Sapling Height Research Articles

Plant diversity and habitat structure affect tree growth, herbivory and natural enemies in shelterbelts

Abstract Shelterbelts have become a refuge and source of food for wildlife because of habitat loss in farmlands. However, effects of shelterbelt attributes such as plant diversity and habitat structure on different trophic levels within shelterbelts are unclear. Effects of shelterbelt woody plant diversity and habitat structure (lower vegetation strata, logs, litter and rocks) were measured on the growth and herbivory of Eucalyptus blakelyi saplings that were caged from birds, caged from birds and arthropods and un-caged. Arthropod diversity of E. blakelyi saplings and shelterbelts was evaluated. Height and stem diameter of saplings in all treatments was positively correlated with plant diversity. Habitat structure was negatively correlated with numbers of leaves on E. blakelyi saplings and positively correlated with herbivory, which was greater in saplings caged from birds. The overall abundance of arthropods inhabiting shelterbelts correlated positively with plant diversity, but negatively with habitat structure. Araneae and Formicidae were the most common taxa on E. blakelyi saplings and were more numerous on saplings caged from birds, suggesting an important role of these vertebrates as predators of shelterbelt arthropods.

THE EFFECT OF DIFFERENT N, P, K FERTILIZER LEVELS ON GROWTH OF WALNUT SAPLINGS

Two-year old walnut (Juglans regia L.) cultivars were used to study the effects of different N, P, K fertilizer levels on growth of grafted walnut saplings. The results indicated that application of N, P, K fertilizer could increase shoot length, tree height, trunk girth, root biomass and total biomass of walnut saplings, but the effect of N fertilizer on enhancing trunk girth of walnut was not significant. The best concentration of N, P, K fertilizers were all 100 mg nutrient/kg of soil.

Patterns of tree growth in a single tree selection silver fir–European beech forest

The basal area and height growth of trees and saplings in silver fir–European beech single stem selection forest were studied with regard to their social status and crown parameters of size, coverage, shading and vitality. On 24 permanent research plots (20 m × 20 m each) all trees [diameter at breast height (dbh) ≥10 cm] and saplings (≥1.3 m tall and dbh <10 cm) were surveyed. Repeated measurements of dbh (N = 1,608) and height (N = 1,135) 10 years apart enabled the calculation of annual basal area increment (BAI) of trees and saplings, and annual height (HI) increment of saplings. To obtain the growth characteristics for individual trees and saplings, their social status and crown parameters were assessed by rank. In the multivariate general linear model for BAI, social status, crown size and crown coverage of individuals as the predictors, and dbh2 as the covariate, explained 70% of total variability. Similarly, social status, crown size, crown coverage and crown shading had a significant impact on the HI of saplings, explaining 70% of total variability. Among the observed variables, social status determined according to the individual's position in vertical stand structure was, in addition to dbh, the most important predictor for both BAI and HI. Significant differences were observed between the BAI and HI models for the main tree species (European beech and silver fir), indicating their different growth characteristics. The applied method could be used as a supplement to the more widely used approaches for studying basal area and height growth of individual trees in selection forest stands.

MODEL DISTRIBUSI DIAMETER LIMA JENIS POHON PADA HUTAN TROPIKA BASAH DI KABUPATEN MAMUJU, SULAWESI BARAT

The objective of this research is to establish the most suitable tree diameter distribution model for five tree species on tropical rain forest in Mamuju District. This research was conducted on two locations. The 50 square plots were sampled systematically for seedling, sapling, pole and tree measurements of bintangur, jambu-jambu, lada-lada, matoa and nyatoh species. The distance among plots was 50 m. Variables to be measured were stem number of seedlings to trees and tree diameter at breast height (1,3 m) of saplings to trees. About 70% of the data were used to establish the best model, the rest of 30% were used to validate the model. Models to be analyzed were fourth-order semi-logarithmic transformed polynomial function, Weibull density function and monotonic decreasing Weibull function. The results show that the five tree species have a similar diameter distribution pattern. The shape of this distribution is the typical of uneven-aged stand distribution on natural forest, namely reversed J shape. The most suitable model for five species is second-order semi-logarithmic transformed polynomial function. Key words: model, diameter distribution, natural forest, uneven-aged stand.

