Ungulate herbivory of regenerating conifers in relation to foliar nutrition and terpenoid production

Ungulate browsing greatly influences regeneration dynamics of some forest ecosystems, yet the relationship between browse susceptibility and foliar chemistry of forest tree seedlings is not well understood. We applied field fertilization (15N-9P-10K controlled-release fertilizer at 0, 20, 40, and 60 g per seedling) and investigated how subsequent changes in terpenoid production and foliar nutrition influence ungulate browse preference for Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco), western hemlock (Tsuga heterophylla Raf. Sarg.), and western redcedar (Thujaplicata Donn ex D. Don) seedlings across four sites in northwestern Oregon, USA. Fertilization increased foliar N concentration of all three species, but above-ground growth of only Douglas-fir and western hemlock. Foliar monoterpene concentrations for western hemlock and western redcedar also increased at higher fertilization rates, while Douglas-fir monoterpene production was not affected by fertilization. Regardless of monoterpene levels, ungulate browse preference was greater for fertilized western hemlock seedlings. The opposite response, however, was observed for western redcedar at two of the four study sites where the likelihood of browse was greater for non-fertilized than fertilized seedlings. Differences in browse preference among species may depend on the type and amount of individual monoterpenes manufactured in response to fertilization. Western redcedar produce α- and β-thujone, oxygenated monoterpenes known to promote gastroenteritis and possibly inhibit microbial rumen activity, which were absent from Douglas-fir or western hemlock. Higher concentrations of α- and β-thujone associated with increasing fertilizer rate provide a plausible explanation as to why ungulates preferred non-fertilized western redcedar. Our results illustrate species-specific adaptation in browse avoidance and selective ungulate browsing behavior of individual trees as linked to foliar chemistry.     

Biodiversity,exotic plant species,and herbivory: The good,the bad,and the ungulate

Invasion of natural ecosystems by exotic plant species is a major threat to biodiversity. Disturbance to native plant communities, whether natural or management induced, is a primary factor contributing to successful invasion by exotic plant species. Herbivory by both wild and domestic ungulates exerts considerable impact on structure and composition of native plant communities. Intensive herbivory by ungulates can enhance exotic plant invasion, establishment, and spread for three reasons: (1) many exotic plants are adapted to ground disturbances such as those caused by ungulate feeding, trampling, and movements; (2) many exotic plants are adapted for easy transport from one area to another by ungulates via endozoochory and epizoochory; (3) many exotic plants are not palatable or are of low palatability to ungulates, and consequently, their survival is favored as ungulates reduce or eliminate palatable, native plants. Ungulate herbivory is a chronic, landscape-scale disturbance capable of influencing plant communities as much as episodic events such as fire. Consequently, ungulate herbivory has the potential to facilitate the invasion and establishment of exotic plants in the interior Pacific Northwest where ungulates occupy nearly every ecosystem. Moreover, ungulate herbivory has intensified in many ecosystems, owing to the addition of domestic ungulates with that of existing, wild ungulates, coupled with the reduction or elimination of migratory movements and predators that previously regulated wild ungulate populations and influenced their distributions. Despite the observational evidence for ungulate herbivory as a strong facilitator of exotic plant invasion and establishment, current knowledge of cause–effect relations is severely limited by a lack of manipulative experiments. Most studies have been observational, unreplicated, and lack the experimental controls needed to eliminate or account for confounding sources of variation. Heightened attention to conservation of biodiversity will increase the importance of managing ungulates in balance with the plant communities that support them.     

Trees and shrubs as sources of fodder in Australia

Experience with browse plants in Australia is briefly reviewed in terms of their forage value to animals, their economic value to the landholder and their ecological contribution to landscape stability. Of the cultivated species only two have achieved any degree of commercial acceptance (Leucaena leucocephala and Chamaecytisus palmensis). Both of these are of sufficiently high forage value to be used as the sole source of feed during seasonal periods of nutritional shortage. Both are also leguminous shrubs that establish readily from seed. It is suggested that a limitation in their present use is the reliance on stands of single species which leaves these grazing systems vulnerable to disease and insects. Grazing systems so far developed for high production and persistence of cultivated species involve short periods of intense grazing followed by long periods of recovery. Similar management may be necessary in the arid and semi-arid rangelands where palatable browse species are in decline.     

