Effects of planting design on planted seedlings and spontaneous vegetation 16 years after establishment of forest edges

In afforestation, studies of forest edges seldom span the effects of planting design and the self-designing capacities of spontaneous vegetation. This study revisited experimental forest edge sections 16 years after their establishment to assess the impact of five design elements on (1) horizontal and vertical edge structure, (2) growth of planted species and species groups, and (3) spontaneous establishment of woody vegetation. The design elements were: exposure to direct solar radiation; edge typology (shrub mixture, mixture of trees and shrubs, no edge planting); width of edge planting (5 or 10 m); species mixture principle (intimate mixtures or single species grouping); and planting row position from outermost to interior planting row (max. 6 rows). The results demonstrate that edge plantings support significantly more spontaneous woody vegetation than stand boundaries without such edge plantings. This result was consistent across the different design elements. Position across the planting rows from the outermost to innermost row was the most influential design element for the development of planted seedlings. Planted tree and shrub species of similar shade tolerance had contradicting development, where light-demanding pioneer tree species had obtained dominant positions while shade-tolerant shrub species had outgrown more light-demanding species. These results demonstrate that important successional processes can be activated by establishing the initial components and structures of forest edges. When designing such edges, species should preferably be allocated to different row cohorts reflecting their growth form and shade tolerance.     

Spatial variation of local stand structure in an Abies forest, 45 years after a large disturbance by the Isewan typhoon

Heterogeneity of forest stand structure often results from repeated small disturbances, but structural variation also arises in a stand that has regenerated after a single large stand-replacing disturbance. We explored the structural variation within a subalpine Abies forest in Japan that regenerated after a large typhoon in 1959. In 2004, four 50 × 50 m plots were established at two sites in the regenerated forest. To characterize local stand structure within each plot, we determined the stem density, stand basal area, mean diameter at breast height (DBH), and coefficient of variation (CV) of DBH in 10 × 10 m subplots. We analyzed the spatial distribution pattern of the trees in each subplot using the L(t) function and categorized the distributions as clumped or non-clumped. The analysis revealed marked variation among subplots in the stand’s structural characteristics. Although the spatial distribution patterns of the trees in all plots were clumped, 11 of 50 subplots at one site and 39 of 50 subplots at the other site were non-clumped. Subplots with a clumped distribution pattern generally had a smaller basal area, smaller mean DBH, and greater CV of DBH than subplots with the same density but a non-clumped pattern. These results illustrated the spatial heterogeneity of forest structure that can arise in Abies forest that has experienced a large disturbance, probably because of the different densities and distribution of saplings surviving the disturbance and the different forest growth dynamics that result.     

Tree spatial patterns of Abies alba and Fagus sylvatica in the Western Carpathians over 30 years

The decline of Abies alba (fir) in natural fir–beech forests in Europe has fascinated scientists for over a century. During this period, Fagus sylvatica (beech) became the dominant species in this forest type. We hypothesised that (1) the success of beech over fir is significantly connected with the fact that beech suffers less than fir from the presence of conspecific neighbours; that (2) shade tolerance is not a factor which favours beech over fir; and that (3) this is due to a significantly reduced proportion of litter treethrow mounds with suitable conditions for the successful regeneration of fir. We investigated these hypotheses by means of tree spatial pattern analysis. Eight rectangular plots (2–8 ha) were analysed in mountain fir–beech forests of the Outer Western Carpathians, Czech Republic. Various types of the pair correlation function and L function were used to describe the tree density variability of trees with DBH ≥10 cm. The analyses were carried out on datasets from the 1970s, 1990s and 2000s. Our results suggest that negative density dependence is not responsible for the current decline of fir. It seems that a higher shade tolerance of the advanced regeneration could be one of the factors which favour beech over fir. It is evident that fir trees have a markedly stronger positive association to mounds than beech trees.     