Pits and rocky microsites in a subalpine forest stand facilitate regeneration of spruce saplings by suppressing dwarf bamboo growth inside a deer-proof fence

We determined patterns of microsite suppression in dwarf bamboo Sasa nipponica when grazing deer were absent. This bamboo species is able to outcompete Hondo spruce (Picea jezoensis var. hondoensis) saplings under many environmental circumstances. We set up two 10 × 100 m plots inside a deer-proof fence within a subalpine forest on Mt. Ohdaigahara, central Japan, and two similarly sized plots outside the fence. Within the plots, we surveyed microsites where spruce saplings grew. We measured height and shoot elongation of all spruce saplings, and culm height and cover ratios of dwarf bamboo growing around each spruce sapling. Spruce sapling density and average height were higher inside the deer-proof fence than outside, as were bamboo height and cover. Thus, there was a negative effect of deer browsing on vegetation parameters outside the fence and a suppression of the negative effect of bamboo on spruce sapling growth inside the fence. Spruce sapling height was higher in tree-fall pits than in other microsites inside the fence, whereas both dwarf bamboo height and cover were lower in pits and rocky sites than elsewhere. In soil and collar microsites, spruce sapling shoot growth was lower and bamboo height and cover were higher than in pits and rocky sites. Inside the fence, dwarf bamboo cover was high, but pits and rocks suppressed its growth, allowing spruce saplings to flourish. To restore heavily damaged spruce forests with advanced saplings, it will be necessary to construct deer-proof fences and create and maintain microsites with pits and rocks.

Growth properties of 16 non‐pioneer rain forest tree species differing in sapling architecture

Summary 1. Sapling architecture may be an important determinant of performance traits, such as light interception and height growth, but few studies have examined the direct relationship between sapling architecture and growth properties. To study this relationship and the potential for strategic diversification, we analysed the growth properties in saplings of 16 Bornean tree species that differ in architecture. 2. Annual net production significantly differed amongst species and was positively correlated with total above‐ground dry mass, total leaf area and crown area. In contrast, the net assimilation rate was weakly but negatively correlated with these architectural traits. The net assimilation rate was virtually independent of leaf size and specific leaf area. Relationships between sapling architecture and relative growth rate in mass were weak. 3. The relative growth rate in height did not significantly differ amongst species, although their total dry mass, a proxy for extension cost, varied fourfold across species for a given sapling height. This is because the proportional increase in net production with total dry mass, which is based on a larger total leaf area and larger crown area, cancelled out the higher extension cost. All architectural traits, including leaf size and specific leaf area, failed to predict height growth rate. 4. Synthesis. Relative growth rates in both mass and height were relatively independent of sapling architecture. Of the architectural traits, leaf size, specific leaf area and stem diameter were poor predictors of growth properties, even though they were considered functionally important. These results clearly reject the classic hypothesis that architectural variation leads to a trade‐off between height growth and light interception, at least for the species that are under shaded conditions. However, functional variation ranging from species with high net production and low net assimilation rates (in saplings of equal height) to species with the opposite traits, which was accompanied by architectural variation in total dry mass and related size factors, may be important for the coexistence of these tree species. The possibility that small total dry mass may be advantageous in height growth under well‐lit conditions should be examined in future studies.

Costs of height gain in rainforest saplings: main-stem scaling, functional traits and strategy variation across 75 species

Height gain plays an important role in plant life-history strategies and species coexistence. Here main-stem costs of height gain of saplings across species within a rainforest community are compared. Scaling relationships of height to diameter at the sapling stage were compared among 75 woody rainforest plant species in subtropical eastern Australia using standardized major axis regression. Main-stem costs of height gain were then related to other functional traits that reflect aspects of species ecological strategies. Slopes (beta) for the height-diameter (H-D) scaling relationship were close to 1.3, in line with previous reports and with theory. Main-stem volume to achieve 5 m in height varied substantially between species, including between species within groups based on adult height and successional status. The variation was largely independent of other species traits, being uncorrelated with mature plant height (H(max)) and with leaf size, and weakly negatively correlated with wood density and seed size. The relationship between volume to reach 5 m and wood density was too weak to be regarded as a trade-off. Estimated main-stem dry mass to achieve 5 m height varied almost three-fold across species, with wood density and stem volume contributing roughly equally to the variation. The wide range in economy of sapling height gain reported here is presumed to be associated with a trade-off between faster growth and higher mortality rates. It is suggested that wide diameters would have a stronger effect in preventing main-stem breakage in the short term, while high wood density would have a stronger effect in sustaining stem strength over time.

