Central British Columbia Research Articles

Migration and Winter Habitat Use of Glaucous-Winged Gulls (Larus glaucescens) from Triangle Island, British Columbia

Understanding the movements and habitat use of marine birds is essential to inform conservation and marine spatial planning. Here, satellite transmitters were used to study the migration and winter habitat use of adult Glaucous-winged Gulls (Larus glaucescens) from a colony in central British Columbia. Three of four tracked gulls overwintered locally, while the fourth followed a coastal migration route to northern California. All four gulls maintained small winter home ranges and spent an average of 72% of their time in nearshore coastal waters (average distance to coast: 0.6-1.7 km) characterized by low levels of anthropogenic activity. The remainder of their time was spent in naturally vegetated areas. One gull overwintered in an area with high human population density (northern California), with limited use of cropland (4% of locations) and urban (6% of locations) areas. This study is part of on-going efforts to understand the distribution and habitat use of marine birds throughout British Columbia to inform marine spatial planning and associated threats at various scales.

DENSITY OF FISHERS (PEKANIA PENNANTI) AT THE SOUTHWESTERN EDGE OF THE SPECIES' RANGE IN BRITISH COLUMBIA

Fishers (Pekania pennanti) are a species of conservation concern in central British Columbia for which distribution and abundance information is needed to help guide conservation efforts. We conducted a DNA-based spatial capture-recapture study in the Bridge River watershed to gain a better understanding of their density in the dry forests at the southwestern edge of the species' range in the province. We established and monitored baited hair traps at 152 sites spread throughout 771.4 km2 over 4 mo in early 2012, detecting 8 individual Fishers (3 females, 5 males) at 16 different sites. We used spatially explicit capture-recapture methods to estimate the density of Fishers to be 13.1 Fishers/1000 km2 (95% CI: 6.3 to 27.4 Fishers/1000 km2) when we constrained the plausible sampling area to biogeoclimatic zones that are known to support Fishers. This study provides resource managers and trappers with a snapshot of local Fisher densities at the southern edge of the species range in British Columbia that will help estimate sustainable harvest levels and refine the estimate of the provincial population of Fishers.

Multi-sensor change detection for within-year capture and labelling of forest disturbance

Knowledge of forest change type and timing is required for forest management, reporting, and science. Time series of historic satellite data (e.g. Landsat) have resulted in an invaluable record of changes in forest conditions. Natural resource management and reporting typically operate at an annual time step, yet the recent addition of data streams from compatible satellites (e.g., Sentinel-2) offer the possibility of generating frequent, management-relevant forest status assessments and maps of change. Analytical approaches that rely on a time series of observations to identify change often struggle to provide reliable estimates of change events in terminal years of the time series until subsequent, additional observations are available. Methods to meaningfully integrate observations from compatible satellite platforms can provide short-term information to augment and refine estimates of change area and type in those terminal years of the time series. In this research we fuse Landsat-8 and Sentinel-2A and -2B data streams to capture, with reduced latency, stand replacing forest change (harvest and wildfire), tagged to a temporal window of occurrence over an ~10,000 km2 area of central British Columbia, Canada. We introduce a new algorithm, SLIMS (Shrinking Latency in Multiple Streams), to rapidly and reliably detect change, and then use an established Bayesian approach to meaningfully combine changes detected in the Landsat and Sentinel data streams. Our results indicate that the type and timing of stand-replacing disturbances can be identified in these forests with high accuracy. Overall, 13.9% of the study area was disturbed between the end of 2016 and the end of 2017, with the majority of disturbed area attributable to wildfire and a smaller amount attributed to forest harvesting, mostly in the winter 2016–2017 with some limited summer harvest also occurring. Overall accuracy of the change, assessed using independent validation data, was 95% ± 2.3%. The capacity of these change results to augment a trend-based assessment of change for 2017 was also demonstrated and provides a framework for how short- and long-term change detection approaches provide complementary information that can increase the timeliness and accuracy of change area estimates in the terminal years of a time series. These findings also demonstrate the capacity to regard Landsat and Sentinel-2 sensors as elements of a virtual constellation to obtain forest change information in a timely (i.e., end of growing season) and reliable fashion over large areas.

