Native woody species regeneration in exotic tree plantations at Munessa-Shashemene Forest,southern Ethiopia

Regeneration of native woody species was studied in the plantations and the adjacent natural forest at Munessa-Shashemene Forest Project Area, Ethiopia. The aim of the study was to test the hypothesis that tree plantations foster regeneration of native woody species. A total of 60 plots, having 10 × 10 m area each, were studied in monoculture plantations of 4 exotic species (Cupressus lusitanica, Eucalyptus globulus, E. saligna, Pinus patula) and an adjacent natural forest. Ages of the plantations ranged between 9 and 28 years. Soil seed bank analysis was also undertaken from soil samples collected in each of the 60 plots to examine the similarity between the soil seed flora and aboveground vegetation. A total of 56 naturally regenerated woody species were recorded beneath all plantation stands with densities ranging between 2300 and 18650 individuals / ha in different stands. There was a significant difference among plantation stands with regard to understorey density (standard deviation: 4836 ± 1341). Vegetation diversity was assessed through analyses of floristic composition, species richness and abundance. Generally, seedling populations were the most abundant components of the regeneration in most of the plantation stands, forming 68 % of the total regeneration count in all stands. A total of 77 plant species represented by 44 herbs, 13 woody species, 8 grasses and 12 unidentified species were recorded in the soil seed bank from all stands. Similarity between the soil seed bank and aboveground flora was very low implying that the role of soil seed banks is negligible rather dispersal plays an important role in the process of regeneration. These results support the concept that forest plantations can foster the regeneration of native woody species, thereby increasing biological diversity, provided that there are seed sources in the vicinity of the plantations.     

Tree regeneration in gap-understory mosaics in a subtropical Shorea robusta(Sal) forest

Spatial variation in tree-regeneration density is attributed to the specialization of tree species to light availability for germination and growth. Light availability,in turn, varies across the gap-understorey mosaic. Canopy gaps provide an important habitat for the regeneration of tree species that would otherwise be suppressed in the understory. In subtropical forests, there is still a knowledge-gap relating to how canopy disturbances influence tree-regeneration patterns at local scale, and if they disproportionately favor regeneration of certain species. We aim to analyze whether canopy gaps promote tree regeneration, and tree species are specialized to gaps or understory for germination and growth. We sampled vegetation in 128 plots(0.01 ha), equally distributed in gaps and below canopy, in two subtropical Shorea robusta Gaertn.(Sal) forests in Nepal, recording the number of tree seedlings and saplings in each plot. We compared the regeneration density of seedlings and saplings separately between gaps and the understorey. The mean densities of seedlings and saplings were higher in the gaps at both sites;although there was no difference in the seedling density of the majority of the species between the habitats. No species were confined to either gap or understorey at the seedling stage. We conclude that gaps are not critical for the germination of tree species in Sal forests but these are an important habitat for enabling seedlings to survive into saplings. The classification of trees into regeneration guilds mainly based on germination does not apply to the majority of tree species in subtropical Sal forests. Our results reaffirm that gap creation promotes tree regeneration by favouring seedling survival and growth and can influence forest management for conservation, as well as for plantations.     

Seed supply and the regeneration potential for plantations and shrubland in southern China

Assessing the characteristics of seed supply will be vital to better understand the dynamics of forest regeneration. In this study, we surveyed the aboveground vegetation, the seed rain, the seed bank, and natural seedling emergence in four typical 24-year-old plantations (eucalyptus, mixed-native, mixed-legume, and mixed-conifer) and a naturally successioned shrubland in southern China. The dominant species in the understory were similar among the five plant communities. The seed rain and the seed bank were dominated by shrubs and herbs but indigenous tree species were rare. Species that were common to all five-plant communities represented a great proportion of the seeds in the seed rain and seed bank. The seed rain consisted mostly of seeds derived from the local plant community. Seed abundance was greater in the seed bank than in the seed rain, and species richness was greater in the seed bank and in the corresponding plant community than in the seed rain. Species composition similarity between the seed rain, the seed bank, and the aboveground vegetation was low, because the seed rain contained much fewer species, and the seed bank and aboveground vegetation contained many different species, respectively. These findings indicate that both the seed rain and the seed bank play important roles in providing seeds for plant recruitment in the understory, but the seed bank contributes more than the current seed rain to the diversity of recruited plants. The current plant community has little impact on the qualitative composition of the seed rain and seed bank. Based on these data, it appears that succession to the desired zonal, mature forest community is unlikely to result from seeds in the seed rain or seed bank. Lack of seed availability of desired zonal mature forest species is the main bottleneck currently limiting succession in the plantations. Reintroduction of late-successional species could facilitate the desired succession.     

