Understory responses to restoration in aspen‐conifer forests around the Lake Tahoe Basin: residual stand attributes predict recovery

The removal of conifers from aspen (Populus tremuloides) stands is being undertaken throughout the western United States to restore aspen for local‐ and landscape‐level biodiversity. Current practices include mechanically removing conifers or hand thinning, piling, and burning cut conifers in and adjacent to aspen‐conifer stands. To evaluate the effectiveness of restoration treatments, we examined tree regeneration and herbaceous vegetation cover in thinned, thinned and pile burned, and non‐thinned control stands. Growth rates of small conifer saplings threatening to outcompete and replace aspen were also measured. Two to four years after pile burning, herbaceous vegetation cover within the footprint of burned piles (i.e. burn scars) was 35–73% of that in adjacent areas. Aspen was more likely to regenerate inside burn scars where fewer surrounding trees were true firs. Conifer seedlings were more likely to regenerate in burn scars where more of the surrounding trees were conifers (pine or fir) as opposed to aspen. Fir saplings had much slower growth than did aspen saplings. Overall, our findings show that restoration treatments are promoting desirable outcomes such as enhancing aspen regeneration but that follow‐up treatments will be needed to remove numerous conifer seedlings becoming established after restoration activities. Eliminating conifers, while they are small, growing slowly, and contributing little to fuel loads may be an economical way to prolong restoration treatment effectiveness.     

Regeneration of a Coastal Pine (Pinus thunbergii Parl.) Forest 11 Years after Thinning,Niigata, Japan

To examine the effects of thinning intensity on wind vulnerability and regeneration in a coastal pine (Pinus thunbergii) forest, thinning with intensities of 20%, 30% and 50% was conducted in December 1997; there was an unthinned treatment as the control (total 8 stands). We re-measured the permanent sites to assess the regeneration characteristics 11 years after thinning. In the 50% thinned stand, seedlings aged from 2 to 10 years exhibited the highest pine seedling density and growth. The age composition ranged from 1–3 years with densities of 9.9 and 5.1 seedlings m⁻² in 30% and 20% thinned stands; only 1-year-old seedlings with a density of 6.1 seedlings m⁻² in the unthinned stand. Similar trends were found for the regeneration of broadleaved species such as Robinia pseudoacacia and Prunus serrulata. We speculate that the canopy openness and moss coverage contributed to the regeneration success in the 50% thinned stand, while the higher litter depth and lack of soil moisture induced the regeneration failure in the unthinned stand. The stands thinned at 20% or 30% were less favourable for pine regeneration than the stands thinned at 50%. Therefore, thinning with less than 30% canopy openness (20% and 30% thinned stands) should be avoided, and thinning at higher than 30% canopy openness (50% thinned stand, approximately 1500 stems ha⁻¹ at ages 40–50 years) is suggested for increasing regeneration in the coastal pine forest. The implications of thinning-based silviculture in the coastal pine forest management are also discussed. The ongoing development of the broadleaved seedlings calls for further observations.     

Monitoring Landscape‐Scale Ponderosa Pine Restoration Treatment Implementation and Effectiveness

We evaluated landscape‐scale forest restoration treatment implementation and effectiveness in meeting objectives in a ponderosa pine forest at Mt. Trumbull, Arizona, U.S.A. The goal of the project was to alter forest structure by thinning and burning to more closely resemble forest conditions prior to Euro‐American settlement in 1870. We measured 117 permanent plots before (1996/1997) and after (2003) treatments. The plots were evenly distributed across the landscape (approximately 1,200 ha), about half of which was an untreated control. We evaluated treatment implementation and effectiveness based on 1870 structure and/or goals outlined by managers. The success of treatment implementation varied: about 94% of the area originally planned for restoration was treated in some manner by 2003, but only 70% received the full planned treatment (thin and burn). Although density of ponderosa pines >2.5 cm was reduced significantly by 66% from approximately 429 pines/ha to approximately 146 pines/ha in the treated area, the targeted residual density was exceeded by 111–256% (all plots) or 10–85% (thinned and burned plots). Thirteen percent of the pre‐settlement pines died in the treated area by 2003, but 9% percent also died in the control, indicating that pre‐settlement pines in untreated areas were nearly as vulnerable as those exposed to restoration treatments. Large snags increased 45%, and 65% of logs >50 cm were retained, achieving implementation goals. Although restoration treatments were not implemented totally to specifications, they were effective in attaining the overall project goal of restoring more open forest structure while preserving more than 75% of the pre‐settlement pines. Canopy fuel loads were substantially reduced, allowing for the reintroduction of surface fires.     