Size‐dependence of growth and mortality influence the shade tolerance of trees in a lowland temperate rain forest

Summary 1. A trade-off between growth in high-light and survival in low-light of species is often proposed as a key mechanism underpinning the dynamics of trees in forest communities. Yet, growth and survival are known to depend on plant size and few studies have analysed how this trade-off can vary between juvenile life stages and the potential consequences of the trade-off for the differences in regeneration rate between species in mixed forests. 2. We quantified growth and mortality for two different juvenile life stages ‐ seedlings and saplings ‐ of seven tree species common in temperate rain forests in New Zealand using data from field studies. We found strong evidence that the ranking of species for survival in shade and growth in full light was affected by size. There was a trade-off between seedling survival in low light and sapling height growth in high light, but no trade-offs were observed when considering other combinations of life stages (seedling growth vs. seedling survival, seedling growth vs. sapling survival, or sapling growth vs. sapling survival). 3. We ran simulations with an individual-based forest dynamics model ‐ SORTIE/NZ ‐ to explore how the trade-off drives the differences in tree species regeneration success in gaps vs. under closed forest conditions. These simulations indicate that because species’ ranks in shade tolerance varied with life stage, regeneration success was not predicted from knowledge of tree performance at a single life stage. For instance, high-light sapling growth was a strong determinant of regeneration success in forest gaps, but seedling growth was also influential. Under closed forest, regeneration success was primarily limited by low-light mortality at the seedling stage, but seedling growth and sapling survival were also influential. 4. Synthesis. Growth-survival trade-offs can be strongly affected by the size of the individual analysed, resulting in completely different rankings of the shade tolerance of species across different juvenile life stages. Performance of both seedlings and saplings influenced regeneration success, highlighting the need to consider growth-survival trade-offs and the shade-tolerance strategies of tree species over a large range of juvenile sizes.

Ontogenetic strategy shift in sapling architecture of Fagus crenata in the dense understorey vegetation of canopy gaps created by selective cutting

Ontogenetic architectural variation is a key aspect of the light foraging of saplings under canopy gaps, where the interactions with the surrounding understorey plants are intense and change as saplings grow. Therefore, relationships between the allometry of 58 Fagus saplings (15–184 cm tall) and both the surrounding vegetation and light environment were investigated in the dense understorey of canopy gaps. The light available to the saplings exhibited a positive exponential relationship to their height, and at a given sapling height, it was inversely related to the height of the surrounding understorey. The slenderness of the saplings' stems increased as their height increased, and their crown architecture shifted from horizontally spread monolayer to vertically extended multilayer forms, indicating an ontogenetic strategy shift from shade tolerance to shade avoidance. These changes in sapling architecture were independent of the height of the surrounding understorey and, therefore, light availability, although the length of their current-year shoots (reflecting the rate of architectural development) was inversely related to the surrounding understorey height. Thus, ontogenetic architectural variation in Fagus saplings probably has the character of a developmentally programmed growth trajectory preadjusted to the most likely environments; the surrounding environments mainly affect the rate at which saplings move along this trajectory.

Effects of clonal selection on biomass production and quality in Robinia pseudoacacia var. monophylla Carr.

In this paper, the results of the effects of clonal selection on biomass production and quality in monophylla black locust ( Robinia pseudoacacia var. monophylla Carr.) were studied. The genetic material included seedlings of open pollinated families, ramets of selected clones within them and seedlings of common black locust ( Robinia pseudoacacia L.) as a control. Both seedlings and ramets were planted in the field in April 1994. At the end of the first and the subsequent growing seasons (1994–2002) all of them were cut at 20 cm aboveground. Measurements were done at the end of October–beginning of November and included height and oven-dry weight of saplings, stem number, leaf/stem ratio of oven-dry weight and length of the longest thorn. It was found that height and oven-dry weight were increased in the first three years but they declined thereafter both in clones and families. Overall, however, clones were superior to families. Stem number was increased with age more in families than in clones. Leaf/stem ratio of oven-dry weigh t declined with time but clones were superior to families. Thorn length, finally, increased over the years but clones had significantly lower values than families. The results showed that the most productive clones were also better in quality characteristics (leaf/stem ratio of oven-dry weight and thorn length) than most families and the control. It is concluded that clonal selection can result in significant increase of biomass quantity and improvement of its quality.

