Medium-density Stands Research Articles

Does stand density affect understory vegetation and soil properties of differently aged Robinia pseudoacacia plantations?

Robinia pseudoacacia is the most important tree species used for afforestation on the Chinese Loess Plateau. However, most R. pseudoacacia plantations face environmental problems due to inappropriate initial densities. The sustainable development of R. pseudoacacia plantations is challenging due to significant knowledge gaps regarding the appropriate stand densities for maximizing ecological benefits. Herein, R. pseudoacacia plantations of three age classes—young, middle-aged, and mature—were sampled in the loess hilly-gully region of northern Shaanxi Province, China. Based on stand density, R. pseudoacacia plantations in each age class were categorized as low (<1000 trees ha−1), medium (1000–1500 trees ha−1), and high (>1500 trees ha−1) density. We analyzed the effects of stand density on soil physicochemical properties, understory vegetation community structure, and ecosystem multifunctionality. In young stands, a medium stand density significantly increased the Shannon-Wiener index, species richness, and above-ground biomass of herbaceous communities. In middle-aged stands, stand density had no significant effects on understory diversity, whereas medium-density stands showed increased understory above-ground biomass. In mature stands, low-density stands significantly increased understory above-ground biomass and species richness of herbaceous communities. In all age classes, stand density did not significantly affect shrubby community composition, but herbaceous communities shifted compositionally towards shade-tolerant and drought-tolerant species as stand density increased. In the soils of young and middle-aged stands, organic carbon, ammonium nitrogen, nitrate nitrogen, available phosphorus, and water content were highest in medium-density stands, whereas in mature stands, these variables were highest in low-density plantations. In young, middle-aged, and mature stands, the ecosystem multifunctionality indices were highest at densities of 1000–1500, 1000–1500, and < 1000 trees ha−1, respectively. We concluded that the effects of stand density on ecosystem functions in R. pseudoacacia plantations varied with stand age. Our findings highlight a need to implement age-based stand density management strategies for R. pseudoacacia plantations to improve their ecological benefits.

Детрит в высокополнотных сосновых насаждениях подтаежно-лесостепного района Средней Сибири

At the present time, certain harmful effects are observed that affect forest ecosystems. They are forest fires, phytopathogenic activities, and invasive influence, in addition to changes in climatic conditions, in particular an increase in temperature. The study is intended to determine the potential stock of wood and carbon compounds in detritus. The principal categories for it are snags, downed dead wood, and stumps. Additionally, it predicts the amount of wood residues in the conditions of the taiga forest-steppe subzone of Central Siberia. A coarse woody detritus was examined in the structurally pure forests of Scots pine (Pinus sylvestris L.). A circular area of constant radius was used as an accounting unit. The cause woody detritus in snag was 82 %, in downed dead wood was 16 % (1.5–18.3 m3‧ha–1), in stumps was 2 % (0–2.6 m3‧ha–1). The content of detritus was found in only 11 % of the total stock of the stand. The environmental quality at the location of growth had a strong effect on the amount of detritus because of the growth rate of the trees, which is higher in the ideal conditions. Most of the coarse woody detritus (66.4 %) was accumulated in the stands of productivity class I, which was almost double that in the stands of productivity class II (33.6 %). The carbon content in snags, downed dead wood, and stumps was higher in high-density stands (0.81 or more) than in medium-density stands (0.6–0.8). The age and average height of the stand were considerable indicators for predicting stocks of wood and carbon in snags. The amount of wood and carbon in the downed dead wood also depended on the growth density and total stock of wood at the location. The regression equations were generated to predict the volume of the coarse wood detritus. According to the results, it can be concluded that in the investigated stands the destructive processes were identified, which were determined by the concentration of detritus. The production of detritus was activated by both age composition, when a major part of the trees enters the mature or overmature stages, and biogenic factors, which were stimulated by pathogenesis and climatic changes. For citation: Vais A.A., Varaksin G.S., Mamedova S.K., Anuev E.A., Gerasimova O.A. Detritus Inside High Density Pine Stands in the Taiga Forest-Steppe Subzone of Central Siberia. Lesnoy Zhurnal = Russian Forestry Journal, 2023, no. 3, pp. 9–20. (In Russ.). https:// doi.org/10.37482/0536-1036-2023-3-9-20

