Unfertilized Stands Research Articles

Nutrient supply modulates species interactions belowground: dynamics and traits of fine roots in mixed plantations of Eucalyptus and Acacia mangium

Belowground interactions are still poorly understood in mixed-species forests. We investigated the effects of soil fertility on belowground processes in mixed planted forests. The dynamics and traits of Eucalyptus and Acacia mangium fine roots (diameter < 2 mm) in plantations with 50% of each species were studied in a randomized block design established in a nutrient depleted soil. Stands with NPK fertilization applied at planting (F+) were compared to unfertilized stands (F-). In the 0–15 cm soil layer, Eucalyptus root mass density (RMD) was higher than Acacia RMD by 50% in F+ and 10% in F-, considering both ages. At 34 months of age, Eucalyptus RMD was 94% higher near Acacia trees than near Eucalyptus trees in F-. In this layer, Eucalyptus specific root length (SRL) was 21% higher than Acacia SRL at 16 months of age and was 10% higher in F- than in F+ at 34 months of age. The cumulative Eucalyptus fine root length production between 16 and 34 months was 66% higher in F- than in F+ in the 0–1 m soil layer. Fertilization increased the competition between species and led to a partial exclusion of Acacia fine roots from the nutrient-rich topsoil. Soil exploration by Eucalyptus roots in the vicinity of Acacia trees was higher in F- than in F+, which suggests that unfertilized trees benefited from facilitation through higher soil N availability and direct N transfer from Acacia trees.

Twenty-Five Years after Stand Thinning and Repeated Fertilization in Lodgepole Pine Forest: Implications for Tree Growth, Stand Structure, and Carbon Sequestration

Silvicultural practices such as pre-commercial thinning (PCT) and repeated fertilization have been used successfully around the world to increase forest biomass for conventional wood products, biofuels, and carbon sequestration. Two complementary studies were designed to test the hypotheses (H) that large-scale PCT and PCT with repeated fertilization of young (13–17 years old) lodgepole pine (Pinus contorta var. latifolia) stands, at 25 years after the onset of treatments, would enhance (H1) productivity and structural features (diameter and height growth, crown volume and dimensions) of crop trees; (H2) merchantable volume of crop trees, (H3) abundance of understory conifer, herb and shrub layers, and (H4) carbon storage (sequestration) of all layers. Results are from two studies in south-central British Columbia, Canada. The PCT study had three densities: 500, 1000, and 2000 stems/ha, an unthinned, and old-growth stand replicated at three areas. The PCT-FERT study had four densities: 250, 500, 1000, and 2000 stems/ha with and without a repeated fertilization treatment, and an unthinned-unfertilized stand, replicated at two areas. Heavily thinned (≤1000 stems/ha) and fertilized stands generally had larger mean diameters and crown dimensions than lightly thinned or unfertilized stands, whereas mean heights of crop trees remained relatively unaffected, and hence partial support for H1. Despite differences in stand density (4- and 8-fold) of original crop trees, ingress of intermediate crop trees over the 25 years changed density dramatically. There was no support for H2, as mean merchantable volume of total crop trees was similar across stand densities owing to ingress, and was also similar in fertilized and unfertilized stands. In stands thinned to ≤500 trees/ha, there is an anticipated increase in crop tree density of 2.2 to 4.3 times over 25 years compared with the original post-thinning densities. Mean abundance of understory conifers was generally similar among stands owing to successional development towards canopy closure, whereas herbs and shrubs persisted only in canopy gaps in heavily thinned stands, thereby providing no support for H3. Mean carbon storage was similar across densities in both studies with ingress contributing a considerable amount to carbon sequestration at the lower densities. Fertilization increased (1.4 times) mean carbon storage significantly among total crop trees, total conifers, and the grand total of all layers, thereby providing partial support for H4. Thus, much of the potential above-ground carbon storage lost by thinning was restored in the heavily thinned stands at 25 years post-treatment.

