The influence of timber harvest on the structure and composition of riparian forests in the Coastal Redwood region

The composition and structure of riparian forests in the coast redwood region were analyzed in relation to the length of time since timber harvest, and the width of riparian buffer zone. Ten sites were sampled in the central range of the coast redwood forest type within a variety of post-harvest age groups and riparian buffer zone widths. Data was collected using randomly selected sample plots adjacent to perennial coastal steams. Correlation Fisher's r to z tests and two-tailed t-test were used to examine the relationship between the sample variables and the experimental parameters “years since harvest”, and “width of buffer.” Results indicate that canopy cover was negatively correlated to “years since harvest” with the highest level of canopy cover found on the youngest sites and the lowest level found on the old-growth sites. The hardwood to conifer dominance ratio and the basal area of Alnus rubra (red alder) were correlated negatively to both “years since harvest” and “buffer width” indicating that timber harvest favored hardwood species. Late seral associates such as Oxalis oregana (redwood sorrel), Anthyrium filix-femina (lady fern), and Vaccinium parviflorum (billberry) were found preferentially in older forests and sites with wider buffer zones, while non-native species such as Hedera helix (English ivy), Pampas cortedaria (pampas grass), and Myosotis latifolia (forget-me-not) were found preferentially in younger forests and areas with smaller buffer zones.     

Responses of stream macroinvertebrate communities to progressive forest harvesting: Influences of harvest intensity,stream size and riparian buffers

Harvesting of forests causes a range of disturbances, including changes to hydrology, nutrient inputs, water quality, food sources, habitat structure and channel morphology, which can impact streams over several years and are reflected in changes in community structure. We aimed to determine the relative magnitudes of impact and rates of recovery of benthic macroinvertebrate communities, and associated changes in biotic indices (Quantitative Macroinvertebrate Community Index and an Index of Biotic Integrity), in reaches of different sized streams within progressively logged catchments. We conducted annual summer surveys over seventeen years in fifteen New Zealand streams that differed in size (upstream catchment area between 40 and 2360 ha, mean channel widths between 2.5 and 16 m) and harvest intensity in the surrounding catchment. The largest post-harvest changes in biotic indices and community structures occurred in streams draining relatively small to medium catchments (<500 ha) where >40% of the upstream catchment had been harvested, and particularly after harvesting of overstorey riparian vegetation adjacent to study reaches. The impacts of harvest on invertebrate communities were less evident in wider streams draining catchments over 500 ha, but the largest changes from pre-harvest biotic indices and community structure still generally occurred after harvesting of riparian vegetation along these streams. The changes in community structure after harvesting of riparian vegetation typically included increases in the densities of Diptera, Mollusca and Oligochaetes, and decreases in the densities of Ephemeroptera. These results demonstrate that impacts on benthic macroinvertebrate communities increased as the proportion of upstream catchment harvested increased and/or after riparian vegetation was harvested. Some of the communities in headwater streams had largely recovered towards pre-harvest structures, whereas post-harvest recovery was less evident in relatively large streams, over the duration of the study.     

Impact of timber harvesting on litterfall inputs and benthic coarse particulate organic matter (CPOM) storage in a small stream draining a eucalyptus plantation

Eucalyptus plantations have a short rotation cycle and harvesting occurs every 12-15 years, with the potential to modify the ecological integrity of the small streams draining the harvested areas through the reduction of litterfall inputs. We studied litterfall inputs and benthic coarse particulate organic matter (CPOM) storage in a small headwater stream draining a eucalyptus (Eucalyptus globulus Labill.) plantation before and after clear felling of the plantation. We hypothesized that wood harvesting will result in a reduction of CPOM inputs and storage in the stream. Litterfall inputs ranged 530-700 g m⁻² y⁻¹ and were approximately halved (200-320 g m⁻² y⁻¹) after the harvesting of the eucalyptus trees. Bark and woody materials showed the largest reduction. Leaf inputs were initially reduced sharply, but, during the second year after the harvest, they recovered to about 90% of the values observed before the harvesting. Harvesting of the eucalyptus plantation caused an increase of benthic CPOM storage to 535 g m⁻², but this was a temporary effect and these materials were washed downstream of the study reach. One year after the harvesting, benthic CPOM was reduced below 15 g m⁻². Bark, twigs and other woody residues generated during the preparation of the logs for transportation were retained within the study site and represented the main component (>90%) of the benthic CPOM after timber harvesting. However, 2 years after the harvesting, low inputs of these materials caused an overall reduction of in-stream retention and residence time of benthic CPOM. Amount and composition of benthic CPOM changed quickly in response to alterations of the riparian forest, so we propose the use of CPOM as an indicator of the impact of forestry activities on the ecological functioning of small streams.     