The More the Merrier or the Fewer the Better Fare? Effects of Stand Density on Tree Growth and Climatic Response in a Scots Pine Plantation

In forests, the growth and productivity of individual trees and stands as a whole are regulated by stand density among other factors, because access to vital resources is limited by competition between trees. On 18 experimental plots of Scots pine (Pinus sylvestris L.) planted with a density of 500–128,000 trees/ha in the south taiga (Middle Siberia), interactions between stand density, tree- and stand-scale productivity, and tree-ring parameters were investigated. Tree-scale productivity variables, tree-ring width, and latewood width had stable negative allometric relationships with stand density (R2 &gt; 0.75), except for tree height (insignificant for inventory surveys at ages of 20 and 25 years; R2 &gt; 0.4 at the age of 35 years), while positive allometry was registered for stand productivity variables (R2 &gt; 0.7) and the all-time average latewood ratio (R2 = 0.5 with planting density). Tree-ring parameters aside from the age trends correlate (p &lt; 0.05) between the plots and demonstrate common responses to moderate moisture deficit. Although, its seasonality apparently depends on the resource base and intensity changes with stand density. February–June precipitation is more important for pine growth in dense stands, July–August conditions affect the latewood ratio stronger in sparse stands, and medium-density stands are more resistant to winter frosts.

Trade-Offs and Synergies between Plant Species Diversity and Water Retention Capacity of Pinus massoniana Plantation Community in Danjiangkou Reservoir Area

In order to quantify the plant species diversity characteristics of Pinus massoniana plantations with different stand densities in the Danjiangkou reservoir area of Hubei Province and the relationship of their trade-offs and synergies with the water retention capacity in the reservoir area to give full play to the forest ecosystem services in the reservoir area and improve the level of sustainable management of plantations, we used the typical plot method, selected 35-year-old Pinus massoniana with low density (925–1000 plants·ha), medium density (1425–1625 plants·ha), and high density (2375–2525 plants·ha), and its community structure, species composition, and understory plant species diversity were studied, respectively, and the relationship of the trade-offs and synergies between the two services of water retention capacity and plant species diversity in Pinus massoniana plantations were calculated. We found that: (1) According to the survey statistics, there were 69 species of plants in the shrub and herb layers under forest including 32 species of shrubs and 37 species of herbs, belonging to 33 families and 62 genera. (2) The species richness of the shrub layer increased with the increase in the stand density, which was opposite in the herb layer. The Shannon–Wiener diversity index and Simpson dominance index of the shrub layer showed the regularity of high density &gt; low density &gt; medium density, while the herb layer decreased gradually with the increase in density. The Pielou evenness index of the shrub layer and herb layer was the highest in the high-density and medium-density stands, respectively. (3) Trunk flow, soil layer water storage and plant species diversity under medium and high density conditions, litter layer water storage and plant species diversity under low-medium density conditions showed synergistic relationships in the shrub layer and herb layer, everything else were trade-off relationships. As far as the Danjiangkou reservoir area is concerned, the low-density Pinus massoniana plantations have higher understory plant species diversity and more stable community structure, and there is a trade-off relationship between the water retention capacity and understory plant species diversity.

Sparse Pinus Tabuliformis Stands Have Higher Canopy Transpiration Than Dense Stands Three Decades After Thinning