Nitrogen Availability Decreases the Severity of Snow Storm Damage in a Temperate Forest

Abstract Storms are among the greatest natural disturbances in temperate forests, and increased nitrogen (N) availability is thought to increase storm damage. However, the extent to which N availability increases damage from snowfall is less clear. To test how N availability might affect the susceptibility of trees to snow damage in a temperate forest, we took advantage of an opportunistic storm and surveyed damage in fertilized and unfertilized stands, and across a native N availability gradient. In response to a severe, early season snow storm—a consequence of Superstorm Sandy—the percentages of both basal area and stems damaged were lower in a fertilized watershed than in an unfertilized watershed. Across the native N availability gradient, the percentage of basal area damaged by snow decreased with higher soil N. The effects of N availability on damage were also affected by tree species. Our results suggest that N availability decreases damage from snow storms, contrary to our hypotheses drawn from broader studies. Understanding the relation between storm damage and N availability is important, considering the global increase in N deposition, and since severe storms are likely to become more prevalent with climate change.

Forage yield, water- and solar radiation-productivities of perennial pastures and annual crops sequences in the south-eastern Pampas of Argentina

Livestock production systems of Argentina show an ongoing process of change in the composition of their forage base, with a gradual increase in the proportion of their area assigned to forage crop sequences (FCS) −in particular that involving successive winter and summer annual forage crops–, at the expense of the area assigned to perennial pastures (PP). However, there are several concerns regarding the efficient use of available environmental resources due to differences in the extent of the establishment periods and due to the occurrence of fallow periods in FCS, as well as regarding the species involved in these systems. Therefore, the main objective of this study was to evaluate the water (WP) and solar radiation productivity (RP) of PP [pure stands of alfalfa (Medicago sativa L.), fertilized and unfertilized stands of tall fescue (Festuca arundinacea Schreb.), and fertilized and unfertilized mixed stands of alfalfa/tall fescue] and FCS [including a summer alternative and oats (Avena sativa L.); the summer alternative was either maize (Zea mays L.) or intercropped maize/soybean (Glycine max L.)] through the analysis of their components, i.e. water (WC) and radiation capture (RC), and their water (WUE) and radiation use efficiency (RUE). Resource capture (WC and RC) was defined as the ratio between captured (evapotranspiration and intercepted solar radiation) and annual available resource (rainfall and incident solar radiation). Resource use efficiency (WUE and RUE) was computed as the dry matter (DM) yield per unit of captured resource. A field experiment was conducted during two consecutive years under rainfed conditions and under non-limiting nitrogen availability in the south-eastern Pampas of Argentina. Perennial pastures were evaluated during both their initial establishment year (Y1) and when already fully established (Y2). Annual-based forage DM yield ranged between 13.0 and 32.4 Mg ha−1 in Y1 and between 5.1 and 23.5 Mg ha−1 in Y2. Differences in resource capture between PP and FCS were directly associated with the crop establishment and fallow periods depending on the nature of the considered resource. The highest WP (2.75–3.64 g DM m−2 mm−1) and RP (0.93–1.42 g DM MJ−1) were reached by FCS, which did not differ (P > 0.05) from that of fully established fertilized PP. Our results demonstrate that resource productivity in FCS is not necessarily higher than for PP, once PP are fully established.

Interactions with successional stage and nutrient status determines the life-form-specific effects of increased soil temperature on boreal forest floor vegetation.

The boreal forest is one of the largest terrestrial biomes and plays a key role for the global carbon balance and climate. The forest floor vegetation has a strong influence on the carbon and nitrogen cycles of the forests and is sensitive to changes in temperature conditions and nutrient availability. Additionally, the effects of climate warming on forest floor vegetation have been suggested to be moderated by the tree layer. Data on the effects of soil warming on forest floor vegetation from the boreal forest are, however, very scarce. We studied the effects on the forest floor vegetation in a long-term (18 years) soil warming and fertilization experiment in a Norway spruce stand in northern Sweden. During the first 9 years, warming favored early successional species such as grasses and forbs at the expense of dwarf shrubs and bryophytes in unfertilized stands, while the effects were smaller after fertilization. Hence, warming led to significant changes in species composition and an increase in species richness in the open canopy nutrient limited forest. After another 9 years of warming and increasing tree canopy closure, most of the initial effects had ceased, indicating an interaction between forest succession and warming. The only remaining effect of warming was on the abundance of bryophytes, which contrary to the initial phase was strongly favored by warming. We propose that the suggested moderating effects of the tree layer are specific to plant life-form and conclude that the successional phase of the forest may have a considerable impact on the effects of climate change on forest floor vegetation and its feedback effects on the carbon and nitrogen cycles, and thus on the climate.

