Background

(1) To evaluate the effects of various forest removal treatments, including differing levels of variable retention harvesting, and regeneration using various tree species mixtures, on regeneration success, carbon cycling, productivity and biodiversity.
(2) To evaluate the effects of legacy trees (trees that remain on site) (healthy, stressed, and dying) on forest regeneration, specifically their impacts on seedling survival success via soil properties, including root symbiosis.
(3) To investigate the performance of local wild, selected, and migrated seed sources during the establishment years, with the aim of optimizing seed mixtures for regeneration success
(4) To quantify the links between forest ecosystem structure and function, above- and below-ground, and how they are moderated by alternative renewal methods

Maintaining key structural and functional properties of ecosystems has long been a central objective of sustainable resource management in British Columbia. However, the risks and uncertainties associated with climate change mean that protecting and promoting forest renewal and the various ecosystem goods and services will be increasingly challenging. Recent mortality in plantations and natural forests in British Columbia, including that caused by insects and diseases amplified by climate change, indicate that standard operating practices (clearcutting and replanting with nursery-grown seedlings) urgently require reassessment. We need to understand ways to achieve successful forest renewal after harvesting or natural disturbances in a changing climate. This is crucial to the long-term sustainability of our forests, including their ability to promote a healthy Canadian forest sector, support biodiversity and store carbon. Our project includes several above- and below-ground studies, which in combination will ultimately identify optimal harvesting and regeneration methods for Interior Douglas-fir forests in British Columbia within the context of a changing climate.

Site selection

In summer/fall of 2016, we identified three locations, each with 3 replicate 20-ha sites, where our research will take place. The locations are: (1) UBC Alex Fraser Research Forest near Williams Lake (2) John Prince Research Forest near Fort St James, and (3) Redfish Creek near Nelson. Other locations where we are making progress in selecting 3 replicate sites are: (1) Cranbrook, (2) Siringa/Castlegar, and (3) Kamloops/Merritt. This is a total of 6 locations, whereas we only require 5, but because all of these areas may not be work out logistically we are continuing to pursue them all at this point.

The Studies Objective
Objective 1 – Renewal treatments

Under this objective we will investigate effects of forest renewal methods along a climatic gradient on regeneration, productivity, biodiversity and carbon cycling. The same 5 tree removal treatments, each done in a 4-5 ha block, will be done at each 20-25 ha site. The treatments follow a gradient of tree removal, from complete to no removal, and are:
1. Conventional clearcut, involving removal of all overstory trees and slashing of understory trees
2. Single tree retention, similar to a seed tree system. Inter-tree spacing of leave trees will be 20-25 m. (25-36 SPH retained). Retained trees will be evenly distributed and preference given to preserving large/old Douglas-fir.
3. Retention of 30% of the forest in patches (70% of the forest would have all overstorey and understorey trees cut). Retained patches can have an irregular distribution, and would be about 50 m across. They would be centred on large old Douglas-fir rather than laid out at random..
4. Retention of 60% of the forest in patches centred on large, old Douglas-fir (40% of the forest would become openings 15-30 m across with all overstorey or understorey trees cut), The retained patches would be thinned from below, by reaching in with a feller buncher. The specifics of the which trees would be thinned out are still being worked out.
5. Unlogged control.
Nested within these harvesting treatments will be regeneration treatments. Seedlings are being custom grown in a commercial nursery as 1-0 plugs (all seedlings grown in the same nursery). At each site, the local provenance and five other provenances representing different climates, including the climate expected at the study area 80 years into the future, will be planted at a density of 2.5 x 2.5 m in the open areas. Douglas-fir seedlings will be planted from both class A and B seed. Ponderosa pine, lodgepole pine and western larch will also be planted. We will also plant seedlings in small (10 m2) subplots, with 21 seedlings per subplot. These subplots will include pure and mixed provenances. These subplots are for very short-term experiments. The ability of seedlings in the subplots to link into mycorrhizal networks with residual trees and plants will be controlled by growing them inside mesh-lined cylinders of different pore sizes, similar to those used in prior studies (mycorrhiza will only be accessible with the large pore size). Both the 2.5 x 2.5 m spaced seedlings and seedlings in the subplots will be monitored for survival, growth and health after planting. Under this grant, only short-term monitoring will be possible, but the plan is to continue monitoring in subsequent years, enabling long-term assessment of treatment effects on regeneration, productivity, carbon cycling and resilience.
The basic pre-treatment measurements will be conducted according to the National Forest Inventory protocol in conjunction with the provincial Change Monitoring Inventory protocol. This protocol includes: (1) measuring all dead and live trees >9 cm dbh in an 11.28 m radius plot, (2) measuring trees < 9 cm dbh and large shrubs in a 3.99 m radius plot, (3) recording % cover of shrubs and trees in a 10.0 m radius plot and % cover of herbs and bryoids in a 5.64 m radius plot, (4) describing the soil and humus form with a 60+ cm deep soil pit, (5) measuring coarse woody debris along two 30-m transects, (6) assessing ground substrate every 2 m along the CWD transects, (7) collecting vegetation, fine woody debris, small stump, forest floor, and mineral soil samples to quantify their contribution to the carbon budget, and to determine soil nutrients, and (8) a site description (slope, aspect, slope position, elevation, site series, successional stage etc).

Objective 2 – Legacy trees                                                                                                                     <Top

A survey will be conducted before harvesting to characterize legacy tree, bacterial, and fungal communities in the inner 1-ha core of the 4-5-ha treatment blocks. The survey will be repeated in following years to examine any harvesting treatment effects on characterized communities and forest regeneration.

Objective 3 – Seed sources

Field studies will be conducted to investigate the interacting effects of climate-harvesting and regeneration-mycorrhiza factors on seedling regeneration, plant diversity, mycorrhizal communities and environmental resources and conditions post-treatment. We have previously established that the two year establishment window is crucial for interior Douglas-fir regeneration success in the field. Microclimate data will be collected and complement that collected at nearby AMAT sites. Tree seedlings will be harvested and measured for height and diameter, root and shoot biomass, foliar nutrients, natural abundance 13C and 15N (for water use and photosynthetic efficiency) and foliar defense enzymes. To quantify C and N sources, natural abundance of 13C and 15N in soil, plant, fungal and mycorrhizal root tip samples will be analyzed. DNA will be extracted from roots to identify the fungal taxa associated with harvested seedlings.
One of our studies will investigate whether defense signals are preferentially transmitted from injured seedlings to related, rather than unrelated seedlings. This has previously been measured in the greenhouse, but our field studies will determine which, if any, of the factors of climate, mycorrhizal network, or relatedness affect inter-tree signaling. This study will be done in the clearcut treatment blocks.
Two greenhouse experiments will also be conducted, using soil collected from the field sites. These will examine the effects of stress from resource depletion due to (1) density and (2) pest (western spruce budworm) injury on donor seedling transmission of stress seedlings and C to neighbouring related vs unrelated seedlings (receivers) through mycorrhizal networks. The first experiment will determine whether kin cooperation or kin competition between trees is more important at low versus high stress levels. The second experiment will determine whether injured seedlings preferentially warn related vs unrelated seedlings of invaded pests.