Mixed Pine Research Articles

Verification of a One-Dimensional Model of $$\hbox {CO}_{2}$$ CO 2 Atmospheric Transport Inside and Above a Forest Canopy Using Observations at the Norunda Research Station

A model of (Formula presented.) atmospheric transport in vegetated canopies is tested against measurements of the flow, as well as (Formula presented.) concentrations at the Norunda research station located inside a mixed pine–spruce forest. We present the results of simulations of wind-speed profiles and (Formula presented.) concentrations inside and above the forest canopy with a one-dimensional model of profiles of the turbulent diffusion coefficient above the canopy accounting for the influence of the roughness sub-layer on turbulent mixing according to Harman and Finnigan (Boundary-Layer Meteorol 129:323–351, 2008; hereafter HF08). Different modelling approaches are used to define the turbulent exchange coefficients for momentum and concentration inside the canopy: (1) the modified HF08 theory—numerical solution of the momentum and concentration equations with a non-constant distribution of leaf area per unit volume; (2) empirical parametrization of the turbulent diffusion coefficient using empirical data concerning the vertical profiles of the Lagrangian time scale and root-mean-square deviation of the vertical velocity component. For neutral, daytime conditions, the second-order turbulence model is also used. The flexibility of the empirical model enables the best fit of the simulated (Formula presented.) concentrations inside the canopy to the observations, with the results of simulations for daytime conditions inside the canopy layer only successful provided the respiration fluxes are properly considered. The application of the developed model for radiocarbon atmospheric transport released in the form of (Formula presented.) is presented and discussed. (Less)

Host preference of ectomycorrhizal fungi in mixed pine–oak woodlands

Many ectomycorrhizal fungi (EMF) are generalists, but most plant genera that form ectomycorrhizas have at least some fungal partners that are specific to that host genus. Because shared mycorrhizal fungi mediate plant community interactions, host preference has implications for plant succession and competition. We studied the EMF of oaks (Quercus spp.) and pines (Pinus spp.) in a forest in northern Florida, USA, focusing on symbionts shared with longleaf pine (Pinus palustris Mill.). Longleaf pine is an important species in the southeastern USA, both for timber plantations and for restoring savanna and woodland habitat. However, we found no research on the composition of naturally occurring EMF on longleaf pine roots. A lower proportion of EMF operational taxonomic units (OTUs) were found colonizing both oaks and pines than expected, providing evidence of host preference within the community. Although most EMF were detected only on either oaks or pines, the OTUs found on both tended to be frequently occurring and abundant. Cenococcum OTUs were found to be significantly associated with oaks, an unexpected finding as this genus is widespread, with a broad host range. These results suggest that host preference of EMF may structure EMF communities and therefore influence ecosystem effects of mycorrhizal networks.

Variability after 15 Years of Vegetation Recovery in Natural Secondary Forest with Timber Harvesting at Different Intensities in Southeastern China: Community Diversity and Stability

The mixed Cunninghamia lanceolata (Lamb.) Hook., Pinus massoniana Lamb., and hardwood forest in southeastern China is a major assemblage in natural secondary forests, and of national and international importance in terms of both timber and ecosystem services. However, over-harvesting has threatened its long-term sustainability, and there is a knowledge gap relating to the effect of harvesting on the ecosystem. After conifer species were selected for harvesting, the mixed Chinese fir, pine, and hardwood forest was changed into mixed evergreen broadleaf forest. In this context, we observed the restoration dynamics of plant communities over a period of 15 years (1996 to 2011) with different levels of harvesting intensity, including selective harvesting at low (13.0% removal of growing stock volume), medium (29.1%), high (45.8%), and extra-high (67.1%) intensities, as well as clear-cut harvesting (100.0%), with non-harvesting as the control, based on permanent sample plots established in a randomized block design in these forests in southeastern China. The impact on the richness, diversity, and evenness of plant species derived from descriptive statistical analyses was shown to initially increase, and then decrease, with an increase in harvesting intensity. The most critical impacts were on the richness, diversity, and evenness of shrub and herb species. Richness, diversity, and evenness of plant species recovered and increased under selective harvesting at low and medium intensities, while these parameters had not recovered and significantly decreased under selective harvesting at high and extra-high intensities, as well as with clear-cut harvesting. The impact on the plant community stability was derived from the stability test method of the improved Godron M. The plant community stability was closest to the point of stability (20/80) under selective harvesting at medium intensity, followed by selective harvesting at low intensity. The plant community stability was far from the point of stability (20/80) under selective harvesting at high and extra-high intensities, as well as with clear-cut harvesting. Of these treatments, clear-cut harvesting had the greatest effect with regard to reducing stability. Therefore, these results indicate that the selective harvesting at low and medium intensities is conducive to preserve or increase the species diversity and community stability. In order to prioritize promoting plant species diversity, clear-cut harvesting and selective harvesting at high and extra-high intensities should be avoided with regard to this type of forest in this region. This study sheds light on the practice of forest operation in the study region and subtropical forests with the same environment.