Managing for water-use efficient wood production in Eucalyptus globulus plantations

This paper tests the hypothesis that thinning and nitrogen fertiliser can increase the mass of wood produced per volume of water used (evapotranspiration) by plantations of Eucalyptus globulus. We have called this plantation water productivity (PWPWOOD) and argue that, for a given genotype, this term integrates the effects of management, site and climate on both production and evapotranspiration. This is done using annual estimates of wood production and evapotranspiration from age three years to harvest age (∼age 10years) in three E. globulus stocking density by nitrogen experiments. The ratio of annual rainfall to potential evaporation at these three sites varied from 0.85 to 0.45.Plantation water productivity (PWPWOOD) was calculated as the ratio of annual growth to annual evapotranspiration. In this study, the PWPWOOD of E. globulus varied from 0.2 to 3.1gkg−1 and was significantly increased by the application of nitrogen at two sites where growth was nitrogen limited. In fertilised stands, soil stored water was depleted early in the summer while in contrast, unfertilised stands used the water more slowly, thereby extending the growth season to late summer when average daily evaporation was much higher. Increased PWPWOOD in response to nitrogen was associated with an increase in water stress that could be mitigated by reducing stocking density without affecting either production or PWPWOOD.Plantations are managed at the compartment scale while water resources are monitored and managed at the catchment scale or larger. At the compartment scale, growth and PWPWOOD are correlated with evapotranspiration; managing plantations to maximise water use can also minimise the impact of wood production on water resources.

Fertilisation, cattle grazing and voles: collapse of meadow vole populations in young forests?

Context A puzzling aspect of microtine population fluctuations is the damping out or collapsing of cycles over the last three decades, particularly in northern Europe. Occasional population fluctuations of Microtus may also have been damped out in temperate and boreal forests of the Pacific North-west of North America. One cause might be the presence of cattle (Bos taurus) grazing in forest habitats that offer summer forage. Aims We tested hypotheses (H) that abundance, population fluctuations, and demographic parameters of reproduction, recruitment and survival, of Microtus pennsylvanicus would be driven by understory plant productivity. Two predictions follow from this hypothesis: (H1) enhanced abundance and demography in fertilised stands, and (H2) reduced abundance and demography in stands with cattle grazing. Methods Study areas were located in ‘grazed’ and ‘ungrazed’ young forests in south-central British Columbia, Canada. Each study area had four replicate units of unfertilised and repeatedly fertilised stands. Herbaceous vegetation and meadow vole (M. pennsylvanicus) populations were sampled from 1993 to 2002. Key results Mean abundance of total herbs, grasses, and fireweed (Epilobium angustifolium) increased dramatically (8 to 34 times higher) with fertilisation in the ungrazed stands. Mean abundance of meadow voles was 3.1 to 8.5 times higher in the nutrient-enriched herbaceous vegetation in the ungrazed fertilised than grazed fertilised stands. Demographic variables also followed this pattern of abundance. Except for two years, mean abundance of meadow voles was similar between fertilised and unfertilised stands at the grazed area, with some degree of fluctuations generated in grazed stands. Thus, H1 and H2 were at least partly supported for M. pennsylvanicus in fertilised stands. Conclusions In high-quality habitats where cover and other attributes of vegetation are substantial enough to generate population increases and fluctuations of Microtus, grazing of vegetation by cattle or other livestock may indeed lead to potential collapse of fluctuations. Degree of grazing pressure would be crucial, but considering the widespread nature of grazing in the continuum of post-harvest forested sites in the Pacific North-west of North America, moderate to heavy grazing pressure is common. Implications Reductions in populations of microtines have serious consequences for predator communities and other ecological functions.