Hydrological effects of forest thinning have been studied at small watershed scales using the paired watershed approach since the 1920s. However, how forest transpiration, a critical component of evapotranspiration, changes decades after thinning is not well understood despite its importance for modifying drought resilience of forest ecosystem under climate change. In a semi-arid mountainous area of northern China, we measured growing season sap flow of Pinus tabuliformis, a widely planted afforestation species, in 44-year-old monoculture plantation stands with low (983 stems ha−1), medium (1688 stems ha−1), and high (2160 stems ha−1) density. Three decades after thinning, diameters at breast height (DBH) were larger in sparse stands than in dense stands. While its relation with sapwood area was density independent, the accompanying high sapwood area at the tree level for sparse stands resulted the highest stand sapwood area in the medium density stand (33.26 m2 ha−1), rather than in the high density stand (29.84 m2 ha−1). Similar to short-term studies, sparse stands demonstrated higher sensitivity to climatic fluctuations and drought depressions than dense ones. Nevertheless, stand density had no effect on the isohydric strategy of Pinus tabuliformis. Contrary to the positive relation between stand density and stand canopy transpiration soon after thinning, sparse stands exhibited higher growing season canopy transpiration than dense stands three decades later. In the dry year 2014, these density differences were relatively most pronounced, with July-September transpiration totals of 56.7 mm, 31.1 mm, and 22.1 mm in the low, medium, and high density stands, respectively. Our findings highlighted that stand density was not an appropriate indicator of thinned forest transpiration over long time scales. Interactions between soil droughts and thinning on forest transpiration need to be further clarified, especially in longer periods of time.

Response of understory vegetation, tree regeneration, and soil quality to manipulated stand density in a Pinus massoniana plantation

Tree density affects species diversity in forest plantations. Understory species diversity, tree regeneration, and soil physicochemical characteristics were assessed under three planting densities of Pinus massoniana in Taizishan Mountains, Hubei, China. There was a higher degree of shrub and herb species diversity in lower density stands. Total species richness was higher for herbs (n = 42) than for shrubs (n = 30) but the two groups exhibited a similar pattern with greater species richness at lower stand density. Changes in community structure and composition were more frequent in high density stands. Community structure in low and medium density stands was more similar to one another than to high stand densities for both herbs and shrubs. The regeneration status of tree species was more abundant in low and medium density stands. Low and medium density stands had significantly more favorable chemical properties such as soil organic matter, total phosphorus, available phosphorus, and nitrogen, as well as on physical soil properties such as non-capillary pores and minimum water holding capacity. Lower planting density was beneficial with regard to natural regeneration, plant species diversity, and soil quality. Reducing tree density of existing high-density P. massoniana plantations can promote both understory plant species diversity and tree regeneration to sustain forest ecosystem services.

How do mixing tree species and stand density affect seasonal radial growth during drought events?

Forecasted climate change impacts on temperate forest ecosystems include increased summer drought. Forest managers can increase the resistance of forest stands against summer drought by reducing stand density and favoring tree species mixtures. These strategies have been studied separately, but their combined effect on increasing forest stand resistance to summer drought is unknown.The main objective of our study was to quantify tree species interaction effects on radial growth during a water stress period and to determine whether these effects changed with different levels of competition reflected by stand density.The study was based in the Orleans state forest (Central France) at a long-term triplet experimental site (OPTMix) with pure and mixed stands of mature Quercus petraea and Pinus sylvestris. The experimental design comprised three repetitions of two densities (low and medium) in each composition (pure oak, mixed stands, pure pine). We monitored tree radial growth with 216 manual dendrometers placed throughout 18 plots, on small, medium and large trees. We analyzed three consecutive years with contrasted water stress: no water stress, a summer stress period, and a late summer stress period.We found that mixture did not improve tree growth of the either species during the summer water stress period. On the other hand, there was a mixture effect during the late summer water stress period but only in medium-density stands inversely for the two species studied. More growth occurred for oaks in mixtures while, inversely, more growth occurred for pines in monocultures. A density effect occurred only for oaks, which grew more in lower-density stands than in medium-density stands. Finally, tree size did not influence seasonal resistance to drought.

