An Analysis of Vegetation Restoration on Opencast Oil Shale Mines in Estonia

We compared four types of 30‐year‐old forest stands growing on spoil of opencast oil shale mines in Estonia. The stand types were: (1) natural stands formed by spontaneous succession, and plantations of (2) Pinus sylvestris (Scots pine), (3) Betula pendula (silver birch), and (4) Alnus glutinosa (European black alder). In all stands we measured properties of the tree layer (species richness, stand density, and volume of growing stock), understory (density and species richness of shrubs and tree saplings), and ground vegetation (aboveground biomass, species richness, and species diversity). The tree layer was most diverse though sparse in the natural stands. Understory species richness per 100‐m² plot was highest in the natural stand, but total stand richness was equal in the natural and alder stands, which were higher than the birch and pine stands. The understory sapling density was lower than 50 saplings/100 m² in the plantations, while it varied between 50 and 180 saplings/100 m² in the natural stands. Growing stock volume was the least in natural stands and greatest in birch stands. The aboveground biomass of ground vegetation was highest in alder stands and lowest in the pine stands. We can conclude that spontaneous succession promotes establishment of diverse vegetation. In plantations the establishment of diverse ground vegetation depends on planted tree species.     

The potential contribution of conifer plantations to the UK Biodiversity Action Plan

Summary

The detrimental effects of conifer plantations on open ground habitats have been well catalogued and discussed, but the potential contribution of planted forests to the conservation of woodland biodiversity has not been quantified to the same extent. This quantification is needed urgently to help forest managers fulfil commitments to biodiversity enhancement as outlined in the UK Biodiversity Action Plan, the UK Forestry Standard and the UK Woodland Assurance Scheme (UKWAS). Results are presented from a five-year programme of research aimed at obtaining baseline information on biodiversity in planted forests and evaluating the contribution of planted forests to the conservation of native flora and fauna. Fifty-two plots were surveyed in total, covering a range of different tree crops (Scots pine Pinus sylvestris L., Sitka spruce Picea sitchensis (Bong.) Carr., Norway spruce Picea abies L. and Corsican pine Pinus nigra var maritima (Aitón) Melville) and stand ages (pre-thicket, mid-rotation, mature and over-mature) in three contrasting bioclimatic zones (upland, foothills and lowlands) throughout Britain. Additional plots were established in semi-natural woodland to allow comparisons between the biodiversity of plantations and native stands. Over 2000 species were recorded in total, including 45 Red Data Book species. Planted stands had similar or richer fungal and invertebrate communities to those of the native stands but poorer lichen and vascular plant communities. The latter were strongly affected by shading, dense, mid-rotation Sitka spruce stands having the lowest species counts. In contrast, these stands had a high diversity of mycorrhizal fungi, including a number of rare and threatened species normally associated with native pine wood. Bryophyte species-richness was related more to climate than woodland type, with the wetter upland spruce and native oak stands having the most diverse communities. Compared to the younger planted stands, over-mature planted stands had a higher proportion of species characteristic of semi-natural woodland stands. This related to greater structural diversity and higher deadwood volumes in the over-mature stands. It is concluded that conifer plantations make a positive contribution to biodiversity conservation in the UK and hence to the UK Biodiversity Action Plan. No single stand or crop type provides ‘optimal’ conditions for biodiversity, but the habitat value of plantations could be enhanced by increasing the area managed under alternative systems to clear-felling, such as ‘continuous cover’ and/or non-intervention natural reserves.     

Determinants of woody species richness in Scot pine and beech forests: climate, forest patch size and forest structure

We analysed patterns of woody species richness in Pinus sylvestris and Fagus sylvatica forests in Catalonia (NE Spain) from forestry inventory databank in relation to climate and landscape structure. Both types of forests are found within the same climatic range, although they have been managed following somewhat different goals. Overall, woody species richness significantly increased when conditions get closer to the Mediterranean ones, with milder temperatures. Differences between the two types of forests arose when comparing the relationship between richness and forest patch size. Woody species richness increased in pine forests with patch size, while the opposite trend was observed in beech forests. This pattern is explained by the different behaviour of structural canopy properties, since leaf area index and canopy cover showed a steeper increase with increasing forest patch size in Fagus forests than in Pinus ones. Accordingly, richness decreased with canopy cover in Fagus plots, but not in Pinus ones. We suggest that these differences would be related to management history, which may have enhanced the preservation of beech stands in larger forest landscape units.     

