Mixed Broadleaf Research Articles

Silviculture guidelines for developing mixed forests in old coniferous plantations under long-rotation stand density control

This study presents guidelines for developing mixed broadleaf–conifer forests in old coniferous plantations under a long-rotation silviculture system. We established nine square sample plots in Chamaecyparis obtusa (hinoki) plantation forests of various stand ages (22–116 years) and densities (250–1650 trees ha−1). Tree height and diameter at breast height were recorded for all standing trees taller than 1.3 m. This step revealed the varying diameters of coniferous plantation trees and natural broadleaf trees and showed that the density of large trees increased with stand age. The older the plantation forest, the smaller its canopy openness. The standard deviation of canopy openness ranged from 20–30%, with the largest values observed in the middle-aged forests. We estimated the stand density index under which understory vegetation may be established; the maximum stand density index (1028) in the forest studied was considered to be the critical upper limit of stand density control for introducing understory vegetation. Finally, we reviewed previous studies to confirm the validity of our recommendations of long rotation and low stand density control for the development of mixed old plantation forests.

Effect of gap size on mid-rotation stand structure and species composition in a naturally regenerated mixed broadleaf forest

This paper is an assessment of the effect of gap size on stand structure and species composition 48 years following treatment in a mixed broadleaf upland forest. Established in 1960, the study tests three circular openings, 15.2 m (0.02 ha), 45.7 m (0.16 ha), and 76.2 m (0.46 ha). Forty-eight years following treatment (2008) basal area, top height, and quadratic mean diameter were significantly lower in 15.2 m openings. Maple (Acer spp.) species had the highest mean importance value across treatments (0.40). Trends suggest that species composition of dominant and codominant trees among opening sizes may have been influenced by shade tolerance adaptations of the species groups present. Whereas 15.2 m openings were dominated by shade tolerant maple species, 45.7 and 76.2 m openings produced a mixture of commercial species including shade intolerant species such as yellow-poplar (Liriodendron tulipifera L.), trees of intermediate shade tolerance like oak (Quercus spp.), and shade tolerant maple. Data further suggest the density of overstory oak was highest in the intermediate opening size (45.7 m), while yellow-poplar increased in the larger opening sizes. Evaluation of species shifts between 1981 and 2008 showed that relative basal area of maple increased across all treatments. Relative basal areas from 45.7 to 76.2 m openings suggest declines in yellow-poplar and other non-commercial species were balanced by increases in oak and maple.

Relationships between net primary productivity and stand age for several forest types and their influence on China’s carbon balance

Affected by natural and anthropogenic disturbances such as forest fires, insect-induced mortality and harvesting, forest stand age plays an important role in determining the distribution of carbon pools and fluxes in a variety of forest ecosystems. An improved understanding of the relationship between net primary productivity (NPP) and stand age (i.e., age-related increase and decline in forest productivity) is essential for the simulation and prediction of the global carbon cycle at annual, decadal, centurial, or even longer temporal scales. In this paper, we developed functions describing the relationship between national mean NPP and stand age using stand age information derived from forest inventory data and NPP simulated by the BEPS (Boreal Ecosystem Productivity Simulator) model in 2001. Due to differences in ecobiophysical characteristics of different forest types, NPP-age equations were developed for five typical forest ecosystems in China (deciduous needleleaf forest (DNF), evergreen needleleaf forest in tropic and subtropical zones (ENF-S), deciduous broadleaf forest (DBF), evergreen broadleaf forest (EBF), and mixed broadleaf forest (MBF)). For DNF, ENF-S, EBF, and MBF, changes in NPP with age were well fitted with a common non-linear function, with R2 values equal to 0.90, 0.75, 0.66, and 0.67, respectively. In contrast, a second order polynomial was best suitable for simulating the change of NPP for DBF, with an R2 value of 0.79. The timing and magnitude of the maximum NPP varied with forest types. DNF, EBF, and MBF reached the peak NPP at the age of 54, 40, and 32 years, respectively, while the NPP of ENF-S maximizes at the age of 13 years. The highest NPP of DBF appeared at 122 years. NPP was generally lower in older stands with the exception of DBF, and this particular finding runs counter to the paradigm of age-related decline in forest growth.Evaluation based on measurements of NPP and stand age at the plot-level demonstrates the reliability and applicability of the fitted NPP-age relationships. These relationships were used to replace the normalized NPP-age relationship used in the original InTEC (Integrated Terrestrial Ecosystem Carbon) model, to improve the accuracy of estimated carbon balance for China’s forest ecosystems. With the revised NPP-age relationship, the InTEC model simulated a larger carbon source from 1950–1980 and a larger carbon sink from 1985–2001 for China’s forests than the original InTEC model did because of the modification to the age-related carbon dynamics in forests. This finding confirms the importance of considering the dynamics of NPP related to forest age in estimating regional and global terrestrial carbon budgets.

