Effect of shoot size and phenological variation of host plants on the spatial patterns of cynipid galls

The effects of shoot size and differences in budburst phenology ofQuercus serrata trees on the spatial patterns of galls were investigated for two cynipid species: the sexual generation ofAndricus moriokae and the agamic generation ofAphelonyx glanduliferae. There were marked differences in budburst phenology, but these did not affect the gall density on the tree. The galls of both cynipids showed a contagious distribution in their respective trees, but different abundance patterns under high gall density. The mean number of galls ofA. glanduliferae over a shoot size range was positively correlated with shoot size. More galls ofA. moriokae appeared on larger shoots on trees on which many buds had started growing before oviposition by the agamic adults. In the case of a tree on which a few buds had burst by the time of oviposition, the mean numbers ofA. moriokae galls on shoots of particular size ranges depended on the frequency of shoots in the size class. These results suggest that, although these cynipids prefer to attack larger shoots within a host tree, they may exhibit plasticity in their preference in response to changes in budburst phenology of the host plant relative to the time of oviposition.     

Height growth of young larch (Larix kaempferi) in relation to the frequency of deer browsing damage in Hokkaido, Japan

The effect of browsing frequency by Sika deer (Cervus nippon yezoensis) on the height growth of Japanese larch (Larix kaempferi) in Hokkaido, Japan, was analyzed. Tree heights at the time of the census and at the start of the current growing season were determined for 100 trees selected randomly at each site. The tallest shoot on each tree was identified and the number of browsing occurrences on the current-year shoot was determined. Young larches browsed by deer repeatedly develop new shoots during a growing season. Larch is a browsing-tolerant species, and the average height growth of the most heavily browsed trees was >15 cm. Although resprouting partly compensated for decreased height growth caused by browsing, the annual increase in height decreased with increased browsing frequency. Thus, browsing frequency during a growing season best reflects the intensity of browsing damage to larch trees.     

Responses of Young Norway Spruce (Picea abies) to Winter Browsing by Roe Deer (Capreolus capreolus): Effects on Height Growth and Stem Morphology

The effects of natural and simulated winter browsing by roe deer on mortality, growth and defects in tree form among young recently planted Norway spruces were studied in two field studies and one simulation (clipping) experiment. No effect of browsing or clipping on mortality was observed. However, height growth was reduced by browsing and clipping, and the reduction increased with increases in the number of years in which they were browsed or clipped. Browsing or clipping in three successive years reduced height growth by the equivalent of about 1 yr. Spruces frequently became multi-trunked and/or developed multiple leaders as long as browsing and clipping lasted. However, when the browsing or clipping ceased, almost all spruces became single-trunked again. A more persistent effect was that many of the multiple trunks developed into large, abnormal branches or "spike-knots". The characteristics of the spike-knots resulting from browsing and clipping were very similar to those caused by other types of damage. The results indicate that roe deer browsing on spruce is less harmful than many Swedish foresters have feared.     

Height growth recovery and crown development in top‐damaged Pinus sylvestris trees

Leader shoot damage was imposed on young Scots pines (3 m high) in four ways: by caging the uppermost whorl including the leader shoot with 10 pine shoot beetles; by caging the two uppermost whorls with 20 beetles; by topping the tree below the 1984 whorl; by topping the trees as above and removing all current shoots in whorl 1983. Six years later, top‐damaged trees were still significantly shorter than undamaged controls, although the annual height growth rate had recovered to the pre‐damage level within 3 years. Recovery occurred in two ways: lateral branches from the nearest intact whorl took dominance over the damaged leader or secondary branches developed from interfascicular buds on the damaged leader shoot. Approximately one and two years of height growth were lost in the former and latter case, respectively. Only 5 of the 34 top‐damaged trees escaped technical defects (crooks and/or vertical branches). Stem diameter and crown development were slightly affected.     