Post-fire movements of Pacific marten (Martes caurina) depend on the severity of landscape change

BackgroundWildfires and forestry activities such as post-fire salvage logging are altering North American forests on a massive scale. Habitat change and fragmentation on forested landscapes may threaten forest specialists, such as Pacific marten (Martes caurina), that require closed, connected, and highly structured habitats. Although marten use burned landscapes, it is unclear how these animals respond to differing burn severities, or how well they tolerate additional landscape change from salvage logging.MethodsWe used snow tracking and GPS collars to examine marten movements in three large burns in north-central Washington, USA (burned in 2006) and central British Columbia, Canada (burned in 2010 and 2017). We also assessed marten habitat use in relation to areas salvage-logged in the 2010 burn. We evaluated marten path characteristics in relation to post-fire habitat quality, including shifts in behaviour when crossing severely-disturbed habitats. Using GPS locations, we investigated marten home range characteristics and habitat selection in relation to forest cover, burn severity, and salvage logging.ResultsMarten in the 2006 burn shifted from random to directed movement in areas burned at high severity; in BC, they chose highly straight paths when crossing salvage-blocks and meadows. Collared marten structured their home ranges around forest cover and burn severity, avoiding sparsely-covered habitats and selecting areas burned at low severity. Marten selected areas farther from roads in both Washington and BC, selected areas closer to water in the 2006 burn, and strongly avoided salvage-logged areas of the 2010 burn. Marten home ranges overlapped extensively, including two males tracked concurrently in the 2010 burn.ConclusionsAreas burned at low severity provide critical habitat for marten post-fire. Encouragingly, our results indicate that both male and female marten can maintain home ranges in large burns and use a wide range of post-fire conditions. However, salvage-logged areas are not suitable for marten and may represent significant barriers to foraging and dispersal.

The effectiveness of decommissioning roadside mineral licks on reducing moose (Alces alces) activity near highways: implications for moose–vehicle collisions

Roadside mineral licks form when road salt used to de-ice highways in winter runs off road surfaces and accumulates in roadside ditches. Some ungulates are attracted to these roadside licks as they seek to satisfy their mineral requirements. Within the distribution of moose (Alces alces (Linnaeus, 1758)) in North America, motorists often encounter moose visiting roadside licks in mid-summer, with many jurisdictions reporting summer peaks in moose–vehicle collisions (MVCs) at these locations. We used camera traps to monitor the moose visitation of 22 roadside locations (including roadside licks, roadside ponds, and dry roadsides) in central British Columbia, Canada, from December 2009 to July 2020. We tested the efficacy of treatment (decommissioning) methods used to reduce moose visitation to roadside licks and roughly estimated decommissioning costs. Moose visitation to roadside licks was greatest from May to July. As we hypothesized, untreated licks were visited more often by moose than decommissioned licks, roadside ponds (absence of road salt), and dry roadsides. Decommissioning roadside licks by replacing or mixing lick waters and soils with materials, such as riprap, cedar mulch, pine logs, or dog (Canis lupus familiaris Linnaeus, 1758) fur and human (Homo sapiens Linnaeus, 1758) hair, is an effective and inexpensive means of reducing moose visitations to roadside areas and should increase motorist safety where roadside licks are visited by moose.

CORALLORHIZA MACULATA (ORCHIDACEAE) NEW TO ALASKA AND ITS DISTRIBUTIONAL RELATIONSHIP TO CORALLORHIZA MERTENSIANA

In the Pacific Northwest, the spotted coralroot, Corallorhiza maculata (Raf.) Raf., has been recognized as occurring as far north as central British Columbia, but excluded from the flora of Alaska. The western coralroot, C. mertensiana Bong., reaches its northern range limit in Southeast Alaska, where collections of this sister species may be confused with C. maculata. In 2019-20, we conducted herbarium and field studies that verified eight C. maculata stations in northern Southeast Alaska. Two of these stations are represented by collections made in 2000 and 2007, which were identified as C. mertensiana; 14 C. mertensiana collections had been identified as C. maculata. This confusion may have resulted from nomenclatural changes, as well as rarity of actual C. maculata material. These species differ in morphological features that reflect different breeding systems, and occupy different habitats in Alaska. The Alaska stations of C. maculata represent a 650 km range extension that is disjunct from locations in central British Columbia. These stations occur in a summer-dry climate zone caused by a rainshadow from coastal mountains. We advance the hypothesis that this area provides habitat for populations of C. maculata that represent relics of a floristic migration that occurred during the Xerothermic interval 10-7500 yr BP. In contrast, C. mertensiana is widespread in humid coastal habitats in southeast Alaska, and its distribution is contiguous with more southern coastal populations. Though both species occur in Southeast Alaska, they occupy different climate zones, and their distributions are narrowly allopatric.

