Reduced Tree Density Research Articles

Piñon-juniper fuels reduction treatment impacts pinyon jay nesting habitat

Across multiple continents, mechanical thinning of forests and woodlands is an increasingly common management approach to reduce potential fire risks or improve ecological condition. Thinning programs designed to reduce fire risk typically place priority on human needs with little consideration of impacts to wildlife. We report on the results of a fuels reduction treatment at a traditional pinyon jay (Gymnorhinus cyanocephalus) nesting colony in persistent piñon-juniper woodlands in New Mexico, USA. The treatment affected 21% of the traditional colony site, reducing tree density in treated areas from a mean of 1893 trees per hectare to a mean of 248 trees per hectare, an 87% reduction. Generalized linear mixed models indicated tree density and basal area were significantly greater at pinyon jay nests than in untreated areas and greater in untreated areas than treated areas. Tree diameter was greater in treated areas than in untreated areas and at nests, indicating that treatments retained larger trees. Areas treated in 2018 included 11 nests active in 2017. No nests found in 2018 were within the treated areas, with tests indicating that pinyon jays avoided nesting in treated areas. Although the treatment rendered previously suitable pinyon jay nesting habitat unsuitable, pinyon jays continued to nest near treated areas. While treatments should be planned to avoid direct losses of habitat, pinyon jays may be tolerant of treatments near traditional nesting areas in the short run, suggesting that slightly altering the location of treatments might allow them to occur without impacting traditional nesting areas. Longer-term monitoring across additional areas will help improve understanding of the impacts of thinning on wildlife and their habitat.

Recalling open old growth forests in the Southeastern Mixed Forest province of the United States

ABSTRACTHistorical forests in the Southeastern Mixed Forest province of the United States have been less researched than other regions using historical tree surveys. We used 81,000 tree records from surveys during the 1800s to quantify composition of this ecological province. Upland oaks and pines comprised about 75% of all trees, with relatively equal composition. Oak composition may have comprised ≥ 45% to the northern and eastern sides of the province. Hickories were about 10% of composition and a few species were present at 1% to 2% composition. Currently, pine has increased to 49% composition; loblolly pine was 46% of all trees. Upland oaks decreased to 8% composition. Paralleling other historically oak- or pine-dominated regions, fire-intolerant species increased to 40% of composition, particularly early-successional sweetgum. Historical oak-pine forests mostly have converted to loblolly pine plantations and broadleaf forests in this region. A large extent of the eastern United States historically was dominated by oak or pine forests, which likely were open old growth forests due to a frequent, low-to-moderate severity fire regime that reduced tree densities and infrequently disturbed overstory trees. Open old growth forests should be recognized as distinct ecosystems with unique characteristics, ecological functioning, and associated management practices.

Transitioning western U.S. dry forests to limited committed warming with bet‐hedging and natural disturbances

AbstractHistorical evidence suggests natural disturbances could allow more forest persistence, than expected from models, over 40 yr of transition to the net‐zero emissions needed to limit warming to <2.0°C (e.g., Paris Agreement). Forests must ultimately equilibrate with committed warming from accumulated emissions. Historical dry‐forest landscapes were heterogeneous from large, infrequent disturbances (LIDs) that reduced tree density and basal area, followed by slow, variable tree regeneration and recovery for 1–3 centuries. These together effectively provided bet‐hedging through stand‐ and landscape‐level heterogeneity that enhanced resistance and resilience to a diversity of unpredictable subsequent disturbances. Recent disturbances have not yet exceeded historical variability in rates and patterns, but could cause mortality of ∼26–51% of dry‐forest area in the transition. This also means 1/2 to 3/4 of dry‐forest area could escape most mortality and the mortality area could also have substantial forest persistence. Projections are unavailable for droughts or beetle outbreaks, but they recently caused about 3–4 times as much tree mortality as did moderate‐ to high‐severity fires. Mortality could reduce forest area if new trees do not regenerate, but 24 studies showed recent regeneration after high‐severity fires was slow, but indistinct from historical variability. Survival of smaller trees provided regeneration after beetle outbreaks and droughts. Regeneration in general was projected by 2060 to decline by ∼10% in one study and increase by 50% in another. If openings from disturbances increased, some grasslands and shrublands could be restored, increasing landscape heterogeneity and resistance to disturbance spread. Given these trends and our limited ability to prevent LIDs, I suggest (1) refocusing restoration to increase bet‐hedging resilience to droughts and beetle outbreaks by retaining small trees and diverse tree species, (2) expanding development of fire‐safe landscapes to protect people and infrastructure from unavoidable increased fire, (3) enabling more managed fire to restore and enhance stand‐ and landscape‐scale bet‐hedging, and (4) accepting that LIDs will revise resistance, resilience, and adaptation, which enhance forest persistence, particularly if post‐disturbance survivors are not logged and trees are not planted. Natural disturbance and slow recovery, if bet‐hedged to increase resistance and resilience, could enable substantial forest persistence.

