National assessment of the fragmentation, accessibility and anthropogenic pressure on the forests in Mexico

Forest managers and policy makers increasingly demand to have access to estimates of forest fragmentation,human accessibility to forest areas and levels of anthropogenic pressure on the remaining forests to integrate them into monitoring systems,management and conservation plans.Forest fragmentation is defined as the breaking up of a forest unit,where the number of patches and the amount of expose edge increase while the amount of core area decreases.Forest fragmentation studies in Mexico have been limited to local or regional levels and have concentrated only on specific forest types.This paper presents an assessment of the fragmentation of all forest types at the national level,their effective proximity to anthropogenic influences,and the development of an indicator of anthropogenic pressure on the forests areas.Broadleaf forests,tropical evergreen forests and tropical dry deciduous forests show the greatest fragmentation.Almost half(47%) of the tropical forests are in close effective proximity to anthropogenic influences and only 12% of their area can be considered isolated from anthropogenic influences.The values for the temperate forests are 23% and 29% respectively.Anthropogenic pressure in the immediate vicinity of anthropogenic activities is much higher in the tropical forests(75 in a scale 0-100) than in the temperate forests(30).When considering these results jointly,the tropical forests,and more specifically,the tropical evergreen forests and tropical dry deciduous forests are under the greatest pressure and risks of degradation.     

Variation in vegetation structure and soil properties related to land use history of old-growth and secondary tropical dry forests in northwestern Mexico

The objective of this study was to compare the vegetation structure and soil properties among old-growth tropical dry forests representing three categories of grazing intensity by cattle (light, moderate and heavy grazing) and a category of 20–30-yr-old secondary forest experiencing occasional grazing in a locality in northwestern Mexico. Within each forest type, three 0.1 ha plots located in different grazing ranges (“potreros”) were used as replicates. All woody plants (stem ≥ 2.0 cm diameter at 1.30 m height, DBH) were identified and measured in each plot. Mean basal area and above-ground biomass (AGB) were significantly higher in the moderately grazed old-growth forest. Species density was significantly lower in the secondary forest, where a leguminous tree species was dominant. Accumulation of AGB after 20–30 yr of secondary forest recovery accounted for 43% of the old-growth forest AGB. Soil properties varied among forest categories but did not follow a consistent pattern: mean total N and organic matter content were highest in the old-growth forest with moderate grazing; cation exchange capacity (CEC) was similar among the three old-growth forests categories, but it was significantly lower in the secondary forest compared to the old-growth forest with low grazing. Canonical Correspondence Analysis showed that CEC was highly correlated with the actual species distribution in the study area, especially with Acacia cochliacantha the dominant species of the secondary forest category. Resprouting capacity of the persisting species in the old-growth forests experiencing chronic disturbance could have contributed to the maintenance of some of the structural characteristics of a mature forest. Tropical secondary forests seem to accumulate AGB relatively fast, reflecting their potential for carbon storage and provision for other ecosystem services; therefore, they deserve urgent protection measures.     

The forest vegetation and its differentiation under disturbance in a temperate mountain, China

Composition and structure of the main forest types, as well as the species changes under disturbance, were described as the representation of the forest vegetation in the north slope of Changbai mountain, northeast China. There were 3 forest zones from 600 m to 2,000 m asl, (1) broad-leaved-conifer mixed forest zone, 600–1,100 m asl, dominated byPinus koraiensis, Tilia amurensis, Acer mono, Ulmus japonica, (2) coniferous forest zone, 1,100–1,700 m asl, dominated byPicea jezoensis var.komarovii, P. koraiensis, Abies nephrolepis, and (3)Betula ermanii forest zone, 1,700–2,000 m asl, dominated byBetula ermanii, except for the east slope which was occupied byLarix olgensis. The evergreen component increased with elevation up to the upper limit of the coniferous forest zone (1,700 m), but disappeared in theB. ermanii zone. Species richness was significantly related to elevation. Towards higher elevation, the lapse rate of species-number was 1.6 species per 100 m, and it was only one species near the timberline. Species richness was reduced sharply under intensive disturbance, such as clear cutting, windfalletc. The species diversity was very low in the early stage of succession, and high in the later.     

