G. L. Rapson

Sensitivity of leaf size and shape to climate: global patterns and paleoclimatic applications

• Paleobotanists have long used models based on leaf size and shape to reconstruct paleoclimate. However, most models incorporate a single variable or use traits that are not physiologically or functionally linked to climate, limiting their predictive power. Further, they often underestimate paleotemperature relative to other proxies. • Here we quantify leaf-climate correlations from 92 globally distributed, climatically diverse sites, and explore potential confounding factors. Multiple linear regression models for mean annual temperature (MAT) and mean annual precipitation (MAP) are developed and applied to nine well-studied fossil floras. • We find that leaves in cold climates typically have larger, more numerous teeth, and are more highly dissected. Leaf habit (deciduous vs evergreen), local water availability, and phylogenetic history all affect these relationships. Leaves in wet climates are larger and have fewer, smaller teeth. Our multivariate MAT and MAP models offer moderate improvements in precision over univariate approaches (± 4.0 vs 4.8°C for MAT) and strong improvements in accuracy. For example, our provisional MAT estimates for most North American fossil floras are considerably warmer and in better agreement with independent paleoclimate evidence. • Our study demonstrates that the inclusion of additional leaf traits that are functionally linked to climate improves paleoclimate reconstructions. This work also illustrates the need for better understanding of the impact of phylogeny and leaf habit on leaf-climate relationships.

Properties of ecotones: Evidence from five ecotones objectively determined from a coastal vegetation gradient

Abstract Several properties have been suggested to be characteristic of ecotones, but their prevalence has rarely been tested. We sampled five ecotones to seek evidence on seven generalizations that are commonly made about ecotones: vegetational sharpness, physiognomic change, occurrence of a spatial community mosaic, many exotic species, ecotonal species, spatial mass effect, and species richness higher or lower than either side of the ecotone. The ecotones were in a sequence from scattered mangroves, through salt marsh, rush-marsh, scrub, woodland, to pasture. We developed a method to objectively define, by rapid vegetational change, the position and depth of an ecotone, identifying five ecotones. Their positions were consistent across three sampling schemes and two spatial grain sizes. One ecotone is a switch ecotone, produced by positive feedback between community and environment. Another is anthropogenic, due to clearing for agriculture. Two others are probably environmental in cause, and one may be largely a relict environmental ecotone. Sharp changes in species composition occurred. Three ecotones were associated with a change in plant physiognomy. In two, the ecotone was located just outside a woodland canopy, in the zone influenced by the canopy. Community mosaicity was evident at only one ecotone. There were few strictly ecotonal species; many species occurred more frequently within ecotones than in adjacent vegetation, but there were never significantly more ecotonal species than expected at random. There was little evidence for the spatial mass effect reducing ecotonal sharpness, or leading to higher species richness within ecotones. Species richness was higher than in the adjacent habitat in only one ecotone. It seems that supposedly characteristic ecotone features depend on the particular ecological situation, and the ecology of the species present, rather than being intrinsic properties of ecotones. Nomenclature: Connor & Edgar (1987) and references therein, and Stace (1997), except where indicated.

Distributions and climatic correlations of some exotic species along roadsides in South Island, New Zealand

A survey was made of the distribution of twentyfour exotic species along roadsides on South Island, New

Non-adaptation in Agrostis capillaris L. (Poaceae)

The idea that all plant species are perfectly adapted to their environment is well embedded in ecology. In an attempt to test this concept, within-species differences in the grass Agrostis capillaris L. (Poaceae) were examined. We randomly sampled genotypes as tillers from populations over a wide environmental range in southern New Zealand, and transplanted them back into their own and each others sites. Growth, floral phenology and tiller population dynamics all gave very little evidence of adaptation at the

A comparison of realised niche relations of species in New Zealand and Britain

SummaryMany plant species prominent in the native vegetation of the dry shingle banks at Dungeness (Britain) are also prominent as exotics in the dry Upper Clutha catchment (New Zealand). To examine the realised niche relations of these species, vegetation was sampled in the two areas. Inverse classification and ordination were used to determine the relative beta niches of the species in the two areas. There was little agreement; it seems that the exotic species in the Upper Clutha were pre-adapted to different niches from those in their native range.