Spatial patterns of forest fires in Catalonia (NE of Spain) along the period 1975–1995: Analysis of vegetation recovery after fire

This paper revises the results of applying a semiautomatic methodology for fire scars mapping from a time series of Landsat MSS images over the forest and shrubby surface of Catalonia (1975–1993). Perimeters of fires which occurred in 1994 and 1995 were added enlarging the whole series to 21 years from TM imagery. Results are a map series of fire history during 21 years as well as a map of the fire recurrence level. Omission errors are 23% for burned areas greater than 2 km² while commission errors are 8% for areas greater than 0.5 km². Detected fire scars were incorporated into a geographic information system in order to characterise the fire regime of the study area. Fire size distribution and the number of spot fires originated from each fire as well as the maximum distance reached from the main fire are analysed. A first approach to monitor post-burn regeneration through normalised difference vegetation index is also shown.     

Reforestation with loblolly pine can restore the initial soil carbon stock relative to a subtropical natural forest after 30 years

We hypothesized that long-term loblolly pine (Pinus taeda L.) land-use restores SOC stock and lability of a subtropical Cambisol to the original levels of the natural forest (NF). Additionally, we hypothesized that roots are the major contributor to SOC and that soil stores most of the ecosystem total carbon (ETC). We investigated a chronosequence of loblolly pine land-use of 17 (first rotation) and 32 years (second rotation, unthinned or thinned) following clearing of the NF. The original SOC stock to 100 cm of NF (209?±?9.4 Mg C ha^?1) was depleted by 22% after 17 years of pine, possibly because of intense soil disturbance and low quantity and quality of the residue inputted during the pine stand implementation. However, the SOC stock was restored to the original stock of NF after 32 years of pine, with the input of above and belowground biomass at harvest of the first rotation possibly playing a role in this recovery. Thinning did not affect SOC stocks after 1 year. The POM-C reduced after 17 years and was not recovered after 32 years. We could not ascertain in 5-year evaluation whether root or litter was the major contributor to SOC. Soil held 72% of the ETC in NF and 48–59% in pine plantations, confirming that it stores most of the ETC. Overall, long-term loblolly pine land-use seems to restore the original soil carbon stock in this subtropical site, regardless of some lability losses.     

Growth of graded sweetgum 3 years after root and shoot pruning

Nursery grown 1–0 bareroot sweetgum seedlings were lifted and graded into two diameter classes (12–16 and 4–8 mm) during the dormant season. Large and small grades were top and/or root pruned and then outplanted on two sites in the lower Coastal Plain of the southeastern United States. Seedling shoots were pruned to 50% of tree height, a 5 cm stump, or no pruning. Seedling roots were pruned to a 15 cm length or left unpruned. Site affected survival but not growth. Smaller, top pruned seedlings performed worse on one site, probably due to greater weed competition. Large seedlings increased survival and growth which increased 3 year average plot volumes by 89%. Top pruning stimulated height growth, but reduced diameter growth and decreased third year seedling volumes. Root pruning did not affect seedling growth. Diameter growth may better indicate treatment impact that height, which has been most commonly used in previous studies.     

Role reversal in the stand dynamics of an angiosperm–conifer forest: Colonising angiosperms precede a shade-tolerant conifer in Afrotemperate forest

