Este trabalho discute a variabilidade dos fluxos de energia à superfície e de CO2 sobre uma área de Cerrado Sensu stricto no interior de São Paulo, e de uma área de ecótono Floresta-Cerrado (sazonalmente alagável) no Estado do Tocantins. Foram utilizadas medidas micrometeorológicas médias de 30 min, do clima (temperatura e umidade do ar, precipitação, velocidade do vento), dos fluxos de radiação (solar, PAR, saldo de radiação) e fluxos turbulentos de calor sensível, latente e CO2, coletadas no Cerrado durante o período de 2001 a 2003, e no ecótono durante Outubro de 2003 a Setembro de 2004. O ecótono e o Cerrado estão sob solos arenosos, homogêneos, com alta capacidade de infiltração e baixa de armazenamento. O Cerrado s.s. mostrou-se um ecossistema com forte sazonalidade da capacidade fotossintética, do Albedo-PAR e dos fluxos atmosféricos de CO2. Há uma fase de sumidouro e outra de fonte de CO2, corroborando os dados da literatura. Na escala da variabilidade interanual, as variações dos estados funcionais do Cerrado, como sumidouro ou fonte de CO2, foram fortemente dependentes das variações da precipitação e da temperatura mínima. No ecótono Floresta-Cerrado, a fase de inundação induz à uma diminuição gradual da respiração do sistema e da produtividade primária. A diminuição na produtividade ocorre com um atraso de ~45 dias, que poderia ser um tempo de assimilação e tolerância do sistema ao estresse induzido por anóxia. A redução da respiração do ecossistema ocorre ao passo que no regime alagado as perdas de CO2 ocorrem por evasão da superfície de água livre, um processo que aparentemente tem uma fonte de emissão menor que os processos de respiração do solo em condições secas. Durante a maior parte da inundação o ecótono continua a manter-se como um sumidouro de CO2 atmosférico durante, ao menos, 3 meses. O parâmetro RUE do ecótono foi cerca de 5 vezes maior do que o do Cerrado. A diferença de eficiência se deve possivelmente ao maior índice de área foliar das formações florestais da transição Floresta-Cerrado. A funcionalidade é controlada por fatores ambientais de maior escala que as locais. No caso do Cerrado s.s. há uma forte dependência do regime de chuvas e da temperatura mínima. No caso do ecótono Floresta-Cerrado, a suscetibilidade parece ser uma função do tempo de inundação. / This work discusses the energy and CO2 flux variability over a Cerrado Sensu stricto, in São Paulo state, Brazil, and over a seasonally inundated Forest-Cerrado ecotone in Tocantins state, Brazil. Micrometeorological measurements (30 minute average) of weather (temperature, relative humidity, precipitation and wind speed), radiation fluxes (solar radiation, PAR and net radiation), and CO2, latent and sensible heat turbulent fluxes were made for the Cerrado from 2001 to 2003. Measurements for the ecotone were made from October 2003 to September 2004. Both environments have sandy, homogeneous soils, with high infiltration capacity and low water storage. Cerrado s.s. showed strong seasonality for photosynthetic capacity, Albedo-PAR and CO2 atmospheric fluxes. As seen in other works, the Cerrado has both a CO2 sink and a CO2 source phase. These are strongly dependent on the precipitation and minimal temperature. Inundation of the Forest-Cerrado ecotone results in a gradual decrease in the system’s respiration and primary productivity. A lag of approximately 45 days is seen in the primary productivity reduction. This could represent the system’s resistance and tolerance due to anoxia stress. Ecosystem respiration in the inundated period is lower than in the dry period, apparently due to the lower CO2 outflux from the free water surface, in comparison with the CO2 flux from the soil. During most of the inundation period, the ecotone acts as a sink for CO2, for at least 3 months. The RUE for the ecotone was proximately 5 times higher than the Cerrado. This is probably due to the higher leaf area index of the forest area in the ecotone. The functionality of both biomes is controlled by larger scale environmental factors, as opposed to local factors. The Cerrado s.s. has a strong dependence precipitation and minimal temperature. The Forest-Cerrado ecotone shows a high dependence on the length of the inundated period.

