Floristic Relationships Among Vegetation Types of ... - Oxford Journals

Annals of Botany 101: 1401– 1412, 2008 doi:10.1093/aob/mcn049, available online at www.aob.oxfordjournals.org

Floristic Relationships Among Vegetation Types of New Zealand and the Southern Andes: Similarities and Biogeographic Implications ´ 2 and PE T E R WARD L E 3 C E C I L I A E Z C U R R A 1, * , N O R A B AC CA L A 1 Departamento de Botańica, 2Departamento de Estadı´stica, Centro Regional Universitario Bariloche, Universidad Nacional del Comahue, Quintral 1250, 8400 San Carlos de Bariloche, Argentina and 3Landcare Research, Lincoln, New Zealand Received: 20 December 2007 Returned for revision: 25 January 2008 Accepted: 26 February 2008 Published electronically: 3 April 2008

† Background and Aims Similarities between the floras of geographically comparable regions of New Zealand (NZ) and the southern Andes (SA) have interested biologists for over 150 years. The present work selects vegetation types that are physiognomically similar between the two regions, compares their floristic composition, assesses the environmental factors that characterize these matching vegetation types, and determines whether phylogenetic groups of ancestral versus modern origin are represented in different proportions in their floras, in the context of their biogeographic history. † Methods Floristic relationships based on 369 genera of ten vegetation types present in both regions were investigated with correspondence analysis (CA) and ascending hierarchical clustering (AHC). The resulting ordination and classification were related to the environmental characteristics of the different vegetation types. The proportions of different phylogenetic groups between the regions (NZ, SA) were also compared, and between forest and non-forest communities. † Key Results Floristic similarities between NZ and SA tend to increase from forest to non-forest vegetation, and are highest in coastal vegetation and bog. The floras of NZ and SA also differ in their phylogenetic origin, NZ being characterized by an ‘excess’ of genera of basal origin, especially in forests. † Conclusions The relatively low similarities between forests of SA and NZ are related to the former being largely of in situ South American and Gondwanan origin, whereas the latter have been mostly reconstituted though transoceanic dispersal of propagules since the Oligocene. The greater similarities among non-forest plant communities of the two regions result from varied dispersal routes, including relatively recent transoceanic dispersal for coastal vegetation, possible dispersal via a still-vegetated Antarctica especially for bog plants, and independent immigration from Northern Hemisphere sources for many genera of alpine vegetation and grassland. Key words: Biogeographic history, floristic similarities, generic composition, local floras, New Zealand, phylogenetic origin, southern Andes, vegetation types.

IN TROD UCT IO N The similarities among the floras of the southern continents have attracted the attention of biologists for more than 150 years (Hooker, 1853; Darwin, 1859). Alhough Nothofagus, with species dominating many forests in New Guinea, New Caledonia, Tasmania, New Zealand and South America is iconic in relation to these ‘southern connections’, many other animal and plant groups with related taxa on either side of the Pacific have shared the same focus (e.g. Skottsberg, 1915; Godley, 1960; Moore, 1972; Thorne, 1972; Sanmartıń and Ronquist, 2004). Two principal biogeographic hypotheses have been advanced to explain these similarities: tectonic vicariance due to fragmentation of previously contiguous landmasses, and transoceanic dispersal of taxa. After decades of emphasis on vicariance and cladistic biogeography (e.g. Nelson, 1974; Platnick and Nelson, 1978; Rosen, 1978; Nelson and Ladiges, 2001; Morrone, 2002), dispersal biogeography has received renewed emphasis (e.g. Pennington and Dick, 2004; Pennington et al., 2004; Sanmartıń and Ronquist, * For correspondence. E-mail [email protected]

2004; deQueiroz, 2005; McGlone, 2005; Cowie and Holland, 2006; Sanmartıń et al., 2007) as molecular phylogenies now support the view that both processes have contributed to the biotas of the southern continents. Even though the best evidence for the biogeographic origins of regional biotas is provided by fossil records and timecalibrated phylogenies of extant taxa, additional light can be shed through floristic and environmental comparisons of similar vegetation types in different regions, as has been shown for the Northern Hemisphere (e.g. Qian, 2002; Qian et al., 2006). New Zealand and south-western South America are situated at the same latitudes on either side of the Pacific, share similar climates and topographies, and were both united to Antarctica, up to the end of the Cretaceous for New Zealand and the middle of the Cenozoic for South America (Lee et al., 2001; McLoughlin, 2001). Striking similarities in the vegetation of the two regions led to early comparisons of their floras (e.g. Hooker 1853; Skottsberg, 1915; Godley, 1960; Thorne, 1972). Recently, phytogeographic categories of the genera present in the various vegetation types of both regions have been assessed, and the timing of the separation of lineages leading to extant congeneric

