Home About us Contact
|
Home About us Contact | ||
|
|
||
Forest Growth (forest + growth)
Selected AbstractsSpatial analysis of an invasion front of Acer platanoides: dynamic inferences from static dataECOGRAPHY, Issue 3 2005Wei Fang It is an open question whether the invading tree species Acer platanoides is invading and displacing native trees within pre-existing forest stands, or merely preferentially occupying new stands of secondary forest growth at the edges of existing forests. Several threads of spatial pattern analyses were used to assess the invasibility of A. platanoides, and to link the invasion to the structure of a plant community in the deciduous forest of the northeastern United States. The analyses were based on maps of a contiguous 100×50 m area along an A. platanoides infestation gradient. The distribution of A. platanoides was highly aggregated and the population importance value increased from 28.1 to 38.5% according to mortality estimated from standing dead trees, while the distribution of native tree species was close to random and importance value of Quercus spp. decreased from 33.4 to 26.9% over time. The size distributions of each tree species across distance indicated that A. platanoides was progressively invading the interior of the forest while the native species (including A. rubrum) were not spreading back towards the A. platanoides monospecific patch. The null hypothesis of no invasibility was rejected based on quantile regressions. There were negative correlations between A. platanoides density and the densities of native species in different functional groups, and negative correlation of A. platanoides density and the species diversity in forest understory. The null hypothesis that A. platanoides invasion did not suppress native trees or understory was rejected based on Dutilleul's modified t-test for correlation, consistent with experimental results in the same study site. The combination of multiple spatial analyses of static data can be used to infer historical dynamical processes that shape a plant community structure. The concept of "envelop effects" was discussed and further developed. [source] Effect Of Height On Tree Hydraulic Conductance Incompletely Compensated By Xylem TaperingFUNCTIONAL ECOLOGY, Issue 2 2005S. ZAEHLE Summary 1The hydraulic limitation theory proposes that the decline of forest productivity with age is a consequence of the loss of whole-plant and leaf-specific hydraulic conductance with tree height caused by increased friction. Recent theoretical analyses have suggested that tapering (the broadening of xylem vessel diameter from terminal branches to the base of the stem) could compensate completely for the effect of tree height on hydraulic conductance, and thus on tree growth. 2The data available for testing this hypothesis are limited, but they do not support the implication that whole-tree and leaf-specific hydraulic conductance are generally independent of tree height. Tapering cannot exclude hydraulic limitation as the principle mechanism for the observed decline in growth. 3Reduction of the leaf-to-sapwood area ratio, decreased leaf water potential, loss of leaf-cell turgor, or osmotic adjustments in taller trees could reduce the effect of increased plant hydraulic resistance on stomatal conductance with height. However, these mechanisms operate with diminishing returns, as they infer increased costs to the tree that will ultimately limit tree growth. To understand the decline in forest growth, the effects of these acclimation mechanisms on carbon uptake and allocation should be considered. [source] Interannual climatic variation mediates elevated CO2 and O3 effects on forest growthGLOBAL CHANGE BIOLOGY, Issue 6 2006MARK E. KUBISKE Abstract We analyzed growth data from model aspen (Populus tremuloides Michx.) forest ecosystems grown in elevated atmospheric carbon dioxide ([CO2]; 518 ,L L,1) and ozone concentrations ([O3]; 1.5 × background of 30,40 nL L,1 during daylight hours) for 7 years using free-air CO2 enrichment technology to determine how interannual variability in present-day climate might affect growth responses to either gas. We also tested whether growth effects of those gasses were sustained over time. Elevated [CO2] increased tree heights, diameters, and main stem volumes by 11%, 16%, and 20%, respectively, whereas elevated ozone [O3] decreased them by 11%, 8%, and 29%, respectively. Responses similar to these were found for stand volume and basal area. There were no growth responses to the combination of elevated [CO2+O3]. The elevated [CO2] growth stimulation was found to be decreasing, but relative growth rates varied considerably from year to year. Neither the variation in annual relative growth rates nor the apparent decline in CO2 growth response could be explained in terms of nitrogen or water limitations. Instead, growth responses to elevated [CO2] and [O3] interacted strongly with present-day interannual variability in climatic conditions. The amount of photosynthetically active radiation and temperature during specific times of the year coinciding with growth phenology explained 20,63% of the annual variation in growth response to elevated [CO2] and [O3]. Years with higher photosynthetic photon flux (PPF) during the month of July resulted in more positive growth responses to elevated [CO2] and more negative growth responses to elevated [O3]. Mean daily temperatures