Browser selectivity alters post-fire competition between <Emphasis Type="Italic">Erica arborea</Emphasis> and <Emphasis Type="Italic">E. trimera</Emphasis> in the sub-alpine heathlands of Ethiopia

Mammalian herbivores have the potential to alter the competitive relations of woody species, if consumption is unevenly distributed between species. At elevations above 3,500 m in the southern Ethiopian highlands, vegetation is dominated by Erica arborea and E. trimera. Both species can potentially grow into short trees, but are burnt on a rotation of 6–10 years, and regenerate by re-sprouting from belowground lignotubers. The regenerating scrub is heavily browsed by cattle. We set up browsing exclosures at three burnt sites to quantify the impact of browsing over a 3-year period. When protected from browsing, E. trimera had similar or better height growth than E. arborea, but in browsed vegetation, E. arborea instead grew taller. Browsing was more intense on E. trimera in the first years after fire, indicating a difference in palatability between the species. We checked if browse quality differed, by analysing shoot contents of acid detergent fibre (ADF), protein, phenolics and tannins. Contrary to expectations, the preferred E. trimera contained more ADF, less protein and had a higher tannin activity than E. arborea. Although the vegetative growth of E. arborea is favoured relative to E. trimera under high browsing pressure, rapid change in abundance would not be expected, since short-interval fire will repeatedly eradicate any gains in vegetative growth. However, within the typical fire return interval of less than 10 years, E. trimera barely reach a reproductive state, whereas E. arborea flower profusely. Under the current regime of fire and browsing, this may in the long run be more important than differences in height growth, leading to a gradual increase in the proportion of E. arborea.     

Stand and self-thinning dynamics in natural <Emphasis Type="Italic">Abies</Emphasis> stands in northern Hokkaido,Japan

Stand dynamics and self-thinning were analyzed in relation to the dynamics of above-ground biomass in natural Abies sachalinensis stands growing on sand dunes in northern Hokkaido, Japan. This was done in order to examine wave-type regeneration in the stands. Fifty-two plots were established in almost pure Abies stands that ranged from saplings to the mature and collapsing growth stages. Above-ground biomass and tree height reached asymptotic levels prior to the collapsing phase, unlike wave-regeneration Abies stands in central Japan and North America. Stand density was high in the young growth stages, but the self-thinning rate, that is, the density decrease per biomass growth in the study stands was greater than in wave-regeneration stands in central Japan, as indicated by a large self-thinning exponent (–1.26 by reduced major axis regression). The range of tree height distribution was very narrow, and the stands vertical structure was typically single-layered. The slenderness ratio of trees was large, except in young stands. In mature and collapsing stands, advanced seedling density increased markedly. These stand and tree characteristics were considered to be correlated with the wave-type regeneration in the study stands, and it is assumed that prevailing winds affect tree mortality.     

Cascading effects of moose (<Emphasis Type="Italic">Alces alces</Emphasis>) management on birds

Large herbivores often have key functions in their ecosystems, and may affect ecosystem processes with cascading effects on other animals. The mechanisms often involve relocations of resources of various kinds, including reduction in resource availability following foraging and increase in resources from animal excreta. As large herbivore populations in Europe generally are intensely managed, management activities may interact with the activities of the herbivores themselves in the effect on other ecosystem components. We investigated the effects of moose (Alces alces) winter browsing, together with the effect of net nutrient input via supplementary winter feeding of moose on functional composition and species richness of birds in a boreal forest. Supplementary feeding stations for moose had a net zero effect on bird species richness and abundance, because negative effects of moose browsing were balanced by positive effects of nutrient input. Sites with a similar browsing intensity as at feeding stations but without nutrient input had lower abundance and species richness than feeding stations. Functional groups of bird species showed differing responses: birds nesting at or below browsing height were negatively affected by moose browsing, whereas species nesting above the browsing zone were positively affected by moose browsing. Insect-eating species responded negatively to moose browsing on birch but positively to nutrient input at feeding stations, whereas seed-eating species responded positively to birch browsing and negatively to feeding stations. This study showed that both high levels of cervid activity and human management interventions influence bird communities.     

