|Forest Investment Account (FIA) - Forest Science Program|
|FIA Project Y093262|
|Effects of partial retention and common mycorrhizal networks on seedling recruitment in Douglas-fir forests across British Columbia|
|Project lead: Simard, Suzanne (University of British Columbia)|
|Author: Simard, Suzanne W.|
|Subject: Forest Investment Account (FIA), British Columbia|
|Series: Forest Investment Account (FIA) - Forest Science Program|
|This project builds on an ongoing research program examining biotic and environmental factors affecting stand establishment in complex stands (Simard and Vyse 2006). Predicting seedling recruitment under a variety of residual stand structures in a range of climatic regions, and therefore the design of silvicultural systems across forests and landscapes under changing climatic conditions requires a basic understanding of the competitive and facilitative processes underlying residual tree effects on seedling recruitment and growth. Our earlier work established that competition for light and soil water, mediation of resource availability through soil organisms (particularly mycorrhizas), and carbon acquisition through established common mycorrhizal networks (CMNs), were important determinants of seedling growth in Douglas-fir forests, but that these relationships changed as stands developed, and varied across ecosystems (Simard et al. 1997; Simard and Sachs 2004; Simard et al. 2005). Proximity, density, composition and age of neighbors, presence of an established CMN, as well as forest productivity (as determined by climate and site), were important factors in the performance of establishing seedlings. CMNs appeared to facilitate seedling establishment through rapid fungal inoculation as well as transfer of carbon, nutrients or water from neighboring residual trees (Simard and Durall 2004). |
With the recent summer drought occurrences in southern interior BC, and the predicted increase in average annual temperature for all of BC with rising atmospheric CO2 concentrations (Hamann and Wang 2006), concerns are increasing about forest recruitment following harvest or natural disturbance. Ensuring forests regenerate and remain healthy under increasing climatic stress, particularly those in the most vulnerable ecosystems (e.g., Douglas-fir forest near its climatic limits; Hamann and Wang 2006), requires that we design silvicultural systems using a sound understanding of the climatic, site and biotic factors regulating recruitment.
To that end, we are conducting field and growth chamber experiments examining Douglas-fir seedling establishment as a function of BGC subzone, proximity to residual trees, links into CMNs with residual trees, seedling origin (seed or seedling) and provenance, and atmospheric CO2 concentrations. To predict climatic change effects on seedling recruitment, we are assessing the interaction of these factors at field locations in different interior BGC subzones, using spatial climatic variability as a proxy for climate change. We predict that partial retention and linkage into a CMN will be of increasing importance to seedling recruitment in BGC zones with greater summer drought stress, and hence in regions that will experience greater drought stress with climate change. The experimental design, which includes replication at the stand and climatic region levels, will provide basic information for designing silvicultural systems across multiple scales. Additionally, ambient CO2 levels are predicted to nearly double by the year 2100, so inferences made about stand dynamic changes in response to climate change will be inaccurate without accounting for atmospheric CO2 changes, given that ambient CO2 levels affect basic plant physiology and therefore competitiveness with neighbors. Manipulating CO2 levels, along with climatic variables, will be accomplished in a growth chamber experiment.
The field study is being conducted in three interior BGC subzones that include forests with a major component of Douglas-fir. Three interior subzones were selected to represent a climatic moisture gradient, and include interior sites in the IDFxh2, IDFdk and ICHwm3. Three replicate sites are distributed across a broad area in each BGC unit to capture within-BGC unit variability.
Additional factors tested in each BGC unit are presence of a CMN (three levels using different sized mesh barriers that exclude roots and hyphae), distance from the parent tree (four distances), seedling origin (seed or seedling), and provenance. Treatments have been applied in recently partially cut stands. Douglas-fir seeds and seedlings have been planted adjacent to mature, residual Douglas-fir trees. Treatments are replicated 7 times within sites. Periodically, measurements will be taken to determine establishment success and productivity. Physiological parameters, ectomycorrhizal (ECM) status (using morphotyping and molecular analysis), germination rate, soil parameters, and root morphology will be monitored at all sites.
To determine whether there is a difference in the effect of CMNs on newly germinated seedlings versus one-year-old seedlings, both seeds and one-year-old seedlings have been planted as a factor, using nylon meshes (Johnson et al. 2001) to control for the presence of a CMN. Seedlings that are randomly predetermined to grow within nylon mesh (pore sizes of either 0.5 Ám (restricting hyphae, roots and invertebrates) or 35 Ám (restricting roots and invertebrates)) have been planted in the center of a cylinder of soil enveloped by the mesh, while those that are not planted in mesh have been planted in a cylinder of soil that has been disturbed in the same manner for installing the mesh treatments. This method allows us to: (a) separate soil water from mycorrhizal hyphal, root and invertebrate conduits of nutrient flow; (b) have a CMN and non-CMN treatment without the confounding factor of digging large trenches around CMN treatments; and (c) ensure that differences between treatments are unaffected by experimental disturbance of the soil.
For the growth chamber study, Douglas-fir seedlings are being grown together in terracosms following protocols developed by Simard et al. (1997a), using the same hyphal mesh barriers as in the field study. The growth chamber study is being conducted at UBC. The experiment is controlling for the concentration of CO2 ([CO2]), ambient temperature, and soil water to test the interactions among these factors, as well as competitive-facilitative relations between different-sized Douglas-fir seedlings. Different sized Douglas-fir seedlings are being grown in the growth chamber terracosms, in which we are manipulating ambient CO2, temperature, soil water and CMN status (using the same mesh treatments as in the field study) to test their effects on seedling establishment and performance. Methods for controlling CO2 and temperature in environmentally controlled chambers are well established (e.g. (Rygiewicz et al. 2000, Lewis et al. 2002, Tingey et al. 2003, Lewis et al. 2004), and growth chambers retrofitted to control for [CO2] and temperature by the manufacturer are being used. While each growth chamber has one level of [CO2] and one level of ambient temperature, multiple levels of soil moisture are being applied in each growth chamber, following daily testing of soil water content. Four growth chambers are being utilized for two levels of [CO2], two levels of ambient temperature, and three levels of soil moisture. Treatments are being replicated 10 times in each growth chamber, for a total of 20 replications for the experiment.
a) Seedlings: Seeds have been monitored for germination rate. Seedlings are being monitored for growth, physiological activity and mortality. Root morphology, biomass and nutrient status are being quantified at the end of each trial.
b) Atmospheric conditions: Light transmittance data using a line ceptometer and climate data from nearby stations will be obtained.
c) Soils: At each site, we are measuring soil moisture and temperature using probes, and soil nutrients using cores.
d) ECM status: Morphotyping and molecular analysis will be used to determine mycorrhizal and CMN status.
e) Nutrient transfer: Isotope labeling will be used to measure interplant transfer in the growth chambers.
|Related projects:  FSP_Y071262,  FSP_Y082262|
Final report (69Kb)
Updated August 16, 2010
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