Leaf weight per area and leaf size of 85 Estonian woody species in relation to shade tolerance and light availability

Leaf weight per area (LWA) and leaf size were examined in 85 species of woody plants representing 83% of Estonian native flora.

Average values of 68.6 g m⁻² for LWA and 6.62 cm² for leaf size were estimated for the medium light availability. Mean LWA values can be used to correct for the bias in estimating foliage functional properties in forest stand models and for converting leaf biomass into foliage area. LWA increased with relative light availability (1 minus stand canopy cover) and species light demand, indicating that LWA was higher at the same light availability for more intolerant species. Leaf size is a canopy parameter that should be considered when canopy radiative balance and distribution of solar radiation is of interest. Mean leaf size was not so closely related to light availability as LWA, decreasing with species light demand and increasing with total plant height. Variation in leaf size is discussed in terms of species shade tolerance and height growth.     

Establishing forest tree species on peatland in a reflooded area of the Huleh Valley, Israel

The study evaluates the establishment performance of four treespecies (Ficus carica, Fraxinus syriaca, Salix acmophylla, Platanusorientalis) 3 years after planting in the peatland in the HulehValley. To develop good tree establishment and avoid uprooting,two types of soils were tested as alternatives for the rhizosphere.For each tree 6 m³ of soil (2 x 2 x 1.5 m) were replaced withriver bed alluvium or terra-rossa, in which the tree was planted.Control trees were planted directly in the peat. Changing therhizosphere soil type to river bed alluvium significantly improvedthe establishment and performance of Salix acmophylla and Fraxinussyriaca (survival, height, diameter and canopy shade area).Ficus carica was not affected by changing the soil in the rhizosphere,while Platanus orientalis was affected mainly in canopy shadearea. Terra-rossa improved establishment only of Salix acmophylla;it did not affect the other species.     

Regeneration growth in different light environments of mixed species, multiaged, mountainous forests of Romania

Growth of regenerating trees in different light environments was studied for the mountainous, mixed-species forests in the Carpathian Mountains of Romania. The primary species in these mixtures were silver fir (Abies alba Mill.), European beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) Karst). Seedlings/saplings of these species were selected and measured in different stands from two different geographical locations. Regenerating trees were measured for height and diameter growth during the summer of 2002. For each seedling/sapling, percentage of above canopy light (PACL) and stand basal area (BA) were used to assess available and occupied growing space respectively. Regeneration growth was compared against these two variables and regression relationships were developed. Using these models, we predicted the dynamics of regeneration as both growth and species composition. Our results showed that in low-light environments (PACL<20–35%; BA>30 m²/ha), shade tolerant fir and beech clearly outcompeted the spruce. Therefore, in dense stands, spruce could be eliminated by the shade tolerant species. For intermediate levels of cover (PACL=35–70%; BA=15–35 m²/ha) the spruce grew at comparable rates as the beech and fir. All three species showed similar growth rates in open conditions (PACL>80–90%; BA<15–20 m²/ha) with the spruce having a tendency to outgrow the others. However, in terms of establishment, such conditions favor spruce and inhibit fir and beech.     

Experimental evidence supporting the concept of light-mediated modulation of stem hydraulic conductance