Tree squirrel abundance and demography in managed coniferous forests of British Columbia are within the range of natural fluctuations of old-growth stands

The American red squirrel (Tamiasciurus hudsonicus Exrleben) and northern flying squirrel (Glaucomys sabrinus Shaw) are important mammal species in coniferous forests that are widely distributed across temperate and boreal ecological zones. Although T. hudsonicus and G. sabrinus apparently prefer late-successional forests, their population dynamics show no clear pattern in young second-growth and old-growth conifer forests. We used a compilation of study results that had standardized methodology and sampling effort to compare tree squirrel responses across a range of forest conditions. We tested the hypotheses (H) that abundance, reproduction, recruitment, and survival would be higher in (H1) old-growth than second-growth stands, (H2) unthinned than thinned second-growth stands, and (H3) lightly than heavily thinned stands. Tree squirrel populations in old-growth stands were considered the “standard” treatment to which other treatments in second-growth stands (unthinned and variously thinned) were compared. Thinned stands were grouped into low, medium, and high densities of trees. Datasets from seven published studies included 2804 Tamiasciurus and 837 G. sabrinus individuals, 25 study years, and 158 trapping periods. Mean abundance of Tamiasciurus was similar among treatment stands, ranging from 0.62 to 1.29·ha−1. Mean numbers of G. sabrinus were highest in old-growth stands at 0.65·ha−1, followed by the low- and medium-density stands at 0.50·ha−1, the high-density stands at 0.25·ha−1, and finally the unthinned second-growth stands at a low of 0.12·ha−1. In terms of effect size, mean proportional change in abundance, relative to that within old-growth stands, of both squirrel species in the three thinned stands were within the range of natural fluctuations in old-growth stands. Populations of Tamiasciurus in the unthinned stands were not within the range of fluctuations in the old-growth stands. Mean number of successful pregnancies and total recruits were similar among stands for Tamiasciurus, with variability in female breeding and winter survival. Mean number of recruits of G. sabrinus was highest in old-growth stands with no other differences in demographic attributes among stands. The biological significance of these differences in demographic variables was small in terms of effect sizes. Tamiasciurus and G. sabrinus seem to persist in a relatively broad range of young managed forest habitats, as well as in old-growth stands.

Old-growth characteristics 20 years after thinning and repeated fertilization of lodgepole pine forest: Tree growth, structural attributes, and red-backed voles

Restoration of old forests by developing late seral structural attributes in young forests may utilize pre-commercial thinning (PCT) and fertilization to accelerate stand growth and development. These silvicultural interventions are very likely required to develop complex stand structure in young forests, both vertically and horizontally, and late-seral structural features over decades, rather than centuries. We evaluated hypotheses (H) that large-scale PCT of young lodgepole pine (Pinus contorta) stands to a wide range of densities, and repeated fertilization, at 20-years after initiation of treatments would enhance (H1) size (diameter and height growth), structural features, and merchantable volume of crop trees; (H2) development of old-growth structural attributes; and (H3) abundance, reproduction, and survival of the southern red-backed vole (Myodes gapperi). Study areas were located near Summerland and Kelowna in south-central British Columbia, Canada. Each study area had ten treatments: four pairs of stands thinned to densities of ∼250 (very low), ∼500 (low), ∼1000 (medium), and ∼2000 (high) stems/ha with one stand of each pair fertilized five times at 2-year intervals, an unthinned stand, and an old-growth stand.Mean 20-year diameter of lodgepole pine crop trees was similar (19–20cm) in the heavily thinned (≤1000 stems/ha) fertilized stands with that (19–22cm) in the old-growth stands. Mean height of all managed stands (9–12m) was lower than that (18–20m) of the old-growth stands. Mean crown volume of crop trees was highest in the very low-, low, and fertilized medium-density stands (3.5–5.9 times higher, on average) than those in the unthinned and old-growth stands. Large tree diameters and crowns occurred in the heavily thinned and fertilized stands, but mean stand merchantable volume was much reduced, primarily because of the lower densities of trees, and hence provided partial support for H1. Mean species diversity of conifers was highest in the very low-density stands and old-growth stands. Mean structural diversity of conifers was generally similar among stands. Old-growth structural attributes: large dominant trees with substantial crowns, multi-layered canopies of conifers, some canopy openings, and understory abundance and diversity of herbs and shrubs appeared in the heavily thinned and fertilized stands, and hence partially supported H2. M. gapperi populations in 5 of 8 managed stands at Summerland were at the same or higher abundance (particularly the very low-density) than in the old-growth stand, with resident breeding animals and recruitment of both adult and juvenile voles, and hence H3 seemed to be supported. Heavy thinning to ≤1000 stems/ha combined with fertilization seemed necessary to achieve these structural developments in our 33-year-old second-growth stands.

