Low-density Forest Research Articles

Forest recovery following synchronous outbreaks of spruce and western balsam bark beetle is slowed by ungulate browsing.

Understanding how severe disturbances and their interactions affect forests is key to projecting ecological change under a warming climate. Substantial increases in some biotic disturbances, such as bark beetle outbreaks, in temperate forest ecosystemsmay compromise recovery to a forest vegetation type (i.e., physiognomic recovery or resilience), especially if subsequent biotic disturbances (e.g., herbivory) alter recovery mechanisms. From 2005 to 2017, severe outbreaks (>90% mortality) of spruce bark beetles (SB, Dendroctonus rufipennis) affected Engelmann spruce (Picea engelmannii) across 325,000ha of spruce and subalpine fir (Abies lasiocarpa) forest in the southern Rocky Mountains, USA. Concurrently, an outbreak of western balsam bark beetle (WBBB, Dryocoetes confuses) infested subalpine fir across at least 47,000 of these hectares. We explored the capacity of 105 stands affected by one or two bark beetle outbreaks and browsing of juvenile trees by ungulates to return to a forest vegetation type in the context of pre-outbreak forest conditions and topography. Nine initial forest trajectories (i.e., at least several decades) were identified from four pre-outbreak forest types affected by three biotic disturbances that occurred at different spatial scales and severities. Most stands (86%) contained surviving nonhost adult trees in the main canopy (fir and aspen [Populus tremuloides]) and many surviving juveniles of all species, implying that they are currently on a trajectory for physiognomic recovery. Stands composed exclusively of large-diameter spruce were affected by a severe SB outbreak and were most vulnerable to a transition to a low-density forest, below regional stocking levels (<370trees/ha). Greater pre-outbreak stand structural complexity and species diversity were key traits of stands with a higher potential for physiognomic recovery. However, all multispecies stands shifted in relative composition of the main canopy to nonhost species, suggesting low potential for compositional recovery over the next several decades. Most post-outbreak stands (86%) exceeded regional stocking levels with trees taller than the browse zone (<2m). As such, ungulate browsing on over half of all juveniles will primarily affect the rate of infilling of the forest canopy and preferential browsing of more palatable species will influence the composition of the future forest canopy.

Estimation of the Value of Ecosystem Carbon Sequestration Services under Different Scenarios in the Central China (the Qinling-Daba Mountain Area)

The Qinling-Daba Mountain area is a transitional zone between north and south China and not much is known about its carbon storage, particularly its pool of soil organic carbon (SOC). Given this shortcoming, more reliable information regarding its SOC is needed. In light of this, we quantified above and below-ground carbon sinks using both the Carnegie-Ames-Stanford approach (CASA) model and an improved carbon cycle process model. We also assessed the net present value (NPV) for carbon budgets under different carbon price and discount rate scenarios using the NPV model. Our results indicated that the net primary productivity (NPP) was lower in places with low density forests that were situated at high elevation. The spatial distribution of carbon storage depended on NPP production and litter decompositon, which reflected specific vegetation as well as temperature and moisture gradients. The lowest amounts of carbon storage were in the center of the Qinling Mountains and also partly in the Daba area, which is a location associated with sparse grassland. Contrastingly, the broad-leaved forested area showed the highest amount of carbon storage. NPV was positively correlated with discount rate and carbon prices, thus resulting in the highest values in the forests and grassland. The net present value of total soil carbon sequestration in the six scenarios in 2015 was 3.555 b yuan, 3.621 b yuan, 5.421 b yuan, 5.579 b yuan, 7.530 b yuan, 7.929 b yuan; The net present value of total soil carbon sequestration in 6 scenarios in 2017 is 2.816 b yuan, 2.845 b yuan, 4.361 b yuan, 4.468 b yuan, 6.144 b yuan, 6.338 b yuan (billion = 109; b; RMB is the legal currency of the China, and its unit is yuan, 1 euro = 7.7949 yuan, and 1 pound = 9.2590 yuan). Levying a carbon tax would be a notable option for decision makers as they develop carbon emission reduction policies. Given this, incorporating discount rates and carbon pricing would allow for more realistic value estimations of soil organic carbon. This approach would also provide a theoretical basis and underscore the practical significance for the government to set a reasonable carbon price.

