Bruce R. Burns

Fire-induced dynamics of Araucaria araucana-Nothofagus antarctica forest in the southern Andes.

The emergent conifer Araucaria araucana (Mol.) K. Koch and the small deciduous broadleaved tree Nothofagus antarctica (Forst.) Oerst. occur as mixed post-fire stands in south-central Chile and Argentina. Both species are adapted to survive fire. Adaptations of A. araucana include thick bark, sprouting from epicormic buds and protected terminal buds on branches. N. antarctica resprouts vigorously after fire with multiple shoots. This study investigated the dynamics of this community, particularly in relation to fire. Recently burnt stands were examined for size-related response to fire. All A. araucana < 30 cm d.b.h. were killed with larger trees surviving. The size of these surviving A. araucana is probably related to fire intensity. Stand disturbance histories, population size and age distributions, diameter growth rate patterns and spatial relationships of different size classes, within and between species, were examined in intact stands. Most of these stands contained evidence of past fire. Within the first decade after fire, A. araucana (but not N. antarctica) seedlings or root suckers began to establish beneath the resprouted N. antarctica canopy. However, establishment was spatially clustered around surviving female A. araucana or abandoned caches of unknown seed predators. Once established, A. araucana grew through the sparse N. antarctica canopy, eventually overtopping it. This suppression of N. antarctica, if uninterrupted for more than 150 years, may lead to pure stands of A. araucana. However, fires are common in this region and both species possess attributes that promote accidental fires once ignited. Fire usually leads to formation of stands with clustered 10-20 m tall A. araucana over a 2-5 m tall N. antarctica subcanopy. Therefore, fire acts as a medium of species co-existence between a vigorously sprouting, shade-intolerant species (N. antarctica), and one that partly survives fire above-ground and is more shade-tolerant (A. araucana). The history of fire frequency and intensity on a site largely determine population structures for these species in mixed stands.

Differences in benthic fauna and sediment among mangrove (Avicennia marina var. australasica) stands of different ages in New Zealand

Management of coastal environments requires understanding of ecological relationships among different habitats and their biotas. Changes in abundance and distribution of mangroves, like those of other coastal habitats, have generally been interpreted in terms of changes in biodiversity or fisheries resources within individual stands. In several parts of their range, anthropogenically increased inputs of sediment to estuaries have led to the spread of mangroves. There is, however, little information on the relative ecological properties, or conservational values, of stands of different ages. The faunal, floral and sedimentological properties of mangrove (Avicennia marina var. australasica) stands of two different ages in New Zealand has been compared. Older (>60 years) and younger (3-12 years) stands showed clear separation on the basis of environmental characteristics and benthic macrofauna. Numbers of faunal taxa were generally larger at younger sites, and numbers of individuals of several taxa were also larger at these sites. The total number of individuals was not different between the two age-classes, largely due to the presence of large numbers of the surface-living gastropod Potamopyrgus antipodarum at the older sites. It is hypothesized that as mangrove stands mature, the focus of faunal diversity may shift from the benthos to animals living on the mangrove plants themselves, such as insects and spiders, though these were not included in the present study. Differences in the faunas were coincident with differences in the nature of the sediment. Sediments in older stands were more compacted and contained more organic matter and leaf litter. Measurement of leaf chemistry suggested that mangrove plants in the younger stands were able to take up more N and P than those in the older stands

THE IMPORTANCE OF GAP PROCESSES IN THE DEVELOPMENT AND MAINTENANCE OF OAK SAVANNAS AND DRY FORESTS

1 We examined the dynamics of a Quercus-dominated dry forest-savanna complex in the Ozark Highlands of the central United States, focusing on regeneration patterns within gaps. The study area includes one of very few temperate Quercus ecosystems not degraded by fire suppression, logging or excessive grazing. 2 We compared patterns of tree seedling establishment, tree height growth and postfire survival in gaps between savanna, found only on south and west aspects in our study area, and dry forest, found only on north and east aspects, to determine which factors contributed to maintaining structural differences. 3 Canopy gaps constituted 42% of savanna area compared with 17% for dry forest. Mean canopy gap size in savanna was 316 m2 compared with 185 m2 for dry forest, but gap sizes were highly variable and the difference was not significant. Remnants of canopy trees were found in 37 of 38 gaps, indicating that gaps in both savanna and dry forest can usually support trees. 4 Savanna and dry forest gaps were generally favourable for seedlings and growth of small trees. Seedlings of most woody species were widespread in the understoreys of both savanna and dry forest but were more abundant in gaps than under closed canopies. Species had different height growth patterns depending on site, with growth rates ordered as follows: Quercus velutina in savanna > Q. velutina in forest > Q. stellata in forest > Q. stellata in savanna. Site differences were significant for Q. stellata but not for Q. velutina. 5 Tree survival in two surface fires was significantly lower in gaps in savanna compared with gaps in dry forest. Survival within individual gaps was inversely related to grass cover. In savanna, survival of small trees (2 5-7 cm d.b.h.) ranged from >80% for gaps with 90% grass cover. 6 Canopy gaps in the Ozarks are created primarily by windfall and drought-related dieback, but fire influences the timing and rate of gap infilling. Understanding the interactions among these disturbances may help clarify the dynamics of many temperate woodlands once dominated by surface fires.

