Wind-related Mortality Research Articles

Genetic diversity, population structure, and effective population size in two yellow bat species in south Texas.

There are increasing concerns regarding bat mortality at wind energy facilities, especially as installed capacity continues to grow. In North America, wind energy development has recently expanded into the Lower Rio Grande Valley in south Texas where bat species had not previously been exposed to wind turbines. Our study sought to characterize genetic diversity, population structure, and effective population size in Dasypterus ega and D. intermedius, two tree-roosting yellow bats native to this region and for which little is known about their population biology and seasonal movements. There was no evidence of population substructure in either species. Genetic diversity at mitochondrial and microsatellite loci was lower in these yellow bat taxa than in previously studied migratory tree bat species in North America, which may be due to the non-migratory nature of these species at our study site, the fact that our study site is located at a geographic range end for both taxa, and possibly weak ascertainment bias at microsatellite loci. Historical effective population size (NEF) was large for both species, while current estimates of Ne had upper 95% confidence limits that encompassed infinity. We found evidence of strong mitochondrial differentiation between the two putative subspecies of D. intermedius (D. i. floridanus and D. i. intermedius) which are sympatric in this region of Texas, yet little differentiation using microsatellite loci. We suggest this pattern is due to secondary contact and hybridization and possibly incomplete lineage sorting at microsatellite loci. We also found evidence of some hybridization between D. ega and D. intermedius in this region of Texas. We recommend that our data serve as a starting point for the long-term genetic monitoring of these species in order to better understand the impacts of wind-related mortality on these populations over time.

Estimation of spatiotemporal trends in bat abundance from mortality data collected at wind turbines.

Renewable energy sources, such as wind energy, are essential tools for reducing the causes of climate change, but wind turbines can pose a collision risk for bats. To date, the population‐level effects of wind‐related mortality have been estimated for only 1 bat species. To estimate temporal trends in bat abundance, we considered wind turbines as opportunistic sampling tools for flying bats (analogous to fishing nets), where catch per unit effort (carcass abundance per monitored turbine) is a proxy for aerial abundance of bats, after accounting for seasonal variation in activity. We used a large, standardized data set of records of bat carcasses from 594 turbines in southern Ontario, Canada, and corrected these data to account for surveyor efficiency and scavenger removal. We used Bayesian hierarchical models to estimate temporal trends in aerial abundance of bats and to explore the effect of spatial factors, including landscape features associated with bat habitat (e.g., wetlands, croplands, and forested lands), on the number of mortalities for each species. The models showed a rapid decline in the abundance of 4 species in our study area; declines in capture of carcasses over 7 years ranged from 65% (big brown bat [Eptesicus fuscus]) to 91% (silver‐haired bat [Lasionycteris noctivagans]). Estimated declines were independent of the effects of mitigation (increasing wind speed at which turbines begin to generate electricity from 3.5 to 5.5 m/s), which significantly reduced but did not eliminate bat mortality. Late‐summer mortality of hoary (Lasiurus cinereus), eastern red (Lasiurus borealis), and silver‐haired bats was predicted by woodlot cover, and mortality of big brown bats decreased with increasing elevation. These landscape predictors of bat mortality can inform the siting of future wind energy operations. Our most important result is the apparent decline in abundance of four common species of bat in the airspace, which requires further investigation.

The Long-Term Effects of Wind Disturbance on a Sitka Spruce-Western Hemlock Forest

