Models to Assess the Risk of Snow and Wind Damage in Pine, Spruce, and Birch Forests in Sweden

3 are damaged annually by snow and wind, roughly corresponding to a value of US$150 million, and in Europe, the damage amounts to hundreds of millions of US dollars each year. To help to reduce these losses, tools for risk assessment within forest management have been developed. Predictions were developed of the risk of damage from snow and wind to Scots pine (Pinus sylvestris L.), Norway spruce [Picea abies (L.) Karst.] and Birch (Betula spp. L.) plots using tree, stand, and site characteristics. The data were obtained from 6756 permanent sample plots within the Swedish National Forest Inventory, which were inventoried twice at five-year intervals between 1983 and 1992. Input data for model development used measurements from the first inventory of tree characteristics for the largest sample tree, stand, and site data, and records of snow and wind damage from the second inventory. Models were developed for three different regions for pine- and spruce-dominated sites, while models for the whole country were developed for birch sites. In general the estimated proportion of damaged plots was highly overestimated (31.7%–56.2%), compared with the observed proportion of 3.4%–11.9%. The models for Norway spruce comprising tree, stand, and site data show the best predictability of damaged plots, with 60.6%–67.6% of plots correctly classified. It is concluded that the models developed can be used to detect sites with a high probability of damage from snow and wind, and thus be used as tools to reduce future damage and costs in practical forestry.     

Sampling and Mapping a Soil Erosion Cover Factor by Integrating Stratification,Model Updating and Cokriging with Images

Cost-efficient sample designs for collection of ground data and accurate mapping of variables are required to monitor natural resources and environmental and ecological systems. In this study, a sample design and mapping method was developed by integrating stratification, model updating, and cokriging with Landsat Thematic Mapper (TM) imagery. This method is based on the spatial autocorrelation of variables and the spatial cross-correlation among them. It can lead to sample designs with variable grid spacing, where sampling distances between plots vary depending on spatial variability of the variables from location to location. This has potential cost-efficiencies in terms of sample design and mapping. This method is also applicable for mapping in the case in which no ground data can be collected in some parts of a study area because of the high cost. The method was validated in a case study in which a ground and vegetation cover factor was sampled and mapped for monitoring soil erosion. The results showed that when the sample obtained with three strata using the developed method was used for sampling and mapping the cover factor, the sampling cost was greatly decreased, although the error of the map was slightly increased compared to that without stratification; that is, the sample cost-efficiency quantified by the product of cost and error was greatly increased. The increase of cost-efficiency was more obvious when the cover factor values of the plots within the no-significant-change stratum were updated by a model developed using the previous observations instead of remeasuring them in the field.     

The role of stand history in assessing forest impacts

Air pollution, harvesting practices, and natural disturbances can affect the growth of trees and forest development. To make predictions about anthropogenic impacts on forests, we need to understand how these factors affect tree growth. In this study the effect of disturbance history on tree growth and stand structure was examined by using a computer model of forest development. The model was run under the climatic conditions of east Tennessee, USA, and the results compared to stand structure and tree growth data from a yellow poplar-white oak forest. Basal area growth and forest biomass were more accurately projected when rough approximations of the thinning and fire history typical of the measured plots were included in the simulation model. Stand history can influence tree growth rates and forest structure and should be included in any attempt to assess forest impacts.     

A Water Yield‐Oriented Practical Approach for Multifunctional Forest Management and its Application in Dryland Regions of China