Soil seed banks in four 22-year-old plantations in South China: Implications for restoration

To better understand the potentials of the soil seed banks in facilitating succession towards a more natural forest of native tree species, we quantified the size and composition of the soil seed banks in established plantations in South China. The seed banks were from four typical 22-year-old plantations, i.e., legume, mixed-conifer, mixed-native, and Eucalyptus overstory species. Species diversity in the seed banks was low, and the vegetation species differed from those found in the seed bank in each plantation. A total of 1211 seedlings belonging to eight species emerged in a seedling germination assay, among which Cyrtococcum patens was most abundant. All species detected were shrubs and herbs, and no viable indigenous tree seeds were found in soil samples. Size and species composition of the seed banks might be related to the overstory species compositions of the established plantations. The seed bank density in soils was highest in the mixed-conifer plantation followed by Eucalyptus, mixed-native, and legume plantations. Species richness among the seed banks of plantations was ranked as follows: Eucalyptus > mixed-conifer > mixed-native = legume. The results indicated that the soil seed banks of the current plantations are ineffective in regenerating the former communities after human disturbances. Particularly, the absence of indigenous tree species seeds in the seed banks would limit regeneration and probably contribute to arrested succession at the pioneer community stage. It would appear from these data that the soil seed banks under the current plantations should not be considered as a useful tool leading the succession to more natural stages. Introduction of target indigenous species by artificial seeding or seedling planting should be considered to accelerate forest regeneration.     

凉风坳亚热带次生常绿阔叶林土壤种子库和种子雨的特征研究

选择四川省沐川县凉风坳亚热带次生常绿阔叶林为研究对象,在2004年5月、2004年12月和2005年5月对其林下土壤种子库、种子雨以及种子天然萌发状况等方面进行系统调查及分析研究。结果显示,种子下落前后土壤种子库储量,变动为643.2～889.2粒.m-2,物种和种子密度多年生草本物种均占优势。天然林土壤种子库Shannon-Wiener指数均在2004年5月最大,2004年12月次之,2005年5月最小;Simpson指数却和Shannon-Wiener指数H＇的变化趋势相反;Pielou均匀度指数在2004年12月有所降低,此后又升高。种子均呈明显垂直分布,其中0～2 cm土层种子数量最多,其次是枯枝落叶层,其数量随着土层加深而降低。土壤种子库年输入活力种子142.3粒.m-2,年输出活力种子268.9粒.m-2,动物取食是造成种子损失的主要原因。对照人工林土壤种子库物种和密度均低于天然林地;种子库与地上植被物种相似性系数,人工林较高,而天然次生常绿阔叶林较低。     

云南绿春县天然次生林和4种人工林树冠层蚂蚁群落多样性

[目的]探讨天然次生林和人工林及人工林树种选择对树冠层蚂蚁群落多样性的影响。[方法]运用树栖蚂蚁陷阱法调查云南省绿春县天然次生林和4种人工林的树冠层蚂蚁群落、植物多样性及植物垂直密度变化。[结果](1)共采集蚂蚁标本17 998头,隶属于6亚科29属68种。(2)树冠层蚂蚁多度:紫胶林-玉米混农林紫胶林桉树林橡胶林天然次生林。(3)树冠层蚂蚁丰富度:紫胶林-玉米混农林紫胶林天然次生林橡胶林桉树林。(4)树冠层蚂蚁ACE估计值:紫胶林-玉米混农林紫胶林天然次生林桉树林橡胶林。(5)树冠层蚂蚁多度和丰富度与枯落物盖度、300 cm处垂直密度和乔木郁闭度呈显著或极显著负相关,而与植物盖度显著正相关;ACE估计值与枯落物盖度、草本植物盖度和乔木郁闭度显著负相关,与175 199.9 cm区段内垂直密度显著正相关。[结论]人工林对蚂蚁多样性保护有一定积极作用,尤其选择乡土树种保护效果更显著,对人工林进行合理的管理有利于保护生物多样性。     