Adoption of riparian forest buffers on private lands in Nebraska, USA

Pesticide and nutrient runoff from agricultural fields is a socio-environmental problem in the Midwestern United States. Riparian forest buffers (RFBs) are a proven conservation practice that effectively manage this problem, though adoption rates are low. A mail survey was conducted to determine differences between adopter and nonadopter characteristics and attitudes with regard to the use of RFBs. Data were collected from 48 RFB adopters and 261 RFB nonadopters in two Nebraska watersheds. Inferential and multivariate statistics were used to identify differences between adopter status and producer status groups. About half (50.8%) the respondents were nonproducers. Nonproducers are agricultural landowners not farming that make decisions about whether to install conservation practices on their land. Among the adopter respondents, non-farming agricultural landowners (nonproducers, n=25) were as likely to adopt RFBs as producers (n=23). Adopters were more informed about RFBs and willing to accept government payments. Receiving technical and financial assistance was a major key to adoption. The research has identified important opportunities for more effective and targeted RFB extension education programming.     

Vegetation structure,composition and effect of pine plantation harvesting on riparian buffers in New Zealand

The composition and structure of vegetation within riparian buffers prior to, and immediately post-harvesting in a managed radiata pine (Pinus radiata D.Don) forest is described and compared with riparian buffers in residual adjoining native forest on the Coromandel Peninsula, New Zealand. One hundred and twenty-one species (71% native) representing life forms from grasses to trees were recorded. The highest species richness, including both native and adventive (non-native) species, was found in riparian buffers in the post-harvest and native reference sites which had 18–25 species per site. Riparian buffers in mature pine plantations contained a mix of native species that was generally similar to, and not significantly reduced in species richness, from the reference native forest. Native species comprised 82–92% of the total cover in mature pre-harvest sites (irrespective of riparian width), and 99.8% in native reference sites. Compared with native forest the principal difference was a reduction of total cover in the upper tiers (5–12 m), and some increase in cover in the lower tiers. Adventive species in post-harvest sites comprised 16–67% of the total cover and were most frequently found in riparian areas highly disturbed by recent harvesting of the pines, particularly where riparian buffers were narrow or absent. Invasion by light-demanding adventives is expected to be temporary and most species are likely to be shaded out as the new rotation of pine trees develops. Radiata pine plantations in Whangapoua Forest can provide suitable conditions for the development of riparian buffer zones that will become dominated by native species, similar in richness and structure to neighbouring native forest.     

Efficacy of riparian buffers in mitigating local population declines and the effects of even-aged timber harvest on larval salamanders

Headwater streams are an important and prevalent feature of the eastern North American landscape. These streams provide a wealth of ecosystem services and support tremendous biological diversity, which is predominated by salamanders in the Appalachian region. Salamanders are ubiquitous throughout the region, contributing a significant biomass that supports ecological and ecosystem processes. One of the greatest threats to salamanders is loss of headwater-riparian habitat through timber harvest. In this study, we measured larval salamander abundance at five headwater streams with different riparian buffer widths retained following logging. By sampling larval salamanders using leaf litter bags, we assessed the impacts of even-aged timber harvest on aquatic larval salamander abundances, where it was found that larvae are negatively impacted by increased stream sedimentation and a decrease in riparian buffer width. We found that retention of a 9-m buffer was effectively no different than complete removal of all riparian forest, and as such, current regulations to protect headwater streams are ineffectual. Furthermore, no significant differences were observed between the 30 m buffer treatment and uncut control treatments suggesting that a 30 m or larger riparian buffer may assuage the in-stream effects of riparian timber harvest. Management guidelines for Appalachian forests should be revised to accommodate the biology of plethodontid salamanders.     