Disentangling the effects of crown scorch and competition release on the physiological and growth response of Pinus halepensis Mill. using δ13C and δ18O isotopes

Prescribed burning (PB) can decrease the likelihood of crown fires by increasing canopy base height via canopy scorching and sometimes by reducing tree density through fire-induced tree mortality, especially in fire-pronestands. However, little is known about the effect of moderate PB on tree functioning, especially in Mediterranean species such as Pinus halepensis Mill. In this study we combined dendrochronology and isotope analysis to understand the physiological effects of PB that determine the short-term post-burning growth response of crown-scorched and unscorched P. halepensis with different levels of competition release. PB was carried out in spring 2013. Scorched and unscorched pines showed higher post-burning growth rates than before PB as well as control pines. In the first year post-burning, unscorched pines had similar growth rates and δ18O-δ13C values to the control pines, which indicates that PB only had a minor impact on tree functioning. In contrast, scorched pines showed a significant reduction in growth and wood δ13C, but had similar δ18O as the unscorched and control (no-PB managed) pines. This suggests that the pines’ response mechanism to scorch was to reduce their photosynthetic capacity. At two years post-burning (2015), the growth of scorched pines was similar to control pines. Moreover, the radial growth of pines increased significantly when PB resulted in a relevant competition release and crown volume scorch was low. At two years post-burning (2015), a smaller change in δ13C in scorched trees compared to 2014 was found and no changes in δ13C in unscorched pines; however, lower δ18O was found in scorched and unscorched pines compared to the controls, which suggests an increase in stomatal conductance probably due to improved water availability through fire induced thinning. The increase in stomatal conductance in scorched and unscorched pines coincided with an extreme drought year (2015), which indicates that the control pines adopted a more conservative water-use efficiency. No effects of burning on needle N content or δ15N were detected. As a management conclusion, our study suggests that moderate PB can be implemented to disrupt the vertical continuity of fuels in crown fire prone landscapes, enhancing water availability during drought episodes with only minor effects on tree functioning.

Environmental parameters and tree physiology in two semiarid land use systems in Brazil

To determine if reduced tree densities (number of trees per unit area) lead to changes in micro-meteorological and tree physiological characteristics, two areas with different tree densities were assessed. One was an agrosilvopastoral system (AGP) with low tree density, and the other, a secondary forest (SF) with greater tree numbers, both located in a semiarid region of Brazil. Data were collected simultaneously by two automated weather stations: rainfall, air (Ta) and soil temperatures (Ts5cm), relative humidity (RHair), photosynthetically active radiation (PAR), soil moisture at two depths (Ms30cm and Ms50cm), and wind velocity (Vw). Net photosynthesis in Cordia oncocalyx Allemao trees was measured with an infrared gas analyzer in February, March, May, July, August and September 2011, which encompasses a rainy period followed by a dry period. Average values of Ta, Ts5cm, Vw and PAR were greater and average values of RHair and Ms50cm were lesser in the AGP. Photosynthetic rates were greater in plants growing under the AGP at the onset of the dry season when Vw, PAR and Ts5cm were greater and Ms50cm was lesser. Photosynthetic rates correlated strongly with physical parameters during the dry season, especially under SF. Differences in tree numbers between AGP and SF led to differences in physical environmental parameters; however, the latter had less influence on photosynthetic rates in C. oncocalyx during the rainy season. During the dry season, all physical parameters had an impact on net photosynthesis under SF but not under AGP. This indicates a certain independence of plants in AGP.

