Pumilio Forests Research Articles

Effects of fire severity in a north Patagonian subalpine forest

Question: What is the relative importance of fire-induced canopy mortality, soil burning and post-fire herbivory on tree seedling performance? Location: Subalpine Nothofagus pumilio forests at Challhuaco valley (41°13'S, 71°19'W), Nahuel Huapi National Park, Argentina. Methods: We fenced and transplanted soils of three burning severities along a fire severity gradient produced by a fire in 1996. Over two growing seasons we monitored soil water, direct incoming solar radiation, seedling survival, final seedling total biomass and root/shoot ratio. Additionally, we assessed severity-related changes in soil properties. Results: Incoming radiation (an indicator of the amount of canopy cover left by the fire) was the primary factor influencing spring and summer top soil water availability, first and second-year seedling survival and seedling growth. While seedling survival and soil water content were negatively affected by increased radiation, seedling final biomass was highest in very open microsites. Burned soils showed lower water holding capacity and soil carbon; however these changes did not affect topsoil water, and, contrary to expectation, there was a slight tendency toward higher seedling survival on more heavily burned soils. Herbivory significantly reduced seedling survival, but only under high-radiation conditions. While the effect of radiation on final seedling biomass was not affected by herbivory, R/S ratios were significantly reduced by herbivory in high radiation microsites. Conclusions: Despite inducing faster aerial growth, increased radiation and herbivory in severely burned sites may effectively prevent post-fire regeneration in north Patagonian subalpine forest where seed sources are not limiting.

Browsing by guanaco ( Lama guanicoe) on Nothofagus pumilio forest gaps in Tierra del Fuego, Chile

The presence of guanaco ( Lama guanicoe, Muller 1776, Camelidae) in forests of Nothofagus pumilio (Poepp. et Endl.) Krasser. (lenga) in Tierra del Fuego has been associated with browsing damage in the regeneration of these forests, but little quantitative data are available. In developing and implementing forest management plans for N. pumilio forests, the effects of guanaco browsing are a major source of variation in attaining regeneration and growth goals, however, guanaco is not generally accounted for in management planning in the region. In this study we examined the browsing damage levels of guanaco and introduced livestock on N. pumilio regeneration occurring in canopy gaps of forests in Tierra del Fuego, Chile (54°12′S, 68°45′W). Relationships were established between browsing levels and gap characteristics like gap size, gap age and abundance of regeneration. Results indicated that 88.7% of regeneration growing in gaps experienced some degree of damage by browsing, and that the degree of damage was higher in smaller gaps, which might depend on the size of guanaco herds. We also found that the degree of damage was positively related with the abundance of guanacos. However, no relationship was found between gap size and abundance of guanacos.

Soil–plant relationships and tree distribution in old growth Nothofagus betuloides and Nothofagus pumilio forests of Tierra del Fuego

The evergreen Nothofagus betuloides and deciduous Nothofagus pumilio live close together in Tierra del Fuego. The fact that these two species rarely form mixed forests suggests that the soil factor can contribute to the distribution of two species on a local scale. Most of these forests are undisturbed; therefore, soil characteristics may reflect both the influence of the species and of the dominant pedogenetic processes. In this paper, we aim to study how soil characteristics can affect nutrient cycling, the strategies of tree nutrition and the distribution of Nothofagus forests in Tierra del Fuego. Twenty-two soils in these two types of forests in contrasted topographic positions were sampled and analysed. The dominant soil processes were waterlogging in the evergreen forest and podzolisation in the deciduous one. Within each type of forest we observed large variability in soils. Nutrient-poor litter slowed down nitrogen cycling. However, phosphorus mobilisation was high in nutrient-poor environments because of low pH and waterlogging. Chemical and biological characteristics of the Oa horizon were able to discriminate between forest types while mineral soil characteristics were not. Biological activity of the organic horizons was limited by low pH and, in N. betuloides forests, also by waterlogging conditions. According to this pattern, N. betuloides grows in less fertile soils and thus has lower nutrient concentrations in leaves. In contrast, N. pumilio grows in soils with higher fertility and consequently has high nutrient content in leaves. Despite growing in low fertility sites, N. betuloides grows at a rate similar to that of N. pumilio. This suggests that the evergreen species is more efficient in using nutrients and better adapted to waterlogging conditions.