Vegetation change along a geothermal stress gradient at the Te Kopia steamfield

Naturally thermotolerant vegetation in New Zealand is concentrated in approximately 39 geothermally heated areas totalling only 580 ha scattered along the 300 km length of the Taupo Volcanic Zone. Relationships between composition and structure of vegetation and environment were analysed at the comparatively large (95 ha) and unmodified Te Kopia geothermal steamfield. Vascular vegetation was mostly influenced by a strong gradient in soil temperature, ranging at 15 cm depth from 15°C to 90°C across the steamfield. Dominant species changed from evergreen, broadleaved forest at the cool end of this gradient to dominance on increasingly hot soils by myrtaceous and epacrid (southern heath) shrubs with small needle‐like leaves and shallow roots. While differences in cryptogam composition were mostly associated with spatial variation in soil temperature, they were also significantly influenced by soil acidity and Al concentration. All soils sampled along the gradient had low fertility, high acidity, and high lev...

The Use and Potential of Pest-Proof Fencing for Ecosystem Restoration and Fauna Conservation in New Zealand

The use of fences designed to exclude all exotic mammals from natural habitats is a recent conservation strategy being implemented on the main islands of New Zealand for ecosystem restoration and fauna conservation. As well as contributing to conservation outcomes, it has focused and galvanized public involvement in conservation. This chapter reviews the development of conservation fencing in New Zealand, the extent and distribution of conservation areas based on pest-proof fences, the experience of conservation managers with these fences and their current contribution. Between 1999 and 2009, 28 areas covering a total of 8,396 ha have been enclosed by 113 km of pest-proof fences and cleared of mammalian pests. Fenced areas have been located to exploit landscape features such as peninsulas, catchment boundaries, or fragments. Over this 10-year period, 63 translocations (mostly reintroductions) of 40 species have been made to these sites. This is similar to the number of translocations made to pest-free off-shore islands in New Zealand over the same time period. Notable species translocated to or managed within pest-proof fenced areas include: (1) several highly threatened, in which protection by fences is a key strategy to prevent extinction; (2) seabirds at new or existing nesting sites; and (3) several species reintroduced to the main islands of New Zealand after a substantial absence. The removal of pest mammals from the ecosystems enclosed by pest-proof fences is leading to changes in the composition of residual communities, and increasing the abundance of pest-sensitive populations as they are released from previous limits imposed by pest predation or herbivory. Failure to eradicate them or reinvasions of species such as mice Mus musculus are, however, an ongoing challenge.

Dynamics of upland podocarp/broadleaved forest on Mamaku Plateau, central North Island, New Zealand.

Forest composition was examined on one hectare of upland Dacrydium cupressinum‐Prumnopitys taxifolia/Weinmannia racemosa‐Beilschmiedia tawa forest on south Mamaku Plateau, central North Island, New Zealand, a site of catastrophic volcanic disturbance c 1900 years ago The phasic model (gap, building, mature) of the forest growth cycle was used Mean age of sampled stems differed significantly between gap (13 yr), building‐phase (68 yr), and mature forest (252 yr), which comprised 10%, 50%, and 40% respectively of the area and persisted on average for 20 yr (gaps) and 60 yr (building phase) ‘Expanded’ gaps averaged 0 008 ha in size Tree ferns ‐ mostly Dicksoma squarrosa and Cyathea smithn ‐ were numerically dominant throughout, and dominated basal area in younger ( 80 yr) forest Current diameter growth rates among broadleaved species followed the ranking Griselinia littoralis, Elaeocarpus dentatus>B tawa>Ixerba brexioides, W racemosa, and were si...

