Adjacent Clearcuts Research Articles

Distribution of Carabid Beetles (Coleoptera, Carabidae) across a Boreal Forest–Clearcut Ecotone

Abstract: We studied the occurrence of carabid beetles (Coleoptera, Carabidae) in boreal forest fragments, their edges, and adjacent clearcuts in central Finland. Beetles were collected with pitfall traps along transects extending 60 m from the edge into clearcuts and 60 m into forest interior. Our main findings were that (1) species richness was significantly higher in the clearcut than in the forest fragments, (2) clearcuts hosted many open‐habitat species, which increased overall species richness in these sites, (3) carabid assemblages in the edges were more similar to forest assemblages than to those found in the clearcuts, (4) no edge specialists were found, and (5) open‐habitat species did not penetrate into the forest fragments from the clearcut. Because forest specialists occurred all the way to the edge on the forest side, it seems that edge effects per se do not adversely affect these species, at least in the short term. In the long term, however, habitat conditions in the edges may deteriorate for interior species because of trees falling over in strong winds, thereby reducing the size of the fragments and widening the edge zone.

Post-Clearcutting Chronosequence in the B.C. Coastal Western Hemlock Zone

There is increasing interest in the use of simulation models to evaluate the sustainability of various forest management decisions. A key need in the development and use of such models is field validation of their predictions. Data from studies of a 26-year post-clearcutting chronosequence in the coastal western hemlock (CWH) zone of British Columbia, undertaken originally as an evaluation of the FORCYTE-11 and FORECAST models, were synthesized into a simple input-output model of forest floor N-storage. This model estimated forest floor N storage within 10% of field measured values in a 400-year-old Pacific silver fir (Abies amabilis [Dougl.] Forbes)-western hemlock (Tsuga heterophylla [Raf.] Sarg.) stand, and in three of four adjacent clearcuts ranging in age from 3- to 26-years. However, it overestimated forest floor N storage on the 6-year-old clearcut site by 78% (1027 kg N ha∼1). There appear to be three main possible causes of this overestimate: (i) the 6-year-old site was not a valid member of the chronosequence, (ii) overestimation of forest floor N inputs, or (iii) underestimation of forest floor N outputs. The latter was considered to be the most likely, and the source of error was hypothesised to be the failure to include dentrification losses in the model. Two laboratory studies were conducted to measure the production of N2O in soils from the old forest and clearcut sites that had been amended with various substrates and placed in an atmosphere enriched with acetylene. Actual and potential in situ de nitrification rates were estimated from these measurements. Actual denitrification rates increased after clearcutting but remained far too low to explain the discrepancy between the modeled and the measured forest floor N storage on the 6-year-old site. Potential denitrification rates were, however, within the range of values needed to balance the N-budget model with measured field values. Based on these measured potential rates, on a review of the factors controlling denitrification rates, and on past studies reporting high in situ rates occurring in favorable settings, it is proposed that enough presumptive evidence exists to support the theory that hotspots or hot intervals of denitrification occur during the assart flush following clearcutting, and that this may substantially reduce forest floor N storage.

Effects of clear-cutting on decomposition rates of litter and forest floor in forests of British Columbia

The rate of mass loss of three standard substrates (pine needle litter, aspen leaf litter, and forest floor material) was measured in forests and adjacent clearcuts at 21 sites throughout British Columbia, to test the hypotheses that (i) rates of mass loss are greater in clearcuts than in forests and (ii) clear-cutting would stimulate decomposition most in colder zones. Mass loss ranged from 53 to 75% after four years in pine needles, 49 to 70% after 3 years in aspen leaves, and 11 to 20% after 4 years in forest floor material. Mass loss from pine needles was significantly slower in clearcuts throughout the 4-year incubation. Aspen leaf litter and forest floor material lost mass at similar rates in forests and clearcuts. The effect of clear-cutting did not vary between relatively cold and warm sites. The effect of clear-cutting was not related to the size of the clearcuts, which ranged from 1 to 97 ha.

Elevated numbers of flying insects and insectivorous birds in riparian buffer strips

We compared the abundances of flying insects along undisturbed lakeshores and riparian buffer strips in balsam fir (Abies balsamea) forests in western Newfoundland. Insects were collected in pan traps placed on the forest floor and tanglefoot (sticky) traps suspended within the live canopy. Significantly greater numbers of insects were captured in riparian buffer strips than in undisturbed shorelines for four of five size classes in the canopy and two of five size classes in the understory. Collections were dominated by adult Diptera and Hymenoptera. Mean capture rates along buffer strips were 120-200% of the mean capture rates along undisturbed shorelines. This increase was greatest for large-bodied insects. A likely explanation for our observations is that buffer strips act as windbreaks, collecting airborne insects blown in from adjacent clearcuts and lakes. This phenomenon has been widely documented in agricultural landscapes. Understory wind speed was generally greater along buffer strips than controls, which is a reflection of increased exposure caused by clear-cutting. A concurrent parallel study conducted at the same sites investigated the effects of riparian buffering on breeding bird assemblages. Ubiquitous insectivorous birds, including the yellow-rumped warbler (Dendroica coronata) and blackpoll warbler (Dendroica striata), were more abundant along buffer strips than undisturbed shorelines, possibly in response to increased prey availability. Increased food availability may in part explain the high numbers of insectivorous birds typically observed in riparian buffer strips in boreal forests.