People or place? An exploration of social and ecological drivers of urban forest species composition

Urban forests have garnered increasing attention as providers of an array of beneficial ecosystem services. However, urban forest ecosystems are highly complex and heterogeneous systems whose structure are shaped by interacting social and ecological processes. Approaches to reliably identify and differentiate these processes could be valuable for addressing complexity and reducing uncertainty in decision-making in urban forestry. The purpose of this study is to identify and quantify a range of social and ecological drivers of urban forest species composition, distribution, and diversity. This was done using hierarchical cluster analysis and discriminant analysis with empirical plot data describing the tree species composition in Toronto, Canada. Tree density and imperviousness were by far the most influential drivers of species composition. Increasing imperviousness saw not just reduced tree density but a decline in native species abundance. Additionally, single-detached housing, homeownership, and income were closely associated and explained higher tree densities and abundances of native species. However, income had a lower than expected influence on urban forest species composition given its importance in canopy cover research. Continuous forest patches were highly distinct compared to the remainder of the urban landscape, which highlights the ecological distinctiveness of residual forests within cities and lends support to their conservation. Increasing the understanding of social and ecological drivers of tree species composition, distribution, and diversity within cities is an integral part of urban forest ecosystem classification, which can be a valuable decision-support tool for ecosystem-based management in urban forestry.

Large‐scale restoration increases carbon stability under projected climate and wildfire regimes

Changing climate and increasing area burned pose a challenge to forest carbon (C) storage, which is compounded by an elevated risk of high‐severity wildfire due to long‐term fire suppression in the westernUS. Restoration treatments that reduce tree density and reintroduce surface fire are effective at moderating fire effects and may help build adaptive capacity to changing environmental conditions. However, treatment implementation has been slow and spatially limited relative to the extent of the area affected by fire suppression. Using model simulations, we quantified how large‐scale restoration treatments in frequent‐fire forest types would influence C outcomes in the Sierra Nevada mountain range under projected climate–wildfire interactions. Our results indicate that large‐scale restoration treatments are an effective means of reducing fire hazard and increasing C storage and stability under future climate and wildfire conditions. The effects of implementation timing suggest that accelerated implementation of large‐scale restoration treatments may confer greater C‐storage benefits, supporting California's efforts to combat climate change.

A synthesis on the impact of non-native conifer plantations on ant and beetle diversity in north-western Patagonia

Softwood forestry with non-native tree species is increasing worldwide and especially in many developing countries of the Southern Hemisphere. Tree plantations are beneficial in environmental and socioeconomic aspects, but at the same time there are recognised costs associated with afforestation. Our aim was to revise the existing information on the impact of exotic conifer plantations in north-western Patagonia on insect biodiversity. A total of five studies were selected and, in these, not every insect group responded in a similar manner to the habitat replacement. There was a tendency towards a reduction in abundance and species richness of several insects inside pine plantations. This change in abundance and richness was especially evident for ant assemblages and when pine plantations were dense. Beetle assemblages, in turn, showed diverse responses to the replacement of native vegetation with forests depending on the native habitat matrix. Our findings confirm that practices that reduce tree density (via thinning or during plantation) should be recommended to minimise their impact on insect biodiversity in north-western Patagonia. The consistent behaviour of ant assemblages, coupled with their abundance, ease to sample and unambiguous taxonomy make them reliable candidates for long-term monitoring of the impact conifer forestation in north-western Patagonia, as well as probably in other regions of the world in which non-native pines replace natural environments.

