The influence of soil rutting severity on regeneration potential and seedling performance for black spruce-dominated peatlands

Excessive rutting continues to be recorded in post-harvest compliance inspections in black spruce peatlands across Ontario. These qualitative, visual assessments, however, cannot provide the necessary data to determine a site disturbance threshold that is linked to poor regeneration and seedling growth. In an attempt to provide this quantitative link, harvested black spruce [Picea mariana (Mill.) B.S.P.] peatland sites were surveyed and divided into severely rutted (non-compliant), moderately rutted, and non-rutted (compliant) blocks. In 1995, 2001, and 2006, each block was assessed for areal extent of rutting, number of plantable spots, moisture status, planting medium, competition level, stand density, species composition, and black spruce seedling survival and growth. Black spruce seedling survival in the severely-rutted block was significantly lower when compared with either the moderately rutted or the non-rutted blocks. A derived seedling survival model identified moisture class as having the largest influence on the probability of seedling survival. In terms of seedling growth, however, it was the non-rutted blocks that had the poorest performance. Based on a canonical discriminant analysis (CDA), competition factors, particularly ericaceous shrub cover, were the most important microsite factors influencing black spruce seedling growth. Overall, the moderately rutted block generated conditions that resulted in high conifer recruitment and good seedling survival and growth. Although the inference space of the study is small, the results suggest that black spruce peatland sites may benefit from a moderate level of site disturbance caused during harvest operations. Key words: Rutting severity, black spruce peatlands, survival, growth, microsite assessment

The role of salal in forest regeneration problems in coastal British Columbia: problem or symptom?

The ericaceous shrub, salal (Gaultheria shallon Pursch) is associated with forest regeneration problems on a variety of site types along the west coast of North America. On dry sites, salal is a serious competitor for water; on wet (cedar-salal) sites, salal is thought to limit nutrient availability to trees by competing, interfering with mycorrhizae and "short-circuiting" the nitrogen cycle through production of phenolic compounds. Short-term field experiments and laboratory and greenhouse studies provided some evidence of each of these effects. However, long-term results from a suite of silvicultural trials and associated ecological studies indicated that salal is not the fundamental problem for regenerating conifers on cedar-salal sites. Fertilization of cedar-salal sites caused a large and sustained response in tree growth regardless of the presence of salal, and growth responses to salal removal were much smaller than fertilization responses. Greenhouse experiments indicated that salal does not have allelopathic effects on germination or growth of conifer seedlings. In laboratory studies, salal did not demonstrate a greater capacity to take up organic N forms than the conifers, and molecular studies uncovered a vast diversity of mycorrhizal fungi associated with salal and hemlock roots. Together these findings indicate that the nutrient "short-circuiting" hypothesis, based on assumptions about ericoid versus non-ericoid mycorrhizal plants does not adequately describe the nutrition of plants in these ecosystems. We conclude that salal should be viewed as a symptom of the underlying problem of poor nutrient supply on cedar-salal sites, and that fertilization, rather than salal control, is the optimal solution for improving forest regeneration on these sites. Key words: ericaceous shrubs, fertilization, scarification, allelopathy,mycorrhizae, Gaultheria shallon, nitrogen

Natural revegetation of two block-cut mined peatlands in eastern Canada

Limited areas of post-mined peatlands are recolonized by Sphagnum-dominated communities. This study aims to recognize the spontaneous Sphagnum re-establishment process and to verify if Sphagnum directly colonizes the residual peat. Conditions favoring Sphagnum revegetation are suggested. Analyses of vegetation macrofossils of the newly formed peat allow the identification of colonizing species and vegetation succession profile. Botanical components of the pioneer horizon suggest that Sphagnum species can directly colonize the residual peat. When Polytrichum strictum (Kaulf.) Presl and Eriophorum spissum Fernald are present as early colonists, they are rapidly overgrown by Sphagnum species in the succession profile. Vegetation succession resulted mainly in the formation of hummocks and lawns dominated by Sphagnum fuscum (Schimp.) Klinggr., Sphagnum capillifolium (Ehrh.) Hedw., and Sphagnum magellanicum Brid., with a more or less dense ericaceous shrub cover. Floristic, hydrological, and chemical features indicate that a fibric peat accumulation ecosystem is progressively or partially restored.Key words: cut-over peatlands, restoration, Sphagnum, vegetation macrofossil, acrotelm.