Soil salinity mapping in Everglades National Park using remote sensing techniques and vegetation salt tolerance

Everglades National Park (ENP) is a hydro-ecologically enriched wetland with varying salinity contents, which is a concern for terrestrial ecosystem balance and its nearby urban sustainability. In this study, spatio-temporal soil salinity maps are created using remote sensing techniques, coupled with literature review to understand vegetation salt tolerance properties, and field assessments entailing insitu electric conductivity (EC) measurements. The mapping first entailed the execution of a supervised machine learning technique—the maximum likelihood classification algorithm—to delineate seven vegetation-based land cover classes for the area, namely, mangrove forest, mangrove scrub, low-density forest, sawgrass, prairies and marshes, barren lands with woodland hammock and water, for the years 1996, 2000, 2006, 2010 and 2015. The classifications for 1996–2010 yielded accuracies of 82%–94%, and the 2015 classification was supported through ground truthing. Afterwards, EC tolerance thresholds for each vegetation class were established, which yielded soil salinity maps comprising four soil salinity classes—i.e., the non- (EC = 0–2 dS/m), low- (EC = 2–4 dS/m) and high-saline (EC ≥4 dS/m) areas. The soil salinity maps visualized the spatial distribution of soil salinity with no significant temporal changes. Furthermore, insitu EC measurements carried out at 23 sampling sites covering all land cover classes mostly validated (91% samples were tested within range) the estimated soil salinity ranges for the latest distribution. The approach of using land cover classes to sense salinity ranges in an urban-proximal ecosystem is pragmatic and application oriented, attributing to novel and useful study upshots considering the diversifying ecological context.

A Monte Carlo appraisal of tree abundance and stand basal area estimation in forest inventories based on terrestrial laser scanning

Non-detection of trees is an important issue when using single-scan TLS in forest inventories. A hybrid inference approach is adopted. Quoting from distance sampling, a detection function is assumed, so that the inclusion probability of each tree included within each plot can be determined. A simulation study is performed to compare the TLS-based estimators corrected and uncorrected for non-detection with the Horvitz–Thompson estimator based on conventional plot sampling, in which all the trees within plots are recorded. Results show that single-scan TLS provides more efficient estimators with respect to those provided by the conventional plot sampling in the case of low-density forests when no distance sampling correction is performed. In low-density forests, uncorrected estimators lead to a small bias (1%–6%), increasing with plot size. Therefore, care must be taken in enlarging the plot radius too much. The bias increases in forests with clustered spatial structures and in dense forests, where the bias levels (30%–50%) deteriorate the performance of uncorrected estimators. Even if the bias-corrected estimators prove to be effective in reducing the bias (below 15%), these reductions are not sufficient to outperform conventional plot sampling. Therefore, there is no convenience in using TLS-based estimation in high-density forests.

Long-term forest management after wildfire (Catalonia, NE Iberian Peninsula)

Studies of post-fire soil status in Mediterranean ecosystems are common; however, few have examined the effects of long-term forest management after a wildfire on physicochemical soil properties. Here, we analyzed differences in soil properties attributable to long-term post-fire management and assessed the sustainability of these management practices in relation to the soil properties. The study area is located in Odena in the northeast region of the Iberian Peninsula consisted of the control forest (burned more than 30 years ago), low density forest (LD; burned in a wildfire in 1986 and managed in 2005) and high density forest (HD; burned in a wildfire in 1986 and no managed). For soils from each plot, we measured soil water repellency, aggregate stability, total nitrogen (TN), soil organic matter (SOM), inorganic carbon (IC), pH, electrical conductivity, extractable calcium, magnesium, sodium, potassium (K), phosphorus, aluminum (Al), manganese (Mn), iron (Fe), zinc, copper, boron, chrome, silicon and sulfur and calculated the ratios of C/N, Ca + Mg/(Na + K)1/2, Ca/Al and Ca/Mg. Significant differences were found in TN, IC, SOM, pH, K, Al, Mn, Fe and C/N ratio (p < 0.05). All soil properties were found to have largely recovered their pre-fire values. Soils were affected by the post-fire management practices implemented 20 years after the fire, as reflected in their respective physicochemical properties, so that soil properties at the control and LD sites are more similar today than those at the control and HD sites. Thus, sustainable forest management can overcome soil degradation in areas affected by wildfire in the medium- and long-term by improving soil properties.

