Ecosystem-specific forest management requires comprehension of tree species productivity in managed settings, and how this productivity varies with the ecological determinants of site quality, i.e., the environmental factors that directly affect the growth of plants: light, heat, soil moisture, soil nutrients, and soil aeration. A good understanding of this variation is necessary for making species- and site-specific silvicultural decisions to maximize productivity. Productivity of a given species is usually measured by site index (tree height at 50 years at breast height age). Quantitative relationships between site index and these measures of site quality provide predictive models for estimating site index. Pacific silver fir (Abies amabilis (Dougl. ex Loud.) Forbes) is an important timber crop species in the coastal forests of British Columbia. In relation to climate, its range in southwestern British Columbia extends from sea level to almost timberline, and from the hypermaritime region on western Vancouver Island to the subcontinental region on the leeward side of the Coast Mountains. In relation to soils, its range extends from slightly dry to wet sites and from very poor to very rich sites. In view of this relatively wide climatic amplitude, a large variability in productivity can be expected. It is particularly important to consider the growth performance of Pacific silver fir when decisions are made regarding whether or not to cut stands on high-elevation sites. In the study summarized here, relationships between Pacific silver fir site index and selected ecological measures of site quality were examined, and site index models using these measures as predictors were developed.

In the wetter climates associated with the coastal forests of the Pacific Northwest, coarse woody debris (CWD) accumulations in the form of snags, downed boles, and large branches can be large in natural forest ecosystems. Although maintaining organic matter for sustainable site productivity is not in dispute, the importance of CWD as a source of soil organic matter is questionable. Forest managers attempting to optimize timber production need to know how CWD affects short-term forest tree growth and productivity. This study addresses the question of the immediate value of CWD for growth of mature (90 year old) western hemlock (Hw). Because of practical difficulty with mature trees growing in different substrates, we utilized fine root distribution or proliferation, as an indicator of important substrates.

In BC, it is required that harvested areas be regenerated with a mixture of tree species whenever appropriate to the site. This policy is based upon the assumption that increases in stand productivity, reliability, and/or biodiversity can be achieved in mixed-species stands. However, the knowledge justifying this policy is at best incomplete. Differences in forest productivity of mixed-species stands have been attributed mostly to competition. However, an increasing number of studies are providing evidence to support alternate theories, in which positive plant interactions play a major role. Positive plant interactions are divided into two components: (i) competitive reduction through structural and physiological differences in above and below ground structures, and (ii) facilitation through any positive effect on the growing environment of one plant species by another. These theories have yet to be tested in forest ecosystems. The objectives of this study, with respect to naturally established, unmanaged, second-growth stands of western hemlock (Hw) (Tsuga heterophylla (Raf.) Sarg.), western redcedar (Cw) (Thuja plicata Donn ex D. Don in Lamb.), and their mixtures, were: (1) to review the mechanisms of positive plant interactions and their potential to occur in these mixtures, and (2) to compare the productivity of these three stand types, using relative and absolute yield.

The three major components in the site classification of the biogeoclimatic ecosystem classification system are: climatic regimes, soil moisture regimes (SMRs) and soil nutrient regimes (SNRs). Both SMRs and SNRs can be identified in the field using soil characteristics and indicator plants. In the case of SMRs a quantitative classification was also developed that allow comparison of SMRs in different subzones. However, similar quantitative classification has not yet been developed for SNRs. This pamphlet summarizes and compares the results of several regional studies conducted in different biogeclimatic zones. Each of theses studies aimes to develop a quantitative SNR classification (Table 1). The comparison will examine: (1) how well the field-based classification matches quantitative classification, and (2) which direct measures distinguish best between field-identified SNRs.