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Ezcurra et al. — Floristic Relationships of New Zealand and the Southern Andes

species on either side of the Pacific has been estimated through molecular studies. For many taxa, the divergence estimates suggest relatively recent dispersal between regions (Wardle et al., 2001). However, similarities among corresponding vegetation types in the two regions in relation to environmental factors, and differences in proportions of the diverse phylogenetic groups involved, have not hitherto been quantified. Floristic similarities and differences between regions can be analysed at different taxonomic levels, i.e. species, genera or families. Similarities at lower taxonomic levels, i.e. presence of the same or closely related species, usually reflect dispersal during late Cenozoic (Neogene), Quaternary or recent times; whereas similarities at higher taxonomic levels, e.g. presence of the same family, may suggest vicariance dating from the break-up of continents (e.g. Raven and Axelrod, 1974; Renner, 2004). By the end of the Cretaceous many extant fern and gymnosperm genera were already present, whereas many angiosperm genera originated and radiated during the Cenozoic (Neogene and Paleogene; Friis and Crepet, 1987). Therefore, the historical bases of regional and continental biogeography related to Cenozoic changes are usually inferred from floristic comparisons at generic level (e.g. Simpson and Todzia, 1990; Arroyo et al., 1996; Aizen and Ezcurra, 1998; Qian, 2002; Renner, 2004). Regions can also be compared floristically by considering the different lineages that comprise a flora. For example, East Asia shows high floristic similarities with eastern North America, but is more diverse in pteridophytes, gymnosperms and ranunculids, i.e. phylogenetically basal groups, whereas eastern North America has more caryophyllids, rosids and asterids, i.e. phylogenetically derived groups (Qian, 2001). Such information can indicate the level of ‘evolutionary development’ (Hawkins et al., 2005) of the floras of each region. The differences can then be related to the different geographic and climatic histories of the regions that have affected rates of speciation, immigration and extinction of the different lineages (Qian, 2001). The southern continents (Australia, New Zealand and South America) that were united to Antarctica to form part of Gondwana were warm and wet, and in great part covered by rain forest during the Late Cretaceous and early Cenozoic (100 – 26 Mya). New Zealand separated first from Gondwana to lie 1200 km east of Australia by the early Eocene (50 Mya); Australia in turn drifted northwards from Antarctica and was completely separated by the end of Eocene (35.5 Mys ago), whereas South America remained united to Antarctica at least until the second half of the Oligocene (32 – 28 Mya; McLoughlin, 2001), and is now separated from the Antarctic Peninsula by only 800 km. This final separation allowed the circum-Antarctic current to develop from approx. 15 Mya. This produced extensive glaciations in Antarctica and a pronounced equator-to-pole thermal gradient in the Southern Hemisphere. From this time on, the wet forests of the southern lands mostly gave way to vegetation of more arid, cooler and seasonal climates (Hinojosa and Villagrań, 1997; Lee et al., 2001; Crisp et al., 2004;

Markgraf and McGlone, 2004; Ortiz-Jaureguizar and Cladera, 2006). During Pliocene and Pleistocene times (less than 10 Mya) drying and cooling were maximal, which, together with mountain building, resulted in rapid radiations of desert and cold-adapted high-elevation taxa. Radiations of desert taxa were probably in genera that originally occupied dry pockets or low-nutrient soils in southern areas, or that originated in arid subtropical biomes more to the north (e.g. Crisp et al., 2004). Radiations among cold-adapted taxa frequently involved genera originating in cold areas in the Northern Hemisphere, but also occurred in genera pre-adapted to cold from southern regions, which included high mountains, volcanoes and the Antarctic continent (e.g. Moore, 1972). Conversely, taxa restricted to the equable wet forests that had reduced in area did not radiate and were depleted by extinction (Villagrań and Hinojosa, 1997; Lee et al., 2001; Crisp et al., 2004; Markgraf and McGlone, 2004; Ortiz-Jaureguizar and Cladera, 2006). Drying was probably maximal in Australia, as the continent moved northwards towards the southern subtropical belt of arid latitudes (Crisp et al., 2004), and in southern South America, where the development of the high Andes from the middle of the Cenozoic (Neogene) produced a strong rain-shadow from the westerly winds, resulting in the wide desert of Patagonia (Ortiz-Jaureguizar and Cladera, 2006). Cooling was probably very important in South America, being exacerbated by the cold Humboldt current and the development of the Andes (Simpson, 1983; Ortiz-Jaureguizar and Cladera, 2006). In New Zealand, however, drying was less extreme because the archipelago did not drift as far north as Australia, and was isolated from arid subtropical latitudes by extensive ocean. Cooling was important in New Zealand due to late Cenozoic climatic deterioration and tectonic activity that produced mountains and new temperate habitats, although not extreme because of the surrounding ocean. As a result, rain forest covered most of the archipelago during interglacial times, and significant areas persisted even during times of maximum glacial extension (Lee et al., 2001; Markgraf and McGlone, 2004). Although semi-arid environments developed in the rain shadow of the axial ranges, they do not seem to have persisted through the mildest interglacial episodes. Therefore, the Neogene changes in climate appear to have affected the biota of the southern landmasses in different ways according to their tectonic history, resulting in different selection pressures in the different regions. While increased aridity has been most important in Australia and South America, cooling has been most important in South America and New Zealand. Thus, the extant floras of these regions can be expected to present different proportions of phylogenetic groups, representing not only differences in their original floras, but also evolutionary radiations and dispersals filtered by the different selective pressures that they have experienced during the Neogene. With this objective, here we re-examine the floristic relationships in generic composition among different vegetation types between New Zealand and the southern

Ezcurra et al. — Floristic Relationships of New Zealand and the Southern Andes Andes. The aims of the study were: (1) to determine which vegetation types are floristically most similar between the two regions; (2) to assess environmental factors that characterize the most similar vegetation types; and (3) to show which lineages (i.e. of ancestral or modern origin) characterize the vegetation types that are most similar. Finally, we discuss these results in the context of the biogeographic history of the southern regions, formerly connected with Antarctica as part of Gondwana but now separated by vast oceanic distances. M AT E R I A L S A N D M E T H O D S Geographic regions

