Patch selection by wintering white-tailed deer : consequences for eastern hemlock regeneration at local and landscape scales

Tsuga canadensis (eastern hemlock) is a highly shade-tolerant, late-successional, and long-lived conifer species found throughout eastern North America. It is most often found in pure or nearly pure stands, because highly acidic and nutrient poor forest floor conditions are thought to favor T. canadensis regeneration while simultaneously limiting the establishment of some hardwood species with greater nutrient requirements. Once a common species, T. canadensis is currently experiencing widescale declines across its range. The hemlock woolly adelgid (Adelges tsugae) is decimating the population across its eastern distribution. Across the Upper Great Lakes region, where the adelgid is currently being held at bay by cold winter temperatures, T. canadensis has been experiencing failures in regeneration attributed, in part, to herbivory by white-tailed deer (Odocoileus virginianus). Deer utilize T. canadensis stands as winter habitat in areas of high snow depth. Tsuga canadensis, once a major component of these forests, currently exists at just a fraction of its pre-settlement abundance due to historic logging and contemporary forest management practices, and what remains is found in small remnant patches surrounded by second- and third-growth deciduous forests. The deer population across the region, however, is likely double that of pre-European settlement times. In this dissertation I explore the relationship between white-tailed deer use of T. canadensis as winter habitat and the effect this use is having on regeneration and forest succession. For this research I quantified stand composition and structure and abiotic variables of elevation and snow depth in 39 randomly selected T. canadensis stands from across the western Upper Peninsula of Michigan. I also quantified composition and the configuration of the landscapes surrounding these stands. I measured relative deer use of T. canadensis stands as pellet group piles deposited in each stand during each of three consecutive winters, 2005-06, 2006-07, and 2007-08. The results of this research suggest that deer use of T. canadensis stands as winter habitat is influenced primarily by snow depth, elevation, and the composition and configuration of the greater landscapes surrounding these stands. Specifically, stands with more heterogeneous landscapes surrounding them (i.e., a patchy mosaic of conifer, deciduous, and open cover) had higher relative deer use than stands surrounded by homogenous deciduous forest cover. Additionally, the intensity of use and the number of stands used was greater in years with higher average snow depth. Tsuga canadensis regeneration in these stands was negatively associated with deer use and Acer saccharum (sugar maple) basal area. Of the 39 stands, 17 and 22 stands had no T. canadensis regeneration in small and large sapling categories, respectively. Acer saccharum was the most common understory tree species, and the importance of A. saccharum in the understory (stems < 10 cm dbh) of the stands was positively associated with overstory A. saccharum dominance. Tsuga canadensis establishment was associated with high-decay coarse woody debris and moss, and deciduous leaf litter inputs in these stands may be limiting access to these important microsites. Furthermore, A. saccharum is more tolerant to the effects of deer herbivory than T. canadensis, giving A. saccharum a competitive advantage in stands being utilized as winter habitat by deer. My research suggests that limited microsite availability, in conjunction with deer herbivory, may be leading to an erosion in T. canadensis patch stability and an altered successional trajectory toward one of A. saccharum dominance, an alternately stable climax species.

The spatial distribution of Copernicia alba (Morong) in the district of Bahia Negra, Paraguay

The Humid Chaco of Northeast Paraguay harbors monoculture palm savannas in which Copernicia alba is the only dominant overstory species. The study’s objective was to provide the complete spatial distribution of a simple ecosystem lacking confounding factors of overstory competition and changes in slope. Palms within six, 50 x 50m plots were marked by their GPS location and measured for dbh and total stem height. The spatial distribution was individually analyzed for each plot at the local scale up to 12 m using Ripley’s K test. For the total population including juvenile and adult plants, the sample plots contained both random and clustered distribution patterns. In each of the six plots, the juvenile populations exhibited more clustered patterns than the adult population of each plot.