Ocean Indicators Predict Range Expansion of an Introduced Species: Invasion History of the European Green Crab Carcinus maenas on the North American Pacific Coast

An introduced population of European green crabs Carcinus maenas (Linneaus, 1758) was established in San Francisco Bay prior to 1991. Their subsequent northern range expansion is linked to larval transport in the Davidson Current to northern California (1993), southern Oregon (approximately 1996), the Oregon and Washington coastal estuaries and the west coast of Vancouver Island, British Columbia (1998). Range expansions through larval transport to the central British Columbia coast occurred before 2010, to Haida Gwaii in 2020, and into the inland Salish Sea in 2015 and 2016. Both the range expansions of C. maenas and local abundance are strongly linked to oceanic factors during their larval development. These include (1) strong northward flow of coastal waters during winter; (2) warm surface water temperatures (>10°C for larval development); and (3) coastal circulation patterns that keep larvae close to shore, where they can be carried by wind and tidal currents into estuaries and embayments to settle. The strongest year classes and largest range expansions occurred during the last two major El Niño events. The 1997 to 1998 El Niño resulted in the colonization of embayments in Oregon, coastal Washington, and on the west coast of Vancouver Island, while the El Niño of 2015 to 2016 and the Pacific Warm Blob are linked to the range expansion into the Salish Sea. More local range expansions along the west coast of Vancouver Island, to the central British Columbia Coast, to Haida Gwaii, and inside the Salish Sea occurred during non-El Niño years.

Channel-amphitheatre landforms resulting from liquefaction flowslides during rapid drawdown of glacial Lake Fraser, British Columbia, Canada

Unusual channel-amphitheatre landforms are present in Late Pleistocene–early Holocene, subaqueous fan and delta deposits in the glacial Lake Fraser basin, central British Columbia. The lake formed during the decay of the last Cordilleran Ice Sheet and drained ~11,500 years ago during a large outburst flood. The fronts of a delta and two subaqueous fans consisting of silt to fine sand are marked by branching networks of wide, nearly flat channels that terminate upstream in digitate, steep-walled amphitheatres. We propose that these channel-amphitheatre landforms formed by liquefaction flowslides that were induced by the rapid drawdown of glacial Lake Fraser during the outburst flood. Similar geomorphic forms, which we believe also to be associated with rapid drawdowns of large Late Pleistocene–early Holocene lakes, occur elsewhere in North America. A recent tailings dam failure and an intentional breaching of a 100-year-old hydroelectric dam provide insights into the processes responsible for the landforms. By using geomechanical analysis, we show how rapid lake drawdown can trigger liquefaction flowslides in deposits of silt to fine sand. The novelty of our approach lies in combining geomechanical reasoning with geomorphic analogues to understand histories of ancient glacier-dammed lakes and of the glacial lake outburst floods that are sourced from them.

Conservation Values and Actor Networks that Shape the Adams River Salmon Run in Tsútswecw Provincial Park, British Columbia

Sockeye salmon are deemed essential to life by Secwépemc Indigenous communities living near the Adams River in South Central British Columbia (BC). They are also an ecological keystone species and a significant contributor to the BC economy. However, salmon populations are in decline throughout the Pacific Northwest, putting communities, economies and ecosystems at risk. Using Actor-Network Theory (ANT) as a lens, we identify the network of actors connected to the Adams River salmon run, examine actor relationships, and consider the impacts these relations have on sustainable conservation practices. We use a community-based participatory research methodology and interviews to investigate the complexity of stakeholder relationships to wild Pacific salmon in BC. Based on our results, there is strong evidence to suggest that localized approaches to salmon conservation, ones guided by local experience and knowledge, are critical to developing inclusive and effective policies.