The study regions in the southern Andes and New Zealand (designated SA and NZ, respectively) are characterized by both having similar climates and a mountainous north – south axis rising to permanently glaciated summits. The range of mean monthly temperatures is almost identical in the two regions, indicating an oceanic climate west of the mountain axes, although in NZ the coastal currents are subtropical in origin, whereas in SA the Humboldt current results in mean temperatures that are about 1 8C cooler than at corresponding latitudes in NZ (Wardle et al., 2001). Rainfall in NZ and in the southwest of SA is, on average, equably distributed through the year, although droughts occur at irregular intervals. In the east and north of SA there is a summer rainfall minimum, indicating a transition to the Mediterranean climate of central Chile, although within the forested parts this does not lead to regular water deficits. Vegetation samples

The flora of ten different vegetation types were listed in geographically similar regions in NZ and SA; details about the localities and their environments are provided in Wardle et al. (2001). To construct the lists, 55 vegetation samples that appear comparable in terms of physiognomy and environment were selected, from 22 New Zealand localities and 18 in the southern Andes that range from sealevel to alpine (Table 1). For NZ, the samples are distributed from latitude 388 to 45830’S along the mountainous axis of the two main islands. For SA the samples are distributed from 398 to 458S along the Andean chain, thereby spanning a large proportion of the latitudinal extent of the humid western side of the Andes (35º to 55ºS) and containing nearly all the woody genera found therein (Aizen and Ezcurra, 2008). Vegetation types sampled were coded as follows: LF, low-elevation forest; MF, mid-elevation forest; HF, highelevation forest; DG, dry grassland; HG, high-elevation grassland; AV, alpine vegetation; PV, pioneer vegetation on rock, bouldery outwash, tephra and landslides; CV, coastal vegetation; WL, inland wetland; and BV, cushion bog. The samples were selected subjectively. Sampling areas were of no fixed dimensions and aimed to be large enough to include all the vascular species of the community being sampled. Types LF, MF, DG and HG comprise

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more-or-less uniform vegetation, whereas HF, representing the upper forest limit, includes forest, scrub and shrubland. AV, PV, CV, WL and BV each comprise different plant communities existing as mosaics within larger areas. To verify if the climatic patterns in physiognomically similar vegetation types from NZ and SA were generally coincident, mean annual temperature conditions and annual precipitation of all the samples were estimated (n ¼ 55) using the global WorldClim database available at www.worldclim.org (Hijmans et al., 2005), and an ordination was then performed using principal component analysis (PCA). In this analysis we included latitude, longitude and elevation as supplemantary or illustrative variables that do not participate in the conformation of the factorial axes, but are projected on them once these have been determined by the active elements of the analysis (ter Braak and Sˇmilauer, 1998; Lebart et al., 1995). The ordination (see Supplementary Information, Fig. 1, available online) resulted in sample sites from both NZ and SA appearing distributed along the precipitation gradient, from drier places from DG, AV and HG samples, to wetter sites with PV, WL, LF and CV. In addition, both NZ and SA samples appeared distributed along the temperature gradient, with high-elevation AV, HF and HG sites, to low-elevation LF and CV sites. In general, NZ and SA vegetation types can be considered similar, although NZ vegetation types were somewhat wetter than equivalent SA types, and SA vegetation types in some cases were colder. From the floristic field data, a database was constructed (see Supplementary Information, table 1, available online) that shows presence/absence of all genera in each vegetation type (n ¼ 20). Supplementary rows and columns indicate, respectively, the environmental characteristics of the plant communities sampled, and the phylogenetic group to which each genus was assigned (for details of the latter see Data Analysis, below). Genera and infrageneric entities are named as in Wardle et al. (2001), i.e. we mostly follow the Flora of New Zealand (Webb et al., 1988, and earlier volumes) for NZ, and Zuloaga et al. (1994) and Zuloaga and Morrone (1996, 1999a, b) for SA. Environmental variables selected were those related to temperature, light and water, that appear to be important determinants of generic composition together with region (NZ or SA). They included three qualitative variables: lower or higher elevations, i.e. below vs. above 1000 m a.s.l. (L vs. H); presence of a forest canopy vs. non-forest vegetation (FO vs. NF); and soils free-draining vs. waterlogged (D vs. W). A second database was also constructed (see Supplementary Information, Table 2, available online) that shows presence/absence of all genera in each sample (n ¼ 55). Floristic comparisons at regional levels are usually based on complete floras (e.g. Qian, 2001, 2002; Qian et al., 2006). Although our sampled communities represent the broad pattern of vegetation in SA and NZ and include most of the genera present therein, the number of genera recorded may fall short of the total regional floras, which we could not use as a basis because catalogues of vascular plants of southern South America that document all generic distributions are not yet available.

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TA B L E 1. Sampled localities of New Zealand (NZ) and the southern Andes (SA), vegetations sampled, sample code, altitude, and geographic latitude and longitude (in decimal degrees, W for SA, E for NZ)

St Arnaud Range Arthurs Pass Black Birch Range Arthurs Pass Lake Mueller Bradshaw Arm Greenpark Sands Hall Arm Ship Creek Lake Pukaki Mackenzie district Craigieburn Range Earnslaw Burn Rahu Valley Ruapehu Arthurs Pass Craigieburn Range St Arnaud Range Haast Valley Ship Creek Waioeka Gorge Earnslaw Burn Secretary Island Copland Pass Franz Josef Glacier Big Bay Lake Manapouri Paringa Cerro Catedral Cerro Catedral Bog near Sta. Lucia Mehuin Mehuin Seno Queulat Cholila Esquel San Ramoń Cerro Catedral Pampa del Toro Paso Puyehue Volcań Puyehue Pampa del Toro Volcań Puyehue Aguas Calientes Oncol San Martıń Lago Nahuel Huapi Portezuelo Queulat Glacier near Sta. Lucıá Glacier near Sta. Lucıá Ventisquero Colgante Volcań Puyehue Lago Nahuel Huapi Lago Nahuel Huapi Rio Queulat