肯尼亚泰塔山区东部弧形山云层森林的外来森林与本土森林树种多样性、丰富度和相似性比较(英文)

对肯尼亚东南部泰塔(Taita)山区的3片破碎的森林进行了树种生物多样性评估,比较外来的松树、柏树、桉树人工林的物种多样性以及外来树种森林和本土森林物种多样性。研究地点为Ngangao(120 hm2)、Chawia(86 hm2)和Mbololo(185 hm2)。采用Y型设计设立32个样区,包含65个小样区。按树种记录每个小样区胸高直径5cm和5cm以上的幼树,同时也记录了各树木的更新情况(幼苗和树苗)。用 Shannon-weiner指数计算了物种的多样性和均匀度。导处的 Shannon指数被进一步转化成有效的数值,用于展示物种多样性的差别幅度。为了评估物种多样性的差别,进行单因素方差分析,为了分离均值,分别用Tukey HSD法和Duncan检测法验证偶数和奇数样品。采用Jaccard相似指数评估物种的类似性。共有58个树种的林木密度变化在每公顷10到2000棵树之间。森林类型和立地之间的物种多样性存在显著差异。本地森林的物种多样性比外来树种森林高;Chawia立地的物种多样性比Nganga和Mbololo立地高,且更新的树种数量也比其他2个立地多,包括野柠檬木(Xymalos monospora)、黑皮密花木(Rapanea melanophloeos)、和(几内亚蒲桃(Syzygium guineense),这些树种具有低干扰属性。这些发现说明,本地森林物种多样性比较高,正如热带地区所预期。Chawia立地的物种多样性高说明此地经历干扰比其他2个立地大。在Chawia地区发现有低干扰树种更新,说明有长期土壤种子库的存在。在Nganga和Mbololo地区发现的外来树种样地上的更新较差情况,可能是缺少种子库所致,因为很多人工林是造在裸地上(如Nganga地区),或者是因为某些树种固有的生理特性(相生相克)抑制了其他树种的更新。     

Potential use of pine plantations to restore native forests in a highly fragmented river basin

? In forests, the substitution of broadleaf species by conifers can reduce biodiversity because coniferous forests generally provide less diverse vascular understories than broadleaf forests. However, in some cases, former pine plantations might be useful for restoring native forests. We compared plant species composition on the plot scale in natural beech and mixed oak forests with that in plantations of Pinus radiata. Links between plant diversity and landscape parameters (patch size, fractal dimension and distance to the nearest patch of the same type) were investigated.

? The objective of this study was to evaluate the use of pine plantations for restoring native diversity in a zone where native forests are very fragmented.

? Similar to oak forests, plant diversity in pine plantations was high, mainly due to the presence of generalist species. Some species characteristic of oak forests also appeared in pine plantations, suggesting the onset of natural forest regeneration.

? These results suggest that pine plantations could be used to promote natural regeneration of original oak forests. Moreover, residual native stands should be conserved as important sources of native species and their seeds.

     

Response of fungal and plant communities to management-induced overstorey changes in montane forests of the Western Carpathians

The effect of forest management on biodiversity is a crucial issue for sustainable forestry and nature conservation. However, the ways in which management affects macrofungal and plant communities and diversity of mountain temperate forests still remain poorly understood. We performed a random sampling stratified by stand age and stand type on the sites of temperate montane fir–beech forests. Diversity of macrofungi and the vascular plant understorey in beech- and spruce-dominated managed stands was investigated and compared to primeval forests located in the Po?ana Biosphere Reserve, Western Carpathians. Both the vascular plant and the macrofungal communities were altered by management, and the response of the macrofungal species (especially wood-inhabiting fungi) was more pronounced in terms of species composition change. Species turnover evaluation seems to be an important tool of forest natural status assessment, because alpha diversity did not change as much as species composition. Certain species of Carpathian primeval forests were confirmed as good indicators for natural forest change; others were proposed. Species pool and mean number of species per plot were the highest in unmanaged fir–beech forests, and species diversity significantly decreased in spruce plantations. The number of species decreased significantly due to the change of canopy tree species composition only in the macrofungal communities. As an outcome for forest management, we recommend keeping mixed forests involving all natural tree species and providing at least a minimal amount of dead wood necessary for wood-inhabiting organisms and leaving some area of unmanaged natural forests within complexes of managed stands.     

