Stand and landscape-level factors related to bird assemblages in exotic pine plantations: Implications for forest management

Plantations cover a substantial amount of Earth's terrestrial surface and this area is expected to increase dramatically in the coming decades. Pinus plantations make up approximately 32% of the global plantation estate. They are primarily managed for wood production, but have some capacity to support native fauna. This capacity likely varies with plantation management. We examined changes in the richness and frequency of occurrence of bird species at 32 plots within a Pinus radiata plantation (a management unit comprising multiple Pinus stands) in south-eastern Australia. Plots were stratified by distance to native forest, stand age class and thinning regime. We also assessed the landscape context of each plot to determine relationships between bird assemblages and stand and landscape-level factors. Bird species richness was significantly higher at plots ≥300 m from native forest and in mature (∼20 years since planting) and old (∼27 years since planting) thinned pine stands. We were able to separate the often confounding effects of stand age and thinning regime by including old stands that had never been thinned. These stands had significantly fewer species than thinned stands suggesting thinning regime, not age is a key factor to improving the capacity of pine plantations to support native species (although an age × thinning interaction may influence this result). At the landscape level, species richness increased in pine stands when they were closer to native riparian vegetation. There were no significant differences in species composition across plots. Our study indicates the importance of stand thinning and retention of native riparian vegetation in improving the value of pine plantations for the conservation of native fauna.     

Tropical reptiles in pine forests: Assemblage responses to plantations and plantation management by burning

Worldwide, the land area devoted to timber plantations is expanding rapidly, especially in the tropics, where reptile diversity is high. The impacts of plantation forestry and its management on native species are poorly known, but are important, because plantation management goals often include protecting biodiversity. We examined the impact of pine (Pinus caribaea) plantations, and their management by fire, on the abundance and richness of reptiles, a significant proportion of the native biodiversity in tropical northern Australia, by (i) comparing abundance and diversity of reptiles among pine plantations (on land cleared specifically for plantation establishment), and two adjacent native forest types, eucalypt and Melaleuca woodlands, and (ii) comparing reptile abundance and richness in pine forest burnt one year prior to the study to remove understorey vegetation with pine forest burnt two years prior to the study. We also examined the influence of fire on reptile assemblages in native vegetation, by comparing eucalypt woodland burnt two years prior to the study and unburnt for eight years. To quantify mechanisms driving differences in reptile richness and abundance among forest types and management regimes, we measured forest structure, the temperatures used by reptiles (operative temperature) and solar radiation, at replicate sites in all forest types and management regimes. Compared to native forests, pine forests had taller trees, lower shrub cover in the understorey, more and deeper exotic litter (other than pine), and were cooler and shadier. Reptile assemblages in pine forests were as rich as those in native forests, but pine assemblages were composed mainly of species that typically use closed-canopy rainforest and prefer cooler, shadier habitats. Burning did not appear to influence the assemblage structure of reptiles in native forest, but burning under pine was associated with increased skink abundance and species richness. Burned pine was not warmer or sunnier than unburned pine, a common driver of reptile abundance, so the shift in lizard use after burning may have been driven by structural differences in understorey vegetation, especially amounts of non-native litter, which were reduced by burning. Thus, burning for management under pine increased the abundance and richness of lizard assemblages using pine. Pine plantations do not support the snake diversity common to sclerophyllous native forests, but pine may have the potential to complement rainforest lizard diversity if appropriately managed.     

Patterns of forest use and endemism in resident bird communities of north-central Michoacán, Mexico