Variation in carbon content of tropical tree species from Ghana

Most research on carbon content of trees has focused on temperate tree species with little information existing on the carbon content of tropical tree species. This study investigated the variation in carbon content of selected tropical tree species and compared carbon content of Khaya spp from two ecozones in Ghana. Allometric equations developed for mixed-plantation stands for wet evergreen forest verified the expected strong relationship between tree volumes and dbh (r2>0.93) and volume and dbh2×height (r2>0.97). Carbon concentration, wood density and carbon content differed significantly among species. Volume at age 12 ranged from 0.01 to 1.04 m3 per tree, and wood density was highly variable among species, ranging from 0.27 to 0.76 g cm-3. This suggests that species specific density data is critical for accurate conversion of volumes derived from allometric relationships into carbon contents. Significant differences in density of Khaya spp existed between the wet and moist semi-deciduous ecozones. The baseline species-level information from this study will be useful for carbon accounting and development of carbon sequestration strategies in Ghana and other tropical African countries.

Towards greater accuracy in individual-tree mortality regression

Background mortality is an essential component of any forest growth and yield model. Forecasts of mortality contribute largely to the variability and accuracy of model predictions at the tree, stand and forest level. In the present study, I implement and evaluate state-of-the-art techniques to increase the accuracy of individual tree mortality models, similar to those used in many of the current variants of the Forest Vegetation Simulator, using data from North Idaho and Montana. The first technique addresses methods to correct for bias induced by measurement error typically present in competition variables. The second implements survival regression and evaluates its performance against the traditional logistic regression approach. I selected the regression calibration (RC) algorithm as a good candidate for addressing the measurement error problem. Two logistic regression models for each species were fitted, one ignoring the measurement error, which is the “naïve” approach, and the other applying RC. The models fitted with RC outperformed the naïve models in terms of discrimination when the competition variable was found to be statistically significant. The effect of RC was more obvious where measurement error variance was large and for more shade-intolerant species. The process of model fitting and variable selection revealed that past emphasis on DBH as a predictor variable for mortality, while producing models with strong metrics of fit, may make models less generalizable. The evaluation of the error variance estimator developed by Stage and Wykoff (1998), and core to the implementation of RC, in different spatial patterns and diameter distributions, revealed that the Stage and Wykoff estimate notably overestimated the true variance in all simulated stands, but those that are clustered. Results show a systematic bias even when all the assumptions made by the authors are guaranteed. I argue that this is the result of the Poisson-based estimate ignoring the overlapping area of potential plots around a tree. Effects, especially in the application phase, of the variance estimate justify suggested future efforts of improving the accuracy of the variance estimate. The second technique implemented and evaluated is a survival regression model that accounts for the time dependent nature of variables, such as diameter and competition variables, and the interval-censored nature of data collected from remeasured plots. The performance of the model is compared with the traditional logistic regression model as a tool to predict individual tree mortality. Validation of both approaches shows that the survival regression approach discriminates better between dead and alive trees for all species. In conclusion, I showed that the proposed techniques do increase the accuracy of individual tree mortality models, and are a promising first step towards the next generation of background mortality models. I have also identified the next steps to undertake in order to advance mortality models further.

Small-scale timber stand management techniques : a case study of woodlots in Isangati, Tanzania

Small-scale village woodlots of less than 0.5ha are the preferred use of land for local farmers with extra land in the village of Isangati, a small community located in the southern highlands of Tanzania. Farmers view woodlots as lucrative investments that do not involve intensive labor or time. The climate is ideal for the types of trees grown and the risks are minimal with no serious threats from insects, fires, thieves, or grazing livestock. It was hypothesized that small-scale village woodlot owners were not maximizing timber outputs with their current timber stand management and harvesting techniques. Personal interviews were conducted over a five month period and field data was collected at each farmer’s woodlots over a seven month period. Woodlot field data included woodlot size, number of trees, tree species, tree height, dbh, age, and spacing. The results indicated that the lack of proper woodlot management techniques results in failure to fully capitalize on the investment of woodlots. While farmers should continue with their current harvesting rotations, some of the reasons for not maximizing tree growth include close spacing (2m x 2m), no tree thinning, extreme pruning (60% of tree), and little to no weeding. Through education and hands-on woodlot management workshops, the farmers could increase their timber output and value of woodlots.