Seven-Year Results of Thinning and Burning Restoration Treatments on Old Ponderosa Pines at the Gus Pearson Natural Area

Abstract We examined the 7‐year effects of three restoration treatments on leaf physiology and insect‐resistance characteristics of pre‐settlement age ponderosa pines (Pinus ponderosa Dougl. ex Laws.) at the Gus Pearson Natural Area (GPNA) in northern Arizona. Restoration treatments were: (1) thinned in 1993 to approximate pre‐Euro‐American settlement stand structure, (2) thinned plus prescribed burned in 1994 and 1998, and (3) untreated control. Tree physiological and insect‐resistance characteristics were measured in year 2000, 7 years after thinning, using the same procedures as an earlier study performed in 1996. Consistent with the 1996 results, pre‐dawn water potential in 2000 was consistently lower in the control than both thinned treatments. Both thinned treatments continued to have increased foliar nitrogen concentration in leaves 7 years after treatment. However lower leaf nitrogen concentration in the thinned and burned compared with the thinned treatment suggests lower nitrogen availability to trees in repeatedly burned plots. Analysis of leaf gas exchange characteristics and carbon isotope content (δ¹³C) suggests continued stimulation of photosynthesis by both thinning treatments. Differences among treatments in resin volume, a measure of bark beetle resistance, depended on season of measurement. Trees in both thinning treatments continued to have increased leaf toughness, a measure of resistance to insect folivores. Our results show that many beneficial effects of restoration treatments on carbon, water, and nitrogen relations and insect‐resistance characteristics of pre‐settlement ponderosa pines continue to be expressed 7 years after treatment at the GPNA.     

间伐对日本黑松海岸林更新的影响

为弄清间伐对海岸林内环境因子 ,进而对海岸林天然更新的影响 ,在黑松海岸林内进行了 4种不同强度的块状间伐试验 .林分间伐后 ,对更新状况和环境因子进行了连续观测 .结果表明 ,间伐可以改善林内光环境、提高土壤的含水量、加强空气流动、促进枯枝落叶的分解等 .4 0年生的黑松海岸林 5 0 %间伐处理后 (密度为 15 0 0株·hm-2 ,林冠开阔度 >30 % )不会对海岸林本身造成风害 ,也不会对防护功能产生较大影响 ,但却能为黑松海岸林天然更新提供良好的生态环境 .试验结果证实了间伐产生的林隙内日本黑松的更新规律 ,提出间伐可作为同龄黑松海岸林向复层、异龄海岸林演化的主要经营措施 .     

Large-Scale Patterns of Quercus ilex, Quercus suber, and Quercus pyrenaica Regeneration in Central-Western Spain

