Causes of spatial patterns of dead trees in forest fragments in Illinois

Natural disturbances introduce spatial heterogeneity into forests by causing non-random mortality of trees. We examined whether wind was the primary cause of spatial patterns of dead trees at fragment- and individual tree-levels in three fragments of temperate deciduous forests in Illinois, USA. Dead trees and wind-caused types of mortality were expected to be higher at forest edges, on windward aspects, in poorly-drained soils, and adjacent to existing canopy gaps. The extent of wind-related mortality was determined by comparing spatial and temporal patterns of dead trees, as well as characteristics of trees downed by single windstorms versus all dead trees. At the fragment-level, we used randomly located quadrats of 25×25 m to sample edge and interior areas of Trelease Woods, Brownfield Woods, and Hart Woods in 1995-1996 and again in 1999-2000. We noted type of mortality (standing dead, snapped-off, or uprooted trees), and measured DBH ( 10 cm) and direction of fall of each dead tree. The same measures were made for trees felled by two single storms in 1994. At the individual tree-level, domino effects were evaluated by comparing openness surrounding target treefalls vs. an equal sample size of living trees. The study provided limited evidence that wind caused spatial patterns of dead trees. Instead, spatial patterns of dead trees in the fragments accumulated from domino effects at the individual tree-level in two of the three fragments. Dead trees were more associated with preexisting gaps. Contrary to our predictions at the fragment-level, the frequency of dead trees was not greater at edges, on windward aspects, or in poorly drained soils. This study demonstrated the complexity of spatial patterns of dead trees in forest fragments. The significant domino effects indicated that the occurrence of dead trees was not random, but determined by previous disturbances.     

Seed arrival under different genera of trees in a neotropical pasture

Trees in pastures attract seed dispersers, leading to increased seed arrival under their canopies and more rapid regrowth around them. The characteristics that make some trees better `recruitment foci' than others, however, are poorly understood. In a neotropical pasture, we examined the arrival of seeds to open areas and underneath four genera of trees that varied in canopy architecture and type of fruit produced: Ficus trees had dense canopies and fleshy fruits, Pentaclethra trees had dense canopies and dry fruits, Cecropia trees had sparse canopies and fleshy fruits, and Cordia trees had sparse canopies and dry fruits. We found that all trees received more seeds than open pasture, probably because trees provided seed dispersers with better perches, protection from predators, nesting sites, etc. Among the tree genera, more seeds arrived under trees that produced fleshy fruits than trees that did not. This occured even during periods when trees were not fruiting (i.e., non-fruiting Ficus and Cecropia trees received more seeds than Cordia or Pentaclethra trees). Seed dispersers may periodically check Ficus and Cecropia trees for fruits, or they may become familiar with these trees while feeding and thereafter use them for other reasons. Height of trees had a slight positive effect on seed arrival, possibly because taller trees offered more protection from predators. Canopy architecture and distance to forest edge did not significantly affect seed arrival. This study demonstrates that trees in general are potentially important recruitment foci, but that different types of trees vary in the kind of recruitment that they foster in pastures.     

Reproductive biology of the dry forest tree Enterolobium cyclocarpum (guanacaste) in Costa Rica: a comparison between trees left in pastures and trees in continuous forest

We compared the rate of pollen deposition, the likelihood of fruit production, the number of seeds per fruit, the outcrossing rate, and the progeny vigor of the tropical dry forest tree Enterolobium cyclocarpum for individuals in pastures vs. individuals in continuous forest. We found that flowers from trees growing in continuous forests were more likely to have pollen deposited on their stigmas than flowers from trees in pastures (52.1 vs. 32.3%, respectively). We also found that trees from continuous forests were almost six times more likely to set fruits and produce more seeds per fruit than trees in pastures. Morever, progeny from trees in continuous forests were, on average, more vigorous than the progeny from trees in pastures, as indicated by 12 of 16 indicators of plant vigor. However, there was no significant difference in the multilocus estimate of the outcrossing rate between the two groups of trees (tm = 1.00 and 0.99 for trees from continuous forest and trees from pastures, respectively). But there are differences in the correlation of paternity between the progeny of the two groups, where the progeny from trees in pastures showed a lower correlation of paternity than progeny of trees from continuous forests (r(p) = 0.104 and r(p) = 0.189, respectively). We argue that the mechanisms that regulate progeny vigor are disrupted in trees from pastures. We discuss the implications of these findings for the conservation of E. cyclocarpum.     