In mixed angiosperm–conifer forests worldwide, infrequent landscape-level catastrophic disturbances create a mosaic of persistent and different aged forest stands in the landscape with varying levels of dominance by the conifer component. In the ‘temporal stand replacement model’ (TSRM), disturbance creates conditions favouring a colonising cohort that is replaced by a suite of relatively shade-tolerant canopy species, which establish following the synchronous senescence of the pioneer canopy. In most southern hemisphere mixed angiosperm–conifer forests, with the exception of those in southern Africa, the establishing cohort is usually a large and very long-lived (550–650 years) conifer that is gradually replaced by angiosperms. As an explanation of the apparent dominance of the conifer Podocarpus latifolius, we examine the efficacy of the TSRM in mixed Afrotemperate forests where the establishing cohort is not a conifer. Forest succession in Afrotemperate forests was deterministic with the successive replacement of species determined first by their establishment success in shaded environments, and second, by their relative longevity. Several angiosperm species that were common canopy dominants established a pioneer cohort but were gradually replaced by P. latifolius, a shade-tolerant species. Continuous regeneration beneath the angiosperm canopy by P. latifolius eliminates synchronous canopy senescence, a key feature of the TSRM, as a mechanism driving the temporal replacement of canopy species. Senescing angiosperms created canopy gaps that were colonised by grasses and ferns, which suppressed canopy tree regeneration. In contrast, with continuous regeneration beneath the shaded canopy, P. latifolius gains a critical advantage over angiosperms at gap formation. Thus, in the absence of fairly large-scale natural disturbances, conifers come to dominate Afrotemperate forests. Commensurate with the latter, conifers in Podocarpus-forest were dated to approximately 320 years, more than 100 years older than the oldest P. latifolius in angiosperm-dominated forest. Tree life-history differences (shade tolerance, longevity) and the time since disturbance drive successional change from an angiosperm-dominated system to a stage dominated by P. latifolius. In general, the TSRM is a plausible explanation for the observed canopy tree structure and dynamics in mixed Afrotemperate forests. South African Afrotemperate forest is unusual among other southern hemisphere mixed angiosperm–conifer forests in that a suite of angiosperm canopy species, rather than a single conifer species, forms the colonising cohort.     

Field performance of conifer and hardwood species 5 years after nursery inoculation in the Canadian Prairie Provinces

The field performance of conifer and hardwood species inoculated with different inoculation treatments was evaluated 5 or 3 years after outplanting in the field trials established in the Canadian Prairie Provinces. In conifer trials, the growth of white spruce, black spruce, lodgepole pine, and larch seedlings observed on different sites varied greatly to different inoculation treatments depending on plant and fungal species involved. Five years after outplanting, most of the introduced fungi were replaced by several indigenous ectomycorrhizal fungal species except for Laccaria bicolor strain. Survival rates of most of the inoculated seedlings were not significantly different from control seedlings naturally colonized by other resident fungi. In hardwood trial, the effects of nursery inoculation of different poplar clones, aspen and balsam poplar were very limited. Growth and survival data were combined into seedling volume and plot volume index (PVI) for measurement of total growth response of seedlings. Our results demonstrated that certain inoculated plant-fungus combinations have played a positive role during the initial establishment of these seedlings in the field, which was reflected on significantly greater stem volume and PVI compared to non-inoculated control seedlings. The results from this study provided useful information on field evaluation for potential benefits of mycorrhizal inoculation in nursery.     

Individual-based analysis of tree establishment and forest stand development within 25?years after wind throw

Wind throw is a common disturbance in forest ecosystems. Because many forests are intensively used our knowledge on forest dynamics after such disturbances is limited. In the Bavarian Forest National Park/Germany after the wind throw event in summer 1983, we started our long-term observation in nearly natural Norway spruce forests within 5-year intervals up to 2010. A part of the affected stands was cleared, while another part was left untouched for natural development. Here, we focused on the tree species regeneration, using an individual-based approach. We expected that tree species regeneration in both management types would follow different succession pathways. Indeed, we found different regeneration characteristics, depending on whether the area had been cleared or left unmanaged. For example, for the target species Norway spruce, a chronic regeneration during the first two decades with low numbers, but a high survival rate of individuals, and for the pioneer species birch, pulse regeneration with high numbers of individuals only at the beginning and high individual loss during the following years occurred. Unmanaged and cleared wind throw areas, respectively, offer different quantities of micro-sites: the pit and mound structure as mineral soil disturbance was limited to less than 1/4 in the untouched area, whereas there was mineral soil disturbance more or less everywhere on the cleared parts. Type and intensity of disturbance allow a wide range of succession pathways after wind throw, based on the fundamental processes of germination and competition. Therefore, for protection area management as well as for forest management, the human activity immediately after the event is crucial. Because each management impact will change the succession pathway fundamentally any impact has to be omitted in protection areas with the main goal of natural vegetation succession. Also in managed forests abdication of any impact on small areas may improve the natural structures and biodiversity of forests.     