SPATIOTEMPORAL INFLUENCES OF CLIMATE ON ALTITUDINAL TREELINE IN NORTHERN PATAGONIA

Tree radial growth and seedling establishment of Nothofagus pumilio at alpine treeline near 40° S latitude in Chile and Argentina show time- and site-dependent relationships to interannual-and decadal-scale climate variation. Six treelines were sampled at two spatial scales corresponding to regional and local climates. A shift in climate from cool–wet to warm–dry conditions facilitated comparison of climate–vegetation relationships during two distinct periods: 1957–1976 and 1977–1996. For each treeline, tree radial growth and seedling establishment were correlated against monthly and seasonal temperature, precipitation, moisture availability, and two indices of El Niño–Southern Oscillation (ENSO): southern oscillation index (SOI) and sea surface temperature (SST). Four key aspects of climatic influences on N. pumilio radial growth and seedling establishment were as follows. (1) The relationship between krummholz radial growth and temperature variation was nonlinear. (2) Moisture availability was the dominant climatic factor influencing seedling establishment, although temperature–precipitation interactions resulted in variability among study areas. (3) Climate conditions that facilitated Nothofagus pumilio seedling establishment were distinct, and often opposite, from those that enhanced radial growth. (4) The relationships of radial growth and seedling demography with climate and ENSO differed among study areas and have been unstable over the past 40 years. Observed spatial and temporal instabilities in vegetation–climate relationships demonstrate the complexity of treeline dynamics in northern Patagonia under a changing climate. We conclude that a directional increase in temperature, as predicted by current global climate scenarios, will not necessarily result in an upslope expansion of the N. pumilio forests growing at altitudinal treeline in northern Patagonia.

Wildfires in NW Patagonia: long-term effects on a Nothofagus forest soil

In NW Patagonia, Argentina, poor regeneration after fires of Nothofagus pumilio (Poepp. and Endl.) Krasser forests located in drier environments has been attributed to probable edaphic changes. We studied the long-term effects of wildfire on the mineralogical, physical, chemical and biological properties of a soil developed from volcanic-ashes under N. pumilio forests. Soils from six small patches burned in January 1996 and of undisturbed forest were sampled at a depth of 0–10 cm in March 1996, 1997, 1998 and 2000. As biological soil indicators we assessed N in microbial biomass (N-MB) and potential N mineralization (pNmin). Chemical properties were analyzed for all 4 years in dry samples, N-BM and pNmin in rewetted samples in 1996 and 1997, and in field-moist samples in 1998 (pNmin) and 2000 (N-MB). Additionally, we measured soil moisture twice during the growing seasons of 1998 and 2000 at 0–16 cm, and mineralogical and physical properties once in 1998. The main effects of fire were: (i) a significant increase in pH, electrical conductivity, extractable P and cations (Ca, Mg, Na, K) and a significant decrease in organic C and total N; 4 years after the fire, C and N were still, respectively, 52 and 20% lower, pH was one unit higher, and electrical conductivity and extractable P were twice as high as in the unburned control; (ii) a considerable decrease in N-MB (>90%), without significant recovery in subsequent years; (iii) an increase of pNmin at the beginning of the incubation period, decreasing afterwards to only 4–44% the levels in the unburned soil; and (iv) a decrease of 31% in field capacity and 56% in soil moisture. No mineralogical changes in the amorphous soil components were observed. Although volcanic soils show a high capacity to stabilize organic matter, buffer pH, retain P and store water, the magnitude of the changes of all soil properties indicated that the intensity of the fire was very high, and might have a powerful effect on seedling emergence and survival.

Changes in Understory Species Diversity during the Nothofagus pumilio Forest Management Cycle

Human commercial activities must be compatible with sustainable management to achieve species conservation in the natural environment. After harvesting, diversity and abundance of understory species differ substantially from the pre-harvest situation. Have knowledge of the changes that logging produces in all components of the system allows us to develop management alternatives with reduced impacts. The objective of this work was to evaluate changes in density, biomass and diversity of understory species along a forest shelterwood cut system management cycle in a Nothofagus pumilio forest. Six forest management situations (postharvesting stands and different phases of forest development) were sampled in a pure N. pumilio forest of Tierra del Fuego (Argentina) of middle-high site class (from class I to III). Species number, density and biomass were modified substantially after a shelterwood cut. These were being greatest after cutting and falling substantially when the forest canopy closes during the initial growth phase, returning to values similar to this virgin forest when the mature phase was reached. The impact of the forest management on understory species diversity is analyzed and discussed. The silvicultural practices applied to N. pumilio forest in Tierra del Fuego permit the introduction of alien flora to the system, and produce great changes during the forest management cycle.

