Brian D. Titus

Patterns of Carbon, Nitrogen and Phosphorus Dynamics in Decomposing Foliar Litter in Canadian Forests

We examined the patterns of nitrogen (N) and phosphorus (P) gain, retention or loss in ten foliar tissues in a litterbag experiment over 6 years at 18 upland forest sites in Canada, ranging from subarctic to cool temperate. N was usually retained in the decomposing litter until about 50% of the original C remained. The peak N content in the litter was observed at between 72 and 99% of the original C remaining, with C:N mass quotients between 37 and 71 (mean 55). The rate of N release from the litters was not related to the original N concentration, which may be associated with the generally narrow range (0.59–1.28% N) in the litters. P was immediately lost from all litters, except beech leaves, with critical litter C:P mass quotients for P release being in the range 700–900. The rate of P loss was inversely correlated with the original litter P concentration, which ranged from 0.02 to 0.13%. The soil underlying the litterbags influenced the pattern of N and P dynamics in the litters; there were weak correlations between the N and P remaining at 60% C remaining in the litters and the C:N and C:P quotients of the surface layer of the soil. There was a trend for higher N and P retention in the litter at sites with lower soil C:N and N:P quotients, respectively. Although there was a large variation in C:N, C:P and N:P quotients in the original litters (29–83, 369–2122 and 5–26, respectively), and some variation in the retention or loss of N and P in the early stages of decomposition, litters converged on C:N, C:P and N:P quotients of 30, 450 and 16, when the C remaining fell below 30%. These quotients are similar to that found in the surface organic matter of these ecosystems.

Changes to mineral N cycling and microbial communities in black spruce humus after additions of (NH4)2SO4 and condensed tannins extracted from Kalmia angustifolia and balsam fir

Abstract Mechanisms responsible for conifer growth “check” on cutovers invaded by Kalmia angustifolia L. in central Newfoundland were studied by examining effects of added Kalmia and balsam fir ( Abies balsamea (L.) Mill) condensed tannins on black spruce humus N dynamics and microbial community development over 10 weeks using microcosms. Because of the silvicultural implications, interactions of tannins with fertiliser N, applied as (NH 4 ) 2 SO 4 , were also studied. Both tannin types significantly reduced NH + 4 –N leaching, whereas only Kalmia tannins reduced NO − 3 –N leaching, and then only from non-fertilised humus. Tannins did not significantly affect mineral N leaching from fertilised humus. Fertiliser N increased gross N mineralisation rates such that the increase in actively cycling N was many times greater than the increase in N leaching due to fertiliser N addition. Gross N mineralisation rates were higher in fertilised humus amended with tannins, suggesting possible toxicity of tannins on microbes at high N concentrations. Recovery of added tannins in leachate and in post-treatment humus samples was low. Net anaerobic N mineralisation decreased with tannin additions but increased with fertiliser N additions. There were few significant treatment effects on microbial properties derived from humus respirometry. Microbial biomass and basal respiration rates of all treatments declined by 30 and 37% respectively, indicating a general loss of available C during the experiment. The ratio of C mic -to-N mineralised as well as the nutrient deficiency index was lowest in humus amended with Kalmia tannins, suggesting higher microbial N deficiency in this treatment. Utilisation rates of various C sources by microbial communities showed distinctive patterns between pre-treatment and post-treatment humus samples, but did not reveal distinctive patterns among different treatments. Overall, results suggested that (1) condensed tannins decreased mineral N cycling abiotically by binding to and sequestering organic N sources, (2) fertiliser N counteracted negative effects of condensed tannins on humus N cycling, (3) microbial communities were N limited, which prevented abundant leaching of fertiliser N while maintaining fertiliser N in an active pool, and (4) the physiology and functional diversity of soil heterotrophic communities were controlled by C availability but were unaffected by tannin or fertiliser N additions. Further work is needed to determine the ecological importance of Kalmia tannins, relative to tannins produced by other plants, in reducing humus N availability on spruce cutovers.

The effect of Kalmia angustifolia on the growth, nutrition, and ectomycorrhizal symbiont community of black spruce

Abstract Kalmia angustifolia L. is an ericaceous shrub that frequently invades black spruce (Picea mariana Mill.) clear-cuts in central Newfoundland. Field observations suggest that on many sites where K. angustifolia grows, black spruce seedlings become chlorotic and stunted. Previous laboratory research has suggested that allelochemicals of K. angustifolia affect the growth and development of black spruce as well as the growth of certain ectomycorrhizal (ECM) fungi associated with black spruce. Black spruce seedlings close to ( 1 m) K. angustifolia were sampled from a clear-cut in central Newfoundland. The ECM community structure, degree of mycorrhizal infection, height, mass, root:shoot ratio, and the foliar concentrations of N, P, K, Ca, and Mg of spruce seedlings growing close to and far from K. angustifolia were examined. Seedlings close to K. angustifolia had significantly lower foliar concentrations of N and P, had a lower rate of mycorrhizal infection, and were more frequently associated with Phialocephala dimorphospora Kendrick, a potential root pathogen of black spruce, than seedlings growing far from K. angustifolia. There were positive linear relationships between black spruce foliar N concentration and total seedling height and biomass for seedlings growing away from K. angustifolia, but not for seedlings in close proximity to K. angustifolia. Hypotheses suggesting possible roles for nutrient competition, allelopathy, and K. angustifolias ability to increase the occurrence of the pseudomycorrhizal P. dimorphospora on black spruce are proposed.