Mountainous forest areas are vitally important for water supply in dryland regions which suffer from high erosion risk and severe water shortage. Massive afforestation, mainly for erosion control, may reduce the water yield and threaten local water supply security. Moreover, many over‐dense forests due to a strict logging ban policy have produced remarkably negative impacts for both forests (e.g., low timber quality, restricted natural regeneration, and high stand instability) and water yield. To satisfy the rapidly increasing demands on water supply and other services, a practical approach for managing forest stands in a multifunctional way, which particularly addresses water yielding, is urgently required. For this purpose, we integrated the existing knowledge and experience, designed an “ideal” stand structure to represent multifunctional forest (MFF) and determined its key parameters (a ground coverage of >0.7, a canopy density around 0.7, and an H/DBH ratio (tree height [m] to the diameter at breast height [cm]) of <0.7). Moreover, a decision process for MFF stand management was recommended as: (1) investigating the site quality; (2) identifying the site‐specific main forest functions; (3) quantifying the stand structure; (4) diagnosing the stand structure by comparing with the “ideal” one; and (5) arranging the functions/structure‐oriented management measures. In this way, the water‐yielding function can be improved and meanwhile other forest functions can be promoted.     

Mechanistic Simulation of Tree Effects in an Urban Water Balance Model1

Abstract: A semidistributed, physical‐based Urban Forest Effects – Hydrology (UFORE‐Hydro) model was created to simulate and study tree effects on urban hydrology and guide management of urban runoff at the catchment scale. The model simulates hydrological processes of precipitation, interception, evaporation, infiltration, and runoff using data inputs of weather, elevation, and land cover along with nine channel, soil, and vegetation parameters. Weather data are pre‐processed by UFORE using Penman‐Monteith equations to provide potential evaporation terms for open water and vegetation. Canopy interception algorithms modified established routines to better account for variable density urban trees, short vegetation, and seasonal growth phenology. Actual evaporation algorithms allocate potential energy between leaf surface storage and transpiration from soil storage. Infiltration algorithms use a variable rain rate Green‐Ampt formulation and handle both infiltration excess and saturation excess ponding and runoff. Stream discharge is the sum of surface runoff and TOPMODEL‐based subsurface flow equations. Automated calibration routines that use observed discharge has been coupled to the model. Once calibrated, the model can examine how alternative tree management schemes impact urban runoff. UFORE‐Hydro model testing in the urban Dead Run catchment of Baltimore, Maryland, illustrated how trees significantly reduce runoff for low intensity and short duration precipitation events.     

NATURAL EROSION RATES AND THEIR PREDICTION IN THE IDAHO BATHOLITH1

ABSTRACT: Natural rates of surface erosion on forested granitic soils in central Idaho were measured in 40 m² bordered erosion plots over a period of four years. In addition, we measured a variety of site variables, soil properties, and summer rainstorm intensities in order to relate erosion rates to site attributes. Median winter erosion rates are approximately twice summer period rates, however mean summer rates are nearly twice winter rates because of infrequent high erosion caused by summer rainstorms. Regression equation models and regression tree models were constructed to explore relationships between erosion and factors that control erosion rates. Ground cover is the single factor that has the greatest influence on erosion rates during both summer and winter periods. Rainstorm intensity (erosivity index) strongly influences summer erosion rates, even on soils with high ground cover percentages. Few summer storms were of sufficient duration and intensity to cause rilling on the plots, and the data set was too small to elucidate differences in rill vs. interrill erosion. The regression tree models are relatively less biased than the regression equations developed, and explained 70 and 84 percent of the variability in summer and winter erosion rates, respectively.     

Mapping probability of fire occurrence in San Jacinto Mountains,California, USA

An ecological data base for the San Jacinto Mountains, California, USA, was used to construct a probability model of wildland fire occurrence. The model incorporates both environmental and human factors, including vegetation, temperature, precipitation, human structures, and transportation. Spatial autocorrelation was examined for both fire activity and vegetation to determine the specification of neighborhood effects in the model. Parameters were estimated using stepwise logistic regressions. Among the explanatory variables, the variable that represents the neighborhood effects of spatial processes is shown to be of great importance in the distribution of wildland fires. An important implication of this result is that the management of wildland fires must take into consideration neighborhood effects in addition to environmental and human factors. The distribution of fire occurrence probability is more accurately mapped when the model incorporates the spatial term of neighborhood effects. The map of fire occurrence probability is useful for designing large-scale management strategies of wildfire prevention.     