Interactive effects of vegetation structure and composition describe bird habitat associations in mixed broadleaf–conifer forest

AbstractThe effects that changes in forest structure and composition have on wildlife have often been considered independently, such that the potential for interactive effects has received relatively little attention. We investigated the importance of vegetation structure, floristic composition, and their interaction for predicting bird distribution in mixed broadleaf–conifer forest. We collected vegetation and bird data at 979 stations in a watershed in southern Oregon in the spring of 2001. At each station, we described the vegetation using measures of structure (total vegetation volume) and of floristic composition (broadleaf–conifer composition). We then used logistic regression to model the probability of occurrence of bird species as a function of these 2 variables, their quadratic terms, and their interaction. Using stepwise model selection we identified the best model for each species and used area under the curve (AUC) scores to evaluate model performance. Of the 44 bird species we investigated, 20 had models with AUC scores ≥0.70. Of the best models for these 20 species, 1 included vegetation composition alone, 12 included just the main effects of vegetation composition and structure, and 7 included both the main effects and interaction terms. In summer of 2001 a wildfire burned 2,500 ha of the study area, resulting in substantial changes in the vegetation structure and composition. We used 4 yr of postfire bird and vegetation surveys to test the predictive performance of the habitat models for 9 species that occurred at >15% of the burned stations. Models for 3 of these species performed poorly (AUC < 0.7) in all 4 yr. For the other 6 species, predictive performance was low in the first year after fire and improved during subsequent years, suggesting a lagged response to changes in vegetation structure and composition. Quantifying the interactive effects of vegetation structure and composition improves our understanding of how birds respond to forest management and large‐scale disturbances, such as wildfires. © 2011 The Wildlife Society.

Quantitative Classification of Plant Functional Types Based on Photosynthesis

Classifying plant functional types by a general and quantitative technique is important for sustainable forest management. Here, the time series of diurnal net photosynthetic rate and other related external and internal factors of 11 tree species in a young mixed broadleaf and coniferous Korean pine forest in Northeast China were recorded during the growing season. All time series data were analyzed by a newly proposed model, by which the relative importance of external environmental factors and internal factors on leaf photosynthetic rate among tree species was evaluated. The analysis showed that this method can be useful to identify environmentally sensitive tree species and to quantitatively classify plant functional types. Photosynthetic rate in most pioneer tree species is less sensitive to variation in environmental conditions than in late successional species. The photosynthetic rate of all 11 tree species was mainly determined by their internal factors. The results may also have implications for tree species selection in forest plantations and forest restoration.

Selection and Plant Community Characteristics of Foraging Sites for Hume’s Pheasant (<I>Syramticus humiae</I>) in Nanhua Part of Ailaoshan National Nature Reserve