Passive Restoration of Atlantic Forest Following Pinus taeda Harvesting in Southern Brazil

The understory of exotic tree plantations can have non‐negligible native species richness. Ecological restoration of these sites may include the harvest of trees, depending on the tradeoff between timber income and harvest impacts on biodiversity. This study aimed to investigate how a site can recover from harvest disturbance, by comparing the regeneration of woody species in the understory of two types of 37‐year‐old Pinus taeda plantation (P1 and P2, high and low relative density of pine seedlings in the understory, respectively), with stands that were similar to P2 but subjected to harvest and then abandoned for 15 years (R sites). Secondary forests (SF) were used as references. We sampled three different sites for each stand condition; soil chemical properties, estimations of litter mass, and canopy cover were measured. P1 had low species diversity, and P2 and R had 50 and 46% of SF richness, respectively. The R site contained few pine saplings and was floristically similar to P2; this indicated that 15 years was sufficient for the recovery of plant diversity to near pre‐harvesting levels. Soil fertility was highest in SF and lowest in P1. Thus old plantations of P. taeda with low relative density of pine juveniles can be cost‐effective starting points for restoration. Despite the destructive effects of pine harvest, recovery of native species can occur rapidly. In situations in which clearcutting of pine stands is not planned or possible, modest thinning of P. taeda adults and/or intensive thinning of juveniles could expedite restoration.     

Abiotic factors modulate post-drought growth resilience of Scots pine plantations and rear-edge Scots pine and oak forests

The proportion of planted forests in the Mediterranean Basin is one of the largest in the world. These plantations are dominated by pine species and present a series of characteristics such as low elevation, high competition or small tree size that make them more vulnerable to droughts. However, quantitative assessments of their post-drought growth resilience in accordance with species, site factors and tree characteristics are lacking. In this study we sampled 164 trees at four forest sites located in the drought-prone Sierra Nevada, southeastern Spain. We compared growth responsiveness to drought in rear-edge planted vs. relic natural Scots pine (Pinus sylvestris) and coexisting Pyrenean oak (Quercus pyrenaica) stands. Our objective was to characterize and compare the different growth responses to drought between species and sites and the effect of the main physiographic factors (altitude, aspect, and slope) on these responses since the influence of these factors on post-drought resistance and resilience has received little attention to date. Our results reveal that the planted pine sites with the lowest mean growth rates displayed greater resistance during drought, and that higher altitude was associated with improved resistance and/or resilience for all species and sites. Natural pine and Pyrenean oak stands were better adapted to the dry climatic conditions of the Mediterranean region where the study was undertaken, displaying greater resistance and/or resilience and lower influence of drought on growth in comparison to stands of planted pines. These results suggest that promoting the conservation of high-elevation pine plantations and enhancing the regeneration of natural pine and oak may improve the resistance and resilience of these drought-prone forest ecosystems.     

Underplanting degraded exotic Pinus with indigenous conifers assists forest restoration

We propose that nonharvest plantations could provide important opportunities for restoration of indigenous forest cover and related ecosystem services. We assessed the relative performance of three Podocarpaceae (podocarps) species planted into a degraded Ponderosa Pine (Pinus ponderosa) plantation, central North Island, New Zealand. We hypothesised that the degraded pine plantation overstorey could provide suitable conditions for the development of a podocarp‐dominated forest structure within ca. 50 years of underplanting and that podocarp growth would differ depending on the species suitability to the site. Rimu (Dacrydium cupressinum) significantly outperformed both Totara (Podocarpus totara) and Kahikatea (Dacrycarpus dacrydioides) in height and diameter growth. Rimu was now the structurally dominant tree where it occurred rather than pine. Per annum scaled carbon storage within Rimu stands was significantly greater than the Totara, Kahikatea or Pine stands. All podocarp species had attained a greater stand density compared to the pine overstorey. Possible reasons for the differing podocarp growth performance include different light requirements, response to soil nutrients, elevational distributions and frost susceptibility. There were significant differences in understorey species richness among the different stands of podocarp species. Underplanting accelerated successional development by incorporating late‐successional indigenous canopy dominants within the forest succession and overcame limitations imposed on forest succession at the site from its isolation from indigenous forest tree seed sources.     

Restoration of Young Forests in Eastern Finland: Benefits for Saproxylic Beetles (Coleoptera)

Effective fire suppression in combination with intensive forestry has caused a large number of dead wood‐dependent (saproxylic) species to become threatened in Fennoscandia. In order to return the fire disturbance dynamics and to increase the amount of dead wood, restoration actions are urgently needed. We studied the effects of restoring young (under 30 years old) pine‐dominated (Pinus sylvestris L.) forest stands on saproxylic beetle assemblages in eastern Finland, focusing especially on rare, red‐listed, and pyrophilous (RRLP) species. Our experiment included a restoration treatment including two tree felling levels for fuel load (10 or 20 m³/ha) followed by burning, and an untreated control. We sampled beetles before restoration in 2005, during the year of restoration in 2006, and in two post‐treatment years in 2007 and 2011. Both restoration treatments increased the number of saproxylic and RRLP species. The species richness increased most in the year of restoration in 2006 and this trend continued in the following year 2007, but no differences in species assemblages were detected between the two fuel load levels. By 2011, however, the species richness and abundance had declined back to the pre‐treatment level. We suggest that restoration burning can also be directed to young forests where biodiversity values are initially low. On the basis of the observed decline in the species richness, we suggest that fire could be introduced in neighboring areas in approximately 5‐year intervals to maintain populations of the most demanding pyrophilous species .     