Population structure and regeneration patterns of tree species in climate-sensitive subalpine forests of Indian western Himalaya

The population structure of tree species has been explored in order to elucidate regeneration potential of the subalpine forests of Indian western Himalaya. For this study, the subalpine forest area was divided into three strata, i.e., lower altitude （〈3000 m）; mid-altitude （3000-3200 m）; and high altitude （〉3200m）. Considering the major compositional attributes, an increase in altitude came with a significant decline in tree density and the total basal area for all the sites. However, no such clear trends were observed for recruits （i.e., seedlings and saplings）. Seedling density did not exhibit uniform patterns for sites and altitude strata. In general, overall seedling density was greater at the Pindari site compared to the Lata and Tungnath sites. By comparison, significant variation in seedling density along the altitude strata was recorded for the Tungnath and Pindari sites only. Likewise, sapling density patterns varied across the sites and altitude strata, and significant variation in sapling density along the altitude strata was recorded only for the Lata site. At the Pin- daft site, the continuous increase in sapling density along with increasing altitude was revealing. The Pindari forests of exhibited expanding population structure. In contrast, greater accumulation of individuals in the sapling class and sharp decline toward both higher tree classes and lower seedling classes was generally apparent for the Lata and Tungnath sites. This indicates that the replacement in tree size classes from sapling stage is not proportional and the population may decline in the long-term. Considerable variation in patterns of forest and dominant species popula- tion structure were evident across altitude strata. But in all cases irrespective of sites, we found growth at the high-altitude stratum, in the form of entire forests or dominant species. This trend deserves further investigation to explore its relevance under changing climate scenarios.     

Patterns of litterfall and return of nutrients across anthropogenic disturbance gradients in three subalpine forests of west Himalaya, India

The study was conducted to improve our understanding of the effects of forest disturbance on litterfall and patterns of nutrient return in three subalpine forest ecosystems (i.e. Betula utilis-dominated, Abies pindrow-dominated, and Acer mixed broadleaf) of Indian west Himalaya. Total litterfall (t ha⁻¹ yr⁻¹) ranged between 2.6–3.6 and 2.1–2.6 for pristine and degraded stands, respectively. Whereas total litterfall decrease from pristine to degraded stand was about 25–30% in B. utilis and Acer mixed-broadleaf forests, the level of disturbance did not affect total litterfall in A. pindrow (coniferous) forest. Nutrient (N, P, and K) concentrations in litter components of the forests studied also varied across forest types and disturbance intensities. For pristine stands, among all the forests, return of total nutrients via litterfall was higher. The study revealed that patterns of litterfall and nutrient return in the forests studied were sensitive to intensity of disturbance, although sensitivity varied among forest types and nutrient contents. Increased intensity of disturbance greatly affected the total annual amount of nutrient return in broadleaf forests. Maximum impact was recorded in B. utilis forest with a significant decline in nutrient return from pristine to degraded stands (i.e. 64% for N, 38% for P, and 67% for K). Corresponding values for decline in Acer mixed forest were 17, 13, and 33% for N, P, and K, respectively, whereas in A. Pindrow forest N return was 15% higher and P return was 33% lower. This study indicates that the litterfall and litter nutrient concentrations in these forests are sensitive to the intensity of disturbance, which affects the amount of nutrient return. This will have a strong bearing on forest nutrient cycling.     

Effect of livestock grazing and human uses on herbaceous species diversity in oriental beech （Fagus orientalis Lipsky） forests,Guilan, Masal,northern Iran

Plant diversity plays key ecological roles in forest ecosystems, including influencing succession, resilience and nutrient cycling. This study was conducted to investigate the effect of livestock grazing and human uses on herbaceous species diversity. We surveyed 50 ha of protected area and 50 ha of unprotected area to evaluate herbaceous species diversity in oriental beech （Fagus orientalis Lipsky） forests in northern Iran. We calculated and compared three indices each of diversity and evenness, and species richness between the two areas. Herbaceous cover was higher in the unprotected area while leaf litter depth and tree canopy cover were higher in the protected area. The diversity indices, H （Shan- non-Wiener index ）, N~ （McArthur index）, N2 （Hill＇s index）, EQ （Modified Nee index）, E,ar （Smith-Wilson index）, E5 （modified index of Hill） and R=S （species richness） and species richness R=S were greater in the protected area than in the unprotected area, suggesting that protection from grazing results in increased numbers of plants and species. The effect of land protection on plant diversity was more pronounced for evenness than for species richness and the positive correlation between diversity and evenness indices was higher than that between diversity and richness.     