Acceleration of old-growth structural attributes in lodgepole pine forest: Tree growth and stand structure 25 years after thinning

Acceleration of forest succession to develop late-seral structural characteristics in younger stands may be achieved by silvicultural practices such as pre-commercial thinning (PCT). Young second-growth stands of lodgepole pine (Pinus contorta) range across several million ha of the inland Pacific Northwest of North America and respond positively to various stand treatments. Objectives of this project were that large-scale stand thinning to a wide range of densities, at a 25-year period after PCT, would enhance: (1) productivity and structural features (diameter and height growth, and crown volume and dimensions of crop trees; (2) merchantable volume of crop trees; and (3) development of old-growth structural attributes. Three stands thinned to densities of ∼500 (low), ∼1000 (medium), and ∼2000 (high) stems/ha at age 17years, with an unthinned young pine and old-growth pine stand for comparison, were located near Penticton in south-central British Columbia.Lodgepole pine grew faster in mean diameter (cm) in the low- (13.89) than either of the medium- (10.2) or high-density (9.2) stands, but mean height growth increment (8.8–9.7m) was similar over the 25-year period since PCT. Mean diameter was 2.2 times greater in the low-density stand than unthinned stand. The medium- and high-density stands also tended to have large diameters (1.7–1.9 times that of the unthinned stand) and crowns, but still with mean heights 5–6m less than trees in the pine component of the old-growth stand. Mean merchantable stand volume (m3/ha) was 1.7–1.9 times higher in the medium- (231) and high-density (257) stands than low-density (137) stand, and comparable to the old-growth pine (225). Mean crown volume (m3) of crop trees was substantially greater in the low- (88) than in the medium- (27) and high-density (31), unthinned (4), or old-growth stands (4 pine only). Mean structural diversity of five layers of coniferous trees was highest in the low- and medium-density stands, with declining diversity from the high-density to unthinned to old-growth stands. In terms of old-growth structural attributes, large dominant trees with substantial crowns, multi-layered canopies of conifers, some canopy gaps, and understory patchiness of herbs and shrubs appeared in the heavily thinned (⩽1000stems/ha) stands at 25years post-thinning. These stands were 42years old at this re-measurement, and hence were not considered “old-growth” but the heavily thinned stands seemed to have some old-growth structural attributes. Silvicultural trade-off of stand volume gain vs. old-growth attributes may be necessary for low-density stands.

Stand structure and small mammals in intensively managed forests: Scale, time, and testing extremes

