Philip J. Burton

A GAP-BASED APPROACH FOR DEVELOPMENT OF SILVICULTURAL SYSTEMS TO ADDRESS ECOSYSTEM MANAGEMENT OBJECTIVES

Abstract Foresters have traditionally managed forests with silvicultural systems that prescribe stand homogeneity for optimized tree growth. The primacy of timber as the dominant objective is giving way to broader objectives such as sustaining the function and dynamics of ecosystems, maintaining ecosystem diversity and resilience or protecting sensitive species, while providing for a variety of ecosystem services of value to humanity. Protection and production of more diverse forest values demands consideration of the fine-scale variability found within forest stands and an understanding of the spatial and temporal response of forest ecosystems to manipulation. Studies of gap dynamics have contributed significantly to our understanding of the role of small-scale disturbance in forest ecosystems, but have been used little by foresters for predicting ecosystem response to partial cutting. We review the gap dynamics literature paying special attention to papers that use gap size or position as predictive variables for responses indicative of silvicultural success or maintenance of ecosystem function. Like canopy gaps created by natural tree death or windthrow, gaps are also generated by silvicultural systems which remove dominant trees. Results from the Date Creek silvicultural systems study in northwestern British Columbia presented here demonstrate the utility of a gap-based approach for understanding ecosystem responses to tree cutting. We propose a gap-based approach for study response to silvicultural manipulation that: (1) aids development of cutting prescriptions that maintain functional mature or old-growth conditions; (2) refines and extends our understanding of how biological structures, organisms and ecosystem processes are affected by fine-scale variation within stands; and (3) leads to development of novel silvicultural systems that meet timber production objectives, without compromising ecosystem management principles.

Phenology-mediated effects of climatic change on some simulated British Columbia forests

We added certain aspects of species-specific phenology, and of local frost regimes to a standard invididual-based patch model of forest stand dynamics, which we used to explore the possible consequences of four climate-change scenarios in eight distinct forest regions in British Columbia, Canada. According to model projections, lowland temperate coastal forests will be severely stressed because forest tree species will no longer have their winter-chilling requirements met. High-elevation coastal forests may either remain stable or decrease in productivity, while interior subalpine forests may eventually resemble those now found in the coastal mountains. Southern interior forests are likely to persist relatively unchanged, while boreal and sub-boreal forests of the northern interior may become dominated by Douglas-fir and western larch, rather than by spruce and pine as at present. The rate of change in forest composition may be very high in some cases. Changes under the four climate-change scenarios generally vary in magnitude but not in direction. This exercise illustrates that different forest types might respond to a changing climate for different reasons, and at different rates.

Potential conflicts between timber supply and habitat protection in the boreal mixedwood of Alberta, Canada: a simulation study

Abstract The boreal mixedwood forests of northern Alberta, Canada, are now being brought under management for pulpwood production. A simulation modelling exercise was undertaken to evaluate the sustainability of planned logging operations, and to explore their potential effects on wildlife habitat. Model inputs include the species composition and age structure of the forest, annual coniferous and deciduous volume requirements, and descriptions of natural stand mortality and regeneration, operational constraints, and silvicultural policies. Simple habitat suitability submodels simulate the effect of changes in forest composition on wildlife species. The model was used to explore the implications of a variety of management policies over a 73 000 km 2 forest estate in the mixedwood region. Simulations of current harvesting plans indicate that projected levels of harvesting may be sustainable, but many wildlife species will lose substantial amounts of preferred habitat. Harvesting can probably not be sustained without converting most of the regions characteristic mixed-species stands to production of single species. Alternative plans which maintain unharvested reserve areas can protect habitat (areas of mixed stands in particular) for some wildlife species, but may entail significant increases in operating costs or reductions in harvest levels. Furthermore, the reserve strategies we considered are able to maintain only between 12% and 41% of high-quality habitat for species dependent upon older stands of commercially valuable timber. Because species have different habitat requirements, increased protection for some species may exacerbate habitat losses for others.

Root-zone soil temperature variation associated with microsite characteristics in high-elevation forest openings in the interior of British Columbia

Low soil temperatures have been suggested as a factor contributing to poor rooting of planted conifer seedlings and hence a cause for failure of some high-elevation reforestation efforts. Few studies have attempted to document soil temperature variation and its causal factors in post-logged, high-elevation openings during the growing season. A field survey of afternoon soil temperature (at a depth of −10 cm from the mineral soil surface) was conducted in six high-elevation clear-cuts located in the Engelmann Spruce-Subalpine Fir (ESSF) biogeoclimatic zone in central British Columbia, Canada. On a clear summer day, a difference of 8°C in afternoon soil temperatures was measured between the warmest microsites (bare mineral soil, 17.6 ± 2.5°C) and the coolest microsites (covered by forest floor and vegetation, 9.3 ± 0.7°C). Heavily covered microsites showed little diurnal or spot-to-spot (microsite) variation in soil temperature. Conversely, microsites with little surface cover exhibited the greatest spatial and temporal variability in soil temperature. Variation in afternoon root-zone soil temperature (T) was most strongly associated with the combination of thickness of duff (forest floor) (D), cumulative % vegetation cover (C), and % soil moisture (M). Comprised of these three microsite attributes, a multiple regression model, T = 24.06 − [1.05(ln(C) + 1.64(ln(D)) + 1.38(ln(M))] (R2 + 0.73) was created which predicts high-elevation afternoon soil temperatures to within ±2.0°C. Multiple regression models including relative surface irradiance (as a percentage of above canopy light), cumulative % vegetation height, micro-slope and micro-aspect were less predictive. The relationship between afternoon soil temperature and each microsite attribute generally showed a strongly negative curvilinear pattern, described by double exponential decay functions. Microsites associated with suboptimally low afternoon soil temperatures (< 12°C) during the growing season were widespread (70 to 80% of the sampled areas) in the surveyed high-elevation openings.