Wind is an important disturbance in many forested regions, but research has largely focused on immediate to short-term (<10 years) effects on species composition and structure of stands and landscapes. We used a set of ten, 0.4-ha plots established in 1935 and measured every 5–13 years to examine the cumulative effects of multiple wind disturbance events in the coastal forests of Oregon. Since 1935 there have been ten documented wind events in coastal Oregon with hurricane-force winds. Most of the eight windstorms since 1962 noticeably influenced at least one plot; however, no individual storm clearly influenced all plots. Net rate of biomass accumulation of plots was negative when biomass mortality exceeded 29–41 Mg/ha per 5-year period (or 3.4%–5.8% per 5 years). In contrast, wind disturbance did not clearly reduce NPP (Net Primary Production) in any plot until biomass mortality exceeded 50%. Major wind-related mortality episodes in individual plots did not necessarily strongly influence the average loss of biomass across all plots. For example, a biomass loss of 88% in one plot resulted in an average loss of only 3.4% across all plots. In contrast, the cumulative effect of multiple plots with repeated wind-related mortality did decrease biomass at the multi-plot level. Depending on the plot, wind caused 16%–59% of the total mortality over time, and the proportion of wind-related mortality has increased 5- to 8-fold since 1940. The majority (80%) of wind-related mortality was “immediate”, but some trees survived up to 35 years after being significantly wind damaged. Despite western hemlock having a wind-related mortality rate that was at least twice that of Sitka spruce, the number of stems of the former species increased over time. This trend may be related to the predominant recovery mechanism which was the release of existing small trees and the fact that the majority of ingrowth was western hemlock. This study suggests that wind disturbance is a heterogeneous, gradual process and that while individual events have a detectable impact on structure and function, the largest impacts, at least in systems where it reoccurs each decade, are cumulative.

Reserve tree mortality in two expanding-gap silvicultural systems 20 years after establishment in the Acadian forest of Maine, USA

Land managers are increasingly called upon to maintain ecosystem function and restore late-successional forest structures by retaining trees (“reserves”) in harvest prescriptions. Such retention practices often result in mortality of reserve trees owing to increased exposure to wind and ‘gap shock’, thereby compromising management objectives. This study investigated the mortality of reserve trees (n=787) retained over 20years in the Acadian Forest Ecosystem Research Project (AFERP), a long-term ecological forestry experiment in central Maine, USA. Cumulative mortality across 18 species was very low (8.4%±3.3%, mean±SD) relative to similar studies throughout the world. Annualized mortality of reserve trees of the two silvicultural systems was 1.1% for the large-gap treatment and 0.4% for the small-gap treatment. Cumulative mortality of Tsuga canadensis was lowest (2%) among species with >50 individuals, while the cumulative mortality of Thuja occidentalis was highest at 19%. Over 59% of cumulative mortality was wind-related. Annualized wind-related mortality of the reserve trees was 0.6% in the large-gap treatment and 0.2% in the small-gap treatment. More vigorous trees showed lower mortality rates. Cumulative mortality and wind-related deaths were somewhat higher in large gaps, and were influenced by spatial position within gaps. The non-traditional, expanding-gap, multi-aged silvicultural systems in this study may explain the lower incidence of windthrow and gap shock experienced by reserve trees relative to the annualized mortality rates from studies of similar, though predominantly single-cohort, silvicultural systems.

Growth and mortality of balsam fir- and spruce-tolerant hardwood stands as influenced by stand characteristics and spruce budworm defoliation

Balsam fir (Abies balsamea (L.) Mill.)-tolerant hardwood and spruce (Picea sp.)-tolerant hardwood stands were compared along a gradient of hardwood composition (12–82%). Using permanent sample plot data, influences of stand hardwood content, past spruce budworm (Choristoneura fumiferana Clem.) defoliation, insecticide spraying, and stand and site characteristics on survivor growth and mortality of the fir–spruce (spruce budworm host species) component of these stands were determined. Balsam fir basal area, spruce basal area, and percent hardwood were significantly related to fir–spruce survivor growth. Balsam fir mixedwood plots had four to five times higher fir–spruce cumulative mortality (3.7–13.3m2ha−1) than spruce mixedwood plots (1.0–2.9m2ha−1) from 1990 to 2004, and sustained higher wind-related mortality after the budworm outbreak ended in the late 1980s to early 1990s. A mortality regression tree model indicated that initial balsam fir basal area, % tolerant hardwood basal area, maximum cumulative defoliation from 1983 to 1987, and spruce budworm outbreak zone (north, central, south New Brunswick) all significantly influenced fir–spruce mortality. Results demonstrated differences in stand dynamics between these stand types, with lower spruce budworm vulnerability and higher longevity and more stable structure of spruce mixedwood than of fir mixedwood.