We compared breeding avian communities among 11 habitat types in north-central Michoacán, Mexico, to determine patterns of forest use by endemic and nonendemic resident species. Point counts of birds and vegetation measurements were conducted at 124 sampling localities from May through July, in 1994 and 1995. Six native forest types sampled were pine, pine–oak, oak–pine, oak, fir, and cloud forests; three habitat types were plantations of Eucalyptus, pine, and mixed species; and the remaining two habitats were shrublands and pastures. Pastures had lower bird-species richness and abundance than pine, oak–pine, and mixed-species plantations. Pine forests had greater bird abundance and species richness than oak forests and shrublands. Species richness and abundance of endemics were greatest in fir forests, followed by cloud forests. Bird abundance and richness significantly increased with greater tree-layer complexity, although sites with intermediate tree complexity also supported high abundances. When detrended correspondence-analysis scores were plotted for each site, bird species composition did not differ substantially among the four native oak-and-pine forest types, but cloud and fir forests, Eucalyptus plantations, and mixed-species plantations formed relatively distinct groups. Plantations supported a mixture of species found in native forests, shrublands, and pastures. Pastures and shrublands shared many species in common, varied greatly among sites in bird-species composition, and contained more species specific to these habitats than did forest types.     

Understory plant diversity and biomass in hybrid poplar riparian buffer strips in pastures

Understory plant biomass, species richness and canopy openness were measured in six-year old hybrid poplar riparian buffer strips, in the understory of two unrelated clones (MxB-915311 and DxN-3570), planted along headwater streams at three pasture sites of southern Quebec. Canopy openness was an important factor affecting understory biomass in hybrid poplar buffers, with lower understory biomass observed on sites and under the clone with lower canopy openness. Although tree size was an important factor affecting canopy openness, relationships between total stem volume and canopy openness, for each clone, also support the hypothesis of a clonal effect on canopy openness. Understory biomass and canopy openness as low as 3.6 g m⁻² and 7.6% in 1 m² microplots were measured under clone MxB-915311 at the most productive site. This reduction of understory plant growth could compromise important buffer functions for water quality protection (runoff control, sediment trapping and surface soil stabilisation), particularly were concentrated runoff flow paths enter the buffer. On the other hand, tree buffers that maintain relatively low canopy openness could be interesting to promote native and wetland plant diversity. Significant positive relationships between canopy openness and introduced species richness (R ² = 0.46, p < 0.001) and cover (R ² = 0.51, p < 0.001) were obtained, while no significant relationship was observed between canopy openness and native (wetland) species richness and cover. These results suggest that planting riparian buffer strips of fast-growing trees can rapidly lead to the exclusion of shade-intolerant introduced species, typical colonisers of disturbed habitats such as riparian areas of pastures, while having no significant effect on native (wetland) diversity. Forest canopy created by the poplars was probably an important physical barrier controlling introduced plant richness and abundance in agricultural riparian corridors. A strong linear relationship (R ² = 0.73) between mean total species richness and mean introduced species richness was also observed, supporting the hypothesis that the richest communities are the most invaded by introduced species, possibly because of higher canopy openness, as seen at the least productive site (low poplar growth). Finally, results of this study highlight the need for a better understanding of relationships between tree growth, canopy openness, understory biomass and plant diversity in narrow strips of planted trees. This would be useful in designing multifunctional riparian buffer systems in agricultural landscapes.     

What can tree plantations do for forest birds in fragmented forest landscapes? A case study in southern Brazil

Despite the fact that tree plantations are not able to completely replace the ecological function of natural forests, the present study proposes to evaluate for which bird species or avian groups tree plantations act as habitat in fragmented landscape in southern Brazil. We compared the richness and abundance of bird species in a natural forest to adjacent plantations of Araucaria, a native tree species and of pine, an exotic plant in South America. Moreover, we evaluated the impact of tree plantations on richness of avian groups with different levels of dependence on forest habitat, feeding habits and foraging strata as well as on threatened species. The fixed 100 m radius point-counts method was used. A total of 114 bird species were recorded in all areas. Of those, 93 occurred in natural forest, 87 in Araucaria plantations and 81 in pine plantations. These results indicate that richness and abundance were lower in the pine plantations than in the natural forest and in the Araucaria plantations. Araucaria plantations can be used by a high number of bird species and their richness was not significantly lower than that observed in the adjacent natural forest. Our results suggest that Araucaria plantations could act as habitat for a large number of bird species, especially for forest-dependents species, insectivores, frugivores and species at different threat categories.     