Changes in shoot allometry with increasing tree height in a tropical canopy species,Elateriospermum tapos

Allometry of shoot extension units (hereafter termed "current shoots") was analyzed in a Malaysian canopy species, Elateriospermum tapos Bl. (Euphorbiaceae). Changes in current shoot allometry with increasing tree height were related to growth and maintenance of tree crowns. Total biomass, biomass allocation ratio of non-photosynthetic to photosynthetic organs, and wood density of current shoots were unrelated to tree height. However, shoot structure changed with tree height. Compared with short trees, tall trees produced current shoots of the same mass but with thicker and shorter stems. Current shoots with thin and long stems enhanced height growth in short trees, whereas in tall trees, thick and short current shoots may reduce mechanical and hydraulic stresses. Furthermore, compared with short trees, tall trees produced current shoots with more leaves of lower dry mass, smaller area, and smaller specific leaf area (SLA). Short trees adapted to low light flux density by reducing mutual shading with large leaves having a large SLA. In contrast, tall trees reduced mutual shading within a shoot by producing more small leaves in distal than in proximal parts of the shoot stem. The production of a large number of small leaves promoted light penetration into the dense crowns of tall trees. All of these characteristics suggest that the change in current shoot structure with increasing tree height is adaptive in E. tapos, enabling short trees to maximize height growth and tall trees to maximize light capture.     

Patterns of shoot mortality in Betula platyphylla in northern Japan

To understand the development of crown structure in Betula platyphylla Sukatch., mortality patterns of long shoots were analyzed quantitatively. We selected 25 saplings growing under various light conditions and measured the relative photosynthetically active radiation (rPAR) at, and the three-dimensional position of, first-order branches. A long shoot was assigned "no buds" (NB) status if it lacked buds at the end of the growing season, including at the tips of short shoots. A long shoot was classified as dead if it was NB and all the offspring long shoots issuing from it were NB. The probability that a leafy long shoot (a current-year long shoot with leaves or an older long shoot with short shoots with leaves) would become NB by the end of the season was positively dependent on shoot age and branch age, and negatively dependent on shoot length, centripetal shoot order, branch height and rPAR at the branch. Randomization tests revealed that shoots became NB and dead in clusters of connected shoots. In particular, shoot clusters originating from 3-year-old shoots were more likely to die than expected if each shoot was assumed to become NB regardless of the connection. Stepwise logistic regression revealed that the maximum rPAR within the crown of an individual tree had a significant effect on the mortality rate of 3-year-old shoot clusters, together with the rPAR at the level of the branch and other structural entities. Correlative inhibition is an important mechanism for determining shoot mortality patterns.     

Browsing affects intra-ring carbon allocation in species with contrasting wood anatomy

Current knowledge on tree carbon (C) allocation to wood is particularly scarce in plants subjected to disturbance factors, such as browsing, which affects forest regeneration worldwide and has an impact on the C balance of trees. Furthermore, quantifying the degree to which tree rings are formed from freshly assimilated vs. stored carbohydrates is highly relevant for our understanding of tree C allocation. We used (13)C labelling to quantify seasonal allocation of stored C to wood formation in two species with contrasting wood anatomy: Betula pubescens Ehrh. (diffuse-porous) and Quercus petraea [Matt.] Liebl. (ring-porous). Clipping treatments (66% shoot removal, and unclipped) were applied to analyse the effect of browsing on C allocation into tree rings, plus the effects on tree growth, architecture, ring width and non-structural carbohydrates (NSCs). The relative contribution of stored C to wood formation was greater in the ring-porous (55-70%) than in the diffuse-porous species (35-60%), although each species followed different seasonal trends. Clipping did not cause a significant depletion of C stores in either species. Nonetheless, a significant increase in the proportion of stored C allocated to earlywood growth was observed in clipped birches, and this could be explained through changes in tree architecture after clipping. The size of C pools across tree species seems to be important in determining the variability of seasonal C allocation patterns to wood and their sensibility to disturbances such as browsing. Our results indicate that the observed changes in C allocation to earlywood in birch were not related to variations in the amount or concentration of NSC stores, but to changes in the seasonal availability of recently assimilated C caused by modifications in tree architecture after browsing.     