during the month of October affected growth in a similar fashion the following year. These results indicate that a several-year trend of increasingly cloudy summers and cool autumns were responsible for the decrease in CO2 growth response. [source] Assessing forest growth across southwestern Oregon under a range of current and future global change scenarios using a process model, 3-PGGLOBAL CHANGE BIOLOGY, Issue 1 2001N. C. Coops Summary With improvements in mapping regional distributions of vegetation using satellite-derived information, there is an increasing interest in the assessment of current limitations on forest growth and in making projections of how productivity may be altered in response to changing climatic conditions and management policies. We utilised a simplified physiologically based process model (3-PG) across a 54 000 km2 mountainous region of southwestern Oregon, USA, to evaluate the degree to which maximum periodic mean annual increment (PAI) of forests could be predicted at a set of 448 forest inventory plots. The survey data were pooled into six broad forest types (coastal rain forest, interior coast range forest, mixed conifer, dry-site Douglas-fir, subalpine forest, and pine forest) and compared to the 3-PG predictions at a spatial resolution of 1 km2. We found good agreement (r2 = 0.84) between mean PAI values of forest productivity for the six forest types with those obtained from field surveys. With confidence at this broader level of integration, we then ran model simulations to evaluate the constraints imposed by (i) soil fertility under current climatic conditions, (ii) the effect of doubling monthly precipitation across the region, and (iii) a widely used climatic change scenario that involves modifications in monthly mean temperatures and precipitation, as well as a doubling in atmospheric CO2 concentrations. These analyses showed that optimum soil fertility would more than double growth, with the greatest response in the subalpine type and the least increase in the coastal rain forests. Doubling the precipitation increased productivity in the pine type (> 50%) with reduced responses elsewhere. The climate change scenario with doubled atmospheric CO2 increased growth by 50% on average across all forest types, primarily as a result of a projected 33% increase in photosynthetic capacity. This modelling exercise indicates that, at a regional scale, a general relationship exists between simulated maximum leaf area index and maximum aboveground growth, supporting the contention that satellite-derived estimates of leaf area index may be good measures of the potential productivity of temperate evergreen forests. [source] Jobs, Houses, and Trees: Changing Regional Structure, Local Land-Use Patterns, and Forest Cover in Southern IndianaGROWTH AND CHANGE, Issue 3 2003Darla K. Munroe Land-use and -cover change is a topic of increasing concern as interest in forest and agricultural land preservation grows. Urban and residential land use is quickly replacing extractive land use in southern Indiana. The interaction between land quality and urban growth pressures is also causing secondary forest growth and forest clearing to occur jointly in a complex spatial pattern. It is argued that similar processes fuel the abandonment of agricultural land leading to private forest regrowth, changes in topography and land quality, and declining real farm product prices. However, the impact of urban growth and development on forests depends more strongly on changes in both the residential housing and labor markets. Using location quotient analysis of aggregate employment patterns, and the relationship between regional labor market changes, the extent of private forest cover was examined from 1967 to 1998. Then an econometric model of land-use shares in forty southern Indiana counties was developed based on the net benefits to agriculture, forestland, and urban uses. To test the need to control explicitly for changes in residential demand and regional economic structure, a series of nested models was estimated. Some evidence was found that changing agricultural profitability is leading to private forest regrowth. It was also uncovered that the ratio of urban to forest land uses is better explained by incorporating measures of residential land value and industrial concentration than simply considering population density alone. [source] SWAT2000: current capabilities and research opportunities in applied watershed modellingHYDROLOGICAL PROCESSES, Issue 3 2005J. G. Arnold Abstract SWAT (Soil and Water Assessment Tool) is a conceptual, continuous time model that was developed in the early 1990s to assist water resource managers in assessing the impact of management and climate on water supplies and non-point source pollution in watersheds and large river basins. SWAT is the continuation of over 30 years of model development within the US Department of Agriculture's Agricultural Research Service and was developed to ,scale up' past field-scale models to large river basins. Model components include weather, hydrology, erosion/sedimentation, plant growth, nutrients, pesticides, agricultural management, stream routing and pond/reservoir routing. The latest version, SWAT2000, has several significant enhancements that include: bacteria transport routines; urban routines; Green and Ampt infiltration equation; improved weather generator; ability to read in daily