In Central-Western Spain, forests and woodlands composed of Quercus sp. support outstanding levels of biodiversity, but there is increasing concern about their long-term persistence due to a lack of regeneration. We hypothesize that this regenerative lack is operating on a large geographic scale; that there are differences in the abundance of regeneration between three oak species; that oak regeneration is governed mainly by forest management and structure; and that shrubs act as important physical protectors of seedlings and saplings. We analyzed whether densities of oak seedlings and saplings in several size classes were related to stand-structure, understory, and physiographic variables potentially affecting regeneration. Data collected at a regional level (1 km × 1 km grid) by the Spanish Forest Inventory were evaluated from 2,816 plots. Results revealed that regeneration failure was common for all size categories, from small seedlings to large saplings, and for the three oak species studied, especially the evergreens. Of the Quercus ilex, Q. suber, and Q. pyrenaica plots studied, 49%, 62%, and 20% were lacking any small seedlings, and 82%, 96%, and 56% did not have any large saplings, respectively. Regeneration was positively correlated with tree cover and density, especially of small and medium-sized trees, and negatively correlated with the presence of large trees, indicating that regeneration failure is mostly associated with more open, uniform, and/or aged woodlands. Regeneration densities of Q. ilex and Q. suber were positively correlated with all understory variables, suggesting that the presence of pioneer shrubs represent a major safe site for early tree recruitment, independent from specific shrub species.     

Thinning improves growth and resilience after severe droughts in Quercus subpyrenaica coppice forests in the Spanish Pre-Pyrenees

During the past years, growth and productivity of different oak species have been constrained by water shortage in seasonally dry regions such as the Mediterranean Basin. Thinning could improve oak radial growth in these drought-prone regions through the reduction of tree competition for soil water in summer. However, we still lack adequate, long-term assessments on how lasting are thinning treatments effects and to what extent they contribute to oak growth recovery after drought. Here we aim: (i) to study the radial growth sensitivity to drought of Quercus subpyrenaica in the Spanish Pre-Pyrenees, and (ii) to verify if thinning represents a suitable option to enhance growth resistance to drought and post-drought growth recovery. We analysed basal area increment (BAI) trends in the period 1960–2020 of formerly coppiced oak stands thinned in 1984 and compared them with unthinned plots and also with coexisting Scots pine (Pinus sylvestris) growing in thinned plots. We used the Standardized Precipitation Evapotranspiration Index (SPEI) to estimate the severity of droughts and we also assessed climate-growth relationships. Oaks in thinned plots showed higher BAI (369 mm²) than those in unthinned plots (221 mm²). Growth rates remained higher in thinned than in unthinned plots also under severe drought stress. A severe summer drought in 1986 caused abrupt BAI reductions in both oaks (- 40.5%) and pines (- 40.1%). The positive effect of thinning on growth lasted for over 20 years and slightly declined as canopies closed. In the thinned plots, trees with smaller diameter showed the greatest growth release. Oaks in unthinned plots and Scots pine were more sensitive to short-term droughts in terms of growth reduction than oaks in thinned plots, while long term droughts have similar effects on oaks from both thinned and unthinned plots. Oaks were resilient to drought, showing recovery periods lasting from 1 to 2 years in both thinned and unthinned plots. However, intense and prolonged droughts could strongly reverse the expected growth enhancement of thinned plots, and a greater frequency of droughts would limit coppice growth and productivity thus lengthening the rotation periods.     

Effects of a Hurricane Disturbance on Aboveground Forest Structure, Arbuscular Mycorrhizae and Belowground Carbon in a Restored Tropical Forest

To better understand how management and restoration practices influence the response of terrestrial ecosystems to large-scale disturbances, it is critical to study above- and belowground effects. In this study, we examined the immediate effect of a major hurricane on aboveground forest structure, arbuscular mycorrhizae (AM) and belowground carbon pools in experimentally thinned plots in a tropical forest. The hurricane occurred five years after a thinning treatment, when thinned plots had similar aboveground carbon stocks but different forest structure compared to control plots. Thinned plots had more large diameter (>10 cm) trees compared to the control plots, which were characterized by a higher density of small diameter (<10 cm) trees. Despite pre-hurricane differences in forest structure, there were no significant differences between treatments in changes of canopy openness or number of affected trees following the hurricane. Thinned plots had larger belowground carbon pools than the controls plots before the hurricane, and these differences remained after the hurricane despite rapid decomposition of organic matter rich in nitrogen. There were no pre-hurricane differences in AM fungal spores or total AM root colonization. The hurricane reduced AM sporulation by nearly 50% in both treatments, yet we observed a significant increase in AM root colonization after the hurricane with greater AM colonization in the thinned plots. Hurricanes have well-known visible aboveground effects, but here we showed that less visible belowground effects are influenced by forest management and may play an important role in forest recovery.     