Comparison of drag and velocity in model mangrove forests with random and in-line tree distributions

This study examined the role of tree arrangement (random versus aligned) on the drag forces and velocity inside a 1/12th-scale model mangrove forest over a range of tree density (trees m−2). Each model tree included an aerial root system geometrically similar to Rhizophora, with maximum root height HRmax and water depth H > HRmax. The non-dimensional root density was defined as ar HRmax, with root zone frontal area per volume, ar. For both random and aligned low-density forests, ar HRmax < 0.1, the vertical profile of velocity followed a boundary layer shape. Within both random and aligned high-density forests, ar HRmax > 0.1, the velocity was diminished in the root zone (z < HRmax) and enhanced above the root zone, relative to the boundary layer profile. For all forest arrangements, the force on the roots dominated the force on the entire tree, even in cases with diminished velocity within the root zone. Compared with a tree at the leading edge, a tree inside a randomly distributed forest could experience either a greater or lesser force, and the variation in drag force increased with tree density. In contrast, for an aligned distribution of trees the force on an individual tree within the forest was always diminished relative to a tree at the leading edge. A drag coefficient was defined using a quadratic drag law. The forest-average drag coefficient, defined using the channel-average velocity, was up to 30 percent higher for random tree arrangements, compared to in-line tree arrangements.

Land use change modeling through an integrated Multi-Layer Perceptron Neural Network and Markov Chain analysis (case study: Arasbaran region, Iran)

Temporal land use/land cover (LULC) change information provides a variety of applications for informed management of land resources. The aim of this study was to detect and predict LULC changes in the Arasbaran region using an integrated Multi-Layer Perceptron Neural Network and Markov Chain analysis. At the first step, multi-temporal Landsat images (1990, 2002 and 2014) were processed using ancillary data and were classified into seven LULC categories of high density forest, low-density forest, agriculture, grassland, barren land, water and urban area. Next, LULC changes were detected for three time profiles, 1990–2002, 2002–2014 and 1990–2014. A 2014 LULC map of the study area was further simulated (for model performance evaluation) applying 1990 and 2002 map layers. In addition, a collection of spatial variables was also used for modeling LULC change processes as driving forces. The actual and simulated 2014 LULC change maps were cross-tabulated and compared to ensure model simulation success and the results indicated an overall accuracy and kappa coefficient of 97.79% and 0.992, respectively. Having the model properly validated, LULC change was predicted up to the year 2025. The results demonstrated that 992 and 1592 ha of high and low-density forests were degraded during 1990–2014, respectively, while 422 ha were added to the extent of residential areas with a growth rate of 17.58 ha per year. The developed model predicted a considerable degradation trend for the forest categories through 2025, accounting for 489 and 531 ha of loss for high and low-density forests, respectively. By way of contrast, residential area and farmland categories will increase up to 211 and 427 ha, respectively. The integrated prediction model and customary area data can be used for practical management efforts by simulating vegetation dynamics and future LULC change trajectories.

Pervasive Rise of Small-scale Deforestation in Amazonia

Understanding forest loss patterns in Amazonia, the Earth’s largest rainforest region, is critical for effective forest conservation and management. Following the most detailed analysis to date, spanning the entire Amazon and extending over a 14-year period (2001–2014), we reveal significant shifts in deforestation dynamics of Amazonian forests. Firstly, hotspots of Amazonian forest loss are moving away from the southern Brazilian Amazon to Peru and Bolivia. Secondly, while the number of new large forest clearings (>50 ha) has declined significantly over time (46%), the number of new small clearings (<1 ha) increased by 34% between 2001–2007 and 2008–2014. Thirdly, we find that small-scale low-density forest loss expanded markedly in geographical extent during 2008–2014. This shift presents an important and alarming new challenge for forest conservation, despite reductions in overall deforestation rates.