Host physiological condition regulates parasitic plant performance: <Emphasis Type="Italic">Arceuthobium vaginatum</Emphasis> subsp. <Emphasis Type="Italic">cryptopodum</Emphasis> on <Emphasis Type="Italic">Pinus ponderosa</Emphasis>

Much research has focused on effects of plant parasites on host-plant physiology and growth, but little is known about effects of host physiological condition on parasite growth. Using the parasitic dwarf mistletoe Arceuthobium vaginatum subsp. cryptopodum (Viscaceae) and its host Pinus ponderosa, we investigated whether changes in host physiological condition influenced mistletoe shoot development in northern Arizona forests. We conducted two studies in two consecutive years and used forest thinning (i.e., competitive release) to manipulate host physiological condition. We removed dwarf mistletoe shoots in April, before the onset of the growing season, and measured the amount of regrowth in the first season after forest thinning (Study I: n=38 trees; Study II: n=35 trees). Thinning increased tree uptake of water and carbon in both studies, but had no effect on leaf N concentration or δ¹³C. Mistletoe shoot growth was greater on trees with high uptake of water and carbon in thinned stands than trees with low uptake in unthinned stands. These findings show that increased resource uptake by host trees increases resources to these heterotrophic dwarf mistletoes, and links mistletoe performance to changes in host physiological condition.     

Defoliation depletes the carbohydrate reserves of resprouting <Emphasis Type="Italic">Acacia</Emphasis> saplings in an African savanna

Over the past century there has been a global trend towards tree expansion and densification in rangelands and savannas. This phenomenon is commonly referred to as bush encroachment. In South Africa Acacia karroo is one of the key species responsible for bush encroachment. It has been suggested that the combination of fire and browsing might limit bush encroachment by A. karroo more effectively than either browsing or fire alone. We hypothesized that these repeated disturbances progressively deplete root carbohydrates and compromise resprouting ability. This was tested by burning and then manually defoliating A. karroo once a month for 1 year. Manual defoliation did not inhibit the rapid shoot elongation after topkill of A. karroo saplings. During this initial phase, the growth of the new shoots of A. karroo was dependent more on mobilised root reserves than on photoassimilates from the new shoots. Frequent manual defoliation of resprouting A. karroo saplings prevented the replenishment of starch reserves. We suggest a mechanism for how the interaction of browsing and fire can suppress and perhaps reverse bush encroachment in African savannas. Saplings that have reduced starch reserves at the end of dry season due to browsing will struggle to resprout if they are burnt. Even if they do not die, they will be less able to escape fire damage in the next fire than if they had been able to resprout unimpeded.     

Response of young<Emphasis Type="Italic"> Tsuga heterophylla</Emphasis> to deer browsing: developing tools to assess deer impact on forest dynamics

We used dendroecology to describe and understand the consequences of deer browsing on regenerating western hemlock (Tsuga heterophylla). We compared tree shape, growth rate, height and age at four different sites in Haida Gwaii (British Columbia, Canada) that had trees representative of the range of deer impact on trees: (1) trees showing no sign of browsing, (2) escaped trees which were still browsed below the browse line and (3) stunted and heavily browsed trees. Repeated and intense browsing resulted in the small size, compact heavily ramified shape of stunted trees and in the short compact and ramified lower branches of escaped trees. These contrasted with the shape of non-browsed trees, a shape that was also found in escaped trees above the browse line. Before release, all browsed trees experienced stagnation in growth characterised by narrow rings (0.3 mm/year) and a small annual height increment (2.5 cm/year). At release, growth rate increased and stabilised: rings were wider (1.3 mm/year) and annual height increments were greater (10.5 cm/year). Non-browsed trees had a mean ring-width of 1.3 mm/year and an annual height increment of 22 cm/year. Delay in tree recruitment caused by deer varied from site to site. It had been about 15 years for the escaped trees and is estimated at 30–40 years for the stunted trees. Spatial variation in deer impact may reflect spatial variation of browsing pressure resulting from local differences in the availability of preferred forage or to differences in tree chemical defences/nutritional values.     