Effects of variable retention logging in the boreal forest on the bumble bee-influenced pollination community,evaluated 8–9 years post-logging

Boreal forests are currently facing intensified logging pressures, yet we know little about impacts of logging on the pollination community. This study extends research done immediately before and after logging, to consider its longer term effects. We censused bumble bee and flower communities 8–9 years after experimental variable retention logging. Harvest treatments left 0%, 10–20%, 50–75%, or 100% of the original trees after logging. Total bumble bee and floral abundances were increased by all forms of logging; however the floral community in retention cuts (i.e., 10–20% and 50–75% of trees remaining) was more similar to undisturbed controls than was the community in clearcuts. Bumble bees in low-retention treatments (i.e. 10–20%) were in an ideal free distribution (IFD) with their floral resources, which allows for equal per-flower rate of visitation, regardless of local flower density. In clearcuts (i.e. 0%) and high-retention areas (i.e. 50–75%) bees were at an IFD with respect to the density of their floral resources, but undermatched (in 50–75% treatments) or were resource-independent (in 0% treatments) with respect to the energetic value of their floral resources. Bees in unlogged forest controls (i.e., 100%) deviated from an IFD by undermatching. Overall, low-retention logging (10–20%) was an improvement over clearcutting, because there was less change to the floral community, while still allowing for the achievement of an ideal free distribution. However, unlogged forest appeared to be negatively affected (in the lack of an IFD) by the presence of adjacent logged forests: numerical responses of bees to flowers were altered, with implications for bee foraging success and plant pollination service. Forest reserves should therefore incorporate buffer zones when adjacent to logged forest, to preserve the inter-relationships in their bee-influenced pollination community.     

Deforestation and fragmentation of Chaco dry forest in NW Argentina (1972–2007)

The sustained increase in the global food demand has favoured the recent expansion of industrial agriculture into neotropical dry forest ecosystems, with resulting changes in their extent and spatial configuration. Based on Landsat satellite images, we analyzed changes in forest cover and landscape configuration over an area of 600 by 100 km located in NW Argentina (Tucumán and Salta provinces) in four periods between 1972 and 2007. The study area, one of the most active deforestation frontiers of South American dry forest, was divided into six relatively homogeneous sectors in terms of land property structure and biophysical characteristics. During the study period 1.4 millions hectares of dry forest were cleared. Deforestation started in the 1970s as a result of technological changes and increasing rainfall; continued (with spatial and temporal fluctuations) during the 1980s and 1990s in association to the sustained global demand of soybean, and was accelerated (to ca. 100,000 ha year⁻¹) between 2001 and 2007 following the global increase in commodity prices, and the national peso devaluation. We described the landscape structure using eight landscape indices, summarized as one synthesis value: the Euclidian distance across the seven dimensions from a theoretical non-fragmented situation. In areas with soil limitations deforestation resulted in relatively stable, highly fragmented landscapes. In contrast, the sites with regional coarser-scale limitations (rainfall), deforestation produced a less fragmented landscape where agriculture concentrates in sites with high rainfall. Sites with no limitations for agriculture tend to a largely deforested landscape with few small and poorly connected forest patches. The land properties size seems to influence some indices of fragmentation, but the synthetic index of fragmentation suggests an overall convergence of fragmentation patterns towards a similar configuration across different biophysical and land tenure conditions.     

Does inorganic nitrogen limit plant growth 3–5 years after fire in a Wyoming,USA, lodgepole pine forest?