Establishment patterns of woody species in low intensity-grazed pastures after the cessation of intensive agricultural use

Low intensity grazing with large herbivores is increasingly used to steer the development of mosaic landscapes (including wood-pastures) and woodland expansion on former agricultural land. We studied the establishment and early growth pattern of woody species in grasslands (formerly used for high intensity summer cattle grazing) in which a low intensity-grazing regime was set up between 4 and 11 years ago. We tested whether the developing vegetation patches, consisting of tall herbs and scrub, influenced this pattern. Further, we investigated if increased susceptibility to trampling disturbance by large herbivores on wet soils in floodplains influenced sapling establishment. Formerly intensively used grasslands were studied at six sites, four in floodplains and two in interfluvial zones on nutrient rich, heavy soils. In total, we sampled 141 plots with grassland, tall herb or scrub vegetation and recorded individuals of established tree and shrub species, their height, diameter, browsing damage and distance to potential seed sources. In the floodplains, we recorded soil disturbance by large herbivores (hoofprints) in wet and moist soils. Sapling frequencies, with Fraxinus excelsior as the most common species (>50% of all individuals), were two to three times higher in tall herb and scrub patches compared to grassland. Only the spiny Crataegus monogyna established in higher frequencies in grassland plots. In floodplains, we found two to three times more established woody saplings in wet tall herb plots, compared to moist and wet grassland plots and moist tall herb plots. Browsing reduced sapling height in grassland and tall herb patches. Only in scrub patches did average height (±2.5 m) reach above the browse line. We found 30–70% less browsing damage to saplings in scrub compared to damage in grassland and tall herb plots. In particular, damage to the apical shoot was strongly reduced. Our findings show that tree establishment occurs in spatial association with non-grassland patches that offer protection against browsing. Fast growing spiny shrubs like Rubus sp. offer protection for palatable saplings, allowing establishment and growing out beyond the browse line. Alternatively, increased establishment occurs in wet tall herb patches, where soil disturbance by moderate trampling favours germination and, subsequently, saplings are protected at least temporarily against browsing by unpalatable tall herbs.

Influence of species richness and environmental context on early survival of replanted mangroves at Gazi bay, Kenya

Mangrove reforestation projects often suffer from low sapling survival, especially after transplanting saplings from nurseries to reforestation areas. This may be due to the sediment conditions at the target site, the planting strategy or failure to re-establish ecosystem processes. We examined experimentally the influence of environmental context, species richness and identity, sapling height and position on sapling survival and environmental variables linked to ecosystem functioning at deforested sites in Gazi Bay, Kenya. At site 1, a high shore location, 32 plots (36 m2) were planted with 8 treatments: all possible combinations of Avicennia marina, Bruguiera gymnorrhiza, and Ceriops tagal and an unplanted control (total: 3390 saplings; 4 plots/treatment). At site 2, a low shore location, the influence of sapling height, sapling position and sediment depth were tested by planting with 697 Sonneratia alba in a single monospecific plot (341 m2). After ∼2 years, there were significant differences in survival among the three species at site 1 with Bruguiera gymnorrhiza recording the lowest survival rate (29%). Survival was correlated with salinity (a strong effect) and height above chart datum (a weaker effect) at site 1. Sapling position did not significantly affect survival at either site. There was thus no evidence that early survival of transplanted saplings is influenced by the species mix in which they are grown, or by their position in the plot. Rather the tolerance of individual species to salinity was the key to their survival at the high tidal site. Species mix also had no significant effects on environmental variables in the plots. The former presence of a species at a site does not guarantee it will succeed there again if environmental degradation has exceeded species’ tolerance.

