Habitation Sites Influence Tree Community Assemblages in the Great Bear Rainforest, British Columbia, Canada

Identifying how past human actions have influenced their environment is essential for understanding the ecological factors that structure contemporary ecosystems. Intertidal resource use by Indigenous Peoples for thousands of years has led to habitation sites containing vast shell midden deposits and facilitating long-term impacts on soil chemistry and drainage. Here we examine how these shell middens have impacted various forest metrics, such as species diversity, community composition, canopy height, and regeneration recruitment to determine if forests on habitation sites differ from the surrounding matrix. We surveyed known habitation sites with archeological evidence indicating past year-round human occupation, within the Hakai Lúxvbálís Conservancy on Calvert and Hecate Islands within the Great Bear Rainforest along British Columbia’s Central Coast. Our results demonstrate that habitation sites exhibit lower tree species richness, less relative species abundances, as such, displayed lower Shannon diversity and inverse Simpson values. The composition of tree communities on habitation sites was statistically different, with western hemlock and western redcedar densities increasing on non-habitation sites. Conversely, regeneration diversity at habitation sites was more even and exhibited elevated Shannon diversity and inverse Simpson values. The community composition of regeneration was more consistent among habitation and non-habitation sites; however, western redcedar, western hemlock and Sitka spruce were more abundant at habitation sites. For all tree species, maximum height was higher within the habitation sites; however, this trend was the most notable in western redcedar and Sitka spruce, which increased by an average of 4.8 m relative to non-habitation sites. Collectively, our findings suggest that long-term habitation alters forest community compositions. The landscape alterations within habitation sites promote conditions needed to support diverse, even, and abundant regeneration communities and consequently increase the height of the dominant coastal tree species. Thus, our results offer evidence that long-term influence by Indigenous communities have a persistent influence on coastal forests.

Productivity of coastal Douglas-fir and western redcedar in response to species mixture, planting density, and soil carbon:nitrogen ratio

Mixed-species plantations have been suggested as ecologically and economically viable alternatives to monocultures. We examined the growth response of coastal Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco) and western redcedar (Thuja plicata Donn ex D. Don in Lamb.) to different species mixtures (Douglas-fir : western redcedar mixtures of 1:0, 1:1, 1:3, and 0:1) and planting densities (500, 1000, and 1500 stems·ha−1) in a dry maritime forest on eastern Vancouver Island, Canada. Twenty-two years postplanting, species mixture significantly affected diameter and height growth (p < 0.001), with stand diameter and height generally decreasing with increasing redcedar composition. Inherent variation in soil productivity across the plantation (carbon:nitrogen ratio) equally constrained stand growth. The widest spacing had larger diameter than the closest spacing (p = 0.025) but the least stand basal area compared with the other spacing treatments (p = 0.003–0.031). Stand volume was significantly affected by mixture × density interaction (p = 0.024) and generally declined with increasing proportion of redcedar and decreasing stand density. In the first decades after plantation establishment, inherent species growth traits and soil fertility were most important in dictating stand productivity. Because of the differences in resource utilization of both species, stand dynamics may change as competition for light and soil resources increases. Evaluation of silvicultural recommendations regarding mixtures of both species will continue with plantation development.