Reduction of herbivore density as a tool for reduction of herbivore browsing on palatable tree species

Browsing of overabundant free-living herbivores often limits the natural as well as artificial regeneration of forest in Central-European Mountains. The aim of the study was to assess the efficiency of the extensive reductions of herbivore populations for protection of forest regeneration in preferred areas. We analysed the relationship between the intensity of shoot browsing and relative density of herbivores in viewpoint of natural regeneration of secondary mountain spruce stands with low proportion of broadleaved trees in Králicky Sněžník Reserve (Czech Republic). The distribution of seasonally migrating herbivores was established by counting faecal pellet groups (standing crop method) in growing season. The intensity of browsing of spruce, beech and rowan was assessed using the proportion of browsed shoots on individual tree sapling. Density of red deer was re-counted from the number of pellet groups and it was 15–56 individual/km². The intensity of spruce browsing was low in the whole area in all seasons. In general, the intensity of rowan and beech shoot browsing was high in the whole area. There were no correlations between deer density and browsing intensity of rowan (browsing was severe in all plots). We conclude that the natural regeneration of attractive trees and shrubs is nearly impossible in habitats where proportion of these food items is too small, even when the density of herbivores is low. Reduction of herbivores density is useful for protecting spruce and other tree species with low preference by herbivores. Forest managers should take into account the high palatability of deciduous tree species and distribution of herbivores on localities. Preference of localities is often based on grasses in the food supply. Regeneration of highly palatable tree species requires both low density of herbivores and sufficient protection of saplings.     

川西云杉无性系苗期选育

通过对120株优良川西云杉进行扦插无性系化,采用强化培育技术对无性系苗培育4年后,调查观测各个无性系苗高、新梢长、一级侧枝数及主梢上的芽数,达到筛选优良无性系的目的。最后,利用标准差法,从该批无性系中选择筛选出优良无性系14个。结果表明,川西云杉扦插无性系间不同性状的变异系数差异较大,其中一级侧枝数和主梢上芽数的变异系数最大,与生长相关最强,进行无性系早期选择最有潜力。同时,一级侧枝数和主梢上芽数的变异系数也可能是多阶段选择的重要指标。因此,芽和侧枝数的数量是影响扦插苗生长的重要因子,是川西云杉无性系早期选择应考虑的主要性状。     

Young conifer stands form a deer browsing refuge for an oak admixture: silvicultural implications for forest regeneration under herbivore pressure

There is little knowledge how ungulate pressure on forest regeneration may be mitigated by silvicultural methods. The knowledge is especially needed for artificially regenerated, deciduous tree species. We studied factors affecting browsing incidence by deer in the Pisz Forest District in Poland, an area where 10,000 ha of forest was damaged by a 2002 hurricane. In 2006, we established three experimental plots (in total, 22.6 ha), in which the main species was Scots pine (Pinus sylvestris) admixed with pedunculate oak (Quercus robur). The data on browsing were collected in 2008–2015. In general, oak browsing incidence was unrelated to oak planting density. On a plantation scale, it was significantly affected by the pine age. Although in each variant all the oaks were browsed for four consecutive years (2009–2012), in 2013 browsing incidence began to decrease. When the pines grew higher and formed a physical barrier, it was harder for deer—roe deer (Capreolus capreolus), red deer (Cervus elaphus) and moose (Alces alces)—to move through and locate the oaks. Moreover, within plantations, oak browsing incidence was higher in the patches with shorter pines. Browsing of individual saplings or small groups of saplings was also negatively affected by the height of neighbouring pine saplings. Oak density influenced deer selectivity depending on the tree height. In a low oak tree density, browsing incidence was unrelated to oak height, while in higher tree density, deer selected oaks of the height between 40 and 100 cm. We postulate that deciduous admixture in a coniferous (unattractive) stand can be planted with a few year delay. Older coniferous trees should impede locating of attractive tree species by deer and the browsing incidence.     

Photoperiodic control of seasonal development and dormancy in tropical stem-succulent trees