Plant diversity, population structure, and regeneration status in disturbed tropical forests in Assam, northeast India

We investigated the plant population structure and the phy-tosociological and regeneration status in two disturbed tropical forests in Assam Province, the Hojai Reserve Forest and Kumorakata Reserve Fo...     

火干扰对天然红松林结构和演替过程的影响

Investigations on charcoal in the soil, fire-scarred trees, stand composition, forest structure as well as regeneration status were carried out in the natural broad-leaved/Korean pine (Pinus koraiensis) forest after fire disturbance at Liangshui Nature Reserve on the mid-north of Xiaoxing‘an Mountains from 1990 to 1992, and the ecological effects of fire disturbance on the formation and succession of this kind of forest were analyzed according to the survey results. The average depth of charcoal in the soil was related to the timing of the fire. According to the characteristic of fire-scarred trees, the dynamic map of the fire behavior was drawn onto the topographic map. It showed that the dimension and extent of the fire disturbance was closely related with site conditions. Fire disturbance only led to a significant difference in stand composition and diameter class structurefor the stands at different locations, rather than completely destroying the forest. After fire disturbance, the horizontal community structure was a mosaic of different patches, which were made up of different deciduous species or different sizes of Korean pines, and the succession trend of each patch was also different. In the sites with the heavy fire disturbance, the intolerant hardwood species were dominant, and there were a large number of regenerative Korean pine saplings under the canopy. In the moderate -disturbed sites, the tolerant hardwood species were dominant, and a small number of large size Korean pines still survived. In the light-disturbed sites, large size Korean pines were dominant.     

台风对天童地区常绿阔叶林干扰的一般特征

调查分析了天童国家森林公园常绿阔叶林受2005年“麦莎”和“卡努”两次强台风干扰后形成的倒木和林隙的现状特征，结果表明，在调查的111株倒木中共有19个物种，其中以木荷和栲树所占的比例最大；所有倒木中以掘根方式形成的倒木所占比例最大，且主要发生在林道旁和林内沟谷边；倒木径级多集中在50cm以下，以10-30cm区间所占的比例最大，高度的分布范围集中在10-20m；在林内所形成的10个林隙中，以小林隙型为主，面积较大的林隙都集中在沟谷边。     

人为干扰对独叶草生长的影响研究

独叶草Kingdonia uniflora Balfourf.et W. W. Smith是我国特有的单种属植物,也是国家一级重点保护植物。为了探讨人为干扰对独叶草生长的影响,我们在陕西省太白山下板寺至上板寺设置样方,对生境完全遭受破坏和无破坏两种条件下独叶草根状茎生长情况进行了比较研究。结果表明:人为破坏的环境下独叶草根状茎长度较短、年生长长度也较短,其生长状况受到影响,生境的破坏是独叶草致濒的原因之一。     

Effect of habitat and grazing on the regeneration of wild Agave cupreata in Guerrero, Mexico

Agave cupreata is harvested from tropical dry forests, oak forests, and other habitats by rural communities in the Chilapa region of Guerrero, Mexico to make mescal, a traditional and culturally important liquor. Local management systems use various techniques to regulate Agave harvest and encourage regeneration, including the exclusion of cattle. This study examines the impacts of cattle exclusion and of the different habitat types on the population structure and density of A. cupreata. Sampling was conducted in pastures, oak forest, tropical dry forest, and mixed oak-tropical dry forest using 54 transects of 1000 m², where Agave was counted by size-class and measurements were taken of the vegetation and physical environment. Transects were divided between areas with cattle present and cattle excluded in all four habitats except for oak forest, where all areas were open to cattle. Agave density per 1000 m² was highest in pasture (148 ± 5, mean ± SE), followed by oak forest (100 ± 4), tropical dry forest (88 ± 5) and mixed oak-dry forest (81 ± 2). The size-class structures of Agave populations were also significantly different between vegetation types, with oak forest supporting higher seedling densities but lower numbers of juveniles. A regression subset selection algorithm showed that one of the most important factors influencing Agave populations was the presence of cattle, which can reduce densities by trampling and grazing on seedlings and floral stalks. Cattle presence significantly lowered Agave densities in the smaller size classes in all vegetation types but did not significantly alter size-class structure. Total Agave density per 1000 m² was significantly higher in transects where cattle were absent (148 ± 4) than where cattle were present (81 ± 1). In all areas sampled, the high number of juveniles relative to other size-classes suggests that Agave populations are successfully regenerating in the Chilapa region, and the higher Agave densities in fenced areas suggest that local management techniques are effectively increasing Agave yields. These results highlight the potential for sustainable management of Agave to conserve forest habitats while also providing important income from mescal to local communities in the region.     