Leaf-rust resistance in rye (<Emphasis Type="Italic">Secale cereale</Emphasis> L.). 2. Genetic analysis and mapping of resistance genes <Emphasis Type="Italic">Pr3</Emphasis>, <Emphasis Type="Italic">Pr4</Emphasis>, and <Emphasis Type="Italic">Pr5</Emphasis>

The conventional way to drive modifications in old forest tree seed orchards is to establish progeny trials involving each parent tree and then evaluate its contribution to the performance of the progeny by estimating its general and specific combining ability (GCA and SCA). In this work, we successfully applied an alternative parent selection tactic based on paternity testing of superior offspring derived from a hybrid seed orchard established with a single Eucalyptus grandis seed parents and six E. urophylla pollen parents. A battery of 14 microsatellite markers was used to carry out parentage tests of 256 progeny individuals including two independent samples of selected trees and one control unselected sample, all derived from 6-year-old forest stands in eastern Brazil. Paternity determination was carried out for all progeny individuals by a sequential paternity exclusion procedure. Exclusion was declared only when the obligatory paternal allele in the progeny tree was not present in the alleged parent tree for at least four independent markers to avoid false exclusions due to mutation or null alleles. After maternity checks to identify seed mixtures and selfed individuals, the paternity tests revealed that approximately 29% of the offspring was sired by pollen parents outside the orchard. No selfed progeny were found in the selected samples. Three pollen parents were found to have sired essentially all of the offspring in the samples of selected and non-selected progeny individuals. One of these three parents sired significantly more selected progeny than unselected ones (P0.0002 in a Fisher exact test). Based on these results, low-reproductive-successful parents were culled from the orchard, and management procedures were adopted to minimize external pollen contamination. A significant difference (P<0.01) in mean annual increment was observed between forest stands produced with seed from the orchard before and after selection of parents and revitalization of the orchard. An average realized gain of 24.3% in volume growth was obtained from the selection of parents as measured in forest stands at age 2–4 years. The marker-assisted tree-breeding tactic presented herein efficiently identified top parents in a seed orchard and resulted in an improved seed variety. It should be applicable for rapidly improving the output quality of seed orchards, especially when an emergency demand for improved seed is faced by the breeder.Communicated by D.B. Neale     

Frost damage and its cascading negative effects on <Emphasis Type="Italic">Aesculus</Emphasis><Emphasis Type="Italic">glabra</Emphasis>

Frost damage and re-foliation are seldom quantified for forest species, but are of ecological and evolutionary importance. This study of Aesculus glabra (Ohio buckeye) in a deciduous forest remnant in Illinois, USA, quantified frost damage to leaves and flowers after sub-freezing temperatures in April 2007. It also documented re-foliation and later growth, reproduction, and survival in 2007–2009 for the 355 study individuals of four life stages growing 0–200 m from the forest edge. Life stages differed in % leaf damage because of differences in phenology during the frost. Large saplings with fully expanded, immature leaves had higher % damage and lower % canopy fullness after re-foliation than smaller saplings with partially or fully mature leaves and canopy trees undergoing shoot expansion with folded leaflets. Percent damage increased for saplings closer to edges. Large saplings with heavier frost damage to leaves had partial re-foliation in deep shade, lower % canopy fullness, earlier senescence, a shorter growing season, and greater death of next year’s buds. By 2008, large saplings with greater damage in 2007 had more dead branches and lower % canopy fullness. By 2009, 11% of large saplings had died. In 2007, frost damaged no flowers, but final fruit crop size was negatively related to % leaf damage. Edge trees with total leaf damage aborted all fruits. The frost event differentially affected individuals in their length and time of growing season, energy budget, and, ultimately, reproduction, and survival. The population’s local-scale demography and spatial pattern also changed as large saplings died.     