Tropical stem-succulent trees store large quantities of water in their trunks yet remain leafless during the early and mid dry season. In contrast to most other tropical trees, bud break of vegetative buds is not induced in fully hydrated stem succulents between the winter solstice and the spring equinox by leaf abscission, abnormal rain showers or irrigation. Vegetative buds of leafless trees are therefore in a state of endo-dormancy similar to that of temperate perennial plants during early winter. Highly synchronous bud break regularly occurs soon after the spring equinox, often weeks before the first rainfalls of the wet season. These observations suggested that endo-dormancy and bud break might be induced by declining and increasing photoperiods after the autumn and spring equinoxes, respectively. In phenological field observations, we confirmed highly synchronous bud break after the spring equinox in many trees of five stem-succulent species in the northern and southern hemispheres. Shoot growth of potted saplings of Plumeria rubra L. was arrested by a decline in day length below 12 h after the autumn equinox, but continued in saplings maintained in a 13-h photoperiod. Conversely, exposure to a 13-h photoperiod induced bud break of dormant apical buds in saplings and cuttings in January, whereas plants maintained in the natural day length of < 11.7 h remained dormant. Photoperiodic control of endo-dormancy of vegetative buds in stem succulents is thus supported by field observations and experimental variation of the photoperiod. At low latitudes, where annual variation of day length is less than 1 h, bud dormancy is induced and broken by variations in photoperiod of less than 30 min.     

Influence of Cattle Stocking Rate on Browsing of Norway Spruce in Subalpine Wood Pastures

In the Swiss Alps, 15% of Swiss mountain forests are grazed during summer, mainly by cattle. The forest laws of various Swiss cantons characterise forest grazing as a detrimental form of land use and stipulate that this grazing practice should be restricted. However, little is known about tree damage actually caused by cattle. Seven subalpine ranges in the Swiss Canton Grisons, grazed by cattle at different stocking rates, were investigated. The condition of naturally regenerated young trees (Picea abies (L.) Karst.) was assessed before and after the cattle grazing period. In order to characterise the influence of wild ungulates on the young trees during winter, the assessment of tree condition was repeated in the proximate spring. In total, 4% of the young trees were browsed on the apical shoot, 10% were browsed on lateral shoots, 13% of the trees showed other damage. The variation among ranges could almost completely be explained by the cattle stocking rate (livestock units per hectare). During winter, wild ungulates browsed 3 times as many young trees as the cattle during summer. The results suggest that cattle stocking rates on subalpine wood pastures should not exceed one livestock unit per hectare in order to avoid intensive browsing and other damage by cattle on young Norway spruces.     

Phenology and growth dynamics in Mediterranean evergreen oaks: Effects of environmental conditions and water relations

Budburst date and shoot elongation were measured in two mature Mediterranean evergreen oaks (Quercus suber and Quercus ilex) and their relationships with meteorological and tree water status (predawn leaf water potential) data were analysed. Experimental work took place at two sites: Mitra 2 - Southern Portugal (2002-2003) and Lezirias - Central Portugal (2007-2010). Quercus suber phenology was studied at both sites whereas Q. ilex was only studied at Mitra 2. Quercus suber budburst date occurred at a photoperiod around 13.8 h (± 0.26) - late April/early May - and was highly related to the average daily temperature in the period 25 March - budburst date (ca. 1.5 months prior to budburst), irrespective of site location. In that period, budburst date was much more dependent on average maximum than average minimum daily temperature. Base temperature and thermal time for Q. suber were estimated as 6.2 °C (within the reported literature values) and 323 degree-days, respectively. Q. ilex budburst occurred about 6 weeks earlier than in Q. suber (photoperiod: 12.3 h (±0.3)). Relationships of Q. ilex budburst date and temperature were not studied since only 2 years of data were available for this species. Q. suber shoot elongation underlying mechanisms were quite different in the two sites. At Mitra 2 (Q. suber and Q. ilex), there was a considerable tree water stress during the dry season which restricted shoot elongation. Shoot growth was resumed later in the wet autumn when tree water status recovered again. At the Lezirias site Q. suber water status was not restrictive. Therefore, shoot elongation was mainly dependent on nutrient availability in top soil, as suggested by the strong and positive relationships between annual shoot growth and long-term cumulative rainfall (2-4 months) and short-term average temperature (1 month) prior to budburst. Annual shoot elongation at this well-watered site was higher than in Mitra 2, and variability of growth between trees was enhanced after warm, wet springs when shoot elongation was higher. Results obtained are relevant to the carbon balance, productivity and management of evergreen Mediterranean oak woodlands, particularly under the foreseen climate change scenarios.     

