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In south-central Chile, the dynamics of southern beech (Nothofagaceae) stands vary predictably along climatic gradients. Beeches form persistent stands at high elevations, but their establishment on lowland sites depends mainly on catastrophic disturbances. In New Zealand, nearly all studies of beech forest dynamics to date have reported all-sized, persistent populations. However, previous work has focused largely on the South Island or on North Island mountains, where beeches are widespread and often dominant. Little is known about beech dynamics in the warm North Island lowlands, where beeches are less common. We aimed to clarify the circumstances that enable beeches to establish on lowland sites in the North Island. We measured population structures of beeches and associated species on 11 plots distributed across a range of climate, lithology and topography. On sites where the most shade-tolerant broadleaved trees were absent or uncommon, all-sized populations showed that beech regeneration did not depend on major disturbances. These stands were located mostly on steep faces or ridges with soil carbon:nitrogen ratios > 18, usually with ericaceous understoreys. On sites with higher N availability, where shade-tolerant broadleaved trees were abundant, beech populations were generally sparser, with restricted age ranges. One of these ± even-aged beech stands appeared to have established after windthrow, the other four after fires. Recent dieback of Weinmannia racemosa associated with insect attack had resulted in another wave of beech regeneration in one of the post-fire stands. Establishment on landslides appears to only rarely enable beeches to capture new sites in the lowland North Island. We conclude that beeches form stable self-replacing stands on lowland North Island sites with low nitrogen availability, but that exogenous disturbances occasionally enable beeches to establish as pioneers on sites with higher nitrogen availability. The early successionalrole commonly seen in lowland south-central Chile thus appears less widespread in New Zealand. [ABSTRACT FROM AUTHOR]

Background: Several smartphone applications have been developed for the purpose of low-cost and convenient assessments of vegetation canopy structure and understorey illumination. Like standard hemispherical photography, most of these applications require user decisions about image processing, posing challenges for repeatability of measurements. Here I report a test of CanopyCapture, an application that instantaneously estimates percentage canopy gap fraction without any input from the user, and has the added advantage of an intuitive levelling mechanism. Methods: Gap fraction estimates by CanopyCapture were compared with gap fraction values computed by the LAI-2200C Canopy Analyzer, in two contrasting evergreen temperate forests in New Zealand: an even-aged southern beech (Nothofagus) stand and an old-growth podocarp/broadleaf forest. These comparisons were repeated using a wide-angle adapter to enhance the smartphone camera's field of view from 45 to 65°. I also asked if CanopyCapture results depended on sky condition (sunny vs. overcast) and on the type of smartphone used. Results: CanopyCapture output was significantly correlated with gap fraction computed by the LAI-2200C (R² = 0.39), and use of the wide-angle adapter lifted this value to 0.56. However, CanopyCapture output was not significantly correlated with LAI-2200C output in the even-aged Nothofagus stand, where there was less spatial variation in canopy structure. Despite being much less sensitive to variation in gap fraction than the LAI-2200C, CanopyCapture was nevertheless able to detect differences in average gap fraction between the two forests studied. CanopyCapture results beneath intact canopies were not significantly affected by sky condition, but reflection of direct light off tree trunks in sunny weather caused slight overestimation of gap fraction beneath broken canopies and gaps. Uneven or patchy cloud cover can also cause erroneous readings beneath large canopy openings. Three different models of smartphone gave different results. Conclusions: CanopyCapture offers a rapid and repeatable proxy for comparisons of average canopy gap fraction in multiple stands/forests, provided large sample sizes are used. Measurement under even overcast skies is recommended, and studies involving multiple operators will need to standardize smartphones to ensure comparability of results. Although wide-angle adapters can improve performance, CanopyCapture's low sensitivity prevents high-resolution comparisons of the light environments of individual understorey plants within a stand. [ABSTRACT FROM AUTHOR]

Aim: Global studies show strong climatic control of leaf area index (LAI) and related ecosystem properties. However, alternative states stabilized by positive feedbacks have the potential to produce appreciable differences in LAI in a given environment. On certain sites in New Zealand, ectomycorrhizal (EM) southern beech forest (Nothofagaceae) appear to form a stable alternative to more species‐rich conifer‐broadleaved forest dominated by arbuscular mycorrhizal (AM) trees. We asked which climate variables best predict LAI of New Zealand's remaining old‐growth forests, and if stands dominated by Nothofagaceae have lower LAI and better‐lit understories than conifer‐broadleaved forests, when climate and other site factors are held constant. Location: New Zealand. Taxon: Seventy‐two tree species belonging to 37 angiosperm, conifer and pteridophyte families, the most frequent occurrences being Cunoniaceae, Cyatheaceae, Dicksoniaceae, Lauraceae, Nothofagaceae, Podocarpaceae and Violaceae. Methods: We quantified overstorey composition of 45 old‐growth stands, and used the LAI‐2200C Plant Canopy Analyzer to measure LAI and understorey light. We used generalized linear mixed models to determine how these variables were influenced by environment and by dominance of Nothofagaceae. Results: LAI ranged from 3.5 to 6.9, and increased linearly with mean annual temperature (MAT); percentage light transmission to the understorey spanned an order of magnitude and decreased exponentially with increasing MAT. However, at a given MAT, LAI of stands dominated by Nothofagaceae averaged 0.8–0.9 units lower than conifer‐broadleaf stands, resulting in twofold higher understorey light levels in the former. Soil water deficits also significantly depressed LAI, and increased understorey light; atmospheric water deficits had the opposite effect. Main conclusions: Temperature is the best climatic predictor of LAI and understorey light in New Zealand's remaining old‐growth forests. However, the lower LAI and canopy light interception in southern beech stands presumably reflects the light‐demanding nature of Nothofagaceae, and their apparent ability to inhibit invasion by more shade‐tolerant AM trees with heavier crowns. This inhibitory effect may reflect reduced N supply to AM plants because of suppression of N mineralization by EM fungi, as observed in some EM systems elsewhere. [ABSTRACT FROM AUTHOR]