Phytosociological, structural and conservation analysis of the habitats of Dupont’s lark in Europe: a phytosociological survey applied to the conservation of an endangered species

Based on an updated census for the endangered Dupont’s lark (Chersophilus duponti), we conducted a phytosociological survey of 167 sites representative of the distribution area of the species in Europe. Results were used as a starting point for conservation assessment. According to our observations, the bird selects flat deforested areas colonized by small shrubs corresponding to successional, subclimax stages that are either naturally or artificially exploited. Four groups of scrubs were occupied by the bird: (1) supramediterranean dwarf cushion scrubs dominated by Genista pumila ssp. rigidissima or Erinacea anthyllis; (2) gypicolous shrublands and grasslands associated with Lygeum spartum; (3) shrubs dominated by chamaephytes producing allelopathic substances (Thymus, Lavandula, Salvia) and showing different facies according to the level of disturbance; and (4) supramediterranean acidophilous scrubs dominated by Cistus, Erica or Cytisus species. As management measures, we propose reducing tree density in flat areas, promoting the growth of chamaephytes by clearing phanerophytes, and encouraging traditional low-level transhumance grazing. These measures will provide high-quality habitats and help preserve, or even expand, habitable patches to ensure the viability of the European metapopulation of this rare and sensitive songbird.

Long-Term Effects of Burn Season and Frequency on Ponderosa Pine Forest Fuels and Seedlings

Prescribed fire is widely applied in western US forests to limit future fire severity by reducing tree density, fuels, and excessive seedlings. Repeated prescribed burning attempts to simulate historical fire regimes in frequent-fire forests, yet there is limited long-term information regarding optimal burn season and frequency. In addition, burns are operationally feasible only in the spring and late fall, largely outside the historical wildfire season. This study quantifies the effect of seasonal reburns on woody surface fuels, forest floor fuels, and understory tree regeneration abundance in six previously thinned ponderosa pine (Pinus ponderosa Lawson & C. Lawson) stands in the southern Blue Mountain Ecoregion of Oregon, USA. Each stand consisted of an unburned control, and four season by reburn treatments: spring 5 yr, spring 15 yr, fall 5 yr, and fall 15 yr. We evaluated season and frequency of reburn for woody surface fuel (1 hr to 1000 hr), forest floor fuel (litter and duff, undifferentiated), and understory conifer seedling density (regeneration). Burning was initiated in the fall of 1997 and spring of 1998; we present results in this paper through 2014 for fuel, and 2015 for seedlings. All reburn treatments reduced the forest floor depth compared to those areas not burned (controls). Fall burning, regardless of frequency, generated 1000 hr fuel primarily from overstory mortality resulting from the initial entry burns and subsequent snag and branch fall. But, for the other woody fuel types, reburning had minimal impact, regardless of season or frequency. All reburn treatments reduced regeneration survival, but 5 yr fall reburning was most effective in reducing excessive conifer seedlings. Repeated spring or fall reburns following thinning will reduce forest floor depth but, to achieve low woody fuel loads and control excessive conifer regeneration, it may be necessary to conduct reburns using different timing, such as during drier periods when wildfire ignitions by lightning occurred historically.

Restoration benefits of re-entry with resource objective wildfire on a ponderosa pine landscape in northern Arizona, USA

Abstract Prescriptions for ecological restoration of ponderosa pine (Pinus ponderosa) forests of the American Southwest are generally aimed at approximating pre-fire-exclusion conditions by reducing tree densities and hazardous fuels, and reintroducing surface fire. Increasingly, land managers are utilizing natural fire ignitions to achieve restoration and hazardous fuels reduction objectives, but to minimize risk of escape and reduce potential for undesirable outcomes fires are commonly managed under weather and fuel moisture conditions that produce lower burn severities. Few studies have examined effectiveness of incremental approaches that attempt to restore these ecosystems by allowing repeated, low-severity wildfires to reburn sites. We analyzed a 12,035-ha landscape on the Kaibab National Forest in northern Arizona and compared forest structure, hazardous fuel loading, and potential fire behavior in areas that had burned once (single fire) to others that had burned twice (re-entry) over the preceding 13 years. Forest structure and hazardous fuels characteristics in re-entry areas tended to be closer to historical ranges of variability (HRV) than in single fire areas; however, we found few statistically significant differences and tree densities in both single and re-entry fires remained higher than HRV by up to 3.5-fold. Similarly, potential fire behavior variables were statistically similar between single and re-entry fire areas. Analysis of burn severity effects suggested that trends toward reduced tree density and canopy fuels in re-entry areas were consistently driven by “cleanup effects”, whereby re-entry fires produced low-severity effects in areas showing unburned/low severity after first-entry fires. Evidence of “additive effects”, whereby restoration and hazardous fuels reduction objectives were being met incrementally by repeated low-severity fire, was difficult to detect on the re-entry fire landscape. Thus, with similar management, several additional fire entries will be required to restore tree densities to within the historical range. Further, our findings suggest that managing resource objective wildfires to allow for more moderate-severity burning, even with a single entry, may be more effective for restoring these forests than repeated low-severity entries.