<p>Nearly one-third of the world&rsquo / s tortoises live in South Africa, but little is known about their habitat requirements and feeding ecology. Chersina angulata, the angulate tortoise, is endemic to&nbsp / southern Africa, with a wide distribution along the western and southern coasts. Because this tortoise occupies a number of different habitat types, it has always been considered a generalist&nbsp / herbivore, although little is known about its&nbsp / diet and other needs. This study evaluates the habitat characteristics and feeding ecology of C. angulata at two study sites in the southwestern&nbsp / &nbsp / &nbsp / Cape, the West Coast National Park (WCNP) and Dassen Island (DI). The WCNP is a large conserved area in the Fynbos biome, along the southwestern coast of South Africa, whereas DI is a&nbsp / small offshore island with low floral and faunal diversity, just south of the WCNP. The efficacy of three methods used to study the feeding ecology of herbivores, focal observations, macroscopic faecal analysis and histological analysis of scats, was evaluated. Plant cover, species diversity, and the variety of growth forms were substantially larger at the WCNP than on DI.&nbsp / In the WCNP, shrubs and grasses were the dominant growth forms but the vegetation also included herbs, succulents, restios, sedges and parasitic plants. A few perennial species such as&nbsp / the grass Ehrharta villosa, shrubs such as Helichrysum niveum, Nylandtia spinosa and Rhus spp., and succulents such as Carpobrotus edulis and Ruschia spp., provided most of the plant&nbsp / cover. DI had a depauperate flora, consisting of succulents and herbs, and ephemeral plants contributed more than perennials did to plant cover throughout the year. The succulents Mesembryanthemum crystallinum and Tetragonia fruticosa provided most of the cover on DI. Angulate tortoises are herbivores and 72 diet plants in 32 plant families were identified to the&nbsp / species or genus level. Several diet species, however, could not be identified. In&nbsp / addition to angiosperms, the tortoises&rsquo / diet included mosses, mushrooms, insects,snails and animal faeces.&nbsp / The most important growth forms in the diet were herbs and grasses. The diet of the WCNP tortoises was more diverse than the diet of DI tortoises, but the number of principal food items in&nbsp / the diet did not differ between the two sites. Over an annual cycle, WCNP tortoises had four principal food plants while DI tortoises had five principal food plants. At both sites, principal food&nbsp / &nbsp / plants changed with the season and few plants remained principal food items in more than one season. Cynodon dactylon was a principal food item in three of the four seasons in the WCNP, whereas Trachyandra divaricata was a principal food plant each season on DI. Most principal food plants were grass or herb species but the sedge Ficinia nigrescens, and a succulent that&nbsp / could be identified only to the family level (Aizoaceae), featured strongly in the spring diets of DI and WCNP tortoises, respectively.&nbsp / The three study methods did not provide the same type or quality of information about the feeding ecology of angulate tortoises. The small size and wary nature of angulate tortoises compromised focal studies because it was often not possible to see&nbsp / what the tortoises ate. This method, however, provided the interesting observation that rabbit&nbsp / faecal pellets contributed nearly 30% to summer and autumn diets on DI when food was scarce.&nbsp / Rabbit faeces may not only provide a source of nutrients but may also supplement the microflora, required to digest cellulose, in the tortoises&rsquo / guts. Macroscopic evaluation of the tortoises&rsquo / &nbsp / scats appeared to be an ineffective method to identify diet plants, and the bulk of the scat mass could not be identified. This indicates&nbsp / that angulate tortoises either selected food low in fibrous&nbsp / content or that the digestive system of the tortoises dealt efficiently with tough plant material. The macroscopic method was the only method that highlighted the large contribution of&nbsp / fruits / seeds to the diet of angulate tortoises. Since the tortoises digested many seeds only partially, or not at all, C. angulata is potentially an important agent of seed dispersal in the southwestern Cape. The macroscopic study showed that on DI, sand made up 28% of the scat mass in spring, whereas sand never made a substantial contribution to the scat composition of WCNP tortoises. Lithophagy may be an important strategy in a depauperate habitat, such as DI, because the abrasive action of sand may help with the digestion of tough plants, or the sand may&nbsp / provide the tortoises with important minerals that are deficient in their food plants.The histological analysis of scats provided the most comprehensive diet list for C. angulata. Selection indices&nbsp / based on data from the histological analysis indicated that angulate tortoises were highly selective in their food choice. Most of the principal food items were selected out of proportion to their&nbsp / availability and the tortoises avoided the most abundant plants in their habitats. Several factors, such as palatability, accessibility and profitability, may have influenced their food choice. The proportional similarity indices for WCNP and DI tortoises, respectively, were 0.31 and 0.16, confirming that C. angulata is a food specialist and not a food generalist as was previously thought. This factor should be considered in the management of this species and in future conservation planning of its habitat.&nbsp / &nbsp / </p>