It is a well-described phenomenon that plant leaves respond to changes in light intensity and duration by adjusting leaf hydraulic efficiency, and there is current consensus that up- or down-regulation of water channels (aquaporins) in the plasma membrane of the bundle sheath and mesophyll cells play a central role in the underlying mechanisms. Recently, experimental evidence has been provided also for light-mediated changes of stem hydraulic conductance (K(stem)) in field-grown laurel plants. This effect was attributed to differences in potassium ion concentration of xylem sap as a function of light conditions. In the present article, we report evidence obtained in silver birch (Betula pendula Roth), supporting the concept of light-mediated modulation of K(stem). Both canopy position (long-term effect) and current photosynthetic photon flux density (PPFD; short-term effect) had a significant impact (P < 0.001) on K(stem) measured in shoots taken from the lower (shade shoots) and upper (sun shoots) third of the crowns of ～25-year-old trees growing in a natural forest stand. The shade shoots responded more sensitively to light manipulation: K(stem) increased by 51% in shade shoots and 26% in sun shoots when PPFD increased from 70 to 330 μmol m?2 s?1. In 4-year-old trees growing in a dense experimental plantation, K(stem), specific conductivity of branch-wood (k(bw)) and potassium ion concentration ([K(+)]) in xylem sap varied in accordance with canopy position (P < 0.001). Both K(stem) and k(bw) increased considerably with light availability, increasing within the tree crowns from bottom to top; there was a strong relationship between mean values of K(stem) and [K(+)] in hydraulically sampled branches.     

Effects of site preparation on emergence and early establishment of Larix olgensis in montane regions of northeastern China

Larix olgensis is one of the important commercial timber tree species in northeastern China, but it does not naturally regenerate in L. olgensis forests even after cutting. To identify the causes of the regeneration failure, the authors tested the effects of site preparation in a thinned stand and in a clearcut on the emergence and early establishment of L. olgensis seedlings. The results indicated that there was no correlation between cumulative emergence percentage (CEP) of L. olgensis seedlings and canopy openness, but the CEP was significantly affected by site preparation (P < 0.001). The average seedling survival rates after treatments consisting of removing both litter cover and understory vegetation cover were significantly higher in the clearcut than in the thinned stand (P < 0.001). Without site preparation, all seedlings in both the thinned stand and the clearcut disappeared within the first growing season, meaning that ground cover (understory vegetation cover and litter cover) was not beneficial to seedling survival. The average growth of seedlings exhibited significant differences between the thinned stand and the clearcut, and among the site preparations (P < 0.001). Intensely thinned stands without ground cover improved seedling growth. These results imply that light and ground cover might be the main factors limiting the early establishment of L. olgensis seedlings in managed plantation forests     

The Development of a New Dendrometer and Its Application to Deciduous Broadleaf Tree Species in Hokkaido,Northern Japan

Abstract

A new sensitive dendrometer system was invented by using a potentiometer and datalogger and applied to the stem of some canopy trees of a stand of deciduous broad-leaf tree species native to Hokkaido, northern Japan. Different types of diameter/age growth curves were observed at the fine level for different species: (1) an ordinary type with smooth and gradual growth; and (2) a slow growth curve mixed with intermittent stair-like periods of rapid growth. Possible reasons for the presence of stair-like rapid growth were examined, including the significance of water availability condition.     

Growth and mortality in underplanted tree seedlings in response to variations in canopy closure of Norway spruce stands

Six broadleaved tree species and Picea abies (L.) Karst. wereplanted under spruce plantations of varying densities, in Sweden.Treatments included control (994 stems ha^–1), dense (538stems ha^–1), sparse (294 stems ha^–1) and gap (0stems ha^–1) overstory treatments. There was an increasein height and diameter growth from control to sparse overstorytreatment of all underplanted tree species except for ash (Fraxinusexcelsior L.) and Norway maple (Acer platanoides L.). Site conditionsmay have hampered the growth of these species, as well as wildcherry (Prunus avium L.). Both oak (Quercus robur L.) and sprucehad greater growth in the gap treatment, relative to the othertreatments. Insecticide application did not influence seedlinggrowth or survival. The performance of beech (Fagus sylvaticaL.), lime (Tilia cordata Mill.), spruce and oak was consistentwith shade tolerance ranking. Beech and lime had a very highsurvival rate, even under the densest canopy. The growth andmortality of ash, maple and wild cherry differed significantlyfrom what was expected. This experiment demonstrated significantvariation in interspecific growth and mortality between sevenplanted tree species in relation to canopy density. Correctsite and species selection is crucial when underplanting inshelterwood systems.     