Trembling aspen (Populus tremuloides Michx.) is one of the most common tree species in the boreal and temperate forests of North America. It grows on many different sites and associates with a variety of tree species. In BC, aspen is frequent throughout all submontane and montane continental forested zones. Relationships between environmental factors and forest productivity have been the subjects of many studies. Most of these studies, using various topographic, soil, physical and chemical properties as independent variables, had limited success in accounting for the variation in SI over a large geographic area. The objectives of this study were (1) to quantify relationships between aspen SI and environmental factors at two spatial scales, and (2) to develop predictive SI models from easily measurable environmental factors.

The structure of a forest stand is characterized by: (a) species composition, (b) age, (c) size (diameter and height), and (d) spatial (horizontal and vertical) arrangement of the trees. Depending on the species, site, and disturbance history, the stand structure varies with time, thus providing a snapshot of a particular development stage. Research on growth and stand structure has shown that the spatial distribution of trees is one of the key determinants of stand productivity. Forest inventories and ecological surveys carried out in British Columbia (BC) have shown that the structure of naturally established, unmanaged stands varies from simple (single-species, single-storied, and even-aged) to complex (multi-species, multi-storied, and uneven-aged). Only a few studies have quantitatively characterized this range of structural complexity, with nearly all studies focusing on old-growth stands. BC forest policy requires that harvested areas be regenerated with a mixture of tree species whenever a mixture is suited to the site. This policy is based upon the assumption that under appropriate conditions, increases in stand productivity, reliability, and/or biodiversity can be attained in mixed-species stands. This assumption has not yet been tested for forest ecosystems. One mechanism by which different tree species can reduce crown competition for light is through vertical separation (the development of multiple canopy strata). Canopy stratification is not easily recognized in mixed-species stands, particularly when species have similar shade tolerance and height growth patterns, and no quantitative methods have been developed to detect stratification. The diameter frequency distribution of two-storied stands have been characterized by inverted J-shaped as well as modal curves. Although it would be more appropriate to characterize stand structure by height frequency distributions, these distributions have not been developed. We suggest that (i) a stand is stratified if there are distinct, quantitatifiable modes in the size distribution; either diameter, height, or crown height, and (ii) height or crown height distributions will be the most sensitive measures. To characterize the structure of western hemlock (Tsuga heterophylla (Raf.) Sarg.) (Hw) and western redcedar (Thuja plicata Donn ex D. Don in Lamb.) (Cw) second-growth stands, and to investigate its influence on tree growth, we (1) described and compared size (diameter, height, and crown height) frequency distributions in single- and mixed-species stands, (2) determined whether mixed-species stands develop a stratified canopy, and (3) examined whether interactions between hemlock and redcedar affect tree growth.

Thesis (MScFor)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: In South Africa fertilizer applications at establishment is a common practice in the forestry industry. Recommendations are based on past research with conventional sources (CV) and as a result there have only been slight improvements in additional plantation production over recent years. The objective of this study was to investigate initial stand responses in terms of leaf are index (LAI), foliar nutrient content, biomass index (BI) and volume growth to the application of controlled release fertilizers (CRF) at re-establishment. Nitrogen (N), phosphorus (P) and potassium (K) were applied in a three way factorial combination to Pinus radiata at planting on a site in the Western Cape. The design was replicated five times across the study area. N (CRF) and P (CV) were applied in a two way factorial combination at planting to two Eucalyptus grandis x urophylla hybrids and Eucalyptus dunnii across three sites, one ex-agricultural and two re-establishment sites, on the Zululand coastal plain and the Midlands region. The design was replicated nine times on each study site. Harvesting residues were burnt on the eucalypt sites prior to establishment and may have had an impact on the responses found. An outbreak of