Critical evaluation of diameter increment modelling in the Great Lakes region

Simulations of forest stand dynamics in a modelling framework including Forest Vegetation Simulator (FVS) are diameter driven, thus the diameter or basal area increment model needs a special attention. This dissertation critically evaluates diameter or basal area increment models and modelling approaches in the context of the Great Lakes region of the United States and Canada. A set of related studies are presented that critically evaluate the sub-model for change in individual tree basal diameter used in the Forest Vegetation Simulator (FVS), a dominant forestry model in the Great Lakes region. Various historical implementations of the STEMS (Stand and Tree Evaluation and Modeling System) family of diameter increment models, including the current public release of the Lake States variant of FVS (LS-FVS), were tested for the 30 most common tree species using data from the Michigan Forest Inventory and Analysis (FIA) program. The results showed that current public release of the LS-FVS diameter increment model over-predicts 10-year diameter increment by 17% on average. Also the study affirms that a simple adjustment factor as a function of a single predictor, dbh (diameter at breast height) used in the past versions, provides an inadequate correction of model prediction bias. In order to re-engineer the basal diameter increment model, the historical, conceptual and philosophical differences among the individual tree increment model families and their modelling approaches were analyzed and discussed. Two underlying conceptual approaches toward diameter or basal area increment modelling have been often used: the potential-modifier (POTMOD) and composite (COMP) approaches, which are exemplified by the STEMS/TWIGS and Prognosis models, respectively. It is argued that both approaches essentially use a similar base function and neither is conceptually different from a biological perspective, even though they look different in their model forms. No matter what modelling approach is used, the base function is the foundation of an increment model. Two base functions – gamma and Box-Lucas – were identified as candidate base functions for forestry applications. The results of a comparative analysis of empirical fits showed that quality of fit is essentially similar, and both are sufficiently detailed and flexible for forestry applications. The choice of either base function in order to model diameter or basal area increment is dependent upon personal preference; however, the gamma base function may be preferred over the Box-Lucas, as it fits the periodic increment data in both a linear and nonlinear composite model form. Finally, the utility of site index as a predictor variable has been criticized, as it has been widely used in models for complex, mixed species forest stands though not well suited for this purpose. An alternative to site index in an increment model was explored, using site index and a combination of climate variables and Forest Ecosystem Classification (FEC) ecosites and data from the Province of Ontario, Canada. The results showed that a combination of climate and FEC ecosites variables can replace site index in the diameter increment model.

Secondary succession and dipterocarp recruitment in Bornean rain forest after logging

To understand succession in dipterocarp rain forest after logging, the structure, species composition and dynamics of primary (PF) and secondary (SF) forest at Danum were compared. In 10 replicate 0.16-ha plots per forest type trees >= 10 cm gbh (3.2 cm dbh) were measured in 1995 and 2001. The SF had been logged in 1988, which allowed successional change to be recorded at 8 and 13 years. In 2001, saplings (1.0-3.1 cm dbh) were measured in nested quadrats. The forest types were similar in mean radiation at 2 m height, and in density, basal area and species number of all trees. Among small (10 <= 31.4) and large ( >= 31.4 cm gbh) trees, in both 1995 and 2001, there were 10- and 3-fold more dipterocarps in SF than PF respectively; and averaging over the two dates, there were correspondingly ca. 10- and 18-fold more pioneers. Mortality was ca. 60% higher in SF than PF, largely due to a seven-fold difference for pioneers: for dipterocarps there was little difference. Recruitment was similar in PF and SE Stem growth rates were 37% higher in SF than PF for all trees, although dipterocarps showed the opposite trend. Among saplings, dipterocarps dominated SF with a 10-fold higher density than in PF. For dipterocarps, the light (LH) and medium-heavy (MHH) canopy hardwoods, and the shade-tolerant, smaller-stature other (OTH) species (e.g. Hopea and Vatica) were in the ratios ca. 40:15:45 in SF and 85: < 1:15 in PF. LHs had higher mortality than OTHs in SE In PF ca. 80% of the saplings were LH: in SF ca. 70% were OTH. The predominance of OTHs in SF is explained by the logging of primary rain forest which was in a likely late stage of recovery from natural disturbance, plus the continuing shaded conditions in the understorey promoted by dense pioneer vegetation. At 13 years after logging succession appeared to be inhibited: LHs were being suppressed but MHHs and OTHs persisted. Succession in lowland dipterocarp, rain forests may therefore depend on the successional state of the primary forest when it is logged. A review of logged versus unlogged studies in Borneo highlights the need for more detailed ecological comparisons.

