Escala de independencia espacial de la mesofauna edáfica en un transecto bosque-pastizal del Jardín Botánico Francisco Javier Clavijero

In order to evaluate the scale of spatial patterns in edaphic mesofauna in a pasture-forest gradient, a collection of soil samples was obtained from a transect, followed by faunal extraction, counting and sorting. Only Sternorrhyncha (except Coccidae) and Coccidae geostatistical analysis showed spatial dependence within the scale 25-500 cm. Results suggest a revision of the current methods of soilfauna sampling, in which sampling intensity and intervals could be optimized for each taxon

Integrating soil macroinvertebrate diversity, litter decomposition and secondary succession in a tropical montane cloud forest in Mexico

This research considers human impacts on three components of biodiversity (composition, spatial structure and function). Given the relict character and unusual biogeochemical balance of tropical montane cloud forests in Mexico, logging poses a pressing threat to their survival. Specifically, this thesis explores the effect of selective logging and above-ground secondary succession on the biogeochemical cycling and soil macroinvertebrate community in a cloud forest in Oaxaca, Mexico. The research investigates: (1) whether the above-ground chain of successional changes in tree dominance, litterfall, litter diversity and soil microenvironmental conditions are coupled with a below-ground succession of soil nutrient availability and macroinvertebrate communities, (2) the role of spatial structuring of environmental conditions and litter resources as determinates of the nutrient availability and macroinvertebrate taxa abundance, (3) the implications of successional changes for decomposition and (4) whether the local influence of single trees explains the spatial structure of macroinvertebrate communities in late successional forests. The work was carried out in three chronosequences (c.15, 45, 75 and 100 year-old stages) of high altitude (1500-2000m) tropical montane cloud forest, two recently logged sites and two pristine sites. the macroinvertebrates in the litter and mineral soil were hand sorted from monoliths. Parametric statistics and canonical correspondance analysis were used to determine mean successional trends, and Spatial Analysis by Distance Indices and geostatistical methods were used in combination to determine spatial patterns. Two decompositional experiments were performed to explore the relationship between decompositional rate, litter quality and macroinvertebrate community higher taxa composition in different successional stages and under the canopy of different tree species. The research showed that: 1. The macroinvertebrate community composition in both recently logged sites and pristine forests were distinct compared to secondary successional stages. A decrease in soil temperature and nutrient availablity but increase in litter diversity and soil organic matter recorded through succession were accompanied by an increase in the number of macroinvertebrate taxa in the soil. For exampl, Collembola were most abundant in recently logged sites and earthworms (Megascolecidae) were almost excluvely found in pristine forests. 2. The oldest secondary forest (100 year-old) showed the highest frequency of aggregation in the abundance of individual macroinvertebrate taxa, and the highest and most uniform value of Shannon's diversity. This suggests that high levels of diversity in litter resources and soil chemistry in late succession are associated with complex spatial structuring of highly diverse macroinvertebrate communities. 3. The leaves of a late successional species (Persea americana)decomposed at a slightly slower rate than an early successional species (Pinus chiapensis) in all successional stages, yet the number and Shannon's diversity of macroinvertebrate taxa that invaded decomposing P.Americana leaves was consistently higher. The preference of macroinvertebrate taxa for the late-successional leaves was ultimately explained by differences in leaf quality during decomposition. P.americana leaves had higher concentrations of cations throughout decomposition and their concentration of lignin and nitrogen became higher. 4. In the 100-year-old forest, the effect of seasonal variation on soil microenvironmental conditions and litter availability was different under the canopy of different tree species. Furthermore, the chemical evolution of the same leaf type (e.g. Oreopanax xalapensis) was differentwhen decomposing under different canopies. The highly diverse and spatially complex macroinvertebrate community found in late succession (and experimental litter) was largely explained by the interactive effects of seasonal variation, tree species, litter quality and availability of the decomposing leaf type. The results provide the first analysis of the relationship between soil biodiversity and the tight biogeochemical cycling in this relict ecosystem type. Overall the results indicate that mature cloud forests sustain a diverse and spatially heterogenous macroinvertebrate community. The compositional and spatial components of soil biodiversity are compromised by logging and full recovery may take mopre than 100 years