A Disrupted Historical Fire Regime in Central British Columbia

In the 2017 and 2018, 2.55 million hectares burned across British Columbia, Canada, including unanticipated large and high-severity fires in many dry forests. To transform forest and fire management to achieve resilience to future megafires requires improved understanding historical fire frequency, severity, and spatial patterns. Our dendroecological reconstructions of 35 plots in a 161-hectare study area in a dry Douglas-fir forest revealed historical fires that burned at a wide range of frequencies and severities at both the plot- and study-area scales. The 23 fires between 1619 and 1943 burned at intervals of 10–30 years, primarily at low- to moderate-severity that scarred trees but generated few cohorts. In contrast, current fire-free intervals of 70–180 years exceed historical maximum intervals. Of the six widespread fires from 1790 to 1905, the 1863 fire affected 86% of plots and was moderate in severity with patches of higher severity that generated cohorts at fine scales only. These results indicate the severity of fires varied at fine spatial scales, and offer little support for the common assertion that periodic, high-severity, stand-initiating events were a component of the mixed-severity fire regime in these forest types. Many studies consider fires in the late 1800s relatively severe because they generated new cohorts of trees, and thus, emphasize the importance of high-severity fires in a mixed-severity fire regime. In our study area, the most widespread and severe fire was not a stand-initiating fire. Rather, the post-1863 cohorts persisted due disruption of the fire regime in the twentieth century when land-use shifted from Indigenous fire stewardship and early European settler fires to fire exclusion and suppression. In absence of low- to moderate-severity fires, contemporary forests are dense with closed canopies that are vulnerable to high-severity fire. Future management should reduce forest densities and to restore stand- and landscape-level heterogeneity and increase forest resilience. The timing and size of repeat treatments such as thinning of subcanopy trees and prescribed burning, including Indigenous fire stewardship, can be guided by our refined understanding of the mixed-severity fire regime that was historically dominated by low- to moderate-severity fires in this dry forest ecosystem.

Culturally safe dementia care: Building nursing capacity to care for First Nation Elders with memory loss.

Nursing staff require culturally relevant and dementia-specific education to care for the increasing number of First Nation Elders experiencing memory loss. The culturally safe dementia care (CSDC) research team, composed of researchers, decision makers and Secwepemc Elders, was formed to address this. To increase the capacity of nurses to care for First Nations Elders with memory loss in a culturally safe way. Our community-based research used purposive sampling and mixed methods to create, implement and evaluate an education programme for nurses. Thirty-four Elders from six Secwepemc communities participated in roundtables to share views and stories of dementia and nursing care. These data were used to create four teaching stories for the storytelling sessions and talking circles with Elders which, together with the Indigenous Cultural Competency (ICC) training, comprised the CSDC education programme. Thirty-eight nurses (healthcare aides, licensed practical nurses and registered nurses) working in Central British Columbia began the CSDC study and 15 nurses took part in the education programme, evaluated the storytelling session and completed the three pre- and post-measures (Approaches to Dementia Questionnaire (ADQ), ICC knowledge quiz and self-assessment, and Care Plans). The pre- and post-tests were scored, and the data were analysed statistically. The data from the roundtables and talking circles were analysed thematically through a collaborative process. The scores for the ADQ Hope sub-scale, the ICC knowledge quiz and the Care Plans increased from pre- to post-test. All nurse participants judged the storytelling session to be effective and their learning outcomes reflected culturally safe dementia care. This programme can improve the knowledge, skills and values of nurses to provide culturally safe dementia care.

Contrasting root and shoot cold tolerance of a conifer with indeterminate growth

Yellow-cedar (Callitropsis nootkatensis (D. Don) D.P. Little), a conifer in the Cupressaceae with indeterminate growth, is undergoing severe decline and mortality in southeast Alaska and the coast of northern and central British Columbia. This decline is attributed to cold damage to roots associated with climate warming and reduced snowpack. The cold tolerance of indeterminate conifer species is little studied, and less is known about root cold tolerance, as most studies focus on shoots. We compared the seasonal cycle of cold hardiness in roots and shoots of yellow-cedar seedlings from high- and low-elevation populations over 1 year. Freezing tolerance of shoots followed a typical seasonal cycle, with low levels of cold tolerance observed from April to October and moderate levels of cold tolerance observed in mid-winter. Differences in shoot cold tolerance among populations were consistent with the latitude and elevation of origin. In contrast, at the same freezing temperatures, roots of all seedlings had consistent, high levels of cold damage throughout the year.