小兴安岭阔叶红松林地表甲虫Metacommunity格局

小兴安岭阔叶红松林地表甲虫Metacommunity格局

Growth dynamics, climate sensitivity and water use efficiency in pure vs. mixed pine and beech stands in Trentino (Italy)

Abstract Understanding to what extent species mixtures modify the growth of trees and their responses to climate, in comparison with pure stands, is important to support forest adaptation and mitigation strategies. In this sense, information stored in tree rings can be useful to evaluate whether the positive relationship between species diversity and tree productivity holds true under disturbance (e.g., drought). This paper aimed at assessing (i) how radial growth of trees responded to local variation in climate patterns (Standardised Precipitation-Evapotranspiration Index; SPEI), and (ii) whether there was a relationship with intrinsic water use efficiency (WUEi) and tree-ring δ18O in two important tree species, occurring in pure and mixed forest stands. Three sites with similar topographic and pedo-climatic conditions were identified in a single location in the Italian Alps. The first two are characterized by pure stands, respectively dominated by European beech (Fagus sylvatica L.) and Scots pine (Pinus sylvestris L.). The third site refers to a mixed stand of both previous species. In particular, in order to assess the annual changes in WUEi, we analysed δ13C in tree rings. The influence of the stomatal conductance was also investigated through δ18O. Our results indicated that: (i) Basal Area Increments (BAI) consistently increased in all stands except for the pure Scots pine stand, in the 1994–2003 period; (ii) SPEI highlighted a drought period between 1991 and 2007 (62.2% of the average precipitation); and (iii) the WUEi values were generally higher in pure than in mixed stands, especially for European beech. The divergence between BAI and SPEI values in the 1990s and early 2000s could be a consequence of moderate thinning. We conclude that past forest management (namely thinning) can be more influential on tree growth than current climatic oscillations.

Accumulation of soil organic C and N in planted forests fostered by tree species mixture

Abstract. With the increasing trend of converting monocultures into mixed forests, more and more studies have been carried out to investigate the admixing effects on tree growth and aboveground carbon storage. However, few studies have considered the impact of mixed forests on belowground carbon sequestration, particularly changes in soil carbon and nitrogen stocks as a forest grows. In this study, paired pure Pinus massoniana plantations, Cinnamomum camphora plantations and mixed Pinus massoniana–Cinnamomum camphora plantations at ages of 10, 24 and 45 years were selected to test whether the mixed plantations sequestrate more organic carbon (OC) and nitrogen (N) in soils and whether this admixing effect becomes more pronounced with stand ages. The results showed that tree species identification, composition and stand age significantly affected soil OC and N stocks. The soil OC and N stocks were the highest in mixed Pinus–Cinnamomum stands compared to those in counterpart monocultures with the same age in the whole soil profile or specific soil depth layers (0–10, 10–20 and 20–30 cm) for most cases, followed by Cinnamomum stands and Pinus stands with the lowest. These positive admixing effects were mostly nonadditive. Along the chronosequence, the soil OC stock peaked in the 24-year-old stand and was maintained as relatively stable thereafter. The admixing effects were also the highest at this stage. However, in the topsoil layer, the admixing effects increased with stand ages in terms of soil OC stocks. When comparing mixed Pinus–Cinnamomum plantations with corresponding monocultures within the same age, the soil N stock in mixed stands was 8.30, 11.17 and 31.45 % higher than the predicted mean value estimated from counterpart pure species plantations in 10-, 24- and 45-year-old stands, respectively. This suggests that these admixing effects were more pronounced along the chronosequence.