Riparian forest strips as habitat for snowshoe hare in a boreal balsam fir forest

Riparian forest strips are usually protected from logging for their buffer effect on aquatic habitats. However, their value to terrestrial wildlife species such as snowshoe hare (Lepus americanus Erxleben) is unknown. From 1990 to 1996, we compared habitat characteristics (shrubs and saplings 0.25-2.25 m high), hare browsing, and hare pellet densities in five types of experimental riparian forest strips (20, 40, 60, and >300 m wide intact strips, and 20 m wide thinned strips), in a humid boreal balsam fir (Abies balsamea (L.) Mill.) landscape managed primarily for timber harvesting in Quebec. Based on coniferous and deciduous shrub densities, all riparian forest strips and adjacent clearcuts remained low-quality habitats for hare over 6 years following clear-cutting. Only 103 shrubs were browsed in a 1500-m2 area sampled over 3 years, of which only 33 had >20% of browsed stems. Nevertheless, pellet data revealed a low but sustained use of all strips each summer and winter, and there were no changes over 6 years (mean 280 pellets/ha per month; P > 0.05). Whether hare populations are cyclic or not in our region remains an open question. However, they show some fluctuations and timber harvesting coincided with "high" hare populations in our study area. Sampling in "low" years might show that fewer hares occupy the forest strips. Further work is required to determine the influence of regional and local perturbations on the use of riparian forest strips by snowshoe hares.

Use of Riparian Buffer Strips as Movement Corridors by Forest Birds

We conducted a 3‐year field experiment to measure the frequency of bird movements through riparian buffer strips before and after harvesting of adjacent forest. Our study was conducted in the boreal mixed wood forest of Alberta and was designed to determine empirically whether songbirds use riparian buffer strips of forest connecting forest reserves as corridors and if they move along these buffer strips more frequently than they cross adjacent clearcuts. We used mist nets to obtain an index of the frequency of bird movement in the forest, and we observed bird movements across adjacent clearcuts for comparison. We predicted that the frequency of movement would be greater (1) in buffer strips after harvesting of adjacent forest than before harvesting, (2) in buffer strips than across clearcuts and, (3) in buffer strips than at control sites (lakeshore forest with no adjacent clearcuts). After adjusting for year‐to‐year variation in abundance, we found that capture rates increased significantly from pre‐ to post‐harvest, but only for juveniles. Capture rates of adults decreased immediately after harvesting, probably because of the removal of an adjacent source of birds that previously moved through the lakeside forest. Movement rates of forest species in clearcuts were significantly lower than capture rates in the forest. The number of adults captured was positively correlated with the number of territories in the buffer strips, indicating that most birds captured were probably residents. The number of local territories was a poor predictor of juvenile captures, supporting the notion that juveniles were likely dispersing individuals. Our results indicate that buffer strips enhanced movements of juveniles (i.e., acted as corridors) and maintained movement rates of adults. Furthermore, there appeared to be a threshold distance between reserves below which birds may be less reluctant to fly across openings, making corridor use less important.

Seed Banks of Carolina Bays: Potential Contributions from Surrounding Landscape Vegetation

-We used the seedling emergence method to evaluate the influence of the dominant vegetation (herbaceous, shrubby, forested) and the surrounding landscape on seed bank composition in seven Carolina bays. Landscape influence was evaluated indirectly by determining whether seed banks in wetlands close to clearcuts had more upland weedy species than those farther from clearcuts. Seed bank species composition and richness differed among forested, shrubby and herbaceous bays. DECORANA ordination identified a gradient of species composition from herbaceous bays, to shrubby bays, to forested bays. Bays near clearcuts had significantly more upland weedy species in their seed banks, with bays 20 m from clearcuts containing 79% more weedy species on average than bays 100 m from clearcuts. Within a bay, drier vegetation zones had 2.4 times more weedy species than did deep water zones. These results illustrate the potential contributions from surrounding landscape units to bay seed banks and highlight the need for further studies directly assessing the impact of adjacent clearcuts on bay vegetation dynamics.

