Search

Plant resorption of multiple nutrients during leaf senescence has been established but stoichiometric changes among N, P and K during resorption and after fertilization are poorly understood. We anticipated that increased N supply would lead to further P limitation or co-limitation with N or K [i.e. P-(co)limitation], decrease N resorption and increase P and K resorption, while P and K addition would decrease P and K resorption and increase N resorption. Furthermore, Ca would accumulate while Mg would be resorbed during leaf senescence, irrespective of fertilization. We investigated the effect of N, P and K addition on resorption in two evergreen shrubs ( Chamaedaphne calyculata and Rhododendron groenlandicum) in a long-term fertilization experiment at Mer Bleue bog, Ontario, Canada. In general, N addition caused further P-(co)limitation, increased P and K resorption efficiency but did not affect N resorption. P and K addition did not shift the system to N limitation and affect K resorption, but reduced P resorption proficiency. C. calyculata resorbed both Ca and Mg while R. groenlandicum resorbed neither. C. calyculata showed a higher resorption than R. groenlandicum, suggesting it is better adapted to nutrient deficiency than R. groenlandicum. Resorption during leaf senescence decreased N:P, N:K and K:P ratios. The limited response of N and K and the response of P resorption to fertilization reflect the stoichiometric coupling of nutrient cycling, which varies among the two shrub species; changes in species composition may affect nutrient cycling in bogs. [ABSTRACT FROM AUTHOR]

Density estimates for habitat objects are used for a variety of forestry and wildlife management applications, but supporting field work can be costly. We used point simulations and field studies of snags and shrub stems to evaluate and compare the plotless Batcheler-corrected point distance (BCPD) method of data collection with the plot-based belt transect (BT) method for estimating object density (snags and shrub stems). The program Transect Point Density () was used to calculate density and confidence limits. Relative to the BT method, we found the BCPD method performs well under a range of clustered and random dispersion patterns and point densities, with measurements made to the nearest neighbour of the initial point object allowing correction of bias caused by nonrandom spatial dispersion patterns. The BCPD parameter of spatial dispersion, A1, was correlated with I, the variance-to-mean ratio used to estimate spatial dispersion in plot-based samples. The BCPD method also allows measurement to the third object (next-nearest neighbour) to account for second-order clumping, but we found that this estimate was sensitive to measurement error or technique where dense mats of wetland shrub species Ledum groenlandicum Oeder or Myrica gale L. occurred. We also used BCPD to characterize shrub community structure and found no evident bias, relative to BT data, for estimating relative species composition, richness, and diversity. The BCPD method was cost-effective relative to the BT method, with cost ratios 4-47 times higher for the BT method, and for a given investment allowed sampling of a greater area and diversity of stand conditions. Consequently, the BCPD method will facilitate collection of better data for developing and testing habitat models as well as evaluating the effects and effectiveness of forest management options at both the stand and landscape scales. [ABSTRACT FROM AUTHOR]

Harvesting of medicinal plants from wild populations is increasing worldwide, however, studies on sustainable harvesting techniques are lacking. In this exploratory study, we investigated the impact of leaf harvesting on (Oeder) Kron & Judd, a North American temperate shrub, used traditionally as a medicinal plant by the Cree Nation. The species is widely distributed, but Crees are worried that commercial harvesting could threaten local plant populations. Our study was conducted near the Cree Nation of Mistissini (James Bay, Northern Quebec). Three leaf harvest regimes were tested in 2008 and 2009: no harvest, all leaves harvested, and only old leaves harvested; each treatment was performed on 30 plants. The harvesting of all leaves had a negative impact on stem elongation after the first harvest, while leaf production and stem radial growth decreased after the second harvest. Two-thirds of the plants also died following the second regime of harvesting all leaves. The harvesting of old leaves had no significant impact on growth, leaf production, or survival of R. groenlandicum, even after 2 years of harvest. These results lead to the conclusion that sustainable harvest of this species is possible, but further study is required to make definite recommendations. [ABSTRACT FROM AUTHOR]

