Retrieving Foliar Traits of Quercus garryana var. garryana across a Modified Landscape Using Leaf Spectroscopy and LiDAR

Understanding the ecological effects of human activities on an ecosystem is integral to the implementation of conservation management plans. The plasticity of plant functional traits presents an opportunity to examine the capacity for intraspecific functional trait variations to be indicators of anthropogenic landscape modifications. The presence of intraspecific trait variation would indicate that plants of a single species could to be used to evaluate and map functional diversity, a common metric used to measure biodiversity. This study uses leaf spectroscopy, light detection and ranging (LiDAR) and partial least squares regression (PLSR) to examine the intraspecific variation of functional traits in a population of 40 Quercus garryana experiencing varying levels of anthropogenic influence at the site level (<0.3 km2) in Duncan, B.C., Canada. These individuals vary in their spatial relationship to roads, agricultural land use change and an encroaching Coastal Douglas-fir forest. A total of 14 functional traits were estimated using pre-determined PLSR coefficients from a multi-species dataset. LiDAR data for each tree and were organized into functional categories based on their influence of plant lifeform, leaf growth or leaf structure. Principal components analysis was performed on each functional category to determine the relative influence of each trait. Results show that leaf growth and lifeform functional trait categories express significant variation in relation to three anthropogenic landscape modifications, while traits associated to leaf structure only varied between land use types (p = 0.05). Diameter at breast height (DBH), mass-based chlorophyll and leaf mass per area (LMA) showed the strongest variation across treatments. These findings support the hypothesis that trait variation exists in small populations of the same species and illustrate that spectroscopy can be used to indirectly sense land use via the leaf functional traits of a single tree species.

Implications of an exceptional autumn bud flush on subsequent cold tolerance of Garry oak (Quercus garryana)

In the fall of 2016, an unusual phenological event occurred in Quercus garryana Douglas ex Hook. in Victoria, British Columbia. After normal autumn leaf drop, some trees burst bud and leafed out prematurely in late October. This allowed a comparison of the cold hardiness of the prematurely flushed and non-flushed trees over the following year. Cold hardiness of five tree pairs (premature fall flush and non-flush) in three locations in Victoria was assessed bi-weekly over the dehardening period in January–March 2017 and again over the hardening period in September–December 2017. Cold hardiness of 10 non-flushed trees from the most northerly population of Q. garryana was also assessed twice in spring 2017. Between January and March, all trees dehardened, but cold hardiness was greatest in non-flushed trees on the first sampling date, and thereafter, the non-flushed trees dehardened more rapidly than the prematurely flushed trees. Index of injury was consistently 10% greater in Victoria than in northern trees. In fall 2017, trees that had flushed prematurely in fall 2016 had the same cold hardiness as non-flushed trees. Hardiness of all trees decreased from mid-September to the end of October, followed by rapid hardening in November and December of 2017.

Stand Structure and Composition Affect the Drought Sensitivity of Oregon White Oak (Quercus garryana Douglas ex Hook.) and Douglas-Fir (Pseudotsuga menziesii (Mirb.) Franco)

Due to a suite of environmental changes, Oregon white oak (Quercus garryana Douglas ex Hook; called Gary oak in Canada) associated ecosystems at many North American sites are being encroached upon by Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii) and other conifer species. Alteration of stand structure and composition is causing substantial changes in the dynamics of these ecosystems, creating an environment in which Oregon white oak is not thriving. In this study we used dendrochronology to investigate the competitive dynamics between Oregon white oak and Douglas-fir in a mixed forest stand on Southern Vancouver Island. Significant species-specific differences in radial growth sensitivity to drought were found between Oregon white oak and Douglas-fir. Oregon white oak trees growing at high densities, or competing with Douglas-fir for moisture were found to be more sensitive to drought and more sensitive to growing conditions during the prior year. The response of Douglas-fir to drought was less variable, possibly due to the relatively low conifer densities at our study site, as well as the species’ ability to root graft, its higher shade tolerance than Oregon white oak, and its rapid growth rates that allow it to achieve a more dominant canopy position. The non-stationary response to climate exhibited by Oregon white oak provides insights into the mechanisms by which Oregon white oak savannas are being converted to coniferous woodland, but also suggest that tree-ring reconstructions of climate need to explicitly address changes in stand dynamics that could influence the growth–climate relationship

The Biology of Canadian Weeds: 156.Daphne laureolaL.