Seasonal prevalence of arthropods after line thinning of overstocked Japanese cedar (<Emphasis Type="Italic">Cryptomeria japonica</Emphasis> D. Don) plantations in central Japan

We investigated the seasonal changes in the abundance of coleopteran and hymenopteran functional groups to evaluate the ecological suitability of line thinning in overstocked Japanese cedar plantations in central Japan. In line thinning, 3- to 5-m-wide sections of the stand are harvested parallel to the mountain slope and perpendicular to the forest roads. The thinning intensity varies from 25 to 35% of the total number of trees. We compared the seasonal abundance between the thinned stand and the unthinned (control) stand in two plantation forests: a low-elevation Sugi site (4 years since thinning) and a high-elevation Kuchiotani site (6 years since thinning). Most coleopteran and hymenopteran functional groups were consistently more abundant in the thinned stand than in the unthinned stand. The differences in arthropod abundance between the thinned and unthinned stands were mainly caused by marked differences in the abundance of seasonally strongly changing functional groups during their peak seasons. The predators and parasitoids of insects as well as the plant and pollen feeders (plant-dependent functional groups) responded to seasonal changes in the vegetation (food and microhabitats) and microclimate. The ants were less affected by line thinning. Our results indicate that line thinning is an ecologically suitable silvicultural treatment for the improvement of biodiversity conditions in the overstocked plantation forests.     

天然林重建过程中单优箬叶竹灌丛对树木更新的影响

利用1996年在湖南省会同林区布置的20个1 hm~2的实验样地,以剔除或林下不含箬叶竹样地作为对照(C),保留箬叶竹作为处理(I),评估了天然林重建过程中林下单优箬叶竹灌丛形成对树种更新过程的影响.处理10a以后结果显示,箬叶竹灌丛盖度上升到95%.进一步通过2007年两种样地乔木多度、多样性、生物量以及物种组成等指标的测量表明,单优箬叶竹灌丛显著抑制了树种的存活与生长,18～390 cm高度级别的树种多度和多样性显著降低,尽管高度18 cm以下级别的幼苗以及成年树的多度和多样性没有显著下降,但是生物量从幼苗到成年树,处理样地普遍下降.幼苗、幼树、成年树地上部分生物量分别下降47.45%、39.87%、59.64%,地下部分生物量分别下降55.70%、46.08%、63.62%.NMS(非计量多元尺度法)排序进一步表明两种样地具有显著不同的树种组成,揭示两种样地处于不同的演替更新阶段.结果表明单优箬叶竹灌丛的形成能延缓树种更新的进程,因此天然林重建过程中应注意避免该类林下植被的出现.     

The effect of environmental factors on the regeneration of Quercus semecarpifolia Sm. in Central Himalaya,Nepal

Poor regeneration of oak forest has been observed in north America and Eurasia. In the Himalaya it has mainly been explained by anthropogenic pressures. This study analyses the regeneration of two Quercus semecarpifolia Sm. forests (2–3000 m a.s.l.), where one forest has almost nil disturbance and the other has different degrees of canopy disturbance. The relationships between biotic and abiotic environmental variables and the number of Quercus semecarpifolia seedlings and saplings (i.e., recruits <10 cm Diameter at Breast Height (DBH)) were analysed by means of Generalized Additive Models (GAM). The two forests were compared with respect to size-class distributions of mature trees (i.e., >10 cm DBH), and the number of recruits.The size-class distributions indicate that regeneration is most reliable in the nearly undisturbed forest. Most recruits were found under high canopy cover and high potential radiation. Canopy disturbance has a negative effect on the number of seedlings. Seedlings seem to prefer a pH of around 6, Loss-on-Ignition between 20 and 30 %, and total nitrogen between 2 and 3 %. In general, there were very few plots with saplings, and there was not a clear relationship between the number of saplings and the soil variables. The size-class diagrams indicate a lack of young trees in the disturbed forest, and it is hypothesized that fire may inhibit recruits reaching the canopy phase.     