The establishment and early growth of three leguminous tree species for use in silvopastoral systems of the southeastern USA

Demand for goat meat in the eastern USA is growing as a result of preference by ethnic communities. Meat goat production systems in the southeastern USA should be designed to take advantage of the goats' natural preference for browse. Trees could contribute to system productivity by supplying required nutrients when demand by growing animals is critical and the quality of forage is limited. A field study was established in Wake County, NC to evaluate the establishment and early growth characteristics of three leguminous tree species, Robinia pseudoacacia, Gleditsia triacanthos, and Albizia julibrissin. The three tree species were planted in single-row plots following a randomized complete block design (3 × 2 × 2, replicated six times) with two planting densities (intra-row spacing of 50 or 100 cm) and two coppice heights (25 or 50 cm). Bare-root seedlings were planted in March 1995, evaluated for browse quality (composited samples) in August 1995, coppiced in February 1996, evaluated for herbage mass and quality in July 1996, and evaluated for goat preference in August 1996. Herbage mass produced during the second season ranged from about 200 (G. tricanthos) to 3,200 kg/ha (R. pseudoacacia). Estimates of herbage quality were high for all species. Crude protein and acid detergent fiber of leaflets ranged from 23 to 28% and 12 to 22%, respectively. Robinia pseudoacacia has a high potential as a browse species for goats due to high herbage production (mean of 2,390 kg/ha) and goat preference. Gleditsia triacanthos was judged to be a low value browse species. Albizia julibrissin, although not highly preferred by goats in the trial holds sufficient potential to warrant further investigation. This revised version was published online in June 2006 with corrections to the Cover Date.     

Role of plant defense in the utilization of native browse in southern Ethiopia

Browse is an important forage in pastoral systems, especially during dry seasons, because it is high in nitrogen and digestibility. However, browse palatability may be reduced by possible plant defenses such as tannins and physical attributes. Chemical and physical properties of 20 browse species were correlated with the feeding preference of camels, sheep and goats during wet and dry seasons in a densely wooded, semi-arid savanna. Preference was assessed by comparing relative use with abundance of browse species. Chemical components included nitrogen, available nitrogen, acid-detergent fibre, in vitro digestibility, total tannins and condensed tannins. Physical defenses included thorns, hooks, spines, and leaf surface properties. Animal preference was negatively related to chemical and physical defense factors, positively related to N content, and unrelated to fibre and digestibility with results depending on animal species and season. Understanding the physical and chemical factors which influence browse selectivity aids in identifying promising forage resources.     

Trophic consequences of postfire logging in a wolf–ungulate system

Controversy surrounds postfire logging, often because of negative effects on snag-dependent wildlife species. Few studies, however, have examined effects on early-seral species that may benefit from postfire logging, nor effects on trophic relationships. We studied the effects of postfire logging on trophic dynamics between wolves (Canis lupus), three ungulate species and ungulate forage biomass during the first 3 years in a large burn in the Canadian Rockies, Alberta, Canada. We examined plant biomass and ungulate responses to two treatments (post- and prefire logging) compared to a burned but unlogged area (control). We evaluated resource selection for the three treatments by elk (Cervus elaphus) using radiotelemetry and for deer (Odocoileus spp.), moose (Alces alces), and, secondarily, elk using pellet counts. Elk resource selection was modeled as a function of the trade-off between wolf predation risk and herbaceous forage biomass to test for trophic impacts of postfire treatments. Postfire logging had transient effects on total herbaceous biomass; while forb biomass was reduced, increases in graminoid biomass more than compensated by the third year. Prefire logging areas were dominated by a few species, but had generally higher forage biomass by the third year. Ungulates avoided postfire and prefire logged areas despite greater herbaceous biomass. Only when we considered elk resource selection as a function of both forage and wolf predation risk was the extent to which trophic interactions affected by postfire logging revealed. Wolves selected proximity to roads and the higher forage biomass associated with postfire logging in open logged areas. This translated to the highest predation risk for elk in postfire logged areas. Thus, ungulates avoided postfire logged areas because of human alteration of top-down predation risk despite enhancements to bottom-up forage biomass. Managers should consider trophic consequences of postfire logging on the interactions among species when gauging logging effects on terrestrial ecosystems. Making use of existing roads, minimizing the construction of new roads, and managing road removal following postfire logging will help mitigate the negative effects of postfire logging on terrestrial ecosystems.     