Litter decomposition can detect effects of high and moderate levels of forest disturbance on stream condition

Considerable research efforts have been devoted to determining what forest management practices most affect stream ecosystems, and how those impacts might be mitigated. Recent studies have stressed the relevance of litter decomposition to assess the conditions of headwater streams affected by riparian and upland forest harvest. Here we specifically examined whether litter decomposition can detect ecological effects of clearcutting to stream edges on headwater streams eight years after logging and if large (30 m) and narrow (10 m) riparian reserves (8-year post-harvest), and selection logging at 50% removal of basal area of riparian trees (1-year post-harvest), are effective protection measures for streams. We measured decomposition rates of red alder (Alnus rubra) leaf litter in sixteen stream reaches, including reference reaches in a 70-year-old forest. We further examined assemblages of two main litter consumer groups, shredder invertebrates in riffles and aquatic hyphomycete fungi developing on decaying alder leaves. Alder decay rate was significantly lower in clearcut reaches than in reference reaches, and we found no evidence that any alternative riparian management practices examined in this study were able to mitigate against such an effect of logging. In unlogged reaches, rapid litter decomposition (0.0050–0.0118 day⁻¹) was associated with high density and diversity of shredders (up to ten taxa). Slower litter decomposition in wide and narrow reserve reaches (0.0019–0.0054 day⁻¹) and clearcut reaches (0.0024–0.0054 day⁻¹) was attributed to lower density and richness of shredders. By contrast, the low decay rate in recently established thinned reaches (0.0031–0.0049 day⁻¹) was not associated with a numerical response of shredders. Smothering of submerged leaves by sediments may have caused the reduction in alder decay rate in thinned reaches. Across all forest treatments fungal biomass or diversity remained fairly similar. Our findings suggest that stream ecosystems are extremely sensitive to small changes in riparian and upland forest cover. We propose that litter decomposition as a key ecosystem function in streams could be incorporated into further efforts to evaluate and improve forestry best management practices.     

Bird communities in tropical agroforestry ecosystems: an underappreciated conservation resource

Tropical conservation and research focus primarily on protected areas and often ignore conservation values of surrounding agricultural lands. Understanding how species utilize agricultural land will maximize conservation efforts. We compared bird community composition in four habitats in northeastern Costa Rica: shade-grown cacao, live fences, riparian forest buffers, and preserved late-successional rainforest. Point counts over 2 months found 167 species from 36 families. Rainforest contained the most species unique to a habitat although richness per point was lower than in agricultural habitats. Half, 31, of the rainforest species did not occur in other habitats, while 106 species, mostly those preferring open areas, occurred in agroforest habitats but not rainforest. While agricultural habitats had fairly similar species composition to each other as determined by distance in an ordination, each also contained significant numbers, 9–30, of unique species. While intact rainforest remains central to conservation of tropical birds, agricultural lands with substantial trees, e.g., live fences, riparian buffers, and plantations with shade trees, can support a high richness of birds. These avian communities are not simply subsets of the rainforest species but include substantial numbers of unique species. Conservation contributions of these lands to species richness and complexity should be considered in conservation, and trees in these habitats preserved.     

Ecological integrity of remnant montane forests along an urban gradient in the Sierra Nevada

Urban development typically has extensive and intensive effects on native ecosystems, including vegetation communities and their associated biota. Increasingly, urban planning strives to retain elements of native ecosystems to meet multiple social and ecological objectives. The ecological integrity of native forests in an urbanizing landscape is challenged by a myriad of impacts, such as forest management and invasive species. Environmental protection efforts in the Lake Tahoe basin, spanning the California/Nevada border in the Sierra Nevada mountains, over the past half century have resulted in the retention of thousands of parcels of remnant native forest located throughout the urbanizing landscape. The basin landscape provides an opportunity to evaluate the effects of land development on the composition and structure of remnant native forests along a gradient of urbanization. We sampled 118 sites located in remnant forests in the lower montane zone surrounded by 0–70% development. We also sampled forest structure in the landscape surrounding 75 of these sites to evaluate the contribution of remnant forests to the retention of native forest elements in the larger landscape. We characterized plant species composition and cover, vertical structure, and the density of trees, snags, and logs, as well as levels of ground disturbance and human activity. We found that remnant native forests retained much of their compositional and structural character along the development gradient, including large tree density, total canopy cover, and plant species richness. Notable exceptions were reductions in the density and decay stage of snags and logs, and the density of understory trees. We also observed increases in the richness and cover of herb and grass species and increases in the number of exotic plant species. In contrast, structural complexity was reduced in the landscape surrounding forest remnants in all measures except large tree density. We conclude that remnant native forests contribute significantly to maintaining native species in an urbanizing landscape, and that land conservation practices have an important role to play in protecting native forest ecosystems.     