Plant communities of foraging sites of Hume’s Pheasant (Syramticus humiae) had been surveyed by systematic sampling method since April 25 to May 16, 2008 in Nanhua part of Ailaoshan National Nature Reserve. And 133 plant species were recorded, belonging to 86 genera and 49 families. The results by spearman correlation analysis showed that there was a significant relativity between occurrence frequency of S. humiae and distribution of evergreen broadleaf forest, which meant the vertical distribution and territory of the birds were affected by the distribution of evergreen broadleaf forest. S. humiae preferred to select evergreen broadleaf forest as habitats. The results by important value ordination of plant and detrended correspondence analysis showed that the plant composition in foraging sites was conformed to evergreen broadleaf forest whereas greatly different from other forest types. The composition among plant layers in evergreen broadleaf forest could provide preferable coverage, either leaves or stalks of pteridophyte and nuts of fagaceae were foods for S. humiae. The results of diversity comparison showed that plant diversity in foraging sites were significantly higher than Pinus armandii forest and deciduous broadleaf forest because both forests lacked vegetable foods. So habitat selection of Hume’s pheasant was affected by plant diversity and food richness. The results by comparison of vegetation factors and detrended correspondence analysis showed that tree coverage in foraging sites were higher than other forest types except evergreen broadleaf forest. The degree of similarity in foraging sites and other forest types differed. Deciduous broadleaf forest was less similar to foraging sites in vegetation factors where trees were sparse and S. humiae liked to graze greatly. There were short trees and few shrubs in P. armandii forests. However, mixed broadleaf and coniferous forest were more similar to foraging sites in vegetation factors, where human disturbance was serious. Coverage and human disturbance were dominant factors that influenced foraging sites selection of S. humia. The results by analysis of dissimilarity showed that the most studied area could supply basic conditions for the survival of S. humiae but the best suitable area was less indeed.

Herb layer response to broadleaf tree species with different leaf litter quality and canopy structure in temperate forests

AbstractQuestion: How do broadleaf tree species affect humus characteristics, herb layer composition and species diversity through their leaf litter quality and canopy structure?Location: Mixed broadleaf forests in Brandenburg, NE Germany.Methods: We studied the herb and tree layer composition in 129 undisturbed stands using a 10‐degree cover‐abundance and percentage scale, respectively. The main floristic gradients were extracted by non‐metric multidimensional scaling. Effects of tree species on the herb layer were analysed with partial Spearman rank correlation. We assessed affinities for specific tree species using indicator species analysis.Results: Both beech and oak influenced herb layer composition mainly through their litter quality, which resulted in deep Ol and Of horizons, respectively. The less dense canopy of oak, in contrast to the dense beech canopy, enhanced species diversity in favour of indifferent herb species (species not closely tied to forests). Lime was correlated with a distinct floristic gradient, but a direct effect on the herb layer cannot be proven with the available data. Effects of hornbeam were less pronounced.Conclusions: The relationship between the tree and herb layer must be partly attributed to pH differences. However, tree species effects on humus characteristics and on light flux to the ground were largely responsible as well. The results suggest that tree species can influence herb layer composition and diversity, but the missing correlation with lime and hornbeam raise questions requiring further detailed investigation.

Owner-specific factors associated with conversion activity in secondary pine plantations

The conversion of secondary pine plantations into mixed broadleaf stands is considered to be an important mechanism in the process of sustainable forest management. The silvicultural process of forest conversion in ageing pine plantations is associated with active management aimed at inducing, steering or accelerating stand development. The aim of the present study was to investigate owner-specific factors – socio-demographic and forest-related characteristics, and motivation of ownership – influencing NIPF owners' active engagement in silvicultural conversion (henceforth referred to as ‘conversion activity’). The study relies on a survey of non-industrial private owners ( n = 276) of pine plantations on poor sandy soils in Flanders (northern Belgium). The study revealed that NIPF owners, in general, make only minor contributions to forest conversion. Conversion activity (including thinning, making space for broadleaves, removing invasive species, clear-cut, planting) was rather low, but positively influenced by a number of factors. Private forest owners with clear motivations of ownership were more likely to engage in conversion activity. However, the nature of motivation was not very decisive as most of the items listed (with exception of land investment goals) had a positive influence. Furthermore, the conversion activity of owners called ‘economists’ did not significantly differ from those of ‘recreationists’, but ‘passive owners’ (those with unclear motivations of ownership) were less active. We thus suggest that it is the absence of clear motivations of ownership, rather than a particular ownership goal that would explain low conversion activity. Socio-demographics like age, gender and education, and also forest size had only marginal influence. But frequency of forest visits and proximity to the forest had a significant influence. As an overall conclusion from this study, we emphasize the importance for active forest management, and silvicultural conversion in particular, of forest owners being connected to their forest. In this sense, mental connectedness (motivation of ownership), as well as physical connectedness (living close to the forest and visiting it frequently) do matter.