Effects of light availability and soil flooding on growth and photosynthetic characteristics of Genipa americana L. seedlings

Genipa americana L. (Rubiaceae) is a late successional neotropical fruit tree used in riparian forest restoration programs. We analyze the effects of light availability and soil flooding on the growth and photosynthetic characteristics of G. americana seedlings under nursery and natural light conditions. Two light levels (full sunlight and shade), and two levels of soil water (flooded and control) were used in the experiment. Flooding induced significant changes in the total seedling biomass (P < 0.01). The differences among water treatments were 70 and 10% at full sunlight and shade, respectively. These changes were explained by alterations in the maximum quantum efficiency of the photosystem 2 (Fv/Fm), light-saturated net photosynthetic rates (A _sat) and intrinsic water use efficiency (WUE). G. americana has high physiological plasticity in relation to the light availability and flooding, although significant interactive effects between high light exposure and soil flooding were observed in several photosynthetic and growth variables. The results highlight the importance of the synergistic effects between physical environmental variables on the establishment and growth of G. americana seedlings. In the practical point of view we can indicate that, in degraded riparian forests subjected to soil flooding, seedlings of this species should be planted under partially shaded environments.     

Trade-offs among establishment success,stem morphology and productivity of underplanted Toona ciliata: Effects of nurse-species and thinning density

Toona ciliata (Australian red cedar), a valuable hardwood species, requires a nurse-tree overstorey to prevent damage from frost and drought in some regions of north-eastern Argentina. Different nurse-species offer different degrees of protection, resource competition, and thinning revenues. In addition, choice of nurse-species will influence trade-offs between T. ciliata establishment success, stem quality and productivity as well as revenue from intermediate and final harvests. We tested the effects of overstorey species and planting density on underplanted T. ciliata survival, stem morphology and growth. Initial stand densities of nurse-species Pinus taeda (625 stems/ha), P. elliottii × P. caribaea (625 stems/ha), and Grevillea robusta (833 stems/ha) were thinned by 0%, 25%, 50%, and 75% in three experiments, each using a randomized block design. Initial mortality, light availability and growth of T. ciliata, as well as growth of its nurse-trees, were measured before and two years after thinning. In the third year, we characterized T. ciliata stem morphology (straightness and height-to-diameter-ratio) and destructively harvested a subsample of T. ciliata in order to investigate T. ciliata biomass production and allocation patterns in response to overstorey species, thinning density and light availability. T. ciliata mortality was lower when planted under G. robusta than the pines, and increased in plots with greater exposure to solar radiation. T. ciliata productivity was also greater under G. robusta than under the pines, and was generally greatest where any of the nurse-species were thinned by 75%. Stem form was best when growing under P. taeda and in stands thinned by 50%, regardless of nurse-species. With the exception of early mortality, light levels appeared to have limited effects on T. ciliata growth dynamics. Neither growth rate nor stem morphology was strongly correlated with light availability. Total overstorey basal-area was highest in P. taeda stands and individual overstorey tree growth generally increased with decreasing stand densities, except for slower height growth of G. robusta in more open stands. Thinning operations resulted in sawn-wood revenue for the pine species only. Because stand productivity and stem quality were optimized under different nurse-species and thinning treatments, we conclude that the choice of nurse-species and thinning intensity will depend on management objectives and will change with market preferences and conditions.     