Does forest restoration using taungya foster tree species diversity? The case of Afram Headwaters Forest Reserve in Ghana

The taungya agro‐forestry system is an under‐researched means of forest restoration that may result in high tree diversity. Within a forest reserve in Ghana, the forest core and its surrounding Teak‐ and Cedrela‐taungya on logged, cropped and burned land were mapped with ALOS satellite imagery. Native trees, seedlings and saplings were enumerated in 70 random, nested plots, equally divided between forest and taungya. The native tree regeneration was assessed by species richness (SR), Shannon‐Wiener Index (SWI), Shannon Evenness Index (SEI) and species density (SeD) for seedlings, saplings and trees separately and combined and subsequently correlated with canopy covers (CC) in taungya. As anticipated, the taungya diversity was lower than the forest diversity but higher than reported from nontaungya exotic plantations. In the forest, the diversity of native trees increased from seedlings through saplings to trees. The reverse was found in the taungya. Taungya seedling diversity was not significantly different from the forest, while the sapling and tree diversity were significantly lower. Weak correlations of CC with SR, SWI, SEI and SeD were found. Our results suggest the need for treatment to maintain the tree diversity beyond the seedling stage in the taungya.     

The remnant mangroves of Sei Kecil,Simpang Hilir,West Kalimantan,Indonesia

Phytosociological analysis of the remnant mangrove forest was carried out in Sei Kecil, Telok Melano, West Kalimantan, to describe the forest composition and structure, and to assess the regeneration strategy of the important mangrove species. Six transect plots of 20 × 60 m, 20 × 80 m and 20 × 90 m, with a total area of one hectare were established perpendicular to the coast line.A total of 20 species of trees and saplings, two species of herbs and one species of nypa palm was recorded. Three community types were recognized namely Rhizophora apiculata, Excoecaria agallocha-Rhizophora apiculata and Excoecaria agallocha reflecting the zonation in this forest.The number of trees, saplings and seedlings were 510, 1220 and 11 085 per ha respectively. Rhizophora apiculata was most successful in regeneration with 6231 seedlings per ha (56.2%) and followed by Bruguiera parviflora with 3810 seedlings per ha (34.4%). Seedlings of the first species were mostly growing under gaps while the second species occurred mostly around the mother trees.     