Vegetation-environment relationships at Waipoua Forest, Northland, New Zealand

Abstract The Waipoua Forest Sanctuary and Waipoua Kauri Management and Research Area together form a large (approx. 13 000 ha), continuous protected natural area on the west coast of Northland, New Zealand. This reserve complex contains comparatively unmodified examples of Northland forest including large areas dominated by the tall conifer kauri (Agathis australis). It also includes substantial areas of “heathland” scrub dominated by manuka (Leptospermum scoparium) and Dracophyllum lessonianum. Landscape-scale vegetation patterns are described from 294 vegetation samples located in both forest and scrub, and their relationships with the environment are examined using indirect gradient analysis techniques. Results suggest that vegetation patterns in both forest and scrub are determined largely by topographically linked variation in soil fertility and soil moisture and by altitudinally determined temperature and precipitation gradients. Conifers tend to occur on the infertile soils often found on ridges, w...

Changes in structure and composition over fifteen years in a secondary kauri (Agathis australis)-tanekaha (Phyllocladus trichomanoides) forest stand, Coromandel Peninsula, New Zealand

Abstract Changes in structure and composition were assessed after an interval of 15 years in an old secondary Agathis australis (kauri) — Phyllocladus trichomanoides (tanekaha) stand on Coromandel Peninsula, North Island, New Zealand. Stand structure was intermediate between previously described young and mature A. australis stands. Agathis australis, mostly 100–200 years old, had fastest diameter increment (4.3 mm yr−1 in trees ≥25 cm d.b.h.) and contributed almost all the stand basal area increment; its seedling population contracted and larger trees were developing mature crowns. Phyllocladus trichomanoides, also mostly 100–200 years old, had slower diameter increment (2.2 mm yr−1) and contributed most of the remaining stand basal area increment; its seedling population also contracted. Weinmannia silvicola (towai), probably of similar age, incurred mortality at all sizes while Kunzea ericoides var. ericoides (kanuka), 40–80 years old, incurred most mortality in large saplings and small trees. Stand ba...

Predicting plant invasions under climate change: are species distribution models validated by field trials?

Climate change may facilitate alien species invasion into new areas, particularly for species from warm native ranges introduced into areas currently marginal for temperature. Although conclusions from modelling approaches and experimental studies are generally similar, combining the two approaches has rarely occurred. The aim of this study was to validate species distribution models by conducting field trials in sites of differing suitability as predicted by the models, thus increasing confidence in their ability to assess invasion risk. Three recently naturalized alien plants in New Zealand were used as study species (Archontophoenix cunninghamiana, Psidium guajava and Schefflera actinophylla): they originate from warm native ranges, are woody bird-dispersed species and of concern as potential weeds. Seedlings were grown in six sites across the country, differing both in climate and suitability (as predicted by the species distribution models). Seedling growth and survival were recorded over two summers and one or two winter seasons, and temperature and precipitation were monitored hourly at each site. Additionally, alien seedling performances were compared to those of closely related native species (Rhopalostylis sapida, Lophomyrtus bullata and Schefflera digitata). Furthermore, half of the seedlings were sprayed with pesticide, to investigate whether enemy release may influence performance. The results showed large differences in growth and survival of the alien species among the six sites. In the more suitable sites, performance was frequently higher compared to the native species. Leaf damage from invertebrate herbivory was low for both alien and native seedlings, with little evidence that the alien species should have an advantage over the native species because of enemy release. Correlations between performance in the field and predicted suitability of species distribution models were generally high. The projected increase in minimum temperature and reduced frosts with climate change may provide more suitable habitats and enable the spread of these species.

Species assemblage patterns around a dominant emergent tree are associated with drought resistance

Water availability has long been recognized as an important driver of species distribution patterns in forests. The conifer Agathis australis (D. Don) Lindl. (kauri; Araucariaceae) grows in the species-rich forests of northern New Zealand. It is accompanied by distinctive species assemblages, and during summer the soil beneath A. australis is often significantly drier than soils beneath surrounding broadleaved angiosperm canopy species. We used a shade house dry-down experiment to determine whether species that grow close to A. australis differed in drought tolerance physiology compared with species that rarely grow close to A. australis. Stomatal conductance (g(s)) was plotted against leaf water potential (ψ) to identify drought tolerance strategies. Seedlings of species that occur in close spatial association with A. australis (including A. australis seedlings) were most resistant to drought stress, and all displayed a drought avoidance strategy of either declining gs to maintain ψ or simultaneous declines in g(s) and ψ. The species not commonly occurring beneath A. australis, but abundant in the surrounding forest, were the most drought-sensitive species and succumbed relatively quickly to drought-induced mortality with rapidly declining gs and ψ values. These results were confirmed with diurnal measurements of g(s) and assimilation rates throughout the day, and leaf wilting analysis. We conclude that the varied abilities of the species to survive periods of drought stress as seedlings shapes the composition of the plant communities beneath A. australis trees. Furthermore, forest diversity may be impacted by climate change as the predicted intensification of droughts in northern New Zealand is likely to select for drought-tolerant species over drought-intolerant species.