Effects of intermediate-severity disturbance on composition and structure in mixed Pinus-hardwood stands

Increasingly, forest managers intend to create or maintain mixed Pinus-hardwood stands. This stand assemblage may be driven by a variety of objectives but is often motivated by the desire to enhance native forest diversity and promote resilience to perturbations. Documenting the effects of natural disturbances on species composition and stand structure, and thus successional and developmental pathways, in stands with these mixtures is essential to achieve these goals. The specific objectives of this study were to quantify and compare the impacts of an intermediate-severity canopy disturbance on woody species composition, canopy structure, understory light regimes, and species diversity in mixed Pinus (Pinus taeda and Pinus virginiana)-hardwood stands on the Cumberland Plateau in Alabama. The natural intermediate-severity disturbance disproportionately removed large Pinus stems, promoted hardwood dominance, and effectively accelerated succession. The resultant stand structure did not resemble one of the widely recognized stages of stand development and was best characterized by the mixed-stage of development. The canopy disturbance did not significantly alter canopy-layer species diversity, but seedling- and sapling-layer diversity was significantly greater in disturbed neighborhoods. Results from this study may be used as guidelines by managers of mixed Pinus-hardwood systems. To maintain a Pinus component in stands that are succeeding to hardwood dominance, canopy disturbance alone is insufficient and must be planned in conjunction with competition reduction measures in the regeneration layer, such as fire or herbicide application. Conversely, if managers wish to promote a hardwood component in pure or near pure Pinus stands, creation of variably sized canopy openings throughout the stand may recruit hardwood reproduction to larger size classes, as the intermediate-severity disturbance documented here accelerated succession toward hardwood dominance.

Pengaruh Jenis Kayu dan Jumlah Lapisan Terhadap Sifat Venir Lamina

This study aims to determine the effect of wood species and the number of layers of veneer against laminated veneer properties. Wood species consist of sengon, pine, and mixed pine sengon. Laminated veener made by a number of layers consist of 4, 6, and 8 layers. The difference of a number of layers was to identify quality of laminated veneer. The adhesive used is urea formaldehyde (UF) liquid. The results showed that the average moisture content of 10.76%, density of 0.54 g/cm3, delamination 5.8%, MOE 124.108 kg/cm2, and MOR 450.74 kg/cm2. The moisture content and delamination made all meet the Indonesian National Standard. Statistically, wood species were a significant effect on moisture content, density, MOE, and MOR, while various of layers were a significant effect on moisture content, density, delamination, MOE, and MOR. The number of layer’s laminated veneer made higher of water content, density, delamination, and MOR.

A TSVD-Based Method for Forest Height Inversion from Single-Baseline PolInSAR Data

The random volume over ground (RVoG) model associates vegetation vertical structure parameters with multiple complex interferometric coherence observables. In this paper, on the basis of the RVoG model, a truncated singular value decomposition (TSVD)-based method is proposed for forest height inversion from single-baseline polarimetric interferometric synthetic aperture radar (PolInSAR) data. In addition, in order to improve the applicability of TSVD for this issue, a new truncation method is proposed for TSVD. Differing from the traditional three-stage method, the TSVD-based inversion method estimates the pure volume coherence directly from the complex interferometric coherence, and estimates the forest height from the estimated pure volume coherence with a least-squares method. As a result, the TSVD-based method can adjust the contributions of the polarizations in the estimation of the model parameters and avoid the null ground-to-volume ratio assumption. The simulated experiments undertaken in this study confirmed that the TSVD-based method performs better than the three-stage method in forest height inversion. The TSVD-based method was also applied to E-SAR P-band data acquired over the Krycklan Catchment, Sweden, which is covered with mixed pine forest. The results showed that the TSVD-based method improves the root-mean-square error by 48.6% when compared to the three-stage method, which further validates the performance of the TSVD-based method.

Suitability of eastern pines for oviposition and survival of Sirex noctilio F.

The European woodwasp, Sirex noctilio F., is a pest of pines in many areas around the world. Since its introduction to North America, the distribution of S. noctilio overlaps with a known host (Pinus sylvestris) and hosts native to North America. Direct comparisons of suitability for oviposition and larval survival among these pines have not been made. We tested the relative suitability of four common pine species in northeastern North America (P. sylvestris, P. resinosa, P. banksiana, and P. strobus) as hosts for S. noctilio in a controlled, but in situ experiment. In a mixed pine forest in northern Ontario, we caged S. noctilio mating pairs on 10 freshly cut pine logs of each species, and estimated oviposition, counted adult S. noctilio (F1 generation) that emerged from logs, and calculated survivorship from egg to adult. Pinus sylvestris and P. resinosa were optimal hosts according to all three metrics of S. noctilio performance. Pinus strobus was a suitable larval host, but was not perceived as such by females, as evidenced by lower oviposition. Pinus banksiana was perceived as a suitable host by females, but was the least suitable larval host. Our results suggest that P. sylvestris and P. resinosa are more suitable hosts, at least in cut logs, than P. strobus and P. banksiana for S. noctilio in eastern North America.