The relation of harvesting intensity to changes in soil, soil water, and stream chemistry in a northern hardwood forest, Catskill Mountains, USA

Previous studies have shown that clearcutting of northern hardwood forests mobilizes base cations, inorganic monomeric aluminum (Al_im), and nitrate (NO₃⁻-N) from soils to surface waters, but the effects of partial harvests on NO₃⁻-N have been less frequently studied. In this study we describe the effects of a series of partial harvests of varying proportions of basal area removal (22%, 28% and 68%) on Al_im, calcium (Ca²⁺), and NO₃⁻-N concentrations in soil extracts, soil water, and surface water in the Catskill Mountains of New York, USA. Increases in NO₃⁻-N concentrations relative to pre-harvest values were observed within a few months after harvest in soils, soil water, and stream water for all three harvests. Increases in Al_im and Ca²⁺ concentrations were also evident in soil water and stream water over the same time period for all three harvests. The increases in Al_im, Ca²⁺, and NO₃⁻-N concentrations in the 68% harvest were statistically significant as measured by comparing the 18-month pre-harvest period with the 18-month post-harvest period, with fewer significant responses in the two harvests of lowest intensity. All three solutes returned to pre-harvest concentrations in soil water and stream water in the two lowest intensity harvests in 2-3 years compared to a full 3 years in the 68% harvest. When the results of this study were combined with those of a previous nearby clearcut and 40% harvest, the post-harvest increases in NO₃⁻-N concentrations in stream water and soil water suggest a harvesting level above which the relation between concentration and harvest intensity changes; there was a greater change in concentration per unit change in harvest intensity when basal area removal was greater than 40%. These results indicate that the deleterious effects on aquatic ecosystems previously demonstrated for intensive harvests in northern hardwood forests of northeastern North America that receive high levels of atmospheric N deposition can be greatly diminished as harvesting intensity decreases below 40-68%. These results await confirmation through additional incremental forest harvest studies at other locations throughout the world that receive high levels of atmospheric N deposition.     

Influence of skidder traffic and canopy removal intensities on the ground flora in a clearcut-with-reserves northern hardwood stand in Minnesota,USA

We investigated the effects of skidder traffic intensity, soil disturbance intensity, and canopy removal intensity on the richness, diversity, composition, and cover of the entire ground flora (woody and herbaceous vegetation ≤2 m tall), various individual life forms, invasive/noxious species, and species with different requirements with respect to moisture, nutrients, heat, and light (synecological coordinates) in a mesic northern hardwood stand 6 years after a clearcut-with-reserves regeneration harvest removed 50–100% of the canopy. Skidder traffic was restricted to a network of trails and a global positioning system (GPS) tracked skidder movement to quantify the number of passes at pre-established sampling points along the anticipated soil disturbance gradient on and off skid trails. Soil disturbance intensity within the top 15 cm of soil was quantified by relativized resistance to penetration (RRP) compared to untrafficked plots; post-harvest increases in RRP ranged from 81 to 272%. Regression analysis and ordination revealed a pattern of increasing difference from pre-disturbance composition with increasing skidder traffic (i.e., forest floor disturbance), with increased RRP (i.e., soil compaction) and (less so) canopy removal intensity. The ground flora shifted from interior forest species such as Anemone quiquefolia, Aralia nudicaulis, Clintonia borealis, Maianthemum canadense, and Oryzopsis asperifolia to more ruderal, invasive/noxious, and disturbed-forest species such as Aster lateriflorus, Cirsium spp., Phleum pretense, Rubus idaeus, and Trifolium spp. The relative resistance of the initial ground flora to change (inverse of the distances between pre- and post-harvest samples in ordination space) was nonlinearly related to skidder traffic intensity and linearly related to RRP, indicating that the largest compositional changes occurred with the first few passes of the skidder. Mean plot scores for the synecological coordinates revealed that the post-harvest species were on average less demanding of water and nutrients; the opposite was true for light. Plots exposed to less skidder traffic and RRP had higher herb cover and higher nutrient scores; those with more skidder traffic and higher RRP levels had higher shrub cover and higher light scores. We conclude that protection of the ground flora from forest floor and soil disturbance requires careful planning of skid trail networks. Concentrating skidder traffic to a designated skid trail system can result in less area disturbed and spatially connected networks of larger, untrafficked remnant forest patches that may maintain species that are sensitive to forest floor and soil disturbance.     