Forest structure, diversity and regeneration in unburnt and burnt Anogeissus latifolia forests in Garhwal Himalayas

The present study was carried out at two different gradients of unburnt and burnt Anogeissus latifolia forest sites in the Garhwal region, India. At each gradient, the unburnt and burnt forest sites were further categorized into three different elevations, i.e., lower (700 m), middle (850 m) and upper (1000 m). At each elevation, the density of trees, saplings and seedlings was higher at the unburnt sites except for trees at the upper elevation which was higher at the burnt sites. The total basal area of each layer of forest was also higher at the unburnt sites. The study revealed that the lower number of saplings and seedlings at the burnt forest sites might be due to the effect of fire. Most trees in the lower dbh classes were affected by forest fire at the burnt sites which reduced the total density and total basal area of the trees compared to the unburnt sites. The diversity of trees increased with increasing elevation. However, the diversity of saplings and seedlings reduced with increasing elevation.     

广西太平狮山国家森林公园旅游资源评价与规划设计

对广西太平狮山国家森林公园的资源特色、资源等级以及风景质量的分析评价的基础上,提出该森林公园规划的思路和规划方案。     

广州城区公园风景游憩林径级和高度级结构分布

【目的】探明广州风景游憩林群落结构现状以及存在的问题,进一步为城市风景游憩林群落结构调整和配置优化提供理论依据。【方法】以900 m^2样方为单元分别在广州发展公园风景游憩林群落样地设置样方15个,华南农业大学风景游憩林群落样地设置样方25个,火炉山森林公园风景游憩林群落样地设置样方20个,采用群落生态学的方法,研究了不同生态位风景游憩林径级和高度级结构分布。【结果】1)3个样地风景游憩林径级结构呈现一定差异:广州发展公园以大、中径级乔木占绝对优势,华南农业大学样地风景游憩林小径级乔木相对优势明显,火炉山样地风景游憩林群落以中、小径级乔木占绝对优势。2)根据群落中个体的胸径和树高呈现不同的相关关系表明:广州发展公园样地风景游憩林大径级树木开始出现衰退现象;华南农业大学样地风景游憩林由于存在大量小径级的速生树种,导致胸径—树高曲线在初期迅速增高;火炉山样地风景游憩林结构配置拟自然化,胸径—树高曲线增长较为平稳。【结论】根据高度级比重、相对频度和分布均匀度分析结果得出:广州发展公园样地风景游憩林中、大高度级树木比重较大,且分布更为集中,华南农业大学样地风景游憩林的小、中高度级的树木所占比重较高,小高度级树木分布更为集中;火炉山样地风景游憩林小高度级比重,且分布更为集中。建议通过人工择伐、补植特定树种的方式,调控城市风景游憩林群落的径级和高度级结构分布,促进风景游憩林的逐步稳定。     

Post-1935 changes in forest vegetation of Grand Canyon National Park, Arizona, USA: Part 2—Mixed conifer, spruce-fir, and quaking aspen forests