The role of tree size in the leafing phenology of a seasonally dry tropical forest in Belize, Central America

Leafing phenology of two dry-forest sites on soils of different depth (S = shallow, D = deep) at Shipstern Reserve, Belize, were compared at the start of the rainy season (April-June 2000). Trees greater than or equal to 2.5 cm dbh were recorded weekly for 8 wk in three 0.04-ha plots per site. Ten species were analysed individually for their phenological patterns, of which the three most common were Bursera simaruba, Metopium brownei and Jatropha gaumeri. Trees were divided into those in the canopy (> 10 cm dbh) and the subcanopy (less than or equal to 10 cm dbh). Site S had larger trees on average than site D. The proportion of trees flushing leaves at any one time was generally higher in site S than in site D, for both canopy and subcanopy trees. Leaf flush started 2 wk earlier in site S than site D for subcanopy trees, but only 0.5 wk earlier for the canopy trees. Leaf flush duration was 1.5 wk longer in site S than site D. Large trees in the subcanopy flushed leaves earlier than small ones at both sites but in the canopy just at site D. Large trees flushed leaves earlier than small ones in three species and small trees flushed leaves more rapidly in two species. Bursera and Jatropha followed the general trends but Metopium, with larger trees in site D than site S, showed the converse with onset of flushing I wk earlier in site D than site S. Differences in response of the canopy and subcanopy trees on each site can be accounted for by the predominance of spring-flushing or stem-succulent species in site S and a tendency for evergreen species to occur in site D. Early flushing of relatively larger trees in site D most likely requires access to deeper soil water reserves but small and large trees utilize stored tree water in site S.

Forest structure and composition of previously selectively logged and non-logged montane forests at Mt. Kilimanjaro

The montane forests of Mount Kilimanjaro in Tanzania have been subjected to a long history of selective logging. However, since 1984 logging of indigenous trees is prohibited. Today, these forests allow us to evaluate the long-term effects of selective logging. We mapped the height and diameter at breast height (DBH) of all trees >10 cm DBH on 10 sites of 0.25 ha. Five sites represent non-logged forests, another five selectively logged forests. We tested whether forests were still visibly affected 30–40 years after selective logging in terms of their forest structure and tree diversity. Additionally we compared tree densities of different species guilds, including disturbance-indicator species, late-successional species and main timber species. Furthermore, we specifically compared the community size distributions of selectively logged and non-logged forests, first across all species and then for the most important timber species, Ocotea usambarensis, alone. 30–40 years after selective logging forests still showed a higher overall stem density, mainly due to higher relative abundances of small trees (<50 cm DBH) in general, and higher densities of small size class stems of late-successional species specifically. For O. usambarensis, the selectively logged sites harboured higher relative abundances of small trees and lower relative abundances of harvestable trees. The higher relative abundance of small O. usambarensis-stems in selectively logged forests appears promising for future forest recovery. Thus, outside protected areas, selective logging may be a sustainable management option if logging cycles are considerably longer than 40 years, enough large source trees remain, and the recruiting O. usambarensis individuals find open space for their establishment.