Stand thinning and fertilization have the potential to create a diversity of forest habitat conditions to meet the goals of biodiversity conservation while sustaining wood and biomass production. Three factors are crucial to a better scientific understanding of how wildlife habitats develop in managed forests: real-world scale of treatments using adaptive management, several decades of time to monitor responses, and the testing of extreme treatments. Communities of arboreal and forest-floor small mammals occupy young coniferous stands and may serve as indicators of change in forest structure and function, and hence biodiversity. We tested the hypotheses (H) that, when compared with unmanaged (unthinned and old-growth) stands, large-scale pre-commercial thinning (PCT) and PCT with repeated fertilization, up to 16–21years after the onset of treatments, would enhance (H1) stand structure, (H2) abundance of southern red-backed voles (Myodes gapperi) and species diversity of forest-floor small mammals, and (H3) abundance of northern flying squirrels (Glaucomys sabrinus), in young lodgepole pine (Pinus contorta) stands in the south-central interior of British Columbia, Canada.Mean diameters and heights of crop trees in thinned stands were less than those in old-growth stands, but the low-density stands did have greater mean diameters than those in unthinned stands. Mean crown volume of pine crop trees was significantly greater in the low- and medium-density stands than in the high-density, unthinned, or old-growth stands. Mean density of overstory (range of 1010–1590 stems/ha) and understory conifers were similar in the thinned and old-growth stands. Mean species and structural diversity of total conifers were significantly higher in the heavily thinned (⩽1000stems/ha) than other stands. For vascular plants, mean abundance of understory herbs and total structural diversity were higher in heavily thinned and fertilized stands. Thus, some aspects of stand structure supported H1 while others did not.Mean abundance of M. gapperi was higher in old-growth forest than the younger managed and unthinned stands, except in years of low numbers, and hence did not support H2 that these treatments over a longer time-frame would enhance abundance of this species. Fluctuations in numbers, drier forest ecosystems, and slow development of forest-floor habitat with decaying woody debris and fungi may contribute to flexible habitat occupancy for M. gapperi. The second part of H2, that mean species diversity of forest-floor small mammals would be enhanced in heavily thinned and fertilized stands tended to be supported, particularly in the period prior to canopy closure. H3, that abundance of G. sabrinus would be maintained at levels recorded in old-growth forests by PCT of young stands, was supported for medium- and high-density stands.A sustained flow of wood products and structural features with their habitats for wildlife and biodiversity should be achievable with a wide range of stand densities from PCT and variable regimes of nutrient additions in intensively managed forests. Essential key elements include large-scale (operational-size) treatment units and long-term monitoring of installations over decades, preferably at 5- to 10-year intervals.

Growth response of young lodgepole pine to thinning and repeated fertilization treatments: 10-year results

This study was designed to test the hypothesis that large-scale pre-commercial thinning (PCT) to various stand densities, at ages 12–14 years, combined with repeated fertilization, would, over a 10-year treatment period, enhance productivity of lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) crop trees. Study areas were located near Summerland, Kelowna and Williams Lake in south-central British Columbia, Canada. Each study area had nine treatments: four pairs of stands thinned to densities of ∼250 (very low), ∼500 (low), ∼1000 (medium) and ∼2000 (high) stems ha−1, with one stand of each pair fertilized five times at 2-year intervals, and an unthinned stand. The very low, low- and medium-density stands were also pruned to a 3-m lift 5 years after thinning. At the tree level, fertilization treatments significantly increased diameter at breast height (DBH), basal area (BA) and volume growth and heavy PCT significantly increased DBH and BA growth. Pruning may mitigate some of the negative stem form and wood quality attributes associated with fast-growing trees without adversely affecting stem growth. At the stand level, PCT to very low and low densities significantly decreased the volume growth compared with high-density stands. The potential beneficial impacts that PCT and repeated fertilization treatments have for mitigating timber supply shortfalls, as well as potentially minimizing crop tree losses due to mountain pine beetle (Dendroctonus ponderosae Hopk.), are also discussed.

Long-term responses of ecosystem components to stand thinning in young lodgepole pine forest: III. Growth of crop trees and coniferous stand structure