Managing Wildlife Habitat: Complex Interactions With Biotic and Abiotic Disturbances

Sustainable forest management strategies include emulating historical disturbance regimes to achieve multiple objectives. Partial-harvesting strategies are used to overcome conflicts between timber production and wildlife habitat conservation; however, the potential impacts on complex disturbance interactions and ecological functions remain largely unknown. In 1984, a controlled experiment was initiated in the dry forests of central British Columbia, Canada, to test partial harvesting intended to enhance mule deer habitat while allowing timber extraction. To determine the short- and long-term impacts on complex disturbance regimes, we quantified changes in forest structure and susceptibility to western spruce budworm, Douglas-fir beetle, and wildfire. We compared structural attributes in 2014 (30 years after the first harvest) and 2015 (1 year after the second harvest) in treated forests, and contrasted them with control forests that were measured in 2015. In the short term (1 year post-harvest), partial harvesting altered forest structure by reducing total canopy cover, subcanopy tree density and basal area, and increasing the abundance of large woody surface fuels. In the long term (30 years post-harvest), the forest canopy attributes did not differ between the treatment and control areas, partly due to increased growth of subcanopy trees. Harvesting had little impact on forest susceptibility to western spruce budworm. Susceptibility to Douglas-fir beetle was lower in the short term due to fewer available mature host trees, but increased to levels similar to the control forest over the long term. Reduced canopy fuels and increased canopy base height decreased the likelihood of crown fire in favor of surface fire. In the long term, canopy fuels and likelihood of crown fire recovered, but woody fuel loads remained low after 30 years. Harvesting to enhance mule deer habitat interacts with biotic and abiotic disturbances in the short and long term. Potential cascading affects depended more on the decision to remove harvesting residuals to mitigate potential Douglas-fir beetle infestations and wildfire than on time since treatment. Provided partial harvesting occurs at intervals ≤ 30 years and residuals are immediately removed, timber extraction and mule deer habitat can be compatible with complex disturbance regimes and sustainable forest management.

Erosion, deposition and contamination by high‐magnitude subaqueous debris flows and turbidity currents: Insights from the failure of a tailings dam near Quesnel Lake, British Columbia

AbstractThe 4 August 2014 failure of Mount Polley mine tailings dam in central British Columbia, Canada, is the worst environmental disaster in British Columbia history. Around 25 million m3 of water, tailings solids and dam construction materials travelled as a slurry flow down nearby Hazeltine Creek. About 18.6 million m3 of tailings and displaced coarse sediment entered into the narrow, deep, fjord‐like Quesnel Lake. Multibeam echosounding, sub‐bottom profiling, sediment cores and theoretical models are used to examine erosion and deposition on the Hazeltine Creek fan‐delta and the bed of Quesnel Lake by subaqueous sediment density flows generated from the slurry. Strong to very strong subaqueous debris flows eroded two deep subaqueous channels on the fan‐delta in a period of less than 12 h. A model for subaerial debris‐flow erosion overestimates submerged delta‐front erosion rates in the channels because of evolution of the subaqueous debris flows and incomplete liquefaction of the eroding bed. The debris flows deposited a localized debrite with a hummocky surface composed of fine tailings and coarse displaced fan‐delta and fluvial sediment. A flat, featureless, surface composed of fine‐grained sediment adjacent to the debrite is interpreted as debrite/turbidite resulting from debris flows proximally and turbidity currents distally. Copper concentrations in cores are highly elevated compared to background concentrations in pre‐event native lacustrine sediment. Deposits from subaqueous sediment flows generated by earthquakes and glacial lake outburst floods are generally thinner than those in Quesnel Lake caused by the tailings dam failure.

Growth sensitivity to climate varies with soil moisture regime in spruce\u2013fir forests in central British Columbia

Key messageGrowth sensitivity to climate varies with soil moisture regime in spruce–fir forests in central British Columbia. Stands growing at their dry edaphic limits displayed especially strong and unique climatic sensitivities.Soil moisture regime is an important influence of productivity, process, and structure in forested ecosystems. In western North America, projected warming trends may result in decreasing available soil moisture; however, the potential effects on forest growth remain unclear. This study aimed to determine the influence of stand-level soil moisture regime on the climatic sensitivity of mature hybrid white spruce (Picea glauca (Moensch) Voss x Picea engelmannii Parry) and subalpine fir (Abies lasiocarpa (Hook.) Nutt.) forests in central British Columbia, Canada. We collected and analyzed tree-ring data from 51 stands spanning a range of soil moisture regimes. Dendroecological analyses of climate–growth relationships indicated that warm summer temperatures and drought limit growth for both species across all soil moisture regimes; however, responses were strongest on the driest sites. Spruce populations across the gradient of soil moisture regimes displayed unique climate-growth relationships; growth in populations on wetter sites was more correlated with summer climate from the year prior to growth. Radial growth responses to prior summer temperatures strengthened over the past ca. 80 years in both species and across most sites, suggesting that climate–growth relationships are shifting in this region. This study presents evidence of the importance of considering site-level ecological factors such as soil moisture regime when studying forest growth responses to climate.