Although 'shade tolerance' has featured prominently in the vocabulary of foresters and ecologists for a century, we have yet to agree on a standardized method for quantifying this elusive property. The 'whole-plant compensation point', interpolated from stem growth measurements across a wide range of light environments, has been proposed as a simple, robust measure of species shade tolerance. Others have argued that shade tolerance is primarily a function of differential ability to survive periods of slow growth ('suppression'), implying that measurements of survival are vital., We measured growth of juveniles (500-1000 mm tall) of five evergreen trees over 12 months in a cool-temperate rain forest in New Zealand, to determine whether whole-plant compensation points predicted species differences in occupancy of understorey light environments, which were quantified using hemispherical photography., The five species encompassed 3·5-fold variation in whole-plant compensation points. Compensation points of most species fell within the first quartile of the distribution of light environments occupied by juveniles; they were also correlated with low-light mortality rates of juveniles, estimated from permanent plot data archived in the National Vegetation Survey Databank. Compensation points were also significantly positively correlated with height growth rates in high light, confirming the presence of the growth vs. shade tolerance trade-off detected in many other forest tree assemblages., Results show that, in temperate evergreen forests, the whole-plant compensation point distinguishes reliably between species of differing shade tolerance. Excepting situations involving parameterization of demographic models, shade tolerance can therefore be assessed without survival measurements. However, estimating whole-plant compensation points may prove more difficult in deciduous forests, where seasonal variation in understorey light transmission poses additional challenges. [ABSTRACT FROM AUTHOR]

Question: Does overyielding of tree species mixtures in vertically stratified forests depend on complementary light use? Location: Andes of south-central Chile. Methods: Basal area data were obtained from 80 circular plots distributed regularly throughout old-growth stands with an emergent Nothofagus dombeyi tier over a canopy composed mainly of Laureliopsis philippiana and Saxegothaea conspicua. Radial growth was measured from cores obtained from trees at the centre of each plot. The effects of competition on growth were evaluated through a competition index (CI) based on distances to and diameters of the two nearest neighbours. Results: Overall, basal area of the canopy species was only weakly affected by the number of N. dombeyi per plot, and with basal area of N. dombeyi. However, the two main canopy species responded differently: whereas basal area of S. conspicua was negatively correlated with that of N. dombeyi, that of L. philippiana showed no response. Radial growth of S. conspicua was negatively correlated with CI calculated from canopy trees and more weakly so from emergent N. dombeyi. In contrast, radial growth of L. philippiana was not affected by competition with either canopy or emergent neighbours. Conclusions: Results indicate that emergent N. dombeyi tend to depress growth and basal area of S. conspicua, but not of the more shade-tolerant L. philippiana. This supports the proposal that enhancement of wood production in stratified mixtures will be greatest when component species have strongly contrasting light use traits. [ABSTRACT FROM AUTHOR]

Summary 1. Some studies have shown that mixed forest stands can develop more biomass or basal area than pure stands when the component species occupy different strata. It has been predicted that such additive effects are most likely in moist habitat sites where size-asymmetric competition controls stand development. 2. In south-central Chile, secondary succession often gives rise to vertically stratified mixed forest stands, with a Nothofagus overstorey overtopping lower tiers dominated by more shade-tolerant taxa. We examined the relationship between the degree of understorey development and total basal area accumulated by 83 second-growth Nothofagus stands aged 40–70 years. Basal area is defined as the cross-sectional area at breast height of all trees in a stand, per unit land area. 3. When age, overstorey leaf habit and geographical location were controlled by ancova, stands with a heavy understorey (> 6 m2 ha-1 ) yielded > 25% more total basal area on average than stands with little or no understorey. The average basal area of the Nothofagus component did not differ significantly between stand structure categories. 4. The total basal area of stands dominated by evergreen N. dombeyi was nearly 50% higher on average than that of stands of similar age dominated by deciduous N. obliqua and/or N. nervosa , reflecting denser stockings in the former as a result of allometric differences. Although the percentage of total stand basal area contributed by the understorey was higher on deciduous-dominant plots, mean absolute basal area of understorey associates was similar beneath evergreen and deciduous Nothofagus overstoreys. 5. Synthesis and applications . The results broaden the evidence for additive effects in mixtures of species with complementary light use, suggesting that no significant advantage to overstorey wood production will be gained by eliminating a woody understorey in Nothofagus second-growth stands on mesic sites. Despite... [ABSTRACT FROM AUTHOR]