Using plant functional traits and phylogenies to understand patterns of plant community assembly in a seasonal tropical forest in Lao PDR

Plant functional traits reflect different evolutionary responses to environmental variation, and among extant species determine the outcomes of interactions between plants and their environment, including other plant species. Thus, combining phylogenetic and trait-based information can be a powerful approach for understanding community assembly processes across a range of spatial scales. We used this approach to investigate tree community composition at Phou Khao Khouay National Park (18°14’-18°32’N; 102°38’- 102°59’E), Laos, where several distinct forest types occur in close proximity. The aim of our study was to examine patterns of plant community assembly across the strong environmental gradients evident at our site. We hypothesized that differences in tree community composition were being driven by an underlying gradient in soil conditions. Thus, we predicted that environmental filtering would predominate at the site and that the filtering would be strongest on sandier soil with low pH, as these are the conditions least favorable to plant growth. We surveyed eleven 0.25 ha (50x50 m) plots for all trees above 10 cm dbh (1221 individual trees, including 47 families, 70 genera and 123 species) and sampled soils in each plot. For each species in the community, we measured 11 commonly studied plant functional traits covering both the leaf and wood economic spectrum traits and we reconstructed a phylogenetic tree for 115 of the species in the community using rbcL and matK sequences downloaded from Genebank (other species were not available). Finally we compared the distribution of trait values and species at two scales (among plots and 10x10m subplots) to examine trait and phylogenetic community structures. Although there was strong evidence that an underlying soil gradient was determining patterns of species composition at the site, our results did not support the hypothesis that the environmental filtering dominated community assembly processes. For the measured plant functional traits there was no consistent pattern of trait dispersion across the site, either when traits were considered individually or when combined in a multivariate analysis. However, there was a significant correlation between the degree of phylogenetic dispersion and the first principle component axis (PCA1) for the soil parameters.Moreover, the more phylogenetically clustered plots were on sandier soils with lower pH. Hence, we suggest that the community assembly processes across our sitemay reflect the influence ofmore conserved traits that we did not measure. Nevertheless, our results are equivocal and other interpretations are possible. Our study illustrates some difficulties in combining trait and phylogenetic approaches that may result from the complexities of integrating spatial and evolutionary processes that vary at different scales.

What drives European beech (Fagus sylvatica L.) mortality after forest fires of varying severity?

Predicting the timing and amount of tree mortality after a forest fire is of paramount importance for post-fire management decisions, such as salvage logging or reforestation. Such knowledge is particularly needed in mountainous regions where forest stands often serve as protection against natural hazards (e.g., snow avalanches, rockfalls, landslides). In this paper, we focus on the drivers and timing of mortality in fire-injured beech trees (Fagus sylvatica L.) in mountain regions. We studied beech forests in the southwestern European Alps, which burned between 1970 and 2012. The results show that beech trees, which lack fire-resistance traits, experience increased mortality within the first two decades post-fire with a timing and amount strongly related to the burn severity. Beech mortality is fast and ubiquitous in high severity sites, whereas small- (DBH <12 cm) and intermediate-diameter (DBH 12–36 cm) trees face a higher risk to die in moderate-severity sites. Large-diameter trees mostly survive, representing a crucial ecological legacy for beech regeneration. Mortality remains low and at a level similar to unburnt beech forests for low burn severity sites. Beech trees diameter, the presence of fungal infestation and elevation are the most significant drivers of mortality. The risk of beech to die increases toward higher elevation and is higher for small-diameter than for large-diameter trees. In case of secondary fungi infestation beech faces generally a higher risk to die. Interestingly, fungi that initiate post-fire tree mortality differ from fungi occurring after mechanical injury. From a management point of view, the insights about the controls of post-fire mortality provided by this study should help in planning post-fire silvicultural measures in montane beech forests.