An index for tracking old-growth value in disturbance-prone forest landscapes

Forests in their later stages of development attain attributes that support biodiversity and provide a variety of ecological benefits (e.g. clean water and carbon storage). Despite their values, old-growth forests are declining worldwide in part due to anthropogenic pressures. A persistent challenge to managing and conserving old-growth forest has been establishing a reliable method for measuring old-growth values across large landscapes at an appropriately fine ecological and spatial scale. Using data from a community-managed forest in central British Columbia, Canada, an Aerial Laser Scanning (ALS) based metric was developed, using a random forest modeling framework, to predict an old-growth index across the forest. Using this old-growth index, we estimated that forests with “Very-high” old-growth values cover 14.7% of the study area (18,183.2 ha), and that only 25% (4,545.9 ha) of this “very-high” old growth value areas are current inside designated old-growth management areas (OGMAs). Additionally, the forests with “very-high” old-growth values that are currently inside OGMAs are fragmented, as only 1 out of 40 OGMAs have more than 50% of its area covered by forests with “Very-high” old-growth value. This research provides a clear ecological indicator that uses fine-scale remotely sensed data to measure old-growth and assess its conservation status within reserves. While the index developed is specific to the study site, the framework, is generic enough to be adapted to other forest types and ecosystems. More importantly, the identification of the amount and location of old-growth forests over the landscape can aid in the management and conservation of this rare resource and its services.

A huge flood in the Fraser River valley, British Columbia, near the Pleistocene Termination

Near the Pleistocene Termination, a glacier-dammed lake in central British Columbia suddenly drained to the south along the Fraser River valley. Floodwater travelled 330 km down the valley to Hope, British Columbia, and from there to the west into the Salish Sea near Vancouver. The flood was caused by the failure of an ice dam formed by the terminus of glaciers flowing from the central Coast Mountains across the British Columbia Interior Plateau. The ice dam impounded several hundred cubic kilometres of water to a maximum elevation of about 810 m asl (above sea level); at its maximum, the lake at the ice dam was over 250 m deep. Geomorphic and sedimentary evidence for the flood includes streamlined boulder-strewn bars, gravel dune fields, and terraces sloping up Fraser and lowermost Thompson valleys, opposite the present direction of river flow. The gravel bars and flood terraces are underlain by sheets of massive to poorly sorted gravel containing large boulders and rip-up clasts of silt and till. Shortly after the flood, a landslide near the northern margin of the former glacier dam impounded water to an elevation of about 550 m asl. This lake emptied due to overflow and incision of the landslide dam. The outburst flood from glacial Lake Fraser and the subsequent draining of the landslide-dammed lake deeply incised the older sediment fill in Fraser Valley and transported much of this sediment into the proto-Salish Sea west of Vancouver, British Columbia and Bellingham, Washington. TCN ages on flood-transported boulders at three localities along the flood path agree with radiocarbon ages on inferred flood layers in ODP cores collected from Saanich Inlet, a fiord on southern Vancouver Island, 80 km south-southwest of Vancouver.

How much does the host matter to the parasitoid? Distribution of Eurytoma (Hymenoptera, Chalcidoidea) species amongst two locally co-occurring gall-inducing hosts in the genus Diplolepis (Hymenoptera, Cynipidae)

AbstractGall wasps in the cynipid genus Diplolepis Geoffroy (Hymenoptera: Cynipidae) attack various species of native and introduced roses in Canada. Although gall forms are diverse, gall wasps are parasitised by highly concordant complexes of parasitoids and inquilines. Many species of gall wasps attack the same host plants and develop over the same periods in the season, suggesting that opportunistic parasitoids may be exploiting a range of hosts rather than specialising. We sampled larvae of Eurytoma Illiger (Hymenoptera: Cynipidae) from galls of D. variabilis (Bassett) and D. rosaefolii (Cockerell), gall inducers that develop fairly synchronously late in the growing season on leaves of Rosa woodsii Lindl. (Rosaceae) in the Okanagan Valley of central British Columbia, Canada. Galls were sampled at five different sites along a gradient from the north end of the valley to the Canada–United States border, a distance of 100 km. We extracted DNA, then amplified and sequenced the cytochrome b segment for each Eurytoma larva. We identified two well-supported clades that were differentiated by neither sampling location nor host. Instead, at least two species of Eurytoma, E. imminuta Bugbee and E. longavena Bugbee, exist at these localities, and both exploit at least two of the Diplolepis hosts found at these sites.