Cacao trees under different shade tree shelter: effects on water use

We asked how shade tree admixture affects cacao water use in agroforests. In Central Sulawesi, Indonesia, cacao and shade tree sap flux was monitored in a monoculture, in a stand with admixed Gliricidia trees and in a mixture with a multi-species tree assemblage, with both mixtures having similar canopy openness. A Jarvis type sap flux model suggested a distinct difference in sap flux response to changes in vapor pressure deficit and radiation among cacao trees in the individual cultivation systems. We argue that differences originate from stomatal control of transpiration in the monoculture and altered radiation conditions and a different degree of uncoupling of the VPD from the bulk atmosphere inside shaded stands. Probably due to high sap flux variability among trees, these differences however did not result in significantly altered average daily cacao water use rates which were 16 L day^?1 in the multi-species assemblage and 22 L day^?1 in the other plots. In shaded stands, water use of single cacao trees increased with decreasing canopy gap fraction in the overstory since shading enhanced vegetative growth of cacao fostering transpiration per unit ground area. Estimated transpiration rates of the cacao tree layer were further controlled by stem density and amounted to 1.2 mm day^?1 in the monoculture, 2.2 mm day^?1 for cacao in the cacao/Gliricidia stand, and 1.1 mm day^?1 in the cacao/multi-species stand. The additional transpiration by the shade trees is estimated at 0.5 mm day^?1 for the Gliricidia and 1 mm day^?1 for the mixed-species cultivation system.     

Spatiotemporally interactive growth dynamics in selected South African forests: Edaphoclimatic environment, crowding and climate effects

Stand-level tree diameter growth patterns were explored for evergreen moist forests in the southern Cape, South Africa. Results of standard multiple regression analyses, involving 934 permanent sample plots with data spanning a 10-year interval, revealed that stand-level increment of canopy species in the canopy layer (>30 cm dbh) was significantly determined by inherent species-specific growth capacities (species composition of the stand), water availability, forest matrix crowding and tree condition impairment (age-related manifestations of reduced vitality indicated by signs of crown die-back, damage and stem rot). In contrast, stand-level increment of trees of canopy species in the subcanopy layer (10-20 cm dbh) was prominently shaped by light availability, as mainly determined by the degree of canopy-level disturbance (mortality rate of trees >30 cm dbh), crowding (canopy-level overhead and forest matrix crowding) and proximity to conspecific adults (within 6-8 m). In addition to species-inherent and resource factors, considerable variation in stand-level growth resulted from site-climate interactions. For 507 of the permanent sample plots, increment data was available for two consecutive 10-year intervals; permitting the analysis of spatiotemporal interactions of growth patterns (repeated measures ANOVA). In the Knysna forests higher canopy-level increment rates were associated with the moister southerly facing slope sites in comparison with the drier northerly facing and ridge sites during the first increment period. During the second increment period, increment rates on the drier, but better illuminated sites had increased disproportionately. In contrast, in the Tsitsikamma forests, higher increment rates during the second increment period were encountered on moister flat bottomland sites (with extended periods of subsoil wetness) than on the comparatively drier southerly facing slope sites (increment period × site-based water availability × forests interaction). In both forests relatively higher growth performance of subcanopy-level trees during the second increment period was associated with stands experiencing conditions of enhanced light availability. Atmospheric temperatures were higher during the second increment period (mean periodic T_max: + 0.64 °C). The detected spatiotemporal interactions were interpreted as site × climate interactions where site-related conditions of favourable light or water availability resulted in enhanced temperature-linked growth responses during the second increment period. A metabolic performance trade-off model provided a framework for the interpretation of these complex site-climate interactions by placing the patterns of forest growth into an ecophysiological explanatory context.     

Physiological performance of three pine species provides evidence for gap partitioning