Efficacy of variable density thinning and prescribed fire for restoring forest heterogeneity to mixed-conifer forest in the central Sierra Nevada, CA

Abstract Frequent-fire forests were historically characterized by lower tree density, a higher proportion of pine species, and greater within-stand spatial variability, compared to many contemporary forests where fire has been excluded. As a result, such forests are now increasingly unstable, prone to uncharacteristically severe wildfire or high levels of tree mortality in times of drought stress. While reducing tree density might help to restore resilience, thinning treatments are frequently seen as conflicting with management for other resources such as wildlife habitat, in part because standard thinning prescriptions don’t typically produce the degree of within-stand heterogeneity found in historical forests. In this study, we compare stand structures and heterogeneity produced by two different mechanical thinning treatments and in an unthinned control, all with or without prescribed fire as a follow-up treatment. The “high variability” thinning treatment was designed to produce the spatial variability once found in frequent fire forests and was based on historical data from nearby old-growth stands, while the “low variability” thinning treatment retained a similar number of trees but at a relatively even crown spacing. Stand averages and degree of variation for common forest metrics were calculated and values compared to a historical old-growth reference stand. Both thinning treatments reduced tree density and basal area, and shifted species composition towards historical values. Thinning treatments contained a deficit of trees in both the smallest ( 80 cm) size classes, relative to historical conditions. The high variability thinning treatment increased forest structure variation more than the low variability thinning treatment for most measures and retained a broader distribution of canopy closure values across the treatment units. While prescribed fire also reduced stand density and increased the amount of within-stand heterogeneity (when delayed mortality was included), the magnitude was much less than that produced by thinning. Prescribed fire did not significantly reduce basal area or alter the species composition. Prescribed burning did significantly reduce surface fuel loads, while thinning alone had no effect for most fuel classes. Our results show that high variability thinning coupled with prescribed burning resulted in a forest better aligned with the conditions present in historical frequent-fire forests, which were known to be more resilient to both wildfire and drought.

Litter decomposition in Mediterranean pine forests is enhanced by reduced canopy cover

This study investigated the impact of canopy cover and seasonality on litter decay in Mediterranean pine forests to enhance climate predictions. We conducted litterbag experiments in plots of different tree densities in two Mediterranean pine forests differing in precipitation amounts. In each plot, local litter was placed in forest gaps and under tree canopies for 613 days, starting in the dry season. Litter mass loss was greater in forest gaps than under tree canopies across forests and tree densities. Similarly, a reduction in tree density tended to increase mass loss. Additionally, while the decay rate slowed down from the first to the second wet season, the decay rate remained constant during the first and the second dry season, and the dry seasons contributed 30% to the overall mass loss. Reduction in canopy cover enhances litter decay, and the stability and magnitude of the dry season contribution to annual mass loss have the potential to control litter mass loss when accounting also for the dry periods in the wet season. Combined, the ongoing tree mortality and the predicted prolongation of dry periods due to climate change may enhance litter decay, possibly reducing ecosystem carbon stocks in drylands.

The impact of land use on water loss and soil desiccation in the soil profile

Farmlands have gradually been replaced by apple orchards in Shaanxi province, China, and there will be a risk of severe soil-water-storage deficit with the increasing age of the apple trees. To provide a theoretical basis for the sustainable development of agriculture and forestry in the Loess Plateau, soil water content in a 19-year-old apple orchard, a 9-year-old apple orchard, a cornfield and a wheat field in the Changwu Tableland was investigated at different depths from January to October 2014. The results showed that: (1) the soil moisture content is different across the soil profile—for the four plots, the soil moisture of the cornfield is the highest, followed by the 9-year-old apple orchard and the wheat field, and the 19-year-old apple orchard has the lowest soil moisture. (2) There are varying degrees of soil desiccation in the four plots: the most serious degree of desiccation is in the 19-year-old apple orchard, followed by the wheat field and the cornfield, with the least severe desiccation occurring in the 9-year-old apple orchard. Farmland should replace apple orchards for an indefinite period while there is an extremely desiccated soil layer in the apple orchard so as to achieve the purpose of sustainable development. It will be necessary to reduce tree densities, and to carry out other research, if development of the economy and ecology of Changwu is to be sustainable.