贵州特有植物红花瘤果茶种群空间格局及数量动态研究

红花瘤果茶(Camellia rubituberculata)为地理分布狭窄的贵州特有植物,颇具经济价值。为查清其分布特征和评估其濒危状况,该文在红花瘤果茶的集中分布区设置三个典型样地进行调查,采用空间点格局及多元点格局分析法分析种群空间分布格局,利用种群动态量化指数分析预测种群数量动态规律。结果表明:(1)兴仁县新寨村大皮坡1号样地幼龄树的小尺度呈集群分布、大尺度呈随机分布,中龄树和老龄树均呈随机分布; 兴仁县新寨村槽子土2号样地的幼龄树均呈集群分布,中龄树和老龄树均呈随机分布; 晴隆县紫马乡龙头村上捧碧林区3号样地幼龄树、中龄树和老龄树均呈随机分布。(2)不同发育阶段的空间关联主要表现为1号样地幼龄树和中龄树均为负相关,幼龄树和老龄树在中小尺度上为负相关,在大尺度上为无相关,中龄树和老龄树均为无相关。2号样地幼龄树和中龄树在小尺度上为负相关,中大尺度上为无相关; 幼龄树和老龄树在中小尺度上为负相关,中大尺度上为无相关; 中龄树和老龄树均为无相关。3号样地的幼龄树和中龄树均为正相关; 幼龄树与老龄树在小尺度上为负相关,中尺度上为无相关,大尺度上为正相关; 中龄树和老龄树均为无相关。(3)种群数量动态分析表明3个样地中幼苗补充充裕,种群结构为增长型,但易受外界环境干扰、生态脆弱。(4)红花瘤果茶的生境异质性及其种内种间关系相互作用的结果是影响种群数量扩大和物种散布的主要因素。     

浙江磐安红叶树种资源及其应用调查

对浙江省磐安县红叶树种资源及其应用情况进行初步调查,结果表明,该县共有乔木、灌木、藤本红叶木本植物37种,分属19科26属,其中,落叶乔木所占比例最大,有21种,占该县红叶树种的56.8%。根据叶片变色规律可分成秋叶变红、嫩叶红色、秋叶和嫩叶均呈红色、常年有红叶等四大类型,种数最多的是秋叶变红类,有26种,占该县红叶树种的70.3%。本文对部分重要的红叶树种的园林应用价值进行综合评价,并对该县红叶树种资源的开发利用提出建议。     

Sources of variation in the incidence of ant–aphid mutualism in boreal forests

• 1 The mutualism between wood ants of the Formica rufa group and aphids living in the canopy of trees is a widespread phenomenon in boreal forests, and it can affect tree growth. However, not all trees in the forest are involved in this interaction.
• 2 To assess the incidence of host trees involved in this ant–aphid mutualism and its spatial distribution in boreal forests, we inventoried sample plots with a radius of 10–15 m around wood ant mounds in 12 forest stands of two age classes (5–12‐year‐old sapling stands and 30–45‐year‐old pole stands) and two dominant tree species (Scots pine and silver birch) in Eastern Finland from 2007 to 2009.
• 3 The proportion of trees visited by ants out of all trees on the individual study plots were in the range 4–62%, and 1.5–39% of the trees on the plots were consistently visited by ants during all 3 years. The percentage of host trees increased with the ant mound base area on the plots. Trees visited by ants were larger and closer to the mound than trees not visited by ants. Within the group of visited trees, more ants were found on bigger trees and on trees close to the ant mounds.
• 4 Extrapolated from plot to stand level, we estimated that 0.5–6.6% of the trees were host trees in at least one of the three study years, and that only 0.01–2.3% of all the trees were consistently visited by ants during all 3 years. It is concluded that ant–aphid mutualism is a minor occurrence at the stand level.