This study examined changes in never-harvested mixed conifer (MCF), spruce-fir (SFF), and quaking aspen forests (QAF) in Grand Canyon National Park (GCNP), Arizona, USA based on repeat sampling of two sets of vegetation study plots, one originally sampled in 1935 and the other in 1984. The 1935 plots are the earliest-known, sample-intensive, quantitative documentation of forest vegetation over a Southwest USA landscape. Findings documented that previously described increases in densities and basal areas attributed to fire exclusion were followed by decreases in 1935-2004 and 1984-2005. Decreases in MCF were attributable primarily to quaking aspen (Populus tremuloides) and white fir (Abies concolor), but there were differences between dry-mesic and moist-mesic MCF subtypes. Decreases in SFF were attributable to quaking aspen, spruce (Picea engelmannii + Picea pungens), and subalpine fir (Abies lasiocarpa). Decreases in QAF resulted from the loss of quaking aspen during succession. Changes in ponderosa pine forest (PPF) are described in a parallel paper (Vankat, J.L., 2011. Post-1935 changes in forest vegetation of Grand Canyon National Park, Arizona, USA: part 1 - ponderosa pine forest. Forest Ecology and Management 261, 309-325). Graphical synthesis of historical and modern MCF data sets for GCNP indicated tree densities and basal areas increased from the late 19th to the mid 20th century and then decreased to the 21st century. Changes began earlier, occurred more rapidly, and/or were larger at higher elevation. Plot data showed that basal area decreased earlier and/or more rapidly than density and that decreases from 1935 to 2004 resulted in convergence among MCF, SFF, and PPF. If GCNP coniferous forests are trending toward conditions present before fire exclusion, this implies density and basal area were more similar among these forests in the late 19th century than in 1935. Changes in MCF and SFF can be placed in a general framework of forest accretion, inflection, and recession in which increases in tree density and basal area are followed by an inflection point and decreases. Accretion was triggered by the exogenous factor of fire exclusion, and inflection and recession apparently were driven by the endogenous factor of density-dependent mortality combined with exogenous factors such as climate. Although the decreases in density and basal area could be unique to GCNP, it is likely that the historical study plots provided a unique opportunity to quantitatively determine forest trends since 1935. This documentation of post-1935 decreases in MCF and SFF densities and basal areas indicates a shift in perspective on Southwestern forests is needed.     

Effect of intervention and type of forest management on quality and quantity characteristics of dead wood in managed and reserve forests: A case study

We compared the dead wood (DW) conditions of Cheshmeh-sar forest and Sardab forest with different management history,including reserve forest and harvested forest. The First forest took 100% inventory from all the available DW. Also dead trees were compared interms of species, shape, location and quality of fracture in both forests.Volumes of dead wood in Cheshmeh-sar and Sardab forests were 207.47and 142.74 m3, respectively. Due to this significant difference, impact onthe management level was determined. In Cheshmeh-sar forest, 42% ofdead trees were standing and 58% were fallen type while in Sardab forest 38.6% were standing and 61.4% fallen. But the difference was not statistically significant between them (p = 0.0587). In terms of quality, dead trees of hard, soft and hollow had the highest frequency, respectively.However, 71.5% of DW was seen as hard dead in Cheshmeh-sar forestwhile hard dead trees in Sardab forests were 54.2%. Soft quality degree ofdead trees which formed in Cheshmeh-sar and Sardab forest were calculated as 26.6% and 43.4% respectively. Also 30% of the dead trees of Sardab forest were eradicated while in Cheshmeh-sar this amount was reduced to 12%. Due to this significant difference ((Р=0/018), it is concluded that the type of management and human interference are affecting the quality of dead trees and makes us to think the human interferences could effect on the ecosystem of touched forests.     

Hurricane disturbances,tree diversity,and succession in North Carolina Piedmont forests,USA

Windthrow plays a critical role in maintaining species diversity in temperate forests. Do large-scale strong wind events(i.e., tropical cyclones, including hurricanes,typhoons and severe cyclonic storms) increase tree diversity in severely damaged forest areas? Do hurricanes(tropical cyclones that occurs in the Atlantic Ocean and northeastern Pacific Ocean) lead to altered relative abundance of shade-tolerant and shade-intolerant species? Did historic hurricanes alter the succession trajectory of the damaged forests? We used nearly 70-year tree demographic data to assess the effects of two major hurricanes on woody species diversity in Piedmont forests, North Carolina, USA. Species richness(S) and Shannon–Wiener's diversity index(H') were used to evaluate the changes in tree diversity. The changes in composition were assessed with Nonmetric Multidimensional Scaling. The pre-hurricane successional phase can strongly influence both the damage severity and subsequent responses. Although there is often an immediate drop in diversity following a hurricane, understory tree diversity quickly increases to levels that exceed those prior to the disturbance. This leads to an increase in diversity in stands that were substantially damaged. Hurricanes significantly decrease the dominance of shade-intolerant canopy species while increasing preestablished, more shade-tolerant species. We conclude that large, and infrequent hurricanes help to maintain local tree diversity, but also accelerate the increase in dominance of understory species such as red maple and beech.     