The article presents the Rhododendrum groenlandicum (Oeder) Kron and Judd, bog Labrador tea, an evergreen shrub from the Ericacae family native to North America. Its other names include bot tea, rusty Labrador tea and Hudson Bay tea and has long been known as Ledum groenlandicym Oeder 1771, non Retzius 1779. Its leaves are described as alternate, simple 2.5 cm long and 0.5-2 cm wide sessile or short-petioled. It cites its responses to herbivory such as mammals, insects and nematodes, diseases such as fungi, viruses and bacteria.

Abstract: Vegetative layering of black spruce (Picea mariana [Mill.] B.S.P.) is the principal mode of regeneration for over mature, uneven-aged stands subject to long fire cycles (>300 years) in northeastern Québec, Canada. However, growth response of black spruce layers following disturbance by fire or harvest can be slow, due to a lag of morphological acclimation and potential nutrient limitation. This phenomenon can be accentuated if black spruce is associated with ericaceous shrubs such as Kalmia angustifolia and Rhododendron groenlandicum, which are known to interfere with conifer growth through direct and indirect competition. Such interactions can result in productive stands being converted to unproductive heathlands. It is not known whether these effects of ericaceous shrubs on black spruce are accentuated on low fertility sites, or if the impacts are independent of inherent site fertility. The objectives of this study were to evaluate the effects of ericaceous shrubs on both resource availability and on functional traits of black spruce advance regeneration across a gradient of site fertility (as defined by a site classification system). We monitored black spruce advanced regeneration physiology and soil nutrient availability over two growing seasons on a gradient of ecological site types in northeastern Québec (Canada). The eradication of competing vegetation favored higher soil NH4-N and K availability, with increases of 67% and 28% compared to control conditions, respectively. Black spruce photosynthesis rate (A) and foliar K content were higher in plots where vegetation was eradicated, compared to the control plots, but did not vary among ecological site types. Photosynthesis did not appear to be limited by nitrogen or water relations, but was possibly limited by a deficit of foliar K+, probably resulting from reduced availability following sequestration by the ericaceous root systems. The absence of interaction between inherent site fertility and the eradication of ericaceous shrubs suggests that vegetation management of ericaceous shrubs must be planned independently from the ecological site type. [Copyright &y& Elsevier]

Northern peatlands are substantial sinks of carbon (C), yet the sources of carbon dioxide (CO2) emitted from peatlands are largely unknown. Since the relationship between roots and peat in C cycling is important, vascular plants growing on the surface of peat deposits should influence CO2 efflux from the peat surface and the overall C balance in peatlands. In our study, 30-cm peat cores were removed from an ombrotrophic bog in boreal, continental western Canada. Surface vegetation in the cores remained intact and included a continuous bryophyte cover dominated by Sphagnum fuscum. In addition, some cores were collected such that either ericaceous shrubs (Ledum groenlandicum) or sedges (Eriopho rum vaginatum) were present. We investigated how the presence of each vegetation type influenced soil respiration and the microbial mineralization of root exudates using a pulse 14C labeling of vegetation in the intact peat cores. The role of root biomass and root respiration in CO2 emission and C allocation was quantified for each type of vegetation and compared through both measurement and modeling. Our results show that vascular plants contributed 35-57% of total CO2 efflux from the peat surface, primarily derived from rhizosphere processes, including root respiration as well as microbial mineralization of root exudates. The mineralization of root exudates contributed 14-53 μmol C-CO2∙m-2d-1 (17- 24% of total) to CO2 efflux, depending on vegetation type and moisture conditions. The type of vegetation present did not influence the total amount of photosynthetic fixation over the course of the study, but did affect how C was allocated within and between both the aboveground and belowground components of the peat column. [ABSTRACT FROM AUTHOR]