Tree replacement patterns in subalpine Abies-Betula forests,Wolong Natural Reserve,China

Vegetation in canopy gaps of two old-growth Abies-Betula forest stands, one with bamboo the other without, was measured. The structure of gap vegetation at each site was used to derive tree replacement probabilities. Transition probabilities indicate different tree replacement trends in forests with bamboo compared to those without. Projected compositions show Betula to be the most abundant species in bamboo stands while Abies remains most abundant where bamboo was absent. A dense bamboo sward seems to reduce the probability of Abies filling gaps by inhibiting establishment and growth of seedlings. Bamboo preempts space after canopy gap formation by increasing shoot production which reduces opportunities for establishment and growth of other woody species. Differences in dispersal ability and longevity of Abies and Betula appear to be important factors contributing to their coexistence forests with a small canopy gap disturbance regime.     

A note on the dynamics of montane virginPicea yezoensis forest in the Greater Khingan Mts,Northeastern China

The vertical growth ofLarix gmelini in the north of the Greater Khingan Mts., north-eastern China is very fast during the first 50 yr. ThoughPinus sylvestris var.mongolica shows a higher growth rate, it will be replaced by the larch population.Picea jezoensis is the most tolerant tree species and will replace all other trees.The fire cycle is 110–120 yr. Most of the montane areas from 800 to 1000 m a.s.l. are not occupied by spruce forest.There is a sapling bank with large numbers of saplings at ages below 20 yr in the understory in the spruce forest. The sapling bank is the key to maintain the steady state of the spruce forest. The persistent sapling bank in the life history of spruce governs the dynamics of the spruce forest controlled by the intensity and frequency of disturbances.The author is H. Q. Wu     

Structure,dynamics and disturbance regime of temperate broad-leaved forests in Japan

Abstract. Structure, diversity and dynamics of five Japanese temperate old-growth forests were compared, differing from each other in, i.a., climate, dominant tree type, topography, disturbance regime. The forests were Aya, Ogawa, Kanumazawa Riparian, Kanumazawa upland and Senju. A permanent plot (1–6 ha) was established in each forest and trees were censused several times at intervals of two years. Mean annual recruitment rates and mortality rates in these forests were both in the range of 0.5 to 4.6 %/yr at the community level. Analyses of the structure and dynamics of populations showed that the underlying process was different among the forests. Some forests experienced compositional shifts in their canopies, others had a constant canopy composition but appeared to lack effective regeneration in recent years. The recruitment rate appeared to be strongly affected by competitive undergrowth vegetation such as dwarf bamboo which has been controlled by natural disturbance or human impact. It is likely that the forests with mostly low recruitment rates had a low species diversity. The current variation in structure, diversity and dynamics of the studied forests might have been determined not only by physical conditions (e.g. climate) but also by chance factors (e.g. disturbance, outbreak of deer population).     

沙地云杉种群结构与动态的研究

本文用种群大小结构代替年龄结构研究了沙地云杉种群的大小结构、分布格局和动态规律。结果表明,样地1、2、3、5的沙地云杉种群属于增长型,样地4的沙地云杉种群为稳定型,将样地1、2、3作为一块样地,其分布格局为集群型,但从幼树到大树,则由集群分布变为随机分布。     

湖南小溪自然保护区巴东木莲群落结构

巴东木莲(Manglietia patungensis)分布于湖南西北部、湖北西南部和重庆市,是中国特有的稀有濒危物种。湖南小溪自然保护区是巴东木莲分布面积最大且最集中的地区。对巴东木莲群落乔木层结构及优势树种径级组成的分析结果表明,该群落属于典型的常绿阔叶林,群落乔木层可分为三个亚层:第一亚层优势树种为落叶树种枫香(Liquidam bar form osana)和常绿树种巴东木莲;第二亚层以利川润楠(Machilus lichuanensis)为优势树种;第三亚层的优势树种是长叶石栎(Lithocarpus henryi);优势树种径级组成表明,巴东木莲在该群落中与其它优势树种形成稳定的共存群落;巴东木莲在群落中呈聚集分布格局。本研究为正处于生境消失、群落结构被破坏的巴东木莲群落恢复与重建提供科学依据。建议在小溪自然保护区内严格限制对巴东木莲种子的采收,禁止在林下采挖巴东木莲的幼苗,确保巴东木莲在自然状态下得以保持其种群和个体数量的自然增长。     