Silvicultural options to promote seedling establishment on Kalmia–Vaccinium-dominated sites

Seedling growth is often hampered on sites dominated by Kalmia angustifolia. In June 2000, a trial was established on a clear-cut site in Quebec, Canada, with a high cover of Kalmia and Vaccinium species. The objectives were to evaluate how soil scarification and fertilization at the time of planting influence early growth and establishment of black spruce [Picea mariana (Mill.) BSP] and jack pine (Pinus banksiana Lamb.) seedlings. During the first 2 years, scarification reduced Kalmia cover three-fold and doubled the distance from seedlings to the nearest Kalmia stem. Scarification did not increase soil-extractable NH4-N concentration, and reduced soil potassium, calcium and magnesium. Scarification had no effect on seedling water stress. Seedling growth improved and foliar nutrient concentrations were generally higher in scarified plots than in unscarified control plots. No differences were observed between single- and double-pass scarification for any variables except for ground-level stem diameter of seedlings, which was greater with double-pass scarification (12.1 vs 13.1 mm). Spot fertilization increased seedling growth and foliar nitrogen concentrations. Jack pine growth was greater than black spruce growth, an effect enhanced when seedlings were fertilized.

Improvement of nutritional site quality 13 years after single application of fertiliser N and P on regenerating cedar-hemlock cutovers on northern Vancouver Island, B.C.

Post-clearcut silvicultural treatments, to improve tree growth and reduce salal (Gaultheria shallon) competition, were established in five different forest blocks on northern Vancouver Island, in 1984. Plots were either left untreated, brushed of competing salal vegetation, fertilized [(250 kg N + 100 kg P) ha-1], or brushed + fertilized. Three of these blocks were revisited 13 years later, in the summer of 1997, and various chemical, biochemical and microbial parameters were measured in forest floor humus samples to determine long-term effects of treatments on nutritional site quality. Brushing resulted in lower humus pH and extractable base cations, whereas fertilization increased Bray-extractable P. Over a 20-week aerobic incubation, significantly more N was mineralised in humus from fertilized plots than from brushed plots. Over a 14-d anaerobic incubation, significantly more N was mineralised in humus from the fertilized treatment than other treatments. Similarly, gross transformation rates of NH4+and NO3-, measured by 15N-dilution, were higher in humus from the fertilized treatment than other treatments. Ecophysiological indices of microbial communities (basal respiration, specific death rate, metabolic quotient, and energy deficiency index), derived by humus respirometry, suggested that there was higher available C in fertilized and brushed + fertilized treatments than in the brushed and control treatments. Total microbial biomass was equal to C-limited microbial biomass, which further confirmed that available C was the growth-limiting factor for microbial communities in all treatments. The prokaryotic fractions of microbial biomass in all treatments were approximately equal (≈ 65%). PCA ordination of microbial communities, based on C source utilisation patterns, showed a distinct clustering of humus samples taken from one of the sites. Within the cluster of samples taken from the other two sites, samples from fertilized plots scored separately from those from control plots. In salal foliage, concentrations of condensed tannins were higher in brushed and control plots than in fertilized and brushed + fertilized plots. In spite of other studies that have reported increased tree height following fertilization and/or removal of salal, results of the present study suggest improvement in nutritional site quality occurs only with fertilization, whereas brushing may in fact be detrimental. The long-term growth of hemlock observed in fertilized plots may be the result of changes to key ecosystem structures and processes brought about by increased speed of succession and accelerated canopy closure.

Interactions between Kalmia humus quality and chronic low C inputs in controlling microbial and soil nutrient dynamics

Abstract Glucose-C was repeatedly added to organic Kalmia humus from two sites of contrasting spruce productivity (i.e. rich and poor) and basal respiration, microbial biomass and metabolic quotient ( q CO 2 ) were measured over a 438 day incubation and compared to post-incubation soil mineral-N pools, anaerobic N mineralization rates, the nutritional deficiency index (NDI) of soil microbial communities and final soil weights. Repeated measures analysis of variance revealed a strong overall soil effect on basal respiration and microbial biomass and a strong overall glucose effect on microbial biomass and q CO 2 , whereas the analysis of within-subjects effects revealed strong interactions of the time factor with both soil and glucose on all three measurements. In the poor soil, glucose supported high microbial biomass and therefore low q CO 2 , until the end of the incubation, whereas in the rich soil, glucose also supported high microbial biomass and low q CO 2 , but these converged towards control (i.e. no glucose) values before the end of the incubation. Mineral-N pools were high in the rich control treatment only, whereas the NDI was high only in the rich + glucose treatment. Anaerobic N mineralization rates did not differ statistically among treatments. Glucose significantly decreased mass loss in the rich soil but not in the poor soil. The data support the conclusion that glucose addition to the rich soil inhibits microbial utilization of nutrient-containing soil OM for maintenance energy thus exacerbating nutritional defiencies, whereas glucose addition to the poor soil does not affect soil N cycling. Based on results of analytical pyrolysis performed on soil subsamples prior to the incubation, we hypothesize that higher amounts of tannins measured in the poor humus may have chemically immobilized and ultimately controlled availability of N.