Ecological Restoration of Native Forest at Aratiatia, North Island, New Zealand

Successional pathways in native forest, planted 15–33 years ago on reconstructed surfaces to restore aesthetic values destroyed by hydro‐electric dam construction at Aratiatia, central North Island, New Zealand, were compared with those on similar surfaces left unplanted. Only native species were planted. Classification identified three canopy communities and several ground layer communities with significant inter‐stratum relationships: Pittosporum tenuifolium‐Sophora tetraptera short forest with ground layers dominated by litter; P. tenuifolium‐Kunzea ericoides short forest over adventive grasses on planted sites; and adventive Cytisus scoparius shrubland over grasses on unplanted sites. Planted communities mirror young secondary forests on intact substrates in the district, but have lower density and similar or higher basal area than such forests elsewhere. Established seedlings of seven planted canopy trees, mostly early successional bird‐dispersed species, are reasonably widespread in floristically rich Pittosporum‐Sophora forest. Seedlings of only two species are widespread in floristically poor Pittosporum‐Kunzea forest, and none on unplanted sites. This first large‐scale attempt at ecological restoration in New Zealand, by mass planting of new surfaces with early successional native woody species, has created aesthetically‐pleasing stands of indigenous forest on sites which would otherwise remain in relatively stable adventive shrubland communities for the foreseeable future. Only continued monitoring will show whether further management is necessary and whether natural processes are operating at a level sufficient to ensure that artificially initiated successions will continue along more or less natural pathways.     

Community homogenization and the invasiveness of commensal species in Mediterranean afforested landscapes

The ecological consequences of homogenization remain relatively unexplored. One example of landscape-homogenizing is the establishment of plantations. We studied the effect of human-made forests by contrasting plant and small-mammal community composition between planted tree stands and adjacent natural habitat in two different Mediterranean habitats in Israel: (1) inland habitat where we focused on pine (Pinus halepensis) and carob (Ceratonia siliqua) stands, and (2) coastal sand dune habitat where we focused on planted acacia (Acacia saligna) stands. We first wanted to verify whether planted trees modify plant species composition, and second, if and how the small-mammal community is affected by the different habitat conditions created in plantations with different canopy cover. We were especially interested in the abundance of the commensal house mouse (Mus musculus). All tree stands underwent biotic homogenization indicated by abundance of house mice coupled with lower diversity of indigenous vegetation and small-mammal abundances and diversities. Habitat structural diversity was positively related with small-mammals diversity and was lower in artificial tree stands in both habitats. Our results suggest that using the abundance of commensal generalist species such as the house mouse relative to other more specialist small-mammals is a good approach to determine ecosystem integrity. Pre-commercial thinning treatment is a potential management tool to maintain a proportion of native tree species within the canopy of planted tree stands. However, until sufficient data is available for making generalizations, the exact level of thinning necessary to reverse the homogenization processes in man-made plantations and keeping indigenous small-mammal communities diverse and less prone to invasion must be determined empirically.     

Restoring Fire to Long-Unburned Pinus palustris Ecosystems: Novel Fire Effects and Consequences for Long-Unburned Ecosystems

Biologically rich savannas and woodlands dominated by Pinus palustris once dominated the southeastern U.S. landscape. With European settlement, fire suppression, and landscape fragmentation, this ecosystem has been reduced in area by 97%. Half of remnant forests are not burned with sufficient frequency, leading to declines in plant and animal species richness. For these fire‐suppressed ecosystems a major regional conservation goal has been ecological restoration, primarily through the reinitiation of historic fire regimes. Unfortunately, fire reintroduction in long‐unburned Longleaf pine stands can have novel, undesirable effects. We review case studies of Longleaf pine ecosystem restoration, highlighting novel fire behavior, patterns of tree mortality, and unintended outcomes resulting from reintroduction of fire. Many of these pineland restoration efforts have resulted in excessive overstory pine mortality (often >50%) and produced substantial quantities of noxious smoke. The most compelling mechanisms of high tree mortality after reintroduction of fire are related to smoldering combustion of surface layers of organic matter (duff) around the bases of old pines. Development of effective methods to reduce fuels and competing vegetation while encouraging native vegetation is a restoration challenge common to fire‐prone ecosystems worldwide that will require understanding of the responses of altered ecosystems to the resumption of historically natural disturbances.