maine

Patterns of tree mortality and seedling responses to canopy disturbance were investigated in northern Maine, where an outbreak of the spruce budworm (Choristoneurafumiferana (Clem.)) affected the forests of balsam fir (Abiesbalsamea (L.) Mill.) and spruce (Picea spp.) continuously between 1972 and 1984. The outbreak created a gradient of canopy tree mortality that ranged between 8.5 and 100% of the cumulative basal area in 1984. This was a result of the difference in vulnerability among the host species (balsam fir > spruce) and of their spatial distribution patterns along the site drainage gradient. Two groups of plant species responded differently to the gradient of canopy disturbance: balsam fir, spruce, and white birch (Betulapapyrifera Marsh.) regenerated mostly at the intermediate levels of mortality (≈20%by basal area) of the canopy balsam fir; raspberry (Rubusidaeus L.) and pin cherry (Prunuspensylvanica L.) were most abundant at ≈100% fir mortality. Overall, the observed responses in space and time of the seedlings to budworm-caused canopy disturbance could be mostly explained by the concept of patch dynamics. Long-term changes in species composition of the spruce–fir forests cannot be predicted with precision with the present knowledge. However, I hypothesize, based on the species-specific vulnerability to budworm damage and patterns of regeneration, that the proportion of spruce to fir trees would not differ very much in the long run regardless of extensive tree mortality by the spruce budworm.

Vegetation Dynamics and Slope Management on the Mountains of the Hawaiian Islands

Lyon's conclusion (cf. 1919) with regard to the stand reduction dieback on the lower wet slope of Haleakala Mountain led to a forest management policy that saw importation of alien tree species as necessary for protecting Hawaiian watersheds. Unfortunately, this also led to a further demise of native vegetation.It is possible that the low-canopy species diversity in Hawaii may increase the rate of paludification and swamp (or bog) formation, under wet climatic conditions, over that in a similar environment with a broader spectrum of successional species. However, a boggy landscape can also be a good watershed. Historic evidence comes from the sugar-cane planters on Maui—the supposed beneficiaries of the exotic tree-planting programme—who had objected to it on empirical grounds (Holt, 1983). A more recent study of a canopy dieback in the Hilo watershed showed that extensive tree mortality had no effect on the rate and quality of the water yield from this area. The forest hydrologist, R.D. Doty (1983), who investigated this relationship, attribut ed the outcome to the vigorous undergrowth which remained intact during the dieback event.Further landscape ageing in Hawaii's shield-shaped mountains involves a process of fluviomorphic dissecting of the gentle slopes lying inland. This results first in amphitheatre-headed valleys and eventually, on the windward sides, in steep residual escarpments with numerous secondary footslopes. Wirthmann & Hüser (1987) derived details of this process from the side-by-side comparison of younger with older Hawaiian mountains. When the waterlogged surfaces of the plateau-like lower wet slopes of shield volcanoes become laterally drained, closedMetrosiderosforests can become re-established. That this natural re-establishment process works in the Hawaiian mountains can be seen by going from the shield-shaped slopes of the younger, to the more dissected slopes of the older, high islands. VigorousMetrosidewsforests occur also on the older islands, but they are typically of lower stature than those on the younger mountains.Unfortunately, most of the secondary slopes formed at the base of the steeply-cut windward mountain slopes of the older high islands have been deforested to make way for crop agriculture. Many of these lower slopes have subsequently been abandoned for economic reasons; but instead of reverting to forests, they have become invaded in many areas by alien grasses and shrubs. Particularly damaging has been the introduced pyrophytic Broomsedge (Andropogon virginicus). This grass has retained a temperate-zone phenology, whereby it undergoes partial dormancy during the winter season when rainfall increases (Sorenson, 1980). As such it has contributed to accelerated erosion in two ways: (1) by preventing recirculation of soil water in areas where excessive runoff is a problem, and (2) by attracting repeated fires and preventing succession to a forest, which would provide much-improved protection against the accelerated soil erosion (Mueller-Dombois, 1973) that is such a common feature on the lower windward slopes of the older islands.