Legal Enforcement on Environmental Impact of Palm Oil Plantation of Merauke District

Merauke City is one of the cities in Papua which has 4.6 million hectares consisting of 3.1 million hectare for forest coverage and the rest is 1.5 non-forest coverage. Around 66% forest coverage consists of primary forest, high-density secondary forest, low-density secondary forest, primary swamp forest, secondary swamp forest, eucalyptus/acacia forest, primary mangrove forest, and secondary mangrove forests. Merauke City is one of the place which has a great potential to maintain and sustain ecological system with its vast territory and its evergreen forest which people keep its sustainability. However, the government and some companies expanding their business take a toll for the balance of the nature, since some of the forest areas are cut down and the industrial waste affects the ecosystem. Some territories in Merauke become heavily polluted from the wastes. One of the pollution cases is from six palm oil companies which has polluted some forests in Merauke, Papua. The companies responsible for the decreasing environmental condition are operating in Malind Bian such as PT Dongin Prabhawa ( Korindo Group), PT Bio Inti Agrindo (Korindo group), PT Central Cipta Murdaya (CCM), PT Agriprima Cipta Persada, PT Hardaya Sawit Papua and PT Berkat Cipta Abadi. The method is of this study is normative legal approach. The result of this study reveals that the government are advised to include the society and the locals to make a decision and to find a good solution for the environment which has been sustaining their life. This may resolve the problem between the palm oil company, the government, and the society to uphold a new law. The government should be strict to set rules in order to be beneficial not only for the companies, but also for the society, the government, and the environment in Merauke City. When the law has been issued, the companies indicated to be violating certain set of rules regarding environmental pollution and contamination, can be evaluated and revoked of their warrant to do business in Merauke. This will be a good solution to make sure the sustainability of the environment, forests, and the society depending on it.

Impacts of land use change due to biofuel crops on climate regulation services: Five case studies in Malawi, Mozambique and Swaziland

Understanding changes in carbon sequestration due to land conversion is key for elucidating the true potential of biofuel landscapes to provide climate regulation ecosystem services. In this study, we focus on the two most promoted biofuel crops in southern Africa, Jatropha and sugarcane, to analyse the land use change effects and associated carbon impacts of growing biofuel crops in five study sites in Mozambique, Malawi and Swaziland. We found that, considering a 20-year cycle, carbon stocks in aboveground biomass are higher for sugarcane than for Jatropha. However, as soil organic carbon (SOC) is generally the main carbon pool, total carbon stocks (considering biomass and soil) will highly depend on SOC. Our results show that, in our study sites, sugarcane replaced land uses with low carbon stocks (low-density forest and agriculture), and as a result carbon gains occurred due to land use change. In the Jatropha projects, carbon gains are observed in the smallholder scheme as agricultural land was converted to Jatropha, but carbon debts occurred in the Jatropha plantation as high-density forest was cleared to grow this feedstock. Finally we show that, if a plantation of sugarcane or Jatropha is envisioned to be located in the studied regions, more forested land could potentially be converted into sugarcane (30–44% of forest) than into Jatropha (24–32%), without creating carbon debts due to land conversion. To our knowledge, this is the first comparative study of the carbon impacts of land use change of the main biofuel crops in southern Africa.

How much carbon can the Siberian boreal taiga store: a case study of partitioning among the above-ground and soil pools

In the context of global carbon cycle management, accurate knowledge of carbon content in forests is a relevant issue in contemporary forest ecology. We measured the above-ground and soil carbon pools in the dark-coniferous boreal taiga. We compared measured carbon pools to those calculated from the forest inventory records containing volume stock and species composition data. The inventory data heavily underestimated the pools in the study area (Stolby State Nature Reserve, central Krasnoyarsk Territory, Russian Federation). The carbon pool estimated from the forest inventory data varied from 25 (t ha−1) (low-density stands) to 73 (t ha−1) (highly stocked stands). Our estimates ranged from 59 (t ha−1) (low-density stands) to 147 (t ha−1) (highly stocked stands). Our values included living trees, standing deadwood, living cover, brushwood and litter. We found that the proportion of biomass carbon (living trees): soil carbon varied from 99:1 to 8:2 for fully stocked and low-density forest stands, respectively. This contradicts the common understanding that the biomass in the boreal forests represents only 16–20 % of the total carbon pool, with the balance being the soil carbon pool.