Is cut-stump and girdling an efficient method of black cherry Prunus serotina Ehrh. eradication?

Abstract Efforts to prevent the invasion of black cherry Prunus serotina Ehrh. have a long history in Western Europe. However, effective methods of eliminating it that do not bear negative side effects for ecosystems have not yet been developed. Mechanical methods are the first choice in environmentally sensitive areas. In this study, we aimed to find answers to the questions: does the application of cutting at a height of 1 m from the ground limit the sprouting capacities of black cherry? And, is stem girdling an effective method of eliminating black cherry? The study was carried out in the Kampinos National Park, on two mixed pine forest plots with undergrowth of black cherry. Three mechanical methods of elimination were applied: cut-stump at the base, cutting at a height of 1 m above the ground and girdling of the stem at a height of ca 1 m above the ground. In both locations, 225 trees were treated, at three different dates corresponding with three different phenological phases of black cherry development. The evaluation of effectiveness of treatments was based on the sprouting capacity of the tree afterwards, which included: the number of generated sprouts, the length of three longest sprouts, dry mass of sprouts, and the assessment of tree survival rate. It was discovered that girdling is a significantly more effective method of control than ground-level cut-stump or cutting at a height of 1 m above the ground in the conditions of central Poland. However, in the season of treatment, even though recurring sprouts were removed, only a part of the girdled trees died (24% to 54%). There is a slight difference between the sprouting response of cutting at a height of 1 m above the ground (4% to 24% of dead trees) and the basal cut-stump method (0% of dead trees).

Habitat Selection of Northern Bobwhite Coveys on Two Intensive Agriculture Landscapes in Eastern North Carolina (Poster Abstract)

Little information is available for home range size and habitat use of northern bobwhites (Colinus virginianus) on modern agricultural landscapes in autumn. Therefore, we monitored radiomarked bobwhite coveys from September–December 1998 on farms in Wilson and Tyrrell counties, North Carolina. The Tyrrell County farm was a 6084-ha area recently developed for commercial production of corn and soybeans. Dispersed throughout crop areas were forested and fallow blocks at differing stages of succession. The Wilson County farms had small fields (x̄ = 1.8 ha, SE = 0.12) planted in cotton, soybeans, corn, and tobacco and were surrounded by mixed pine and hardwood blocks of differing ages. Mean home range size at the Tyrrell County farm was 33.2 ha (range 4.5–128.5 ha) (n = 10). The two largest home ranges, 70.7 and 128.6 ha, were disproportionately large due to large movements from harvested crop fields to permanent forested cover. Covey home ranges were not established at random (l = 0.124; x2 4= 20.18; P < 0.001). Road and canal edges were selected significantly more than any other habitat followed in rank by soybean fields, corn fields, forested, and fallow blocks. Road and canal edges provided necessary cover for moving between habitat types, especially from forested and fallow blocks to crop fields. Within home ranges, coveys did not allocate their time at random (l = 0.336; x2 4 = 10.89; P < 0.05). Habitats were ranked in the order of forested blocks, fallow areas, soybean fields, road and canal edges, and corn fields, but no significant differences were found between habitats. In Wilson County, average covey home range was 17.4 ha (Range: 4.9–37.6 ha)(n = 11). Coveys did not establish their home range at random (l = 0.407; x22 = 9.87; P < 0.05), selecting forested blocks over crop fields (T9 = 3.02, P < 0.012). Within home ranges coveys did not allocate their time at random (l = 0.1319; x25 = 22.28; P < 0.001), utilizing primarily forested blocks followed by cotton fields, soybean fields, corn fields, and other areas. On both study areas, forested and fallow blocks were the only source of cover to spend time in after crop harvest. Covey use within forested and fallow blocks was concentrated along edges of crop fields, leaving large portions of this habitat type unused. Forested and fallow blocks were primarily used as loafing cover in between feeding periods in adjacent crop fields.