Planted conifer seedling growth under two soil thermal regimes in high-elevation forest openings in interior British Columbia

A field trial was conducted investigating the single season growth response of 1+0 313 PSB Engelmann spruce (Picea engelmannii Parry ex Engelm.) and lodgepole pine (Pinus contorta Dougl. ex Loud.) seedlings planted into two different soil thermal regimes at three high-elevation locations spanning 200 km in the Engelmann Spruce-Subalpine Fir (ESSF) biogeoclimatic zone in the Cariboo Mountains of central British Columbia. Temperature treatments represented the extremes of soil temperature commonly found in high-elevation clear-cuts. A warm soil treatment (clear day, mid-afternoon soil temperature in mid-summer of 18 to 25 °C at −10 cm) consisting of a bare mineral soil hummock (average dimensions of 100 cm × 100 cm × 40 cm) was contrasted with a cool soil treatment (clear day, mid-afternoon soil temperature in mid-summer of 10 to 13 °C at −10 cm) comprised of organic forest floor overlying mineral soil. By the end of the growing season, seedlings of both species planted into the warm treatment generally exhibited greater root, stem, foliage, and total seedling biomass than cool treatment seedlings. Measurements of root growth at 30, 60, and 90 days after planting showed that total root number and total root length were consistently greater for warm treatment seedlings than for cool treatment seedlings. Root growth was greater from the bottom rather than from the side of the root plug for all seedlings. These results suggest that the effect of low soil temperatures on outplanted styroblock conifer seedlings is pronounced and may be limiting growth performance in high-elevation plantations in British Columbia. We recommend silvicultural treatments that secure natural regeneration, ensure that warmer microsites are always planted, and utilize seedling stocktypes able to make rapid lateral root growth into warmer surface organic horizons.

Physiological recovery of freezer-stored white and Engelmann spruce seedlings planted following different thawing regimes

Logistic problems of large-scale reforestation necessitate freezer-storage of conifer seedlings. Frozen stock is typically thawed slowly at low temperatures for up to several weeks before shipping to the plantation site, but the necessity of this practice is questionable. Experiments were conducted to study effects of different thawing regimes on photosynthetic recovery, frost hardiness, water relations and growth initiation in “interior spruce” (white spruce (Picea glauca (Moench) Voss) and Engelmann spruce (Picea engelmannii Parry) hybrid complex). One year-old container-grown seedlings were planted after 9 days post-storage thawing at 5–15 °C or still frozen, directly from the freezer. During a 29 day observation period after planting, both groups showed changes in xylem water potential (Ψw), carbon fixation (A), stomatal conductance (gs), chlorophyll a fluorescence and xanthophyll cycle pigments. Treatment differences in fluorescence and pigments peaked within one hour after planting. All differences in Ψw, A, gs, ratio of internal to external CO2 concentration (Ci/Ca), fluorescence, pigments and root number disappeared after 5 to 8 days. Terminal bud burst occurred 2.6 days earlier in the pre-thawed seedlings. When seedlings were rapidly thawed in the dark at 21 °C they achieved maximum Ψw (−0.2 MPa) in 3–4 hour. When evaluated 45 min after planting, A, gs, Ci/Ca and fluorescence values of rapidly thawed seedlings were intermediate between those for seedlings planted frozen or after 9 days slow thawing, showing that the recovery process was well underway a few hours after removal from the freezer. These results suggested that a suitable on-site operational protocol for rapid thawing might be to lay frozen bundles on the ground at ambient temperature overnight. In field trials of this method, rapidly thawed seedlings broke bud 3.3 days later than slowly thawed stock and also had greater frost hardiness at time of planting. Height, shoot and root mass did not differ after 3 months growth.

The Mendelian compromise: A vision for equitable land use allocation

Abstract Many polarized land use conflicts, especially with respect to the development of natural ecosystems for industrial activity such as commercial forestry, are in need of equitable and flexible solutions. Assuming that major interests can be grouped into two competing proponent groups, that alternative land uses are equally appropriate and that they are equally important to society, the author suggests the use of zoning to protect approximately 25% of the land in an uncompromised natural state, offset by zoning of another 25% of the land for intensive commodity production. The remaining 50% of the land may include various combinations of compatible multiple use, and has the potential to emphasize either protection or production values in an uncertain future.

Effectiveness of soil amendments and revegetation treatments at Huckleberry Mine, Houston, British Columbia

Supplies of topsoil are often limited for use in mine reclamation activities; it may be necessary to build soils using locally available substrates. Revegetation test plots were established at Huckleberry Mine, Houston, B.C., to investigate the performance of seven native plant species treatments on stockpiled topsoils amended with (or without) non-acid generating (NAG) sand (obtained from desulphurized copper tailings) and NPK fertilizer. Seeding treatments (single or mixed species) consisted of species native to the mine site (local genotype) obtained from commercial seed (mixed genotype). Soil sampling and vegetation monitoring were conducted during for two growing seasons. NAG sand reduced some soil properties conducive to plant growth (e.g. cation exchange capacity), yet plant performance was not significantly lower than in soil-only plots. When combined with a fertilizer, plant performance significantly increased over non-amended topsoils. Trace element concentrations in supplemented soils were low and should not adversely affect plants or the local environment. Plant performance of blue wildrye (mixed genotype variety) was shown to be higher than all other species examined and is suggested as the best candidate for the revegetation at Huckleberry Mine.