马尾松人工林近自然化改造对植物自然更新及物种多样性的影响

中国人工林面积居世界第一位,而马尾松是中国人工林面积较大的树种之一,广泛分布于中国的亚热带区域。马尾松适应能力强,耐干旱、瘠薄,是南方低山丘陵区群落演替的先锋树种,也是荒山绿化造林的主要树种,马尾松人工林对生态防护、生态治理有着重大的意义。但是,绝大部分马尾松人工林为人工纯林,生态系统比较脆弱,生态服务功能较差。人工林的近自然改造对于增加林地生物多样性,提升人工林的生态服务功能具有重要意义。2005年,对中国林业科学院热带林业试验中心1993年造林的马尾松人工林进行4种不同强度(50%、40%、30%、20%)间伐后,套种大叶栎(Castanopsis fissa)、米老排(Mytilaria laosensis)、润楠(Machilus pingii)、红锥(C. hystrix)4个乡土阔叶树种,各种套种密度皆为120株/hm²。分别于间伐前(2004年)及2010年对群落生物多样性及人工套种树种生态情况进行调查,结果表明:(1)间伐处理后,自然更新至乔木层的物种种类和数量都有显著的增加,600 m²的样方中,物种数由(2.75±2.56)种增加到(11.17±4.32)种,个体数由(5.75±4.31)株增加到(32.17±19.09)株,群落中乔木亚层的优势种变化不大,主要有南酸枣(Choerospondias axillaris)、水锦树(Wendlandia uvariifolia),枫香(Liquidambar formosana)、破布木(Cordia dichotoma)、白背桐(Mallotus paniculatus)等。新增加到乔木层的物种大都为之前群落中灌木层的种类,主要有三桠苦(Evodia lepta)、鸭脚木(Schefflera minutistellata)、白花龙(Styrax faberi)、中平树(Macaranga denticulata)、黄毛榕(Ficus esquiroliana)、华南毛柃(Eurya ciliata)、罗浮柿(Diospyros morrisiana)、猴耳环(Pithecellobium clypearia)、木姜子(Litsea pungens)、毛黄肉楠(Actinodaphne pilosa)等。(2)间伐处理前,600 m²样方中出现的灌草种类数量为(24.63±4.24)种,间伐处理后,600 m²样方中出现的灌草种类数量为(27.58±3.80)种,不同间伐强度处理后林下灌草的优势种与间伐前大致相同,灌木层优势种为三桠苦,草本层优势种为弓果黍(Cyrtococcum patens)。不同间伐强度处理林分间,灌木层和草本层的物种丰富度指数、Shannon-Wiener指数、Simpson指数和Pielou指数均无显著差异,且与间伐前林分也无显著差异。(3)间伐促进了4个乡土树种幼树的生长,随着间伐强度的增加,大叶栎、红锥幼树的高度和胸径显著增长;50%的间伐强度的林分中,阔叶树种幼树的长势要显著好于其他间伐强度,50%的间伐强度最有利于马尾松林下套种的阔叶树种生长。(4)在马尾松林下套种的4个阔叶树种幼树的初期生长有明显差异。总体而言,大叶栎与米老排幼树的早期生长速率要明显高于红锥和润楠。     

Composition and Dynamics of Functional Groups of Trees During Tropical Forest Succession in Northeastern Costa Rica

We compared the functional type composition of trees ≥10 cm dbh in eight secondary forest monitoring plots with logged and unlogged mature forest plots in lowland wet forests of Northeastern Costa Rica. Five plant functional types were delimited based on diameter growth rates and canopy height of 293 tree species. Mature forests had significantly higher relative abundance of understory trees and slow-growing canopy/emergent trees, but lower relative abundance of fast-growing canopy/emergent trees than secondary forests. Fast-growing subcanopy and canopy trees reached peak densities early in succession. Density of fast-growing canopy/emergent trees increased during the first 20 yr of succession, whereas basal area continued to increase beyond 40 yr. We also assigned canopy tree species to one of three colonization groups, based on the presence of seedlings, saplings, and trees in four secondary forest plots. Among 93 species evaluated, 68 percent were classified as regenerating pioneers (both trees and regeneration present), whereas only 6 percent were classified as nonregenerating pioneers (trees only) and 26 percent as forest colonizers (regeneration only). Slow-growing trees composed 72 percent of the seedling and sapling regeneration for forest colonizers, whereas fast-growing trees composed 63 percent of the seedlings and saplings of regenerating pioneers. Tree stature and growth rates capture much of the functional variation that appears to drive successional dynamics. Results further suggest strong linkages between functional types defined based on adult height and growth rates of large trees and abundance of seedling and sapling regeneration during secondary succession.
Abstract in Spanish is available at http://www.blackwell-synergy.com/loi/btp     

The effects of disturbance on the population structure and regeneration potential of five dominant woody species – in Hugumburda‐Gratkhassu National Forest Priority Area,North‐eastern Ethiopia