Fusarium circinatum on the P. radiata site resulted in unexpected and extremely variable responses. An attempt to quantify the effect of the disease had limited success. The mean BI of the control treatment reached 25. The best CV and CRF treatments yielded improvements of 42 % and 83 % in BI over the control respectively, with only the CRF treatment difference being significant. Foliar analysis results revealed marginal to deficient concentrations of P and Mg being alleviated by the treatments in question. On the KZN Zululand sites there was a marked response of the hybrids to N with P having an additive effect on volume growth, LAI and foliar N content. Application of 120 g N and 20 g P per tree on the ex-agriculture site produced a volume of 8 m3 ha-1 at one year of age, a significant increase of 118 % and 80 % over the control and best CV treatment respectively. Application of 80 g N and 20 g P per tree, on the re-establishment site, yielded a volume of 24.6 m3 ha-1 at one year which equates to a significant 39 % and insignificant 7 % additional volume at one year over the control and best CV treatment respectively. A non-significant suppressive effect was found with 20 g CV P application only. At the KZN Midlands site, the major early response in height were to P application. Applications of 20 g CV P per tree, resulted in a mean height of 162.6 cm at seven months of age, a significant 28 % higher than the control. There was no significant effect of 80 g CRF N and 20 g CV P per tree respectively. CRF N applications up to 120 g per tree provide additional growth over recommended CV applications on coastal Zululand sites with low organic carbon (OC) content. On the KZN Midlands site with higher OC and clay content, early responses were limited to P fertilization only regardless of the fertilizer source. / AFRIKAANSE OPSOMMING: Dit is algemene praktyk in die Suid Afrikaanse bosbou industrie om kunsmis tydens aanplanting toe te dien. Hierdie aanbeveling is gebasseer op navorsing resultate met konvensionele bronne (CV), gevolglik was slegs ‘n klein toename in bykomende plantasie produksie gemeet die afgelope paar jaar. Die doelwit tydens hierdie studie is om die aanvanklike reaksie van die bome in terme van blaar oppervlak indeks (LAI), blaar-voedingstof inhoud, biomassa indeks (BI) en volume op die toediening van beheerde vrylating kunsmis (CRF) tydens aanplanting vas te stel. Stikstof (N), fosfor (P) en kalium (K) is in drie-ledige kombinasie aan Pinus radiata op ’n plantasie in die Weskaap toegedien. Die ontwerp is vyf keer in die studiegebied herhaal. N en P is in twee-ledige kombinasie aan twee Eucalyptus grandis x urophylla hibriede en Eucalyptus dunnii op drie groeiplekke, een eks-landbou en twee eks-bosbou, op die Zoeloeland kusvlakte en in die Natalse Middellande toegedien. Die ontwerp is nege keer in elke studiegebied herhaal. Oesreste is voor aanplanting op die Eucalyptus groeiplekke verbrand. Die voorkoms van Fusarium circinatum op die P. radiata groeiplek het onverwagte en hoogs uiteenlopende reaksies tot gevolg gehad. ’n Poging om die effek van die siekte te kwantifiseer, was slegs gedeeltelik suksesvol. Die gemiddelde BI van die kontrole behandeling, was 25. Die beste CV en CRF behandeling het onderskeidelik 42 % en 83 % hoër BI as die kontrole groep gehad, waarvan slegs die CRF behandeling beduidend was. Blaarontleding het gewys dat daar marginale of ontoereikende konsentrasies van P en Mg was. In Zoeloeland het die Eucalyptus hibriede ’n beduidende reaksie op N en P getoon met meer volume groei, LAI en N inhoud. Die toediening van 120 g N en 20 g P per boom op die eks-landbou groeiplek het ’n volume van 8 m3 ha-1 op eenjarige ouderdom tot gevolg gehad. Dis beduidend beter met 118 % en 80 % onderskeidelik vir die kontrole en beste CV behandeling. Die toediening van 80 g N en 20 g P per boom op die hervestigde eks-bosbou groeiplek, het ’n volume van 24.6 m3 ha-1 op eenjarige ouderdom tot gevolg gehad. Dit is 39 % beduidend en 7 % onbeduidend addisionele volume op eenjarige ouderdom vir onderskeidelik die kontrole groep en beste CV behandeling. ’n Onbeduidende depressie effek is met die alleen toediening van 20 g CV P gevind. In die Natalse Middellande groeiplek het die toediening van P ‘n vroeë reaksie in hoogte groei veroorsaak. Die toediening van 20 g CV P per boom, het ’n gemiddelde hoogte van 162.6 cm op die ouderdom van sewe maande tot gevolg gehad. Dit is 28 % beduidend hoër as die kontrole. Die toediening van 80 g CRF N en 20 g CV P per boom was onbeduidend. Toedienings van CRF N tot en met 120 g per boom het in die kusgebiede van Zoeloeland met ‘n lae organiese koolstof (OC) inhoud, groter groei as die aanbevole CV toedienings gehad. Die Middellande groeiplek met ’n hoër OC en klei inhoud, was die vroeë reaksie alleenlik beperk tot P bemesting.