Temporal Patterns of Oak Mortality in a Southern Appalachian Forest (1991–2006)

The sustainability of eastern oak-dominated forests is threatened by high oak mortality rates and widespread oak regeneration failure, and presents a challenge to natural area managers. We tracked the rate and cause of mortality of 287 mature oak trees of five species for 15 years to determine the temporal patterns and sources of mortality. We observed a 15.3% total mortality rate during the study period. Mortality was due to oak decline (7.3% of trees) and high-intensity wind events (6.6% of trees). Decline-related mortality was gradual, averaging 0.5% annually. Windthrow was episodic, occurring during hurricane-related weather events in 1995 and 2004. Within species, total mortality was disproportionately high for scarlet oak (Quercus coccinea Muenchh) (41.2%) compared to other species in the red oak group (13.8% for northern red oak (Q. rubra L.); 12.5% for black oak (Q. velutina Lam.)) or the white oak group (10.4% for white oak (Q. alba L.); 5.7% for chestnut oak (Q. prinus L.)). Decline-related mortality was highest for scarlet oak (15.7%) followed by black oak (8.3%), white oak (7.5%), northern red oak (6.9%), and chestnut oak (2.3%). Within the red oak group, the average age of decline-affected and surviving trees did not differ, but average dbh of decline-affected trees was smaller. Decline-affected trees in the white oak group were on average older, but average dbh did not differ from surviving trees. Wind-related mortality also was higher for scarlet oak (21.6%) than for northern red oak (5.2%), black oak (4.2%), white oak (3.0%) or chestnut oak (2.3%). Windthrown red oaks were smaller than survivors, but windthrown trees in the white oak group did not differ in size from survivors. Average age did not differ between windthrown and surviving trees for either group. Oak mortality rates observed in this study, coupled with oak regeneration failure, could result in a substantial reduction in the proportion of mature canopy oaks and change the relative abundance of oak species in southern Appalachian forests over the long-term.

Coarse woody debris mass dynamics in temperate natural forests of Mt. Jumbong, Korea

Coarse woody debris (CWD) mass dynamics in three temperate natural forests, dominated by Quercus mongolica, Abies holophylla, and Pinus densiflora, were studied for 5 to 8 years in a Korea National Long-Term Ecological Research (KNLTER) site located in Mt. Jumbong, Korea. CWD mass (Mg/ha), input rate of CWD mass (Mg <TEX>$ha^{-1}\;y^{-1}$</TEX>), and decay rate constant (1/y) were 20.6, 1.20, and 0.058 for Q. mongolica forest, 12.2, 0.44, 0.106 for A. holophylla forest, and 5.0, 0.00, and 0.086 for P. densiflora forest, respectively. CWD mass was classified into species, types (log, snag, and stump), and decay classes (I-V). The proportion of logs was higher than that of the other CWD types in Q. mongolica forest because of wind-related mortality, whereas the proportion of logs was similar to the proportion of snags in A. holophylla forest and P. densiflora forest. CWD mass, input rate, decay rate, and distribution reflected the status of forest regeneration and succession for three forests. Mass dynamics were affected interactively by a variety of factors including species, microclimate, and topography, but these effects were hardly distinguishable in this study because of the limited number of comparable sites and pieces of CWD. Thus, further studies will require data regarding long-term microclimate and CWD mass dynamics in a variety of forest types, which could represent diverse environmental factors.

Legacy of Insect Defoliators: Increased Wind-Related Mortality Two Decades After a Spruce Budworm Outbreak