     

Stand structure, variability in growth and intraspecific competition in a peatland stand of black spruce Picea mariana

Age and size distributions and growth rates of individual trees were examined in a black spruce stand growing on a peatland in Alberta, Canada, 38 years after fire. Both height and basal girth frequency distributions were positively-skewed, with many small and few large individuals. Age distributions were negatively-skewed; most trees were recruited five to seven years after fire and there was little recruitment after 25 years. Stem analysis data indicated that increment in height was nearly constant over the life of the trees but larger trees grew faster than smaller trees. The trees which started growth immediately after the fire maintained faster growth than those recruited some years later. At the time of study, above ground competition and canopy shading were not considered to have a large effect on growth rates of individual trees. Several hypotheses are presented to explain these differences in growth of individual trees.     

关帝山云杉次生林活立木和枯立木的数量特征与分布格局

本研究以山西关帝山庞泉沟自然保护区4 hm²云杉次生林样地2010年和2015年两次调查数据为基础,从物种组成、径级结构、空间格局,以及不同径级活立木与枯立木的空间关联性、枯立木不同径级间的相互关联性4个方面,分析5年间活立木与枯立木的数量特征、分布格局及相互关联性。结果表明: 样地内2010年胸径(DBH)≥1 cm的活立木共有25811株,隶属于11科22属30种,所有个体径级分布呈倒“L”型,个体数量随着径级增大呈断层式减少; 2010—2015年5年间形成枯立木共2145株,涉及5科10属12种,以5～10 cm径级分布为主。在0～50 m尺度上,活立木与枯立木在空间分布上具有一定相似性,表明枯立木的空间格局在一定程度上受活立木空间格局限制。各径级活立木与枯立木空间关联分析表明,随着样地内树木个体径级的增大,对空间资源竞争的加剧可能是导致枯立木产生的主要原因。随着枯立木径级的增大,活立木与枯立木的空间关联性不同程度的减弱,表明环境可能成为大径级枯立木形成的关键因素。从枯立木内部看,5 cm≤DBH<20 cm枯立木与DBH<5 cm枯立木、10 cm≤DBH<20 cm枯立木与5 cm≤DBH<10 cm枯立木、DBH≥20 cm枯立木与5 cm≤DBH<20 cm枯立木整体上都表现为显著正相关,说明枯立木会对后续活立木枯死产生影响。     

Within-tree distribution of nest sites and foraging areas of ants on canopy trees in a tropical rainforest in Borneo

It has been argued that canopy trees in tropical rainforests harbor species-rich ant assemblages; however, how ants partition the space on trees has not been adequately elucidated. Therefore, we investigated within-tree distributions of nest sites and foraging areas of individual ant colonies on canopy trees in a tropical lowland rainforest in Southeast Asia. The species diversity and colony abundance of ants were both significantly greater in crowns than on trunks. The concentration of ant species and colonies in the tree crown seemed to be associated with greater variation in nest cavity type in the crown, compared to the trunk. For ants nesting on canopy trees, the numbers of colonies and species were both higher for ants foraging only during the daytime than for those foraging at night. Similarly, for ants foraging on canopy trees, both values were higher for ants foraging only during the daytime than for those foraging at night. For most ant colonies nesting on canopy trees, foraging areas were limited to nearby nests and within the same type of microhabitat (within-tree position). All ants foraging on canopy trees in the daytime nested on canopy trees, whereas some ants foraging on the canopy trees at night nested on the ground. These results suggest that spatial partitioning by ant assemblages on canopy trees in tropical rainforests is affected by microenvironmental heterogeneity generated by three-dimensional structures (e.g., trees, epiphytes, lianas, and aerial soils) in the crowns of canopy trees. Furthermore, ant diversity appears to be enriched by both temporal (diel) and fine-scale spatial partitioning of foraging activity.     