Enhanced growth of crop trees and development of late-seral structural characteristics in second-growth stands in temperate and boreal forest zones could be achieved by silvicultural practices such as pre-commercial thinning (PCT). This study was designed to test the hypotheses that large-scale stand thinning, at a 15-year period after PCT, would enhance: (i) productivity and structural features (crown volume, diameter, height, and volume growth of lodgepole pine ( Pinus contorta) crop trees); and (ii) coniferous stand structure (abundance, species diversity, and structural diversity of coniferous tree layers). Replicate study areas were located near Penticton, Kamloops, and Prince George in south-central British Columbia, Canada. Each study area had three stands thinned to densities of ∼500 stems/ha (low), ∼1000 stems/ha (medium), and ∼2000 stems/ha (high), with an unthinned young pine and old-growth pine stand for comparison. An overall analysis of tree growth in thinned stands, across these regional replicates, indicated that lodgepole pine grew significantly faster in mean diameter in the low- than either of the medium- or high-density stands. There was no difference in mean height growth among stand densities over the 15-year period since PCT. Mean tree volume increment was significantly higher in the low-density than in the high-density stands. Mean stand volume increment (m 3/ha) was similar in the medium-density (108.53) and high-density (132.51) stands, both of which were significantly higher than the low-density stands (72.88). Mean crown volume of crop trees was significantly greater in the low-density (52.8 m 3) and medium-density (42.9 m 3) stands than in the high-density (27.8 m 3), unthinned (11.7 m 3), or old-growth stands (30.9 m 3 pine only). This measure of crown size was similar among pine trees in the low-density, medium-density, and all conifers (43.2 m 3) in the old-growth stands. Other measurements of crown architecture followed this same pattern. Mean densities of understory trees were similar among stands for height classes up to 3 m. Mean species diversity and structural diversity of coniferous tree layers were highest in the low- and medium-density stands than in other treatment stands. Our results support the hypotheses that PCT enhances productivity (diameter and volume growth, but not height growth) and structural features (crown architecture) of young lodgepole pine, as well as diversity of coniferous tree layers in thinned stands. Accelerated development of some structural features of late-seral forest appeared in our young managed stands.

STAND STRUCTURE AND SMALL MAMMALS IN YOUNG LODGEPOLE PINE FOREST: 10-YEAR RESULTS AFTER THINNING

Management of forested landscapes for biological diversity is a major objective across North America. Perhaps the greatest potential to diversify future forests lies in the vast areas of young second-growth stands which may be managed silviculturally to accelerate ecosystem development. This study was designed to test the hypotheses that large-scale precommercial thinning, at ages 17–27 yr, to various stand densities would, over the 10-yr period since treatment, enhance: (1) productivity of lodgepole pine (Pinus contorta) crop trees, (2) stand structure attributes, and (3) species richness and diversity of forest floor small-mammal communities. Study areas were located near Penticton, Kamloops, and Prince George in south-central British Columbia, Canada, in three forest ecological zones. Each study area had three stands thinned to densities of ∼500 (low), ∼1000 (medium), and ∼2000 (high) stems/ha, with an unthinned juvenile pine and old-growth pine stand for comparison. Understory vegetation was measured in all stands in 1990, 1993, and 1998, and coniferous tree layers were measured in 1998. Small-mammal populations were sampled intensively in 1990, 1991, and 1998. Mean diameter increments of trees in the low-density stands were significantly higher than those in the medium- and high-density stands at all study areas. Mean height increments of trees were similar in the medium- and high-density stands and significantly higher than that in the low-density stands at Penticton and Prince George. Crown volume index (biomass) of herbs was highest in the thinned stands by 1998, but there was no difference among stands for shrubs and trees; volume of mosses was highest in the old-growth stands. Mean species richness and diversity of herbs, shrubs, and trees were similar among stands at 2, 5, and 10 yr after thinning. However, mean species diversity and structural diversity of coniferous trees were significantly higher in the low- and medium-density stands than in the high-density and unthinned stands 10 yr after thinning. Total structural diversity of all vegetation in the low-density stands was significantly greater than that of the medium-density, unthinned, and old-growth stands in 1998. Mean total abundance of all small mammals was similar among stands in 1990–1991, but the low-density and old-growth stands had the most mammals in 1998. Mean abundance of southern red-backed voles (Clethrionomys gapperi) was consistently higher (2.1–3.3 times) in the old-growth stands than in unthinned stands. In seven of nine cases, mean abundance of red-backed voles was similar among old-growth and thinned stands. Mean species richness and species diversity of small mammals were highest in the low-density and medium-density stands. Heavily thinned lodgepole pine stands developed structural attributes such as large diameter trees, large crowns, and structurally diverse vegetative understories. Forest floor small-mammal communities reflected the compositional and structural diversity of these managed stands.