The significance of life history strategies in the developmental history of mixed beech (Nothofagus) forests,New Zealand

Size and age structure analysis, dated past disturbances, treefall replacement patterns, and spatial pattern analysis were used to reconstruct the developmental history of two old-growth Nothofagus fusca/N. menziesii stands, South Island, New Zealand. Diameter and height class distributions suggested that N. menziesii was replacing N. fusca, however, stand history reconstruction analysis showed that both species had regenerated intermittently after small-scale disturbances. Although large-scale disturbances such as blowdowns may occasionally generate even-aged stands, gap-phase regeneration maintains the forests in compositional equilibrium. In the absence of other competing tree species and understorey plants the two species appear to coexist by way of different life history strategies, where one species (N. menziesii) has low juvenile mortality and the other (N. fusca) has faster height growth rates and greater longevity and adult survivorship.     

The structure and dynamics of Abies magnifica forests in the southern Cascade Range,USA

Abies magnifica (Red fir) forests in the Cascade Range and Sierra Nevada of California are composed of groups, or patches, of even-sized individuals that form structurally complex stands. Patches may be even-aged, resulting from synchronous post-disturbance establishment, or multi-aged, reflecting continuous recruitment of seedlings moderately tolerant of shade. We analyze the population structure (i.e. age, size, and spatial patterning) of A magnifica, and associated A concolor, White fir, and reconstruct the disturbance history of two mature to old-growth A. magnifica forests in order to determine the relationship between disturbance and forest structure. Within both stands examined, the distributions of A. magnifica seedlings, saplings, and small understory trees were clumped, with clump sizes corresponding to the area of canopy gaps. Gaps were created by frequent wildfire (mean fire return interval of 41 yr) and by windstorms. Severe fire initiated mass establishment of Abies magnifica, whereas gaps created by windthrowreleasedalreadyestablishedindividuals. Lowinten-sity fire stimulated little recruitment, but Red fir established continuously during fire-free intervals. Thus, the complex age and structures of Red fir forests reflect both episodic and continuous recruitment, as determined by the type and severity of natural disturbance.     

The impact of diffusion and stirring on the dynamics of interacting populations

We investigate the combined effects of diffusion and stirring on the dynamics of interacting populations which have spatial structure. Specifically we consider the marine phytoplankton and zooplankton populations, and model them as an excitable medium. The results are applicable to other biological and chemical systems. Under certain conditions the combination of diffusion and stirring is found to enhance the excitability, and hence population growth of the system. Diffusion is found to play an important role: too much and initial perturbations are smoothed away, too little and insufficient mixing takes place before the reaction is over. A key time-scale is the mix-down time, the time it takes for the spatial scale of a population to be reduced to that of a diffusively controlled filament. If the mix-down time is short compared to the reaction time-scale, then excitation of the system is suppressed. For intermediate values of the mix-down time the peak population can attain values many times that of a population without spatial structure. We highlight the importance of the spatial scale of the initial disturbance to the system.     

川西亚高山不同森林类型土壤呼吸和总硝化速率的季节动态

川西亚高山原始林及其采伐后通过不同恢复措施形成的不同类型森林土壤呼吸和总硝化速率的对比分析及其耦合关系的研究相对匮乏。采用气压过程分离系统(Ba PS)技术研究了川西亚高山岷江冷杉原始林及其砍伐后恢复的粗枝云杉阔叶林、红桦-岷江冷杉天然次生林和粗枝云杉人工林土壤呼吸和总硝化速率的季节动态及其影响因素。结果表明:生长季内平均土壤呼吸速率和总硝化速率分别以粗枝云杉阔叶林和粗枝云杉人工林较高,均以岷江冷杉原始林较低。土壤呼吸和总硝化速率在生长季内具有明显的季节动态,呈以7月份最高的单峰趋势。土壤呼吸和总硝化速率与土壤温度显著相关,而与土壤水分相关性不显著,表明土壤温度是调控呼吸和总硝化作用季节动态的主要因子。土壤呼吸的温度敏感性(Q_(10))介于2.59—4.71,以岷江冷杉原始林最高,表明高海拔的岷江冷杉原始林可能更易受到气候变化的影响。林型间土壤呼吸和总硝化速率主要受凋落物量、p H和有机质的影响。不同林型间土壤呼吸和总硝化速率显著正相关,表明土壤呼吸和总硝化速率存在耦合关系。     

