Benoit Truax

Effects of straw and black plastic mulching on the initial growth and nutrition of butternut, white ash and bur oak

Abstract An experimental hardwood plantation was established in an abandoned field to test the effects of straw and plastic mulches on the growth and nutrition of seedlings of butternut ( Juglans cinerea L.), white ash ( Fraxinus americana L.) and bur oak ( Quercus macrocarpa Michx.). The plantation followed a randomized block design, where the factors were the species (three), the treatments (straw mulch, plastic mulch and control) and three replications (three blocks), for a total of 27 experimental units. Mulching significantly influenced soil temperature and humidity. Black plastic gave the highest values for soil temperature (34.7°C in July), whereas straw mulch produced the lowest (24.8°C in July). White ash and bur oak responded significantly and positively to the mulch treatments; butternut did not respond. Foliar nutrient contents revealed significant differences between species, and butternut had the highest foliar concentrations of N (34.6 and 26.9 mg g −1 ) of the three hardwood species in 1987 and 1988. These differences in nutrient requirements may be responsible for the different growth performances of the three species on the site. The findings will help in prescribing the appropriate species to be used in conjunction with mulches in hardwood plantations.

Herbicide-free plantations of oaks and ashes along a gradient of open to forested mesic environments

Abstract This study seeks to assess whether valuable hardwood species, red oak (Quercus rubra L.), bur oak (Quercus macrocarpa Michx.), white ash (Fraxinus americana L.) and red ash (Fraxinus pennsylvanica Marsh.), could be successfully underplanted in certain early successional vegetation types (alders, poplars, birch) in shelterwood systems, without the use of herbicides to control competing vegetation, as opposed to traditional plantations in abandoned fields. In the Eastern Townships region of southern Quebec, six different plantation sites, occurring along a gradient from open to forested mesic environments, were selected for this study: (1) old-field sprayed with herbicide; (2) old-field without herbicide; (3) alder (Alnus rugosa [Du Roi] Spreng.) stand; (4) aspen (Populus tremuloides Michx.) stand; (5) red pine (Pinus resinosa Ait.) plantation; (6) sugar maple (Acer saccharum Marsh.) forest. All of the forested sites were herbicide-free. After eight years of growth, results show that hardwood species can be successfully grown herbicide-free using shelterwood systems in mesic forested environments in southern Quebec. Planted trees have shown equal and even greater growth gains in forested sites in comparison with the open environments during the last year of growth. Species showed clear differences in growth response between forested environments. In forested sites, bur oak and both ash species had superior growth gains in the alder stand, while red oak had the highest growth gain in all other forested environments. Maximum height growth gain in forested environments was obtained in the aspen stand by red oak. Deer (Odocoileus virginianus) browsing has affected oak and ash species differently. Both ash species had unexpected reduced growth in the open environment with herbicide application, where conditions of resource availability are optimal. Although under heavy browsing pressure early on, red oak has had continuous growth gains in open environments. Both ash species and bur oak achieved better growth in the youngest stands (i.e. old-field and alder stand), whereas red oak achieved better growth in a relatively older stand (i.e. aspen stand) in our spectrum of the successional gradient. Past human activity has resulted in the disappearance of much of the hardwood forests in southern Quebec. However, the resulting successional stands provide an exceptional management opportunity for the herbicide-free reintroduction of valuable hardwood tree species, using shelterwood cuts and an integrated plantation system.

Nitrate reductase and glutamine synthetase activities in relation to growth and nitrogen assimilation in red oak and red ash seedlings: effects of N-forms, N concentration and light intensity

The effects of growing seedlings of red oak (Quercus rubra) and red ash (Fraxinus pennsylvanica) with Hoagland solutions containing five N-regimes, differing in the N-forms (NH4, NO3) and concentrations (High and Low), in relation to light intensity were investigated by the utilization of enzymatic markers of the N assimilation pathway, nitrate reductase (NR) and glutamine synthetase (GS). Red oak and red ash showed different patterns of N-assimilation. Red oak seedlings assimilated NO3 in low amounts in their roots and leaves, whereas red ash seedlings assimilated high amounts of NO3, mostly in the leaves. A significant amount of constitutive NR activity was found in red oak seedlings supplied with NH4 N-regime. This could be characteristic of a species adapted to soils that are poor in nitrogen. Root GS activity was lower in red oak seedlings than in red ash seedlings, indicating that the rate of NH4 assimilation differed in these two hardwood species. Low irradiance reduced growth of both hardwood species, but greatly affected the specific leaf area of red ash and reduced NO3 assimilation (when data are expressed per leaf area). Both species reacted similarly to N-regimes in terms of relative growth rate.