Distribución espacial de la macrofauna edáfica en bosque mesófilo, bosque secundario y pastizal en la reserva La Cortadura, Coatepec, Veracruz, México Spatial distribution of soil macrofauna in cloud forest, secondary forest and grassland in La Cortadura reserve, Coatepec, Veracruz, Mexico

La conversión de un área de bosque para la agricultura o el pastoreo homogeniza las propiedades del suelo y las comunidades de macroinvertebrados. Este trabajo estudió si la diversidad (H'), densidad y heterogeneidad espacial (tamaño de parche) de macroinvertebrados de hojarasca y suelo se recuperan en una secuencia sucesional pastizal (Pas)-bosque secundario (Bsec)-bosque mesófilo maduro (BMM). En el sustrato hojarasca se observó un gradiente de aumento para todas las variables estudiadas en la secuencia Pas-Bsec-BMM. Sin embargo, este patrón no se presentó en el suelo, ya que la mayor diversidad y densidad (por taxón y total) se encontraron en el Bsec. Mediante un análisis de variografía, en la hojarasca se encontraron distribuciones espaciales heterogéneas de los macroinvertebrados en ambos bosques, mientras que en el pastizal la distribución fue homogénea, lo que apoya la idea de que el disturbio va acompañado de una homogenización espacial de las comunidades de macroinvertebrados, pero la restructuración espacial se recupera en la sucesión temprana. En el suelo de los 3 sitios, la distribución de todas las variables fue en parches (5 a 60 m de diámetro), pero no se encontró disminución en la heterogeneidad espacial predicha para la secuencia Pas-Bsec-BMM.<br>The conversion of forest to agriculture or pasture homogenizes soil properties, including the communities of macroinvertebrates. This study examined whether the diversity (H'), density and spatial heterogeneity (patch size) of litter and soil macroinvertebrate recover through the secondary successional sequence pasture (Pas)-secondary forest (Bsec)- mature cloud forest (BMM). In the litter an increasing gradient for all variables was observed through the successional sequence. However, this pattern was not present in the soil, where the highest diversity and density (per taxon and total) were found in the Bsec. Using variography, we found heterogeneous spatial distributions of litter macroinvertebrates in both forests, while their distribution was homogeneous in the pasture. This supports the idea that disturbance is accompanied by a spatial homogenization of macroinvertebrate communities but spatial restructuring occurs in early succession. However, in the soil, macroinvertebrate variables were distributed in patches (5 to 60 m in diameter) in the 3 sites and, the decrease in spatial heterogeneity predicted for the sequence Pas-BSsec-BMM was not observed

Integrating soil macroinvertebrate diversity, litter decomposition and secondary succession in a tropical montane cloud forest in Mexico