川西亚高山/高山森林土壤线虫多样性

为了解青藏高原东缘亚高山/高山森林土壤线虫多样性,于2015年7月以该地区岷江冷杉原始林、混交林和次生林为研究对象,采用淘洗-过筛-蔗糖离心的方法分离土壤线虫,研究了3个海拔森林土壤线虫群落的组成与结构特征.结果表明: 共捕获线虫37950条,隶属于20科27属,平均为4217 条·100 g^-1干土,原始林以丝尾垫刃属为优势属,混交林和次生林以丝尾垫刃属和拟盘旋属为优势属,且优势属个体数量受林型的影响显著.原始林和次生林的优势营养类群为食真菌线虫,混交林则为食细菌线虫.土壤线虫c-p (colonizer-persister)类群c-p 1、c-p 2、 c-p 3和c-p 4数量分别占总数的6.1%、51.1%、30.0%和12.7%.3个海拔森林土壤线虫的自由生活线虫成熟度指数(MI)、总成熟度指数(∑MI)和植物寄生线虫成熟度指数(PPI)随海拔增加而逐渐降低.土壤线虫通路指数(NCR)在混交林高于0.5,在原始林和次生林低于0.5.林型显著影响了土壤线虫成熟度和NCR指数,但林型、土层及二者的交互作用对多样性指数影响不显著.川西亚高山/高山不同森林土壤线虫的组成、营养结构和能流通道存在明显差异,为深入理解土壤线虫在该区森林土壤生态过程中的作用提供了参考.     

川西亚高山森林不同恢复途径物种组成和群落结构动态变化

川西亚高山森林作为西南林区主体,是长江上游的生态屏障,该区域植被恢复方式主要为人工恢复和自然恢复,比较不同恢复方式下森林的物种组成和群落结构动态变化,对于川西亚高山森林恢复与重建有重要的意义,可以为制定合理的森林管理策略提供科学依据。基于茂县山地生态系统定位研究站不同恢复模式形成的的华山松人工林、油松人工林和自然恢复的次生林野外调查数据,分析了2005-2020年乔、灌、草三个层次的群落结构特征和多样性。结果表明:(1)不同恢复途径下,乔木层物种数都呈现增加趋势,华山松人工林、油松人工林、自然恢复的次生林乔木层物种数分别增加了11种、7种、8种;(2)华山松人工林中华山松重要值从48.06%降低到31.1%,乡土阔叶树种四川蜡瓣花进入乔木层,2020年重要值增大至21.62%,油松人工林中油松重要值逐渐降低,从43.59%降至29.76%;自然恢复的次生林中,乡土树种锐齿槲栎逐渐成为第一优势种,2020年重要值增至19.9%。(3) 华山松人工林、油松人工林和自然恢复的次生林中,温带区系成分分别占总属数的71.43%,80.77%和84%,温带区系特征明显。(4)华山松人工林和油松人工林乔木层径级结构均为偏正态分布;而自然恢复的次生林径级分布呈倒"J"形,以小径级个体为主。(5)不同林型的乔木层高度在15年间呈现增加的趋势,具体表现为油松人工林>华山松人工林>自然恢复的次生林。(6)乔木层Shannon-wiener指数和 Simpson指数均表现为自然恢复的次生林显著大于两个人工林,丰富度指数和均匀度指数表现为油松人工林最大;灌木层4个多样性指数均表现为油松人工林最大;草本层的丰富度指数、Shannon-wiener 指数和 Simpson 指数均表现为油松人工林较大,均匀度指数没有显著差异。结论:人工林恢复速度大于自然恢复的次生林,但自然恢复的次生林更新能力更强,且更有利于多样性的保存。两个人工林逐渐由常绿针叶林演替为以常绿针叶树为主的针阔混交林,自然恢复的次生林演替为以常绿阔叶树为主的针阔混交林。     