Vast areas of forests in North‐eastern Ethiopia have been replaced by cropland, shrub land or grazing areas. Thus, information about how vegetation composition and structure varies with disturbance is fundamental to conservation of such areas. This study aimed to investigate the effects of disturbance on the population structure and regeneration potential of five dominant woody species within forest where local communities harvest wood and graze livestock. Vegetation structure and environmental variables were assessed in 50 quadrats (20 m × 20 m). In most of both disturbed and undisturbed treatments, Juniperus procera was the highest contributor to the basal area of the forest, while that of Olinia rochetiana was the lowest. Analysis of population structure showed high density at lower Diameter at Breast Height (DBH) and low density at higher DBH classes. Undisturbed forest treatments had 84% canopy cover, 22 m mean vegetation height and a density of 1320 trees of dominant species and 1024 seedlings/saplings ha^?1. In disturbed habitats, canopy cover (73%), mean vegetation height (18 m) and density of dominant trees and saplings were significantly lower than in undisturbed habitats. Thus, to ensure species, survival and maintain species diversity managed use of the protected area is essential.     

Non-native grass invasion suppresses forest succession

Multiple factors can affect the process of forest succession including seed dispersal patterns, seedling survival, and environmental heterogeneity. A relatively understudied factor affecting the process of succession is invasions by non-native plants. Invasions can increase competition, alter abiotic conditions, and provide refuge for consumers. Functional traits of trees such as seed size and life history stage may mediate the effects of invasions on succession. We tested the effects of the forest invader Microstegium vimineum on planted and naturally regenerating trees in a multi-year field experiment. We established plots containing nine species of small- and large-seeded tree species planted as seeds or saplings, and experimentally added Microstegium to half of all plots. Over 3 years, Microstegium invasion had an overall negative effect on small-seeded species driven primarily by the effect on sweetgum, the most abundant small-seeded species, but did not affect large-seeded species such as hickory and oak species, which have more stored seed resources. Natural regeneration was over 400% greater in control than invaded plots for box elder, red maple, and spicebush, and box elder seedlings were 58% smaller in invaded plots. In contrast to the effects on tree seedlings, invasion did not affect tree sapling survival or growth. Microstegium may be directly reducing tree regeneration through competition. Invaded plots had greater overall herbaceous biomass in 2006 and 2008 and reduced light availability late in the growing season. Indirect effects may also be important. Invaded plots had 120% more thatch biomass, a physical barrier to seedling establishment, and significantly greater vole damage to tree saplings during 2006 and 2007. Our results show that two tree functional traits, seed size and life history stage, determined the effects of Microstegium on tree regeneration. Suppression of tree regeneration by Microstegium invasions may slow the rate of forest succession and alter tree species composition.     

Spatial patterns and associations in a Quercus‐Betula forest in northern China

Question: Are species‐specific regeneration strategies and competition the dominant processes facilitating species coexistence in a Quercus liaotungensis dominated temperate deciduous forest? Location: Dongling Mountains, North China, 1300 m a.s.l. Methods: Ripley's K‐function was used to characterize the spatial patterns and spatial associations of two dominant tree species, Quercus liaotungensis and Betula dahurica, and a common subcanopy species, Acer mono, at different growth stages (adult, sapling, seedling). Results: Seedlings, saplings and adults of all three species exhibited clumped distributions at most spatial scales. Quercus seedlings and saplings were positively associated with conspecific adult trees and spatially independent of dead trees suggesting that seed dispersal and vegetative regeneration influenced the spatial patterning of Quercus trees. Betula seedlings and saplings were positively associated with both live and dead trees of conspecific adults at small scales (<5 m) but negatively associated with live and dead trees of other species indicating sprouting as an important mechanism of reproduction. Saplings of Acer had a strong spatial dependence on the distribution of conspecific adult trees indicating its limited seed dispersal range. Negative associations between adult trees of Betula and Quercus demonstrated interspecific competition at local scales (<5 m). Conclusions: Different regeneration strategies among the three species play an important role in regulating their spatial distribution patterns, while competition between individuals of Betula and Quercus at the adult stage also contributes to spatial patterning of these communities. The recruitment limitations of Betula and Quercus may affect the persistence of these species and the long‐term dynamics of the forest.     