Relationships between insect diversity and habitat characteristics in plantation forests

A methodological approach to the identification of biodiversity indicators in commercial forest stands is illustrated by analysis of the relationships between syrphid (hoverflies) and carabid (ground beetles) community composition and diversity, and stand structure and field layer vegetation. Data were collected from 12 commercial forest sites encompassing a range of climatic conditions and different crop types (Scots pine, Sitka spruce, Norway spruce and Corsican pine) across the UK. Comparisons were also made between unmanaged semi-natural Scots pine woods and Scots pine plantations. For both syrphids and carabids, no differences in species richness and diversity were recorded between semi-natural stands and plantations; one rare syrphid considered to be restricted to semi-natural pine stands was also found in spruce. Syrphid species diversity and richness was higher in southern spruce sites than in the northern sites. Northern sites had distinctive carabid communities, as did sites in the New Forest, a large ancient woodland in southern England. Of the measured habitat variables, vertical stand structure showed the best correlation with species richness and diversity of both carabids and syrphids. Richness and diversity were less in stands with high vertical cover values for canopy layers. Stands with higher field layer cover supported greater syrphid diversity, but lower carabid diversity. Measures of stand structure could be used as potential indicators of syrphid and carabid diversity, but additional habitat parameters also need to be tested.     

Can native vegetation recover after slash pine cultivation in the Brazilian Savanna?

There is a widespread view that forest plantations with exotic species are green deserts, unable to sustain biodiversity. Few studies have demonstrated, however, that planted stands of exotic trees have a greater negative effect on the plant diversity of savanna vegetation. We compared the native woody flora under four stands of slash pine of about 45 years old with four stands where the previously existing native Cerrado vegetation was preserved and protected from disturbances for the same period, has changed into dense vegetation - the “cerradão”, at Assis municipality, São Paulo State, Brazil. Aiming at understanding the potential ecological filters driving these communities, we assessed air and soil humidity, light availability and classified the native species on the basis of shade tolerance, dispersal syndrome and biomes in which they occur (Atlantic Forest or Cerrado). We recorded an average of 70 (±13) species under pine stands and 54 (±16) species in cerradão. Of the total of 136 species recorded, 78 occurred in both habitats, eight were exclusive to the “cerradão” (shade tolerant and also occurring in forest ecosystems) and 18 were recorded only under pine stands (82% heliophytic, exclusive to the Cerrado biome). Among the functional attributes and abiotic variables analyzed, only light availability explained the floristic differences found. Since richness was higher under pine, we refuted the hypothesis that exotic species constrain the establishment of the native species richness in the understory. On the other hand, the dark environment under the closed-canopy of the “cerradão” acts as a filter inhibiting the establishment of typical Cerrado species. Since pine stands, if managed in long cycle, maintain a reasonable pool of Cerrado endemic species in the understory pine plantations may be a good starting point for savanna restoration.     

The potential of transforming simple structured pine plantations into mixed Mediterranean forests through natural regeneration along a rainfall gradient