Different facets of tree sapling diversity influence browsing intensity by deer dependent on spatial scale

Browsing of tree saplings by deer hampers forest regeneration in mixed forests across Europe and North America. It is well known that tree species are differentially affected by deer browsing, but little is known about how different facets of diversity, such as species richness, identity, and composition, affect browsing intensity at different spatial scales. Using forest inventory data from the Hainich National Park, a mixed deciduous forest in central Germany, we applied a hierarchical approach to model the browsing probability of patches (regional scale) as well as the species‐specific proportion of saplings browsed within patches (patch scale). We found that, at the regional scale, the probability that a patch was browsed increased with certain species composition, namely with low abundance of European beech (Fagus sylvatica L.) and high abundance of European ash (Fraxinus excelsior L.), whereas at the patch scale, the proportion of saplings browsed per species was mainly determined by the species’ identity, providing a “preference ranking” of the 11 tree species under study. Interestingly, at the regional scale, species‐rich patches were more likely to be browsed; however, at the patch scale, species‐rich patches showed a lower proportion of saplings per species browsed. Presumably, diverse patches attract deer, but satisfy nutritional needs faster, such that fewer saplings need to be browsed. Some forest stand parameters, such as more open canopies, increased the browsing intensity at either scale. By showing the effects that various facets of diversity, as well as environmental parameters, exerted on browsing intensity at the regional as well as patch scale, our study advances the understanding of mammalian herbivore–plant interactions across scales. Our results also indicate which regeneration patches and species are (least) prone to browsing and show the importance of different facets of diversity for the prediction and management of browsing intensity and regeneration dynamics.     

The physiological advantage of an ecological filter species, <Emphasis Type="Italic">Indocalamus longiauritus</Emphasis>, over co-occurring <Emphasis Type="Italic">Fagus lucida</Emphasis> and <Emphasis Type="Italic">Castanopsis lamontii</Emphasis> seedlings

Indocalamus longiauritus (a dwarf bamboo) dominates forest understory and functions as an ecological filter to hinder the regeneration of canopy tree species in many temperate forests. However, the physiological mechanism underlying the function of ecological filters is not clear. In this study, we measured leaf-level carbon capture ability and use efficiency of the dwarf bamboo and the co-existing Fagus lucida (beech) and Castanopsis lamontii (chinkapin) seedlings in forest understory and small gaps in a beech–chinkapin mixed forest in the summer of 2005. The results indicated that I. longiauritus exhibited greater carbon capture ability, as indexed by light-saturated photosynthetic rate (P _max), maximal carboxylation rate, maximal electron transport rate and carboxylation efficiency, than the co-occurring F. lucida and C. lamontii seedlings in both forest understory and small gaps. Higher carbon capture ability in I. longiauritus was related to its greater partition of absorbed light energy to photochemistry. I. longiauritus had higher photosynthetic nitrogen use efficiency than F. lucida and C. lamontii seedlings in both light environments. However, water use efficiency (WUE) in I. longiauritus was higher than F. lucida but lower than C. lamontii. This intermediate WUE in I. longiauritus was related to its intermediate light-saturated stomatal conductance. In addition, I. longiauritus reduced metabolic cost by increasing the ratio of P _max to respiration rate, leading to increased net carbon balance. On the other hand, F. lucida and C. lamontii seedlings had greater plasticity of carbon capture ability and leaf structural traits, which might facilitate colonization of gaps and realization of natural regeneration in these species.     

Effects of browsing in relation to vegetation cover on common yew (<Emphasis Type="Italic">Taxus baccata</Emphasis> L.) recruitment in Mediterranean environments

Common yew (Taxus baccata L.) stands are recognized as prioritary habitats for biodiversity conservation within the European Union. The effects of browsing on the regeneration capacity and spatial dispersal of T. baccata recruits at the European southern limit of the species in the Mediterranean Basin have been herein studied. The efficacy of T. baccata recruitment has been evaluated at six localities in the Northern Sardinia mountains, which have similar altitude, climate, soil, and vegetation but have different types of uses (three were grazed by livestock and three were not). At each site, five habitats have been identified for T. baccata seed dispersal: reproductive female T. baccata canopy, reproductive female Ilex aquifolium canopy, non-fleshy-fruited tree canopy, fleshy-fruited shrubs, and open areas. The density of seedlings was found to be greater under fleshy-fruited trees (reproductive female T. baccata and I. aquifolium) than under shrubs, whereas the sapling density was higher in shrubby habitats, especially at grazed sites due to the mechanical protection afforded by the spiny shrubs against herbivores. Land use (LU) has been found to be the most important factor in determining the spatial distribution of seedlings and saplings in relation to forest habitats. Although browsers had an ephemeral but positive effect on seed germination through their trampling and the resultant scarification, this process eventually became ineffective as was shown by the occurrence of the lowest density of saplings in those habitats where the density of seedlings was the highest. The ultimate and most important effect of browsing was the sharp decrease in the density of saplings, and their almost complete extinction, in non-shrubby habitats. This study highlights the result that, in Mediterranean ecosystems, browsing constitutes the main negative factor on T. baccata seedling-sapling transition and furthermore confirms the necessity to preserve shrubby patches in the vicinity of reproductive female T. baccata and I. aquifolium to permit the regeneration of T. baccata in the presence of livestock. Moreover, at ungrazed sites, T. baccata is able to colonize non-shrubby shady habitats. The application of different management strategies to ungrazed and grazed sites should therefore be the main direction in the management and preservation of T. baccata stands in the Mediterranean region.     