FOREST GROWTH IMPACT ON PEAK SNOW PACK MEASUREMENTS AT LONG TERM SNOW COURSES1

ABSTRACT: Snow course surveys in late winter provide stream‐flow forecasters with their best information for making water supply and flood forecasts for the subsequent spring and summer runoff period in mountainous regions of western North America. Snow survey data analyses are generally based on a 30‐year “normal” period. It is well documented that forest cover changes over time will affect snow accumulation on the ground within forests. This paper seeks to determine if forest cover changes over decades at long term snow courses decrease measured peak snow water equivalent (SWE) enough to affect runoff prediction. Annual peak SWE records were analyzed at four snow courses in two different forest types having at least 25 years of snowpack data to detect any decreases in SWE due to forest growth. No statistically significant decreases in annual peak SWE over time were found at any of these four snow courses. The wide range of annual winter precipitation and correspondingly highly variable peak snowpack accumulation, as well as many other weather and site variables, masked any minor trends in the data.     

Modeling wilderness campsites: Factors that influence amount of impact

A standard campsite model is proposed and then manipulated to examine the influence of individual variables on amount of vegetation loss. Amount of impact is influenced by amount of use, vegetation fragility, vegetation density, and the degree to which activities are concentrated spatially on the site. Degree of concentration also influences the importance of the other explanatory variables. Amount of use and vegetation fragility are equally important determinants of impact and are most influential where activity concentration is low. The curvilinear relationship between amount of use and amount of impact can be explained by the tendency for activities to become increasingly concentrated as amount of use increases. This relationship should not vary with regional or environmental characteristics except where these influence degree of activity concentration.     

Assessing Natural and Anthropogenic Variability in Wetland Structure for Two Hydrogeomorphic Riverine Wetland Subclasses

The hydrogeomorphic approach (HGM) to wetland classification and functional assessment has been applied regionally throughout the United States, but the ability of HGM functional assessment models to reflect wetland condition has limited verification. Our objective was to determine how variability derived from anthropogenic effects and natural variability impacted site assessment variables within regional wetland subclasses in central Oklahoma. We collected data for nine potential assessment variables including vegetation physiognomy (e.g., tree basal area, herbaceous cover, canopy cover, etc.) and soil organic matter at wetlands of two HGM riverine subclasses (oxbow and riparian) in May and June, 2010. Using Akaike Information Criteria, we identified limited relationships between landscape disturbance metrics and assessment variables within subclasses. The high degree of natural variability from climatic and hydrologic factors within both subclasses may be masking the impact of landscape disturbance on the other measured assessment variables. Precipitation had significant effects on assessment variables within each of the subclasses. To reduce natural climatic variability, the reference domain may need to be further subdivided. The approach used in this study provides fairly rapid and quantitative methods for evaluating the effectiveness of using HGM assessment variables in assessing wetland condition regionally.     

A Comparison of Data Sets Varying in Spatial Accuracy Used to Predict the Occurrence of Wildlife-Vehicle Collisions

Wildlife-vehicle collisions (WVCs) pose a significant safety and conservation concern in areas where high-traffic roads are situated adjacent to wildlife habitat. Improving transportation safety, accurately planning highway mitigation, and identifying key habitat linkage areas may all depend on the quality of WVC data collection. Two common approaches to describe the location of WVCs are spatially accurate data derived from global positioning systems (GPS) or vehicle odometer measurements and less accurate road-marker data derived from reference points (e.g., mile-markers or landmarks) along the roadside. In addition, there are two common variable types used to predict WVC locations: (1) field-derived, site-specific measurements and (2) geographic information system (GIS)-derived information. It is unclear whether these different approaches produce similar results when attempting to identify and explain the location of WVCs. Our first objective was to determine and compare the spatial error found in road-marker data (in our case the closest mile-marker) and landmark-referenced data. Our second objective was to evaluate the performance of models explaining high- and low-probability WVC locations, using congruent, spatially accurate (<3-m) and road-marker (<800-m) response variables in combination with field- and GIS-derived explanatory variables. Our WVC data sets were comprised of ungulate collisions and were located along five major roads in the central Canadian Rocky Mountains. We found that spatial error (mean ± SD) was higher for WVC data referenced to nearby landmarks (516 ± 808 m) than for data referenced to the closest mile-marker data (401 ± 219 m). The top-performing model using the spatially accurate WVC locations contained all explanatory variable types, whereas GIS-derived variables were only influential in the best road-marker model and the spatially accurate reduced model. Our study showed that spatial error and sample size, using road-marker data for ungulate species, are important to consider for model output interpretation, which will impact the appropriate scale on which to apply modeling results. Using road-marker references <1.6 km or GPS-derived data locations may represent an optimal compromise between data acquisition costs and analytical performance. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Temporal and Spatial Relationships Between Watershed Land Use and Salt Marsh Disturbance in a Pacific Estuary