Riparian Forest Strips as Habitat for Breeding Birds in Boreal Forest

Riparian forest strips are usually protected from logging for their buffer effect on aquatic habitats. However, their value to terrestrial wildlife is unknown. From 1989 to 1992, we compared bird abundance and species composition in 5 experimental riparian forest strips (20-m, 40-m, 60-m, and control [>300 m wide], intact strips, and 20-m-wide thinned strips), in boreal balsam fir (Abies balsamea) stands, for 3 years following clear-cutting. Bird densities increased 30-70% (P 0.05) thereafter to approximately pretreatment levels. The 20- and 40-m-wide riparian strips had highest mean bird densities, but also the fastest (P < 0.05) decreases thereafter. By the third year after clear-cutting, forest-dwelling species were less (P = 0.01) abundant than ubiquitous species in the 20-m strips. The golden-crowned kinglet (Regulus satrapa), Swainson's thrush (Catharus ustulatus), blackpoll warbler (Dendroica striata), and black-throated green warbler (D. virens) became nearly absent in 20-m strips. The removal of 33% of the trees in some 20-m strips resulted in a <20% decline of bird densities, a moderate effect that combined with the greater effect of strip narrowness. There was evidence that 60-m-wide strips are required for forest-dwelling birds. Bird populations may continue to decline in strips before regeneration of adjacent clear-cuts provides suitable habitat for forest-dwelling species

Vegetation Responses to Edge Environments in Old-Growth Douglas-Fir Forests.

Forest edges created by dispersed-patch clear-cutting have become a conspicuous landscape feature in western North America, but the effects of edge on forest structure and function are still poorly understood. In this paper we describe responses of stocking density, growth, mortality, and regeneration for three conifer species from the clear-cut edge into the interior of old-growth forest patches adjacent to 10-15 yr old clearcuts in southern Washington and central Oregon. The significance of edge effects for each variable was tested through a single-factor (distance) analysis of variance (F test). Relationships between these variables and depth-of-edge influence (i.e., edge width) on old-growth forest were characterized by nonlinear regression models. Near the edge (forest-clearcut boundary line), the old-growth forest has (1) reduced stocking density, as measured by canopy cover, number of stems per hectare, and basal area; (2) increased growth rates of dominant Douglas-fir (Pseudotsuga menziesii) and western hemlock (Tsuga heterophylla), as calculated by an index of relative growth rate; (3) elevated rates of tree mortality, as measured by standing dead and down trees (snags and logs); and (4) greater numbers of Douglas-fir and western hemlock seedlings (@<100 cm tall) and saplings (101-200 cm) but fewer of Pacific silver fir (Abies amabilis). The depth-of-edge influence, when calculated as the point along the clearcut-forest gradient at which a given variable has returned to a condition representing 2/3 of the interior forest environment, ranged from 16 to 137 m for variables related to distance from the edge. The amount of a square forest patch affected by edge decreased as patch size increased and varied greatly with the depth-of-edge influence. With increasing concerns about organisms and processes that require interior forest habitat, determining the area of residual forest influenced by adjacent clearcut is critical to current and future resource management. Responses of additional biological variables must be explored and information on edge phenomena should be extended to the scale of landscapes.

IN SITU NUTRIENT EXTRACTION BY RESIN FROM FORESTED, CLEAR-CUT AND SITE-PREPARED SOIL

Anion and cation resins were tested as sinks for nutrient ions under variable forest soil conditions. The resins, contained in nylon bags, were placed for periods of 4 wk below the forest floor of a softwood stand, and at approximately 7.5 cm depth on an adjacent clearcut with two different types of site preparation for tree planting. The soil was an Orthic Humo-ferric Podzol. Ion sorption below the forest floor, especially the sorption of ammonium, nitrate and phosphate, was strongly increased after clear-cutting of the forest. Sorption rates were generally lower in the mineral soil than immediately below the forest floor, except for nitrate and sulphate. Mixing of forest floor materials and fine logging debris into the mineral surface horizons generally increased resin sorption if compared to sorption in soil from which the forest floor had been removed. Resin sorption also revealed strong seasonal effects which may have been caused by changes in soil temperature and moisture. Key words: Ion exchange resin, forest soil fertility, seasonal nutrient fluctuation, site preparation

Slash Treatment After Clearcutting Lodgepole Pine Affects Nutrients in Soil Water

Abstract Soil solutions from old-growth lodgepole pine (Pinus contorta Dougl. ex Loud.) stands in western Wyoming differed from solutions beneath adjacent clearcuts where four residue disposal methods were applied. Soil solutions from clearcuts were more concentrated in sodium, potassium, magnesium, calcium, and nitrate. All elements, especially, nitrates, were most concentrated under burned windrows of debris. Phenol concentrations under a mulch of wood chips were high during the first posttreatment year, and sometimes exceeded 1 milligram per liter. Dilution of potassium, nitrate, and phenol concentrations would be expected as water moves from the soil to streamflow.

Effect of Forest Clear-Cut Edge on Breeding Birds in East Texas

Effect of Forest Clear-Cut Edge on Breeding Birds in East Texas