Abstract Effects of spruce budworm (Choristoneura fumiferana Clem.) outbreaks on growth and survival of balsam fir (Abies balsamea [L.] Mill.) and spruce (Picea spp.) are well documented, but few studies extend beyond 10 years after defoliation ceased. We used inventory data from 106 permanent sample plots in &amp;gt;50-year-old balsam fir stands in northern New Brunswick, Canada, to determine legacy effects of the 1969–1993 budworm outbreak on stand development up to 29 years after defoliation ceased. Defoliation data were from annual aerial surveys from 1945 to 1993 and plot ground sampling from 1985 to 1993. Plots were stratified into net stand volume development categories (decreasing, stable, and increasing 1985–2005 stemwood volume) and related to outbreak phases (outbreak, direct 1–10 years after defoliation ceased, and legacy &amp;gt;10 years), outbreak severity (1–4 [low], 5–8 [medium], and 9–12 [high] years of defoliation), and stand age (mature and overmature). Stand age was an important factor influencing outbreak severity (e.g., r2 = 0.383, P &amp;lt; 0.01). Trend and rate of volume development over time were related to past outbreak severity and increased rate of postoutbreak wind-related mortality, which peaked at 11 m3/ha/yr 11–15 years after defoliation ceased. Results indicate that aging postoutbreak stands are more vulnerable to wind disturbance events, effecting rapid stand decline.

Spatiotemporal patterns of mortality in declining balsam fir and spruce stands

We used spatiotemporal inventory data from declining balsam fir ( Abies balsamea (L.) Mill.) and spruce ( Picea spp.) stands in New Brunswick, Canada, to determine the extent of tree-to-tree interactions and their effect on individual-tree mortality and stand break-up. Fifty circular 11.3 m radius permanent sample plots, established from 1987 to 1989 and remeasured every 3–5 years, were stem-mapped for tree and dead wood data in 2003–2005. Data included 1332 live trees and 1160 dead trees. Tree-to-tree interactions were assessed for trees within a 5 m circle of all subject trees in 12 m × 12 m subplots. Logistic regression models of individual-tree mortality were generated for two analysis periods, corresponding to about the end of a spruce budworm ( Choristoneura fumiferana (Clem.)) outbreak (1990–1992) and about 10 years after the cessation of budworm defoliation (1999–2003). From 1990–1992, significant predictor variables included annual diameter increment, moderate–severe spruce budworm defoliation, and stem defects. The mortality model also includes a distance-dependent competition index that outperformed all other measures of competition. By 1999–2003, annual diameter growth had increased by 30% following cessation of defoliation. Predictors of individual-tree mortality of trees alive in 1999–2003 included stem defects and annual wind-related mortality of neighbouring trees. Wind damage was the primary cause of death, and increased as canopies became more open. Treefall events occurred mostly in the winter, as indicated by alignment of easterly treefall direction with winter prevailing winds. Dead treefall collisions accounted for 1.1% of tree deaths and damaged 1.3% of live trees. Mortality model results suggest that when stands reach a critical stage of decline, probability of mortality for residual trees is dramatically increased due to absence of protection from neighbouring trees and increased wind exposure, effecting rapid stand break-up.

Red Spruce Dynamics in an Old Southern Appalachian Forest

BUSING, R.T. (U.S. Geological Survey, 200 SW 35h St., Corvallis, OR 97333). Red spruce dynamics in an old southern Appalachian forest. J. Torrey Bot. Soc. 131: 337-342. 2004.-By the late 1980s the composition and structure of forest stands in the southern Appalachian spruce-fir zone were altered by insect infestations to Fraser fir. The response of red spruce, the sole remaining coniferous forest dominant, to this disturbance was followed over twenty years (1983-2003) in an old spruce-fir forest at Mt. Collins, Great Smoky Mountains National Park. Although diameter growth of canopy red spruce (>30 cm dbh) at six plot sites was considerable (mean 10-yr increment 2.1 cm; 1993-2003), red spruce mortality increased sharply (mean 4% yr-'; 1993-2003). Wind-related mortality of canopy red spruce was substantial after the loss of Fraser fir from the canopy circa 1985 (>70% of the dead spruce had broken or uprooted boles; 1983-2003). Wind damage to red spruce was observed at most plot sites, but it was most pronounced on exposed topographic positions, where canopy gap expansion was extensive. The elevated mortality of red spruce at Mt. Collins was not associated with reduced diameter growth. Altered canopy structure has left large red spruce vulnerable to high winds. With the loss of canopy fir and the subsequent increase in mortality of canopy spruce, total live basal area has declined to about half of its pre-disturbance level.