Detection of sub-canopy forest structure using airborne LiDAR

Knowledge on forest structure is vital for sustainable forest management decisions. Currently, Airborne Laser Scanning (ALS) has been well established as an effective tool to delineate and characterize the structure of canopies across a range of forested biomes. However, the use of ALS to provide information on sub-canopy structure is less well developed. Sub-canopy structure consists of suppressed mature trees, regenerating tree saplings, shrubs, herbs, snags and coarse-woody-debris. With the increasing density of ALS point clouds, new opportunities exist to describe these sub-canopy structural components in forests that were previously difficult to detect using passive remote sensing technologies. In this research we use discrete return ALS data acquired at a density of 23 points × m2 to estimate sub-canopy forest structure for 48,000 ha of conifer dominated forest in central British Columbia, Canada. We first segmented the forest vertical structure into canopy and sub-canopy based on Lorey's mean height (HL). HL, which favours larger trees as a baseline for canopy height, provides separation between the taller trees that dominate the canopy and smaller trees that represent the sub-canopy. We defined sub-canopy trees as those <70% of HL. Both ground-truthed forest inventory data and the ALS point cloud were then segmented into canopy and sub-canopy components. A mixture of standard height-based and density-based ALS metrics were then computed to develop predictive models of sub-canopy component of the stands. Models were calibrated with 28 ground plots and developed using stepwise regression with the strongest predictors being a combination of height, structure and cover-based metrics. Two model sets were developed, one for the entire point cloud, and another for an isolated sub-canopy point cloud defined by HL. The isolated sub-canopy set of models resulted in stronger cross-validated R-squared values of 0.88, 0.68, and 0.55 for tree volume, basal area and number of sub-canopy trees, respectively. We then applied these models over the entire study area to characterize the sub-canopy structure, resulting inventory can be used by land managers for a number of purposes including selecting candidate locations for selective logging to preserve mid-term timber opportunities, fire susceptibility and carbon sequestration modelling, and wildlife habitat values.

Assessing Differences in Competitive Effects Among Tree Species in Central British Columbia, Canada

Research Highlights: We investigated the competitive interactions among three tree species (interior Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco), interior spruce (Picea glauca [Moench] Voss × Picea engelmannii Engelm.), and lodgepole pine (Pinus contorta Dougl. Ex Loud. var. latifolia Englem.)) in multi-aged stands in central British Columbia, Canada. Background and Objectives: Understanding competitive interactions among tree species in mixed-species stands is fundamental to supporting silvicultural decision-making in such stands. Using the periodic annual basal area increment for single trees as our dependent variable, we investigated whether neighboring trees competed with subject trees independently of species identity. We also examined the differences in single-tree basal area growth among the three conifer species over time under different levels of competition. Materials and Methods: We developed several spatially explicit, single-tree basal area growth models for interior Douglas-fir, interior spruce, and lodgepole pine using data from 16 plots in two blocks of a long-term study (five measurements over a 21-year period) on the response to pre-commercial thinning. We compared these equations to assess whether intraspecific or interspecific competition predominated. We also examined the differences in basal area growth among the three conifer species over time under different levels of competition. Results: We found asymmetrical relationships between the conifer trees and their neighbors for all species, indicating that the main driver limiting growth in these stands is aboveground competition for light. There was evidence of higher intraspecific competition for small (&lt;10.0 cm DBH) interior Douglas-fir in one block. However, there was no general pattern among larger subject trees with respect to the identity of neighborhood competitive effects and the equivalence of neighbors. We observed a higher level of basal area growth over time for interior Douglas-fir than for lodgepole pine and interior spruce, irrespective of the competition intensity and, not surprisingly, the growth rate declined with increasing competition levels for the three species. Conclusions: Our results provide an understanding of how interior Douglas-fir stands will develop over time and information on species interactions that could help forest managers explore different silvicultural options and their effects on individual tree growth in these complex stands.