Ecological characteristics of Abies georgei population at timberline on the north-facing slope of Baima Snow Mountain, Southwest China

Abies georgei is one of the endemic trees at timberline on Qinghai-Tibetan Plateau, but little research has been done about its timberline population. One plot was set up at timberline above 4400 m on the north-facing slope of Baima Snow Mountain in Southwest China, covering an area of 0.8 hm 2. Height, DBH (diameter at breast high) or root-collar diameter of seedlings and saplings, and position were recorded for each individual. The population showed a growing trend and the number of individuals decreased with increase of DBH. The survival curve can be described by Deevy-III. The population had 2 distinct peaks of mortality: age I (seedlings, DBH = 0–5 cm) and age V-VI (DBH = 20–30 cm). The highest mortality of seedlings was due to severe climate at timberline. As the saplings grew up, the interspecific and intraspecific competition resulted in another mortality peak. Through SPPA (spatial point pattern analysis), individuals of all age-classes showed uniform, random or clumped distribution with the change of scales; however, they had mainly clumped distribution. Moreover, the relationships between individuals in different age-classes were all significantly correlated with each other. Seedlings showed the highest clumping intensity and scale.

Height development of shade-tolerant conifer saplings in multiaged Acadian forest standsPublication 2954 of the Maine Agricultural and Forest Experiment Station, University of Maine, Orono, Maine.

Understory growth dynamics of northern conifer species were studied in four stands managed under multiaged silvicultural systems in eastern Maine. Height growth of Picea rubens Sarg., Abies balsamea (L.) Mill., and Tsuga canadensis (L.) Carr. saplings between 0.5 and 6.0 m in height was related to the proportion open sky (POS), using sapling height as a covariate. Height growth of T. canadensis equaled A. balsamea and exceeded P. rubens under very low light levels (POS &lt; 0.1) but is much less responsive to both increasing POS and taller heights, reaching 50% of its maximum height growth at a POS of only 0.09. Abies balsamea outgrew P. rubens under similar dark conditions; at higher light levels (POS &gt; 0.10), both species grew similarly. Evidently, no feasible overstory manipulation of light alone can promote more rapid height development of P. rubens saplings over A. balsamea. A nonlinear light-prediction model using stand basal area is linked with height-growth prediction equations to quantify sapling development from 0.5 to 6 m. Depending on overstory density, P. rubens requires a height advantage of 0.14–0.33 m over a 0.5 m tall A. balsamea to reach a height of 6 m over the same time period.

Vegetation Control Treatments to Favor Naturally RegeneratedBetula alleghaniensisSaplings Following Seed‐Tree Cut: Sapling Monitoring Two Years after Treatment

AbstractControl of competing vegetation is recommended to ensure successful Yellow birch (Betula alleghaniensisBritton) regeneration within juvenile stands that do not sustain high enough sapling densities of this species. Four contrasting vegetation control treatments were tested to determine their effect on the growth and vigor of eight‐year‐oldB. alleghaniensissaplings regenerating after final cutting of a shelterwood seed cut. Vegetation control treatments were TC (total circular removal), PC (circular removal of codominant competing vegetation), TS (total semicircular removal on 180° section), and NC (no vegetation control). Two years after treatment application, diameter growth significantly improved in response to vegetation control treatments, whereas sapling height growth did not. This pattern of biomass allocation was directly related to sapling etiolation, which increased with decreasing severity of vegetation removal. As a result, application of vegetation control, especially TC and PC treatments, was valuable in reducing signs of stress in saplings. However, increasing the severity of vegetation removal also made saplings more conspicuous to herbivores, which increased browsing, especially in the TC and PC treatments. Browsing was sufficient in some plots of the TC and PC treatments to overcome the vigor and diameter growth enhancements observed when browsing was negligible. In contrast to the TC and PC treatments, the TS treatment kept browsing very low while largely removing competition. The results suggest thatB. alleghaniensissaplings established after final cutting of a shelterwood seed cut do take advantage of vegetation control treatments, but the decision to apply these treatments must include consideration of local herbivore population densities.

