Clear-cutting is a controversial practice that is widely applied in forests managed for wood production in many parts of the world. This paper aims to provide an objective synthesis of the ecological effects of clear-cutting as a basis for more informed discussion of its merits and disadvantages. A definition of clear-cutting is put forward, and its place in modern productive forestry is described. Effects on microclimate, water, soil, nutrient cycling, and the diversity and composition of plant and animal species are reviewed. The effects of clear-cutting vary considerably depending on site conditions (such as climate, geology, and topography) and on the structure and composition of the forest, the extent and distribution of harvesting, the method used to extract the logs, and the length of time before the forest is removed again. However, it is evident that many of the ecological impacts commonly ascribed to clear-cutting, in fact, result from other stages of the wood-production process, such as the quality and intensity of roading, site preparation practices (such as mechanical disturbance or slash burning), and the intensity of control of noncrop vegetation. Situations where clear-cutting is inappropriate are described. It is argued that in the right situations, with appropriate safeguards, it is an environmentally sound practice that offers many advantages in terms of the production of wood fibre.Key words: clear-cutting, environmental impacts, microclimate, hydrology, soil, forest production, nutrient cycling, wildlife.

No abstract

No abstract

The number of fixed collectors required to sample the volume and cation content of throughfall precipitation in the coastal forests of British Columbia was examined by means of data from 134 collectors for throughfall volume and 83 collectors for throughfall chemistry. The relative heterogeneity of throughfall parameters in four forest plant associations was also examined. It was concluded that a sampling network suitable for quantifying throughfall volume will be inadequate for quantifying throughfall chemical parameters be· cause of the far greater spatial variability of the latter. This variability is compounded if the study area includes more than one forest plant association. The fixed-collector method was found to be far from ideal for accurate studies of the role of leaching in nutrient cycling because of the excessive number of collectors required. An analysis of the suitability of Wilm's method of roving collectors and Attiwill's modification thereof as alternatives indicated that Wilm's method is inapplicable to studies of throughfall chemistry, but that Attiwill's modification might permit a worthwhile reduction in the number of collectors required in some studies, especially those concerned with gross, long-term studies of leaching. Attiwill's method shares many of the drawbacks of Wilm's method, however, and will probably be unsuitable for many studies.The variability of the chemical data was greatest when expressed as concentrations. Conversion to kg/ha did reduce standard deviations somewhat, although the reduction was modest on all but the most highly variable study area. Sampling at longer intervals did not result in any reduction in the standard deviations of mean throughfall cation concentrations: the effect of longer collection periods on the data expressed as kg/ha was to increase standard deviations significantly. Weekly or more frequent collections are recommended for detailed studies of throughfall chemistry.

A variety of competing hypotheses have been described to explain yield decline in Chinese-fir (Cunninghamia lanceolata (Lamb.) Hook.) plantations. The difficulty in implementing field experiments suggests ecosystem modeling as a viable option for examining alternative hypotheses. We present a conceptual model of Chinese-fir yield decline and explore its merits using the ecosystem-based FORECAST model. Model results suggest that yield decline is caused primarily by a decline in soil fertility, largely as a consequence of slash burning in conjunction with short rotations. However, as tree leaf area declines, there is a transition (over subsequent rotations) from seed rain based competition to bud bank based competition, increasing the competitive impact of minor vegetation on tree growth. Short rotations increase understory survival between rotations and may cause a gradual shift from tree dominance to shrub/herb dominance over subsequent rotations. These effects are most evident on nutrient-poor sites, but understory competition poses a significant yield decline risk on good sites as well. We conclude that sustainable production in Chinese-fir plantations requires the avoidance of activities that compromise soil fertility and increase understory competition. The risk and severity of yield decline would be reduced by increasing rotation lengths and avoiding plantations on infertile sites.Résumé : Plusieurs hypothèses concurrentes ont été décrites pour expliquer le déclin du rendement des plantations de sapin chinois (Cunninghamia lanceolata (Lamb.) Hook.). La difficulté d'établir des expériences de terrain nous amène à considérer la modélisation des écosystèmes comme une option viable pour examiner des hypothèses concurrentes. Nous présentons un modèle conceptuel du déclin du rendement du sapin chinois et évaluons sa performance à l'aide du modèle FORECAST qui a l'écosystème pour fondement. Les résultats du modèle indiquent que le déclin du rendement est principalement causé par une diminution de la fertilité du sol qui serait en grande partie attribuable au brûlage des déchets de coupe jumelé à de courtes rotations. Cependant, avec la diminution de la surface foliaire des arbres, une transition s'opère (au fil des rotations), passant d'une compétition basée sur la pluie de graines vers une compétition basée sur la banque de bourgeons, ce qui augmente l'impact compétitif de la végétation basse sur la croissance des arbres. Les courtes rotations ont pour effet d'augmenter la survie des plantes de sous-bois entre les rotations et peuvent causer une transition graduelle d'une dominance des arbres vers une dominance des arbustes et des herbacées au fil des rotations. Ces effets sont plus manifestes dans les stations pauvres en nutriments, mais la compétition par les plantes de sous-bois risque aussi de diminuer significativement le rendement des bonnes stations. Nous concluons que pour obtenir une production soutenue des plantations de sapin chinois, on doit éviter les activités qui compromettent la fertilité du sol et...