Tree rings and genetic control of drought resilience

&lt;p&gt;Severe drought events are affecting forests around the world, even in temperate climates. A viable climate change adaptation strategy may involve planting forests with trees more resilient to drought. The majority of the 300 million seedlings planted annually in western Canada are genetically-selected trees derived from tree breeding programs. Since tree breeding populations supply the seed that is deployed on the landscape, it is important to closely examine the degree of genetic control of drought resilience in these populations &amp;#8211; yet methods for evaluating drought responses in mature experimental trials are limited. We evaluated the potential to use tree rings to infer genetic adaptation to drought. Specifically, we used annual growth increments to evaluate the genetic component behind variation in drought resilience. We also quantified potential genetic trade-offs between drought resilience and growth in long-term progeny trials. We worked with two economically and ecologically valuable sympatric conifers, coastal Douglas-fir (&lt;em&gt;Pseudotsuga menziesii &lt;/em&gt;var. &lt;em&gt;menziesii&lt;/em&gt;) and western redcedar (&lt;em&gt;Thuja plicata&lt;/em&gt;). Annual growth increment and tree height data were obtained from 1980 coastal Douglas-fir trees (93 polycross families on two well-replicated sites at age 19) and 1520 western redcedar trees (26 polycross families on three well-replicated sites at age 18). All trees showed substantial reduction in growth under drought, but there was clear variability in the longer-term response of families within each breeding population. The heritability (h&lt;sup&gt;2&lt;/sup&gt;) of such drought resilience, or proportion of this variation explained by genetics, was high for Douglas-fir (h&lt;sup&gt;2&lt;/sup&gt; = 0.26, SE = 0.07) and moderate for redcedar (h&lt;sup&gt;2&lt;/sup&gt; = 0.13, SE = 0.04). Preliminary genetic correlations between tree height and drought resilience were also positive for both species (Douglas-fir: r&lt;sub&gt;g&lt;/sub&gt; = 0.77, SE = 0.18; redcedar: r&lt;sub&gt;g&lt;/sub&gt; = 0.62, SE = 0.17). Families that were both high-yielding and drought resilient could also be identified. Since growth response to drought is a variable and heritable trait, these traits are therefore under the control of the tree breeder. Moreover, the positive genetic correlations between tree height and an adaptive growth response to drought suggest that historic selection for tree height did not compromise drought resilience of planted seedlings. Tree rings appear to be an effective tool to screen these populations for drought resilience, which will help ensure that planted trees will remain healthy and productive under climate change.&lt;/p&gt;

Identification of Three Monofunctional Diterpene Synthases with Specific Enzyme Activities Expressed during Heartwood Formation in Western Redcedar (Thuja plicata) Trees

Upon harvest, Western redcedar (WRC; Thuja plicata) trees have a high incidence and extent of heartwood rot. While monoterpenoids and lignans have been linked to rot resistance in this species, other specialized metabolites, such as diterpenes, are likely to contribute to rot resistance. Here we report the cloning and functional assessment of three putative diterpene synthase (TpdiTPS) genes expressed during heartwood formation in WRC. The predicted proteins of the three genes lack either of the two catalytically independent active sites typical of most diTPS, indicating monofunctional rather than bifunctional activity. To identify potential catalytic activities of these proteins, we expressed them in genetically engineered Escherichia coli strains that produce four potential substrates, geranylgeranyl diphosphate (GGDP), ent, syn, and normal stereoisomers of copalyl diphosphate (CDP). We found that TpdiTPS3 used GGDP to produce CDP. TpdiTPS2 used normal CDP to produce levopimaradiene. TpdiTPS1 showed stereoselectivity as it used normal CDP to produce sandaracopimaradiene and syn-CDP to produce syn-stemod-13(17)-ene. These genes and protein enzymatic activities have not been previously reported in WRC and provide an opportunity to assess their potential roles in heartwood rot resistance in this economically important species.

Effect of Vegetation Management and Site Conditions on Volume, Biomass and Leaf Area Allometry of Four Coniferous Species in the Pacific Northwest United States

Allometric equations are useful tools for calculating tree and stand-level attributes, such as above-ground biomass or stem volume, using simple measurements that can be obtained from stand inventory data. These equations tend to be species-specific and can be affected by site conditions and silvicultural treatments. Forest vegetation management treatments (VM) are an important component of reforestation programs in the Pacific Northwest of the United States; however, no study has investigated the impact of these treatments on crop tree allometry. In this study we assessed the long-term effects of two contrasting VM treatments on the allometry of sixteen-year-old Douglas-fir, western hemlock, western redcedar, and grand fir trees growing in Oregon’s central Coast Range (CR) and fifteen-year-old Douglas-fir and western redcedar trees growing in Oregon’s Cascade foothills (CF). The VM treatments included a control which received only a pre-planting herbicide application and a VM treatment consisting of five consecutive years of vegetation control after planting. The equations developed in this study were species-specific and were not affected by VM with the exception of western redcedar foliage biomass. For western redcedar, tress of similar diameter had more foliage biomass when growing on plots without VM after planting. The allometry of Douglas-fir and western redcedar was also found to be affected by site, such that trees of similar diameter and height had larger stem volume when growing at the CR site than the CF site. This difference in stem volume was found to be the result of differences in stem tapering. There was a strong relationship between stand basal area and leaf area index that was the same for all species tested and was unaffected by site. The equations presented in this study are useful for calculating stem volume, leaf area and individual tree and component biomass for stands of the studied species that are of similar age.