William G. Lee

The worldwide leaf economics spectrum

Bringing together leaf trait data spanning 2,548 species and 175 sites we describe, for the first time at global scale, a universal spectrum of leaf economics consisting of key chemical, structural and physiological properties. The spectrum runs from quick to slow return on investments of nutrients and dry mass in leaves, and operates largely independently of growth form, plant functional type or biome. Categories along the spectrum would, in general, describe leaf economic variation at the global scale better than plant functional types, because functional types overlap substantially in their leaf traits. Overall, modulation of leaf traits and trait relationships by climate is surprisingly modest, although some striking and significant patterns can be seen. Reliable quantification of the leaf economics spectrum and its interaction with climate will prove valuable for modelling nutrient fluxes and vegetation boundaries under changing land-use and climate.

MASTING BY EIGHTEEN NEW ZEALAND PLANT SPECIES: THE ROLE OF TEMPERATURE AS A SYNCHRONIZING CUE

Masting, the intermittent production of large flower or seed crops by a population of perennial plants, can enhance the reproductive success of participating plants and drive fluctuations in seed-consumer populations and other ecosystem components over large geographic areas. The spatial and taxonomic extent over which masting is synchronized can determine its success in enhancing individual plant fitness as well as its ecosystem-level effects, and it can indicate the types of proximal cues that enable reproductive synchrony. Here, we demonstrate high intra- and intergeneric synchrony in mast seeding by 17 species of New Zealand plants from four families across >150 000 km2. The synchronous species vary ecologically (pollination and dispersal modes) and are geographically widely separated, so intergeneric synchrony seems unlikely to be adaptive per se. Synchronous fruiting by these species was associated with anomalously high temperatures the summer before seedfall, a cue linked with the La Nina phase of ...

Where and why have all the flowers gone? Depletion and turnover in the New Zealand Cenozoic angiosperm flora in relation to palaeogeography and climate

The modern New Zealand angiosperm flora has many notable characteristics, such as a predominance of evergreen, perennial life forms, few nitrogen-fixing species, despecialised floral features and asymmetric genus—species relations. The origin of these features has been attributed to antiquity of the flora, isolation and/or environmental history. Using evidence from palynology and macrofossils, we investigate the characteristics of the mid–late Cenozoic angiosperm flora and the impact of environmental changes in land area and configuration, physiography and climate on the depletion and composition of the New Zealand flora. Climatic cooling, increasing isolation and tectonism have each acted as important environmental filters, contributing to regional extinctions and decreasing floral diversity, and inducing major turnover in the floristic composition of New Zealand. During the Miocene and Pliocene at least 15 families and a minimum of 36 genera were lost from the New Zealand flora. These included a range of life forms and physiognomically important taxa such as Acacia, Bombax, Casuarina, Eucalyptus, Ilex, many Proteaceae and several palms. The extinction and decline in richness of subtropical families was caused by the onset of cooling conditions in the Late Miocene—Pliocene, and exacerbated by the absence of significant land areas to act as refugia at lower latitudes. Many of these genera/families persist today on islands to the north (e.g. New Caledonia), reflecting mid-Cenozoic land conduits, and in Australia. The close floristic links with New Caledonia were probably maintained by intermittent island stepping-stones which facilitated interchange of subtropical taxa until the Late Miocene. The Pleistocene extinction of some genera, tolerant of warm-temperate environments (e.g. Acacia, Eucalyptus) may be a reflection of the fact that persistent mesic conditions favoured widespread dominance of dense rainforest during interglacials. The loss of these groups, containing diverse life forms and floral structures, suggests that many of the present characteristics of the New Zealand flora reflect strong selective pressures, mainly driven by climate change, in the Late Miocene, Pliocene and Pleistocene, rather than events of greater geological antiquity.

ENVIRONMENTAL CONSTRAINTS ON A GLOBAL RELATIONSHIP AMONG LEAF AND ROOT TRAITS OF GRASSES

Uncertainties regarding the relationships between leaf and root traits have impeded an integrated understanding of plant evolution and the efficient parameterization of ecosystem models. We measured key root and leaf traits of grasses from 77 sites in four grassland regions of the world (New Zealand, Australia, South Africa, North America). Within each region, the relationships among leaf traits paralleled those among root traits. Plants with low root or leaf N concentrations had roots or leaves with high tissue density, high lignin concentrations, low amount of mass that was soluble in a neutral detergent solution, large diameter/thickness, and were less enriched in 15N. Yet, whether comparing plants within a region or among all four regions, there was little relationship between root traits and leaf traits, except for a positive relationship between root and leaf N concentration and between root and leaf δ15N. At the global scale, factors such as soil freezing and the type of nutrient limitation appear ...

Covariation in leaf and root traits for native and non-native grasses along an altitudinal gradient in New Zealand

Across 30 grassland sites in New Zealand that ranged from native alpine grasslands to low elevation improved pastures, there were consistent patterns of leaf and root traits and significant differences between native and non-native grasses. Plants of high altitude sites have low N concentrations in both their leaves and roots, have thick leaves and roots, yet no differences in tissue density or photosynthetic water use efficiency when compared to plants of low altitude sites. Both the leaves and roots of the low altitude plants were enriched in 15N relative to the plants of higher altitude, indicating that the low-N set of traits is associated with a more closed N cycle at high altitude. A second independent set of correlations shows that plants of wetter habitats have lower photosynthetic water use efficiency (more negative ∂13C) and lower leaf and root tissue density than the plants of drier sites. For both leaves and roots, plants of native species consistently had traits associated with lower resource availability: lower N concentrations, denser tissues, more negative ∂15N, and more positive ∂13C than non-native species. If root %N is correlated with root longevity as has been shown in other systems, root longevity may be able to be predicted from simple measurements of leaf %N, though a hysteresis in the relationship between leaf and root N concentrations may make prediction of high longevity roots difficult.