Oxidative stress in relation to reproduction,contaminants, gender and age in a long-lived seabird

A key question in savanna ecology is how trees and grasses coexist under N limitation. We used N stable isotopes and N content to study N source partitioning across seasons from trees and associated grasses in a semi-arid savanna. We also used ¹⁵N tracer additions to investigate possible redistribution of N by trees to grasses. Foliar stable N isotope ratio (δ¹⁵N) values were consistent with trees and grasses using mycorrhiza-supplied N in all seasons except in the wet season when they switched to microbially fixed N. The dependence of trees and grasses on mineralized soil N seemed highly unlikely based on seasonal variation in mineralization rates in the Kruger Park region. Remarkably, foliar δ¹⁵N values were similar for all three tree species differing in the potential for N fixation through nodulation. The tracer experiment showed that N was redistributed by trees to understory grasses in all seasons. Our results suggest that the redistribution of N from trees to grasses and uptake of N was independent of water redistribution. Although there is overlap of N sources between trees and grasses, dependence on biological sources of N coupled with redistribution of subsoil N by trees may contribute to the coexistence of trees and grasses in semi-arid savannas.     

基于稳定同位素和热扩散技术的张北杨树水分关系差异

利用稳定氢同位素和热扩散技术研究张北防护林杨树的水分来源和蒸腾耗水,分析确定未退化与退化杨树的水分关系差异.结果表明:在生长季节中退化杨树主要利用0～30 cm土壤水分,未退化杨树主要利用30～80 cm土壤水分,两者的水分来源不同.旱季时,未退化杨树利用深层土壤水分和地下水的比例明显高于退化杨树.雨季中,杨树对0～30 cm土壤水分的利用比例增加,退化杨树增加幅度明显高于未退化杨树,对30～180 cm土壤水分的利用比例均减少.未退化杨树的液流速率大于退化杨树,不同天气中液流速率表现出相似的变化趋势,但未退化杨树液流的启动时间比退化杨树早.相关分析表明,未退化和退化杨树液流速率与土壤温度、风速、太阳辐射、相对湿度、空气温度均呈极显著的相关关系.退化杨树液流速率与土壤温度和空气相对湿度呈极显著负相关,与其他因素呈显著正相关,而未退化杨树仅与空气相对湿度呈极显著负相关,与其他因素均呈显著正相关关系,表明退化和未退化杨树蒸腾耗水易受环境条件的影响.退化杨树液流日累计量明显小于未退化杨树,表明其蒸腾耗水量较少;退化杨树水分来源浅,蒸腾耗水的减少并不能阻止林分退化.     

Ecophysiology of Eucalyptus marginata and Corymbia calophylla in decline in an urban parkland

Eucalypt trees are in decline throughout urban landscapes of south western Australia. This study investigated the cause of decline in Eucalyptus marginata and Corymbia calophylla trees in parkland and compared water and nutrient relations with healthy trees in adjacent bushland in Perth, Western Australia. It was hypothesized that: (i) trees were drought stressed through competition for soil water by the vigorous turf; (ii) excessive uptake of nitrogen, because of fertilizer application to turf, caused toxicity; and/or (iii) micronutrient (Cu, Fe, Mn and/or Zn) deficit was induced by high‐pH irrigation water applied to turf around parkland trees. Leaf water potential showed aseasonal variation in the irrigated parkland trees and foliar δ¹³C indicated that parkland trees generally had low water‐use efficiency and were not drought stressed relative to bushland trees. Foliar N levels were not significantly different between parkland and bushland trees indicating that excess N uptake was not a factor in the decline. Foliar total Fe, ‘metabolically active’ Fe, Cu and Zn concentrations were not significantly different between parkland and bushland trees. Foliar manganese concentrations were indicative of deficiency and significantly lower in parkland trees (5–14 µg g^?1) relative to bushland trees (22–35 µg g^?1). It is concluded that application of alkaline irrigation water to the parkland site reduced the plant‐availability of Mn; however, our study of only one parkland site does not allow us to generalize the results across other parklands.     

The largest trees in Australia

Large old trees have many critical ecological functions. We collated information about Australia's tallest and largest (by circumference) trees from several databases. The 20 tallest trees in Australia are currently all Mountain Ash (Eucalyptus regnans) found primarily in Tasmania. There are also some Mountain Ash trees in Victoria which are over 90 m tall and still increasing in height. The 20 largest (by circumference) trees are distributed throughout four states (NSW, TAS, WA and VIC) with Mountain Ash accounting for more than half of the trees on this list. Making this information available in one location increases its accessibility and allows for priority species and areas for conservation to be more easily identified. Documenting the size and condition of trees, together with their location, will enable them to be revisited and monitored in the future. This practice will allow changes in tree condition, occurring through growth and/or deterioration, to be documented. We trust that by increasing the accessibility of this information, we encourage more people to take an interest in the ecology and conservation of large old trees. This is important given the past and present cultural significance of trees to Australia's First Nations People and the need to preserve this information and appreciation for nature.     