Vegetation sampled*

Code

Altitude (m)

Latitude

Longitude

NZAV NZAV NZAV NZBV NZBV NZCV NZCV NZCV NZCV NZDG NZDG NZHF NZHF NZHF NZHF NZHG NZHG NZHG NZLF NZLF NZLF NZMF NZMF NZPV NZPV NZWL NZWL NZWL SAAV SAAV SABV SACV SACV SACV SADG SADG SADG SAHF SAHF SAHF SAHF SAHG SAHG SALF SALF SALF SAMF SAMF SAPV SAPV SAPV SAPV SAWL SAWL SAWL

NZAVAR NZAVAP NZAVBR NZBVAP NZBVLM NZCVBA NZCVGS NZCVHA NZCVSC NZDGLP NZDGMD NZHFCR NZHFEB NZHFRV NZHFRP NZHGAP NZHGCR NZHGBR NZLFHV NZLFSC NZLFWG NZMFEB NZMFSI NZPVCP NZPVJC NZWLBB NZWLMP NZWLPG SAAVCC SAAVCF SABVSL SACVMD SACVMS SACVSQ SADGCH SADGES SADGSR SAHFCC SAHFPT SAHFPP SAHFVP SAHGPT SAHGVP SALFAC SALFON SALFSM SAMFNH SAMFPQ SAPVLP SAPVLS SAPVVC SAPVVP SAWNHC SAWNHM SAWLRQ

1750 1605 1700 1000 550 0 0 0 0 645 550 1450 800 1225 1430 1330 1750 1750 60 0 100 600 650 800 210 10 177 150 1800 2000 500 0 0 0 500 1030 1050 1500 1100 1520 980 1100 1200 500 640 10 800 500 250 330 100 1440 770 770 20

241.87 242.90 241.75 242.90 243.42 245.32 243.77 245.50 243.88 244.18 244.35 243.15 244.68 242.28 239.30 242.90 243.15 241.75 243.97 243.88 238.23 244.67 245.20 243.50 243.43 244.30 245.53 243.75 241.17 241.17 243.37 239.43 239.43 244.52 242.33 242.83 241.05 241.17 241.53 240.68 240.60 241.53 240.60 240.70 239.70 239.65 241.12 244.60 243.28 243.28 244.50 240.60 241.12 241.12 244.57

172.85 171.57 173.78 171.57 170.03 167.20 172.53 167.05 169.13 170.18 170.15 171.80 168.42 172.13 175.52 171.57 171.80 173.78 169.18 169.13 177.32 168.42 166.93 170.02 170.17 168.13 167.62 169.38 271.50 271.50 272.40 273.22 273.22 272.55 271.33 271.17 271.08 271.50 271.47 271.93 272.15 271.47 272.15 272.23 273.33 273.20 271.42 272.42 272.45 272.45 272.57 272.15 271.42 271.42 272.42

* AV, alpine vegetation; BV, bog vegetation; CV, coastal vegetation; DG, dry grasslands; HF, high-elevation forests; HG, high-elevation grasslands; LF, low forests; MF, middle-elevation forests; PV, pioneer vegetation; WL, interior wetlands.

Data analysis

Using the database of 369 genera recorded in samples of the ten vegetation types in each region (see Supplementary Information, table 1, available online), we compared the number of shared genera to the average number of genera

present in each paired equivalent vegetation type. The presence/absence data of the genera in the ten vegetation types were also subjected to ordination and classification. For this, we eliminated from the database 168 genera that appeared in only one vegetation type in order to avoid the

Ezcurra et al. — Floristic Relationships of New Zealand and the Southern Andes undue influence of their absences in the data analyses. This resulted in a new database with the same 20 vegetation types (ten from NZ and ten from SA) and data on presence/absence of 201 genera (136 present in NZ, 143 in SA, 78 shared by both regions). These data were subjected to correspondence analysis (CA; ter Braak and Sˇmilauer, 1998), also known as reciprocal averaging and as analysis factorielle des correspondences simples (AFC; Escofier and Page`s, 1990; Lebart et al.,1995; ter Braak, 2000). Such analyses allow investigation of relationships between two qualitative variables and, at the same time, representation of the categories of both in a space of reduced dimensions. In this CA, we included as supplementary (ter Braak and Sˇmilauer, 1998) or illustrative (Lebart et al., 1995) the geographical and environmental qualitative variables that appear important determinants of generic composition: region (NZ vs. SA), elevation (L vs. H), forest vs. non-forest vegetation (FO vs. NF), and drainage (W vs. D). These supplementary or illustrative variables do not participate in the conformation of the factorial axes, but are projected on them once these have been determined by the active elements of the analysis (ter Braak and Sˇmilauer, 1998; Lebart et al., 1995). In a second CA, we analysed the 55 samples separately (see Supplementary Information, table 2, available online) in order to describe variation not only among vegetation types, but also within vegetation types. To examine the effect of phylogenetic origin on floristic relationships between vegetation types of NZ and SA, each genus was assigned to its family (Mabberley, 1993) and then sorted into seven phylogenetic groups: (1) pteridophytes, (2) gymnosperms, (3) basal angiosperms, (4) monocots, (5) basal eudicots, (6) rosids, and (7) asterids (see Supplementary Information, table 1, available online), following the Angiosperm Phylogeny Website tree (Stevens, 2001) based on the molecular phylogenies published by APG (1998, 2003). The order from (1) pteridophytes to (7) asterids represents an evolutionary trend from lineages of older to younger origin (Qian, 2002). This analysis, therefore, gives a measure of the level of ‘evolutionary development’ (sensu Hawkins et al., 2005) of the floras of each region or vegetation type. The importance of the illustrative variables shown in the supplementary rows in Supplementary Information, table 1 (environment types and regions) in the resulting ordinations was evaluated using a test value (tv) that expresses the distance to the origin of each illustrative category in terms of standard deviations from a normal distribution. Therefore, if tv . 2 in absolute value, the deviation is significant at P , 0.05 in the axis considered (Lebart et al., 1995; SPAD, 2000). To further investigate the floristic relationships between and within the two regions (NZ, SA), ascending hierarchical classification analysis (AHC) was conducted to group the 20 vegetation types into clusters based on generic composition. This used the co-ordinates of the positions of the vegetation types in the most important axes of the CA ordination, and Ward’s method as aggregation algorithm. The resulting classes were characterized by the most characteristic illustrative categories, i.e. region, environment and