Tree-ring growth patterns and temperature reconstruction from Nothofagus pumilio (Fagaceae) forests at the upper tree line of southern Chilean Patagonia

Nothofagus pumilio (Poepp. et Endl. Krasser) es una especie caducifolia que domina el limite arboreo superior de los Andes de Chile y Argentina entre los 35o 36' y 55o 31' S. En este trabajo describimos el desarrollo de 21 cronologias de ancho de anillos de N. pumilio para su rango mas austral de distribucion (51-55o S) en Chile, asi como el analisis de su relacion con el clima. Diez de las cronologias de ancho de anillos estudiadas muestran una tendencia al incremento y/o crecimiento sobre el promedio a partir de aproximadamente 1960 hasta 1996, lo cual coincide con un incremento sostenido en las temperaturas mostrado por los registros instrumentales de la Patagonia austral. Otra caracteristica particular del crecimiento de los arboles es un notable ciclo de cerca de 7 anos presente en tres de los sitios de estudio en la Isla Navarino, el area de estudio mas austral estudiada por nosotros (55o S). Estos dos patrones de crecimiento, representan los principales modos de variacion de los registros de anillos de crecimiento de N. pumilio en la Patagonia austral de Chile, y explican respectivamente el 14 y 28 % de la varianza total. Sobre la base de la correlacion positiva que se verifica entre el crecimiento arboreo y la temperatura en varios de los sitios de estudio analizados en este trabajo, reconstruimos las variaciones de las temperaturas minimas anuales de Punta Arenas para el periodo 1829-1996. La reconstruccion muestra que durante la mayor parte del siglo 19 las temperaturas minimas anuales permanecieron por debajo del promedio, aumentando a valores que fluctuaron en torno a la media durante el periodo 1900-1960, seguido por una clara tendencia sobre la media para el periodo posterior a 1963

Natural mortality patterns in a population of southern argentina huemul(HIppocamelus bisulcus), an endangered andean cervid

The huemul(Hippocamelus bisulcus), an endangered deer living in the Andes of southern South America, numbers 600–700 in Argentina, from at least 63 fragmented subpopulations. Very limited information exists on most populations, but there are indications that the distribution and population sizes continue to diminish, possibly through reduced reproductive rates, elevated mortality rates or both. This is the first analysis of the population ecology of a subpopulation in Argentina, made possible through the only existing compilation of numerous remains of dead huemul (n=19). Surveys were conducted between 1993 and 1999 to locate and collect remains, which were found concentrated at lower elevations. The sex ratio of adults and subadults (n=12) was 1:1, but could not be determined for fawns. Clear signs of predation was found in 37% of all deer: 50% among calves, 50% among subadults and 31% among adults. These signs occurred in 29% of adult females and 50% of adult males. Deaths occurred during winter as judged by the state of the male skulls, which indicated the phase of the antler cycle. Femur fat content of 3 deer averaged 93%. Predation signs frequently were clearly from puma(Puma concolor), which is the only natural predator of huemul. The high predation rate, high marrow fat content and no indications of deaths resulting from disease corroborate the pristine state of the of mature lenga(Nothofagus pumilio) forest. The area with a concentration of huemul carcasses appears to be the huemul's major winter habitat.