Habitat fragmentation and biological invasions are widely considered to be the most significant threats to global biodiversity, and synergistic interactions between these processes have the potential to cause even greater biodiversity loss than either acting alone. The objective of my study was to investigate the effects of fragmentation on plant communities in native forest fragments, and to examine potential interactions between these effects and invasions by exotic plants at multiple spatial scales. I examined edge, area and landscape effects on plant invasions using empirical data from fragmented landscapes on the West Coast of New Zealand. My research revealed significant interactions between the amount of native forest cover in the landscape and the strength of edge and area effects on plant communities in forest fragments. The dominance of exotic plants in the community was highest at forest edges and decreased towards fragment interiors, however the interiors of very small fragments were relatively more invaded by exotic plants than those in larger fragments, reflecting a significant interaction between edge and area effects. Similarly, exotic dominance increased in more heavily deforested landscapes, but this effect was only apparent in very small fragments (<2 ha). The combined effects of small fragment size and low forest cover in the landscape appear to have promoted invasions of exotic plants in very small remnants. I explored the mechanisms underlying edge-mediated invasions in forest fragments and examined whether propagule availability and/or habitat suitability may be limiting invasions into fragments. Experimental addition of exotic plant propagules revealed that landscape forest cover interacted with edge effects on germination, growth and flowering rates of two short-lived, herbaceous species, and this appeared to be driven by elevated light and soil phosphorus levels at edges in heavily deforested landscapes. I also examined the role of traits in influencing plant responses to forest fragmentation. Different traits were associated with exotic invasiveness in edge and interior habitats of forest fragments, indicating that the traits promoting invasiveness were context dependent. Traits also had a major influence on responses of native plants to forest fragmentation, with generalist species appearing to benefit from fragmentation, as they can utilise both forest and open habitats, whereas native forest specialists have been negatively impacted by fragmentation.

New Zealand forests have been reduced and degraded by gross removal, logging, and the effects of mammals introduced by Polynesian and European settlers. These changes increase the value of the remaining forests, so information on the effects of these disturbances will be useful to inform the management of forest protection. Integrated measurements of C and N cycling within forests can be obtained using foliar stable isotope ratios, which may detect differences between forests resulting from natural or anthropogenic disturbances. This thesis characterises the stable isotopic composition distribution and likely drivers of isotopic variation of vegetation in several central South Island forests, and provides a baseline for future ecological New Zealand studies of present and pre-human vegetation. The largest detected stable isotope variation in modern leaf material was that of δ15N values between the eastern and western podocarp-broadleaf forests. This variation was probably controlled by the lower soil N availability associated with the high rainfall of western forests causing low δ15N values (-8.5 ± 3.5 ‰) relative to an eastern forest (+1.6 ± 1.3 ‰) and global temperate forests (average -2.8 ± 2.0 ‰ (Martinelli et al. 1999)). The significant but slightly higher mean δ15N (0.6 ‰) of a historically selectively logged forest (Saltwater Forest) in comparison to the mean in an unlogged forest (Okarito Forest), on the West Coast, could be attributed to either alteration to N cycling from logging, site differences in topography, or local soil N differences between the forests. Although δ13C showed no significant geographical variation, the well-described ‘canopy effect’ was observed in all modern forests, manifested as a positive covariation between δ13C and vegetation height. Similarly, large taxon-specific differences were observed between δ15N and δ13C values in both modern and fossil leaves. Well-preserved fossil leaves, from sediments c. 4500 years B.P in Pyramid Valley, North Canterbury, had higher δ13C (4.2 ‰) and δ15N (2.5 ‰) values than modern vegetation from Riccarton Bush, Christchurch. The difference between ecosystems spanning several millennia probably reflects ecosystem-scale changes in C and N cycling within New Zealand forests following human arrival, particularly from the degradation caused by invasive animals.