solar radiation, relative humidity, wind speed and potential ET; Muskingum channel routing; and modified dormancy calculations for tropical areas. A complete set of model documentation for equations and algorithms, a user manual describing model inputs and outputs, and an ArcView interface manual are now complete for SWAT2000. The model has been recoded into Fortran 90 with a complete data dictionary, dynamic allocation of arrays and modular subroutines. Current research is focusing on bacteria, riparian zones, pothole topography, forest growth, channel downcutting and widening, and input uncertainty analysis. The model SWAT is meanwhile used in many countries all over the world. Recent developments in European Environmental Policy, such as the adoption of the European Water Framework directive in December 2000, demand tools for integrative river basin management. The model SWAT is applicable for this purpose. It is a flexible model that can be used under a wide range of different environmental conditions, as this special issue will show. The papers compiled here are the result of the first International SWAT Conference held in August 2001 in Rauischholzhausen, Germany. More than 50 participants from 14 countries discussed their modelling experiences with the model development team from the USA. Nineteen selected papers with issues reaching from the newest developments, the evaluation of river basin management, interdisciplinary approaches for river basin management, the impact of land use change, methodical aspects and models derived from SWAT are published in this special issue. Copyright © 2005 John Wiley & Sons, Ltd. [source] A world-wide study of high altitude treeline temperaturesJOURNAL OF BIOGEOGRAPHY, Issue 5 2004Christian Körner Abstract Aim, At a coarse scale, the treelines of the world's mountains seem to follow a common isotherm, but the evidence for this has been indirect so far. Here we aim at underpinning this with facts. Location, We present the results of a data-logging campaign at 46 treeline sites between 68° N and 42° S. Methods, We measured root-zone temperatures with an hourly resolution over 1,3 years per site between 1996 and 2003. Results, Disregarding taxon-, landuse- or fire-driven tree limits, high altitude climatic treelines are associated with a seasonal mean ground temperature of 6.7 °C (±0.8 SD; 2.2 K amplitude of means for different climatic zones), a surprisingly narrow range. Temperatures are higher (7,8 °C) in the temperate and Mediterranean zone treelines, and are lower in equatorial treelines (5,6 °C) and in the subarctic and boreal zone (6,7 °C). While air temperatures are higher than soil temperatures in warm periods, and are lower than soil temperatures in cold periods, daily means of air and soil temperature are almost the same at 6,7 °C, a physics driven coincidence with the global mean temperature at treeline. The length of the growing season, thermal extremes or thermal sums have no predictive value for treeline altitude on a global scale. Some Mediterranean (Fagus spp.) and temperate South Hemisphere treelines (Nothofagus spp.) and the native treeline in Hawaii (Metrosideros) are located at substantially higher isotherms and represent genus-specific boundaries rather than boundaries of the life-form tree. In seasonal climates, ground temperatures in winter (absolute minima) reflect local snow pack and seem uncritical. Main conclusions, The data support the hypothesis of a common thermal threshold for forest growth at high elevation, but also reflect a moderate region and substantial taxonomic influence. [source] Linking Amazonian secondary succession forest growth to soil propertiesLAND DEGRADATION AND DEVELOPMENT, Issue 4 2002D. Lu Abstract The Amazon Basin has suffered extensive deforestation in the past 30 years. Deforestation typically leads to changes in climate, biodiversity, hydrological cycle, and soil degradation. Vegetation succession plays an important role in soil restoration through accumulation of vegetation biomass and improved soil/plant interaction. However, relationships between succession and soil properties are not well known. For example, how does vegetation succession affect nutrient accumulation? Which soil factors are important in influencing vegetation growth? What is the best way to evaluate soil fertility in the Amazon basin? This paper focuses on the interrelationships between secondary succession and soil properties. Field soil sample data and vegetation inventory data were collected in two regions of Brazilian Amazonia (Altamira and Bragantina). Soil nutrients and texture were analyzed at successional forest sites. Multiple regression models were used to identify the important soil properties affecting vegetation growth, and a soil evaluation factor (SEF) was developed for evaluating soil fertility in Alfisols, Ultisols, and Oxisols, which differ in the ways they affect vegetation growth. For example, the upper 40,cm of soil is most important for vegetation growth in Alfisols, but in Ultisols and Oxisols deeper horizons significantly influence vegetation growth rates. Accumulation of vegetation biomass increased soil fertility and improved soil physical structure in Alfisols but did not completely compensate for the nutrient losses in Ultisols and Oxisols; however, it significantly reduced the rate of nutrient loss. Copyright © 2002 John Wiley & Sons, Ltd. [source] | |||||||||||||