The aim was to study the potential for using natural regeneration as a basis for transformation of simply structured conifer plantations into mixed Mediterranean forests. We studied the variation along a rainfall gradient, in the natural regeneration of tree species in the understory of planted 40- to 50-year-old Aleppo pine (Pinus halepensis) forests. The study was conducted within the Mediterranean zone of Israel, which extends from the semiarid northern Negev desert (rainfall ca. 300 mm yr⁻¹) in the south to the humid Upper Galilee in the north (ca 900 mm yr⁻¹). Cover and height, density, and species composition of regenerating trees were measured on south- and north-facing slopes in forest sites of comparable silvicultural history (site preparation methodology, planting density and thinning regime) distributed along the rainfall gradient. Altogether, 12 species of regenerating native broadleaved trees were found in the understory of the various forest sites. Surface cover, density and species richness increased linearly along the entire rainfall gradient, on both north- and south-facing slopes, ranging from zero in the driest forest sites up to 85% cover, 7980 trees ha⁻¹ and 4.5 species per 200 m², respectively, in the most humid ones. Species composition of regenerating trees was also related to rainfall amount, through changes in the relative importance of species along the rainfall gradient. The effect of topographic aspect on tree regeneration was inconsistent, i.e., the interaction Rainfall × Aspect was significant. Nevertheless, the general trend showed better regeneration on north-facing slopes. Most of the regenerating trees in the understory were small, i.e., less than 100 cm in height, with no clear effect of rainfall amount and topographic aspect on the relative abundance of height classes. Regeneration by Aleppo pine was highly variable among and within the different forest sites and ranged from 0 to 1565 trees ha⁻¹, with no clear relationships with rainfall amount and topographic aspect. In light of our results we propose that the future structure of forests should vary with respect to annual rainfall amount within possible silvicultural scenarios.     

Large-scale ecological restoration of high-diversity tropical forests in SE Brazil

The complex interactions among endangered ecosystems, landowners’ interests, and different models of land tenure and use, constitute an important series of challenges for those seeking to maintain and restore biodiversity and augment the flow of ecosystem services. Over the past 10 years, we have developed a data-based approach to address these challenges and to achieve medium and large-scale ecological restoration of riparian areas on private lands in the state of São Paulo, southeastern Brazil. Given varying motivations for ecological restoration, the location of riparian areas within landholdings, environmental zoning of different riparian areas, and best-practice restoration methods were developed for each situation. A total of 32 ongoing projects, covering 527,982 ha, were evaluated in large sugarcane farms and small mixed farms, and six different restoration techniques have been developed to help upscale the effort. Small mixed farms had higher portions of land requiring protection as riparian areas (13.3%), and lower forest cover of riparian areas (18.3%), than large sugarcane farms (10.0% and 36.9%, respectively for riparian areas and forest cover values). In both types of farms, forest fragments required some degree of restoration. Historical anthropogenic degradation has compromised forest ecosystem structure and functioning, despite their high-diversity of native tree and shrub species. Notably, land use patterns in riparian areas differed markedly. Large sugarcane farms had higher portions of riparian areas occupied by highly mechanized agriculture, abandoned fields, and anthropogenic wet fields created by siltation in water courses. In contrast, in small mixed crop farms, low or non-mechanized agriculture and pasturelands were predominant. Despite these differences, plantations of native tree species covering the entire area was by far the main restoration method needed both by large sugarcane farms (76.0%) and small mixed farms (92.4%), in view of the low resilience of target sites, reduced forest cover, and high fragmentation, all of which limit the potential for autogenic restoration. We propose that plantations should be carried out with a high-diversity of native species in order to create biologically viable restored forests, and to assist long-term biodiversity persistence at the landscape scale. Finally, we propose strategies to integrate the political, socio-economic and methodological aspects needed to upscale restoration efforts in tropical forest regions throughout Latin America and elsewhere.     

Bird species diversity in riparian buffers,row crop fields,and grazed pastures within agriculturally dominated watersheds

In response to concern about the loss of ecosystem services once provided by natural riparian systems, state and federal agencies have established incentive programs for landowners to convert sensitive lands from agricultural to conservation uses. Enhancement of wildlife habitat, while identified as a function of such systems, has often been of secondary importance to soil conservation and water quality objectives. Though greatly important, little consideration has been given to how specific species will respond to the design and management of riparian buffers or other conservation lands. This study compared avian communities within a chronosequence of riparian buffers established on previously cropped or pastured land with those of the nearby matrix land cover types (row crop fields and an intensively grazed pasture). The riparian buffers consisted of native grasses, forbs, and woody vegetation established at three different times (2, 9, and 14+ years prior to survey). At each site, 10 min point counts for breeding birds were conducted using 50 m fixed radius plots, which were visited eight times between May 15 and July 10, 2008. A total of 54 bird species were observed over all of the study sites. The re-established riparian buffers in this study had higher bird abundance, richness, and diversity than the crop and pasture sites. These results suggest that re-establishing native riparian vegetation in areas of intensive agriculture will provide habitat for a broad suite of bird species, but that specific species will reflect successional stage, horizontal and vertical vegetative structure, and compositional diversity of the buffer vegetation. These results emphasize the importance of matching buffer design and management to species requirements if the objectives are to attract specific target species or species groups.     