Effects of surface and light conditions of fallen logs on the emergence and survival of coniferous seedlings and saplings

We surveyed the germination number (Ncs) of 2-year and a 1-year survival of Abies sachalinensis and Picea jezoensis seedlings and saplings on 29 fallen logs from 2004 to 2005 in a natural coniferous forest in Hokkaido, northern Japan, in relation to the surface and light conditions of fallen logs. Moss height (Hmoss), log hardness (Hardness), and the area of fallen log (Area) were measured as the surface conditions by each 1-m block from bottom to top of all fallen logs. The relative photosynthetic photon flux density (rPPFD) 10 cm above the tallest seedling in each block was measured as the light condition. In addition, the height of the tallest seedling or sapling in each block (Hmax), the difference between a height of each seedling and sapling and the Hmax (Shading), and a height of seedlings and saplings in 2004 (Hini) were considered. Ncs of A. sachalinensis was affected by Hardness and Area, whereas Ncs of P. jezoensis was affected by Hmoss, Hardness, Area, Hmax, and rPPFD. The survival of seedlings (height < 5 cm) and saplings (5 cm ≤ height < 50 cm) were affected by Hini, rPPFD, and shading for both species. However, the survival of P. jezoensis saplings was more sensitive to decrease in rPPFD and increase of shading than that of A. sachalinensis. Therefore, seedling emergence was influenced by surface conditions, whereas survival was affected by light conditions. Furthermore, P. jezoensis emergence and survival were more sensitive to surface and light conditions than that of A. sachalinensis.

Regeneration after 8 years in artificial canopy gaps in Mountain Ash ( Eucalyptus regnans F. Muell.) forest in south-eastern Australia

We report on a study of regeneration of Mountain Ash ( Eucalyptus regnans) forest in S.E. Australia in artificially created canopy gaps (0.01–2 ha) and clearfelled coupes (4–27 ha) with different seedbed treatments. Treatments were applied in 1988, 1989, and 1990. Our results are based on measurements 8 years after harvesting. Gap size had a significant influence on sapling height and diameter growth. The effect was substantial for the canopy openings larger than 2 ha, but inconsistent across the smaller gap sizes. Mean height of the largest diameter saplings was significantly greater in the clearfells (13.2 m) than in the 2 ha gaps (10.7 m), while mean heights in the smaller gaps ranged from 6 to 8.8 m. Mean sapling diameters (at 1.3 m) in clearfells and 2 ha gaps were 9.6 and 7.9 cm respectively compared with 3.8–5.8 cm for the smaller gaps. There was lower stocking in all treatments for the third regeneration year (1990), when regeneration operations were delayed by high summer and autumn rainfall. Stocking ranged from 12 to 33% for the smallest gaps, increasing with increasing gap size to 34–64% for 2 ha gaps and 48–76% for clearfells. Results were consistent with a previous study 3 years after treatment, indicating that stocking at 8 years is still dominated by initial stand establishment rather than by stand development processes. There was no significant influence of seedbed preparation on any of the variables tested at year 8; this was in contrast with earlier findings at year 3 when seedling height was significantly higher on burnt sites compared with mechanically disturbed sites. The growth of non-eucalypt competitors was also influenced by gap size and year of regeneration treatment. The main competitor species differed between larger and smaller clearings and between sites. Results indicate that using a silvicultural system based on smaller gaps (<2 ha) in this forest type is likely to result in reduced timber production potential compared with clearfelling.

Desenvolvimento inicial de plântulas de Theobroma grandiflorum (Willd. ex Spreng.) Schum. sob influência de sombreamento

O presente estudo foi conduzido com o objetivo de avaliar o comportamento inicial de plântulas de Theobroma grandiflorum (Willd. ex Spreng.) Schum. (cupuaçu), em função de diferentes níveis de sombreamento. Ao final de 50 dias, após a emergência, as plântulas de cupuaçu foram submetidas a três níveis de sombreamento, sendo: 0% de sombreamento, 50% de sombreamento e Sombra Natural. O crescimento das mudas foi conduzido em delineamento de blocos casualizados, com 15 repetições, sendo cada planta considerada como uma repetição. Foram avaliados a altura, o diâmetro e o número de folhas aos 60, 82, 103, 124, 145 dias após a emergência das plântulas. A Massa Seca de Folhas (MSF), Massa Seca do Caule (MSC), Massa Seca da Raiz (MSR) e Massa Seca Total (MST), Relação parte aérea/raiz (PA/R) e relação Altura da planta/Diâmetro do colo (A/D), foram avaliadas no final do experimento. O crescimento inicial de Theobroma grandiflorum foi corroborado com os padrões da espécie, que ocorre no interior das matas primárias, tendo melhor desenvolvimento dos parâmetros avaliados em condições de 50% de sombreamento. A condição de 50% de sombreamento pode ser recomendada para a formação de mudas de Theobroma grandiflorum, devido o seu melhor desempenho em altura, diâmetro, número de folhas e alocação de massa nas partes da planta.

