Towards practices favourable to plant diversity in hybrid poplar plantations

Much research effort is being devoted to developing forest management practices with limited impacts on biodiversity. While the impact of poplar Populus sp. plantations on biodiversity is relatively well-known at the landscape scale, the impact of alternative management practices at the plantation scale has received much less attention. Yet biodiversity is likely to be impacted by the choice of the poplar clone, stem density at plantation, type and duration of the understory control, and age at which the poplars are harvested. In this study, we investigated the impact of these factors on herbaceous plant communities with data from plant surveys conducted in 85 young (2–5 years) and 96 mature (11–17 years) hybrid poplar high-forest plantations in northern France. On average, ruderal or generalist plants contributed to 40.5% of the plot species richness; tall herbs (60.2%), forest (26%) and meadow plants (13.8%) contributed to the remaining 59.5% more specialised species. Soil moisture and soil nitrogen were major determinants of plant communities: wet soils were favourable to tall herbs, while meadow and forest species preferred moist soils; a significantly lower diversity of the three species groups was reported in the nutrient richer soils (in mature plantations only for forest plants). Mean species richness decreased with plantation age except for forest species. Plant communities in young plantations showed little differences in composition according to the type of understory control (chemical, mechanical or both). The development of a shrubby layer in mature plantations was restricted to the drier soils and was detrimental to both meadow plants and tall herb species. Effects of previous land use on forest and tall herb species were found only in young plantations, suggesting a rapid reset of plant communities for these two groups. This may not be the case for meadow species as the influence of previous land use was significant in mature plantations only. Finally, clone type and stem density at plantation had no significant impact on plant communities. Adjusting age at which the poplars are harvested seems the only effective way to drive plant communities in high-forest poplar plantations: delaying poplar harvest (probably beyond 15–20 years) would benefit forest plants, while advancing poplar harvest (about 10 years) would benefit tall herbs, especially in wet soil conditions.     

Thinning effects on pine-spruce forest transpiration in central Sweden

This study analyses the effects of thinning on stand transpiration in a typical mixed spruce and pine forest in the southern boreal zone. Studies of transpiration are important for models of water, energy and carbon exchange, and forest management, like thinning, would change those processes. Tree transpiration was measured by the tissue heat-balance sapflow technique, on a reference plot and a thinning plot situated in a 50-year-old stand in central Sweden. Sapflow was measured during one season (1998) on both plots before thinning, to establish reference values. In winter 1998/1999 24% of the basal area was removed from the thinning plot. Thinning was done so as to preserve the initial species composition and the size distribution. The measurements continued after thinning during the growing seasons of 1999 and 2000. The climate showed remarkable differences between the 3 years; 1998 was wet and cool, with frequent rain, and the soil-water content was high throughout the year. In contrast, 1999 was dry and warm, and the soil-water content decreased to very low values, ca. 5–6% by volume. In 2000, the weather was more normal, with variable conditions. Stand transpiration was similar on both plots during the year before thinning; the plot to be thinned transpired 6% more than the reference plot. After thinning, transpiration was initially ca. 40% lower on the thinned plot, but the difference diminished successively. When the following drought was at its worst, the thinned plot transpired up to seven times more than the reference plot. During the second season after thinning, the thinned plot transpired ca. 20% more than the reference plot. The increased transpiration of the thinned plot could not be attributed to environmental variables, but was most probably caused by changes in biological factors, such as a fertilization effect.     