Patterns of litterfall and return of nutrients across anthropogenic disturbance gradients in three subalpine forests of west Himalaya, India

The study was conducted to improve our understanding of the effects of forest disturbance on litterfall and patterns of nutrient return in three subalpine forest ecosystems (i.e. Betula utilis-dominated, Abies pindrow-dominated, and Acer mixed broadleaf) of Indian west Himalaya. Total litterfall (t ha−1 yr−1) ranged between 2.6–3.6 and 2.1–2.6 for pristine and degraded stands, respectively. Whereas total litterfall decrease from pristine to degraded stand was about 25–30% in B. utilis and Acer mixed-broadleaf forests, the level of disturbance did not affect total litterfall in A. pindrow (coniferous) forest. Nutrient (N, P, and K) concentrations in litter components of the forests studied also varied across forest types and disturbance intensities. For pristine stands, among all the forests, return of total nutrients via litterfall was higher. The study revealed that patterns of litterfall and nutrient return in the forests studied were sensitive to intensity of disturbance, although sensitivity varied among forest types and nutrient contents. Increased intensity of disturbance greatly affected the total annual amount of nutrient return in broadleaf forests. Maximum impact was recorded in B. utilis forest with a significant decline in nutrient return from pristine to degraded stands (i.e. 64% for N, 38% for P, and 67% for K). Corresponding values for decline in Acer mixed forest were 17, 13, and 33% for N, P, and K, respectively, whereas in A. Pindrow forest N return was 15% higher and P return was 33% lower. This study indicates that the litterfall and litter nutrient concentrations in these forests are sensitive to the intensity of disturbance, which affects the amount of nutrient return. This will have a strong bearing on forest nutrient cycling.

Effects of Plant Litter Type and Additions of Nitrogen and Phosphorus on Bacterial Community-Level Physiological Profiles in a Brown Forest Soil

Effects of plant litter type (larch needle-leaves, mixed broad-leaves, and sasa green leaves) and nutrient addition (nitrogen and phosphorus) on bacterial community-level physiological profiles (CLPPs) of a forest soil were examined using BIOLOG EcoPlates(TM). Both the litter and nutrient additions significantly increased color development in most of the wells in the BIOLOG microplates, with the effect of the latter being especially great for soils amended with plant leaves low in nutrients. Nitrogen addition to soils decreased the color development of some nitrogenous substrates. Litter type had a dominant effect on the CLPPs. The addition of nitrogen also strongly affected the CLPPs.

Soil properties under Norway spruce differ in spruce dominated and mixed broadleaf forests of the Southern Taiga

In natural forest, disturbance changes tree species composition which in turn affects soil properties. Two areas in the Central Forest State Biosphere Reserve, in the Russian Southern Taiga Zone, differed in the intensity of disturbance: Norway spruce was the dominant species at one site, while at the other spruce was mixed with broadleaves. The presence of broadleaves was due to large gaps in the canopy having been formed, which have triggered vegetation succession. At both sites, five plots were selected to evaluate how the presence of broadleaves influences the properties of the soils under spruce. Soil samples were taken close to spruce trees and the O, A and E horizons were analysed. A difference in the distribution of organic matter in the soil horizons was evident, with a higher concentration in the O and A horizons at the spruce dominated site, while a more homogeneous distribution was found under spruce at the site where broadleaves were abundant. The organic matter did not only differ in quantity, but also in quality as estimated by the C/N ratio, and therefore affected the CEC and element relative availability. No differences at the two sites were found for water-extractable and exchangeable elements, but the ratio between the exchangeable and the acid-extractable forms were different, suggesting a higher relative availability of the elements at the spruce dominated site, and thus potentially higher leaching. Both theoretical and empirical studies have suggested that podzolisation and accumulation of organic matter in the O horizon are related to stagnation of ecosystem processes and ecosystem decline. Our data suggest that the presence to windthrow sites and the inclusion of broadleaf species acts to slow or even reverse podzolisation even in spruce dominated sites.