Relationships between Manicina areolata (Cnidaria: Scleractinia), Thalassia testudinum (Anthophyta) and Neogoniolithon sp. (Rhodophyta)

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 206:135-146 (2000) - doi:10.3354/meps206135 Relationships between Manicina areolata (Cnidaria: Scleractinia), Thalassia testudinum (Anthophyta) and Neogoniolithon sp. (Rhodophyta) Miguel A. Ruiz-Zárate1, Julio Espinoza-Avalos1,*, Juan P. Carricart-Ganivet1, Dalila Fragoso2 1El Colegio de la Frontera Sur, Apdo. Postal 424, Chetumal, Quintana Roo 77000, Mexico 2Laboratorio de Ficología, Facultad de Ciencias, UNAM, Apdo. Postal 70-620, Ciudad Universitaria, Mexico D.F. 04510, Mexico *Corresponding author. E-mail: jespino@ecosur-qroo.mx ABSTRACT: The free-living coral Manicina areolata, the seagrass Thalassia testudinum, and the coralline algae Neogoniolithon sp. co-occur in the reef lagoon of Xahuayxol, Quintana Roo, in the Mexican Caribbean. The distribution and abundance of these organisms was measured. In order to study why the coral was distributed only within the medium-density stands of T. testudinum, but not in the high- or low- density stands of the seagrass, 3 size classes of M. areolata were transplanted into 3 naturally occurring seagrass densities. Mortality, displacement, righting reaction, zooxanthellae, mitotic index, and chlorophyll a were evaluated for the transplanted colonies. High mortality of M. areolata was recorded in the low-density zone of T. testudinum, attributable to siltation and predation, whereas in the high-density zone of this seagrass, the coral was under stress, as indicated by a lowered zooxanthellae density. The fragile, arborescent algae Neogoniolithon sp. was found distributed only within the medium-density zone of T. testudinum, and M. areolata selectively recruited onto that algae. Experiments in which the coral and algae were separated in the medium-density seagrass zone demonstrated that Neogoniolithon sp. offers M. areolata adaptive and ecological advantages: its survivorship was significantly higher when attached to the algae than when this substrate was not available. Because of the natural distribution of Neogoniolithon sp., the coral did not recruit in zones that would cause it stress, or even death. M. areolata and Neogoniolithon sp. eventually separate because of the increase in size (and weight) of the coral, and the fragility of the algae. Thus, the distribution of Neogoniolithon sp. explained the distribution of M. areolata instead of the high negative correlation found between the density of T. testudinum and the coral. KEY WORDS: Recruitment · Corals · Coralline algae · Seagrasses · Caribbean · Mexico · Yucatan Peninsula Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 206. Online publication date: November 03, 2000 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2000 Inter-Research.

Seasonal changes of understorey herbage yield in relation to light intensity and soil moisture content in a Pinus pinaster plantation

The relationship of understorey herbage yield with light intensity and soil moisture content was investigated in a 20-year-old Pinus pinaster plantation in Kilkis of Macedonia, northern Greece, in three seasons (fall, winter and spring). The plantation was thinned at three density levels, high, medium and low (2500, 1750 and 1000 trees/ha respectively) and it was seeded with Dactylis glomerata. In addition, two fertilization levels (0 and 110 N+150 P2O5 kg/ha) and grazing intensity levels (0 and 0.8 sheep/ha/yr) were applied in a split-split plot experimental design. It was found that herbage yield was highest in the ungrazed and fertilized low tree density stands in all seasons. In the medium tree density stand, although light was lacking, fertilized plots produced higher herbage yield as compared to unfertilized low tree density stands while fertilization is of no use in close stands if herbage production is the goal. Animals seemed to prefer fertilized and medium density stands. Third degree polynomial equations were the best to explain herbage variation through the seasons both in fertilized and unfertilized plots.

Distribution des gourmands sur les fûts de 25 essences en bordure de déboisement

Twenty-five species bordering clear-cut strips were classified according to their propensity to produce epicormic branches. The phenomenon occurred on 11 species, mostly on intermediate trees of average health and growing in medium density stands. Epicormic branching appeared generally below the crown on trees bordering the clear-cut. These results are consistent with the literature. They also verify the lack of correlation between the number of epicormic branches and tree mensuration data.