Causes and amelioration of nutrient deficiencies in cutovers of cedar-hemlock forests in coastal British Columbia

Poor growth of conifer regeneration occurred on sites formerly occupied by old-growth cedar-hemlock (CH) forests in coastal British Columbia, 5–8 years after clearcutting and slashburning. Symptoms included chlorotic foliage and growth check of Sitka spruce, western hemlock, western red cedar and amabilis fir, coincident with the expansion of the ericaceous shrub, salal, on the cutovers. Fertilization trials identified N and P deficiencies as the cause of the growth check of conifers, and additions of 300 kg N ha−1 and 100 kg P ha−1 significantly improved tree growth rates. Equivalent growth responses were achieved with additions of sewage sludge and fish silage. Burning, cultivating, liming, higher planting densities or herbicide application, were less effective in promoting conifer growth. The nutrient deficiencies in conifers on CH cutovers were the result of two factors: low nutrient availability in soil and humus, and competition and interference from salal. Salal immobilized substantial amounts of N in biomass and an in vitro study suggested it was able to use organic forms of N through its mycorrhizal fungi. The mycorrhizae of salal also interfered with those of hemlock, which further reduced their ability to take up nutrients. High concentrations of phenolic acids were associated with salal, which interfere with mineralization and uptake of N. The low availability of N and P in CH cutovers originated in forest floors of the old-growth forests prior to clearcutting. Nutrient availability was low in all layers of the forest floor in CH forests, and this appeared to result from three main factors. First, cedar litter contains less N and more decay-resistant material than other species, and produces forest floors with low rates of N mineralization. Second, the forest floors in CH forests are wetter and have less soil fauna than in HA forests, leading to incomplete decomposition and mineralization of N. Third, the salal understorey in CH forests interferes with mineralization of N through the production of tannins. Key words: growth check, fertilization, herbicide, ericaceous shrub, sewage sludge, mycorrhizae, allelopathy, nitrogen availability, nutrient cycling, NMR analysis

Interaction of Douglas-fir with red alder and salal foliage litter during decomposition

Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) foliage litter was incubated in the laboratory in 100/0, 75/25, 50/50, 25/75, and 0/100% mixtures with foliage litters from red alder (Alnusrubra Bong.), a nitrogen-fixing tree species, and salal (Gaultheriashallon Pursh) an ericaceous shrub. Mass loss and mineral nitrogen content were measured at eight dates during the 32-week incubation. The occurrence of interaction between litters, observed as deviation from a linear trend across mixtures at each date, was determined by polynomial contrasts. Douglas-fir–red alder mixtures decomposed faster than predicted by mass loss from pure litters throughout the study, apparently because of nitrogen mineralized by the red alder component. Douglas-fir–salal mixtures decomposed more slowly than predicted between 7 and 25 weeks. The study demonstrates the potential for litters to interact with positive or negative effects on decomposition rates and emphasizes the need to examine such interactions if litter decomposition in the field is to be understood.

Comparison of humus horizons from two ecosystem phases on northern Vancouver Island using 13C CPMAS NMR spectroscopy and CuO oxidation

Much forested land in the wetter zones of northern Vancouver Island is characterized by thick humus layers, with two distinct ecosystem phases: the younger "HA" phase arising from disturbance is productive after clearcutting, but in the old-growth "CH" phase, seedlings suffer growth check after 5–8 yr, with reinvasion of the ericaceous shrub salal (Gaultheria shallon Pursh.). We used solid-state 13C nuclear magnetic resonance (NMR) spectroscopy and CuO oxidation to examine whether chemical differences in the humus might be associated with difference in forest productivity after clearcutting. NMR spectra of woody horizons, which were similar for CH and HA sites, were dominated by signals from lignin of decomposed wood. Non-woody humus types were typical of forest litter layers, and were dominated by signals in the O-alkyl region. The differences between CH and HA sites were: (i) higher tannin content in the CH sites, most likely from salal inputs and (ii) higher ratio of carbohydrate to lignin C, indicating less effective decomposition in CH sites. Oxidation with CuO also showed more advanced decomposition in the non-woody horizons of HA than of CH sites. Less effective decomposition possibly due in part to tannin accumulation could contribute to the lower forest productivity on salal-dominated CH sites in this region. Key words: 13C NMR, CuO oxidation, decomposition, humus, tannin, salal