Regeneration in subalpine coniferous forests

Death of canopy trees when gaps are formed was studied in a subalpine coniferous forest, central Japan, which was composed ofAbies, Tsuga, Picea, Betula, andSorbus. Typhoons were considered to be the most important cause of the death of canopy trees. The degree of disturbance in each of 16 plots (20 m×20 m) was represented by the percentage of the total basal area of dead trees to that of living and dead canopy trees (disturbance magnitude; MAG). The mortality of canopy trees increased as their dbh increase in the plots of lower MAG than 90%. The mortality varied among genera, andTsuga was characterized as having lower mortality than that of the other conifers. 418 dead trees were observed. The standing dead trees made up 10.7% of the trees, the stem broken trees 46.7%, and the uprooted trees 42.2%. The stem breaking was most frequent inAbies, and the uprooting was most frequent inTsuga, Picea, andBetula. Undeveloped forests, which have the L-shaped dbh distribution, were destroyed only in high degree (70%<MAG), while developed forests were destroyed in various degrees (30%<MAG<100%). The percentage of uprooted trees in basal area decreased with the development of the forest, from 60% to 10%.     

Optimal locomotion modes of foraging birds in trees

This paper compares the energy costs of various modes of locomotion of birds foraging in trees. For birds moving vertically in trees by climbing and hopping (but not by flying) the best choice of locomotion mode depends on the distance between visited trees in relation to the height h of the zone searched for food in trees.
When the distance between successively visisted trees is longer than about half the distance coverable in gliding flight with height loss h , then it is cheapest in energy to hop or climb upwards in a tree and fly downwards to the next tree. When the distance between successively visited trees is shorter than about half the distance coverable in gliding flight with height loss h , then it is cheapest in energy to move alternately downwards and upwards in trees (downwards in the first, upwards in the second, downwards in the third tree, etc.) and to fly level between trees.
Treecreepers and woodpeckers are adapted morphologically to the former mode, but more generalized tree foragers might use either mode depending on the spacing of trees.     

基于SSR标记的不同优势等级云南松遗传多样性分析

基于SSR分子标记技术,按树高和胸径（地径）因子将样地内的植株分为优势木、中等木和劣势木3类,对不同生长优势等级云南松林木的遗传多样性变异特征进行了研究。结果表明：在林冠层,优势木的有效等位基因数、Shannon's信息指数、观测杂合度和期望杂合度分别为2.083、0.762、0.290和0.423,略高于中等木和劣势木;在更新层,有效等位基因数、Shannon's信息指数、观测杂合度和期望杂合度分别为2.063、0.774、0.272和0.410,除观测杂合度外,其余3个指标也均表现为优势木略高于中等木和劣势木。从差异显著性检验来看,不同生长优势等级云南松林木间的遗传多样性差异不显著,即林木生长分化对遗传多样性的影响不明显。     

油松优树选择方法的研究

论述了优树选择应遵循优良种源区选择优良林分,优良林分中的选择优良单株的系统选择原则。提出了标准差法选择方法和标准,要求优树胸径大于林分平均胸径加２倍标准差,且优树年平均出长量：胸径大于０．９ｃｍ、树高大于０．５ｍ。根据１９株人工林优树周转的标准地每木实测数据,对小标准地法和大树选优法作了比较;根据３２株优树的选优结果,比较了１－５株大树法选优法之间的相关关系,大树法间相关都显著,但以３株法为最好;     

The occurrence of cavities in fruit trees: effects of tree age and management on biodiversity in traditional European orchards