Understorey vegetation in young naturally regenerated and planted birch (Betula spp.) stands on abandoned agricultural land

The abandonment of agricultural lands in Northern and Eastern Europe increases the area covered by first generation forests, which are either formed as an outcome of secondary succession or established as plantations. However, questions remain as to how these new stands develop and what kind of species they favour, which in turn has impacts on their ecological and economical value. Our aim was to compare understorey vascular plant and bryophyte vegetation characteristics between naturally regenerated and planted birch stands on abandoned agricultural sites in Estonia, focusing on the aspects of species richness and forest understorey recovery. Species richness and diversity of vascular plants were similar in both stand types but the number of forest vascular plant species was significantly higher in naturally regenerated stands. The bryophyte layer of naturally regenerated stands had a higher species richness, diversity, and number of forest bryophyte species. The higher number of forest vascular plant and bryophyte species in naturally regenerated stands can be explained by the longer undisturbed succession period. The recovery of the forest understorey was unaffected by former agricultural land use (crop field or grassland). The influence of soil properties on the recovery of the forest understorey was not detected, but the number of vascular plant species that grow in forests as well as in grasslands was negatively correlated with distance from forest. Overall, understorey vegetation of natural and planted birch stands did not reveal substantial differences. However, in the case of vigorous natural birch regeneration in the vicinity of forest land, unassisted reforestation should be favoured.     

Restoration of dry tropical forests in Central America: A review of pattern and process

Much information on restoration and management exists for wet tropical forests of Central America but comparatively little work has been done in the dry forests of this region. Such information is critical for reforestation efforts that are now occurring throughout Central America. This paper describes processes of degradation due to land use and provides a conceptual framework for the restoration of dry tropical forest. Most of this forest type was initially harvested for timber and then cleared for cattle in the last century (1930-1970). Only 1.7% remains largely restricted to infertile soils and remote areas on the Pacific coastal side of Panama, Costa Rica, Nicaragua and Mexico. These cleared areas are again in a state of transition due to a combination of decreasing land productivity, and land speculation for tourism development. Some farms have been sold to new landowners who are interested in reforesting to increase biodiversity and forest cover. Attempts have therefore been made to reforest by protecting the land from fire and cattle, by supplementing natural regrowth with enrichment planting, or through use of tree plantations. Experimental studies have demonstrated the ability of these lands to grow back to forests because of native species ability to sprout after cutting, and the capacity of remnant trees in field and riparian zones to provide seeds and to moderate edge environment for seed germination and seedling establishment. However, research also shows that on sites with long histories of land clearance, species diversity will remain low with functional groups missing unless some active management occurs. Under-planting with late-successional native tree species can add structure and diversity; enrichment planting with large-fruited shade-intolerant species can initiate new islands of more diverse regeneration beneath their canopies; and plantings of fast-growing, nitrogen-fixing trees that provide light canopy shade can moderate the environment below, promoting regeneration establishment of late-successional species. Plantations are the only option for lands that have lost almost all remnants of native forest, and where soils and vegetation have changed to new states of structure and function. Conversion of pastures to tree plantations that can facilitate natural regeneration beneath them is appropriate when pastures are prone to fire and/or lack immediate seed sources nearby. After the grasses have been shaded out, natural recruitment can slowly occur over a 10-15 years period. Under-planting of shade-tolerant late-successional species can supplement species composition and structure.     

Understory plant diversity assessment of <Emphasis Type="Italic">Eucalyptus</Emphasis> plantations over three vegetation types in Yunnan,China