Nitrate reductase activity in relation to growth and soil N forms in red oak and red ash planted in three different environments: forest, clear-cut and field

Abstract Experimental hardwood plantations were established in three different environments (forest with partial openings, clear-cut and abandoned agricultural field) with different soil nitrogen status (N form and nitrification rates), in order to verify if NO 3 − assimilation of planted red oak and red ash seedlings could be linked to the performance of both species in the different plantation sites (where half of the plots were sprayed with herbicide). Nitrate reductase activity (NRA) in leaves and roots as an index of NO 3 − assimilation was chosen, as this enzyme is inducible and is also the first key enzyme involved in the assimilation of NO 3 − . Results show that NRA varied in relation to time, plantation environment, herbicide application and species of tree. Red ash always had higher values (18.43 μmol NO 2 g −1 dry weight (DW) h −1 ) than red oak (2.06 μmol NO 2 g −1 DW h −1 ) in herbicide plots in open environments, especially in the field plantation in July 1990. Herbicide spraying increased NO 3 − availability in soils and acted as a test for the presence of inducible nitrate reductase in both species. An increase in NRA is found in relation to herbicide application. Red ash shows greater differences than red oak between herbicide and control treatments. Both species show different values of height and diameter increment, and relative growth rate (RGR) in relation to the plantation sites. Red oak seedlings show greater growth gains in clear-cut with herbicide treatment (RGR = 0.79 g g −1 month −1 ), whereas the field plantation site produced the largest red ash seedlings (RGR = 0.56 g g −1 month −1 ) in herbicide plots. In limited light conditions (clear-cut control plots and forest environment), red oak had higher RGR than red ash. These results suggest that NRA in the leaves of hardwood trees can provide a useful index to evaluate the physiological status of tree seedlings, which reflects their response to environmental conditions. The use of such an index could facilitate the matching of hardwood species, according to their N requirements, to plantation sites, evaluated in terms of soil N status and light conditions.

Hybrid poplar plantations are suitable habitat for reintroduced forest herbs with conservation status

Plantations of fast-growing tree species may be of use in conservation by accelerating the restoration of forest habitat on abandoned farmland and increasing connectivity in fragmented landscapes. The objective of this study was to determine if hybrid poplar plantations can be suitable habitats for the reintroduction of native forest plant species and, if so, which abiotic factors predict successful reintroduction. Four species of forest herb species (Trillium grandiflorum, Sanguinaria canadensis, Maianthemum racemosum, Asarum canadense), of which three have legal conservation status, were transplanted into experimental plantations of two hybrid poplar clones and nearby second-growth woodlots at six sites in southern Quebec, Canada. The transplanted individuals were protected from deer browsing with exclusion cages. After two years, the plant responses of all four species were stable or increased over two years in both types of hybrid poplar plantations. Sanguinaria showed a better response in the plantations than in the woodlots, preferring the rich post-agricultural soils of the plantations with low C:N ratios. Asarum and Maianthemum showed no significant difference between stand types, while Trillium grew better in the woodlots than in the plantations. Much of the variability in the response of the latter three species was unexplained by the measured environmental variables. These results suggest that certain forest herb species can be reintroduced as juvenile plants into plantations, knowing that their spontaneous recolonization is often limited by dispersal and/or seedling establishment. Plantations could also contribute to the conservation of biodiversity by providing an environment for the cultivation of forest herb species as an alternative to their destructive harvest from natural populations.