Gradients of light and moisture availability peak at different positions within canopy gaps in northern latitudes providing the opportunity for niche partitioning in and around gaps based on differences in individual species’ life history attributes. This gap partitioning offers potential for increasing diversity in forests impacted by gap-creating disturbances. We examined resource availability and the physiological performance of three Pinus species with varying tolerances for shade and moisture stress across large (0.3 ha) canopy gaps to investigate relationships between gap position and species performance. Light availability was lowest in southern gap edges, while water availability was lowest in northern edges, and higher at gap interior positions than edges. Pinus banksiana seedlings had higher light-saturated CO₂ assimilation rates than P. resinosa or P. strobus seedlings at interior gap positions, and outperformed P. strobus at northern gap edges, but there were no differences between species at southern edges. Both transpiration and stomatal conductance were greatest for P. banksiana in gap centers, but showed few differences between species at edges. Foliar nitrogen concentrations were highest for P. banksiana, suggesting the dominance of this species in central gap locations may be due to a combination of high photosynthetic capacity and tight stomatal control to regulate moisture stress at drier gap positions. Our results suggest P. banksiana seedlings may be competitively superior in gap positions with high light and moisture availability, but P. resinosa and P. strobus become competitive under the drier conditions and moderate shade near gap edges. These findings support the concept of gap partitioning, and suggest silvicultural systems that incorporate patch cuttings could be used to promote diverse regeneration in northern pine forests.     

Modelling growth behaviour in monoculture in subtropical eastern Australia of two eucalypt species that differ in shade tolerance

Growth behaviour of the relatively shade-intolerant species Eucalyptus dunnii and the rather more shade-tolerant Corymbia citriodora was considered during several growth periods over 8–14 years of age in experimental plantation monoculture in subtropical New South Wales. Larger trees dominated growth in any stand; this was consistent with the principle that inter-tree competition in such forests is for light and is asymmetric in that larger trees shade smaller trees but the reverse does not occur. Once competition was established, competition-induced mortality of C. citriodora was less than that of E. dunnii. A model relating tree diameter growth rate to tree diameter, competitive position in the stand and stand basal area was developed. The model showed that smaller, hence partially shaded, trees in stands of C. citriodora were better able to maintain their growth rates than equivalent trees in stands of E. dunnii. It is hypothesised that this reflects the greater shade tolerance of C. citriodora. This pattern of growth led to a more even distribution of tree size classes across the stand in the more shade-tolerant species.     

Effects of shade on growth, biomass allocation and leaf morphology in European yew (Taxus baccata L.)

The impact of shade on the growth of European yew (Taxus baccata L.) saplings was investigated over a three-year period using artificial shading to simulate four different light regimes (3, 7, 27 and 100 % relative photosynthetic photon flux density, RPPFD). There was no mortality attributable to shading even under the 3 % RPPFD treatment. Increasing shade was positively associated with specific leaf area, leaf length, leaf width and total chlorophyll content, but negatively associated with plant height, stem diameter, total dry weight and root to leaf and shoot ratio. Discoloration of the foliage occurred in plants grown in 100 % RPPFD conditions (resulting in reduced growth rates) and those transferred to 100 % RPPFD conditions after being shade-acclimated for 2 years. Evidence suggests that T. baccata has the ability to regenerate beneath a lighter canopy but beneath denser canopies gap dynamics will play an important role in facilitating successful regeneration and this needs to be reflected in management of natural populations of this declining species.     

Conspecific negative density dependence in a long-lived conifer,yew <Emphasis Type="Italic">Taxus baccata</Emphasis> L.

Conspecific negative density dependence in tree species can have major consequences for structuring of communities, yet in temperate forests this phenomenon remains largely unexplored. We investigated density-dependent recruitment in the long-lived conifer yew (Taxus baccata L.), for which low levels of regeneration have been linked with reduced light availability beneath conspecific canopies and speculative autotoxic effects. We combined in situ assessment of yew regeneration in a temperate forest in southwest Ireland with ex situ pot experiments to assess whether light and/or beneath conspecific canopy conditions inhibit the germination and early growth of yew. In field experiments, recruitment was related to distance from adult conspecifics, with higher levels of regeneration found in areas not beneath yew canopies. However, reduced light availability beneath the dense yew canopy was not responsible for this pattern, with abundant seedlings found in areas of equivalent or even lower light availability. Pot experiments showed that seedling survival was highest in deep shade treatments. Experiments also demonstrated that the addition of yew needles negatively affected seedling growth, but not seed germination. Together, our results suggest that under natural forest conditions, the absence of regeneration beneath mature yew canopies, often attributed to low light availability, may at least be partly related to substances in yew canopy or leaf leachates.     