Este trabalho discute a variabilidade dos fluxos de energia à superfície e de CO2 sobre uma área de Cerrado Sensu stricto no interior de São Paulo, e de uma área de ecótono Floresta-Cerrado (sazonalmente alagável) no Estado do Tocantins. Foram utilizadas medidas micrometeorológicas médias de 30 min, do clima (temperatura e umidade do ar, precipitação, velocidade do vento), dos fluxos de radiação (solar, PAR, saldo de radiação) e fluxos turbulentos de calor sensível, latente e CO2, coletadas no Cerrado durante o período de 2001 a 2003, e no ecótono durante Outubro de 2003 a Setembro de 2004. O ecótono e o Cerrado estão sob solos arenosos, homogêneos, com alta capacidade de infiltração e baixa de armazenamento. O Cerrado s.s. mostrou-se um ecossistema com forte sazonalidade da capacidade fotossintética, do Albedo-PAR e dos fluxos atmosféricos de CO2. Há uma fase de sumidouro e outra de fonte de CO2, corroborando os dados da literatura. Na escala da variabilidade interanual, as variações dos estados funcionais do Cerrado, como sumidouro ou fonte de CO2, foram fortemente dependentes das variações da precipitação e da temperatura mínima. No ecótono Floresta-Cerrado, a fase de inundação induz à uma diminuição gradual da respiração do sistema e da produtividade primária. A diminuição na produtividade ocorre com um atraso de ~45 dias, que poderia ser um tempo de assimilação e tolerância do sistema ao estresse induzido por anóxia. A redução da respiração do ecossistema ocorre ao passo que no regime alagado as perdas de CO2 ocorrem por evasão da superfície de água livre, um processo que aparentemente tem uma fonte de emissão menor que os processos de respiração do solo em condições secas. Durante a maior parte da inundação o ecótono continua a manter-se como um sumidouro de CO2 atmosférico durante, ao menos, 3 meses. O parâmetro RUE do ecótono foi cerca de 5 vezes maior do que o do Cerrado. A diferença de eficiência se deve possivelmente ao maior índice de área foliar das formações florestais da transição Floresta-Cerrado. A funcionalidade é controlada por fatores ambientais de maior escala que as locais. No caso do Cerrado s.s. há uma forte dependência do regime de chuvas e da temperatura mínima. No caso do ecótono Floresta-Cerrado, a suscetibilidade parece ser uma função do tempo de inundação. / This work discusses the energy and CO2 flux variability over a Cerrado Sensu stricto, in São Paulo state, Brazil, and over a seasonally inundated Forest-Cerrado ecotone in Tocantins state, Brazil. Micrometeorological measurements (30 minute average) of weather (temperature, relative humidity, precipitation and wind speed), radiation fluxes (solar radiation, PAR and net radiation), and CO2, latent and sensible heat turbulent fluxes were made for the Cerrado from 2001 to 2003. Measurements for the ecotone were made from October 2003 to September 2004. Both environments have sandy, homogeneous soils, with high infiltration capacity and low water storage. Cerrado s.s. showed strong seasonality for photosynthetic capacity, Albedo-PAR and CO2 atmospheric fluxes. As seen in other works, the Cerrado has both a CO2 sink and a CO2 source phase. These are strongly dependent on the precipitation and minimal temperature. Inundation of the Forest-Cerrado ecotone results in a gradual decrease in the system’s respiration and primary productivity. A lag of approximately 45 days is seen in the primary productivity reduction. This could represent the system’s resistance and tolerance due to anoxia stress. Ecosystem respiration in the inundated period is lower than in the dry period, apparently due to the lower CO2 outflux from the free water surface, in comparison with the CO2 flux from the soil. During most of the inundation period, the ecotone acts as a sink for CO2, for at least 3 months. The RUE for the ecotone was proximately 5 times higher than the Cerrado. This is probably due to the higher leaf area index of the forest area in the ecotone. The functionality of both biomes is controlled by larger scale environmental factors, as opposed to local factors. The Cerrado s.s. has a strong dependence precipitation and minimal temperature. The Forest-Cerrado ecotone shows a high dependence on the length of the inundated period.