Nitrogen (N) is the major nutrient limiting plant growth and production in terrestrial ecosystems around the world. However, nutrient limitation is spatially variable, and different species within the same ecosystem may be limited by different nutrients. N constraints on plant growth have been investigated via fertilization experiments in a variety of ecosystems; however, recently burned coniferous forests are notably under-studied. Given the recent increase in fire activity across western North America, it is important to understand what limits plant growth and carbon sequestration in coniferous forests recovering from wildfire. We evaluated potential inorganic N limitation in four common native plant species, 3–5 years after stand-replacing wildfire in a lodgepole pine forest (Pinus contorta var. latifolia) in Wyoming, USA. Granular reagent grade ammonium nitrate was added around individual plants at a rate equal to the natural background rate of net N mineralization and at 10× this rate. The grass Calamagrostis rubescens exhibited clear evidence of inorganic N limitation: above-ground biomass and shoot:root ratio increased with the high-fertilizer treatment. Nitrogen:phosphorus (N:P) ratio in un-fertilized C. rubescens plants was <14, also consistent with N limitation, but N:P ratio shifted to >16 in the high-fertilizer treatment, suggesting the onset of P limitation. The upland sedge Carex rossii and seedlings of lodgepole pine were not limited by inorganic N: neither species showed any growth response to N fertilization; N:P ratios were only slightly <14; and foliar N concentrations were greater than critical values reported for mature lodgepole pine. The N-fixing forb Lupinus argenteus was not limited by N, for it showed no growth response to fertilization; rather its N:P ratio of 21 indicated P limitation. In this study, to our knowledge the first experimental evaluation of N limitation in subalpine coniferous forests following wildfire, N limitation was seen in only one of four species tested.     

Studies on the egg parasitism inThaumetopoea pityocampa over a period of four years (1991–1994) at marikostino/bulgaria

In Bulgaria near Marikostino, in a forest ofPinus nigra Arn. 239 egg batches were sampled over four generations ofThaumetopoea pityocampa (Den. &; Schiff.) (Lep., Thaumetopoeidae) in various seasons. Directly after collection the batches were singled in test tubes, closed with cotton stoppers and stored under laboratory conditions at 20–22°C. Oviposition always started from the base towards the tip of the needles. The emergence of egg parasitoids was observed daily, and the parasitoids were counted and identified. The eggs from which parasitoids emerged were marked for further studies. After removing the adults and opening the eggs, the impact of the species of parasitoids was evaluated by identifying the meconia and other rests (left overs). Ooencyrtus pityocampae (Mercet) was the most abundant egg parasitoid, followed byAnastatus bifasciatus (Fonsc.). Only few individuals ofBaryscapus servadeii (Dom.) were collected. The hyperparasitoidBaryscapus servadeii (Dom.) were collected. The hyperparasitoidBaryscapus transversalis Graham, was found at low densities. Only a few eggs were parasitised byTrichogramma embryophagum Htg. Total mortality of the host eggs varied from 34.7 to 79.7% depending on the period of parasitism and on the numbers of sterile eggs. The impact of the parasitoids was calculated to be 9.3–38.9%, depending on the period when parasitism had taken place. The mean number of eggs per batch varied from 203 to 253. The rate of parasitism was reduced by early sampling of the egg batches. In some cases, a very high percentage (up to 29.2%) of undeveloped eggs was found. In all samples a small percentage of empty eggs was always observed.     

Are small-scale overstory gaps effective in promoting the development of regenerating oaks (Quercus ithaburensis) in the forest understory?

We investigated the effect of small-scale overstory gaps on the ecophysiology and growth of Quercus ithaburensis saplings. The study aim was to characterize how changes in daily exposure to direct beam radiation affect photosynthetic performance in the short term and growth and biomass partitioning in the long term. Using individual net-houses, the following treatments were applied: (a) Unshaded (daily irradiance = 100 %), (b) shading net with no gap (Shade-daily irradiance = 6 %), (c) shading net with 1 h gap allowing direct beam radiation (11:00 am–12:00 pm, Shade+1-irradiance = 20 %), (d) shading net with 3 h gap (11:00 am–2:00 pm, Shade+3-irradiance = 44 %). The experiment was performed in an irrigated field. We measured growth, biomass allocation, leaf traits, daily courses of leaf gas exchange and water potential. Oak dry-weight increased while height to dry-weight ratio and specific leaf area decreased with increasing daily exposure to direct beam radiation. Leaf chlorophyll content was less affected. Higher net carbon assimilation rates (A), stomatal conductance (gs) and A/gs were associated with higher instantaneous photosynthetic photon flux density (PPFD) throughout the entire experimental PPFD range. However, during gap-hours, while exposed to saturating radiation levels of similar level (ca. 1,800 µmol photon m^?2 s^?1), A in the Shade+1 oaks was about half that of the Shade+3 oaks and nearly one-third that of the Unshaded oaks. Patterns of gs, intercellular CO₂ (Ci) and quantum efficiency of photosystem II pointed towards the possibility of a metabolic limitation. In conclusion, oaks benefited significantly from small scale overstory gaps though their capacity to utilize transient saturating radiation levels decreased with decreasing gap duration.     