Spatial pattern in herb diversity and abundance of second growth mixed deciduous-evergreen forest of southern New England,USA

This study was designed to answer questions about the patterns of understory diversity in managed forests of southern New England, and the factors that appear associated with those patterns. At the landscape-level, we used plot data to answer questions regarding the spatial distribution of forest understory plant species. Data from a combination of fixed area (understory vegetation) and variable radius (overstory trees) plot methods are combined with site variables for the analysis. Univariate and multivariate statistical methods are used to test for understory diversity relationships with overstory cover types and topography separately, and in combination. Analyses also test for relationships between specific understory species and cover types. In general the understory flora is dominated by four common clonal species that occur across the range of forest cover types: wild sarsaparilla (Aralia nudicaulis L.), Canada mayflower (Maianthemum candense Desf.), star flower (Trientalis borealis Raf.), and partridgeberry (Mitchella repens L.). Results also show that over story composition and structure can be used to assess understory species richness. Species richness follows a general trend among cover types of: hardwood ≥ regenerating forest, hardwood–pine, and pine ≥ mixed ≥ hardwood–hemlock > hemlock. Eastern hemlock (Tsuga canadensis L. Carriere) and mountain laurel (Kalmia latifolia L.) (which decreased in dominance from ridge to valley) both showed negative trends with understory species richness. Topographic position also appears associated with understory floristic patterns (particularly for the hardwood cover type), both in terms of species richness and compositional diversity which both increased from ridge, to midslope, to valley. However, overstory composition (covertype) appears to have a higher order influence on vegetation and mediates the role of topography. The results from this study provide foresters with a better understanding for maintaining floristic diversity and composition of the understory in managed forests.     

Effects of thinning on plant species diversity and composition of understory herbs in a larch plantation

The effects of thinning on plant species diversity and composition of understory herbs in a larch plantation were investigated. The relationships between plant species diversity and composition of understory herbs and light conditions were established. Twenty-five 1 m × 1 m plots and fifteen 13 m × 1 m transects were set up in unthinned and thinned stands, respectively. All the transects in the thinned stands were set across the thinned rows and unthinned rows, and each of them was divided into nine 1 m × 1 m sub-plots. The herb diversity and light conditions were observed in each plot and sub-plot. The results show that there was a significant difference in herb diversity between the thinned and unthinned stands. All biodiversity indices except for evenness index in the thinned stand were higher than those of the unthinned stand, i.e., the herb diversity increased after thinning. According to the changes in herb densities and whether one species could be found in a stand or not before and after thinning, all herb species were classed into three types: positive, neutral and negative species, which referred to a species newly appeared and having an obviously increased density after thinning, with no obvious changes in its appearance and density after thinning, and disappeared and having an obviously decreased density after thinning, respectively. Many new species were found in the thinned stand like Corydalis pallida, Prenanthes tatarinowii, Vicia unijuga and Sonchus brachyotus etc. However, most species found in both the thinned and unthinned stands were negative species. In all nine subplots, only 11 and 10 species were found in spring and in autumn respectively, accounting for 17.74% and 15.15% of all the species in the thinned stand, respectively. All biodiversity indices were the highest in the center sub-plots and most of them tended to reduce from middle to side sub-plots. There was a close correlation between most of the three types of species and light conditions which was similar to each other in the thinned and unthinned stands. __________ Translated from Chinese Journal of Ecology, 2006, 25(10): 1201–1207 [译自: 生态学杂志]     

Responses of community structure,diversity, and abundance of understory plants and insect assemblages to thinning in plantations

Identifying effective management operations for plantations is important for conservation of biodiversity in a plantation-dominated landscape. We tested whether pre-commercial thinning influenced community structures and could be an effective strategy for increasing diversity and abundance of plants and animals in plantations. We designated thinned and unthinned study stands in Japanese cedar (Cryptomeria japonica) plantations and compared the communities of understory vegetation, bees, butterflies, hoverflies, and longhorn beetles 1 and 3 years after thinning. The analyses of vegetation showed that pre-commercial thinning affected community structure, but species richness and vegetation abundance were not significantly affected. Thinning affected insect community structure, and both species richness and abundance of all insect groups increased 1 year after thinning. However, 3 years after thinning, significant differences only remained in the species richness of bees and the abundance of bees, butterflies, and hoverflies. These results suggest that pre-commercial thinning in plantation stands influences the community structure of understory vegetation and can be an effective way to increase the diversity and abundance of some insect groups in the short term. However, the results also suggest that the duration of the operational effects of pre-commercial thinning varies among insect groups; thus, the variable effects of pre-commercial thinning should be carefully considered in the conservation-based management of plantation stands.     