The distribution of tree biomass and the allocation of production was measured in four stands of lodgepole pine (Pinuscontorta var. latifolia Engelm.), two growing on sites with xeric soil moisture regimes and two on sites with mesic soil moisture regimes. At the time of sampling the stands were 70–78 years old. Aboveground biomass ranged from 116.5 Mg•ha−1 on one xeric site to 313.1 Mg•ha−1 on one mesic site. Stem biomass represented 68 and 73% of total tree biomass on the xeric and mesic sites, respectively. Total root biomass represented between 20 and 28% of total lodgepole pine biomass. Fine and small roots (<5 mm diameter) represented 4 and 1.5% of total tree biomass on the xeric and mesic sites, respectively. Total net primary production ranged from 7.9 Mg•ha−1•year−1 on the xeric sites to 11.9 Mg•ha−1•year−1 on the mesic sites. Stemwood production represented 20 and 27% of total net primary production on the xeric sites and 35% on both mesic sites. Belowground production represented 38 and 46% of total net primary production on the two mesic sites (4.5 and 5.5 Mg•ha−1•year−1, respectively) and 55 and 66% on the two xeric sites (4.3 and 6.3 Mg•ha−1•year−1, respectively). Fine and small roots represented 82–94% of belowground production. Production allocation was in the following order: fine and small roots > stems > foliage > coarse roots > branches, for all but the wettest site, where stem production exceeded fine and small root production.

No abstract

The hydrological, thermal, and chemical characteristics of two small streams flowing through relatively undisturbed, low-elevation mountain watersheds in southwestern British Columbia were investigated. All observations and chemical analyses of ecosystems were consistent with the hypothesis that stormflow originated mainly from flow of water through soil macrochannels to groundwater and thence to streams. Water budgets indicated unmeasured groundwater losses. The streams exhibited annual chemical cycles for most parameters, with maximum values in late summer and early autumn and minimum values in winter and early spring. Nitrate concentrations displayed no consistent seasonal variation, whereas potassium and sulphate concentrations were relatively uniform throughout the year. Most chemical parameters decreased with increasing discharge, whereas dissolved oxygen concentrations increased.Potassium concentrations exhibited some increases and some decreases, and chloride, nitrate, and sulphate concentrations were generally not significantly related to discharge. Concentration-discharge relationships were used to infer the origin of stormflow water. Differences in the chemistry of the two very similar streams have important ramifications for the design of watershed nutrient studies. Nutrient budgets were very similar to those of other watersheds in humid temperate regions, with net losses of calcium, sodium, magnesium, potassium, chloride, and sulphur. Nitrogen and phosphorus exports in dissolved or particulate organic form were not measured. Based on dissolved inorganic measurements, nitrogen was accumulated, while any gains or losses of phosphorus were extremely small. THE STUDY AREATwo watersheds [Fdler, 1977] were studied at the University of British Columbia Research Forest, located at Haney, approximately 60 km east of Vancouver (Figure 1 ). The area has a marine, warm to temperate, rainy climate with an annual precipitation of 220-270 cm. Owing to the low elevation (140-450 m), snow falls only occasionally, and most precipitation is Pseudotsuga menziesii (Douglas fir) forests originating from a fire in 1868. Small amounts of Alnus rubra (red alder), Acer macrophyllum (big-leaf maple), and Betula papyrifera (western white birch) occur in occasional openings or wet sites. Part of one watershed (watershed C) is covered by forest which grew up following logging in the 1920's. METHODSSharp-crested 120 ø V notch weirs were constructed on the streams draining two small watersheds. The larger watershed was split into upper and lower sections by constructing a rectangular broad-crested weir on the stream about 600 m upstream from the V notch weir. This resulted in the collection of data from three distinct drainage areas: a small entire watershed (stream A) and the lower (stream B) and upper (stream C) sections of the second watershed. Thus 'stream B' and 'stream C' are the lower and upper sections of the same stream, respectively. Instrument shelters at the weirs housed Richards-type water level recorders and soil-air...