There is increasing interest in the management and utilization of hybrid poplars and native deciduous broadleaved tree species (hardwoods) in British Columbia. This paper examines aspects of mineral nutrition and fertilization which are currently important or which may become important as management and utilization of the most important species increases. Gaps in knowledge about hardwood nutrition are also identified.
Maintaining nutrition to achieve the highest growth rates possible is more critically important for the culture of hybrid poplars than of native hardwoods. Hybrid poplars are grown under intensive management regimes, mainly to produce pulp, with rotations of 15 years or less. Plantations can be established where moisture is clearly sufficient. Under such management regimes, adequate nutrition and appropriate fertilization are essential for maximizing productivity and shortening rotations. The nutrition of native hardwoods is less important simply because native hard-wood species are not heavily used at present. However, much of the standing volume of hardwood species in interior and coastal British Columbia is in near-mature, mature, or overmature stands. Therefore, it is prudent to assess how nutrient availability affects growth and whether fertilization may be useful in the long-term management of hardwood and mixed-wood stands.
Topics addressed in the review were: (1) the ecological roles and potential growth responses of hardwood species to fertilization as compared with the species' coniferous associates; (2) elements likely to be deficient in hardwoods; (3) growth responses of hardwoods to fertilization as affected by site conditions; (4) effects of fertilization on stress tolerance and mycorrhizal associates; and (5) tactics for ameliorating elemental deficiencies. Species-specific nutritional issues and operational contexts in which fertilization might be beneficial were also reviewed, and priority areas for research identified.
There is a considerable body of literature on the responses to fertilization by conifers, but virtually no published field studies of hardwood responses to fertilization in British Columbia. While principles developed from studies of conifer nutrition apply to hardwoods, site-specific growth responses to fertilization are likely much different in hardwoods than in conifers. The hardwood species of greatest importance generally predominate earlier in succession on wetter and more fertile sites than do coniferous species. These hardwood species also typically have greater growth rates when young, shorter lifespans, and greater annual nutrient requirements than do conifers of similar size. To achieve maximum growth rates, hardwoods may require greater quantities of nutrients than do conifers growing on sites of similar fertility.
Ongoing fertilization trials of hybrid poplar on Vancouver Island suggest that both N and P may limit growth. Growth responses may be considerable. A greater variety of options exist for delivery of nutrients than exist for native hardwood stands. Intensive breeding is producing numerous clones that differ in their growth rates and may differ in their abilities to grow on nutrient- and moisture-limited sites. Important still to do are the following: (1) relating site characteristics and fertilization response; (2) assessing the advantages and disadvantages of establishment-year fertilization vs. later (3rd -year) fertilization; (3) determining which forms of nutrients are most appropriate (e.g., organic vs. inorganic); and (4) predicting how clones vary in response to site fertility and to added nutrients.
Stands of native hardwoods are much less likely to be managed at the same intensity as are hybrid poplar plantations. Virtually nothing is known of native hardwood growth responses to fertilization in British Columbia, except with respect to black cottonwood in the southwestern part of the province. It will be important to confirm what elements are deficient, to predict how growth responses to fertilization will vary with soil moisture and soil nutrient regimes, and to identify at what stand ages it is appropriate to fertilize in order to maximize tree value at harvest. Ongoing fertilization studies of red alder and trembling aspen may provide some of this information. Studies of aspen, alder, and paper birch are of the highest priority because of their extent and potential product value, while studies of black cottonwood, balsam poplar, and bigleaf maple are of lower priority.
Red alder is unique among native hardwood trees in that it fixes atmospheric N2 in symbiotic association with the actinomycete Frankia sp. Fertilization trials and correlative studies of site:growth relations suggest that P may limit growth on some sites. Fertilization of young (1- to 4-year-old) stands has significantly increased growth, but various studies indicate the responses are sensitive to available soil P, soil moisture, and soil pH. Operational contexts in which nutrition may be an important factor include: (1) plantation management on sites considered appropriate for red alder; (2) management on Phellinus-infected sites that might normally be considered too dry and infertile for adequate growth of alder; (3) management on deactivated roads and landings; and (4) management of alder in repeated rotations on sites on which conifers are difficult to establish.
Working Paper 42 (478 KB)
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Updated July 24, 2015