Can pine forest restoration promote a diverse and abundant understory and simultaneously resist nonnative invasion?

An important goal of forest restoration is to increase native plant diversity and abundance. Thinning and burning treatments are a common method of reducing fire risk while simultaneously promoting understory production in ponderosa pine (Pinus ponderosa) forests. In this study we examine the magnitude and direction of understory plant community recovery after thinning and burning restoration treatments in a ponderosa pine forest. Our objective was to determine if the post-treatment community was a diverse, abundant, and persistent assemblage of native species or if ecological restoration treatments resulted in nonnative species invasion. This project was initiated at the Grand Canyon-Parashant National Monument, Arizona, USA in 1997. We established four replicated blocks that spanned a gradient of soil types. Each block contained a control and a treated unit. Treated units were thinned to emulate pre-1870 forest stand conditions and prescribed-burned to reintroduce fire to a system that has not burned since ∼1870. We measured plant cover using the point-line intercept method and recorded species richness and composition on 0.05 ha belt transects. We examined the magnitude of treatment responses using Cohen's d effect size analysis. Changes in community composition were analyzed using nonmetric multidimensional scaling (NMS). Native plant species cover and richness increased in the thinned and burned areas compared to the controls. By the last year of the study, annual species comprised nearly 60% of the understory cover in the treatment units. Cheatgrass (Bromus tectorum), a nonnative annual grass, spread into large areas of the treated units and became the dominant understory species on the study site. The ecological restoration treatments did promote a more diverse and abundant understory community in ponderosa pine forests. The disturbances generated by such treatments also promoted an invasion by an undesirable nonnative species. Our results demonstrate the need to minimize disturbances generated by restoration treatments and argue for the need to proactively facilitate the recovery of native species after treatment.     

间伐对栓皮栎人工林林下更新的影响

栓皮栎是我国温带落叶阔叶林代表树种之一,是河南省山区典型地带性树种和主要造林树种.间伐作为一个重要的森林经营措施,研究其对林下更新的影响,可为改善栓皮栎人工林林分结构,维持林下物种多样性,制定科学合理的森林经营措施提供支撑.对间伐3 a后栓皮栎人工林林下幼苗更新物种及更新多样性进行调查,结果表明:间伐后林地内幼苗种类和...     

The effect of thinning on ground spider diversity and microenvironmental factors of a subtropical spruce plantation forest in East Asia

Currently, information about the effect of forest management on biodiversity of subtropical plantation forests in Asia is quite limited. In this study, we compared the spider community structures and guild compositions of subtropical Cryptomeria japonica plantation forests receiving different degree of thinning (0, 25 and 50 %) in central Taiwan. The ground spider diversities and environmental variables were sampled/measured once every 3 months for 1 year before thinning and 2 years after thinning. Results showed that before thinning spider compositions did not differ significantly among three plantation forest types. Two years after thinning, spider species and family compositions of three plantation forest types differed significantly. In all three plantation forest types, the spider composition differed from year to year, indicating existence of temporal variations in spider diversity. Ground hunters (increased 200–600 % in thinned forests), sheet web weavers (increased 50–300 % in thinned forests) and space web weavers (decreased 30–50 % in thinned forests) were the major contributors of the observed spider composition differences among plantation forests receiving different treatments. The stands receiving thinning treatments also had higher illumination, litter decomposition rate, temperature and understory vegetation density. Thinning treatments might have changed the structures of understory vegetation and canopy cover and consequently resulted in abundance and diversity changes of these guilds. Moreover, the heterogeneity in understory vegetation recovery rate and temporal variation of spider composition might further generate spider diversity variations in subtropical forests receiving different degree of thinning.     