Changes in the natural dynamics of Nothofagus dombeyi forests: population modeling with increasing drought frequencies

AbstractDrought‐induced episodes of tree mortality can determine forest dynamics and structure, particularly in forests dominated by single species. Short‐ and mid‐term climate projections indicate that strong changes in annual precipitation may strike more often in northern Patagonia. Data for recruitment, growth, and survival of Nothofagus dombeyi tree individuals were collected at several sites across the Nahuel Huapi National Park in Argentina. We combined mathematically all these different demographic stages into an Integral Projection Model to simulate 100‐yr projections of simulated stand structure under different frequencies of extreme drought episodes. We projected total basal area and the number of individuals for three different initial stand types (i.e., young, medium, and old) and for varying drought frequencies (i.e., from 1 to 5 drought events every 100 years). Recruitment into the dbh ≥ 10 cm size class under normal conditions (i.e., without drought) was higher than under episodic drought conditions. In addition, survival under normal conditions was higher than under drought conditions, especially for small trees. Differences in growth were also important, with trees growing more vigorously under normal than under drought conditions. Our simulations predicted that N. dombeyi populations would experience a reduction in tree density in the mid‐term if, as predicted by the IPCC projections, the frequency of future drought events increased. The simulations also showed that in those cases, young stands should suffer the most. Drought‐mediated changes may induce a decline in the development of N. dombeyi forests in the mid‐ and long term by a drastic reduction in tree density.

Size Matters a Lot: Drought-Affected Italian Oaks Are Smaller and Show Lower Growth Prior to Tree Death.

Hydraulic theory suggests that tall trees are at greater risk of drought-triggered death caused by hydraulic failure than small trees. In addition the drop in growth, observed in several tree species prior to death, is often interpreted as an early-warning signal of impending death. We test these hypotheses by comparing size, growth, and wood-anatomy patterns of living and now-dead trees in two Italian oak forests showing recent mortality episodes. The mortality probability of trees is modeled as a function of recent growth and tree size. Drift-diffusion-jump (DDJ) metrics are used to detect early-warning signals. We found that the tallest trees of the anisohydric Italian oak better survived drought contrary to what was predicted by the theory. Dead trees were characterized by a lower height and radial-growth trend than living trees in both study sites. The growth reduction of now-dead trees started about 10 years prior to their death and after two severe spring droughts during the early 2000s. This critical transition in growth was detected by DDJ metrics in the most affected site. Dead trees were also more sensitive to drought stress in this site indicating different susceptibility to water shortage between trees. Dead trees did not form earlywood vessels with smaller lumen diameter than surviving trees but tended to form wider latewood vessels with a higher percentage of vessel area. Since living and dead trees showed similar competition we did not expect that moderate thinning and a reduction in tree density would increase the short-term survival probability of trees.

Understory Responses to Tree Thinning and Seeding Indicate Stability of Degraded Pinyon-Juniper Woodlands

Depauperate understory plant communities resulting from intensive livestock grazing in pinyon-juniper woodlands of the western United States may represent degraded stable states, resistant to ecological restoration treatments. In this study, we analyzed 10-yr understory plant community responses to restoration treatments that included tree thinning to approximate historical densities of pinyon pine (Pinus edulis) and juniper (Juniperus osteosperma), scattering of thinning slash to improve soil conditions, and seeding at two woodland sites (Craig Ranch and Goose Pond) in northwestern Arizona. Results showed that thinning resulted in significant reductions in tree density at both sites, as well as reductions in tree basal area at the Goose Pond site. Boles, branches, and tops of the thinned trees scattered across the study sites resulted in few changes to woody surface fuel loading. Thinning and addition of woody material, along with seeding, resulted in only minor changes in understory cover and species richness at both sites. However, plant cover and species richness were both negatively correlated with tree density. Degraded conditions at the sites appeared to be stable, and we suggest that treatments implemented in our studies may have not been intensive enough to produce significant understory responses and meet restoration objectives. Managers aiming to restore understory diversity at similar sites may be required to use heavier thinning prescriptions and repeated seeding. More work is needed to test new restoration approaches that are designed to drive degraded pinyon-juniper woodlands over resilience thresholds toward more diverse understory communities.