Forest-floor temperatures and soil moisture across riparian zones on first- to third-order headwater streams in southern New England,USA

Riparian zones along forest streams in the western United States have been repeatedly shown to be floristically and climatically different from adjacent upland forest, and to be important contributors to forest biodiversity. Similar evidence for the presence or function of riparian zones is lacking for forests of the northeastern U.S. We conducted seasonal surveys of forest-floor temperature and soil moisture across 30-m riparian transects on first- to third-order streams in southern New England. We were unable to detect any effect of distance from the stream channel on either temperature or soil moisture. These preliminary results indicate the absence of a unique riparian forest-floor microclimate within 30 m of low-order streams in southern New England. While this study failed to identify a distinctive riparian microclimatic zone, protection of a riparian buffer during forestry operations or other disturbance is essential for the protection of forest streams and their resources and the maintenance of forest biodiversity.     

Effects of liana load,tree diameter and distances between conspecifics on seed production in tropical timber trees

Seed production in tropical timber trees is limited by abiotic resources, pollination and pre-dispersal seed predation. Resource availability is influenced by the number of competing trees and by lianas that often reach high densities in disturbed parts of tropical forests. The distance between conspecific trees affects pollination efficiency and seed predation intensity, and may therefore indirectly affect the long-term sustainability of selective logging. Here we investigate how reproductive status and the number of seeds dispersed per tree are affected by liana load, distance to the nearest conspecifics, number of competing neighbours and tree diameter in the timber trees Cariniana ianeirensis and Terminalia oblonga. The study is based on a large-scale silvicultural experiment in lowland Bolivia. We found that the reproductive status of the two species was negatively correlated with liana cover and positively with tree diameter. In C. ianeirensis the most liana-infested trees dispersed fewer seeds. In T. oblonga the intensity of pre-dispersal seed predation decreased with distance to the nearest conspecifics. There was no evidence that seed viability or seed production decreased with distance to nearest conspecifics in either species as would be expected if isolation resulted in increased self-pollination. Our results indicate that reproduction can be severely reduced in timber trees if the largest, most healthy and least liana-covered trees are logged, but that liana cutting on the remaining seed trees can considerably improve seed production. In some species seed production may be further improved by ensuring that seed trees are located far apart.     

The influence of silvicultural treatments and site conditions on American chestnut (Castanea dentata) seedling establishment in eastern Kentucky, USA

After more than 50 years of research and selective breeding, blight-resistant American chestnut (Castanea dentata) trees will soon be available for planting into the species’ pre-blight range. Increased understanding of the regeneration requirements of pure American chestnut (C. dentata [Marsh.] Borkh.) will increase the success of future efforts to establish blight-resistant chestnut. We quantified survival and initial growth of bare-root American chestnut seedlings at five locations in eastern Kentucky, USA. We used a split-plot design to compare seedlings planted within adjacent mesic and xeric sites treated with either a two-age shelterwood overstory treatment or a midstory removal treatment. The silvicultural treatments and topographic settings allowed us to evaluate chestnut seedling performance under four light and site productivity combinations. Seedling survival was 57% and seedling height averaged 94 cm following two growing seasons. Seedling survival was negatively related to sand and coarse fragment content, but was unrelated to silviculture treatment or topographic position. Chestnut seedlings grew best in shelterwood overstory treatments areas on mesic sites. Seedlings growing in shelterwood overstory treatment areas added 3- and 3.5-times more height and stem increment compared to seedlings planted after midstory removal. Seedling leaf mass and foliar nitrogen (N) content were also greatest in shelterwood plantings on mesic sites. The high-light environment created by shelterwood overstory removal resulted in better initial seedling growth, but the moderate-light of the midstory removal treatment may ultimately provide chestnut seedlings a greater advantage over competing vegetation.