Effect of the latitude of seed origin on moose ( Alces alces) browsing on silver birch ( Betula pendula)

Moose is a major cause of damage in young plantations of silver birch ( Betula pendula Roth) in Finland, as they break stems and browse twigs and leaves. Damage by moose was measured in a provenance trial of silver birch situated at Loppi, southern Finland. The trial includes stand seed origins from Finland, Sweden, Estonia, Scotland and Russia, ranging in latitudes from 53° to 67°. The trial was established on a typical, southern Finnish moist upland clear-cut area that had been protected against moose by fencing. After the break-down of the fence, at the age of 5–11 years, the trial was frequently visited by moose. The effects of browsing were measured in early spring 2001, when the trees were 11 years old. The average proportion of trees browsed by moose varied between 6 and 86% among the seed origins. Browsing by moose decreased with increasing latitude of seed origin and sapling height. Seed origins transferred from more southern latitudes (southern Estonia, southern Sweden, Scotland, Russia) had a higher proportion of browsed trees than the more northern native ones. A similar pattern was also seen in the proportion of trees with stem breakage and the proportion of repeatedly browsed trees. Latitude of seed origin and sapling height covariate had a significant effect on moose browsing. The moose browsed more branches per browsed tree of southern origins, whereas sapling height had no significant effect. It is suggested that the variation in moose browsing among the seed origins was related to differences in their annual physiological rhythm, i.e. timing of growth cessation, leaf discoloration and abscission, and related changes in digestibility and palatability. It was concluded that importing birch regeneration material to Finland from more southern latitudes should be avoided because of the risk of browsing damage.

Woody plant invasion at a semi‐arid/arid transition zone: importance of ecosystem type to colonization and patch expansion

Abstract:Question: How do patterns in colonization and patch expansion of an invasive woody plant (Larrea tridentata, Zygo‐phyllaceae) differ between two grassland ecosystems at a biome transition zone?Location: Semi‐arid/arid transition zone in central New Mexico.Methods: Frequency of occurrence, height, and surface area of saplings (n= 134) and patches of adult plants (n= 247) of the invasive shrub, L. tridentata, were measured within a mosaic of ecosystems dominated either by the Chihuahuan Desert species, Bouteloua eriopoda (Poaceae), or the shortgrass steppe species, B. gracilis, located within 1 km of the L. tridentata‐dominated ecosystem. Distances between L. tridentata patches and patch area were used to estimate connectivity as a measure of propagule pressure. Sapling age (estimated from height using previously established relationships) and distance to the L. tridentata‐dominated ecosystem was used to evaluate patterns in dispersal. Cover by species or functional group inside each L. tridentata patch was compared with surrounding vegetation to estimate changes in species composition with patch expansion.Results: L. tridentata saplings (&lt; 1%) and adult patches (15%) occurred less frequently in B. gracilis‐dominated ecosystems than expected based on areal extent of this ecosystem type. Propagule pressure did not differ with distance from the core ecosystem dominated by L. tridentata. Evidence for both local and long‐distance dispersal events was found. Similar relationships between number of plants and patch area in both grassland types indicate similar patterns in patch expansion. Cover of perennial forbs was higher and cover of dominant grasses was lower in L. tridentata patches compared with the surrounding vegetation for both ecosystem types.Conclusions Spatial variation in L. tridentata saplings and patches at this biome transition zone is related to the different susceptibilities to invasion by two grassland ecosystems. The persistence of grasslands at this site despite region‐wide expansion by L. tridentata may be related to the spatial distribution of B. gracilis‐dominated ecosystems that resist or deter invasion by this woody plant.