Mule deer–cattle interactions in managed coniferous forests during seasonal grazing periods in southern British Columbia, Canada

Context In young forests of the Pacific North-west of North America, the potential impacts of domestic grazing by cattle (Bos taurus) on forest ecosystems and native ungulates such as mule deer (Odocoileus hemionus) are poorly understood. It is not clear how cattle and deer may interact in young forests used for summer range by both ungulates, and winter range used by deer, where pre-commercial thinning (PCT) and fertilisation enhance both timber and forage. Aims To test the following two hypotheses: (H1) that PCT and repeated fertilisation of young lodgepole pine (Pinus contorta var. latifolia) stands would increase relative habitat use by cattle; and (H2) that increased use of forested range by cattle would result in decreased use by mule deer. Methods Replicate study areas were located near Summerland, Kelowna, and Williams Lake in south-central British Columbia, Canada. Each study area had the following nine treatments: four pairs of stands thinned to densities of ~250 (very low), ~500 (low), ~1000 (medium), and ~2000 (high) stems ha–1 with one stand of each pair fertilised five times at 2-year intervals. Relative habitat use was measured by counting cowpies for cattle in summer and pellet groups for deer in summer and winter periods 1998–2003. Key results Relative habitat use by cattle was significantly enhanced by fertiliser treatments and heavy thinning, supporting H1. Relative habitat use by deer during summer periods was not affected by stand density, but was significantly higher in fertilised than unfertilised stands, with no difference in winter months, thereby not supporting H2. Conclusions Summer habitat use by mule deer appeared to be a function of forage opportunities and no significant correlations in relative habitat use between cattle and mule deer during the summer were detected. Negative correlations were better explained by the need for tree cover by deer during severe winter conditions than a negative response to cattle grazing. Implications Domestic grazing by cattle may be compatible with native ungulates such as mule deer, at least in those forest sites that are managed intensively for timber production. Fertilisation may result in sufficient forage production in the understorey vegetation of these forest ecosystems, to compensate for cattle grazing that reduces the live forage biomass.

Influence of stand thinning and repeated fertilization on plant community abundance and diversity in young lodgepole pine stands: 15-year results

Enhanced forest productivity may provide the supply of wood fiber to keep pace with increasing global demand for wood products and the growing constraints on the harvestable land base imposed by measures to conserve biodiversity. Stand thinning and fertilization are silvicultural practices that increase forest productivity in many situations. Intensive management has debatable impacts on plant species diversity with no consistent predictions from existing models and a general lack of long-term responses to treatments. This 15-year study was designed to test four hypotheses (H), that (H1) the application of a range of pre-commercial thinning (PCT) intensities will increase plant abundance in herb and shrub layers, (H2) fertilization will increase abundance of all plant layers (herbs, shrubs, trees, and combined total), (H3) PCT and fertilization treatments will decrease species and structural diversity of all plant layers, and (H4) enhanced abundance of vegetation will result in a decline in total species diversity and structural diversity. Study areas were located in lodgepole pine (Pinus contorta var. latifolia) stands near Summerland, Kelowna, and Williams Lake in south-central British Columbia, Canada. Each study area had nine treatments: four pairs of stands thinned to densities of ∼250 (very low), ∼500 (low), ∼1000 (medium), and ∼2000 (high) stems/ha with one stand of each pair fertilized five times at 2-year intervals, and an unthinned stand.Mean abundance (crown volume index) of herbs and shrubs were unaffected by stand density, and hence H1 was not supported. Mean abundance of herbs and mean total abundance of the plant community were significantly higher in fertilized than unfertilized stands, and hence H2 was only partially supported. Mean species richness of the herb, shrub, tree, and combined total layers were unaffected by density or fertilization. Mean species diversity of these layers were also unaffected by density, but fertilization reduced herb and shrub diversity, at least temporarily. Neither tree nor total species diversity were affected by fertilization. Mean structural diversity of herb and shrub layers were unaffected by stand density. Mean structural diversity of the tree layer was significantly greater in the most heavily thinned stands (250stems/ha) than in the unthinned and lightly thinned stands (2000stems/ha), and similar to that of the 500 and 1000stems/ha stands. Mean structural diversity of the total plant community was significantly enhanced by fertilization. Thus, H3 was partially supported for the fertilization-induced reduction in herb and shrub diversity, but structural diversity was unaffected or enhanced. A trend of decreasing total species diversity with increasing productivity supported H4. The changing relationship between productivity and structural diversity indicated that structure was more related to succession than productivity, and therefore our results did not support H4.PCT and fertilization clearly influence plant community abundance, diversity, and structure. This is one of the first studies to document the magnitude and longevity of these changes with a replicated, large-scale, and long-term study. PCT and repeated fertilization of young lodgepole pine stands appear to be management strategies compatible with wood production and biodiversity conservation.