Conifer leader browsing by roe deer in English upland forests: Effects of deer density and understorey vegetation

At moderate to high densities ungulates can impact negatively on forest crops and these may be managed by lethal control. In production forestry an understanding of the relationship between ungulate density, habitat-related factors and the incidence of tree damage may promote more efficient ungulate damage management than by lethal control alone. In plantation forests in the north east of England, the incidence of conifer leader browsing by roe deer (Capreolus capreolus) was positively associated with an index of deer density (at the site scale) and planted crop tree density (at the feeding patch scale) and was negatively associated with the relative abundance of palatable understorey vegetation (at the site scale). An interaction between the deer density index and palatable understorey browse abundance was positively associated with leader browsing. Coefficients from the optimal model were used to construct a browse probability surface across a matrix of values of deer dung density and palatable understorey vegetation abundance. This illustrated a very different relationship between dung density and conifer leader browsing probability across the various levels of palatable understorey vegetation abundance. From this we hypothesise that in areas of limited palatable understorey vegetation abundance, higher levels of culling may be required to achieve reductions in the incidence of conifer leader browsing than would be necessary in areas with moderate to high palatable understorey vegetation abundance. Improvements to understorey vegetation in concert with roe deer population control may enhance the efficiency of deer damage management in upland areas with nutrient-poor soils.     

Lack of natural control mechanisms increases wildlife–forestry conflict in managed temperate European forest systems

Across Europe, ungulate numbers have greatly increased over the past decades, leading to increasing concerns about the ecological and economical impacts and pleas for stronger population control. However, focussing on population control only ignores other underlying factors which may enhance the wildlife–forestry conflict. I reviewed factors which shape herbivore top-down effects in natural temperate forest systems aiming at understanding how these interactions are altered in managed forests. Carnivores are important in modifying ungulate–plant interactions. They can directly influence the numbers of ungulates, but this effect is dependent on productivity and predicted to be smallest in highly productive temperate forest. Indirectly, they modify herbivore top-down effects by creating a landscape of fear. Despite the abundance of knowledge from American systems, there is a lack of knowledge on how this process might work in European systems. Next to carnivores, abiotic conditions interact with herbivory by influencing forage quality and availability. Forest gaps lead to concentration of ungulates and their effects, due to increased forage supply. Abiotic conditions also influence the response of plants following herbivory, which can be tolerated by showing increased regrowth or resistance due to chemical or physical defence. In typical managed forest systems, carnivores and abiotic conditions which shape ungulate top-down effects in natural forests are altered or absent. Human hunting might replace the direct effects of carnivores, but does not replace their indirect effects. Forestry practices also have modified herbivore–plant interactions in several ways, creating a forest with lower ungulate carrying capacity and higher sensitivity for ungulate browsing. These changes logically increase the strength of herbivore top-down effects in managed forests and increase the wildlife–forestry conflict. To reduce this conflict, aiming only at reducing wildlife numbers is predicted to have little effects when they do not coincide with habitat ameliorations. Forestry practices may therefore greatly enhance the conflict that exists between wildlife and forestry but can also be an important tool to reduce this conflict by adapting management practices that allow more natural functioning of forests systems.     

Habitat use of large ungulates in northeastern Germany in relation to forest management