This research considers human impacts on three components of biodiversity (composition, spatial structure and function). Given the relict character and unusual biogeochemical balance of tropical montane cloud forests in Mexico, logging poses a pressing threat to their survival. Specifically, this thesis explores the effect of selective logging and above-ground secondary succession on the biogeochemical cycling and soil macroinvertebrate community in a cloud forest in Oaxaca, Mexico. The research investigates: (1) whether the above-ground chain of successional changes in tree dominance, litterfall, litter diversity and soil microenvironmental conditions are coupled with a below-ground succession of soil nutrient availability and macroinvertebrate communities, (2) the role of spatial structuring of environmental conditions and litter resources as determinates of the nutrient availability and macroinvertebrate taxa abundance, (3) the implications of successional changes for decomposition and (4) whether the local influence of single trees explains the spatial structure of macroinvertebrate communities in late successional forests. The work was carried out in three chronosequences (c.15, 45, 75 and 100 year-old stages) of high altitude (1500-2000m) tropical montane cloud forest, two recently logged sites and two pristine sites. the macroinvertebrates in the litter and mineral soil were hand sorted from monoliths. Parametric statistics and canonical correspondance analysis were used to determine mean successional trends, and Spatial Analysis by Distance Indices and geostatistical methods were used in combination to determine spatial patterns. Two decompositional experiments were performed to explore the relationship between decompositional rate, litter quality and macroinvertebrate community higher taxa composition in different successional stages and under the canopy of different tree species. The research showed that: 1. The macroinvertebrate community composition in both recently logged sites and pristine forests were distinct compared to secondary successional stages. A decrease in soil temperature and nutrient availablity but increase in litter diversity and soil organic matter recorded through succession were accompanied by an increase in the number of macroinvertebrate taxa in the soil. For exampl, Collembola were most abundant in recently logged sites and earthworms (Megascolecidae) were almost excluvely found in pristine forests. 2. The oldest secondary forest (100 year-old) showed the highest frequency of aggregation in the abundance of individual macroinvertebrate taxa, and the highest and most uniform value of Shannon's diversity. This suggests that high levels of diversity in litter resources and soil chemistry in late succession are associated with complex spatial structuring of highly diverse macroinvertebrate communities. 3. The leaves of a late successional species (Persea americana)decomposed at a slightly slower rate than an early successional species (Pinus chiapensis) in all successional stages, yet the number and Shannon's diversity of macroinvertebrate taxa that invaded decomposing P.Americana leaves was consistently higher. The preference of macroinvertebrate taxa for the late-successional leaves was ultimately explained by differences in leaf quality during decomposition. P.americana leaves had higher concentrations of cations throughout decomposition and their concentration of lignin and nitrogen became higher. 4. In the 100-year-old forest, the effect of seasonal variation on soil microenvironmental conditions and litter availability was different under the canopy of different tree species. Furthermore, the chemical evolution of the same leaf type (e.g. Oreopanax xalapensis) was differentwhen decomposing under different canopies. The highly diverse and spatially complex macroinvertebrate community found in late succession (and experimental litter) was largely explained by the interactive effects of seasonal variation, tree species, litter quality and availability of the decomposing leaf type. The results provide the first analysis of the relationship between soil biodiversity and the tight biogeochemical cycling in this relict ecosystem type. Overall the results indicate that mature cloud forests sustain a diverse and spatially heterogenous macroinvertebrate community. The compositional and spatial components of soil biodiversity are compromised by logging and full recovery may take mopre than 100 years.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Arbuscular mycorrhizal root colonization and soil P availability are positively related to agrodiversity in Mexican maize polycultures

In Los Tuxtlas, Mexico, the local Popoluca people maintain the traditional management of their maize agroecosystems. However, it is not known whether the loss of agrodiversity over recent decades has affected mycorrhizal populations, nutrient availability, and crop productivity. This study utilized linear mixed effect models to analyze the relationship between agrodiversity (three, six, and greater than or equal to eight cultivated species) and (a) arbuscular mycorrhizal fungi (AMF) inoculum potential, measured as the most probable number (MPN) of propagules and colonization level, (b) nutrient availability, and (c) aboveground maize productivity. We also investigated the relationship between soil nutrient content and inoculum potential. Soil samples were taken before planting, and during flowering, in the 2009 maize cycle. We found that AMF colonization level of maize roots and P availability increased with planted species richness, but that this effect only occurred at the flowering sampling date. Plots with a higher MPN of propagules presented increased C and NO3 − contents and lower C/N ratio than those with lower MPN of propagules, regardless of agrodiversity. Soils that produced the highest maize root colonization level also featured high P availability and N content. We conclude that decreased agrodiversity in these traditional systems does not significantly affect the soil MPN of propagules, but may have a negative impact on the ability of the mycorrhizal community to colonize maize roots, as well as reducing the availability of P, which is often the most limiting nutrient in tropical soils