Influence of different forest conversion strategies on ground vegetation and tree regeneration in pine (<Emphasis Type="Italic">Pinus sylvestris</Emphasis> L.) stands: a case study in NE Germany

The conversion of anthropogenic into more natural, self-regenerating forests is one of the major objectives of forestry throughout Europe. In this study, we present investigations on permanent plots with different silvicultural treatment in NE German pine stands. Management of old-growth pine stands on acidic and nutrient-poor sandy sites differs in fencing, thinning, and planting of certain tree species. The investigations were carried out on the community, population, and individual level of the pine forest ecosystems. Thus, vegetation changes, size and height of tree populations, and height increment of tree individuals were observed over a time span of 6 years. Special attention was paid to short-lived tree species such as, e.g., Frangula alnus and Sorbus aucuparia, as well as to Fagus sylvatica as one of the most typical forest tree species of Central Europe. Vegetation changes are interpreted as a consequence of natural regeneration of formerly degraded forest sites, involving an increase in nutrient availability. High browsing pressure can be considered as a key factor for the inhibition of tree seedlings and growth of saplings. Some Sorbus aucuparia individuals, however, succeeded in growing out of the browsing height also in unfenced stands. Few found specimens of Fagus sylvatica proved that this species is able to establish spontaneously on these relatively dry, acidic sites under continental climate influence. Such natural regeneration processes, also including spontaneous rejuvenation of trees, can be integrated into silviculture as passive forest conversion management. An active management like thinning of stands, planting of trees, and fencing can accelerate forest conversion with regard to height growth and species number of trees.     

Coppicing ability of dry miombo woodland species harvested for traditional charcoal production in Zambia:a win–win strategy for sustaining rural livelihoods and recovering a woodland ecosystem

The miombo woodland is one of the most extensive woodlands in Africa, supporting livelihoods based on biomass fuel for millions of rural people. However, there are growing concerns about the sustainability of harvesting for biomass fuel(mainly charcoal). Thus, the aim of this study was to examine whether regeneration by coppice is a viable option for sustainably managing miombo woodlands for biomass fuel production. We tested the hypotheses that(1) species, stump diameter, stump height and time since cutting significantly affect the number of sprouts per cut stump(coppice density) and mean sprout height(shoot vigour) and(2) higher coppice density reduces shoot vigour due to competition among coppice shoots in a given stump. In an inventory in areas that were harvested for charcoal production by the local people, 369 stumps of 11 species were recorded with mean coppice stumps ranged from 6 to 84. The mean coppice density ranged from 5 to 8 shoots per stump while the mean height of coppice shoots ranged from 46 to 118 cm with marked interspecific variations. Stump size was significantly and positively correlated with coppice density for some of the species, but not with shoot vigour for the majority of the species. However, shoot vigour was significantly positively correlated to time since cutting of trees for nearly half of the species. Coppice density had a significant negative correlation with shoot vigour for two species, and a positive correlation for one species. In conclusion, the results provide evidence about the importance of coppice management as a win–win strategy for sustaining charcoal-based rural livelihoods and recovering the miombo woodland ecosystem.     

Patterns of Stem Damage by Moose (Alces alces) in Young Pinus sylvestris Stands in Sweden

The incidence of recent moose browsing of the main stem on young Scots pine (Pinus sylvestris L.) trees, and correlations with tree or stand characteristics, were examined using data from a large-scale survey in Sweden. On average, 10% of all Scots pine main stems showed one or more types of recent damage, with browsing of the apical leader accounting for about 75% of all damage recorded. Stripping of bark off the main stem occurred most frequently in the southern area, where site productivity is highest. Apical leader browsing was negatively correlated with height of the main stems, length of the apical leader and incidence of pre-commercial thinning, whereas bark stripping and stem breaking were positively correlated with the same variables. All types of recent stem damage correlated positively with the extent of previous stem damage and also with the extent of recent browsing of lateral shoots.     

Evaluation of leaf display of evergreen broadleaved tree species and deciduous tree species in warm temperate conifer plantations

We investigated the sapling leaf display in the shade among trees of various leaf lifespans co-occurring under the canopy of a warm-temperate conifer plantation. We measured leaf-area ratio (aLAR) and morphological traits of saplings of evergreen broadleaved tree species and a deciduous tree species. Although we found large interspecific and intraspecific differences in aLAR even among saplings of similar size in the homogeneous light environment, we did not find a consistent trend in aLAR with leaf lifespan among the species. While deciduous trees annually produced a large leaf area, some evergreen broadleaved trees retained their leaves across years and had aLAR values as high as those of deciduous trees. Among leaf-level, shoot-level, and individual-level morphological traits, aLAR was positively correlated with current-year shoots mass per aboveground biomass in deciduous trees, and with the area of old leaves per aboveground mass in evergreen broadleaved trees. Thus, tree-to-tree variation in the degrees of annual shoot production and the accumulation of old leaves were responsible for the interspecific and intraspecific variations in aLAR.     