Biodiversity in managed plantations has become an important issue for long-term sustainability of ecosystems. The environmental effects of plantations comprised of fast-growing introduced trees have been vigorously debated. On one hand, monocultures have been said to exhaust resources, resulting in decreased biodiversity. Conversely, it has been stated that monocultures may favor regeneration of undergrowth plants from surrounding forests, increasing biodiversity. In order to clarify the effects of planting Eucalyptus trees on species composition, diversity, and functional type of understory vegetation in Yunnan province, a field trial was implemented to compare Eucalyptus plantations (EPs) with two other local current vegetation types (secondary evergreen forests (SEs), and abandoned farmlands (AFs)). Each vegetation type was sampled in each of three elevational ranges (low = 1,000–1,400 meters above sea level (masl), medium = 1,400–1,800 masl, and high = 1,800–2,200 masl). Sample sites within each elevational range had similar environmental characteristics (slope, aspect, etc.). Thus, we sampled three vegetation types at each of three sites at each of three elevations for a total of 27 plots. We calculated relative abundance and importance value of species and diversity indexes to evaluate differences among local current vegetation types and elevational ranges, employing multivariate ordination analyses and other methods such as Analyses of Variance (ANOVA) and Indicator Species Analysis. We found that fast growing introduced Eucalyptus plantations led to reduced plant diversity in the study area, and that rare or threatened species were recorded almost exclusively in the SE plots, being essentially absent from the EP and AF plots. The understory plant diversity did not correlate with the altitude gradient significantly. Eucalyptus plantations (EPs) have a simpler community structure than that of either secondary evergreen forests (SEs; similar to natural state) or abandoned farmlands (AFs). No variable significantly explained variation of the understory shrub layer, but soil moisture-holding capacity and overstory coverage were significant in explaining variation of the understory herb layer, suggesting that the study of soil physical properties is necessary for better understanding of their importance in Eucalyptus plantations and other local current vegetation types.     

Naturally established seedlings on an artificially regenerated area in Northern Sweden

A field experiment in northern Sweden was established to compare different regeneration methods. Pinus sylvestris (L.) seeds of various origins were used. On the plots on the clear‐felled area where local seed had been sown, the naturally established conifer regeneration was recorded. Eleven growing seasons after sowing, the total number of seedlings increased by 335% giving a total of 4 754 seedlings ha^‐1 when the number of naturally established conifers was added to the number of seedlings from the artificial regeneration. The number of main crop plants almost doubled. The number of naturally established seedlings decreased with increasing distance from the neighboring seed‐tree stand. Up to 110 m from the seed‐tree stand 50% of the sowed 2 × 2 m quadrats had at least one naturally regenerated seedling. The extent of natural regeneration found in this study suggest that it could contribute to a significant increase in stand density under appropriate management on suitable sites. Moreover, naturally established seedlings on artificially regenerated sites may serve as an insurance factor in future perturbations, lead to better tree form shaping conditions and maintain genetic diversity even if material from a narrow genetic base is used for planting or sowing.     

Effects of management, environment and landscape conditions on establishment of hardwood seedlings and saplings in central Japanese coniferous plantations

There is an increasing need to restore natural hardwood forests in landscapes dominated by monocultural conifer plantations. A convenient restoration approach is to exploit natural regeneration processes. Natural regeneration, however, is affected by diverse interacting factors, for which better understanding is required, in order to optimize restoration programs. To identify optimal management practices for improving natural regeneration of hardwood trees in coniferous plantations, we examined the effects of multiple factors on the abundance of seedlings, small saplings and large saplings (height <0.3, 0.3-1.3 and ?1.3 m, respectively) of hardwood tree and shrub species in both line thinned (LT) and unthinned (UT) plantations of sugi (Cryptomeria japonica) and hardwood forests (HF) in central Japan. The effects of management practices (number of the times of weeding and cleaning, thinning method, years after thinning and forest age), environment (slope position, slope angle and canopy openness), and landscape conditions (distance from nearest hardwood forest, altitude and landuse before planting) on the number of hardwood individuals were examined by using the data obtained from the LT plantations. We also compared hardwood density between LT and UT plantations to examine the effect of line thinning. Finally, we examined species composition of LT plantations and HF to identify hardwood forest components in the thinned plantations. The effects on hardwood regeneration of environmental conditions, landscape factors and management practices applied in the plantations varied, depending on the size class and life form of the regenerating species. The abundance of large saplings of tall tree species was affected by several management factors, especially number of the times of weeding. Landscape conditions (distance from the nearest hardwood forest and altitude) affected the abundance of small saplings and seedlings of tall tree species, but not the other classes. Seedlings and small saplings of many tall tree species that contribute to hardwood forest canopies were less abundant in the LT plantations. The results show that numerous factors affect the establishment and abundance of naturally regenerating hardwood tree species, and suggest that successful establishment during early plantation stages can have long-lasting effects on natural regeneration of tall tree species.     