模拟林冠损伤对藜蒴栲群落林下植被生物多样性的影响

以2008年冰雪灾害对森林生态系统的破坏为背景,通过人工去除林冠层保留树干模拟森林的机械损伤,研究粤北小坑流域藜蒴栲群落林下植被的变化.结果表明:(1)试验1.5年后,去除林冠层、林下添加枯枝落叶的处理,林下灌木、草本科、种及乔木幼苗种的数量显著增加(P＜0.05);去除林冠层且地表枯落物层保持不变的处理,林下草本科、种数量增加显著,乔木幼苗及灌木科、种差异不显著(P＞0.05);林下添加枯枝落叶,林冠层不做处理,林下植被各生活型物种数有所减少,但差异不显著.(2)去除林冠层后,一些阳生种如野桐、山乌桕、山苍子、红紫珠、蕨状苔草、广东蛇葡萄等大量入侵并占据优势地位,林下植被盖度显著提高.(3)去除林冠层在短期内可显著增加林下植被生物多样性,添加枯落物对林下植被生物多样性影响不显著.     

Understory plant communities of boreal mixedwood forests in western Canada: Natural patterns and response to variable-retention harvesting

We examined patterns of variation in richness, diversity, and composition of understory vascular plant communities in mixedwood boreal forests of varying composition (broadleaf, mixedwood, conifer) in Alberta, Canada, before and for 2 years following variable-retention harvesting (clearcut, 20 and 75% dispersed green tree retention, control). Broadleaf-dominated forests differed from mixedwood or conifer-dominated forests in that they had greater canopy cover, litter depth, soil nitrogen, warmer soils, as well as greater shrub cover, herb and shrub richness and diversity (plot scale). In contrast, conifer, and to a lesser extent mixedwood, forest had greater β diversity than broadleaf forest. Overall, mixedwood and conifer forests were similar to one another, both differed from broadleaf forest. Several species were found to be significant indicators of broadleaf forest but most of these also occurred in the other forest types. Understory composition was related to canopy composition and edaphic conditions. Variable-retention harvesting had little effect on understory cover, richness, or diversity but resulted in reduced richness and β diversity at a larger scale. The clearcut and 20% treatments affected composition in all forest types. Early successional species and those common in disturbed sites were indicators of harvesting while evergreen, shade-tolerant understory herbs were indicators of the control forest and 75% retention harvest. We conclude that it is important to maintain a range of variation in canopy composition of mixedwood forests in order to conserve the associated understory communities. The presence of conifers in these forests has a particularly important influence on understory communities. The threshold for a lifeboat effect of variable-retention harvesting is between 20 and 75% retention. Examination of richness and β diversity at a variety of scales can provide interesting information on effects of harvesting on spatial reorganization and homogenization of understory plant communities.     

A comparison of fire hazard mitigation alternatives in pinyon–juniper woodlands of Arizona

Concern over uncontrollable wildfire in pinyon–juniper woodlands has led public land managers in the southwestern United States to seek approaches for mitigating wildfire hazard, yet little information is available concerning effectiveness and ecological responses of alternative treatments. We established a randomized block experiment at a pinyon–juniper site in northern Arizona and tested effects of no treatment (Control), thinning only (Thin), prescribed fire only (Burn), and thinning followed by prescribed fire (Thin + Burn) on overstory structure, hazardous fuels reduction, and woody understory responses. One year after implementation, mean trees per hectare (TPH) of Utah juniper (Juniperus osteosperma) and pinyon pine (Pinus edulis), and basal area (BA) of pinyon, were significantly (P < 0.05) less in Thin and Thin + Burn treatments than Control. Additionally, pinyon TPH was less in Burn than Control. Quadratic mean diameter was significantly greater in Thin and Thin + Burn than in Control and Burn treatments. Thinning shifted diameter distributions from uneven- to even-sized. Crown fuel load (CFL) of both pinyon and juniper was significantly lower in Thin and Thin + Burn compared with Control and Burn treatments. Thin, Burn, and Thin + Burn treatments resulted in significantly greater 1-h surface fuel loads compared with the Control. The Thin treatment resulted in significantly greater mean load of the 1000-h fuel class compared with Burn and Control treatments, but did not differ from Thin + Burn. Forest floor Oi (litter) layer was not significantly affected by the treatments but Oe + Oa (duff) depth was significantly less in the Burn treatment compared with Thin and Control. Live shrubs and tree regeneration showed no differences among treatments. We concluded that thinning and thinning followed by prescribed fire were effective approaches for fuels reduction; however, resulting stand structures may be novel and outside the historical range of variability. Prescribed fire alone had minimal effects on structure and fuels reduction. Woody shrubs and tree regeneration in the understory suggested that these treatments may not have long-term deleterious ecological effects.     