Litter fluxes and decomposition in Nothofagus pumilio stands in the region of Magallanes, Chile

Seasonal and annual litter fluxes, potential nutrient returns, and litter decomposition were evaluated in two stands, one natural stand and the other under a shelterwood system, within a natural Nothofagus pumilio forest located in the region of Magallanes, Chile. Fluxes were determined by means of 24 collectors installed in each stand. Decomposition was evaluated from the periodical record of the weight losses undergone by decomposition bags extracted from the floor of the stands. Mineral nutrient average concentrations and masses of seasonal litter contributions were determined. Annual litter flux was 2.0 t ha−1 in the natural stand and 1.0 t ha−1 in that under a shelterwood system. In both cases, the highest contributions occurred in the fall (49–51%), with leaves being the component with the highest rate, both seasonally and annually. According to weight losses, annual decomposition reached 35.8 and 53.0% in the natural stand and that under a shelterwood system, respectively. Average decomposition rates for the evaluated periods were 0.38 and 0.50, while rates at the end of the evaluation year were 0.44 and 0.76. In both estimations, the highest rates corresponded to the intervened stand. Results showed that forestry intervention significantly affects seasonal and annual contributions of organic residues, potential nutrient returns, and initial litter decomposition rates.

Changes in Nothofagus pumilio forest biodiversity during the forest management cycle. 1. Insects

Human activities, like logging, modify the dynamics and composition of virgin forest, affecting the equilibrium between the natural species. Nothofagus forests sustain an entomofauna that is endemic, and includes relict species of significant conservation importance. The aim of this work was to evaluate the changes in insect diversity and abundance of a Nothofagus pumilio forest managed by a shelterwood cut system. Insect capture was carried out using a set of traps along a horizontal and vertical gradient. Sampling was taken in day and night conditions, in post-harvesting situations and different phases of stand development. The diversity and abundance of insects varied significantly during the forest cycle (defined as 100–200 years according to site quality). One morphospecies was lost every 11 years until the end of the forest cycle. It may be necessary to modify the current silvicultural system to one that conserves insect diversity through a reduction in disturbance.

Timber production of Nothofagus pumilio forests by a shelterwood system in Tierra del Fuego (Argentina)

Nothofagus pumilio is the most important timber native species from south Patagonia of Argentina and Chile. The total volume and timber production vary according to site quality, stocking, growth phase and previous land management. The aim of this work was to evaluate the existence and the productive potential of wood for the sawmill industry in a shelterwood seed cut of N. pumilio forests along the range of site classes. Sample plots were established in 3 ha of an old-growth virgin forest without regeneration patches (SDI 95–131%) along the five classes of site (I–V). Total stand volumes varied from 400 to 1100 m 3/ha and volume density index (ratio of total volume over basal area) varied from 6 to 14 m 3/m 2. The volume yield present differ significantly among site qualities with log volumes between 40 and 400 m 3/ha. The number of timber logs decreases from the better sites towards the worst (800–200 logs/ha), as well as their volume average (0.5–0.2 m 3/log). Several published studies in timber production were compared and discussed with the obtained results. Considering new alternatives in the N. pumilio timber management allow managers to obtain higher harvesting indexes, increasing the benefits for the forest company and diminishing the annual wood areas necessary to supply the requirements of the sawmills in Tierra del Fuego.

Influences of gap microheterogeneity on the regeneration of Nothofagus pumilio in a xeric old-growth forest of northwestern Patagonia, Argentina

We experimentally examined the influences of within-gap environmental heterogeneity on regeneration patterns of Nothofagus pumilio (Poepp. & Endl.) Krasser near the xeric limit of its distribution in northern Patagonia, Argentina. Results from this xeric old-growth forest are compared with patterns previously described for the same species in mesic forests. Survival of N. pumilio seedlings beneath tree-fall gaps in this relatively xeric forest appears to be strongly influenced by moisture availability. Seedlings and saplings that have survived this demographic bottleneck are found at microsites where soil water potentials are higher, such as in the shady northern edges of tree-fall gaps (Ψ = -0.46 MPa compared with less than -0.6 MPa in other gap positions) and on coarse woody debris (Ψ = -0.29 MPa, compared with -0.51 MPa on the forest floor). Although gap creation in this dry N. pumilio forest is favorable to tree regeneration by releasing light resources, decreased water resources may switch the system from a light- to a water-limited system in some positions of the gap. This may explain the lack of regeneration of N. pumilio often observed after creation of large gaps towards the xeric end of its range and needs to be considered in the management of this important timber species.