Of mast and mean: differential-temperature cue makes mast seeding insensitive to climate change.

Mast-seeding plants often produce high seed crops the year after a warm spring or summer, but the warm-temperature model has inconsistent predictive ability. Here, we show for 26 long-term data sets from five plant families that the temperature difference between the two previous summers (ΔT) better predicts seed crops. This discovery explains how masting species tailor their flowering patterns to sites across altitudinal temperature gradients; predicts that masting will be unaffected by increasing mean temperatures under climate change; improves prediction of impacts on seed consumers; demonstrates that strongly masting species are hypersensitive to climate; explains the rarity of consecutive high-seed years without invoking resource constraints; and generates hypotheses about physiological mechanisms in plants and insect seed predators. For plants, ΔT has many attributes of an ideal cue. This temperature-difference model clarifies our understanding of mast seeding under environmental change, and could also be applied to other cues, such as rainfall.

Succession and dynamics of gorse (Ulex europaeus L.) communities in the dunedin ecological district South Island, New Zealand

Abstract Successional patterns in gorse (Ulex europaeus) communities were determined from an analysis of 125 plots in the Dunedin Ecological District. Stem diameter and height growth of gorse averaged 5 mm yr-1 and 200 mm yr-1 respectively. Plants attained a maximum age of 29 years, a maximum height of 7.0 m, and a maximum diameter of 217 mm at 100 mm above the ground. Gorse matured at about 15 years after establishment with a mean stem density of 60 000 ha-1, mean basal area value of 51 m2 ha-1, and a mean litter depth of 55 mm. Other naturalised woody species, particularly broom (Cytisus scoparius), declined in importance in older gorse stands. The establishment of native woody species was favoured by lower density, taller gorse, where litter depth was shallow, and areas of bryophyte or bare soil were available. In these stands native species reached numerical and basal area equivalence with gorse after 10–15 years on the site. However, at 60% of the sites younger than 25 years, native woody species wer...

Regeneration in indigenous forest after eradication of Norway rats, Breaksea Island, New Zealand

Abstract Population age structures and recruitment of major tree and shrub species on Breaksea Island, Fiordland, New Zealand, were assessed at the time of eradication of Norway rats in 1988 and over the following 5 years. Seedling numbers of many tree and shrub species increased substantially over the period 1988–1993 after rat eradication. Population age structures of the dominant trees Nothofagus menziesii and N. solandri var. cliffortioides suggested a lapse of recruitment starting about 100 years ago, coinciding with the probable time of rat establishment. The recruitment gaps, and increases in seedling numbers are circumstantial evidence that rat predation was an important constraint on plant regeneration on Breaksea Island.

Patterns of Resource Allocation in Fleshy Fruits of Nine European Tall-Shrub Species

Within-fruit reproductive allocation was studied in the nine major fleshy-fruited shrub species of southern England. The partitioning of dry mass and nitrogen between flesh and stone, and between the fibrous coat of the stone and the embryocum-endosperm, was determined, together with the water proportion in each fraction. Mean allocation to flesh was 55% of the fruit dry mass. This did not vary with fruit size over an order of magnitude in total dry mass and a range of 1-26 in number of seeds per fruit. Nitrogen concentration was generally lower in the flesh than the stone (mean ratio 0.56:1), and there was a markedly smaller nitrogen allocation to flesh in larger fruits (...)

Does fluctuating resource availability increase invasibility? Evidence from field experiments in New Zealand short tussock grassland.

The theory of fluctuating resource availability proposes that the susceptibility of a plant community to invasion by new species (i.e., invasibility) depends upon conditions of intermittent resource enrichment coinciding with the presence of invading propagules. We compared the response of a rapidly invading forb (Hieracium pilosella L.) between different experimental treatments in a short tussock grassland in New Zealand, over 6–12 years, to determine whether the theory explains differences in invasibility. The theory predicts that environments subject to periodic resource enrichment will be more invasible than those with more stable resource-supply rates. In our study, H. pilosella did not increase more rapidly in treatments subject to periodic resource pulses (fertiliser and water) than in those with more stable resource supplies. Also contrary to the predictions of the theory, the rate of invasion of H. pilosella did not increase following an increase in the rate of supply of water or nutrient resources, or following treatments that temporarily reduced resource uptake in the community, including grazing. H. pilosella did not increase immediately following abrupt increases in water and nutrient supply and removal of the dominant grass species with herbicide, as predicted by the theory, although temporary increases in resident exotic guilds indicated that the intensity of competition for resources was reduced. Neither H. pilosella nor resident exotic guilds showed increased cover growth rates following resumed grazing. The rate of invasion by H. pilosella was not correlated with species richness, a result consistent with one of the predictions of the theory. Therefore, short-lived events that temporarily reduced or suspended competition did not appear to determine the invasion success of this particular species in this region. In New Zealand’s perennial short tussock grasslands, the characteristics of the resident plant community may be more critical than resource fluctuations in determining invasion success of H. pilosella. Invasion of H. pilosella may be most successfully controlled here by promoting a successional physiognomic shift to a taller, shrub-and-tussock-dominated canopy that competitively excludes low-growing forbs.