尚勇保护区亚洲象种群数量动态、种群结构及季节分布格局

在2006 年6 月至2007 年9 月,通过种群个体识别、社区监测网络、样线调查和村寨访问等方法对尚勇保护区亚洲象的种群动态和季节性分布格局进行研究。结果显示:目前在尚勇保护区的亚洲象种群数量约为68头;拍摄到亚洲象共计347 头次,通过个体识别方法识别出亚洲象53 头,其中幼体、青少年体、亚成体和成体数量及所占比例分别为:3 (5.66%)、11 (20.75% )、15 (28.30% )、24 (45.28% ),在成体中雄性只有两头,成年象的雌雄性比为11∶ 1,高于已知国内外的其他区域。从1992 年至2007 年10 月,至少有32 头亚洲象死亡,其中确认死于猎杀的有7 头,保护区的核心区野牛河、金宝河一带是盗猎亚洲象最严重的地区。严重的盗猎和不断减少的栖息地对当地的亚洲象种群产生了巨大的威胁,也加剧了当地的人象冲突。在雨季和旱季,亚洲象各有五个核心活动区域,食物是导致雨季和旱季分布格局不同的主要因素。     

川西亚高山森林凋落物去除对土壤腐殖质动态的影响

森林凋落物作为森林土壤腐殖质的主要来源, 在土壤腐殖质的形成中发挥着重要作用, 但不同森林类型凋落物因其含量、组成等的不同, 对土壤腐殖质的影响也不同。该研究以川西亚高山针叶林、阔叶林和针阔混交林3种不同森林类型为对象, 采用凋落物原位控制实验, 对比研究不同关键期凋落物去除对土壤可提取腐殖质、胡敏酸和富里酸含量及胡敏酸/富里酸、胡敏酸/可提取腐殖质的影响。主要结果: (1)土壤可提取腐殖质、胡敏酸和富里酸含量在不同森林类型中差异显著。土壤可提取腐殖质含量总体表现为针叶林>针阔混交林>阔叶林, 胡敏酸含量总体表现为针阔混交林>针叶林>阔叶林, 而富里酸含量则表现为针叶林>阔叶林>针阔混交林, 其中3种林型中土壤腐殖质的主要成分为富里酸, 总体均表现为富里酸型。不同采样时期也显著影响了土壤可提取腐殖质、胡敏酸和富里酸含量, 总体均表现为先升高后下降的趋势。除个别采样时期外, 凋落物去除总体降低了土壤可提取腐殖质、胡敏酸和富里酸的含量。(2)胡敏酸/富里酸和胡敏酸/可提取腐殖质的结果显示3种林型土壤总体腐殖化程度均较低, 整体表现为针阔混交林>阔叶林>针叶林, 凋落物去除在一定程度上有利于提高阔叶林与针阔混交林的腐殖质品质。(3)相关分析表明不同凋落物处理间土壤可提取腐殖质与土壤有机碳含量、全氮含量和土壤含水量呈显著正相关关系, 与温度呈显著负相关关系。综上所述, 短期的凋落物去除会降低土壤腐殖物质的含量, 但不同林型间由于凋落物类型差异会导致土壤腐殖质的不同变化, 说明土壤腐殖质的动态变化受凋落物类型以及环境因素的综合调控。因此, 关于凋落物变化对土壤腐殖质的影响还需进一步的长期研究。     

四川卧龙亚高山林线生态交错带群落的种多度关系

以盖度作为物种多度指标,用描述物种多度分布的模型：断棍分布、几体级数分布、对数级数分布和截尾对数正态分布研究了卧龙巴郎山岷江冷棚林线交错带附近草本群落的种－－我镀分布关系。结果表明,截尾对数正态分布和对数级数分布能较好地拟合交错带附近群落的种－多度分布,截尾对数正态分布模型更适合交错带群落,对数级数分布 较好地适合亚高山草甸群落。对数级数分布的参数α和对数正态分布的参数λ是反映群落结构特征内在性质     

Forest development in canopy gaps in old-growth beech (Nothofagus) forests,New Zealand