择伐对吉林蛟河阔叶红松林群落结构及动态的影响

择伐对吉林蛟河阔叶红松林群落结构及动态的影响

Effects of selective thinning and residue removal on ground layer structure and diversity in a mixed pine–oak stand of the Qinling Mountains, China

Plant species in the forest ground layer are the main food resources for animals and other organisms in the Qinling Mountains, China. To optimise forest thinning programs, we examined how different selective thinning and thinning residue removal regimes influence ground layer diversity and cover. We explored these factors for 2 years in a mixed pine–oak stand. Results indicate the treatments resulted in an increase in the numbers of species, genus and family by 10, 10 and six, respectively, after 1 year thinning and by 14, 10 and four, respectively, after 2 years thinning, compared with the starting point. The highest richness index was achieved at a selective thinning intensity of 17% and a residue removal rate of 57% concurrently. The highest evenness index was achieved at a selective thinning intensity and residue removal rate of 25 and 43% concurrently. The highest ground cover layer was achieved at a selective thinning intensity and residue removal rate of 25 and 69% concurrently. Our results suggest medium thinning intensity and thinning residual removal rate may benefit ground layer richness, whereas a high thinning intensity and medium thinning residual removal rate may maximise evenness and ground layer cover in current forest.

Effects of Repeated Growing Season Prescribed Fire on the Structure and Composition of Pine–Hardwood Forests in the Southeastern Piedmont, USA

We examined the effects of repeated growing season prescribed fire on the structure and composition of mixed pine–hardwood forests in the southeastern Piedmont region, Georgia, USA. Plots were burned two to four times over an eight-year period with low intensity surface fires during one of four six-week long periods from early April to mid-September. Density of saplings (0.25–11.6 cm diameter at breast height) was significantly reduced after one or two fires during the first four-year period. Sapling density declined with additional burning over the next four years, but density of mesic hardwoods including sweetgum (Liquidambar styraciflua) and red maple (Acer rubrum) remained relatively high (~865 stems ha−1). Repeated burning had little effect on density or basal area of trees (≥11.7 cm dbh) and changes in overstory structure were limited to small increases in the quadratic mean diameter of all trees and pines. We found little evidence to suggest differential effects on structure or composition due to timing of burn within the growing season. Although repeated growing season burning alters midstory structure and composition, burning alone is unlikely to result in immediate shifts in overstory composition or structure in mixed pine–hardwood forests of the southeastern Piedmont region.

Abiotic disturbances in Bulgarian mountain coniferous forests – An overview

Disturbances are among the most important processes that shape forest dynamics and landscapes. However the historic ranges of variability (HRV) of many coniferous forests in Europe and specifically in the mountains on the Balkan Peninsula are not well understood. We present the first overview of available data on disturbance events in coniferous forests in the high mountains in southwestern Bulgaria. Our study included data from historical publications, documents and archives, newer documentary data obtained through interviews with foresters and verified using satellite images, published studies and new tree-ring data. We documented at least 188 abiotic disturbance events in the Bulgarian mountains including fires (39%), windthrows (31%) and avalanches (20%) and fewer disturbances caused by snow and ice.Fires primarily affected Pine-dominated ecosystems, especially pure Pinus sylvestris and mixed Pinus sylvestris-Pinus nigra forests. Our tree-ring analysis also provided evidence for repeated fires in subalpine Pinus heldreichii and Pinus peuce forests during the last 500 years. Some of these fires affected different valleys within the same year, suggesting either large-scale events or the simultaneous occurrence of fires related to appropriate fuel and climate conditions. We also found data on several large fires in Picea abies-dominated ecosystems. Most of the fires were less than 100 ha, but some were larger, the most extensive of which was the Batalach fire (year 1890, approximately 9000 ha) in the Western Rhodopes. The highest frequency of fires was in 1880–1910, 1940–1950 and 2000–2010. We found evidence for at least 59 windthrows greater than 1ha, mainly in pure Picea abies and mixed Picea abies-Pinus sylvestris forests. There was high variability in the size of windthrows, ranging from small-scale, gap-sized blowdowns to large and infrequent disturbances affecting more than 300ha, the largest of which was the Beglika windthrow (1961, 3000ha). Although avalanches are considered important for subalpine forests on steep slopes they were generally poorly documented and data were limited to several avalanche cycles in 1955, 1963–1974 and in the last two decades. Snow-related damage was important mostly for young pine forests in which several events affected a high stock of wood in the 1930s, 1987, 1988 and 2015.Our data show that natural disturbances of various types and of a range of sizes are part of the natural dynamics of coniferous forests in Bulgaria. Further, our study contributes to the understanding of the historic range of variability of mountain forests in Europe.