Short-Term Effects of Cattle Browsing on Tree Sapling Growth in Mountain Wooded Pastures

Browsing by livestock has been identified as an important factor preventing tree regeneration in wooded pastures. Two field experiments were performed to investigate the effects of cattle browsing on tree sapling growth in a mountain-wooded pasture. Two size classes (ca. 12–17 cm and 41–59 cm) of each of 4 species (Picea abies, Abies alba, Acer pseudoplatanus and Fagus sylvatica) were exposed to zero, low and high grazing intensities. We measured the proportion of saplings browsed and the effect of browsing on growth. A mowing treatment within the zero grazing intensity treatment showed no significant effect on sapling growth. One percent of the large saplings but 25% of the small saplings escaped browsing. Saplings were better protected when surrounded by taller vegetation. The proportion of saplings browsed was not significantly different among species although evergreen tree saplings lost a larger proportion of biomass than deciduous species when browsed. Under grazing, average current-year shoot production and total aboveground biomass of all species were significantly reduced. Browsing effects tended to be smaller at the lower grazing intensity. Because the deciduous species were least reduced in aboveground growth, especially under the low grazing intensity, we conclude that at least in short-term, deciduous species are less affected by cattle browsing.     

Clustered root distribution in mature stands of <Emphasis Type="Italic">Fagus sylvatica</Emphasis> and <Emphasis Type="Italic">Picea abies</Emphasis>

Distribution of small roots (diameter between 2 mm and 5 mm) was studied in 19 pits with a total of 72 m² trench profile walls in pure stands of Fagus sylvatica and Picea abies. Root positions within the walls were marked and transformed into x-coordinates and y-coordinates. In a GIS-based evaluation, zones of potential influence around each root were calculated. The total potential influence produced isoline maps of relative root influence zones, thus indicating small root clustering. The questions studied were (1) whether there were marked clusters of small roots in the soil and (2) whether trees surrounding the pit (defined as tree density) correlate with the root abundance and distribution on the trench profile walls. Small roots of both species showed maximum abundance in the top 20 cm of the soil, where pronounced root clusters occurred next to areas with only low root accumulation. The area of root clusters did not differ significantly between the two stands. Weighted clumping, WC, calculated as a product of root class, and its area was used as an index of root clustering, which again did not differ between beech and spruce stands. However, evaluations on a single root level showed that beech achieved the same degree of clustering with lower number of roots. Regardless of soil properties related to root clusters, a significantly higher clustering acquired per root for beech than for spruce suggests beech to be more efficient in belowground acquisition of space. Because none of the parameters describing root clustering were correlated with tree density around the investigated soil profiles, clusters of small roots are inherently present within the tree stands.     

<Emphasis Type="Italic">Trichoderma harzianum</Emphasis> Rifai 1295-22 Mediates Growth Promotion of Crack Willow (<Emphasis Type="Italic">Salix fragilis</Emphasis>) Saplings in Both Clean and Metal-Contaminated Soil