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phylogenetic group. To select the categories that characterized each class, we considered a test that shows if the proportion of vegetation types of a category within its class is different from the proportion in the total of vegetation types (Lebart et al., 1995). A category (NZ or SA, W or D, F or NF, L or H) was considered characteristic of a class if it presented tv . 3, P , 0.01. Statistical analyses were conducted with SPAD version 4.5 (2000). Finally, the frequencies of different phylogenetic groups according to region (NZ flora vs. SA flora) and environments (forest vs. non-forest vegetation) were also analysed. To achieve this, G-tests (Sokal and Rohlf, 1981) were conducted taking into account the whole set of genera (n ¼ 369 genera; 78 shared by both regions, 137 exclusive of NZ, 154 exclusive of SA). In these analyses we tested whether genera of different phylogenetic groups (i.e. basal or derived) were equally represented in both regions. Therefore, the higher the G-value obtained, the larger the deviation between observed and expected 1 : 1 frequencies. Three tests were performed, considering genera that are exclusive to New Zealand, genera exclusive to the southern Andes, and shared genera (i.e. NZ vs. SA, NZ vs. shared genera, SA vs. shared genera). Proportions of genera of different phylogenetic groups within different environments were also tested (i.e. forest NZ vs. forest SA, and non-forest NZ vs. non-forest SA). In order to conduct these analyses, we had to group phylogenetic categories that included a low number of taxa into more inclusive categories (see Sokal and Rohlf, 1981). Categories 1 and 2 were grouped into (1) pteridophytes and gymnosperms, 3 and 4 were grouped into (2) basal angiosperms and monocots, 5 was left as (3) basal eudicots, and 6 and 7 were grouped into (4) true eudicots. The order of the new categories from 1 to 4 still represents a broad evolutionary trend (APG, 1998, 2003). R E S U LT S The samples included 369 genera, of which 215 occur in New Zealand and 232 in the southern Andes. Seventy-eight genera are shared by both regions, 137 occur in New Zealand but not the southern Andes, and 154 occur in the southern Andes but not New Zealand. Each vegetation type averages 47 genera. The richest communities are low altitude forest, with 66 and 65 genera in NZ and SA, respectively, and the poorest are bogs, with 28 and 29 genera, respectively. Forty of the 947 species sampled are shared by both regions (Wardle et al., 2001). Similarities among vegetation types

Paired comparisons show that 15– 35 % of genera are shared between the equivalent vegetation types of the two regions, with the numbers being lowest in low-altitude forests and highest in coastal vegetation (Table 2). The first ordination is based on generic composition of the 20 vegetation types in the plane determined by the first two CA axes (Fig. 1). The total inertia of the data is 4.29, and the eigenvalues of the first two axes are 0.59 and 0.53,

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F I G . 1. Ordination of vegetation types of New Zealand (NZ) and the southern Andes (SA) based on CA of floristic composition of genera. Black circles represent NZ and SA vegetation types, and their codes are given in Materials and Methods. White circles are the centroids of geographical and environmental variables considered illustrative in the analysis and projected on the plane determined by the first two axes: region (NZ vs. SA), elevation lower vs. higher than 1000 m a.s.l (Alt , vs. Alt .), forests vs. non-forest vegetation (FO vs. NF), water-logged vs. freedraining soils (W vs. D).

respectively. Therefore, the first two factors represent less than 30 % of the total inertia of the data, but in cases such as this, where variables have so many categories (ten vegetation types in each of two regions and 203 genera) and where the data are presence/absence, the percentage of inertia can be low but nevertheless informative (see ter Braak and Sˇmilauer, 1998). The illustrative variables best represented in the plane determined by the first two axes are region (NZ to the left on axis 1, tv ¼ – 4.1, and SA to the right, tv ¼ 4), and

TA B L E 2. Total number of genera found in different vegetation types of New Zealand (NZ) and the southern Andes (SA), and percentage of shared genera in relation to average number in each vegetation type Vegetation type

NZ

SA

% shared

High elevation forests Medium elevation forests Low elevation forests Inland wetlands Dry grasslands High grasslands Bog vegetations Pioneer vegetation Alpine vegetation Coastal vegetation