Moving riparian management guidelines towards a natural disturbance model: An example using boreal riparian and shoreline forest bird communities

Forest harvesting strategies that approximate natural disturbances have been proposed as a means of maintaining natural species’ diversity and richness in the boreal forests of North America. Natural disturbances impact shoreline forests and upland areas at similar rates. However, shoreline forests are generally protected from harvest through the retention of treed buffer strips. We examined bird community responses to forest management guidelines intended to approximate shoreline forest fires by comparing bird community structure in early (1–4 years) post-burned and harvested boreal riparian habitats and the adjacent shoreline forest. We sampled riparian areas with adjacent: (1) burned merchantable shoreline forest (n = 21), (2) burned non-merchantable shoreline forest (n = 29), (3) 10 m treed buffer with 25% retention in the next 30 m (n = 18), and (4) 30 m treed buffer (n = 21). Only minor differences were detected in riparian species’ abundance and bird community composition between treatments with greater differences in these parameters occurring between post-fire and post-harvest upland bird communities. Indicators of all merchantable treatments were dominated by upland species with open-habitat species and habitat generalists being typical upland indicator species of burned merchantable habitats and forest specialists typical upland indicators of harvested treatments. Riparian species indicative of burned riparian habitats were Common Yellowthroat (Geothlypis trichas), Le Conte’s Sparrow (Ammodramus leconteii) and Eastern Kingbird (Tyrannus tyrannus) and indicators of 30 m buffers were Alder Flycatcher (Empidonax alnorum) and Wilson’s Warbler (Wilsonia pusilla). Multivariate Redundancy Analysis (RDA) of the overall (riparian and upland birds) community showed greater divergence than RDA with only riparian species suggesting less effect of fire and forestry on riparian birds than on upland birds. Higher natural range of variability (NRV) of overall post-fire bird communities compared to post-harvest communities emphasizes that harvesting guidelines currently do not achieve this level of variability. However, lack of a large negative effect on common riparian species in the first 4 years post-disturbance allows for the exploration of alternative shoreline forest management that better incorporates bird community composition of post-fire riparian areas and shoreline forests.     

Avian assemblages in eucalypt forests,plantations and pastures in northern NSW,Australia

Eucalypt plantations are expanding rapidly in Australia, and their value for native fauna requires investigation. The relative conservation value of young eucalypt plantations was investigated through assessment of avifauna richness, abundance and composition using transect surveys incorporating point counts in five broad habitat types—dryland forests, riparian forests, dryland plantations, riparian plantations, and riparian pastures (strips of riparian vegetation surrounded by pastures). A total of 73 species were recorded during formal surveys. Species richness and abundance were comparable among all habitat types except dryland plantations, which supported fewer species and in lower numbers. The avifauna assemblage differed according to broad habitat types. Forest habitats (dryland and riparian) harboured more forest- and woodland-dependent species, and a greater abundance of nectarivores and insectivores. Riparian plantations supported a similar number of forest- and woodland-dependent species to forest habitats, but also retained some open-country species. Riparian pastures had the highest cumulative species richness, reflecting a diverse mix of forest- and woodland-dependent birds and open-country species. It was the preferred habitat type for granivores and vertebrate eaters. Dryland plantations were dominated by common species and omnivores, and supported fewer forest- and woodland-dependent birds, insectivores and frugivores compared with other habitat types. The presence of riparian strips increased avifauna diversity and abundance in plantations and pastures to a greater extent than predicted by the proportional area of riparian habitat. The importance of riparian habitats needs to be recognised and incorporated into management policies if biodiversity conservation is to be an objective of plantation establishment.     