皆伐前后油松人工林下植物多样性变化及与土壤水分的关系

【目的】探讨油松人工林皆伐前后林下植物多样性的变化及与土壤水分的关系,为在油松林皆伐后植被恢复和发育阶段维持生物多样性、保持林分结构稳定、发挥更高生态效益等方面提供科学依据和经营措施建议。【方法】采用时序研究法,在河北平泉地区选择立地一致的不同林龄油松人工林(32年中龄林、40年近熟林、53年成熟林)和皆伐后不同时间(5、10、24 a)的天然更新林作为研究对象,分析不同生长发育阶段油松人工林下植物物种组成与多样性的变化规律及与土壤水分间的相关性。【结果】1)皆伐前后6种林分样地共出现灌木植物21种,草本植物65种,不同样地林下植物组成存在差异。胡枝子在各林分样地均有出现,且重要值均> 20%,在灌木层优势地位明显;草本层中菊科植物种类最多,有18种,其次是蔷薇科和禾本科,分别为6种和4种。2)不同林分样地林下植物多样性指数均表现为草本层>灌木层,皆伐前随着林龄增加林下植物多样性逐渐增加;皆伐后灌木层植物多样性表现为先下降后增加再下降,且变化幅度明显,伐后10 a灌木层Margalef丰富度指数、Simpson多样性指数、Shannon-Wiener多样性指数和Pielou均匀度指数最大,分别为1.40、0.61、1.24和0.74,与53年样地差异不显著。皆伐后不同时间的天然更新林草本层植物多样性均与伐前53年样地的差异不显著,皆伐对灌木层植物的影响较大。3)不同林地土壤水分变化规律较一致,表现为伐前随林龄增加而逐渐增加,伐后5~10 a仍保持较高水平,伐后24 a出现下降,经相关分析植物多样性指数与土壤水分之间有显著的正相关关系,与草本层的相关性达极显著水平。【结论】伐前林下植物多样性变化主要与林分密度降低、光照条件改善有关,伐后主要与油松天然更新及种间竞争有关。依靠油松天然更新恢复的林地保持了较高的生物多样性,但在皆伐10 a后出现下降的趋势,建议在此时对油松更新苗进行人工抚育、降低密度以维持植物多样性。土壤水分是影响植物多样性的关键生态因子,良好的土壤水分条件和林下植被的恢复和发展可以相互促进。     

Windthrow and salvage logging in an old-growth hemlock-northern hardwoods forest

Although the initial response to salvage (also known as, post-disturbance or sanitary) logging is known to vary among system components, little is known about longer term forest recovery. We examine forest overstory, understory, soil, and microtopographic response 25 years after a 1977 severe wind disturbance on the Flambeau River State Forest in Wisconsin, USA, a portion of which was salvage logged. Within this former old-growth hemlock-northern hardwoods forest, tree dominance has shifted from Eastern hemlock (Tsuga canadensis) to broad-leaf deciduous species (Ulmus americana, Acer saccharum, Tilia americana, Populus tremuloides, and Betula alleghaniensis) in both the salvaged and unsalvaged areas. While the biological legacies of pre-disturbance seedlings, saplings, and mature trees were initially more abundant in the unsalvaged area, regeneration through root suckers and stump sprouts was common in both areas. After 25 years, tree basal area, sapling density, shrub layer density, and seedling cover had converged between unsalvaged and salvaged areas. In contrast, understory herb communities differed between salvaged and unsalvaged forest, with salvaged forest containing significantly higher understory herb richness and cover, and greater dominance of species benefiting from disturbance, especially Solidago species. Soil bulk density, pH, organic carbon content, and organic nitrogen content were also significantly higher in the salvaged area. The structural legacy of tip-up microtopography remains more pronounced in the unsalvaged area, with significantly taller tip-up mounds and deeper pits. Mosses and some forest herbs, including Athyrium filix-femina and Hydrophyllum virginianum, showed strong positive responses to this tip-up microrelief, highlighting the importance of these structural legacies for understory biodiversity. In sum, although the pathways of recovery differed, this forest appeared to be as resilient to the compound disturbances of windthrow plus salvage logging as to wind disturbance alone, by most vegetative measures.     