Spatial scales influence long-term response of herbivores to prescribed burning in a savanna ecosystem

Both wild and prescribed fire in savanna ecosystems influence habitat use by herbivores by creating or maintaining spatial and temporal heterogeneity in forage quality and vegetation cover. Yet little is known about how spatial scales influence long-term persistence of fire effects. We examined changes over a 6-year period in herbivore preference for experimentally burned patches that varied in spatial extent and grain. Avoidance for the burns by elephants and preference for the burns by impala and Grant’s gazelle decreased significantly. For the rest of the species (zebra, eland, oryx, hartebeest, warthog and hare), there were no significant changes in preference for the burns. Changes in preference for the burned areas depended on the spatial extent and grain of the burn, with intermediate-size (9-ha) burns and large (8-ha) patchy burns being more preferred 6–7 years after fire. Grain, but not the spatial extent of the burned area, influenced changes in grass height. Fire resulted in a delayed reduced tree density irrespective of the spatial scale of the burn. Results of this study indicate that, depending on the scale of fire prescription, the impacts of fire on herbivores may last longer than previous studies suggest.

Methods to Reduce Forest Residue Volume after Timber Harvesting and Produce Black Carbon

Forest restoration often includes thinning to reduce tree density and improve ecosystem processes and function while also reducing the risk of wildfire or insect and disease outbreaks. However, one drawback of these restoration treatments is that slash is often burned in piles that may damage the soil and require further restoration activities. Pile burning is currently used on many forest sites as the preferred method for residue disposal because piles can be burned at various times of the year and are usually more controlled than broadcast burns. In many cases, fire can be beneficial to site conditions and soil properties, but slash piles, with a large concentration of wood, needles, forest floor, and sometimes mineral soil, can cause long-term damage. We describe several alternative methods for reducing nonmerchantable forest residues that will help remove excess woody biomass, minimize detrimental soil impacts, and create charcoal for improving soil organic matter and carbon sequestration.

A multi-scale analysis of habitat selection in peripheral populations of the endangered Dupont’s LarkChersophilus duponti

SummaryHabitat selection of endangered species in peripheral populations must be considered when designing effective conservation plans, as these populations tend to occupy atypical habitats where species-environment relationships are not well understood. We examined patterns of habitat use in peripheral populations of the endangered Dupont’s LarkChersophilus duplontiusing a multi-scale approach and assessed the spatiotemporal transferability of these models to test for their generality. Our results show that at microhabitat (circles of 50-m diameter used by the species versus random points) and macrohabitat (occupied/unoccupied squares of 1 ha) scales the species selected flat and non-forested areas, but at the microhabitat scale the cover of small shrubs was also important. Models developed at patch scale (occupied /unoccupied sites) identified only site size as an important predictor of species occurrence. Habitat models transferred successfully among sites and years, which suggests that these models and our recommendations may be extrapolated over a larger geographic area. A multi-scale approach was used for identifying conservation requirements at different spatial scales. At the patch scale our models confirm it is a priority to maintain or enlarge the extent of habitat patches to ensure the viability of the studied metapopulation. At the macrohabitat scale our results suggest that reducing tree density in low slope areas would be the most effective management action. At the microhabitat scale, encouraging the presence of small and medium-sized shrubs, by clearing certain scrubs (e.g. large broomsGenistaspp. and rosemaryRosmarinus officinalis) or promoting traditional low-level extensive grazing, should increase the availability of high-quality habitats for the species, and thus the number of potential territories within a patch. These recommendations largely coincide with the ones given for core populations at specific scales elsewhere.