Estimating large herbivore density has been a major area of research in recent decades. Previous studies monitoring ungulate density, however, focused mostly on determining animal abundance, and did not interpret animal distribution in relation to habitat parameters. We surveyed large ungulates in the Biodiversity Exploratory Schorfheide-Chorin using faecal pellet group counts. This allowed us to explore the link between relative ungulate abundance, habitat use, and browsing damage on trees in a region with several types of forest, including unharvested and age-class beech forests, as well as age-class pine forests. Our results demonstrate that roe deer and fallow deer relative abundance is negatively correlated with large tree cover, and positively correlated with the cover of small shrubs (Rubus spec., Vaccinium spec.), and winter food supply. Habitat use of roe deer and fallow deer, as estimated by counting faecal pellet groups, revealed a preference for mature pine forests, and avoidance of deciduous forests. This differential habitat use is explained by different distributions of high quality food resources during winter. The response of deer to understory cover differed between roe deer and fallow deer at high cover percentages. The amount of browsing damage we observed on coniferous trees was not consistent with the relative deer abundance. Browsing damage was consistently higher on most deciduous trees, except for beech saplings which sustained less damage when roe deer density was low. Because roe deer is a highly selective feeder, it was reported to affect tree diversity by feeding only on trees with high nutritional value. Consequently, we propose that managing the number of all deer species by hunting is necessary to allow successful forest regeneration. Such an adjustment to deer numbers would need to account for both current tree diversity and alternative food resources. Our findings may be applicable to other forest landscapes in northeastern Germany including mature pine stands and differently harvested deciduous forests.     

Ungulate-adapted forest management: effects of slash treatment at harvest on forage availability and use

Forest management strongly influences the interactions between ungulates and their food resources. Different ungulate-adapted measures have been proposed in forestry to improve forage availability or to reduce browsing damage. However, the potential and feasibility of such measures are inadequately known. We studied the effects of harvest timing and slash treatment in final felling and commercial thinning on the availability of Scots pine Pinus sylvestris forage and its use by ungulates during winter in the Swedish boreal forests. Pellet group counts showed that moose (Alces alces) was the dominating species using the post-harvest stands. Under conventional slash treatment, final felling stands held on average 226 kg pine forage ha^?1 after harvesting and commercial thinning stands 137 kg ha^?1. Ungulate-adapted slash treatment increased the available forage biomass by 20 %, but had no significant effect on consumption of forage by ungulates. Time since harvest had the strongest effect on forage consumption; for example, under conventional slash treatment, there was a tenfold increase in consumption (3 vs. 33 kg ha^?1) following final felling as exposure time increased from 2–3 to 4–5 months. Consumption was higher in thinned stands than in final felling stands for the first 3 months but not later. To increase ungulate use of the forage made available at harvest, pine-dominated stands should be harvested in the late autumn or early in the winter.     

Effects of fertilization and irrigation on American sycamore and black locust planted on a reclaimed surface mine in Appalachia

Short rotation woody biofuel plantations on reclaimed surface mines in Appalachia can diversify domestic energy supplies and facilitate the reforestation of these disturbed lands. This study examined growth, survival, biomass accumulation and allocation, and nitrogen concentrations following two growing seasons in American sycamore (Platanus occidentalis L.) and black locust (Robinia pseudoacacia L.) seedlings receiving irrigation, granular fertilization, and irrigation + fertilization compared with untreated controls. Fertilization increased basal diameter, height, and stem mass of American sycamore following two growing seasons. Increased stem production was attributed to accelerated development and not shifts in biomass allocation due to treatment. Irrigation and irrigation + fertilization treatments did not enhance growth or biomass accumulation of American sycamore. Similarly, black locust basal diameter, height, and stem mass did not differ among the treatments. Browse surveys showed that more than 76% of black locust seedlings experienced arrested or retrogressed growth due to browse; less than 3% of American sycamores were browsed. This intensive browse by ungulates, likely including reintroduced elk, may have affected growth differences among species and confounded the effects of treatments on black locust. Survival was unaffected by treatment in both species, but mean survival was greatest in American sycamore (80%) compared to black locust (58%). Per tree total nitrogen uptake was highest in fertilized American sycamore (7.9 g) and lowest in irrigated American sycamore (0.9 g). The results of our study suggest that granular fertilizer applications can accelerate seedling growth on reclaimed surface mines in the Appalachian region.     