Effect of fertilization on root growth in the wet submontane meadow

Root net primary productivity (RNPP) was assessed in the wet submontane meadow in the highland region of the Czech Republic. RNPP was studied from 1992 to 1995 with help of the in-growth core technique. The effect of different intensities of fertilization on root growth was covered. In comparison with unfertilized stands, the application of fertilizers (90 kg N/ha) resulted, mostly significantly, in greater root productivity (297 g/m&lt;sup&gt;2&lt;/sup&gt;/year and 2.08 g/m&lt;sup&gt;2&lt;/sup&gt;/day, on average). This represented an increase by 72% and 71%, respectively. Variability in the fraction of RNPP to total net primary productivity was examined. Results indicate that this fraction varied from 0.18 to 0.25 across the compared treatments and decreased with increasing fertilization. Data show how different roles can grasslands play in accumulation of plant matter due to different levels of fertilization.

The effect of nitrogen addition on soil organic matter dynamics: a model analysis of the Harvard Forest Chronic Nitrogen Amendment Study and soil carbon response to anthropogenic N deposition

Recent observations indicate that long-term N additions can slow decomposition, leading to C accumulation in soils, but this process has received limited consideration by models. To address this, we developed a model of soil organic matter (SOM) dynamics to be used with the PnET model and applied it to simulate N addition effects on soil organic carbon (SOC) stocks. We developed the model's SOC turnover times and responses to experimental N additions using measurements from the Harvard Forest, Massachusetts. We compared model outcomes to SOC stocks measured during the 20th year of the Harvard Forest Chronic Nitrogen Amendment Study, which includes control, low (5 g N m -2 yr -1 ) and high (15 g N m -2 yr -1 )Na ddi- tion to hardwood and red pine stands. For unfertilized stands, simulated SOC stocks were within 10 % of measurements. Simulations that used measured changes in decomposition rates in response to N accurately captured SOC stocks in the hardwood low N and pine high N treatment, but greatly underestimated SOC stocks in the hardwood high N and the pine low N treatments. Simulated total SOC response to experimental N addition resulted in accumulation of 5.3-7.9 kg C per kg N following N addition at 5 g N m -2 yr -1 and 4.1-5.3 kg C per kg N following N addition at 15 g N m -2 yr -1 . Model simulations suggested that ambient atmospheric N deposition at the Harvard Forest (currently 0.8 g N m -2 yr -1 )h as led to an increase in cumulative O, A, and B horizons C stocks of 211 g C m -2 (3.9 kg C per kg N) and 114 g C m -2 (2.1 kg C per kg N) for hardwood and pine stands, respectively. Simulated SOC accumulation is primarily driven by the modeled decrease in SOM decomposition in the Oa horizon.

Effect of fertilization on below-ground plant mass of submontane Polygono-Cirsietum meadow

We assessed below-ground net primary productivity (BNPP) in the wet submontane Cirsium meadow occurred in the highland region of the Czech Republic. Effect of four different fertilization levels on BNPP was estimated in 1992. At the beginning of the growing season (April 29), total dry mass of rhizomes, roots and total below-ground plant parts of unfertilized stand reached 177, 1478 and 1657 g.m-2, respectively. Their living parts formed 42 % of their total dry mass. In comparison with unfertilized stands, however, the greatest accumulation of dry mass of rhizomes (504 g.m-2), roots (1503 g.m-2) and total below-ground dry mass (2008 g.m-2) was reached after application of 90 kgN.ha-1. Similarly, the highest BNPP values for living (435 g.m-2.yr-1) and total below-ground dry mass (351 g.m-2.yr-1) were calculated for the stand affected by the same amount of fertilization. These data show how variable role grasslands can play in accumulation and turn over of root biomass due to different levels of fertilization.