Growth responses of Lobaria retigera to forest edge and canopy structure in the inland temperate rainforest, British Columbia

The foliose cyanolichen Lobaria retigera is a sensitive old-growth forest indicator in British Columbia's inland rainforest. These forests are increasingly being fragmented by harvesting, raising concerns about edge effects and the maintenance of canopy lichen communities in remaining forest patches. We have examined the response of L. retigera to edge effects, using transplant experiments to compare growth responses between abrupt (hard) edges created by clearcut harvesting and more buffered (soft) edges created by variable-retention harvesting. L. retigera thalli placed along hard edges showed high mortality rates, with most thalli (from 64 to 100%) losing biomass at the end of each of the 3-year's measurement periods. Biomass loss along soft edges was much lower, occurring in fewer than 7% of thalli in the best year, up to 42% in the worst year. When growth rates were expressed against light availability at each branch location, thalli along variable-retention transects showed a positive response to increasing light availability. In contrast, thalli along the hard edge transects showed an abrupt decline in growth rates at equivalent levels of high light availability (canopy openness values >30%), where presumably the benefits of greater light availability were offset by heat or dessication stress. These results show a much greater sensitivity to edge effects in L. retigera, compared to earlier measurements at this site with the more common lichen Lobaria pulmonaria, a species that has a dominant green-algal photobiont partner. We suggest that increased use of variable-retention harvesting systems in which a substantial number of residual trees are left along cutblock edges has the potential to reduce the impacts of forest harvesting on canopy lichen biodiversity.     

Evaluating changes in switchgrass physiology,biomass, and light-use efficiency under artificial shade to estimate yields if intercropped with Pinus taeda L.

There is growing interest in using switchgrass (Panicum virgatum L.) as a biofuel intercrop in forestry systems. However, there are limited data on the longevity of intercropped bioenergy crops, particularly with respect to light availability as the overstory tree canopy matures. Therefore, we conducted a greenhouse study to determine the effects of shading on switchgrass growth. Four treatments, each with different photosynthetically active radiation (PAR) levels, were investigated inside the greenhouse: control (no shade cloth, 49 % of full sunlight), low (under 36 % shade cloth), medium (under 52 % shade cloth), and heavy shade (under 78 % shade cloth). We determined the effect of shading from March to October 2011 on individually potted, multi-tillered switchgrass transplants cut to a stubble height of 10 cm. In the greenhouse, there was a reduction in tiller number, tiller height, gas exchange rates (photosynthesis and stomatal conductance), leaf area, above- and belowground biomass and light-use efficiency with increasing shade. Total (above- and belowground) biomass in the control measured 374 ± 22 compared to 9 ± 2 g pot^?1 under heavy shade (11 % of full sunlight). Corresponding light-use efficiencies were 3.7 ± 0.2 and 1.4 ± 0.2 g MJ^?1, respectively. We also compared PAR levels and associated aboveground switchgrass biomass from inside the greenhouse to PAR levels in the inter-row regions of a range of loblolly pine (Pinus taeda L.) stands from across the southeastern United States (U.S.) to estimate when light may limit the growth of intercropped species under field conditions. Results from the light environment of loblolly pine plantations in the field suggest that switchgrass biomass will be significantly reduced at a loblolly pine leaf area index between 1.95 and 2.25, which occurs on average between ages 6 and 8 years across the U.S. Southeast in intensively managed pine plantations. These leaf area indices correspond to a 60–65 % reduction in PAR from open sky.     