Abstract. Tree size and age structures, treefall and canopy gap characteristics, and regeneration responses to treefalls were compared for three stands of old-growth beech (Nothofagus) forest dominated by N. fusca and N. menziesii on the South Island, New Zealand. Treefall gaps (up to 1000 m²) were most often caused by standing trees killed by drought and/or insect attack, or by trees snapped by wind. The causes of gap formation and the size and age distributions of treefall gaps varied between localities because of spatial and temporal differences in the histories of disturbance. At Fergies Bush where drought-related dieback had produced many large gaps with standing dead trees, gaps were generally young. Conversely, at Station Creek, small, old gaps formed by bolesnap dominated the disturbance regime. At Rough Creek, gaps of all ages and sizes were found along with an almost complete fern cover, and abundant shrubs and occasional subcanopy hardwood trees. Although overall patterns of regeneration were unrelated to differences in gap size, the relative abundance of N. fusca and N. menziesii varied between localities according to the seemingly minor differences in forest structure and disturbance history described above. Interpretations of regeneration response to gap parameters, therefore, need to account for differences in disturbance history between sites. Differences in the disturbance history between localities will also influence rates of gap closure, and because closure rates are used to estimate forest turnover times, meaningful comparisons of disturbance regimes for different forest types can only be made if this intersite variability is addressed.     

大熊猫栖息地亚高山针叶林结构和动态特征

亚高山针叶林是大熊猫适宜的栖息环境 ,其结构和动态规律严重影响大熊猫的生存和繁衍及其进化潜力的维持 ,是恢复退化大熊猫栖息地的唯一科学依据。通过样方法和中心点四分法调查了大熊猫栖息地 4个亚高山针叶林样地和该样地所在森林的 6 2个林窗 ,研究了该类森林的结构及其更新与大熊猫主食竹生长、林窗干扰的关系 ,以期揭示亚高山针叶林的动态规律 ,为大熊猫栖息地的恢复提供科学依据。研究结果表明 :岷江冷杉 Abies faxoniana和紫果云杉 Picea purpurea是亚高山针叶林的主体 ,其所构成的森林是大熊猫重要的栖息环境。岷江冷杉种群年龄呈现连续分布格局 ,而紫果云杉种群年龄呈间歇性分布 ,其在 2 5 0～ 5 0 0 a之间没有更新。该类森林中普遍存在着林窗干扰和更新现象 ,90 %的林窗下分布有岷江冷杉和紫果云杉更新的幼苗、幼树和大树。但林窗内不同树种更新密度不同 :岷江冷杉更新幼苗、幼树和大树占所有更新树种的 82 .5 % ,而紫果云杉和糙皮桦的更新幼苗、幼树和大树占 11.3%。岷江冷杉和紫果云杉的更新同时受林下大熊猫主食竹生长状况的影响 :主食竹盖度高 ,更新树种幼苗、幼树的密度低 ,即主食竹的生长抑制了岷江冷杉和紫果云杉的更新。     

Structure and tree-fall gap dynamics of old-growth Nothofagus forests in Tierra del Fuego,Argentina

Abstract. Tree size and age structure, tree-fall and gap characteristics, and regeneration in gaps were studied in Nothofagus-dominated old-growth forests in Tierra del Fuego, Argentina. Gap-phase regeneration has resulted in all-aged populations for N. pumilio, N. betuloides, and Drimys winteri, and regeneration in gaps appears to be maintaining coexistence between species in mixed stands. N. betuloides fills many gaps via advance regeneration and some individuals persist for > 150 yr in the understory. Multiple periods of release and suppression indicate that N. betuloides may take advantage of several gap events to reach the main canopy. Likewise, Drimys grows well under closed canopy and can rapidly respond to gap formation, sometimes impeding the regeneration of N. betuloides. In contrast, N. pumilio regenerates in gaps mainly from seed or from advance regeneration of small, ephemeral seedlings. Gap turnover times in Fuegian forests were estimated at 300 - 500 yr, although gap formation was highly episodic and possibly associated with regionally extensive windstorms, earthquakes, and stand-level dieback. 92 % of gaps involved multiple tree-falls, and at least 53 % involved secondary expansion. Gap and tree-fall characteristics in Tierra del Fuego were similar to results from northern Patagonia, Chile, and New Zealand; however, we emphasize that regeneration of Nothofagus spp. and Drimys winteri in gaps depends on associated vegetation and varies along both local and regional environmental gradients.     