An integrated terrestrial paleoenvironmental record from the Mid-Pleistocene transition, eastern North Island, New Zealand

A tephra-bearing lake sequence from near Ormond, New Zealand, provided the opportunity to conduct a multi-proxy paleoenvironmental analysis within the Mid-Pleistocene time period. A 10.5-m-thick section was measured and analysed for pollen, spores, diatoms, macrofossils, and tephra geochemistry. Palynological assemblages in the lower 4 m of the section indicate an ameliorating temperate climate and increased humidity. The upper 6.5 m is dominated by diatomite that did not yield sufficient palynomorphs for study. The source vegetation was distal lowland mixed broadleaf podocarp forest, swamp forest from ca. 2.5–4.0 m, and proximal scrubland with sporadic forest encroachment. Abundant freshwater algae in the samples suggest that any brackish influence in the lower part of the section was minor. Marine dinoflagellates found in the basal pollen samples could be mostly recycled. Diatomite samples were overwhelmingly dominated by a freshwater but mildly salt-tolerant diatom. We interpret the section as representing a shallow coastal lowland lake that intermittently had access to the sea. The chronology of the section is based on a single glass-ITPFT age of 0.62±0.09 Ma from a tephra interbed (T8) in the lower part of the section. In addition, the lowermost tephra in the sequence (T1) is geochemically correlated to AT-485, preserved in the marine record east of New Zealand, with an astronomically tuned age of 0.7163 Ma. This chronology places the basal portion of the Ormond section within the Brunhes normal Chron with sequence deposition occurring during either the OIS 18/17 or 16/15 transitions. However, paleomagnetic data indicate a clear reverse polarity from an equivalent stratigraphic position and at this stage it is difficult to reconcile this age discrepancy.

Effects of spatio‐temporal variation in food supply on red squirrel Sciurus vulgaris body size and body mass and its consequences for some fitness components

Food availability is likely to influence body condition and, in turn, fitness. The intensity of this response may vary between populations of the same species on a small spatial and temporal scale. We used 5 yr of data from 6 Eurasian red squirrel Sciurus vulgaris populations from the southern Alps to explore differences in body size and body mass among neighbouring populations, in relation to habitat type and variation in food supply. We also investigated sexual dimorphism in these traits and whether phenotypic variation affects local survival and female reproductive success. Mean hind foot length, a measure of body size, did not differ between sexes but differed between areas. Seasonal variation in body mass was small with no evidence for fattening in autumn. Females were slightly heavier than males, but this difference was largely explained by mass gain of females during reproduction. The size of conifer seed crops, the major food supply, varied strongly over years and between habitats, but this variation corresponded only weakly with autumn body mass. Differences in size and mass between populations were partially explained by habitat‐related differences in body size and variability of seed‐crops, suggesting differential selection for smaller squirrels in spruce‐larch forests against selection for larger and heavier animals in mixed broadleaves and conifer forests and in Scots pine forests with more stable seed production. The probability of reproduction by females increased with body mass, but varied strongly between habitats and years, with more females reproducing in years with rich seed‐crops. In both sexes, body mass positively affected probability of settlement and length of residency. Our results suggest that in temporally variable environments that differ in overall amount of food resources, individual variation in body mass is related to habitat type, and that having a relatively high body mass, within each population, positively affects male and female settlement success and local survival, and female reproductive success.

Effects of spatio-temporal variation in food supply on red squirrel Sciurus vulgaris body size and body mass and its consequences for some fitness components

Food availability is likely to influence body condition and, in turn, fitness. The intensity of this response may vary between populations of the same species on a small spatial and temporal scale. We used 5 yr of data from 6 Eurasian red squirrel Sciurus vulgaris populations from the southern Alps to explore differences in body size and body mass among neighbouring populations, in relation to habitat type and variation in food supply. We also investigated sexual dimorphism in these traits and whether phenotypic variation affects local survival and female reproductive success. Mean hind foot length, a measure of body size, did not differ between sexes but differed between areas. Seasonal variation in body mass was small with no evidence for fattening in autumn. Females were slightly heavier than males, but this difference was largely explained by mass gain of females during reproduction. The size of conifer seed crops, the major food supply, varied strongly over years and between habitats, but this variation corresponded only weakly with autumn body mass. Differences in size and mass between populations were partially explained by habitat-related differences in body size and variability of seed-crops, suggesting differential selection for smaller squirrels in spruce-larch forests against selection for larger and heavier animals in mixed broadleaves and conifer forests and in Scots pine forests with more stable seed production. The probability of reproduction by females increased with body mass, but varied strongly between habitats and years, with more females reproducing in years with rich seed-crops. In both sexes, body mass positively affected probability of settlement and length of residency. Our results suggest that in temporally variable environments that differ in overall amount of food resources, individual variation in body mass is related to habitat type, and that having a relatively high body mass, within each population, positively affects male and female settlement success and local survival, and female reproductive success.