Soil Organic Carbon is Increased in Mixed-Species Plantations of Eucalyptus and Nitrogen-Fixing Acacia

Soil organic carbon (soil C) sequestration in forests is often higher under nitrogen (N2)-fixing than under non-N2-fixing tree species. Here, we examined whether soil C could be increased using mixed-species plantations compared to monocultures, which are less productive aboveground than mixtures. In addition, we compared soil C sequestration under N2-fixing trees with non-N2-fixing trees that received N fertilizer. Monocultures of Eucalyptus globulus (E) and the N2-fixing Acacia mearnsii (A) and mixtures of these species were planted in a replacement series: 100%E, 75%E + 25%A, 50%E + 50%A, 25%E + 75%A and 100%A. Soil samples were also collected from fertilized monoculture treatments (100%EFer) of E. globulus (250 kg N ha−1). Total organic C, N and phosphorus were determined at age 8 years at two soil depths (0–10 cm and 10–30 cm) and three density fractions of soil organic matter (SOM) were quantified for 0–5 cm depth. Soil C was highest in the 50%E + 50%A mixed stand and was highly correlated with aboveground biomass, not to the percentage of A. mearnsii in mixtures. This was largely due to soil C at 10–30 cm because there were no treatment effects on soil C at 0–10 cm. All density fractions of SOM at 0–5 cm increased with the percentage of A. mearnsii. In E. globulus monocultures, N fertilization did not increase soil C when compared with unfertilized stands. These results indicate that the inclusion of N2-fixing trees into eucalypt plantations may increase soil C stocks through increased productivity.

Influence of repeated fertilization and cattle grazing on forest ecosystems: Abundance and diversity of forest-floor small mammals

Intensive silvicultural practices such as pre-commercial thinning (PCT) and repeated fertilization have the potential to provide a diversity of forest habitats and wildlife to meet biodiversity conservation goals while maintaining wood production. Silvopasture combines livestock with trees in some managed forests, but the impact of grazing on biodiversity is unclear. Forest-floor small mammal communities may serve as ecological indicators of changes in forest structure and function, and hence biodiversity. This study was designed to test the hypotheses (H) that in young (13–23years) even-aged lodgepole pine (Pinus contorta) stands, (i) abundance of understory herbaceous vegetation and (ii) abundance and diversity of forest-floor small mammals would be: (H1) enhanced in fertilized stands, and (H2) reduced in stands with cattle grazing. Study areas were located near Kelowna (lightly grazed) and Summerland (heavily grazed) in south-central British Columbia, Canada. Each study area had four pairs of PCT stands thinned to a range of densities with one stand of each pair fertilized four times at 2-year intervals. Herbaceous vegetation and forest-floor small mammal communities were sampled from 1993 to 2002.Mean abundance of total herbs, total grasses, and fireweed (Epilobium angustifolium) all increased dramatically with fertilization in the lightly grazed stands, and hence part (i) of H1 seemed to be supported. Mean total abundance of small mammals was higher in fertilized than unfertilized stands in two years but not overall. Species richness and diversity of small mammals were similar between unfertilized and fertilized stands, and hence part (ii) of H1 was partially supported for abundance, but not for richness or diversity. Lightly grazed fertilized stands had low abundance of Peromyscus maniculatus and Tamias amoenus, but high abundance of Microtus pennsylvanicus, Sorex monticolus, and Sorex cinereus. Phenacomys intermedius and Myodes gapperi also seemed to decline in fertilized stands. Mustela erminea, a principal predator of microtines, was captured more frequently in the lightly grazed fertilized than unfertilized stands.Cattle grazing reduced the abundance of herbaceous vegetation, at least in the fertilized stands at Summerland where they consumed a significant proportion of the biomass, and hence part (i) of H2 was supported. However, this premise did not hold for the unfertilized stands where grazing had little effect on the three plant groups. Part (ii) of H2 was not supported as cattle grazing did not reduce total abundance and species diversity of forest-floor small mammals. Grazing in fertilized stands did limit population fluctuations and dynamics of M. pennsylvanicus and abundance of the two insectivores during certain years. Forest-floor small mammal communities and their myriad ecological functions should be maintained, at least in some years, in those stands intensively managed for wood, biomass, and livestock production.