Current meter records from a long term mooring site on the continental slope off the west coast of Vancouver Island, British Columbia, Canada are used to investigate the scales of variability of the subsurface California Undercurrent and its relation to possible driving mechanisms. Observed along the west coast of North America from Baja California to Vancouver Island, the California Undercurrent is part of the California Current System, a typical basin-scale eastern boundary circulation system. Of the four instruments at nominal depths of 35, 100, 175, and 400 m, the upper two show seasonally reversing flow, while the 175 m instrument registers a year-round poleward flow. The deepest current meter, located approximately 100 m above the bottom, reflects the influence of a nearby submarine canyon. The flow at 100 and 175 m depths, as well as the water properties sampled in the region with CTD casts, are characteristic of the temporal and spatial variability of the California Undercurrent over the continental slope off central and southern Vancouver Island. The correlation of the 175 m flow with local atmospheric forcing (wind stress) in the low-frequency band (periods of months) is higher than with ocean-wide climatic indices, suggesting that regional processes play a key role in the forcing of the subsurface flow.

Habitat fragmentation and biological invasions are widely considered to be the most significant threats to global biodiversity, and synergistic interactions between these processes have the potential to cause even greater biodiversity loss than either acting alone. The objective of my study was to investigate the effects of fragmentation on plant communities in native forest fragments, and to examine potential interactions between these effects and invasions by exotic plants at multiple spatial scales. I examined edge, area and landscape effects on plant invasions using empirical data from fragmented landscapes on the West Coast of New Zealand. My research revealed significant interactions between the amount of native forest cover in the landscape and the strength of edge and area effects on plant communities in forest fragments. The dominance of exotic plants in the community was highest at forest edges and decreased towards fragment interiors, however the interiors of very small fragments were relatively more invaded by exotic plants than those in larger fragments, reflecting a significant interaction between edge and area effects. Similarly, exotic dominance increased in more heavily deforested landscapes, but this effect was only apparent in very small fragments (<2 ha). The combined effects of small fragment size and low forest cover in the landscape appear to have promoted invasions of exotic plants in very small remnants. I explored the mechanisms underlying edge-mediated invasions in forest fragments and examined whether propagule availability and/or habitat suitability may be limiting invasions into fragments. Experimental addition of exotic plant propagules revealed that landscape forest cover interacted with edge effects on germination, growth and flowering rates of two short-lived, herbaceous species, and this appeared to be driven by elevated light and soil phosphorus levels at edges in heavily deforested landscapes. I also examined the role of traits in influencing plant responses to forest fragmentation. Different traits were associated with exotic invasiveness in edge and interior habitats of forest fragments, indicating that the traits promoting invasiveness were context dependent. Traits also had a major influence on responses of native plants to forest fragmentation, with generalist species appearing to benefit from fragmentation, as they can utilise both forest and open habitats, whereas native forest specialists have been negatively impacted by fragmentation.

Current meter records from a long term mooring site on the continental slope off the west coast of Vancouver Island, British Columbia, Canada are used to investigate the scales of variability of the subsurface California Undercurrent and its relation to possible driving mechanisms. Observed along the west coast of North America from Baja California to Vancouver Island, the California Undercurrent is part of the California Current System, a typical basin-scale eastern boundary circulation system. Of the four instruments at nominal depths of 35, 100, 175, and 400 m, the upper two show seasonally reversing flow, while the 175 m instrument registers a year-round poleward flow. The deepest current meter, located approximately 100 m above the bottom, reflects the influence of a nearby submarine canyon. The flow at 100 and 175 m depths, as well as the water properties sampled in the region with CTD casts, are characteristic of the temporal and spatial variability of the California Undercurrent over the continental slope off central and southern Vancouver Island. The correlation of the 175 m flow with local atmospheric forcing (wind stress) in the low-frequency band (periods of months) is higher than with ocean-wide climatic indices, suggesting that regional processes play a key role in the forcing of the subsurface flow.