Criteria and guidance considerations for sustainable tree stump harvesting in British Columbia.

Abstract Stump extraction for forest health has been carried out operationally in British Columbia (BC) for many years. Emerging bioenergy opportunities plus the anticipated need for more fibre because of reductions in timber supply may increase interest in stump harvesting, but there are numerous environmental, economic and policy barriers that must be overcome first before industrial-scale stump harvesting can be seriously considered in BC. The potential for a future change in practice provides an opportunity to learn from the existing literature and identify knowledge gaps. In this article we review the available literature on stump harvesting from the European Union within the context of BCs forests, economy, biodiversity, environment and policies. We provide recommendations on how the government of BC could move forward if they decide to enable stump harvesting for fibre and bioenergy, including assessment of net economic and carbon benefits and environmental effects, improvements in inventory and the scientific knowledge base needed to support policy and guidance, and investigation of operational enhancements.

Soil solution concentrations on three white birch sites in central Newfoundland following different harvesting intensities

Three white birch stands of differing site quality (good, intermediate, rich) in central Newfoundland were monitored using porous cup lysimeters to study changes in nutrient concentrations (NH4N, NO3N, PO4P, K, Ca, Mg, pH) in the soil solution following stem only and whole tree harvesting. Ammonium concentrations on the good and intermediate sites were not greatly affected by cutting, but stem only (STO) harvesting on the rich site led to increased concentrations that persisted for 3 y. Nitrate concentrations increased more on the intermediate than on the good site, but increases were smallest on the richest site. This was attributed to a combination of uptake by more vigorous advance regeneration (mainly alders) on the rich site, as well as wetter soil conditions that limited nitrification. Phosphorous concentrations were not greatly affected by harvesting. Potassium concentrations increased immediately after harvesting as K leached from slash on the STO treatments, plant remains and the forest floor, and decreased as these sources were depleted. Vegetation uptake and leaching associated with movement of NO3N were also controlling mechanisms on some sites. Calcium and Mg concentrations were correlated, and initially increased with harvesting, but on the richest two sites decreased below control stand levels after whole tree harvesting (WTH) at the end of 3 y. Movement of Ca and Mg was associated with NO3N on sites where there was a significant increase in NO3N concentrations following harvesting. Acidity decreased on the good site, increased after STO, but decreased after WTH on the intermediate site, and increased after both intensities of harvesting on the rich site. Nutrient concentrations in the soil solution were generally higher when slash was retained in STO treatments rather than removed in WTH treatments. This was attributed to a combination of increased mineralisation beneath the slash, increased leaching from the slash, and decreased plant uptake. In general, the soil solution data suggest that harvesting effects last for no more than 3 y for most nutrients on these birch sites in Newfoundland, and that whole tree harvesting generally had less impact on nutrient concentrations than stem only harvesting. However, this does not necessarily mean that net losses from sites were less with WTH, as this does not take into account nutrient fluxes or nutrient removals in slash.

Woodfuel Harvesting: A Review of Environmental Risks, Criteria and Indicators, and Certification Standards for Environmental Sustainability

Forest bioenergy feedstock production and harvesting systems range from small-scale fuelwood gathering to large-scale industrial plantations and the potential removal of all available aboveground and belowground biomass from intensively managed forests. Across this wide range of options for production and extraction, there is an equally wide range of potential impacts. It is critical that forest biomass procurement systems do not adversely impact forests or the environment; therefore, effective standards and planning tools, based on the best available scientific knowledge, must be in place to prevent these impacts from being realized, and hence ensure a sustainable industry. Sustainable forest management (SFM) certification schemes are one mechanism for applying measurable environmental standards (in the form of criteria and indicators, or C&I) to forest management systems. How existing SFM certification schemes and frameworks, such as C&I and Adaptive Forest Management, can be used to help guide sustainable biomass operations is discussed. The potential impacts of biomass production and harvesting on soil and water resources, site productivity and biodiversity in the forest, as well as issues related to greenhouse gas balances and global and supply-chain impacts, are evaluated. An example is then given of how principles and criteria for sustainable biomass production can be used to address these potential impacts.

Wood Energy: Protect Local Ecosystems

In their Policy Forum paper “Wood energy in America” (13 March, p. [1432][1]), D. deB. Richter Jr. et al. argue cogently for deployment of advanced wood combustion (AWC) systems to meet a range of objectives, and they demonstrate the potential economic and energy values of community-based AWC in