Effects of repeated fertilization of young Norway spruce on foliar phenolics and arthropods: Implications for insectivorous birds’ food resources

Repeated fertilization of young forests is a promising concept to increase the production of wood fiber, but the consequences of intense fertilization regimes on forest birds and their food resources, mediated through changes in the foliar chemistry are inadequately known. We assessed the effects of repeated fertilization in stands of young Norway spruce (Picea abies) on foliar phenolics and arthropods in an intensively managed forest area in southern Sweden in relation to the abundance of arboreal feeding birds breeding in the same stands. We anticipated leaf-sucking arthropods (viz. Hemiptera (aphids)) to react more strongly to changes in foliar phenolics than other invertebrate groups. Overall, we found small effects of fertilization on abundance and composition of different groups of foliar arthropods. However, the abundance of Hemiptera was much higher in early spring in fertilized stands than in unfertilized stands, whereas mites (Anactinotrichida and Actinotrichida) were more abundant in late spring in the fertilized stands. On the contrary, springtails (Collembola) were more abundant in unfertilized stands than in fertilized stands the late spring. The concentrations of two of the most abundant phenolics (hydroxycinnamic acid derivatives) as well as the sum concentration of HPLC-phenolics, were consistently lower in the fertilized stands. Positive effects on arthropod abundance mediated trough changes in the foliar chemistry following fertilization could help to explain why resident Goldcrest (Regulus regulus), which feeds on folivorous arthropods (i.e. aphids) during winter, was found to be more common in the fertilized stands (Edenius et al., 2011). Our results suggest that in intensively managed forest areas repeated fertilization of young spruce has the potential to enhance the suitability of these stands as winter feeding habitat for coniferous foliage-gleaning insectivorous birds compared to unfertilized stands in the same developmental stage. However, intensification of forest management further impedes habitat quality for more specialized species and generally reduces the diversity of forest birds by simplifying structure and composition of forest stands and shortening the rotation period. Therefore, careful planning of spatial arrangement of treatment units with different management, retention of natural forest and/or structures and legacies such as dead wood and deciduous trees are necessary to promote avian diversity in intensified forest management schemes.

Response of plant community abundance and diversity during 10 years of cattle exclusion within silvopasture systems

The effects of cattle ( Bos taurus L.) grazing on upland plant communities in forested rangelands are poorly understood. Cattle interactions with plant communities were studied in intensively managed (precommercially thinned (PCT) and repeatedly fertilized) silvopasture systems in young lodgepole pine ( Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) forests. We investigated the response of plant community abundance and diversity to cattle grazing and how these responses were affected by PCT and repeated fertilization. The study was conducted inside and outside cattle exclosures over 10 years in two regional replicates in south-central British Columbia, Canada. PCT and repeated fertilization increased both the amount and quality of forage. Effects of cattle grazing on plant community abundance and diversity were variable and significantly influenced by the nutrient status of the site. In fertilized stands, cattle grazing increased species richness and diversity, particularly for the herb layer, although these treatment effects often took several years to be expressed. In unfertilized stands, cattle grazing did not significantly reduce herb or shrub volumes; however, species richness and, to a lesser extent, diversity of the shrub layer declined. In a landscape context, management strategies for silvopasture should promote heterogeneity for conservation of plant diversity through a variety of grazing pressures, as well as forest enhancement treatments such as PCT and repeated fertilization.

Snow damage in lodgepole pine stands brought into thinning and fertilization regimes

Several heavy wet snowfalls occurred during 2007–2009 across a broad-scale thinning and fertilization experiment to bring overstocked juvenile lodgepole pine ( Pinus contorta var. latifolia) in the foothills of Alberta, Canada into an intensive management regime. We examined the bending and breakage of trees in relation to thinning and fertilization and used a multimodel information-theoretic approach to model stand and tree level predictors of snow damage. Fertilized stands suffered the greatest amount of snow damage, and this was most noteworthy when stands were also thinned; here 22% (17% broken stems) of trees were damaged compared to 8% (4% broken stems) in the thinned and unfertilized stands. At the stand level, needle weight and crown cover were reliable predictors of snow damage. At the tree level, separate models were developed for each combination of thinning and fertilization. All models used total tree volume; usually the smaller trees in the stands were more susceptible to damage but in the thinned and fertilized stands larger but slender trees with large asymmetrical crowns tended to be damaged. Also, trees with lower total stem volume were more susceptible to damage. Only in the thinned and fertilized stands were variables related to crown shape and asymmetry important predictors of snow damage. We conclude that snow damage is an important agent for self-thinning in unthinned stands and fertilization tends to exacerbate damage because of increase in foliage size. In areas with regular occurrence of heavy snow, we do not recommend fertilization at the same time as thinning, as the larger and more economically important trees in the stand are at risk.