We investigated if the plant growth promoting fungus Trichoderma harzianum Rifai 1295-22 (also known as “T22”) could be used to enhance the establishment and growth of crack willow (Salix fragilis) in a soil containing no organic or metal pollutants and in a metal-contaminated soil by comparing this fungus with noninoculated controls and an ectomycorrhizal formulation commercially used to enhance the establishment of tree saplings. Crack willow saplings were grown in a temperature-controlled growth room over a period of 5 weeks’ in a garden center topsoil and over 12 weeks in a soil which had been used for disposal of building materials and sewage sludge containing elevated levels of heavy metals including cadmium (30 mg kg⁻¹), lead (350 mg kg⁻¹), manganese (210 mg kg⁻¹), nickel (210 mg kg⁻¹), and zinc (1,100 mg kg⁻¹). After 5 weeks’ growth in clean soil, saplings grown with T. harzianum T22 produced shoots and roots that were 40% longer than those of the controls and shoots that were 20% longer than those of saplings grown with ectomycorrhiza (ECM). T. harzianum T22 saplings produced more than double the dry biomass of controls and more than 50% extra biomass than the ECM-treated saplings. After 12 weeks’ growth, saplings grown with T. harzianum T22 in the metal-contaminated soil produced 39% more dry weight biomass and were 16% taller than the noninoculated controls. This is the first report of tree growth stimulation by application of Trichoderma to roots, and is especially important as willow is a major source of wood fuel in the quest for renewable energy. These results also suggest willow trees inoculated with T. harzianum T22 could be used to increase the rate of revegetation and phytostabilization of metal-contaminated sites, a property of the fungus never previously demonstrated.     

Gap dynamics and regeneration strategies in <Emphasis Type="Italic">Juniperus-Laurus</Emphasis> forests of the Azores Islands

We asked the following questions regarding gap dynamics and regeneration strategies in Juniperus-Laurus forests: How important are gaps for the maintenance of tree diversity? What are the regeneration strategies of the tree species? Thirty canopy openings were randomly selected in the forest and in each the expanded gap area was delimited. Inside expanded gaps the distinction was made between gap and transition zone. In the 30 expanded gaps a plot, enclosing the gap and transition zone, was placed. In order to evaluate the differences in regeneration and size structure of tree species between forest and expanded gaps, 30 control plots were also delimited in the forest, near each expanded gap. In the 60 plots the number of seedlings, saplings, basal sprouts and adults of tree species were registered. Canopy height and width of adult individuals were also measured. The areas of the 30 gaps and expanded gaps were measured and the gap-maker identified. Juniperus-Laurus forests have a gap dynamic associated with small scale disturbances that cause the death, on average, of two trees, mainly of Juniperus brevifolia. Gap and expanded gap average dimensions are 8 and 25 m², respectively. Gaps are of major importance for the maintenance of tree diversity since they are fundamental for the regeneration of all species, with the exception of Ilex azorica. Three types of regeneration behaviour and five regeneration strategies were identified: (1) Juniperus brevifolia and Erica azorica are pioneer species that regenerate in gaps from seedlings recruited after gap formation. However, Juniperus brevifolia is a pioneer persistent species capable of maintaining it self in the forest due to a high longevity and biomass; (2) Laurus azorica and Frangula azorica are primary species that regenerate in gaps from seedlings or saplings recruited before gap formation but Laurus azorica is able to maintain it self in the forest through asexual regeneration thus being considered a primary persistent species; (3) Ilex azorica is a mature species that regenerates in the forest.     

Photosynthetic induction in leaves of co-occurring <Emphasis Type="Italic">Fagus lucida</Emphasis> and <Emphasis Type="Italic">Castanopsis lamontii</Emphasis> saplings grown in contrasting light environments