Comparative regeneration status in a natural forest and enrichment plantations of Chittagong （south） forest division, Bangladesh

于2002年4月至11月,对孟加拉Chittagong (南部)林区天然纯林和肥沃地人工林树种更新情况进行了比较研究。共设100个3m×3m的样地(天然林50个,人工林50个)。共记录天然林更新树种64个,苗木密度为24767株/hm2;人工林更新树种40个,苗木密度为18633株/hm2。天然林更新量最大的树种为Castanopsis spp.(2200 株/hm2),其次是Glochidion lanceolarium (2183 株/hm2);人工林更新量最大的树种为Dipterocarpus gracilis (2117株/hm2),其次是Anogeissus acuminata (2000株/hm2)。对天然林而言, Castanopsis spp 的相对密度最高(8.88%), Glochidion lanceolarium 的相对频度最高(7.36%),Syzygium spp. 的相对富有度最高(3.79%),Glochidion lanceolarium的重要值指数最高(18.24%);对人工林而言,Dipterocarpus gracilis的相对密度最高(11.36%),Glochidion lanceolarium的相对频度最高 (9.71%), Dipterocarpus gracilis的相对富有度最高(5.92%), Glochidion lanceolarium的重要值指数最高 (23.32%)。Dipterocarpus gracilis 常见种在天然林和人工林都有更新苗木,但人工林的苗木要高于天然林。天然更新的苗木非常密集,但由于人为的干扰,这些更新的苗木通常达不到径干生长期。表4参35。     

尼加拉瓜废弃农田次生演替后的土壤种子库

定量分析了被废弃4年、9年和14年的农田地上派生的次生林土壤中种子组成和密度,从而检测在次生林演替形成过程中,土壤种子库是否能随着植物种群的集成而集成。分别在废弃了4年、9年和14年的农田地里（15cm&#215;15cm样方、9cm土层深）,掘取了18,37和48份土壤样品。在废弃了4,9和14年的农田地上,分别发现了3,5和9个物种。在这些不同的生命形态中,在9年和14年的迹地上,土壤种子树木占主要成分,分别为60%和33%,而4年废弃迹地主要被非木本植物所占领。三块废弃地里,4年废弃迹地植物种子的总数为327粒,相应可发育的种子密度为141粒/m2,14年废弃迹地种子的总数为46粒,相应的可发育种子的密度为26粒/m^2,指明种子数、种子密度随废弃地龄成下降趋势。在9年和14年龄废弃地上,土壤种子植物种类与立地木本植物种类的相似度较低,而4年龄地上两者比较则完全不同。我们认为：土壤种子库的物种构成是在次生演替过程中逐渐形成的,但是,所获得的总体种子密度太低,仅仅依赖于这些种子来实现树木自然再生是不可靠的。为了加快这些废弃地次生林的恢复,既要依靠自然集成的土壤种子库,还需要通过直播、所需物种的强化种植和设定人工生长环境以利于种子传播。     

Natural Regeneration in Thinned Douglas-fir Stands in Western Oregon

ABSTRACT

In response to interests by land management agencies to transform even-aged stands to structurally mimic old-growth forests, we evaluated whether thinning in 40- to 80-year-old Douglas-fir (Pseudotsuga menziesii) stands influenced amount and composition of advanced regeneration 5 to 7 years following treatment. We used data from two large-scale management experiments (Density Management Study and Young Stand Thinning and Diversity Study) conducted in western Oregon. Thinning focused on the removal of Douglas-fir, while maintenance of minor species was encouraged. Although both experiments showed higher tree regeneration after thinning, we found that variation in regeneration density was too high (3 orders of magnitude) to find statistical differences among thinning intensities. While seedlings of the major species, Douglas-fir and western hemlock (Tsuga heterophylla), were always present and dominated regeneration on nearly all sites, species trends were driven by high spatial and compositional variation throughout all units, treatments, and sites. Thinning increased the number of species within the regeneration layer. Hereby, species diversity was strongly related to overstory composition, suggesting seed source limitations for minor species. Hence, favoring rare species during thinning operations may be an effective method to increase regeneration species richness. Local conditions, as defined by overstory density appeared more influential than regional climate patterns in determining seedling densities. Shrub and grass competition did not prevent seedling establishment as their cover values were generally not as high as typically found in clearcuts in the region. The high variation in seedling density and species richness within the seedling stratum in the thinned stands may set the stage for development of structural complexity in even-aged Douglas-fir plantations.     