Thinning reduces soil carbon dioxide but not methane flux from southwestern USA ponderosa pine forests

Forest soils are important components of the global carbon cycle because they both store and release carbon. Carbon dioxide is released from soil to the atmosphere as a result of plant root and microbial respiration. Additionally, soils in dry forests are often sinks of methane from the atmosphere. Both carbon dioxide and methane are greenhouse gases whose increasing concentration in the atmosphere contributes to climate warming. Thinning treatments are being implemented in ponderosa pine forests across the southwestern United States to restore historic forest structure and reduce the risk of severe wildfire. This study addresses how thinning alters fluxes of carbon dioxide and methane in ponderosa pine forest soils within one year of management and examines mechanisms of change. Carbon dioxide and methane fluxes, soil temperature, soil water content, forest floor mass, root mass, understory plant biomass, and soil microbial biomass carbon were measured before and after the implementation of a thinning and in an unthinned forest. Carbon dioxide efflux from soil decreased as a result of thinning in two of three summer months. Average summer carbon dioxide efflux declined by an average of 34 mg C m⁻² hr⁻¹ in the first year after thinning. Methane oxidation did not change in response to thinning. Thinning had no significant short-term effect on total forest floor mass, total root biomass, or microbial biomass carbon in the mineral soil. Understory plant biomass increased after thinning. Thinning increased carbon available for decomposition by killing tree roots, but our results suggest that thinning reduced carbon dioxide emissions from the soil because the reduction in belowground autotrophic respiration was larger than the stimulation of heterotrophic respiration. Methane oxidation was probably not affected by thinning because thinning did not alter the forest floor mass enough to affect methane diffusion from the atmosphere into the soil.     

不同间伐强度对长白落叶松-红松林植物多样性和土壤特性的影响

为了提高长白落叶松-红松林的生产力和生物多样性,2005年秋对长白落叶松人工林进行疏伐,伐后林冠下栽植4年生红松。2012年秋又对上层长白落叶松进行生长伐,设计轻度、中度和强度3种间伐强度和1组未间伐林分(对照),分析5年后不同间伐强度对林下植物多样性和土壤理化性质的影响。结果表明:①抚育间伐能提高林下植物多样性,林下灌木层植物丰富度随着间伐强度的增加而增加,轻度、中度和强度间伐差异显著(p<0.05)。林下灌木层植物多样性指数随着间伐强度的增加而增加,对照与中度间伐、强度间伐差异显著(p<0.05),但中度间伐和强度间伐差异不显著。林下草本层植物的丰富度和多样性指数随着间伐强度的增加而增加,各间伐强度均与对照差异显著(p<0.05),但轻度间伐和中度间伐差异不显著。②适度抚育间伐能改善土壤的理化性质,随着间伐强度的增加,土壤容重有所降低,土壤孔隙度和持水量有所提高;土壤pH值呈现先升高后略有降低的趋势,全K、速效K、全P、速效P、全N、速效N含量先升高后略有降低,其中中度间伐效果最好。综合考虑,对长白落叶松林分进行中度间伐较为适宜。     