Geographical Constraints Are Stronger than Invasion Patterns for European Urban Floras

Understanding the mechanisms that affect invasion success of alien species is an important prerequisite for the effective management of present and future aliens. To gain insight into this matter we asked the following questions: Are the geographical patterns of species distributions in urban floras different for native compared with alien plant species? Does the introduction of alien species contribute to the homogenization of urban floras? We used a Mantel test on Jaccard dissimilarity matrices of 30 urban floras across the British Isles, Italy and central Europe to compare the spatial distribution of native species with four classes of alien species: archaeophytes, all neophytes, non-invasive neophytes, and invasive neophytes. Archaeophytes and neophytes are species that were introduced into Europe before and after 1500 AD, respectively. To analyze the homogenizing effect of alien species on the native urban floras, we tested for differences in the average dissimilarity of individual cities from their group centroid in ordination space. Our results show that the compositional patterns of native and alien species seem to respond to the same environmental drivers, such that all four classes of alien species were significantly related to native species across urban floras. In this framework, alien species may have an impact on biogeographic patterns of urban floras in ways that reflect their history of introduction and expansion: archaeophytes and invasive neophytes tended to homogenize, while non-invasive neophytes tended to differentiate urban floras.

Is Empodisma minus the ecosystem engineer of the FBT (fen–bog transition zone) in New Zealand?

Abstract The role of ecosystem engineers (EE) in the formation of ombrotrophic mires (bogs) from fens, called the fen–bog transition (FBT), can be best understood through categorization of the autogenic and allogenic processes causing bog initiation. Here we review these pathways, discuss the drivers of change in both cases, and tabulate an approach for distinguishing between them. We then compare the engineering ability of acknowledged and putative engineers against a number of characters which plants require to cross the FBT, and to stabilize occupancy on the bog side. While some Sphagnum spp. are accepted as the EE of the fen–bog transition in northern hemisphere bogs, they appear unimportant in New Zealand. Instead their role appears to be occupied by a restiad, Empodisma minus, a plant with leafless, wiry stems and capillaroid roots. Empodisma minus appears capable of engineering autogenic transitions from fen to bog across New Zealand, even more efficiently than Sphagnum.

Subalpine gully-head ribbon fens of the Lammerlaw and Lammermoor Ranges, Otago, New Zealand

Abstract Vegetation patterns of subalpine gully‐head mires were investigated in the flat‐topped Lammerlaw and Lammermoor Ranges, South Island, New Zealand. Two intensively studied mires each consist of a series of peaty terraces and scarps. Terraces may contain pools, elongated downslope in the narrow, lower altitude mire, but across slope in the broader, upper mire. A crest occurs on some terrace lips, and marginal “spillways” (channel‐like zones) occur down some scarps. Some mires have drained by subsurface pipes. Vegetation analysis distinguished between grassland or herbfield on gully sides, vegetation of mire margins, showing aspect differences on the steeper, lower mire, and the vegetation of gully floors, including oligotrophic mire centre vegetation and species‐poor pools. The crests, though warmer, bore no special vegetation type. Mineral soil beneath the peat indicates a previous non‐mire vegetation, which has subsequently paludified. Scarp slumps indicate downslope creep of organic material. Peat fissures, and mineral, vegetation, and erosion dams all appear to have initiated development of some pools. Mires are designated gully‐head ribbon fens. Patterning appears to be accentuated because of the mires’ gully‐head location on broad‐topped ranges, and drainage of soligenous water from upslope gully sides. These apparently unique fens give insight into patterning in aapa mires, and merit special conservation.

Genecology of Agrostis capillaris L. (Poaceae) — an invader into New Zealand: 2. Responses to light, soil fertility, and water availability

Abstract Fifteen populations of the naturalised grass, Agrostis capillaris, sampled from southern New Zealand, were examined for responses to a range of levels of light, fertility, and water availability. Populations from open, dry areas had genetically low, but plastic, allocation to shoots. Populations from shady areas were more upright than average, and had greater leaf areas, whereas a lawn population was prostrate, but had high allocation to shoots. There was evidence of genecological variation in response to the marked site differences in soil-water availability. Population-based variation in specific leaf area was correlated with rainfall and soil nitrogen and phosphate levels. Differences between populations in other characters did not correlate with environmental trends. Responses indicate some adaptation of populations to their local environments in New Zealand, but also high within-population variation and some instances of nonadaptation. Plasticity is high — as much as 80% of the total variati...

Genecology of Agrostis capillaris L. (Poaceae) — an invader into New Zealand: 1. Floral phenology

Abstract Agrostis capillaris has spread throughout New Zealand since its introduction 130 or more years ago. Genecological variation is investigated for clues to its success. Inflorescence number, time to 50% inflorescence emergence, time to 50% anthesis, and length of longest lamina and of longest stem were recorded for samples of 15 populations from a range of habitats in southern New Zealand, and for a collection from Campbell Island, grown together in a common garden in Dunedin. Differences between populations were not significantly related to major environmental trends, such as altitude and latitude; there was no evidence for the formation of ecotypes within the species. Populations collected from the same habitat type (e.g., alpine, or dry grassland) did not exhibit comparable floral behaviour. There were significant differences between some populations in the time to 50% completion of inflorescence emergence and anthesis, but no significant differences among populations in the time interval between...