Influences of gap microheterogeneity on the regeneration of <i>Nothofagus pumilio</i> in a xeric old-growth forest of northwestern Patagonia, Argentina

We experimentally examined the influences of within-gap environmental heterogeneity on regeneration patterns of Nothofagus pumilio (Poepp. & Endl.) Krasser near the xeric limit of its distribution in northern Patagonia, Argentina. Results from this xeric old-growth forest are compared with patterns previously described for the same species in mesic forests. Survival of N. pumilio seedlings beneath tree-fall gaps in this relatively xeric forest appears to be strongly influenced by moisture availability. Seedlings and saplings that have survived this demographic bottleneck are found at microsites where soil water potentials are higher, such as in the shady northern edges of tree-fall gaps (Ψ = -0.46 MPa compared with less than -0.6 MPa in other gap positions) and on coarse woody debris (Ψ = -0.29 MPa, compared with -0.51 MPa on the forest floor). Although gap creation in this dry N. pumilio forest is favorable to tree regeneration by releasing light resources, decreased water resources may switch the system...

High‐Andean vegetation and environmental gradients in northwestern Patagonia, Argentina

Abstract. We analysed the heterogeneity of high‐elevation vegetation on three mountains along a west‐east transect at 41 °S lat. in the Andes of northwestern Patagonia, Argentina. In this area, high‐Andean vegetation occurs as islands on mountain tops above Nothofagus pumilio forests ? with the timberline at ca. 1700 m a.s.l. We recorded floristic, topographic and substrate data in 166 sites stratified according to longitude, altitude, slope and aspect. Vegetation data were classified with TWINSPAN and ordinated with Detrended Correspondence Analysis. The relationship between environmental and floristic variation was analysed using Canonical Correspondence Analysis. In order of importance, geographical longitude, altitude and aspect were the major determinants of vegetation variation, whereas substrate texture and slope appeared less important. The combination of these factors resulted in two main vegetation gradients. The first gradient is related to a moisture availability gradient, primarily determined by longitude and secondarily to variation in wind exposure (east vs. west aspect). The second vegetation gradient is related to variation in temperature, primarily determined by altitude, and secondarily by variation in insolation related to the contrast between north and south aspects. The four communities obtained with TWINSPAN are therefore associated with four characteristic habitat types: moist‐cold, moist‐warm, dry‐cold and dry‐warm. The community of warm and dry environments is the richest and has elements in common with dry steppe communities situated at lower elevations to the east, while the vegetation of the cold‐moist habitat type has unique elements that are typical of the southern Andes. Although current climatic factors appear to be the major determinants of high‐Andean vegetation gradients, historical events of Pleistocene times probably also affected the vegetation patterns we see today.

Diametrica growth of two crown classes on half site quality Nothofagus pumilio forests in Santa Cruz (Argentina)

Nothofagus pumilio is the species of largest geographical distribution and economical importance of Patagonia forests. There are few biometric related to the Patagonia forest management planning. Then, the aim of this work coas to construct individual growth models in diameter for different crown classes of medium quality site (IS60 = 9,8 m) N. pumilio forest in Santa Cruz Province (Argentina). The Chapman-Richards model showed good biological significance and statistics. Diameter growth had different behaviour according to the crown classes. The peak of the growth was at 62 and 52 years for the superior and inferior strata, being the maximal averages growth of 0.305 cm/year for dominant trees and of 0,12 cm/year for intermediate trees. The indirect validation of volumetric growth of the threw an error that varied between the 2.5 p. 100 and 20 p. 100

A Qualitative Methodologic Proposal to describe regeneration on Nothofagus pumilio forests

It's presented a new methodologic proposal to be applied in Nothofagus pumilio forests. It arranged by relating on a qualitative way, certain regeneration variables with canopy cover and understory abundance. The field evaluation is quick and it is suggested like an accomplishment of large studies such as Forest Inventories, installation of Permanent Sample Plots and others. The information processing and evaluation allows to build Position and Surface Diagrams and to structure Decision Zones by means of double way numeric charts which relate two variables as average percentage frequencies of the sample. These values are then extended to management surface. Every Decision Zone is a cluster of similar situations that can be under the same silvicultural treatment. The Zones lead the forester towards the most convenient treatment but they must be accompanied by dendrometric analysis.