Lateral bud outgrowth on decapitated shoots of low-pruned mulberry (Morus alba L.)

After decapitation, lateral shoot growth of mulberry coppice (Morus alba L. cv. Shin-ichinose) from 10-year-old stumps had an extremely acrotonic form compared with that of intact one-year-old stems of trees during the spring. When one dominant shoot from each stump was decapitated, only a few upper lateral buds grew out and elongated. Defoliation of the decapitated shoots resulted in an increase in the number of shoots sprouting and a decrease in the rate of elongation of the laterals. Further enhancement of laterals on decapitated dominant shoots resulted from the removal of competing intact coppice shoots from the stumps. 1-Naphthaleneacetic acid (NAA) applied as a spray reduced the number of lateral buds sprouting from both defoliated, decapitated erect shoots and intact horizontally trained shoots. The results suggest that management of mulberry coppice could increase the supply of leaves for commercial silk production.     

Relative shoot height and irradiance and the shoot and leaf properties of Quercus serrata saplings

Effects of relative shoot height and irradiance on shoot and leaf properties of Quercus serrata Thunb. saplings growing in the understory and in gaps were investigated. Photosynthetic photon flux (PPF) at the location of the shoot relative to that in the open (relative PPF; rPPF) and the height of the shoot base relative to tree height (relative height; rHeight) were measured for all current-year shoots of each sapling. Current-year shoot properties (length, leaf area, number of daughter shoots) and mortality, and leaf properties (mass per area (LMA) and nitrogen content per area (N(area))) were examined in relation to rPPF and rHeight. N(area) was used as a proxy for area-based assimilative capacity. Shoot length, leaf area per shoot and number of daughter shoots increased with increasing rHeight, especially in well-lit conditions. Shoot mortality decreased with increasing rHeight and rPPF. Both LMA and N(area) were positively correlated with rPPF, but not rHeight.     

Influence of foliar phenology and shoot inclination on annual photosynthetic gain in individual beech saplings: A functional–structural modeling approach

We developed a functional–structural plant model for Fagus crenata saplings and calculated annual photosynthetic gains to determine the influences of foliar phenology and shoot inclination on the carbon economy of saplings. The model regenerated the three-dimensional shoot structure and spatial and temporal display of leaves; we calculated the hourly light interception of each leaf with a detailed light model that allowed us to estimate hourly leaf photosynthetic gain taking leaf age into account. To evaluate the importance of simultaneous foliar phenology and slanting shoots in beech saplings, we calculated the photosynthetic budgets for saplings with contrasting foliar phenologies and shoot inclinations. In our simulations, we distinguished between simultaneous and successive foliar phenologies, upright and slanting shoot inclinations, and environments with and without a vertical gradient in light intensity. Other model parameters (including photosynthesis vs. light curve, leaf size, and leaf shape) were obtained directly from live beech saplings. With no vertical gradient in light intensity, modeled saplings with simultaneous foliar phenology and slanting shoots (as in live beech) had larger annual photosynthetic gains than saplings with other combinations of traits. Hence, simultaneous foliar phenology and slanting shoots are efficient ways to display leaves in the shaded forest understory light regime where beech saplings thrive. In the presence of vertical light gradients, which can occur in canopy gaps, saplings with upright shoots had larger annual photosynthetic gains than counterparts with slanting shoots. Although mean daily photosynthetic gains of saplings with successive foliar phenology were elevated by exposing leaves to strong light when young and productive, the annual photosynthetic budget of these saplings was reduced (compared to saplings with simultaneous foliar phenology) by their relatively short leaf lifespan. Overall, our results suggest that slanting shoots with simultaneous foliar phenology are particularly successful in shaded environments, where beech often dominates, because they appear to maximize the annual carbon budget by avoiding self-shading and extending leaf lifespans.