The link between aboveground net primary productivity (ANPP) and resource gradients generated by complex terrain (solar radiation, nutrients, and moisture) has been established in the literature. Belowground ecosystem stocks and functions, such as soil organic carbon (SOC), dissolved organic carbon (DOC), and belowground productivity have also been related to the same topography and resource distributions, and therefore it is expected that they share spatial and temporal patterns with ANPP. However, stand structure on complex terrain is a function of multiple trajectories of forest development that interact with existing resource gradients, creating feedbacks that complicate the relationships between resource availability and ANPP. On a 96 ha forested watershed in the H.J. Andrews Experimental Forest in the Western Cascades range of Oregon, spatiotemporal heterogeneity in the secondary succession of a replanted Pseudotsuga menziesii stand following harvest results from the interaction of stand composition and abiotic drivers and may create unique "hot spots" and "hot moments" that complicate gradient relationships. In this dissertation, I tested the hypotheses that (chapter 3) multiple successional trajectories exist and can be predicted from a general linear model using specific topographic, historical, and biological parameters and that an estimated "maximum ANPP" may better represent stand characteristics than ANPP measured at a particular moment in time. I also test that (chapter 4) the distribution of light fraction carbon (LFC; C with a density of less than 1.85 g/cm��) is spatially variable, elevated on hardwood-initiated sites (hardwood biomass > 50% of biomass), and positively correlated with litter fall and ANPP. Chapter 4 also tests that heavy fraction carbon (HFC; C with a density of greater than 1.85 g/cm��) is a function of both soil mineralogy, stand composition, and ANPP, such that edges observed spatially in site mineralogy (changes in soil type) are reflected in sharp changes in the composition of the forest community and the magnitude of HFC stores. Finally, I hypothesized (chapter 5) that in complex terrain, dissolved organic carbon (DOC) export can be predicted from landform characteristics, relates to ANPP, and may be measured by several methods which are well-correlated with one another. In chapter 6, I discuss how litter fall measurements can be extrapolated to a watershed extent, and use litter fall as an example of the error that can occur in scaling up measurements taken at a small scale, within a heterogeneous stand on complex terrain, to a landscape scale extent. / Graduation date: 2013

We are currently faced with the global challenge of conserving biological diversity while also increasing food production to meet the demands of a growing human population. Land-use change, primarily resulting from conversion to production land, is currently the leading cause of biodiversity loss. This occurs through habitat loss, fragmentation of remaining natural habitats, and resulting edge effects. Land-sparing and land-sharing approaches have been discussed as alternative ways to engineer landscapes to mitigate biodiversity loss while meeting production objectives. However, these represent extremes on a continuum of real-world landscapes, and it will be important to understand the mechanisms by which adjacent land use affects natural remnant ecosystems in order to make local land-management decisions that achieve conservation, as well as production, objectives. This thesis investigates the impact of juxtaposing production and natural forest on the community-wide interactions between lepidopteran herbivores and their parasitoids, as mediated by parasitoid spillover between habitats. The first and overarching objective was to determine whether herbivore productivity drives asymmetrical spillover of predators and parasitoids, primarily from managed to natural habitats, and whether this spillover alters trophic interactions in the recipient habitat. The study of trophic interactions at a community level requires understanding of both direct and indirect interactions. However, community-level indirect interactions are generally difficult to predict and measure, and these have therefore remained understudied. Apparent competition is an indirect interaction mechanism thought to be very important in structuring host-parasitoid assemblages. However, this is known primarily from studies of single species pairs, and its community-wide impacts are less clear. Therefore, my second objective was to determine whether apparent competition could be predicted for all species pairs within an herbivore assemblage, based on a measure of parasitoid overlap. My third objective was to determine whether certain host or parasitoid species traits can predict the involvement of those species in apparent competition. My key findings were that there is a net spillover of generalist predators and parasitoids from plantation to native forest, and that for generalists, this depends on herbivore abundance in the plantation forest. Herbivore populations across the edge were linked by shared parasitoids in apparent competition. Consequently, an experimental reduction of herbivore density in the plantation forest changed parasitism rates in the natural forest, as predicted based on parasitoid overlap. Finally, several host and parasitoid traits were identified that can predict the degree to which host or parasitoid species will be involved in apparent competition, a finding which may have extensive application in biological control, as well as in predicting spillover edge effects. Overall, this work suggests that asymmetrical spillover between production and natural habitats occurs in relation to productivity differences, with greater movement of predators and parasitoids in the managed-to-natural forest direction. The degree to which this affected species interactions has implications for landscape design to achieve conservation objectives in production landscapes.