Age structure and dynamics of Patagonian beech forests in Torres del Paine National Park, Chile

This study documents the stem size and age-structure in forests dominated by different species of Nothofagus in Torres del Paine National Park (51° S), in the Chilean Patagonian region. We also explored the relationship between the various types of Nothofagus forest and postglacial succession. Pioneer stands on moraine fields 1–2 km of the glacier front are dominated by Nothofagus betuloides and Nothofagus antarctica. Moraines appear to be first colonized by the evergreen N. betuloides, followed within 5–7 years by deciduous N. antarctica. Nothofagus antarctica may replace the former species and develop monospecific stands on glacial valleys. Most trees in the N. antarctica stand studied were older than 40 years and floods may cause a significant mortality of young trees. Recruitment from seed seems to be infrequent. Old-growth stands dominated by deciduous Nothofagus pumilio occupy more stable substrates, and probably represent the last stage of postglacial succession. This long-lived tree species had recorded ages over 200 years. The canopy of N. pumilio forests appears to be a mosaic of even-aged, old-growth patches. We propose that regeneration episodes follow the blowdown of a large portion of the canopy, with long intervals with little or no regeneration. Windstorms may be an important force influencing the regeneration of N. pumilio. Exogenous disturbances, such as floods and windstorms, are an integral part of the forest cycle in the Patagonian region.

Dry-Matter Production of Two Species of Bamboo (Chusquea Culeou and C. Tenuiflora) in South-Central Chile

SUMMARY (1) In south-central Chile, bamboos of the genus Chusquea often dominate the undergrowth of the mainly broad-leaved rain forests, and where these forests have been burned or logged they frequently form dense thickets in which tree regeneration is greatly impeded. (2) Standing crop and above-ground net primary production were estimated for a pure stand of C. culeou at 700 m altitude, and standing crop for C. tenuiflora in the understorey of a mixed Nothofagus betuloides-N. pumilio forest near the timberline at 1040 m in the Andes. (3) Above-ground biomass of the Chusquea culeou thicket and the C. tenuiflora undergrowth was approximately 156-162 t ha- 1 and 13.0 t ha- 1, respectively. (4) The annual above-ground net primary production for the C. culeou thicket was approximately 10.0-1 1.4 t ha- 1.

Post-glacial vegetation in the South Patagonian territory of the giant ground sloth, Mylodon

By comparison with the major modern plant communities of southern Patagonia, the changing post-glacial vegetation of the region is reconstructed from macrofossils derived from deposits in the Cueva del Mylodon, Ultima Esperanza, S. Chile. The oldest deposits, carbon-dated as c. 12,400 B.P., comprise dung of the extinct ground sloth Mylodon darwinii and show the animal to have fed entirely on Cyperaceae, Gramineae and species associated with these in the modern cool, wet sedge-grasslands of western Patagonia, communities which would be expected after the retreat of the ice. Overlying deposits of well-preserved, wind-blown leaf-litter permitted some quantitative analyses which show a rise of evergreen forest dominated by Nothofagus betuloides that reached its maximum c. 7000 B.P. and then declined as it was replaced by deciduous N. pumilio forest. A break in the fossil plant record, covering the human occupation about 5643 B.P. and the subsequent final appearance of Mylodon remains, is followed by evidence of mixed evergreen/deciduous forest in which Nothofagus pumilio gradually increases in importance to give deciduous forest some 2500 years ago similar to that found in the environs of the cave in historical times. Comparison with pollen diagrams shows that the modern climatic and vegetation difference between E. Fudgia and Ultima Eeperanza has persisted throughout the post-glacial period.

Plant Succession in a Timberline Depressed by Vulcanism in South-Central Chile

The vegetation of the Antillanca Valley in the Andes of southcentral Chile consists of high altitude fellfields, species-rich scrub grasslands, Nothofagus krummholz, deciduous N. pumilio forests, and mixed evergreen deciduous NVothofagus forests. Catastrophic vulcanism has depressed the timberlines an average of 100 to 300 m and greatly affected these vegetation types. Locally, timberline is determined under the influence of such disruptive factors as withthrow, unstable slopes, and avalanches. Succession is interpreted on the bases of species distributions in zones of environmental stress, population structures, and the observed responses of the dominant Nothofagus spp. to avalanche damage and burial by scoria deposition. This study thus documents the dynamic and transitory nature of the frequently-described vegetation zones of southcentral Chile.