Habitat requirements and conservation needs of peripheral populations: the case of the great crested newt (Triturus cristatus) in the Scottish Highlands

Edge populations are of conservation importance because of their roles as reservoirs of evolutionary potential and in understanding a given species’ ecological needs. Mainly due to loss of aquatic breeding sites, the great crested newt Triturus cristatus is amongst the fastest declining amphibian species in Europe. Focusing on the north-westerly limit of the T. cristatus range, in the Scottish Highlands, we aimed to characterise habitat requirements and conservation needs of an isolated set of edge populations. We recorded 129 breeding pond-related environmental parameters, and used a variable selection procedure followed by random forest analysis to build a predictive model for the species’ present occurrence, as well as for population persistence incorporating data on population losses. The most important variables predicting T. cristatus occurrence and persistence were associated with pond quality, pond shore and surrounding terrestrial habitat (especially mixed Pinus sylvestris–Betula woodland), and differed from those identified in the species’ core range. We propose that habitat management and pond creation should focus on the locally most favourable habitat characteristics to improve the conservation status and resilience of populations. This collaborative work, between conservation agencies and scientific researchers, is presented as an illustrative example of linking research, management and conservation.

Mixing effects on growth efficiency in mixed pine forests

Mixing effects on growth efficiency in mixed pine forests

Estimation of Pine Forest Height and Underlying DEM Using Multi-Baseline P-Band PolInSAR Data

On the basis of the Gaussian vertical backscatter (GVB) model, this paper proposes a new method for extracting pine forest height and forest underlying digital elevation model (FUDEM) from multi-baseline (MB) P-band polarimetric-interferometric radar (PolInSAR) data. Considering the linear ground-to-volume relationship, the GVB is linked to the interferometric coherences of different polarizations. Subsequently, an inversion algorithm, weighted complex least squares adjustment (WCLSA), is formulated, including the mathematical model, the stochastic model and the parameter estimation method. The WCLSA method can take full advantage of the redundant observations, adjust the contributions of different observations and avoid null ground-to-volume ratio (GVR) assumption. The simulated experiment demonstrates that the WCLSA method is feasible to estimate the pure ground and volume scattering contributions. Finally, the WCLSA method is applied to E-SAR P-band data acquired over Krycklan Catchment covered with mixed pine forest. It is shown that the FUDEM highly agrees with those derived by LiDAR, with a root mean square error (RMSE) of 3.45 m, improved by 23.0% in comparison to the three-stage method. The difference between the extracted forest height and LiDAR forest height is assessed with a RMSE of 1.45 m, improved by 37.5% and 26.0%, respectively, for model and inversion aspects in comparison to three-stage inversion based on random volume over ground (RVoG) model.

Do shrubs facilitate oak seedling establishment in Mediterranean pine forest understory?

Shrubs have been shown to facilitate tree seedling establishment in open Mediterranean ecosystem habitats, but their effects in forests have been much less explored. We investigated the role played by shrubs in seedling emergence, survival and growth for two co-occurring oak species – Quercusilex and Quercuspubescens – in the understory of clear Aleppo pine stands (10m2/ha). Acorns of both species were sown in two sites in South-East France that contrasted in terms of former land-use (pastoral vs agricultural), soil thickness (shallow vs deep) and type of understory (shrubs+grass vs only shrubs). Oak seedlings had a higher survival and growth on the former agricultural site with deeper soil. In general, the more stress-tolerant Q. ilex performed better than Q. pubescens. In the harsher site, seedling survival decreased with grass cover but increased with shrub cover. Shrub and grass cover decreased seedling diameter and had no effect on seedling height. In the more fertile site, shrub cover had no influence on seedling survival but had a species-specific effect on seedling growth: shrubs mostly competed with Q. ilex but ameliorated Q. pubescens growth, leading to changes in the two species performance ranking at high shrub cover. We conclude that shrubs can act as nurses for oak seedling establishment in pine forest understory, particularly in harsh conditions and for stress-intolerant species. In harsh conditions, shrub cover should be factored in as a way to promote pine forest diversification toward mixed pine–oak stands.