中国热带次生林分布、类型与面积研究

热带林的保护问题已受到世界各国的高度重视,由于占世界热带林面积约三分之一的热带次生林,其经济和生态效益通常较差,处于相对被忽视的状态,因此也往往被进一步破坏。将次生林经营纳入可持续经营的轨道,是实现热带林可持续经营目标的重要战略。通过对中国热带森林研究、经营和统计资料的分析,结合本项目实施过程的实地调研取得的结果,文章对中国热带地区次生林分布、面积和类型作了阐述。热带森林主要分布在海南、广东、广西、云南、台湾,以及福建和西藏的部分地区,包括124个县市的全部和50个县市的部分地区。据可认可的资料统计,中国热带林地面积（不含台湾省）约1125．66万hm^2。其中有林地面积1074．49万hm^2,次生林面积544万hm^2。次生林占热带地区林地面积的48．33％,占有林地总面积的50．63％。中国热带林地和次生林的实际数字估计要比这一数值大6％以上,因为中国这几年高度重视林业建设,森林植被特别是热带森林植被恢复得很快,林地和次生林一直在不断增加。热带森林类型主要有：热带雨林（包括湿润雨林、山地雨林）;热带季雨林（包括半常绿季雨林、落叶季雨林、石灰岩季雨林）;南海珊瑚岛植被;海岸红树林等。从森林经理的角度,中国热带次生林的类型可分为：（1）次生阔叶林,包括次生常绿阔叶雨林、次生季雨林和次生季风常绿阔叶林;（2）次生灌木林;（3）次生针叶林;（4）次生红树林及次生珊瑚岛林等四大类型。     

The effects of selective logging on stand structure and the regeneration of subboreal forests in Hokkaido, northern Japan

We investigated the effects of selective logging on stand structure and regeneration in selectively logged subboreal forests in Taisetsuzan National Park in Hokkaido in northern Japan. The basal area decreased and the size structure of trees altered in the stands studied due to repeated, intense selective logging, in which larger trees were cut down as a priority. Sapling density in the stands was much lower than that in primary forests. In the simple and multiple regression analyses that were used to estimate the effects of selective logging on sapling density, sapling density had a significant positive correlation with tree density and had little correlation with the density of logged stumps or the height ofSasa (dwarf bamboo) growing on the forest floor. These results suggest that the establishment sites around canopy trees influenced the establishment of saplings, rather than the gaps caused by selective logging. However, both the coefficient of determination and the standardized partial regression coefficient of multiple regression analysis were higher for the stand with a dense cover ofSasa than for the stand with a sparse cover ofSasa. Thus, the success of regenerating forests with selective logging depends on both the site of advanced regeneration and the light conditions that regulate growth.     

Limited native plant regeneration in novel, exotic-dominated forests on Hawai’i

Ecological invasions are a major driver of global environmental change. When invasions are frequent and prolonged, exotic species can become dominant and ultimately create novel ecosystem types. These ecosystems are now widespread globally. Recent evidence from Puerto Rico suggests that exotic-dominated forests can provide suitable regeneration sites for native species and promote native species abundance, but this pattern has been little explored elsewhere. We surveyed 46 sites in Hawai’i to determine whether native species occurred in the understories of exotic-dominated forests. Native trees smaller than 10 cm in diameter were absent in 28 of the 46 sites and rare in the others. Natives were never the dominant understory species; in fact, they accounted for less than 10% of understory basal area at all but six sites, and less than 4% on average. Sites with native species in the understory tended to be on young lava substrate lacking human disturbance, and were mostly located close to intact, native-dominated forest stands. Even where we found some native species, however, most were survivors of past exotic encroachment into native forest, rather than products of active recolonization by native species. In contrast with successional trajectories in Puerto Rico, Hawaii's exotic-dominated forests can emerge, via invasion, without human disturbance and native Hawaiian plants are largely unable to colonize them once they appear. We suggest that a wide diversity of growth strategies among the exotic species on Hawai’i may limit the opportunities for native plants to colonize exotic-dominated forests.