Growth and N nutrition, monitored by enzyme assays, in a hardwood plantation: effects of mulching materials and glyphosate application

Abstract The effects of mulching materials (black plastic and straw) and herbicide application (glyphosate) on growth and nitrogen nutrition of butternut ( Juglans cinerea ), white ash ( Fraxinus americana ) and bur oak ( Quercus macrocarpa ) were studied in a plantation established in an abandoned field in southern Quebec (Canada) since 1987. To ascertain the efficiency of mulching materials on the performance of tree seedlings, a herbicide (glyphosate, 6 l ha −1 ) was applied in half of the experimental plots in June 1990 and 1991. Soil parameters (temperature, moisture) and soil nitrate and ammonium concentrations were measured during the growing season in 1991. In summer 1991, nitrogen nutrition of the seedlings was monitored using enzyme assays (nitrate reductase activity (NRA), glutamine synthetase activity (GSA)) of the leaves of the three deciduous tree species. Mulching affected soil parameters, with black plastic producing the highest soil temperature (23.4°C) and straw the highest soil moisture (183.6 g kg −1 ) in June. NRA varied in relation to tree species, herbicide application, mulching material and time. GSA was poorly correlated to silvicultural treatments. Butternut showed the highest NRA, especially in herbicide plots irrespective of mulching material. Bur oak NRA showed less variation between herbicide and non-herbicide plots and reacted more to the mulching treatments. White ash NRA only showed an herbicide effect in June. All species reacted positively to the addition of an herbicide around the mulching material, but not to the same degree. Height and diameter increment ratios (with/without glyphosate application) indicate that butternut growth was the most improved by herbicide applications, followed by white ash and bur oak. This indicates that the effectiveness of mulching alone decreases in the following order: bur oak > white ash > butternut. The utilization of mulching material in abandoned fields as an alternative to herbicide application is closely linked to the species chosen. Enzyme assays (NRA) were shown to be a valuable tool for monitoring physiological status of planted trees subjected to environmental changes brought on by silvicultural practices.

Clone-Specific Response in Leaf Nitrate Reductase Activity among Unrelated Hybrid Poplars in relation to Soil Nitrate Availability

In this field study, we used in vivo NRA activity in hybrid poplar leaves as an indicator of assimilation for five unrelated hybrid poplar clones. We also examined if leaf NRA of these clones is influenced to the same extent by different levels of soil availability in two riparian agroforestry systems located in pastures. Leaf NRA differences of more than one order of magnitude were observed between the clones, clearly showing their different abilities to reduce in leaves. Clone DxN-3570, a P. deltoides x P. nigra hybrid (Aigeiros intrasectional hybrid), always had the highest leaf NRA during the field assays. This clone was also the only one to increase its leaf NRA with increasing soil availability, which resulted in a significant Site x Clone interaction and a positive relationship between soil concentration and NRA. All of the four other clones studied had one or both parental species from the Tacamahaca section. They had relatively low leaf NRA and they did not increase their leaf NRA when grown on the rich site. These results provide evidence that assimilation in leaves varies widely among hybrid poplars of different parentages, suggesting potential preferences for N forms.

Invasive glossy buckthorn impedes growth of red oak and sugar maple under-planted in a mature hybrid poplar plantation

Native tree seedlings (nursery produced) were planted under control and herbicide treatments in the understory of a mature hybrid poplar plantation, naturally invaded by glossy buckthorn, a major invasive exotic shrub of Eastern North America. The objectives were to (1) test the negative effect of the invasive buckthorn on seedling growth, (2) determine if this effect differed for two tree species with different shade tolerances and edaphic requirements (sugar maple, red oak), and (3) determine if the type of canopy influenced this effect (5 clones). Confounding factors were reduced in this design (canopy composition and structure, age/size of seedlings), and several factors were controlled (transplantation date, deer exclusion). Several factors were measured (canopy openness, soil nutrients, canopy biomass, understory vegetation biomass, buckthorn density and biomass). After two growing seasons, seedlings of both species had reduced diameter and height increments under buckthorn. This difference was statistically significant for diameter increment. Canopy type did not have any effect on environmental variables or seedling growth. Buckthorn reduced light availability, but had no effect on soil moisture or soil nutrient availability. Consistent with sugar maple’s ecological requirements, its diameter growth was explained (multiple regression) firstly by edaphic variables (positive effect: soil humidity and K), and secondly by buckthorn biomass (negative effect). Red oak growth was explained firstly by buckthorn biomass, and secondly by understory vegetation biomass, both negative effects. Seedlings of species with higher light requirements (red oak) may have large growth reductions under buckthorn cover and have difficulty overtopping it. These results indicate that under-planting (plantations, forests) or afforestation should occur rapidly after buckthorn removal, otherwise this introduced invasive shrub may greatly reduce survival and growth of planted trees. Restoration of red oak to areas of former abundance will likely be more difficult because of the competition from glossy buckthorn.