Forest harvesting is associated with increased landslide activity during an extreme rainstorm on Vancouver Island, Canada

Abstract. Safe operations of forest practices in mountainous regions require effective development planning to mitigate hazards posed by landslides. British Columbia, Canada, has for the past 2 decades implemented landslide risk management policies aimed at reducing the impacts of the forestry industry on landslides. Consequently, it is required that timber harvesting sites be evaluated for their potential or existing impacts on terrain stability. Statistical landslide susceptibility modelling can enhance this evaluation by geographically highlighting potential hazardous areas. In addition, these statistical models can also improve our understanding of regional landslide controlling factors. The purpose of this research was to explore the regional effects of forest harvesting activities, topography, precipitation and geology on landslides initiated during an extreme rainfall event in November 2006 on Vancouver Island, British Columbia. These effects were analyzed with a nonparametric statistical method, the generalized additive model (GAM). Although topography was the strongest predictor of landslide initiation, low density forest interpreted as regrowth areas and proximity to forest service roads were jointly associated with a 6- to 9-fold increase in the odds of landslide initiation, while accounting for other environmental confounders. This result highlights the importance of continuing proper landslide risk management to control the effects of forest practices on landslide initiation.

Aboveground Biomass Carbon in the Alpine and Arctic Treeline Ecotones in the Ural Region

This paper reports on measured carbon stocks in the forests of two treeline ecotones of the Ural region where climate change might improve growing conditions. The first is an alpine ecotone that is represented by an altitudinal gradient of the spruce-dominated forests on the Western slope of the Tylaiskii Kamen Mountain (Western part of the Konzhakovskii-Tylaiskii-Serebryanskii Mountain system, 59030'N, 59000'E), at the alpine timber line that has risen from 864 to 960 m above sea level in the course of the last 100 years. The second is an arctic ecotone in larch-dominated forests at the lower course of the Pur River (670N, 780E), at the transition zone between closed floodplain forests and open or island-like communities of upland forests on tundra permafrost. According to our results, there are large differences in the carbon of the aboveground biomass of both ecotones across environmental gradients. In the alpine treeline ecotone, a 19-fold drop of the carbon stocks was detected between the lower and higher altitudinal levels. In the arctic ecotone the aboveground biomass carbon stock of forests of similar densities (1300 to 1700 trees per ha) was 7 times as much in the river flood bed, and 5 times as much in mature, dense forests as the low density forests at higher elevations.

Tree density and population size affect pollen flow and mating patterns in small fragmented forest stands of pedunculate oak (Quercus robur L.)

In many parts of the world, once large and continuous forests have been replaced by a mosaic of isolated forest fragments embedded in an agricultural or urban landscape matrix. At the same time, stand characteristics such as tree population size and tree density have been strongly modified as a result of anthropogenic activities. Because increased geographical isolation can impede gene flow among forest fragments, and because decreased population size and tree density may reduce the number of local mating partners, this can be expected to lower the opportunity to trees for outcrossing, and to result in increased inbreeding, negatively impacting the viability of fragmented tree populations. In this study, we examined eight isolated stands of the wind-pollinated tree species Q. robur that strongly differed in population size, tree density and spatial isolation. In the centre of each Q. robur stand, adult leaves and seeds were collected in a circular plot, in which we evaluated the diversity and differentiation of the local pollen pool, and examined mating patterns. Most forest stands showed high proportions of out-of-plot pollen flow (range: 0.24–0.77), which were positively correlated with the number and density of adult trees within the forest stands. Despite high outcrossing rates (>0.998), seeds within seed families were stronger related than what could be expected under panmixia, which could be attributed to small but significant levels of correlated paternity (0.018–0.107) and biparental inbreeding (0.025–0.118) within the study plots. Next to increased coancestry coefficients, deviations from random mating also resulted in significant pollen pool differentiation (0.008–0.059) among seed parents. We also found that stand population size and tree density were significantly correlated to the relatedness of the seedlings and the degree of pollen differentiation within the study plots. These results suggest that, in small and isolated low density forest stands, reduced mate availability may decrease local pollen pool diversity, increasing the likelihood of consanguineous mating and pollen pool differentiation in the next generations. We conclude that preserving high levels of pollen flow within and between forest fragments may be more important in wind-pollinated tree species than what was previously thought.