Structural characteristics and canopy dynamics of Tsuga canadensis in forests of the southern Appalachian Mountains, USA

Tsuga canadensis (L.) Carr. forests of the southern Appalachian Mountains are currently facing imminent decline induced by a nonnative insect pest, the hemlock woolly adelgid (Adelges tsugae Annand). To effectively manage these forest systems now and in the future, land managers need baseline data on forest structure and dynamics prior to large-scale Tsuga canadensis mortality. Most of our knowledge concerning the dynamics of Tsuga canadensis forests comes from more northern locations such as the Great Lakes region and New England and, therefore, may not pertain to the ecological systems found within the southern Appalachian Mountains. We examined the structure and canopy dynamics of four Tsuga canadensis forest stands within the Cataloochee watershed, in the far eastern part of Great Smoky Mountains National Park (GSMNP). We characterized the environmental settings and vertical forest layers, as well as the diameter and age-structures of each Tsuga canadensis forest stand. These environmental and structural data showed that there were indeed differences between forest stands with and without successful Tsuga canadensis regeneration. The two forest stands exhibiting successful Tsuga canadensis regeneration were located above 1,000 m in elevation on well-drained, moderately steep slopes and had the greatest canopy openness. Structural data from these two forest stands indicated a history of more continuous Tsuga canadensis regeneration. We also constructed disturbance chronologies detailing the history of canopy response to disturbance events and related these to Tsuga canadensis regeneration within each forest stand. Student t-tests adjusted for unequal variances indicated significant differences in the number of release events per tree between forest stands with and without successful Tsuga canadensis regeneration. While forest stands with successful Tsuga canadensis regeneration were more frequently disturbed by minor to major canopy disturbances, events of moderate intensity were found to be most significant in terms of regeneration. These data will be of value to land managers maintaining stands of Tsuga canadensis where treatment for hemlock woolly adelgid infestation has been successful. In areas where treatment is impractical or unsuccessful, land managers will be able to use these data to restore Tsuga canadensis forests after the wave of hemlock woolly adelgid induced mortality has passed. As of August 2008, Joshua A. Kincaid will be a member of the Environmental Studies program at Shenandoah University in Winchester, Virginia, USA     

唐家河自然保护区小型兽类群落结构

唐家1989 年4～11 月对唐家河自然保护区的小型兽类进行了研究, 共布放11 000多铗日, 捕获小型兽类846 只。共有小型兽类21 种, 划分为4 个群落。利用方差分析和多重比较分析出了各群落内的优势种, 并比较了方差分析与以捕获比例确定小型兽类群落优势种的差异。根据香农- 威纳公式分析了群落的多样性和均匀性, 发现随着群落内物种数的增加, 群落的多样性和均匀性指数也都增加, 但是随着群落内优势种所占比例增加, 群落的多样性则显著降低, 均匀度也降低。     

The dynamics of old-growth Pseudotsuga forests in the western Cascade Range,Oregon, USA

Size and age structure, spatial analysis, and disturbance history were used to analyse the population structures and regeneration patterns of 8 conifer stands in the central western Cascade Range, Oregon, USA. Variation in forest structure reflected the effects of frequent (20–50 yr) low-intensity fires and treefalls, infrequent (100–200 yr) localised, intense fires, and extensive fires that resulted in stand replacement (every ca 400 yr?).The amount of canopy removed and the size of openings formed by fires and treefalls were important determinants of subsequent forest establishment. Single or several species stands of Pseudotsuga and/or Abies procera, or mixed species stands of Pseudotsuga, Abies procera, Tsuga heterophylla and Abies amabilis established in openings where intense fires had removed most of the canopy trees over several ha. Multi-tiered and multi-aged stands, often containing 400–500 yr-old Pseudotsuga and variously-sized more or less even-aged patches of younger shade tolerant Tsuga heterophylla and/or Abies amabilis, occurred where lower-intensity fires did not kill all overstorey trees or where treefalls occurred after the initial fire.Current regeneration processes are influenced by overstorey composition, the availability and size of canopy openings, and the availability of substrates suitable for regeneration. Tsuga heterophylla and Abies amabilis established under Pseudotsuga menziesii and Abies procera canopies and in small canopy openings (<400 m²) created by windfalls, but rarely under Tsuga. Down logs and stumps were favoured establishment sites for Tsuga.The disturbance regime of fires of low-to moderate-intensity, windfalls, and occasional fires that result in extensive stand replacement contrasts with the pattern of infrequent, catastrophic disturbances proposed for other areas of the Pacific Northwest. Although fires at stand establishment commonly determine much of the composition, structure, and subsequent stand development, canopy replacement by shade tolerant species occurs as the different life histories of the species are expressed in response to various disturbances differing in intensity and frequency. Such a non-equilibrium view of vegetation change is consistent with many other fire-dominated forests of the western United States.