TIME DEPENDENT ALTERATIONS IN CENTRAL NERVOUS SYSTEM DOPAMINE RECEPTORS INDUCED BY DOPAMINE AGONIST TREATMENT

Levodopa, the precursor of dopamine, is currently the drug of choice in the treatment of Parkinson's disease. Recently, two direct dopamine agonists, bromocriptine and pergolide, have been tested for the treatment of Parkinson's disease because of reduced side effects compared to levodopa. Few studies have evaluated the effects of long-term treatment of dopamine agonists on dopamine receptor regulation in the central nervous system. Thus, the purpose of this study was to determine whether chronic dopamine agonist treatment produces a down-regulation of striatal dopamine receptor function and to compare the results of the two classes of dopaminergic drugs.^ Levodopa with carbidopa, a peripheral decarboxylase inhibitor, was administered orally to rats whereas bromocriptine and pergolide were injected intraperitoneally once daily. Several neurochemical parameters were examined from 1 to 28 days.^ Levodopa minimally decreased striatal D-1 receptor activity but increased the number of striatal D-2 binding sites. Levodopa increased the V(,max) of tyrosine hydroxylase (TH) in all brain regions tested. Protein blot analysis of striatal TH indicated a significant increase in the amount of TH present. Dopamine-beta-hydroxylase (DBH) activity was markedly decreased in all brain regions studied and mixing experiments of control and drug-treated cortices did not show the presence of an increased level of endogenous inhibitors.^ Bromocriptine treatment decreased the number of D-2 binding sites. Striatal TH activity was decreased and protein blot analysis indicated no change in TH quantity. The specificity of bromocriptine for striatal TH suggested that bromocriptine preferentially interacts with dopamine autoreceptors.^ Combination levodopa-bromocriptine was administered for 12 days. There was a decrease in both D-1 receptor activity and D-2 binding sites, and a decrease in brain HVA levels suggesting a postsynaptic receptor action. Pergolide produced identical results to the combination levodopa-bromocriptine studies.^ In conclusion, combination levodopa-bromocriptine and pergolide treatments exhibited the expected down-regulation of dopamine receptor activity. In contrast, levodopa appeared to up-regulate dopamine receptor activity. Thus, these data may help to explain, on a biochemical basis, the decrease in the levodopa-induced side effects noted with combination levodopa-bromocriptine or pergolide therapies in the treatment of Parkinson's disease. ^

Epiphytic orchid diversity and community composition in managed and natural moist evergreen Afromontane forest in SW Ethiopia

In SW Ethiopia, the moist evergreen Afromontane forest has become extremely fragmented and most of the remnants are intensively managed for coffee cultivation (Coffea arabica), with considerable impacts on biodiversity and ecosystem functioning. Because epiphytic orchids are potential indicators for forest quality and a proxy for overall forest biodiversity, we assessed the effect of forest management and forest fragmentation on epiphytic orchid diversity. We selected managed forest sites from both large and small forest remnants and compared their epiphytic orchid diversity with the diversity of natural unfragmented forest. We surveyed 339 canopy trees using rope climbing techniques. Orchid richness decreased and community composition changed, from the natural unfragmented forest, over the large managed forest fragments to the small managed forest fragments. This indicates that both forest management and fragmentation contribute to the loss of epiphytic orchids. Both the removal of large canopy trees typical for coffee management, and the occurrence of edge effects accompanying forest fragmentation are likely responsible for species loss and community composition changes. Even though some endangered orchid species persist even in the smallest fragments, large managed forest fragments are better options for the conservation of epiphytic orchids than small managed forests. Our results ultimately show that even though shade coffee cultivation is considered as a close-to-nature practice and is promoted as biodiversity conservation friendly, it cannot compete with the epiphytic orchid conservation benefit generated by unmanaged moist evergreen Afromontane forests.