Assessing the relationships between stand development and understory vegetation using a 420-year chronosequence

The large-scale conversion of old forests to tree plantations has made it increasingly important to understand how understory vegetation responds to such landscape changes. For instance, in some forest types a reduction in understory richness and cover is thought to result from the development of canopy closure in plantations, although there is a paucity of empirical data demonstrating this relationship. We used a 420-year forest chronosequence as a case study to assess the relationship between stand age, tree canopy cover and understory vascular plant richness and composition in the Siskiyou Mountains of Oregon. The chronosequence consisted of six young managed (age 7–44) and nine older unmanaged (age 90–427) stands. All stands were similar in underlying geology, slope, elevation, and aspect. We found a non-linear relationship between stand age and richness, in which richness was highest in the youngest stands, reached a low in mid-aged stands (∼55 years), then increased in the oldest stands. We also found that percent tree canopy cover was correlated with total understory cover, richness, diversity, and species composition. In general, young stands were characterized by high shrub and graminoid cover and old stands were characterized by an abundant herb layer. Our work suggests that a major component of our study landscape is currently entering the forest stage (canopy closure) characterized by low levels of vascular plant species richness and cover. We use our results to discuss the potential effects of future forest management on understory plants.     

Effect of stand age on bird communities in late-successional Macedonian pine forests in Bulgaria

To gain insight into the question of which vegetation characteristics have the most influence on avian assemblages in late-successional forests, the habitat preferences of bird-guilds in old-growth endemic forests of Macedonian pine were studied over 3 years in the Pirin National Park, Bulgaria. Bird–habitat relationships were investigated by comparing vegetation characteristics, and bird species richness, diversity, abundance, and guild structure of birds (determined according to food type, foraging and nesting sites) between mature (60–100 years old) and over-mature (>120 years old) Macedonian pine forest stands. Studied forest age-classes differed mainly by the density, height and diameter of trees, and the amount of dead wood. The first one of these parameters decreased and the latter two parameters increased with the forest succession. The difference in the vegetation structure affected the abundance of bird-guilds and thus, the overall bird abundance and the structure of avian assemblages within Macedonian pine forests. There was no significant difference in bird diversity among studied forest age-classes, but the overall bird abundance increased with forest maturation. Analyzed by study plots, species richness was higher in over-mature forests, but at cluster level, there was no significant difference between mature and over-mature forest age-classes. Half of the studied (insectivorous, hole- and ground-nesters, bark- and canopy-foraging bird species) guilds were more abundant in over-mature forests, while there was no bird-guild exhibiting a preference for mature forest stands. The abundances of bird-guilds were correlated with tree height, diameter at breast height and the amount of dead wood between the studied forest age-classes and this might explain their preferences for over-mature pine forests. Therefore, for future sustainable management of these endemic forests and the conservation of their avifauna, efforts should focus on protecting the remaining native old-growth forest stands and the importance of the structure of Macedonian pine forests on their bird assemblages should be considered in forestry practices.     