香港人工林改造对林下植物自然更新 和物种多样性的早期影响

人工林在保护香港自然环境起着重要作用,但绝大多数人工林为纯林,生态系统较为脆弱。人工林的改造对于增加林地生物多样性、提升人工林的生态服务功能具有重要意义。研究选取20 a 生的尾叶桉（Eucalyptus urophylla）林和马占相思（Acacia mangium）林进行间伐套种处理,套种密度为1665株／hm2;以不间伐林分为对照,比较间伐套种后林分的物种多样性及套种树种的生长表现。结果表明,间伐＋套种3 a后,与未间伐林分相比,尾叶桉间伐林分植物的科、属和种数分别增加了78．6％、116．7％和100％,马占相思间伐林分相反。DCA 分析结果显示,群落中灌木层和草本层物种主要聚集在尾叶桉间伐林分,马占相思未间伐林分物种数次之。与未间伐相比,间伐＋套种措施显著提高了尾叶桉林乔木层 Shannon-Wiener 指数和均匀度指数、灌木层的物种丰富度指数和均匀度指数及草本层的丰富度和 Shannon-Wiener 指数（P ＜0．05）;但马占相思间伐＋套种林分的乔木层、灌木层和草本层的 Shannon-Wiener 指数均显著低于未间伐林分（P ＜0．05）;物种多样性指标总体表现为尾叶桉间伐林＞未间伐林,马占相思未间伐林＞间伐林。套种树种在尾叶桉和马占相思林分中的早期生长表现良好,树种间生长量没有明显差异。     

Comparison of potential non-timber forest products in intensively managed young stands and mature/old-growth forests in south-central British Columbia

Development of understory vegetation has been influenced by the many densely stocked second-growth forest stands in North America, which have an extended stem exclusion successional stage. Understory composition and structure is important for ecosystem functioning, while also having social and economic value through the harvest of certain herb and shrub species. The potential for co-management of young and mature, managed and unmanaged stands for timber and non-timber forest products (NTFPs) was assessed in two separate replicated experiments. Experiment A examined pole-sized lodgepole pine (Pinus contorta) stands that had been pre-commercially thinned (PCT) to target densities of 250, 500, 1000, and 2000 stems/ha. Half of each of these four thinning units was repeatedly fertilized, resulting in eight experimental units. Experiment B examined six different stand types: young plantations, pole-sized lodgepole pine stands either PCT, PCT plus repeated fertilization, or unthinned, mature, and old growth. Fifty-four herb and shrub species were identified as potential NTFPs, with the responses of individual species, as well as mean total herb, shrub, berry-producing and overall total NTFPs being assessed. In Experiment A, mean total abundance (crown volume index) of NTFPs, as well as mean total herb NTFPs were significantly greater in fertilized than in unfertilized stands. Thinning treatments did not significantly affect NTFP volume, however, fertilization treatments produced five significant responses by individual species (Achillea millefolium, Epilobium angustifolium, Taraxacum officinale, Arctostaphylos uva-ursi, Rubus idaeus). In Experiment B, four of the six species responses that were significant had greater abundance in young, managed stands (young plantation, thinned, or thinned-fertilized) than in the unmanaged stands. Mean total NTFP volume and mean total herb NTFP volume also followed this pattern. A. uva-ursi, E. angustifolium, Lonicera involucrata, Sorbus sitchensis and Thalictrum occidentale all had significantly higher abundance in young, managed stands than in all other treatments. Results suggest that co-management for timber and NTFPs is possible in this ecosystem, with further research needed to evaluate livelihood values of these crops.     

红松人工林不同间伐强度效果分析

对不同间伐强度红松人工林的林分生长状况,林下植被生物多样性以及林下土壤的养分状况进行调查研究。结果表明:极强度间伐、强度间伐能有效提高林分直径生长量,增加大径材的出材量,缩短培育大径材的时间,及早达到木材采伐标准。但间伐强度过大影响整个林分的蓄积量。强度间伐有效提高林下植被的丰富度指数和多样性指数,植被状况良好。极强度间伐区土壤的养分状况最好,维持较高的土壤肥力。间伐有利于红松人工林地的可持续利用。     

Response of climate-growth relationships and water use efficiency to thinning in a Pinus nigra afforestation