Sensitisation pattern to birch pollen allergen components in oral allergy syndrome to Rosaceae fruits in patients with spring pollinosis from an East European Sylvosteppe area with low density forests

Methods We evaluated subjects from Southern Romania, a Central European region with temperate continental climate with submediterranean and humid subtropical influences, where sensitization to Betulaceae pollen is less important in pollinosis compared with that to grass or weed pollen. We selected adult patients from the region of sylvosteppe with low density forests dominated by deciduous species, presenting symptoms of rhinoconjunctivitis in March to May and oral allergy syndrome to fresh Rosaceae fruits, allergic reactions in the mouth and throat without systemic symptoms, and having positive skin prick tests to Betulaceae tree pollen and positive prick-to-prick skin tests with fresh intact and unpeeled apple, pear, apricot, peach, cherry or plum. Because allergen components present in Fagales tree pollen and Rosaceae fruits are PR-10 proteins, profilins and isoflavone reductases, we measured the serum levels of specific IgE to European birch pollen and to recombinant allergen components Bet v1 (birch major PR-10 allergen with ribonuclease activity), Bet v2 (birch-pollen profilin), and Bet v6 (birch-pollen isoflavone reductase), using a multiparameter immunoblot test system based on single purified allergen components (SPAC 1).

Transmission of genetic variation from the adult generation to naturally established seedling cohorts in small forest stands of pedunculate oak (Quercus robur L.)

Natural regeneration is being increasingly encouraged as the preferred regeneration method for sustainable forestry. However, the benefits of natural regeneration may be jeopardized in small and low-density forest stands, as genetic drift and inbreeding may reduce genetic diversity of the standing population. Particularly in light-demanding tree species, which are characterized by a narrow recruitment window, conservation of genetic diversity during natural regeneration can be challenging in small forest stands. In this study, we investigated intergenerational transmission of genetic diversity in stands of the light-demanding tree species pedunculate oak (Quercus robur L.) by comparing genetic diversity between adults and recently established seedling cohorts (1–3years old) in four small stands of Q. robur (<4.5ha) that varied in tree density. We also quantified mating patterns and gene flow to investigate their role in shaping the genetic diversity and spatial genetic structure of the studied populations. Because of the closed canopy cover of these stands, only recently established seedlings could be studied. When all stands were pooled, the adult cohort showed a slightly but significantly higher allelic richness (Ar) than the established seedling cohort (Ar=11.5 and 10.7, respectively). However, at the stand level, no significant negative effects on the genetic diversity of the offspring generation were found in the small and low-density forest stands. As expected, acorn dispersal resulting in seedling recruitment was restricted to a few meters from mother trees, resulting in significant small-scale spatial genetic structure in the offspring. Pollen inflow from outside the study plots varied strongly among stands, but all plots showed a significant correlated paternity (rp), with higher estimates of rp found in forest stands with lower effective population sizes (Ne) and lower tree densities. Given that high rp-levels may increase the probability of biparental inbreeding and may incur fitness costs in subsequent offspring generations, we recommend that in small scale forestry of Q. robur, Ne and tree densities should be sufficiently large to maintain genetic diversity over the long term. Allowing gene flow between tree populations through reducing the spatial isolation among forest stands, can help to increase Ne in small-scale silvicultural systems of pedunculate oak, but also in other species characterized by narrow recruitment windows.

Latent resilience in ponderosa pine forest: effects of resumed frequent fire

Ecological systems often exhibit resilient states that are maintained through negative feedbacks. In ponderosa pine forests, fire historically represented the negative feedback mechanism that maintained ecosystem resilience; fire exclusion reduced that resilience, predisposing the transition to an alternative ecosystem state upon reintroduction of fire. We evaluated the effects of reintroduced frequent wildfire in unlogged, fire-excluded, ponderosa pine forest in the Bob Marshall Wilderness, Montana, USA. Initial reintroduction of fire in 2003 reduced tree density and consumed surface fuels, but also stimulated establishment of a dense cohort of lodgepole pine, maintaining a trajectory toward an alternative state. Resumption of a frequent fire regime by a second fire in 2011 restored a low-density forest dominated by large-diameter ponderosa pine by eliminating many regenerating lodgepole pines and by continuing to remove surface fuels and small-diameter lodgepole pine and Douglas-fir that established during the fire suppression era. Our data demonstrate that some unlogged, fire-excluded, ponderosa pine forests possess latent resilience to reintroduced fire. A passive model of simply allowing lightning-ignited fires to burn appears to be a viable approach to restoration of such forests.