A comparison of riparian plant community response to herbivory by beavers (Castor canadensis) and ungulates in Canada's boreal mixed-wood forest

Herbivores, such as beavers (Castor canadensis) and ungulates, can dramatically alter the species composition and structure of riparian vegetation communities. We examined how four different levels of beaver presence and ungulate density influenced the structure and composition of riparian vegetation communities in the mixed-wood boreal region of east-central Alberta, Canada. Beavers, as central-place foragers, focus on similar species utilized by the six ungulate species in our study area. However, we found that vegetation responded differently relative to the percent cover and heights of emergent, shrub, herbaceous dicots, and tree species depending on the varying combinations of beaver presence and ungulate densities. There was an obvious negative effect of ungulate herbivory on shrub heights and cover; however, we were unable to find any significant effects on the overall composition and structure of vegetation communities that were exclusively related to beaver activities. In areas with no beavers and lower ungulate densities there was a positive growth response in preferred species (e.g., Salix spp., Prunus spp.), which clearly demonstrated the degree of combined influence that these herbivores have on riparian communities. In these areas, Salix spp. was four times shorter than in areas where beavers were not present and ungulate densities were lower. In addition percent cover was lowest for emergent vegetation and herbaceous dicots in areas with higher ungulate densities. Many studies focus on single-species effects on forage resources, yet our research shows that the study of combined effects of multiple herbivores can provide a new insight into these complex systems.     

Shrubs facilitating seedling performance in ungulate-dominated systems: biotic versus abiotic mechanisms of plant facilitation

Shrubs are important microsites that facilitate seedling performance in abiotically stressed environments. However, shrub facilitation might work differently in ecosystems with high biotic stress (e.g., ungulate-dominated environments). We wonder whether ungulates through their preferences for different shrubs affect the facilitation process of seedlings, and whether this process remains consistent across different levels of abiotic stress. We study seedling performance (survival and growth) of a Mediterranean oak (Quercus pyrenaica) in three microsites (open, preferred and non-preferred shrubs by ungulates) for two contrasting climatic environments and throughout a complete growing season (increasing abiotic stress). Overall, there was a positive effect of shrubs in seedling survival. We found a microsite effect on seedling growth but this effect differed depending on the abiotic environment, with seedlings growing better in open microsites in the less stressful site. The larger abiotic context (climate) played an important role in determining which microsite is the most favorable for seedling growth but not necessarily for the eventual survival of seedlings. Wild ungulates started to damage seedlings early in the growing season, whereas abiotic stress (desiccation) affected mostly those plants that were not previously attacked by animals, showing the hierarchical effect (earlier and longer effect) of the biotic over the abiotic mortality agents. Non-preferred shrubs worked better as nurse shrubs only under high ungulate pressure. From the abiotic perspective, preferred and non-preferred shrubs did not apparently differ in the facilitation effect. Importantly, we found a greater facilitative effect of shrubs on the survival than on the growth of seedlings.     

内蒙古贺兰山国家级自然保护区饲用植物资源调查

在调查鉴定内蒙古贺兰山国家级自然保护区内的植物标本的基础上,结合查阅有关研究饲用植物资源文献,统计分析了保护区的野生饲用植物资源,结果表明,保护区内分布的野生饲用植物共有370种(含种以下单位),隶属57科188属。其中草本植物占绝对优势,共计302种,占保护区内饲用植物总种数的81.62%;从水分生态型分析,中生植物最多,有199种,占保护区内饲用植物总种数的53.79%。从饲用价值上看优等37种、良等101种、中等121种、低等91种、劣等20种,分别占保护区内饲用植物总种数的10%、27.30%、32.70%、24.59%和5.41%。良等以上饲用植物占该保护区野生饲用植物总种数的37.30%,可以看出该保护区饲用植物价值高,具有很高的开发利用潜力。本文还对该保护区野生饲用植物资源的保护及开发利用提出建议。     

Interspecific interactions of ungulates in European forests: an overview

Mammalian herbivores vary in the degree to which they browse, graze and cause physical disturbance, and so vary in the effects they have on the structure and composition of forest ecosystems. To create predictive models of the interactions of forest ecosystems with herbivore communities, an appreciation of the interactions between the species of herbivore themselves is necessary. This paper reviews interspecific interactions of ungulates, methods used in studying them, and seeks to identify areas to which future research should be directed in the context of European forest systems. Methods that have been used to provide information on interactions include: comparative resource studies, niche theory, physiological and anatomical analyses, modeling and foraging theory, and population studies. The most commonly reported types of interactions appear to be competition and facilitation. Behavioural and social interactions between species are potentially important, but evidence for these is scarce and often anecdotal. It is suggested that there may be considerable potential for ungulates to interact in European forests which are often significantly altered from their natural state. Future research should aim at refining the theoretical understanding of interspecific interactions, particularly between ungulates with different feeding ecologies. The roe deer (Capreolus capreolus) has a major impact on forest ecosystems and is increasing its range throughout Europe. However, there is evidence that it may be displaced or out-competed by a number of ungulate species, and it is suggested as being research priority to quantify these effects.     