Photosynthetic induction times and photoinhibition in relation to simulated sunflecks (sudden increase of irradiance from 20 to 1,500 μmol m⁻² s⁻¹) were examined in leaves of co-occurring Fagus lucida (a deciduous tree) and Castanopsis lamontii (an evergreen tree) saplings grown either in a beech forest understory or in an adjacent open site during a late rainy season. Two hypotheses were tested: (1) understory leaves would display faster photosynthetic induction times and greater photoinhibition than open-grown leaves; and (2) evergreen species would have slower photosynthetic induction times and lighter photoinhibition than deciduous species. Times to reach 90% of maximal CO₂ assimilation rate (t _90%A ) and stomatal conductance did not differ between species, but showed faster by 3–5 min in open-grown leaves than understory leaves due to higher initial stomatal conductance (g _{s initial}) and induction state 1 min into simulated sunflecks (IS_1min) in the former. Our analysis across the published data on photosynthetic induction of 48 broad-leaved woody species again revealed the negative correlations between t _90%A and either g _{s initial} or IS_1min, and the similarity of t _90%A and between evergreen and deciduous species. Measurements of maximum PSII photochemical efficiency (F _v/F _m) indicated that photoinhibition occurred in saplings in any of the growth habitats during sunfleck-induced photosynthetic induction. Despite no interspecific differences in the degree of photoinhibition, understory leaves of both species suffered heavier photoinhibition than open-grown leaves, as indicated by a stronger decrease of F _v/F _m in the former. Dynamic changes in the quantum yields of PSII photochemistry and ΔpH- and xanthophyll-regulated thermal dissipation and adjustments in the partitioning of electron flow between assimilative and non-assimilative processes were functional to resist photoinhibition. However, such photoinhibition, together with stomatal and biochemical limitations, would decrease carbon gain during simulated sunflecks, particularly in understory leaves.     

General allometric equations and biomass allocation of <Emphasis Type="Italic">Pinus massoniana</Emphasis> trees on a regional scale in southern China

Applying allometric equations in combination with forest inventory data is an effective approach to use when qualifying forest biomass and carbon storage on a regional scale. The objectives of this study were to (1) develop general allometric tree component biomass equations and (2) investigate tree biomass allocation patterns for Pinus massoniana, a principal tree species native to southern China, by applying 197 samples across 20 site locations. The additive allometric equations utilized to compute stem, branch, needle, root, aboveground, and total tree biomass were developed by nonlinear seemingly unrelated regression. Results show that the relative proportion of stem biomass to tree biomass increased while the contribution of canopy biomass to tree biomass decreased as trees continued to grow through time. Total root biomass was a large biomass pool in itself, and its relative proportion to tree biomass exhibited a slight increase with tree growth. Although equations employing stem diameter at breast height (dbh) alone as a predictor could accurately predict stem, aboveground, root, and total tree biomass, they were poorly fitted to predict the canopy biomass component. The inclusion of the tree height (H) variable either slightly improved or did not in any way increase model fitness. Validation results demonstrate that these equations are suitable to estimate stem, aboveground, and total tree biomass across a broad range of P. massoniana stands on a regional scale.     

Ecological role of reindeer summer browsing in the mountain birch (<Emphasis Type="Italic">Betula pubescens</Emphasis> ssp. <Emphasis Type="Italic">czerepanovii</Emphasis>) forests: effects on plant defense,litter decomposition,and soil nutrient cycling

Mammalian herbivores commonly alter the concentrations of secondary compounds in plants and, by this mechanism, have indirect effects on litter decomposition and soil carbon and nutrient cycling. In northernmost Fennoscandia, the subarctic mountain birch (Betula pubescens ssp. czerepanovii) forests are important pasture for the semidomestic reindeer (Rangifer tarandus). In the summer ranges, mountain birches are intensively browsed, whereas in the winter ranges, reindeer feed on ground lichens, and the mountain birches remain intact. We analyzed the effect of summer browsing on the concentrations of secondary substances, litter decomposition, and soil nutrient pools in areas that had been separated as summer or winter ranges for at least 20 years, and we predicted that summer browsing may reduce levels of secondary compounds in the mountain birch and, by this mechanism, have an indirect effect on the decomposition of mountain birch leaf litter and soil nutrient cycling. The effect of browsing on the concentration of secondary substances in the mountain birch leaves varied between different years and management districts, but in some cases, the concentration of condensed tannins was lower in the summer than in the winter ranges. In a reciprocal litter decomposition trial, both litter origin and emplacement significantly affected the litter decomposition rate. Decomposition rates were faster for the litter originating from and placed into the summer range. Soil inorganic nitrogen (N) concentrations were higher in the summer than in the winter ranges, which indicates that reindeer summer browsing may enhance the soil nutrient cycling. There was a tight inverse relationship between soil N and foliar tannin concentrations in the winter range but not in the summer range. This suggests that in these strongly nutrient-limited ecosystems, soil N availability regulates the patterns of resource allocation to condensed tannins in the absence but not in the presence of browsing.