Des changements de croissance ont été documentés pour le XXe siècle dans de nombreuses régions en Europe. Cependant une évaluation exhaustive des changements de productivité, à une large échelle géographique, avec une analyse de leur hétérogénéité spatiale et de la diversité interspécifique de la réponse fait encore défaut. L'objectif de cette thèse est d'évaluer les changements récents de la productivité forestière aux échelles nationale, régionale et locale en France, et de rechercher leurs causes environnementales, à partir d'une approche de modélisation statistique de l'accroissement en surface terrière du peuplement (∆G) et d'indicateurs environnementaux. Nous avons utilisé les données de l'inventaire forestier national français pour 8 espèces dont la niche écologique et la distribution diffèrent (Fagus sylvatica, Quercus robur, Quercus petraea, Quercus pubescens, Picea abies, Abies alba, Pinus sylvestris and Pinus halepensis), observées en peuplements purs et réguliers. Nous présentons les facteurs ayant un effet sur la productivité des différentes espèces à l'échelle nationale, ainsi que des cartes de productivité suggérant que l'aire de distribution des espèces n'est pas toujours limitée par les conditions environnementales. Entre 1980 et 2005, nous observons des tendances positives, modales ou non significatives de la productivité pour toutes les espèces à l'exception des deux espèces méditerranéennes dont la productivité a diminué, soulignant ainsi la variabilité interspécifique de ces changements. Nous observons également de fortes variations spatiales des changements de productivité, autant dans leur intensité que dans leur signe, aux échelles régionale et intra-régionale. Ces résultats remettent en question la pertinence d'une évaluation moyenne à large échelle et soulignent le caractère contextuel des estimations. Nous mettons en évidence le rôle du réchauffement climatique récent dans les tendances observées. Ce travail fournit une évaluation plurispécifique et multi-échelle de la réaction de la productivité des espèces arborées à un environnement changeant. Nous avons souligné le caractère spécifique des changements de productivité et leur caractère contextuel, du fait de différences dans l'autécologie des espèces et de variations spatiales des facteurs limitants. Une étude approfondie de l'effet des facteurs environnementaux et de leurs interactions complexes est nécessaire pour la prédiction de la productivité future des espèces. / Growth trends have been reported in many regions of Europe over the twentieth century. However, an integrated assessment of productivity changes, including focus on a wide geographical scale, analysis of spatial heterogeneity, and the inter-specific diversity of growth responses is still lacking. The aim of this Ph.D work was to assess recent changes in forest productivity on a national, regional and local scale in France, and to investigate their potential environmental causes, based on statistical modeling approaches of stand basal area increment (BAI), and environmental indicators. We used the French NFI data for 8 species of contrasted ecological niches and distributions (Fagus sylvatica, Quercus robur, Quercus petraea, Quercus pubescens, Picea abies, Abies alba, Pinus sylvestris and Pinus halepensis), taken in pure and even-aged stands. We identified the main factors influencing tree species productivity on a national scale, and produced productivity maps suggesting that species distribution ranges are not always limited by environmental conditions. Between 1980 and 2005, the productivity trends reported were positive, modal or non-significant for all species, except the two Mediterranean species for which productivity decreased, highlighting inter-specific differences in these changes. We observed strong variations of productivity changes, both in intensity and sign, on a regional and intra-regional scale. These results question the relevance of wide-scale average assessments and highlight their context-dependence. The role of recent climatic warming in featuring the BAI trends was highlighted. This work provides an enriched scale- and species-dependent assessment of tree species reaction to a changing environment. We emphasized the species- and context dependence of productivity changes, due to differences in species autecology and spatial variations in the limiting factors. Further focus on the effect of environmental factors and their complex interactions is needed for the prediction of species future productivity.