Thinning is the main forestry measure to increase tree growth by reducing stand tree density and competition for resources. A thinning experiment was established in 1993 on a 32-year-old Pinus nigra Arn. stand in central Spain. The response of growth, climate-growth relationships and intrinsic water use efficiency (WUEi) to a stand density reduction were compared between moderate thinned plots and a control plot by a combined analysis of basal area increments (BAI), and C and O stable isotope ratios (δ¹³C_c and δ¹⁸O_c). BAI in the control plot showed a decreasing trend that was avoided by thinning in the thinned plot. Thinning also partially buffered tree-ring response to climate and trees were less sensitive to precipitation although more sensitive to temperature. Δ¹³C_c in the thinned plot was not modified indicating that stomatal conductance (g) and photosynthetic capacity (A) did not change or change in the same direction. However, δ¹⁸O_c decreased in the control plot (unrelated to δ¹⁸O of precipitation) but not in the thinned plot, suggesting a relative increase of temperature and irradiance and/or a decrease of air humidity after reducing the density consistent with an increase in A, g and BAI. As WUEi did not increase in the thinned plot, faster growth in this plot was caused by higher abundance of resources per tree. The trend of WUEi in both plots indicated low-moderate CO₂-induced improvements. Thinning might be a useful adaptation measure against climate change in these plantations reducing their vulnerability to droughts. However, because WUEi was not affected, the positive growth response might be limited if droughts and warming continue and certain thresholds are exceeded.     

间伐强度对杉木人工林林下植被和土壤性质的影响

【目的】从发展林下植被、改善群落结构的角度,探讨适合杉木人工林的间伐强度,为提高人工林的稳定性和维护地力、维持人工林的可持续经营提供依据。【方法】2013年对福建省将乐国有林场的杉木人工林采取3种强度间伐:弱度间伐(LT,10%～25%)、中度间伐(MT,25%～35%)和强度间伐(HT,40%～50%),并设置对照样地(CK,未间伐)。于2016年对样地内林木进行每木检尺,调查林下植被物种多样性、盖度、生物量和土壤理化性质。对测定数据进行单因素方差分析,用Tukey法多重比较进行两两差异显著性检验,并对林下植被与土壤理化性质进行Pearson相关分析。【结果】间伐3年后,未间伐、弱度和中度间伐的盖度分别为25.52%、52.81%和58.98%,林下植被均未能形成群落,强度间伐的盖度为100%,林下形成灌木蕨类群落;灌木层物种丰富度、多样性指数、盖度和生物量均随间伐强度增加而增加,均匀度指数随间伐强度的增加而降低;草本层物种丰富度、多样性指数、均匀度指数、盖度和生物量均随间伐强度增加而增加;间伐3年后,弱度、中度、强度间伐林比未间伐林的表层土(0～10 cm)有机质含量分别增加71.41%、39.31%和98.10%,全氮含量分别增加82.76%、51.27%和115.87%,碱解氮含量分别增加49.47%、25.59%和42.22%,有效磷含量分别增加138.29%、112.23%和174.29%,速效钾含量分别增加-16.25%、-24.25%和16.27%,对表层土pH值、全磷含量和土壤物理性质的影响均不显著;灌木的盖度和生物量与土壤的有机质、全氮、全磷和有效磷含量均显著(P<0.05)正相关,此外灌木的盖度还与速效钾含量显著(P<0.05)正相关,草本盖度与土壤理化性质相关性不强,草本生物量与土壤有机质、全氮、全磷、碱解氮以及有效磷含量显著(P<0.05)正相关,林下植被的盖度和生物量均与土壤pH值和物理性质没有显著相关性。【结论】未间伐的杉木人工林林下植被的物种多样性、盖度和生物量均低,林下植被未能形成群落,缺乏稳定性;间伐能够促进林下植被的发育,增加林下植被生物多样性、盖度和生物量,林下植被能形成群落,可提高维护地力的能力,尤其是强度间伐;建议杉木人工幼龄林进行40%～50%强度的抚育间伐,将郁闭度调整到0.6～0.7较为合理。