33 33 65 57 40 38 29 62 47 53

51 41 66 38 47 38 28 50 62 55

12 16 17 19 21 21 25 29 29 39

environment (forest in the upper part on axis 2, tv ¼ 3.4, and non-forest in the lower, tv ¼ – 3.2). Alhough elevation is not as well represented (Alt. in the lower part, tv ¼ – 1.6, Alt, in the upper, tv ¼ 1.7), it generally separates vegetation types of the lower part of the plane from the higher part. Therefore, the first axis clearly separates floristically NZ vegetation types from those of SA, whereas the second axis represents an environmental gradient that separates forests at low elevations from nonforest vegetation at generally higher elevations. Consequently, the vegetation types that are floristically most different between regions and, therefore, bestseparated in Fig. 1 are low- and medium-elevation forests (NZ-LF, NZ-MF vs SA-LF, SA-MF), whereas the most similar between regions, and hence closest, are the coastal NZ-CV and SA-CV, the pioneer NZ- PV and, especially, bog (SA- BV), which is the SA vegetation type most similar floristically to NZ vegetation types in general, as shown by its relative proximity to the centroid of NZ illustrative variables. Vegetation types of NZ are more clustered on the second axis than those of SA, suggesting that the latter exhibit higher floristic turnover (i.e. higher beta diversity) in relation to the environmental gradients represented by the second axis (forest vs. non-forest, and generally higher vs. lower elevations). To confirm this pattern, we analysed the total generic composition (including single occurrences) using the Jaccard average distance calculated between floras of SA and NZ. This resulted in a higher distance for SA (0.852) than for NZ (0.828), but these differences were not significant (Mann – Whitney test, P ¼ 1). Ascending hierarchical classification analysis (AHC) performed with the first eight axes (representing 68.7 % of variation of the data) generally cluster NZ and SA vegetation types in two separate groups in the first division, but include coastal and bog vegetation of SA within the NZ group (Fig. 2). The second and third divisions separate five clusters that define five classes of vegetation types based on generic composition. The classes with environmental variables and region defined by tv . 3 are: (1) lower- and medium-elevation forests of SA; (2) all but two of the remaining SA vegetation types, mostly of nonforest environments; (3) coastal vegetation of NZ and SA; (4) low- and medium-elevation forests and wetlands of NZ; and (5) the remaining vegetation types of NZ, mostly of non-forest environments, plus SA bogs, which cluster with NZ bogs. Classes (1), (3) and (5) are not associated with particular phylogenetic categories, but class (2) is associated with monocots, basal eudicots, rosids and asterids, and class (4) with pteridophytes, gymnosperms and basal angiosperms. In order to describe variation not only among but also within vegetation types, a second CA analysed the 55 samples separately (see Supplementary Information, table 1, available online). In this ordination (Fig. 3) we observed the same tendencies as the ones that resulted with the pooled floristic data of each vegetation type (Figs 1 and 2), e.g. the bog sample of SA (SABVSL) and coastal vegetation of SA (SACVMS, SACVMD, SACVSQ) appear most similar floristically to NZ in general, as shown by their relative proximity to all the


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plane (NZWLMP vs. NZWLBB, and SAWLNH vs. SAWLRQ, also NZCVGS vs. NZCVBA). Differences in proportions of phylogenetic groups

F I G . 2. Ascending hierarchical classification (AHC) of vegetation types of New Zealand (NZ) and the southern Andes (SA) based on generic composition. The vegetation codes are given in Materials and Methods.

NZ samples. In general, all the samples of each vegetation type appear clearly grouped, and only in very few cases (e.g. water-logged sites) do samples from the same vegetation type appear widely separated in the ordination

The numbers of genera distributed among the seven phylogenetic groups differs between regions and vegetation types (Fig. 4). In general, NZ has more genera of pteridophytes, gymnosperms, basal angiosperms and monocots, whereas SA has more basal eudicots, rosids and asterids. This pattern is even more pronounced when the forest floras are compared. The G-statistics confirm that the phylogenetic composition of the floras of the two regions differs significantly (NZ vs. SA: G ¼ 11.27, P ¼ 0.01), and that the proportions of genera shared by both regions relative to proportions in SA (but not in NZ) also differs (SA vs. shared genera: G ¼ 11.42, P ¼ 0.009; NZ vs. shared genera: G ¼ 3.55, P ¼ 0.31). They also show that the proportions of genera of different phylogenetic groups within vegetation types differ among corresponding vegetation of the two regions, both in forests (NZ-FO vs. SA-FO: G ¼ 10.63, P ¼ 0.04) and in non-forest vegetation (NZ-NF vs. SA-NF: G ¼ 7.96, P ¼ 0.04). Specifically, pooling all the vegetation types (Table 3) shows that NZ flora has more genera of basal groups ( pteridophytes and gymnosperms) and SA flora has more genera of basal eudicots. Moreover, floras from forests of NZ are more basal (i.e. have higher contributions of pteridophytes and gymnosperms than expected) and floras of non-forest vegetation types from SA have higher contributions of basal eudicots than expected. In terms of evolutionary development (sensu Hawkins et al., 2005), this indicates that the NZ floras are generally of more basal origin and the SA more derived, especially in respect of the forests.

F I G . 3. Ordination of floristic samples of New Zealand (NZ) and the southern Andes (SA) based on CA of generic composition. NZ and SA sample codes are given in Table 1.

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Ezcurra et al. — Floristic Relationships of New Zealand and the Southern Andes DISCUSSION Similarities among vegetation types

F I G . 4. Histograms showing the frequency of genera assigned to seven phylogenetic groups for New Zealand (NZ), southern Andes (SA) and shared genera, for non-forest vegetation (i.e. shrubby and herbaceous plant communities), for forest vegetation, and for the total floras.