Scots pine (Pinus sylvestris L.) plantations contribute to the regeneration of holly (Ilex aquifolium L.) in mediterranean central Spain

The aim of this study is to evaluate the recruitment possibilities of holly (Ilex aquifolium L.) populations under Pinus sylvestris plantations in the mountains of Central Spain. Population recruitment of holly under P. sylvestris L. plantations was studied at two localities. We sampled holly seed rain, seed bank, and seedling emergence and survival (of both emerged and planted seedlings) in both localities. Seed germination was analysed by randomly sowing Ilex seeds and their subsequent recollection and analysis over the following 3 years (only in one locality). Seed rain, seed bank and emerged seedling densities did not differ between localities. Seed bank density was between 10 and 20 seeds m⁻², considerably higher than the observed seed rain (0.4–1.2 seeds m⁻²), and also higher than the emerged seedling density (0–4 seedlings m⁻²). But Ilex is not very efficient in germinating under pine forests (29.1% germination after 3 years). This may indicate a seed accumulation process of at least 5 years. Seedling survival for the first year differed among the studied sites (50–60 vs. 17%). Nevertheless these survival rates are higher than those found for the same seedling populations in different forest habitats (not Scots pine forests) from near locations. Differences in summer water stress between the study sites are proposed as the main cause of the observed differences in seedling survival. It is concluded that P. sylvestris forests may provide one of the best regeneration habitats for holly in the Mediterranean area, where this species is close to the Southern limit of its distribution.     

Heavy thinning in hinoki plantations in Shikoku (southwestern Japan) has limited effects on recruitment of seedlings of other tree species

Heavy thinning may provide a feasible means to convert single-species coniferous plantations to broadleaved or mixed forests. To assess this possibility, we monitored tree seedling dynamics of other tree species, the understory microenvironment, and seed availability following heavy thinning (50 % by volume) in two hinoki (Chamaecyparis obtusa) plantations in Shikoku, southwestern Japan. Conventional (35 % by volume) and row thinning (50 % by volume) treatments were also applied at one of the sites. Diffuse transmittance in the understory dramatically increased after all thinning treatments then rapidly decreased, except after row thinning. Heavy thinning accelerated recruitment of small seedlings (with stems <30 cm high) at one of the sites. However, the densities of these seedlings declined sharply, and increases in the densities of larger seedlings recorded in subsequent surveys were very small. Furthermore, at the other site, recruitment of small seedlings under heavy thinning was equivalent to that under conventional thinning and lower than that under row thinning. Abundant species in the recruited seedlings were pioneer or subcanopy species found in the soil seed bank. Low seed rain density at both sites appeared to be responsible for the poor recruitment of canopy tree species. Our results suggest that heavy thinning had limited effects on the seedling recruitment of other tree species in these hinoki plantations due to insufficient seed rain and rapid canopy closure.     

Direct seeding of late-successional trees to restore tropical montane forest

Natural regeneration of large-seeded, late-successional trees in fragmented tropical landscapes can be strongly limited by a lack of seed dispersal resulting in the need for more intensive restoration approaches, such as enrichment planting, to include these species in future forests. Direct seeding may be an alternative low-cost approach to planting nursery-raised tree seedlings, but there is minimal information on its efficacy or when in the successional process this technique will be most successful. We tested directly seeding five native tree species into habitats representing passive and active restoration approaches: (1) recently abandoned pasture; (2) naturally establishing, young secondary forests; and (3) young, mixed-species (fast-growing N-fixers and commercially valuable species) tree plantations established to facilitate montane forest recovery in southern Costa Rica. We monitored germination, survival, growth, and above- and below-ground biomass over a 2-year period. Germination in pastures, secondary forests, and tree plantations was similar (∼43%). Seedling survival after one and two years was significantly higher under tree plantations (91% year 1, 75% year 2) compared to secondary forests (76, 44%) or pastures (74, 41%). Moreover, seedlings had greater total biomass and lower root:shoot ratios in the plantations, suggesting higher nutrient availability in that treatment. Costs for direct seeding were 10- to 30-fold less per 100 seedlings after 2-year compared to nursery-raised seedlings planted at the same sites; however, there are important trade-offs to the two restoration approaches. Planting nursery-raised seedling is a more effective but higher cost approach for rapidly establishing canopy cover and restoring large areas whereas direct seeding is a more efficient way to enrich an existing system. We particularly recommend using direct seeding as a complimentary measure to the more intensive restoration approach of planting fast-growing and N-fixing trees.