Historical structure and composition of ponderosa pine and mixed-conifer forests in south-central Oregon

We summarized structure and composition of dry forests from a 90-year-old timber inventory collected by the Bureau of Indian Affairs on the former Klamath Indian Reservation (now part of the Fremont-Winema National Forest). This analysis includes data from 424,626 conifers ⩾15cmdbh on 3068 transects covering 6646ha. The data represent a 10–20% sample of 38,651ha of forest growing on sites that are classified as ponderosa pine (Pinus ponderosa) and mixed-conifer habitat types distributed within the 117,672 ha of the study area. Large, drought- and fire-tolerant ponderosa pine dominated these forests. Large tree (>53cmdbh) basal area (13±7m2/ha) contributed 83±16% of total basal area; 81±20% of the large-tree basal area was ponderosa pine. Composition and structure of forests on mixed-conifer sites were very similar to those on ponderosa pine sites. Variability in composition and structure was recorded on all habitat types and was highest on moist mixed-conifer sites. Stand densities (trees per hectare, tph) have more than tripled over the past 90years from 68±28tph to a current density of 234±122tph recorded in Current Vegetation Survey data collected by the United States Forest Service. Mean basal area, however, increased by less than 20%. Basal area of large trees (>53cmdbh) has declined by >50%, and the abundance of large trees as a proportion of the total number of trees per hectare has decreased by more than a factor of five. This landscape-level record of historical forest conditions allows inferences about structure and composition across tens of thousands of hectares. A historical landscape emerges which supports current working hypotheses that frequent, low- to moderate-severity wildfires maintained a predominantly low-density forest dominated by large, fire- and drought-tolerant ponderosa pines across a significant moisture and productivity gradient from the driest ponderosa pine to the mixed-conifer habitat types.

Mountain vegetation change quantification using surface landscape metrics in Lancang watershed, China

Land cover and vegetation change are among the most important aspects of environmental change. Vegetation change can be quantified by landscape pattern indices (LPI). Landscape indices are routinely calculated using planar land use/land cover (LU/LC) maps, obtained by the projection of a non-flat landscape surface into a two-dimensional Cartesian space. Especially in mountainous areas, quantification on planar maps can lead to underestimation of vegetation and land cover changes. Hoechstetter et al. (2008) developed a method to compute LPIs in a surface structure by calculating landscape patch surface area and surface perimeter from digital elevation models (DEM). As yet there have been no applications of these surface landscape indices on land use/land cover and vegetation change quantification. The objectives of this study are to (1) choose a LPI method (surface metrics pattern analysis or common planimetric metrics pattern analysis) for vegetation change quantification; and (2) employ the selected surface LPI method to assess vegetation pattern change in two mountainous areas of the Lancang watershed, Yunnan Province, China. The results show that the surface approach to estimate changes of class area (CA), mean patch area (MPA), and mean Euclidean Near-Neighbor distance (MENN) may obtain more accurate results for quantifying vegetation change in steep mountain areas. Forest fragmentation increased significantly over time in the two different mountainous study areas. The patches of two land cover classes, (i) agricultural land and (ii) low density forest and tall shrubs, became more aggregated in the northern (temperate) study area. In the southern (tropical) study area, rubber plantations increased considerably in size and became more aggregated.

A meta-analysis of the ecological significance of density in tree invasions

Species richness, resource availability, and disturbance are the primary factors considered in assessing the invasibility of plant communities. Nonetheless, the density of individuals in a community is a common and easy trait to measure. The ecological significance of the density of both native and invasive tree species was assessed using a systematic review and formal meta-analysis. The densities of recipient communities and invasive exotic tree species in novel ranges were identified in the published literature. In addition, we compared by means of a meta-analysis: (i) densities of invasive versus native species in invaded communities; (ii) densities of native species in invaded versus uninvaded communities; and (iii) densities of invasive species along distance gradients from initial locus of invasion. Invasive trees were found at higher densities than native species in recipient communities. Invasions by woody species were also recorded in communities with relatively low densities of natives suggesting that (i) low density forests may be more susceptible to invasion and/or (ii) density of the recipient community may be reduced during the invasion process. In addition, comparison of native species densities between invaded and uninvaded stands from the same community suggests that invasive trees negatively affect density of native trees once established. Therefore, the widely reported low density and often richness of native plants in invaded communities cannot be directly linked to ecosystem susceptibility to invasion without considering concomitant impacts. These findings suggest that density is a key preliminary determinant or factor which should be considered when assessing tree invasion dynamics.