Forest Investment Account (FIA) - Forest Science Program
FIA Project Y071262

    Effects of partial retention and common mycorrhizal networks on seedling recruitment in Douglas-fir forests across British Columbia
Project lead: Simard, Suzanne
Contributing Authors: Bingham, Marcus; Simard, Suzanne W.
Imprint: [BC] :, 2007
Subject: Forest Investment Account (FIA), Mycorrhizal Fungi, British Columbia
Series: Forest Investment Account (FIA) - Forest Science Program
This project builds on an ongoing research program examining biotic and environmental factors affecting forest establishment in complex stands in southern interior British Columbia (see Simard and Vyse 2006). It is aimed at predicting seedling recruitment under a variety of residual stand structures in a range of climatic regions, and therefore applies to the design of silvicultural systems across forests and landscapes under changing climatic conditions. To that end, it will provide basic information on 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 (Pseudotsuga menziesii) forests, but that these relationships changed as stands developed, and varied across ecosystems (Simard et al. 1997b, Simard and Sachs 2004, Simard and Vyse 2006). 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. Common mycorrhizal networks 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). Once seedlings were established, CMNs continued to affect resource allocation patterns (Simard et al. 1997b), but competition for light, nutrients and water appeared to become relatively more important to stand stratification as stands developed (Simard and Sachs 2004, Dickie et al. 2005, Simard and Vyse 2006). Regardless of the shifting importance of interspecific interaction mechanisms with time, CMNs can profoundly affect stand development and productivity by facilitating survival of particular seedlings. This study will focus on the importance of CMNs for seedling establishment in water-stressed forest ecosystems. Successful seedling establishment in stressed ecosystems has been found to be strongly influenced by mycorrhizal fungi (Perry et al. 1989, Smith and Read 1997). Mycorrhizas aid plants in the uptake of water and provide other benefits that are most critical in water-stressed environments (Landhausser et al. 2002, Rillig et al. 2002). Ectomycorrhizas (EM) in particular have been known to aid conifers in nutrient uptake as early as the 1930s (Hatch 1937), and to be important to Douglas-fir regeneration since at least the 1970s (Stack and Sinclair 1975). CMNs have been shown to facilitate seedling recruitment in inhospitable environments (Dickie et al. 2005). 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 2005), concerns are increasing about forest recruitment following harvest or natural disturbance. The role of CMNs in seedling establishment of Douglas-fir in stressed ecosystems is, therefore, a question of increased importance. 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 2005), requires that we design silvicultural systems using a sound understanding of the climatic, site and biotic factors regulating recruitment. To elucidate what effect climatic and atmospheric conditions have on mycorrhizas, and in turn what effect CMNs have on plant community dynamics, it would be beneficial to assess plant-fungus-plant interactions at several field locations that differ in climate, since climatic factors rarely occur in isolation of one another or other ecological factors. To that end, we propose field and growth chamber experiments examining Douglas-fir seedling establishment as a function of biogeoclimatic (BGC) subzone, proximity to residual trees, links into CMNs with residual trees, seedling origin (seed or seedling), seed provenance, and atmospheric CO2 concentrations. To predict climatic change effects on seedling recruitment, we will assess the interaction of these factors at field locations in different interior and coastal 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 (Houghton et al. 2001), 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 (Hoorens et al. 2003, Lewis et al. 2004, Norby and Luo 2004, Handa 2005) and therefore competitiveness with neighbors. Manipulating CO2 levels, along with climatic variables, will be accomplished in a growth chamber experiment. Questions that follow are: (1) With the prospect of rapid climate change, what is the importance of CMNs in facilitating establishment of Douglas-fir seedlings in stressed ecosystems (i.e., where seedlings are water-stressed)? (2) How do the partial pressure of CO2 (pCO2) and climate interact to affect Douglas-fir tree growth, water stress, and facilitation of seedling establishment through CMNs? There are four overall Objectives to this study: (1) To determine the effects of regional climate (precipitation and temperature) on CMN facilitation of Douglas-fir seedling establishment in BC; (2) To determine the interaction among soil water pCO2, and temperature in their effects on CMN-facilitated seedling establishment and C-transfer between different sized Douglas-fir seedlings; (3) To determine the importance of Douglas-fir residual trees on regeneration, and how this changes with climate; and (4) To parse the competitive from facilitative effects of residual Douglas-fir trees on small seedlings. The working Hypotheses are: (1) Differences in Douglas-fir seedling growth and survival between seedlings connected to mature residual trees by a hyphal network and seedlings not connected by a hyphal network will increase with increasing water stress (as determined by climate and/or pCO2). (2) A corollary to the previous hypothesis is, if CMNs facilitate C and/or water transfer between plants, their presence will reduce competitive effects of residual Douglas-fir trees on small seedlings, leading to increased stability of the Douglas-fir seedling community, particularly in drier environments. (3) Soil water and pCO2 will interact to affect seedling water-stress such that Douglas-fir seedling growth and survival will be less responsive to the presence or absence of CMNs under varying soil moisture regimes with increasing pCO2.
Related projects:  FSP_Y082262FSP_Y093262
Contact: Simard, Suzanne, (604) 822-1955,


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Updated August 16, 2010 

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