The influence of canopy patch mosaics on understory plant community composition in boreal mixedwood forest

We assessed the composition of understory vascular plant communities in relation to the mosaic of canopy patch types, and their associated structure and environment, within unmanaged, mature boreal mixedwood forests in western Canada. Within a 30 km² area, we sampled patches of four different canopy types: conifer-dominated, broadleaf-dominated, mixed conifer-broadleaf, and canopy gaps (total n = 98). There were significant differences in understory composition among the four patch types (based on multi-response permutation procedure (MRPP)) and these were mainly due to differences in relative abundances of understory species. The understory communities of conifer patches were characterized by low abundances of shade intolerant species while shade-tolerant and evergreen species were indicators (based on an indicator species analysis (ISA)). Understory communities under gap and broadleaf patches were characterized by higher abundances of grasses and shade intolerant species. Gap, broadleaf, and mixed patches had higher abundances of certain shrub species than did conifer patches. The patch types also differed in terms of their environmental conditions. Conifer patches had drier, cooler soils and the lowest understory light. Broadleaf patches had the warmest soils while understory light during the leaf-off period was similar to that of canopy gaps. Gap patches had the lowest litter cover and PO₄⁻ availability and the highest light. Seven environmental variables (soil moisture, soil temperature, total light during the leaf-off period, cover of coarse and fine downed woody material, and availability of NH₄⁺ and Ca²⁺) were significantly related to understory species composition (in a constrained ordination by means of a distance-based redundancy analysis (db-RDA); 16.5% of variation in understory community data explained). Even within a single patch type, there was substantial environmental variation that was related to understory species composition. Our study suggests that the mosaic of canopy patches within mixedwood forests supports coexistence of both early and late successional understory plant species in mixedwood stands. Maintaining the mixture of canopy patch types within mixedwood stands will be important for conserving the natural patterns of understory plant composition in boreal mixedwood forests.     

Physiological responses of saplings of rainforest timber species differing in successional group to light regimes and nitrogen

Saplings of 19 valuable rain forest timber species representative of three successional status groups (early secondary, late secondary and climax) were grown in a polyhouse to examine their responses to three light intensity/quality treatments and nitrogen supply. Solar radiation was modified using painted polyethylene sheet to mimic natural light environments across a rain forest vertical column as follows: 1. Transparent plastic, 80% of full sunlight, R:FR = 0.95, 2. Blue shade, 14% of full sunlight, R:FR = 0.69; 3. Green shade, 7% of full sunlight, R:FR = 0.50. Transparent plastic conditions promoted an increase in stem height and diameter (i.e., growth), leaf thickness and gas exchange per unit leaf area. Additional nitrogen availability enhanced growth and specific leaf area (i.e., leaves were thinner), particularly in the full sun environment and on early secondary and late secondary successional species, but did not influence photosynthetic rate. Successional status of the species did not affect photosynthetic rate although early secondary successional species grew faster and had fewer branches than species of the other successional groups. We recommend that for a successful mixed stand the high-light requiring species should be planted first, with increased nitrogen supply, and the shade tolerant species should be introduced later with no extra nitrogen supply required.     

Pasture production under densely planted young willow and poplar in a silvopastoral system

New Zealand is subject to summer and autumn droughts that limit pasture growth. The planting of willow and poplar trees is one option used to provide green fodder during drought. However, there is a wide concern that such an option can reduce the overall understorey pasture growth. This study evaluated the comparative establishment and growth of densely planted young willow and poplar and their effects on understorey pasture growth. Two experiments were established for 2 years in Palmerston North and Masterton, North Island, New Zealand. In the first experiment, densely planted willow and poplar significantly reduced understorey pasture growth by 24 and 9%, respectively, mainly due to shade, but coupled with soil moisture deficit in summer. In the second experiment, pasture growth in a willow browse block was 52% of that in open pasture as a result of shade and differences in pasture species composition and management. Willow and poplar survival rates were similar (P > 0.05) after 2 years of establishment (100 vs. 90.5%, respectively). However, willow grew faster than poplar in height (1.90 vs. 1.35 m), stem diameter (43.5 vs. 32.6 mm), canopy diameter (69 vs. 34 cm) and number of shoots (8.7 vs. 2.3) at the age of 2 years.