The environmental similarities between SA and NZ account for physiognomic similarities in the vegetation, but to account for the physiognomic differences and floristic relationships we need to consider the nature of adjoining regions, past geography and floristic links. The results show that in generic composition the vegetation types of NZ and SA have similarities, but that in general these are not as marked between paired vegetation types of the two study regions as among similar vegetation types within one or the other region. Marked differences between forest floras of both regions could be related, in part, to their origins before the beginning of the Cenozoic, when the southern lands were all united to Antarctica in Gondwana. However, ancestral New Zealand was part of south-east Gondwana, and ancestral South America was part of south-west Gondwana (Raven and Axelrod, 1974; McLoughlin, 2001). Thus, connections to other floras of lower latitudes appear to have imprinted different characteristics to the forests, with New Zealand having genera of Australian and south-east Asian affinities and southern South America having genera of Neotropical affinity, many of which still survive in their present floras (Arroyo et al., 1996; Villagrań and Hinojosa, 1997; Lee et al., 2001; Wardle et al., 2001; Crisp et al., 2004). Our analyses showed that floras of non-forest vegetation types, especially bog, pioneer, alpine and coastal vegetation, were most similar between regions, sharing more than 25 % of their genera. These similarities were especially marked in coastal and bog vegetation of SA, which lie nearest the centroid of NZ in the ordination and cluster with NZ vegetation types in the classification. Many of the shared genera that impart strong physiognomic similarities to equivalent non-forest vegetation on either side of the Pacific include the same or closely related species in NZ and SA, which rules out the possibility of vicariance; 40 of these shared entities are listed by Wardle et al. (2001). Phylogenies that show closely related species in the two regions (e.g. Wagstaff et al., 2002, 2006; Meudt and Simpson, 2006; Sanmartıń et al., 2007) also strongly suggest dispersal. Between New Zealand and Tasmania there is also a similar high incidence

TA B L E 3. Results of G-tests of number of genera in each phylogenetic group in different regions (NZ vs. SA), and in forest vegetation (FO) or non-forest (NF) open vegetation of both regions (FO-NZ vs. FO-SA, and NF-NZ vs. NF-SA). In all cases, þ and 2 signs show that NZ has relatively more or fewer genera in a phylogenetic group than SA NZ vs. SA Phylogenetic groups

G

Pteridophytes and gymnosperms Basal angiosperms and monocots Basal eudicots Rosids and asterids

5.06* þ 1.95 þ 5.04* 2 1.56 2

G-values marked with * are significant at the 0.05 level.

FV-NZ vs. FV-SA P-value 0.024 0.162 0.025 0.211

G 6.07* þ 1.42 þ 3.02 2 3.66 2

P-value 0.014 0.233 0.082 0.056

NF-NZ vs. NF-SA G 2.75 þ 0.49 þ 5.56* 2 0.03 þ

P-value 0.097 0.485 0.018 0.865

Ezcurra et al. — Floristic Relationships of New Zealand and the Southern Andes of shared species among aquatic habitats, coastal environments and wet soils, which has also been related to long-distance dispersal, probably by water birds (Jordan, 2001). Plants of non-forest vegetation types are likely to be transported over oceans, e.g. plants of bogs and coasts can be rafted to shores of nearby lands, and pioneer and alpine vegetation can be carried via avalanches and glaciers on to icebergs. Plants of high elevations also tend to grow at lower elevations at higher latitudes, e.g. plants growing at more than 1000 m a.s.l. in New Zealand and South America, at latitudes lower than 40ºS, can be found at sealevel in Tierra del Fuego, at latitudes greater than 50ºS (Moore, 1983). In addition, many shared genera have zoochorous propagules and can attach to feathers or be transported in the gut of dead, floating birds (Darwin, 1859; Skottsberg, 1936; Moore, 1972), and some have seed that can disperse by floating on water (Godley and Sykes, 1968). For the Northern Hemisphere, Munõz et al. (2004) found that floristic relationships in moss, liverwort, lichen and pteridophyte floras correlated more strongly with connections through wind direction than with geographic proximity. In the Southern Hemisphere, the West Wind Drift and the associated Antarctic Circumpolar Current are also sometimes invoked to explain floristic similarities between South America and New Zealand (e.g. Moore, 1972). Were these systems important dispersal vectors, then eastward dispersal should predominate. A clear example is provided by Hebe, a species-rich New Zealand genus with two species that have reached South American coasts (Moore, 1972; Wagstaff et al., 2002). Nevertheless, most phylogenies for Southern Hemisphere plant groups suggest that westward dispersal against the West Wind Drift has been more common (Sanmartıń et al., 2007). From the Late Cretaceous to the early Cenozoic, Antarctica had a forest flora similar to that now found at higher elevations and latitudes in South America (Poole et al., 2003), and until relatively recently appears to have supported open, tundra-like vegetation (e.g. Ashworth and Cantrill, 2004). So even as late as the Pliocene there may have been unglaciated terrain along the Antarctic coasts or mountains, providing stepping-stones for plants to spread between South America and Australasia and vice versa (Wardle et al., 2001; Ashworth and Cantrill, 2004; Sanmartıń et al., 2007). Differences in proportions of phylogenetic categories

The late Cenozoic climatic changes appear to have affected the biota of the southern landmasses in different ways, according to their different histories and selection pressures. The different proportions of phylogenetic groups could represent not only differences in their original early Cenozoic floras, but also evolutionary radiations and dispersals filtered by these different selective pressures. In Australia, biotas from arid habitats support relatively more derived taxa than forests, suggesting a selective loss of genera from older groups. This has been explained as an inability of many families that evolved under the wetter conditions of the first half of the Cenozoic to adapt