Interactions among forestry regeneration treatments,plant vigour and browsing damage by deer.

In a large field experiment we studied the influence of regenerationmethods on the extent to which roe deer (Capreoluscapreolus L.) browse on spruce (Picea abies L.Karst) seedlings. Our objective was to evaluate if treatments that are good atstimulating regeneration may increase browsing damage by deer. Data werecollected between 1993 and 1995, and in the winters of 1993–94 and1994–95 the frequency of browsed seedlings was 13.2% and 13.4%,respectively. The frequency of browsing damage varied considerably betweensitesand clearcuts. Browsing damage was more frequent when the regeneration methodsincluded insecticide treatments. Among insecticide-free treatments, browsingwasheavier on scarified plots than on herbicide-treated or control plots (in whichseedlings were planted on untreated ground and given no post-plantingtreatment). Containerised seedlings were browsed more than bare-rooted ones.Neither the age of clearcut when planting, nor removal of slash, had any effecton browsing. It was demonstrated that regeneration methods that increased plantvigour (as assessed by leader growth and needle colour index) led to morebrowsing damage. Thus, our results support the plant vigour hypothesis, whichstates that many herbivores prefer to feed on vigorous plants because they aremore nutritious. However, the difference in browsing damage betweencontainerised and bare-rooted seedlings could not be explained solely by theplant vigour hypothesis.     

Do ungulates preferentially feed in forest gaps in European temperate forest?

Ungulate populations across Europe have been strongly increasing over the past decades. Simultaneously with this increase, concerns about the impact of ungulates on forest systems, and forestry specifically, are increasing. In this study we discuss how the common forestry practice of creating clear cuts in relatively homogenous, managed forests may increase the potential impact of ungulates. Growth of trees in full light conditions is generally higher, but due to higher photosynthetic activity they tend to have higher C:N ratio in their leaves thus decreasing food quality. Next to that, biomass of herbaceous vegetation is enhanced in clear cuts. These changes likely affect foraging decisions of ungulates and it has been suggested that ungulates forage in forest gaps rather than in closed forest. We tested this hypothesis by using an experimental approach. The experiment was conducted in the Białowieża Primeval Forest in Poland, where a full assemblage of native large herbivores occurs. Six plots (6 m × 6 m) inside small clear cuts were compared to six control plots in adjacent closed forest. To exclude the effect of differences in number and species composition of available tree saplings, equal numbers of trees saplings of five species were planted at each plot. Ungulate visitation frequency and visitation time were measured by means of three methods: track plots, camera- and video trapping, and pellet counts. Visitation frequency of all ungulates combined (European bison, red deer, roe deer, moose and wild boar) was almost twice as high inside forest gaps compared to closed forest. Also cumulative visitation time by all ungulates tended to be higher inside forest gaps. Red deer showed the strongest preference for gaps, and duration of single visits was almost seven times longer for forest gaps than in closed forest. The observed preferential foraging of ungulates in forest gaps leads to an uneven distribution of their browsing behaviour. Hence, the creation of forest gaps by clear cutting followed by reforestation provides attractive foraging patches for ungulates potentially leading to high damage. In this way, forestry practices may enhance damage of ungulates to plantations especially when due to management the surrounding forest has a low carrying capacity for ungulates. We suggest that there is much to gain if management approaches would focus at influencing foraging behaviour of ungulates and reduce their concentration in forest gaps, rather than purely focusing on population control.     