Daphne (Daphne laureola L.) is a perennial evergreen shrub native to Eurasia and northern Africa. Introduced to North America as an ornamental shrub, the plant has readily absconded gardens and can now be found throughout suitable habitats on both the east and west coasts of the continent. In Canada, daphne has naturalized in southwestern British Columbia including Vancouver, southern Vancouver Island, and the Gulf Islands. Daphne is of particular concern to the endangered Garry oak (Quercus garryana Douglas ex Hook.) because it invades shady woodland areas, forming dense mono-specific stands that can suppress and inhibit native vegetation. The berries and all other parts of the daphne plant contain a mixture of toxic chemicals that can be fatal to humans or animals if ingested. Removal teams suggest using gloves for elimination and handling of daphne because of its corrosive sap and oil. Widespread planting combined with a lack of public knowledge regarding the species’ invasiveness has created great concern over its potential to spread. Various methods of control (chemical, manual, and biological) have been developed. The most commonly applied approach in Canada is manual control, but care must be taken to avoid contact with skin and follow-up monitoring and control is advised. A promising biocontrol agent is the fungus Phomopsis sp. denovo, which has been observed to cause high levels of mortality in D. laureola under both laboratory and field conditions.

Spatial and temporal assessments of genetic structure in an endangered Garry oak ecosystem on Vancouver Island

Garry oak (Quercus garryana Douglas ex Hook.) is a deciduous tree whose ecosystem is listed “at risk” throughout its range in British Columbia (BC), Canada, under the Canadian Species at Risk Act. Garry oak ecosystems host the most diverse flora for coastal BC, yet they account for less than 0.3% of the province’s land coverage. Due to the loss and degradation of Garry oak habitat, many associated plant and animal species that rely on these sensitive ecosystems are endangered. Microsatellite markers were used to investigate temporal changes in fine-scale population genetic structure of 121 Garry oak trees from the Nanaimo region (Vancouver Island, BC) using diameter at breast height as a proxy for age. Overall, allelic diversity was moderate, ranging from 3.0 to 7.5 alleles per locus with a mean of 4.4 (±0.4 SE) across all loci. Global fixation indices (FST) of 0.06 and 0.09 suggest significant departures from Hardy–Weinberg equilibrium among all populations and age-classified subpopulations, respectively. We found no evidence for change in genetic diversity across generations. Our results indicate low levels of differentiation within populations and high levels of gene flow among populations, suggesting an adaptive potential for Garry oaks in response to future climate change events.

The death cap mushroom (Amanita phalloides) moves to a native tree in Victoria, British Columbia

Amanita phalloides (Vaill. ex Fr.) Link, the death cap mushroom, is an invasive ectomycorrhizal fungus in North America that was inadvertently introduced from Europe. Death cap mushrooms are highly toxic and have caused three recorded poisonings in British Columbia (BC), including one recent death. In BC, these mushrooms fruit mostly in urban environments in the greater Vancouver and Victoria areas under planted exotic broadleaf trees. In California, A. phalloides was demonstrated to also form ectomycorrhizas with a native oak species. Here we report that A. phalloides forms ectomycorrhizas with Quercus garryana, which is BC’s only native species of oak, and can fruit in association with this tree host. If death cap mushrooms spread in Q. garryana habitat, the risk for serious mushroom poisoning will increase, and mushroom harvesters, the medical community, and park managers will need to be made aware of this increased risk.

Oak mistletoe (Phoradendron villosum) is linked to microhabitat availability and avian diversity in Oregon white oak (Quercus garryana) woodlands

Mistletoes are parasitic or hemiparasitic flowering plants that parasitize woody plants around the globe. Important food and cover resources provided by mistletoes have been related to strong patterns of positive association between wildlife diversity and mistletoe density. Mistletoes also create microhabitat features known to be important to wildlife by causing deformations in their host trees. However, links between availability of mistletoe-formed microhabitat and wildlife diversity has not been well-studied. We investigated this relationship by quantifying microhabitat features and avian abundance and diversity related to infection by oak mistletoe (Phoradendron villosum (Nutt.) Nutt. ex Engelm.) in Oregon white oak (Quercus garryana Douglas ex Hook.). Quercus garryana woodlands support several avian species of conservation concern, so understanding the influence of mistletoe on wildlife habitat is critical. Our results suggest that (i) structural heterogeneity within tree crowns is positively associated with mistletoe load; (ii) avian species richness and abundance are positively associated with mistletoe load; and (iii) the fruit of P. villosum is an important food for Western Bluebird (Sialia mexicana) and other wildlife in late autumn and early winter. If a goal of restoration is to maintain habitat for oak-associated bird species, managers should consider the retention of some oaks hosting mistletoe.