Influencia de la fertilización y el riego sobre aspectos cuali-cuantitavos de la reproducción de cebolla (Allium cepa L.) para la industria del deshidratado

La creciente demanda, en los últimos años, a nivel mundial y nacional de los productos deshidratados hace que esta actividad se perfile como promisoria en la región cuyana. Prácticamente el 100 % de la deshidratación de cebolla (Allium cepa L.) del país se realiza en Mendoza, habiendose hecho sólo producciones aisladas y de escaso volúmen en otras plantas del país. Las estimaciones preveen que se seguirá abasteciendo el mercado local y se incrementaránlas exportaciones de cebolla deshidratada. El objetivo general del presente trabajo fue establecer la influencia de la fertilización y el riego sobre la productividad y calidad de un cultivar mejorado de cebolla de importancia económica para la industria del deshidratado. En el Campo Experimental del INTA La Consulta se llevaron a cabo durante los años 1994-´95 y 1995-´96, dos ciclos de ensayos, con una línea de cebolla para deshidratar derivada del cultivar Southport White Globe. El suelo es de origen aluvial, profundo y de textura franca (Torrifluvente típico). Se determinaron los principales parámetros físicos, químicos e hídricos de la fracción fina del suelo. Para determinar el efecto de la fertilización sobre componentes de crecimiento y calidad y estudiar la variación de la concentración y ritmo de absorción de nutrimentos se ensayaron diferentes tratamientos. En el primer ciclo se ensayaron nueve tratamientos con tres niveles de N (0, 100, 200 kg N ha-1 ) aplicado como urea y tres niveles de P (0, 30, 60 kg P ha-1 ) como superfosfato. En el segundo ciclo se probaron ocho tratamientos con los siguientes niveles de N, P y K, respectivamente: (0 y 100 kg N ha-1), (0 y 40 kg P ha-1) y (0 y 60 kg K ha-1), éste último como sulfato de potasio. Para evaluar el efecto de diferentes regímenes de riego al final del ciclo de cultivo sobre la produccción cuantitativa y cualitativa de cebolla para la industria del deshidratado se programaron cortes anticipados de riegos, según diferentes fechas anteriores a la cosecha. Estas fueron para el primero y segundo ciclo de ensayo, respectivamente: (33, 27, 21, 8) y (21,14, 7) días anteriores a la fecha de cosecha estimada. Las principales conclusiones fueron: A) Con respecto a la fertilización: i) En todos los casos, e independientemente del tratamiento ensayado el mayor incremento relativo de sustancia seca aérea se evidencia durante la II fase de viii desarrollo que tiene lugar entre los primeros días de noviembre y mediados de diciembre ii) En dicha II fase se comienzan a manifestar incrementos absolutos de peso seco aéreo y área foliar atribuibles a la fertilización iii) También en todos los tratamientos se verifica que al finalizar la II fase el peso de los bulbos alcanza el 20 % de su peso de cosecha. En ese momento, los valores determinados para el porcentaje de sólidos totales (% ST) oscilan entre 13 % y 14 % iv) La mayor tasa de crecimiento del bulbo se constató en la III fase en la que se logra el 80% restante de su peso final v) En la III fase el % ST del bulbo sigue en aumento hasta casi el momento de cosecha y alcanzó valores promedios de 20 % y 21 %. La fertilización con diferentes dosis de N, P y K no influyó en el contenido de materia seca de los bulbos aunque sí lo hizo positivamente sobre su peso fresco vi) Los máximos rendimientos de bulbos (37.3 Mg ha-1) y de materia seca (7.92 Mg ha-1) se obtuvieron, en el segundo ciclo de ensayo, con las dosis de 100 kg N ha-1 y 40 kg P ha-1 vii) Los parámetros tisulares aéreos de valor diagnóstico asociados a máximosrendimientos, y al final de la II fase, correspondieron a una Alimentación Global (N, P, K) de 4.96 g % g s. seca y concentraciones de N, P y K respectivamente de: 2.56 g %, 0.22 g % y 2.18 g %. En cuanto a los tenores de Ca y Mg los porcentajes respectivos fueron: 2.10 g % y 0.16 g %. Los valores medios de equilibrios nutricionales fueron: N - P - K: 52 % - 4% - 44%. Con respecto a los micronutrimentos sus concentraciones fueron, en mg kg-1, Fe: 400, Zn: 55, Mn: 35 y Cu:19 y los valores de equilibrios nutricionales : 78.5 % - 11 % - 7 % - 3.5 %, respectivamente viii) La extracción total efectuada por el cultivo para esas máximas producciones, en kg ha-1, de N - P - K - Ca - Mg fueron: 214 - 40 -187 - 184 -19 B) Con respecto a los regímenes de riego: i) El rendimiento máximo obtenido -38.9 Mg ha-1- en el ensayo de cortes anticipados de riego correspondió al tratamiento R7 del ciclo 1995-‘96 ii) El mismo perteneció al tratamiento, que además de la fertilización básica con 100 kg N ha-1, aseguró durante los meses de noviembre, diciembre y enero, ix hasta siete días antes de cosecha, una humedad edáfica mínima (umbral de riego) correspondiente al 50 % del agua disponible. Este tratamiento se caracterizó por un total de 18 riegos y una incorporación de agua de 6120 m3 ha-1. iii) Los rendimientos totales de materia seca fueron afectados detrimentalmente por los otros regímenes de riego de cortes más anticipados iv) Se constató una relación lineal positiva altamente ignificativa entre el rendimiento y la lámina total de agua aplicada al cultivo.