Climate cues and resources interact to determine seed production by a masting species

Summary 1. Mast seeding is the intermittent production of large quantities of seed across a perennial plant population. Such seeding events in many plant species are initiated by climatic cues, but whether these cues act solely as triggers or also via alterations to nutrient availability is unclear. 2. Here, we examine the effect of nitrogenous fertilization on the relationship between seed production in Nothofagus solandri var. cliffortioides and two climatic cues (rainfall and temperature) at specific stages in reproductive development from 1999 to 2008. 3. Foliar nitrogen concentrations were positively correlated with rainfall among years, suggesting rainfall was affecting nitrogen availability. 4. Seedfall mass in unfertilized stands was predominantly determined by rainfall during resource priming, while seed production in fertilized stands was more affected by temperature during floral primordia development. Similarly, seedfall mass in older stands, which contain greater internal nutrient reserves, was predominantly determined by temperature. 5. Synthesis. The results of this study demonstrate that the sensitivity of seed production to climatic cues can be altered by manipulation of resource availability and therefore establish that climatic cues involved in the synchronization of mast seeding can influence reproductive effort via an effect on resource availability. These results also indicate that alterations to resource availability have the potential to alter inter‐annual patterns of seed production, but further study is required to verify this finding.

Can repeated fertilizer applications to young Norway spruce enhance avian diversity in intensively managed forests?

Repeated fertilization of forests to increase biomass production is an environmentally controversial proposal, the effects of which we assessed on breeding birds in stands of young Norway spruce (Picea abies), in an intensively managed forest area in southern Sweden. Our results show that fertilized stands had 38% more species and 21% more individuals than unfertilized stands. Compared with stands under traditional management, the further intensification of forestry by repeated applications of fertilizers thus seemed to enhance species richness and abundance of forest birds. We cannot conclude at this stage whether the response in the bird community was caused by changes in food resources or increased structural complexity in the forest canopy due to the skid roads used for the application of the fertilizers. Future studies should focus on structural and compositional effects of fertilization processes during the entire rotation period and at assessing its effects in a landscape

Impact of nitrogen fertilization on carbon and water balances in a chronosequence of three Douglas-fir stands in the Pacific Northwest

This study investigated the 2-year response to nitrogen (N) fertilization of three different-aged Douglas-fir stands on the west coast of Canada on eddy covariance (EC)-measured net ecosystem productivity (NEP), gross primary productivity (GPP), ecosystem respiration ( R) and evapotranspiration ( E). Fertilizer application took place in January 2007, aerially at 200 kg urea-N ha −1 in 19- and 59-year-old stands (hereafter referred to HDF88 and DF49, respectively), and manually at 80 g urea per tree (60 kg N ha −1) along the tree drip line in a 7-year-old stand (HDF00). N fertilization substantially increased foliar N content as well as needle mass in all the three stands leading to N-sufficiency compared to severe N-deficiency in similar trees in the adjacent unfertilized areas of the respective stands. In the absence of a second EC flux tower in similar unfertilized stands, we used simple empirical models fitted to multi-year pre-fertilization monthly fluxes to calculate C and water fluxes for 2007 and 2008 assuming the stands were not fertilized and compared these with measured fluxes to determine the effects of fertilization. Our modelling analysis suggested that fertilization increased GPP and R in all the three stands with increases in GPP being greater than R in DF49 and HDF88 but smaller than R in HDF00. Fertilizer-induced increase in net C sequestration or NEP was the highest (182 and 179 g C m −2 y −1 in 2007 and 2008, respectively) in HDF88 followed by DF49 (168 and 78 g C m −2 y −1 in 2007 and 2008, respectively) and small decreases (−3 and −82 g C m −2 y −1 in 2007 and 2008, respectively) in HDF00. Fertilization resulted in an insignificant increase in E in all the three stands, thereby resulting in substantial increase in water use efficiency (GPP/ E) in the younger (HDF88 and HDF00) stands but little effect in the intermediate-aged (DF49) stand. Tree ring analysis for DF49 showed that fertilization increased bole volume above that in an adjacent unfertilized control area by about 5.0 and 8.0 m 3 ha −1 in 2007 and 2008, respectively.