Herbage yields and quality in four woody forage plants in a subhumid environment in Ghana

There is keen interest in feeding small ruminants with herbage from forage shrubs and trees in Ghana because of the general perception about these plants being perennial and remaining green for lengthy periods. In this study, plant growth rate, herbage production and quality of two indigenous woody plants, Griffonia simplicifolia and Baphia nitida were compared to those of two introduced shrubs, Leucaena leucocephala and Gliricidia sepium. Gliricidia sepium achieved the greatest height and produced the highest herbage dry matter (2t/ha) compared to average production of 0.15 t/ha by the three other species. Gliricidia sepium herbage also had high contents of crude protein, calcium and ash. In regrowth herbage production at cutting intervals of 6 and 12 weeks, Gliricidia sepium again outperformed the three other species, however, there was little difference in herbage yield among the three other species. In all species one harvest at 12 weeks regrowth interval produced more herbage than the combination of yield of two six week interval harvests. This revised version was published online in June 2006 with corrections to the Cover Date.     

Leaf physiology and sugar concentrations of transplanted Quercus rubra seedlings in relation to nutrient and water availability

Newly planted seedlings incur transplant stress resulting from poor root-soil contact, which limits access to soil moisture and nutrients and reduces growth for one or more growing seasons. Controlled release fertilizer (CRF) applied at planting may reduce transplant stress by augmenting rhizosphere nutrient availability yet with potential risk of root system damage due to elevated fertilizer salt concentrations, which may be further exacerbated by drought. Under controlled conditions, we examined northern red oak (Quercus rubra L.) leaf physiological parameters and soluble sugar concentrations in response to varying nutrient levels (via CRF application) and moisture availability gradients ranging from drought to flooding. Net photosynthetic rates, transpiration rates, and chlorophyll fluorescence parameters responded positively to CRF application, and no interactions were observed between CRF and moisture availability; however, CRF did not increase soluble sugar concentrations. No effects of short-term drought were observed, but flooding exerted a rapid negative influence on net photosynthetic rates, transpiration rates, and chlorophyll fluorescence parameters; flooding also elevated soluble sugar concentrations, indicative of disrupted carbon partitioning and a much greater sensitivity to root-zone hypoxia than to drought in this species. Lack of interactions between CRF application and soil moisture availability indicates relatively similar responses of fertilized seedlings across moisture gradients.     

Fertilization—Effects on deciduous tree growth and browsing by moose

Knowledge of plant–herbivore interactions is fundamental for understanding foraging patterns of herbivores and their effects on the ecosystem as well as the human use of natural resources. The nutrient resources available for plants may determine not only growth rate, but also the amounts of secondary compounds in the plant tissues. As a consequence, browsing pressure on plant communities by large herbivores can be affected by fertilization and nitrogen deposition. We conducted a field fertilization experiment to test the hypothesis that fertilization leads to increased sapling growth and increased browsing by a large herbivore, the moose (Alces alces). The study was conducted on fertilized and unfertilized plots (50 m × 50 m) in northern Sweden. The plots were located in Scots pine (Pinus sylvestris) stands of young succession stages with an intermixture of deciduous species. Fertilization with 600 kg calcium–ammonium–nitrate per ha (=200 kg N ha⁻¹), was conducted in spring on one of the plots in each of 25 paired plots. The other plot in each pair was kept as control. The effect of fertilization on plants and browsing pressure was evaluated on five deciduous tree species in June and August the year after fertilization. Both browsing from preceding winter (bites) and current summer (leaf strips and bites) was recorded. Shoot size and other shoot variables increased with fertilization. Fertilization increased winter browsing for most species, but few differences were statistically significant. The late summer recording (August) showed pronounced differences in browsing pressure (leaf strips and bites) between control and treatment. In June, only a trend of increased browsing (leaf strips) was found for all species on fertilized plots. Generally, the pressure of leaf stripping was low in June, probably due to the short time the annual shoots had been exposed to moose browsing. Number of summer bites (recorded in August) was significantly higher on fertilized plots for the Betula spp., and the trend was similar for the other tree species. Within species, there was no difference in strip length between the treatments. The result indicates that fertilization can be used as a habitat improvement for ungulates within wildlife management. But, fertilization is also likely to lead to an increased risk of browsing damage, which is undesirable if forests are being fertilized for increased forest production.