Using multivariate factorial kriging for multiscale ordination: a case study

Vegetation ordination is usually based on classical data reduction techniques such as principal components analysis, correspondence analysis, or multidimensional scaling. The usual methods do not account for multiscale correlations among species. In this paper, we use a geostatistical method, known as multivariate factorial kriging, for studying multiple-scale correlations. The case study was carried out in a mixed broadleaf forest of central Spain. Six tree species were included in the analysis. Data analysis included (i) experimental variogram calculation and modeling with the use of the linear model of coregionalization, (ii) principal components analysis, and (iii) cokriging. The results indicate that correlations among species are different depending on the spatial scale. We conclude that competition for light is the main factor controlling the spatial distribution of species at the plot-level scale of variation. At larger scales of variation, soil conditions and (or) human intervention are the key factors in determining the observed vegetation pattern. Based on the factor scores for the largest scale of variation, we conducted a cluster analysis to identify plots with similar characteristics. The resulting clusters have the remarkable property of being spatially continuous.

Predicting climate change effects on vegetation, soil thermal dynamics, and carbon cycling in ecosystems of interior Alaska

A dynamic vegetation model has been used to predict patterns of recent past and potential future change in taiga forest ecosystems of interior Alaska. The model, called CASA (Carnegie Ames Stanford Approach), is a process-based ecosystem depiction of plant and soil processes, including all major cycles of water and carbon. CASA’s dynamic vegetation component is intended to facilitate coupling to general circulation models of the atmosphere, which require mechanistic fluxes and feedbacks from terrestrial vegetation. Simulation results for selected Alaska sites of Denali National Park suggest that the past 50-year climate trends of warming temperatures may shift the taiga ecosystem from dominance by evergreen needleleaf trees to a more mixed broadleaf–needleleaf tree composition. For other (higher elevation) areas of Denali, our model predicts that a difference of only about 3 °C in mean annual air temperatures appears to differentiate the permanent presence of tundra vegetation forms over taiga forest. The model predicts that over the 1950–1999 climate record at Denali station, the changing taiga ecosystems were net sinks for atmospheric CO 2 of about 1.3 kg C m −2. During the warm 1990s, these forests were predicted to be net carbon sinks of more than 15 g C m −2 per year in 8 out of 10 years. Predicted NPP for the forest continues to increase with a projected warming trend for the next 25 years at a mean rate of about +1.2 g C m −2 per year. On the basis of these model results, a series of crucial field site measurements can be identified for inclusion in subsequent long-term ecological studies of the changing taiga forest.

Alien species and interspecific competition: effects of introduced eastern grey squirrels on red squirrel population dynamics

Summary Throughout much of Britain, Ireland and north Italy, red squirrels (Sciurus vulgaris L.) have been replaced by alien grey squirrels (S. carolinensis Gmelin) introduced from North America. We have studied squirrels in two mixed woodlands in north Italy and two conifer forests in north England. In each country, one site was occupied by red squirrels and one site by both species. We have previously considered interference competition and exploitation competition for food and space between red and grey squirrels and have showed that grey squirrels caused reduced body growth in juvenile and subadult red squirrels, and compete for tree seeds cached by adult red squirrels in spring. Here we report on the effects of grey squirrels on three fitness components in red squirrels that have consequence at the population level: fecundity, residency and recruitment. Litter production peaked in the spring and summer, but fewer females bred in the summer with grey squirrels present. In addition, fewer individual red squirrel females produced two litters per year in the sites with grey squirrels. Moreover, red squirrel recruitment rate and, in the mixed broadleaf sites, red squirrel juvenile residency, decreased with increasing grey squirrel density. Fecundity of individual female red squirrels was lower in red–grey than in red‐only sites because they had a lower body mass in sites with grey squirrels. Overall, there was no significant effect of grey squirrels on residency of adult red squirrels or on population turnover rate. However, the presence of grey squirrels resulted in a reduction in red squirrel fitness which was evident by lower population summer breeding and a lower recruitment. Over time, this will result in a decline in population size and eventually population extinction.