Soil and vegetation response to thinning White Cypress Pine (Callitris glaucophylla) on the North Western Slopes of New South Wales, Australia

Dense White Cypress Pine (Callitris glaucophylla J. Thompson and L.A.S. Johnson) regrowth occurs frequently across previously cleared landscapes in New South Wales (NSW), and is thought to adversely affect agricultural production and to cause land degradation. The NSW Native Vegetation Act (2003) requires that management of native vegetation including pre-1990 regrowth must ‘improve or maintain’ site condition, yet there is currently limited information regarding techniques for the optimum management of C. glaucophylla in this regard. We conducted a preliminary study to examine floristic composition, soil condition (to 50 cm) and carbon storage under ‘Dense’ (dense regrowth), ‘Thinned’ (dense regrowth thinned 2000/2001) and ‘Un-colonised’ (pasture not yet recolonised by C.␣glaucophylla) plots on private lands in NSW. Reduced tree density from thinning resulted in increased biomass of the remaining individual trees. Un-colonised plots had significantly more groundcover than thinned plots, which had significantly more groundcover than dense plots. Differences in plant diversity however, were explained by site factors rather than land use. Soils in the dense plots were the most acid but soil pH was significantly higher in thinned plots and pH was highest in soil of the un-colonised plots. Mean values for carbon, nitrogen, sulphur and extractable phosphorus varied among sites, although each were significantly more abundant in the mineral soil of dense and thinned plots compared with un-colonised plots, suggesting that thinning had had a minimal effect on the soil parameters assessed. Accounting for all site components, site carbon storage was significantly higher in dense and thinned plots compared with un-colonised plots due to elevated levels of soil and litter carbon as well as the presence of trees. The results indicate that thinning dense C. glaucophylla can maintain and (by some measures) improve site condition. However, given the variability in some of the parameters assessed, further study across a wider range of soil types and rainfall gradients is proposed.     

Competition and regeneration in quaking aspen–white fir (Populus tremuloides–Abies concolor) forests in the Northern Sierra Nevada,USA

Question: How does competition between quaking aspen (Populus tremuloides) and white fir (Abies concolor) affect growth and spatial pattern of each species? Location: The northern Sierra Nevada, California, USA. Methods: In paired plots in mixed aspen‐ (n=3) or white fir‐dominated (n=2) stands, we mapped trees and saplings and recorded DBH, height, species, and condition and took increment cores. We tallied seedlings by species. Tree ring widths were used as a measure of basal area change over the last decade, and canopy openness was identified using hemispherical photographs. Linear mixed models were used to relate neighborhood indices of competition, stand, and tree‐level variables to diameter increment. Spatial patterns of stems were identified using the Neighborhood Density Function. Results: White fir radial growth was higher in aspen‐ than white fir‐dominated plots. Individual‐level variables were more important for white fir than for aspen growth, while variables representing competitive neighborhood were important only for aspen. The forest canopy was more open in aspen‐ than white fir‐dominated stands, but ample aspen seedlings were observed in all stands. Canopy stems of aspen and white fir were randomly distributed, but saplings and small trees were clumped. Aspen saplings were repelled by canopy aspen stems. Conclusions: Variation in canopy openness explained more stand–stand variation in white fir than aspen growth, but high light levels were correlated with recruitment of aspen seedlings to the sapling class. Radial growth of aspen was predicted by indices of neighborhood competition but not radial growth of white fir, indicating that spacing and stem arrangement was more important for aspen than white fir growth. Fire suppression has removed a major disturbance mechanism that promoted aspen persistence and reduced competition from encroaching conifers, and current forests favor species that regenerate best by advance regeneration (white fir).