Historical and recent remote sensing data can be used to address temporal and spatial relationships between upland land cover and downstream vegetation response at the watershed scale. This is demonstrated for sub-watersheds draining into Elkhorn Slough, California, where salt marsh habitat has diminished because of the formation of sediment fans that support woody riparian vegetation. Multiple regression models were used to examine which land cover variables and physical properties of the watershed most influenced sediment fan size within 23 sub-watersheds (1.4 ha to 200 ha). Model explanatory power increased (adjusted R(2) = 0.94 vs. 0.75) among large sub-watersheds (>10 ha) and historical watershed variables, such as average farmland slope, flowpath slope, and flowpath distance between farmland and marsh, were significant. It was also possible to explain the increase in riparian vegetation by historical watershed variables for the larger sub-watersheds. Sub-watershed area is the overriding physical characteristic influencing the extent of sedimentation in a salt marsh, while percent cover of agricultural land use is the most influential land cover variable. The results also reveal that salt marsh recovery depends on relative cover of different land use classes in the watershed, with greater chances of recovery associated with less intensive agriculture. This research reveals a potential delay between watershed impacts and wetland response that can be best revealed when conducting multi-temporal analyses on larger watersheds.     

Fire Regimes and Tree Growth in Low Rainfall Jarrah Forest of South-west Australia

Regular fuel reduction burning is an important management strategy for reducing the scale and intensity of wildfires in south-west Australian native forests, but the long term effects of this on tree and stand growth are not well understood. Five fire treatments, including application of frequent and infrequent low intensity burns, and 25 years of fire exclusion, were applied to small (4 ha) experimental plots in a low rainfall mixed jarrah (Eucalyptus marginata) and marri (Corymbia calophylla) forest to investigate the effects of these treatments on tree stem diameter growth, stand basal area increment and tree mortality. Mean tree stem growth measured over 20 years was lowest in the long unburnt treatment compared with the burn treatments, although surface soil nutrient levels were generally higher in the unburnt treatment, suggesting these sites may be moisture limited. There was no clear pattern of the effects of the burn treatments, including the number of fires and the interval between fires, on tree stem growth, stand basal area increment, crown health or mortality. These factors were strongly influenced by dominance condition, with dominant and co-dominant trees growing most and suppressed trees growing least and experiencing the highest mortality levels. There was no evidence of deteriorating tree or stand health that could be attributed to either regular low intensity burning or to a long period (25 years) of fire exclusion.     