Nitrogen Export from Forested Watersheds in the Oregon Coast Range: The Role of N 2 -fixing Red Alder

Variations in plant community composition across the landscape can influence nutrient retention and loss at the watershed scale. A striking example of plant species importance is the influence of N2-fixing red alder (Alnus rubra) on nutrient cycling in the forests of the Pacific Northwest. To understand the influence of red alder on watershed nutrient export, we studied the chemistry of 26 small watershed streams within the Salmon River basin of the Oregon Coast Range. Nitrate and dissolved organic nitrogen (DON) concentrations were positively related to broadleaf cover (dominated by red alder: 94% of basal area), particularly when near-coastal sites were excluded (r 2 = 0.65 and 0.68 for nitrate-N and DON, respectively). Nitrate and DON concentrations were more strongly related to broadleaf cover within entire watersheds than broadleaf cover within the riparian area alone, which indicates that leaching from upland alder stands plays an important role in watershed nitrogen (N) export. Nitrate dominated over DON in hydrologic export (92% of total dissolved N), and nitrate and DON concentrations were strongly correlated. Annual N export was highly variable among watersheds (2.4–30.8 kg N ha−1 y−1), described by a multiple linear regression combining broadleaf and mixed broadleaf–conifer cover (r 2 = 0.74). Base cation concentrations were positively related to nitrate concentrations, which suggests that nitrate leaching increases cation losses. Our findings provide evidence for strong control of ecosystem function by a single plant species, where leaching from N saturated red alder stands is a major control on N export from these coastal watersheds.

Relationships between runoff and land degradation on non-cultivated land in the Middle Hills of Nepal

SUMMARY Rainfall-surface water runoff relationships have been examined for 912 rainfall events during the 1992 and 1993 monsoon seasons on 15 erosion plots on a variety of non-cultivated land uses in the Middle Hills, Nepal. Vegetation cover and type examined ranged from grassland and relatively undisturbed mixed broadleaf forest to subtropical Sal forest, in various states of degradation, and bare ground. Runoff was frequently generated on most plots and often by relatively small rainfall amounts (less than 5 mm) and low rainfall intensities (3 mm/h). Ground cover and canopy cover were significant factors in determining amounts of runoff. Runoff coefficients ranged from 1–2% under grassland and mixed broadleaf forest to 57–64% on the bare sites. Coefficients for Sal forest were between these two extremes; specific values depended on the level of degradation induced by human activity. The most degraded forest sites experienced runoff coefficients of 33%. Ground cover beneath the trees, especially leaf litter, was more effective in reducing runoff than the amount of canopy cover. Canopy cover was more effective during the less intense storms but was ineffective when the rainfall intensity was high. The results suggest that a minimum ground cover of 60% will keep runoff to within 10% of total rainfall amounts for most normal monsoons in the Middle Hills. This will also reduce the risk of gullying and surface soil erosion. It is the nature of the forest that is important and not its total area. In the study area, although the total area under forest had not changed, some of the forest had become more degraded with a corresponding increase in mean runoff rates. Increased runoff can occur even if the area under forest increases. Estimates of levels of degradation based solely on changing forest areas are likely to be inaccurate.

SOIL LOSS ON NONCULTIVATED LAND IN THE MIDDLE HILLS OF NEPAL

This paper reports soil losses from 15 erosion plots in the Middle Hills, Nepal, for the 1992 and 1993 monsoon and pre-monsoon seasons. In total, 912 rainfall events were monitored. Land cover varied from grassland and relatively undisturbed mixed broadleaf forest, to degraded Sal forest and bare ground. Soil losses ranged from less than 0.1 t ha-1 yr-1 for grassland and undisturbed forest plots, to 3–10 t ha-1 yr-1 for Sal forest in various states of degradation, and over 15 t ha-1 yr-1 for the bare sites. These results are broadly consistent with those reported in other parts of the Himalayan Middle Hills. Soil loss values could be explained by variations in runoff amounts and rainfall intensity, as well as by the nature of the land cover. Ground and low shrub cover was more important than canopy cover in protecting the forest soils. Human activity has unquestionably led to accelerated rates of soil loss but the degree of acceleration depends on the nature of the human activity and especially the care with which the land is managed. [Key words: soil loss, land use, Nepal, land degradation.]