Ground-dwelling invertebrates in reforested conifer plantations

Plantation forests are an important part of the forest estate in many countries. In Ireland, they cover around 9% of the land area and many that are commercially mature are now being felled and reforested. The potential biodiversity value of such second rotation forests has yet to be determined, yet this may be particularly significant in Ireland where cover of semi-natural woodland is only 1%. Invertebrates are a vital component of forest biodiversity, functioning as decomposers and pollinators, herbivores, predators and prey. Spiders and Carabid beetles are often used in biodiversity assessment as they are easily captured using pitfall traps, are taxonomically well known and respond to changes in habitat structure. This study aimed to examine spider and Carabid beetle diversity in second rotation Sitka spruce (Picea sitchensis) plantations at different stages of the forest cycle (5, 8–12, 20–30, 35–50 years), and compare the spiders captured in second rotation forests with those from first rotation. Spider and beetle diversity was influenced by stand structural development in second rotation plantations with numbers of forest-associated species increasing over the forest cycle. Overall, spider richness declined over the forest cycle and this was related to decreasing cover of field layer vegetation and fewer open-associated species. In contrast, total beetle richness increased and became more specialised over the forest cycle which may be related to slower colonisation of disturbed areas by beetles in comparison with spiders, and fewer open specialists at the early stages of second rotation. Spider assemblages were distinguished between rotations. This may be related to differing habitat conditions in second rotation forests including dryer soils with lower pH, differing vegetation complexity and presence of brush piles. Few of the forest species accumulated during first rotation were retained and the early stages of second rotation forest cycle was characterised by a generalist open fauna. Nonetheless, as the forest cycle progressed the spider assemblages between rotations became more similar. Current forest policy supports retaining over-mature trees and creating a mosaic of different aged stands within a plantation. Such measures may provide refuge for forest species after clearfell. In countries where forest fragments exist in a landscape dominated by agriculture, consideration should be given to the capacity of mature forest adjacent to felled stands to support forest species, and to the configuration of over-mature areas retained after felling.     

Can pine forest restoration promote a diverse and abundant understory and simultaneously resist nonnative invasion?

An important goal of forest restoration is to increase native plant diversity and abundance. Thinning and burning treatments are a common method of reducing fire risk while simultaneously promoting understory production in ponderosa pine (Pinus ponderosa) forests. In this study we examine the magnitude and direction of understory plant community recovery after thinning and burning restoration treatments in a ponderosa pine forest. Our objective was to determine if the post-treatment community was a diverse, abundant, and persistent assemblage of native species or if ecological restoration treatments resulted in nonnative species invasion. This project was initiated at the Grand Canyon-Parashant National Monument, Arizona, USA in 1997. We established four replicated blocks that spanned a gradient of soil types. Each block contained a control and a treated unit. Treated units were thinned to emulate pre-1870 forest stand conditions and prescribed-burned to reintroduce fire to a system that has not burned since ∼1870. We measured plant cover using the point-line intercept method and recorded species richness and composition on 0.05 ha belt transects. We examined the magnitude of treatment responses using Cohen's d effect size analysis. Changes in community composition were analyzed using nonmetric multidimensional scaling (NMS). Native plant species cover and richness increased in the thinned and burned areas compared to the controls. By the last year of the study, annual species comprised nearly 60% of the understory cover in the treatment units. Cheatgrass (Bromus tectorum), a nonnative annual grass, spread into large areas of the treated units and became the dominant understory species on the study site. The ecological restoration treatments did promote a more diverse and abundant understory community in ponderosa pine forests. The disturbances generated by such treatments also promoted an invasion by an undesirable nonnative species. Our results demonstrate the need to minimize disturbances generated by restoration treatments and argue for the need to proactively facilitate the recovery of native species after treatment.     

Differences in bird species diversities between a natural mixed forest and a coniferous plantation

Bird species diversity and bird species richness were surveyed in a natural mixed forest (mature forest) and in a coniferous plantation (30–40 years old) monthly from 1990 to 1994. These forests were 20 km apart and had similar weather conditions and soil types. There were larch and cedar plantations, and hardwoods along streams in the coniferous plantation. In the natural mixed forest, 55 bird species were found, whereas 40 species were recorded in the coniferous plantation. The species diversity of bird communities was significantly higher in the natural mixed forest than in the coniferous plantation mixed with hardwood trees. This result indicates that the coniferous plantation mixed with hardwood trees, presumed to be a more simplified environment, is likely to be less inhabitable for many bird species than the natural mixed forest, suggesting a relationship between the diversity of the forest environment and the diversity of the bird community. A higher number of bird species was recorded in the small coniferous forest mixed with hardwood trees compared with those in the coniferous plantation. The mixing of broad-leaved trees in a coniferous plantation was suggested to be effective in increasing number of bird species. These tendencies were recorded all through the year during our study. In snow-covering periods, both the diversity and the bird species richness fell in all study sites every year. Snow cover would have greater effect on bird species diversity in the coniferous plantation than in other forest types probably due to diet shortages caused by the snow cover over the forest floor.