CONCENTRATED FLOW BREAKTHROUGHS MOVING THROUGH SILVICULTURAL STREAMSIDE MANAGEMENT ZONES: SOUTHEASTERN PIEDMONT,USA1

ABSTRACT: Geomorphic characteristics and spatial frequency of ephemeral concentrated flow paths entering streamside management zones (SMZs) were evaluated to determine the efficiency of best management practices (BMPs) in preventing concentrated overland flow and associated sediment from reaching stream channels. Specifically, SMZs of 30 recently clearcut and site prepared commercial forestry units in the Georgia Piedmont were surveyed to find two types of locations: those where flow and/or sediment from the adjacent silvicultural site entered and moved through SMZs into stream channels (breakthroughs), and those where either flow and/or sediment entered SMZs without reaching stream channels or where no overland flow entered SMZs (successes). A total of 187 breakthroughs were identified on 3,773 total acres. On average, sites featured one breakthrough for every 20 acres of clearcut or site prepared area. The average hydrologic contributing area to a breakthrough was 1 acre. The percentage of the total clearcut or site prepared area contributing to breakthroughs was 5 percent. Approximately 50 percent of all breakthroughs occurred in areas of convergence (swales) and gullies, while 25 percent of all breakthroughs occurred where runoff from roads or skid trails was concentrated. Breakthroughs tended to occur in areas with large contributing area, low litter cover, and steep slopes. However, individually these variables did not differentiate well between breakthroughs and successes. The variables that discriminated best between successes and failures were the product of contributing area and percent bare ground, and the same variable multiplied by average slope. Fourteen percent of the breakthroughs traveled more than 100 feet through SMZs before reaching streams. Results imply that reduction of bare ground, better dispersal of road runoff, introduction of hydraulic resistance to likely flow paths, and targeted extensions of SMZ width may be warranted in improving BMPs on Piedmont forests.     

Test of a Model to Assess the Condition of Lodgepole Pine Stands

/ A predictive model for assessing stand condition as a function of suitability for achieving specified management objectives was originally developed using a data set for only 28 stands. In this study, we evaluate the model using an operational-sized data set composed of currently collected stand inventory data for 238 stands in the Snowy Range of the Medicine Bow National Forest in southern Wyoming. We compared its predictions of old growth suitability to results of a separate special old growth survey. Stands were characterized as profiles of variables derived from stand inventory data, and plotted as points in two-dimensional space where similarity between stands was reflected by the distance between their points. Results suggest the model is useful for classifying stand condition using relatively large sets of data currently collected during routine stand inventories.     

Comparison of community composition and species diversity of understorey and overstorey tree species in a dry tropical forest of northern India

The study focuses on understorey-overstorey plant community dynamics in a dry tropical forest to facilitate appropriate management decisions. We compare community composition and species diversity of the understorey vegetation among five dry tropical forest sites in northern India. A total of 1500 quadrats distributed over 15 one-ha permanent plots in five sites differing in the degree of disturbance, were used to enumerate the understorey tree species and the results were compared with overstorey tree layer. The non-metric multidimensional scaling (NMS) ordination revealed that human disturbance intensity, as well as the overall disturbance regimes, and soil water holding capacity controlled the organisation of dry tropical forest understorey composition through effects on soil organic matter. The alpha-diversity and its components decreased with increasing human disturbance intensity, reflecting utilisation pressure and decreased soil fertility, as also revealed by the analysis of overstorey tree layer. There was a significant positive relationship between overstorey and understorey diversity. Results suggest that in the future, the existing understorey tree communities may replace the current dry tropical forest communities under prevailing environmental conditions. The study also asserts that the rate of species accumulation will be greater in more disturbed sites as well as at small spatial scale within each disturbance level.     

Tree Structure and Diversity in Human-Impacted Littoral Forests, Madagascar

This research surveyed human-impacted littoral forests in southeastern Madagascar to determine (i) how forest structural features, indicative of human impact, are related to total, utilitarian, and endemic tree diversity; (ii) the distribution, abundance, and demographics of tree species groups (i.e., total, useful, endemic) across the landscape; and (iii) the amount of basal area available per human use category. We also use these data to consider issues of sustainable use and how human impact may influence littoral forest tree community composition across the landscape. Within 22 transects of 400 m² each, we recorded a total of 135 tree species and 2155 individuals. Seventy-nine species (58%) were utilitarian and 56 (42%) were nonutilitarian species. Of the 2155 individuals, 1827 (84%) trees were utilitarian species. We recorded 23 endemic species (17% of the total species) and 17 (74%) of these were utilitarian species. Basal area was significantly correlated with Shannon Weiner Index values for total (r = 0.64, P < 0.01), utilitarian (r = 0.58, P < 0.01), and endemic tree diversity (r = 0.85, P < 0.01). Basal area was significantly correlated with the Simpson’s index values for the endemic species (r = 0.74, P < 0.01). These correlations suggest that endemic tree species, of high global conservation value, may be the species group most influenced by changes in forest structure. Utilitarian species constituted 84% of the total basal area. The use category contributing the highest amount of basal area to the landscape was firewood. The results presented herein demonstrate that the landscape of southeastern Madagascar, commonly perceived as degraded, retains high value for both global conservation purposes and for local livelihoods. Thus, valuable opportunities may exist for developing conservation incentives that leverage both global and local conservation needs.     