Comportamiento de Eucaliptus Sp. en Mendoza (Argentina)

Debido al interés de empresas siderúrgicas de Mendoza (Argentina) de contar con adecuada provisión de madera para sus plantas industriales, en el Instituto Forestal de la Facultad de Ciencias Agrarias (UNCuyo) se produjeron plantas de Eucalyptus. sp. provenientes de semillas australianas y locales. Dichas plantas fueron llevadas a campo para evaluar su comportamiento en condiciones de cultivo bajo riego. El ensayo se realizó en Nueva California (Dpto. de San Martín, Mendoza), a 653 msnm, en suelos arenosos, profundos, sueltos, permeables y con poca capacidad de retención de agua. Se regó por aspersión con una lámina de 70 mm cada 10 días en verano y cada 20 en invierno. Las especies y procedencias ensayadas fueron: E. camaldulensis procedencias 15022, 15028, 15195, 15799 y local; E. badjensis procedencia 17127; E. intertexta procedencias 15095 y 15886; E. grandis procedencia 12081; E. fastigata procedencia 17126; E. johnstonii procedencia 15352; E. astringens procedencia 12842; E. amygdalina procedencia 12831; E. andrewsii ssp andrewsii procedencia 13037; E. regnans procedencia 12034; E. tereticornis procedencias 13301, 13304, 13309 y local; E. benthami procedencia 17347; E. sargentii procedencia 12406; E. viminalis procedencia 12884; E. globulus ssp. bicostata; E. sideroxylon de procedencia local; E. dalrympleana procedencias 13348 y 15273: E. cinerea procedencia 25 de Mayo (Buenos Aires) y E. leucoxylon de procedencia local. Se evaluó el comportamiento al primer año, expresado por el número de fallas producidas en cada 100 plantas. Las especies más promisorias fueron: E. camaldulensis procedencia 15022, E. camaldulensis procedencia 15799, E. camaldulensis procedencia 15195, E. tereticornis procedencia 13309 y E. camaldulensis de procedencia local, con menos del 30 % de fallas. Además, anualmente se tomaron los datos dasométricos de diámetro altura pecho (DAP) y altura total de cada una de las plantas. Al cuarto año, las especies más destacadas fueron: E. camaldulensis procedencias 15022, 15195 y local, todas ellas con diámetros entre 9 y 12 cm y alturas entre 7 y 9 m.