Spatial variability of nutrient stocks in the humus and soils of a forest massif (Fougères, France)

In this study, the spatial distribution of nutrient stocks (K, Ca, Mg and P) was examined in humus and soils at the forest massif scale (Fougères forest, France). A random stratified sampling plan including 100 sampling points was used and three potential variation factors of nutrient stocks were tested: age of stand, type of stand (broad-leaved or coniferous trees) and type of soil. Sampling classes were then compared and the variation factors were examined. Results demonstrated that nutrient stocks in the humus were not influenced by the cited factors and only the type of soil influenced nutrient stocks in soils. In fact, stocks of exchangeable elements in soils were much higher in Colluviosols-Fluviosols which show redoximorphic characteristics, and available phosphorus stocks were lower than in Alocrisols-Neoluvisols. Moreover, a low variability of nutrient stocks was observed in Alocrisols-Neoluvisols as opposed to Colluviosols-Fluviosols, which may suggest the existence of other variation factors not taken into account in this study (hydromorphic gradient, type and age of stand in hydromorphic zones).     

Analysis of land-cover/use change dynamics in Manica Province in Mozambique in a period of transition (1990–2004)

The land-cover/use change dynamics in Manica Province in Mozambique are analysed, based upon interpretation of LANDSAT images, to assess trends and highlight management suggestions considering current policies in place that include the ownership and participation of local communities in natural resources management and the recognition of traditional ownership systems. Applying an object-oriented approach to compare the year 2004 with 1990, one observes that land-cover/use changes are not distributed evenly in the province. A substantial decrease in areas with trees belonging to the ‘miombo ecosystem’ occurred and an increase of cultivated areas. The nature of agriculture is changing from shifting cultivation to more permanent types. These changes are found in prevalence on gentle slopes and close to the road network.     

Disentangling the effect of topography and microtopography on near-ground growing-season frosts at the boreal-temperate forest ecotone (Québec,Canada)

New Forests - Permanent landscape attributes such as topography (elevation [m]) and microtopography (local variation in elevation [cm]) can increase the risk of cold air drainage down-slopes and in...     

Evapotranspiration of a Populus euphratica forest during the growing season in an extremely arid region of northwest China using the Shuttleworth–Wallace model

Thus far, measurements and estimations of actual evapotranspiration(ET) in extremely arid areas are still insufficient. Based on successive observations from June–September 2014, we simulated ET of a Populus euphratica Oliv. forest during the growing season in an extremely arid region of northwest China using the Shuttleworth–Wallace(S–W) model. Simulated ET values were compared to those of the eddy-covariance(EC) method on a 1 h interval. With a root mean square error(RMSE),relative error(RE) and mean absolute error(MAE) of0.192, 3.100 and 0.165 mm h-1, respectively, model performance was not satisfactory. In particular, on days with strong winds(Sep. 11–13), deviations between simulated and observed ET values increased to 0.275, 0.878 and0.251 mm h-1, RMSE, RE and MAE respectively. These values were significantly greater than those in other study periods and were most likely owing to sharp increases in wind speed. As a result, there were substantial advective effects, which is not consistent with the assumption of the S–W model that there are no advective effects or mesoscale circulation patterns induced by surface discontinuities.