Causes of spatial patterns of dead trees in forest fragments in Illinois

Natural disturbances introduce spatial heterogeneity into forests by causing non-random mortality of trees. We examined whether wind was the primary cause of spatial patterns of dead trees at fragment- and individual tree-levels in three fragments of temperate deciduous forests in Illinois, USA. Dead trees and wind-caused types of mortality were expected to be higher at forest edges, on windward aspects, in poorly-drained soils, and adjacent to existing canopy gaps. The extent of wind-related mortality was determined by comparing spatial and temporal patterns of dead trees, as well as characteristics of trees downed by single windstorms versus all dead trees. At the fragment-level, we used randomly located quadrats of 25×25 m to sample edge and interior areas of Trelease Woods, Brownfield Woods, and Hart Woods in 1995-1996 and again in 1999-2000. We noted type of mortality (standing dead, snapped-off, or uprooted trees), and measured DBH (≥ 10 cm) and direction of fall of each dead tree. The same measures were made for trees felled by two single storms in 1994. At the individual tree-level, domino effects were evaluated by comparing openness surrounding target treefalls vs. an equal sample size of living trees. The study provided limited evidence that wind caused spatial patterns of dead trees. Instead, spatial patterns of dead trees in the fragments accumulated from domino effects at the individual tree-level in two of the three fragments. Dead trees were more associated with preexisting gaps. Contrary to our predictions at the fragment-level, the frequency of dead trees was not greater at edges, on windward aspects, or in poorly drained soils. This study demonstrated the complexity of spatial patterns of dead trees in forest fragments. The significant domino effects indicated that the occurrence of dead trees was not random, but determined by previous disturbances.

Mortality trends in a southern Appalachian red spruce population

Mortality of red spruce ( Picea rubens Sarg.) was assessed in an old-growth spruce-fir forest before and after adelgid-induced mortality of canopy fir at about 1985. Mortality rates of red spruce canopy trees remained low (less than 2% year −1) following the loss of fir from the canopy. However, the proportion of mortality attributable to wind increased from less than 60 to 90%. Transects placed in areas of concentrated wind damage revealed that uprooting or snapping accounted for 94% of the mortality of spruce canopy trees in the winter of 1987–1988. The transect data were biased toward wind-damaged areas and revealed the potential impact of wind-related mortality on spruce. There was no evidence of atypically high wind velocities in the general area, or of a decline in the radial growth of spruce trees prior to death. It was concluded that the loss of Fraser fir ( Abies fraseri (Pursh) Poir.) from adelgid infestation has increased wind exposure to the remaining canopy trees. The increased exposure of southern Appalachian red spruce to wind must be considered in studies of its health.

Electron scattering and transport transport phenomena in small- gap zinc-blende semiconductors

Land managers are increasingly called upon to maintain ecosystem function and restore late-successional forest structures by retaining trees (“reserves”) in harvest prescriptions. Such retention practices often result in mortality of reserve trees owing to increased exposure to wind and ‘gap shock’, thereby compromising management objectives. This study investigated the mortality of reserve trees (n = 787) retained over 20 years in the Acadian Forest Ecosystem Research Project (AFERP), a long-term ecological forestry experiment in central Maine, USA. Cumulative mortality across 18 species was very low (8.4% ± 3.3%, mean ± SD) relative to similar studies throughout the world. Annualized mortality of reserve trees of the two silvicultural systems was 1.1% for the large-gap treatment and 0.4% for the small-gap treatment. Cumulative mortality of Tsuga canadensis was lowest (2%) among species with >50 individuals, while the cumulative mortality of Thuja occidentalis was highest at 19%. Over 59% of cumulative mortality was wind-related. Annualized wind-related mortality of the reserve trees was 0.6% in the large-gap treatment and 0.2% in the small-gap treatment. More vigorous trees showed lower mortality rates. Cumulative mortality and wind-related deaths were somewhat higher in large gaps, and were influenced by spatial position within gaps. The non-traditional, expanding-gap, multi-aged silvicultural systems in this study may explain the lower incidence of windthrow and gap shock experienced by reserve trees relative to the annualized mortality rates from studies of similar, though predominantly single-cohort, silvicultural systems.