The formation of tree-cavities is an important ecological factor since many animals in woody habitats are cavity users. Recent research focuses on tree-cavity formation and the associated cavity networks in forest ecosystems. However, although traditional European orchards are important habitats for secondary cavity users, ecological research on the factors associated with the occurrence of cavities in fruit trees is widely missing. In particular, fruit tree pruning management may affect decay-cavity formation due to the pruning wounds allowing heart rot and decay to enter the tree. Here, we present a cross-sectional study investigating 608 fruit trees in 30 study plots of three European fruit-growing regions to identify factors associated with decay-cavity occurrence in fruit trees. Presence of decay-cavities was positively related to trunk diameter. Moreover, fruit trees of low vitality and with woodpecker-cavities featured more often decay-cavities than trees of high vitality or without woodpecker-cavities. Apple trees featured higher numbers of cavities at younger age than other fruit trees. Occurrence of decay-cavities was also related to the past removal of large main branches. Accordingly, traditional orchards are cavity-rich habitats if they comprise high proportion of old fruit trees, in particular apple trees, and if pruning management produces large pruning wounds. Thus, differential tree pruning and fruit-growing traditions across Europe result in different cavity densities in traditional orchards. Preservation of existing and potential cavity trees and selective removal of large branches from apple trees are recommended as conservation measures establishing high cavity densities and increasing the associated biodiversity in the agricultural landscape.     

Root deformation in plantations of container-grown Scots pine trees: effects on root growth,tree stability and stem straightness

Root system deformation was studied in 23 Scots pine (Pinus sylvestris L.) stands in central Sweden. The study comprised both plantations created with container-grown plants (Paperpot) and natural stands including young (7–9 year old) and older (19–24 year old) trees. Trees were measured with regards to distribution of roots, root deformation, stability, stem straightness and wood properties in stumps. Root distribution was most uniform for naturally regenerated trees. Older trees generally showed a better root distribution than young trees. The young planted trees displayed a high frequency of severely spiralled root systems, while only a few of the older trees had spiralled root systems. No severe root deformations were observed on naturally regenerated trees. Naturally regenerated trees were more stable than those which had been planted. Differences in bending moment, when trees were pulled to an angle of 10°, were considerable between young planted and naturally regenerated trees, but less pronounced for the older trees. Young planted trees had the highest frequency of severely crooked stem bases, while naturally regenerated trees had the straightest mode of growth. Tensile strength in peripheral wood samples of the stumps was substantially lower for planted than for naturally regenerated trees. Strain values to breakage of wood samples, taken from the root collar and the central- and peripheral part of the stump were lower for planted trees. The conclusions from this study are that root distribution, tree stability and stem straightness of planted Paperpot-grown trees will improve after a certain time and approach the state of naturally regenerated trees. As trees grow older, early established crooked stem bases will be compensated by radial growth and the tree will appear straighter. Inside the stem, however, problems may still remain with abnormal fibre direction and compression wood together with inferior root strength due to fibre disturbances as a result of spiralled roots. This revised version was published online in June 2006 with corrections to the Cover Date.     

African Elephants Loxodonta africana Amplify Browse Heterogeneity in African Savanna

There is a growing concern that the feeding habits of the African elephant, which include pushing over, uprooting and snapping trees, may have a negative impact on other herbivores. Browsed trees are known to respond by either increasing production (shoots and leaves) or defence (secondary compounds). It is not clear, however, what proportion of the browsed biomass can be made available at lower feeding heights after a tree is pushed over or snapped; thus, it is also unclear how the forage quality is affected. In a field survey in Kruger National Park, South Africa, 708 Mopane trees were measured over four elephant utilization categories: snapped trees, pushed‐over trees, uprooted trees and control trees. The elephants' impact on the leaf biomass distribution was quantified, and the forage quality (Ca, P, K and Mg, N, digestibility and condensed tannin [CT] concentrations) were analyzed. Pushed‐over and uprooted trees had the maximum leaf biomass at lower heights (<1 m), snapped trees at medium heights (1–2 m) and control trees at higher heights (>2 m). In all three utilization categories, the minimum leaf biomass was seven times higher than it was for control trees at a height of below 1 m. Leaf nitrogen content increased in all three categories and was significantly higher in snapped trees. CT concentrations increased slightly in all trees that were utilized by elephants, especially on granitic soils in the dry season. The results provide the insight that elephants facilitate the redistribution and availability of browse and improve the quality, which may positively affect small browsing herbivores.