Evaluation of two herbicide techniques on electric transmission rights-of-way: Development of relatively stable shrublands

Postmanagement vegetation patterns were studied on five transmission rights-of-way subjected to over a decade of basal or stem-foliar herbicide applications designed to eliminate tall-growing trees. The basally treated lines had a mean of 100% greater shrub and 50% less herbaceous cover than stem-foliar treated lines due primarily to the lack of overspray damage to nontarget plant species with the basal technique. Persisting tree growth was also 50% less with basal treatments whenSassafras albidum, a rootsuckering problem species on all areas, was excluded. Tree seedling establishment on basally treated rights-of-way was 34% less than on stem-foliar treated lines. The creation of stable shrublands can potentially reduce the amount of future herbicide usage. These findings also lend support to the Initial Floristic Composition concept in vegetation development proposed by Egler. In southern New England, commercial basal applications can effectively control unwanted tree growth on rights-of-way while promoting the development of relatively stable shrublands which tend to inhibit the invasion of tree seedlings.     

Effects of tree size and spatial distribution on growth of ponderosa pine forests under alternative management scenarios

Forest ecosystems may be actively managed toward heterogeneous stand structures to provide both economic (e.g., wood production and carbon credits) and environmental benefits (e.g., invasive pest resistance). In order to facilitate wider adoption of possibly more sustainable forest stand structures, defining growth expectations among alternative management scenarios is crucial. To estimate the effect of tree size and spatial distributions on growth for forest structures commonly considered in uneven-aged forest stand management, large (0.2 ha+) plots were established in 14 uneven-aged ponderosa pine stands in eastern Montana. All study trees were stem-mapped and measured for diameter and 10-year sapwood and basal area increment. A generalized growth model was developed to predict both total and merchantable 10-year basal area increment for nine hypothetical stand structures [three diameter distributions (reverse-J, irregular, flat) × three spatial distributions (clumpy, partial clumpy, uniform)]. Results indicate that the size and spatial distributions of individual trees have a considerable effect on overall stand growth. The greatest total stand growth was in stands with reverse “J” shaped tree size distributions, while the greatest merchantable stand growth was in stands with “flat” diameter distributions and uniform spatial distributions. Through better comprehension of generalized uneven-aged stand growth dynamics, forest managers may better assess the effects of alternative stand structures on stand growth while providing forest stand structures that may be more resilient in a changing climate.     

Predicting Root Density in Streambanks1

Abstract: Roots of riparian vegetation increase streambank erosion resistance and structural stability; therefore, knowledge of root density and distribution in streambanks is useful for stream management and restoration. The objective of this study was to compare streambank root distributions for herbaceous and woody vegetation and to develop empirical models to predict root density. Root length density, root volume ratio, soil physical and chemical properties, and above‐ground vegetation densities were measured at 25 sites on six streams in southwestern Virginia. The Mann‐Whitney test was used to determine differences in root density along stream segments dominated by either woody or herbaceous vegetation. Multiple linear regression was used to develop relationships between root density and site characteristics. Study results showed that roots were evenly distributed across the bank face with the majority of roots having diameters less than 2 mm. Soil bulk density and above‐ground vegetation were key factors influencing root density. While significant relationships were developed to predict root density, the predictive capabilities of the equations was low. Because of the highly variable nature of soil and vegetation properties, it is recommended at this time that soil erodibility and root density be measured in the field for design and modeling purposes, rather than estimated based on empirical relationships.