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to regional drying, resulting in major extinctions or, at best, surviving only as relicts in small areas where high rainfall persists (Crisp et al., 2004; Hawkins et al., 2005). The differences in proportions of phylogenetic groups between NZ and SA agree with these predictions. The flora of NZ has a higher contribution of genera of basal groups ( pteridophytes and gymnosperms) overall, and in forest habitats in particular. This may be partly explained through evolutionary radiations in pteridophytes and gymnosperms up to relatively recent times, and less filtering due to the low selective pressure of wet climates and equable temperatures (Lee et al., 2001; Markgraf and McGlone, 2004). However, the large proportion of pteridophytes can also be related to wind dispersal of their spores (Moore, 1972; Munõz et al., 2004). New Zealand became isolated when it rafted from Antarctica and Australia, and its flora was depleted during the Oligocene, when its landmass was reduced to a minimum (Lee et al., 2001). According to some views it became totally submerged, raising the possibility that its flora has resulted entirely through trans-oceanic dispersal (Pole, 1994), in which wind-dispersal of spores could have been important. In contrast, Southern Andean forests have lower proportions of genera in basal groups such as pteridophytes and gymnosperms, which suggests relatively more extinctions within these groups. Many of their families originated and radiated in the mild and humid climates of the Cretaceous and early Cenozoic, and were probably more prone to extinction in the cold, dry environments that appeared in southern South America at the end of the Cenozoic (Neogene). Nevertheless, SA forests still contain many angiosperm woody genera with leaves with entire margins, indicating that they are survivors from lineages of warmer and more equable climates (Aizen and Ezcurra, 2008) that were able to pass through past climatic sieves and endure many environmental transitions, including recent climatic cycles associated with Pleistocene glaciation (Markgraf and McGlone, 2004). The flora of non-forested habitats of NZ in general does not differ significantly from that of corresponding habitats of SA in their representation of phylogenetic groups, except that those from SA have higher contributions of basal eudicots than expected. This suggests that the new high-mountain environments that appeared in both regions at the end of the Cenozoic provided an exceptional opportunity for plants pre-adapted to cold to diversify. This may explain the abundance of alpine genera of derived groups, such as rosids and asterids in both regions (Winkworth et al., 1999). In New Zealand, ancestors of the alpine flora largely arrived by long-distance dispersal late in the Pliocene or Quaternary, whether from the Northern Hemisphere as proposed for Myosotis (Winkworth et al., 2002), or from Australia or South America as proposed for Abrotanella (Wagstaff et al., 2006) and Ourisia (Meudt and Simpson, 2006). Several of these genera diversified rapidly, e.g. the species-rich Hebe (Wagstaff et al., 2002) and Ranunculus (Lockhart et al., 2001) among others (Mark and Adams, 1995; Ferreyra et al., 1998). However, transoceanic dispersal to New Zealand may have resulted in fewer basal eudicot

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genera than in southern South America, where the Andean high-elevation corridor facilitated dispersal from the vast cold, open landscapes of the Northern Hemisphere (Simpson, 1983; Simpson and Todzia, 1990), thereby greatly increasing the diversity of alpine genera. The cold and dry environments that expanded over much of southern South America during the second part of the Cenozoic (Neogene), especially the Patagonian semideserts and the high Andes, provided ample opportunities for evolutionary radiation. The Asteraceae, the largest angiosperm family and typical of open, temperate, frequently dry habitats, has been suggested to have originated in southern South America during Eocene times (Devore and Stuessy, 1995) and is nowadays represented by more than 100 genera in Patagonia and the southern Andes. The Poaceae are also considered to have radiated in open areas during the second part of the Cenozoic, coincident with the rise of grazing mammals (Raven and Axelrod, 1974; Bremer, 2002; Ortiz-Jaureguizar and Cladera, 2006). Temperate regions in the north and south of the New World share many geomorphological and climatic features, being situated at equivalent latitudes and traversed from north to south by the Rocky Mountains and the Andes, which have served both as floristic bridges and barriers. Alhough North and South America developed separately through the first part of the Cenozoic, these mountains connected their temperate regions after the Panama Isthmus closed at the end of the Cenozoic, thereby providing corridors for interchange of taxa (Moore, 1972; Raven and Axelrod, 1974; Simpson, 1983; Simpson and Todzia, 1990; Taylor, 1995). This mutually enriched their floras with angiosperm genera, many of which apparently radiated in open habitats during the second half of the Cenozoic (e.g. Raven and Axelrod, 1974; Devore and Stuessy, 1995), resulting in the derived or ‘modern’ character that seems characteristic of the floras of temperate regions of the New World. In contrast, the higher proportion of genera of basal phylogenetic groups in New Zealand, which imparts a more ‘primitive’ character to its flora, especially in its forests, could reflect New Zealand’s relationship via long-distance dispersal and intervening islands to Southeast Asia, where basal groups are also well represented (Qian, 2001).

S U P PL E M E N TARY I N FOR M AT I O N Supplementary Information for this article is available online at www.aob.oxfordjournals.org and consists of a figure showing ordination of vegetation types of New Zealand and the southern Andes based on PCA of climatic characteristics (temperature and precipitation), and two tables as follows. Table 1: database with a list of 369 vascular plant genera present in New Zealand and the southern Andes and information on their presence/absence in the 20 vegetation types sampled and described in Materials and Methods. Table 2: database with a list of 369 vascular plant genera present in New Zealand and the southern Andes and information on their presence/absence in the 55 vegetation samples.

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