Multi-scale Drivers of Spatial Variation in Old-Growth Forest Carbon Density Disentangled with Lidar and an Individual-Based Landscape Model

Forest ecosystems are the most important terrestrial carbon (C) storage globally, and presently mitigate anthropogenic climate change by acting as a large and persistent sink for atmospheric CO₂. Yet, forest C density varies greatly in space, both globally and at stand and landscape levels. Understanding the multi-scale drivers of this variation is a prerequisite for robust and effective climate change mitigation in ecosystem management. Here, we used airborne light detection and ranging (Lidar) and a novel high-resolution simulation model of landscape dynamics (iLand) to identify the drivers of variation in C density for an old-growth forest landscape in Oregon, USA. With total ecosystem C in excess of 1?Gt?ha^?1 these ecosystems are among the most C-rich globally. Our findings revealed considerable spatial variability in stand-level C density across the landscape. Notwithstanding the distinct environmental gradients in our mountainous study area only 55.3% of this variation was explained by environmental drivers, with radiation and soil physical properties having a stronger influence than temperature and precipitation. The remaining variation in C stocks was largely attributable to emerging properties of stand dynamics (that is, stand structure and composition). Not only were density- and size-related indicators positively associated with C stocks but also diversity in composition and structure, documenting a close link between biodiversity and ecosystem functioning. We conclude that the complexity of old-growth forests contributes to their sustained high C levels, a finding that is relevant to managing forests for climate change mitigation.     

Dead Wood Necromass in a Moist Tropical Forest: Stocks,Fluxes, and Spatiotemporal Variability

Ecosystems - Woody debris (WD) stocks and fluxes are important components of forest carbon budgets and yet remain understudied, particularly in tropical forests. Here we present the most...     

Simulating Daily and Half-Hourly Fluxes of Forest Carbon Dioxide and Water Vapor Exchange with a Simple Model of Light and Water Use

For the large-scale application of simple, aggregated models, it is important to be able to link the values of model parameters to easily measurable ecosystem characteristics. However, the aggregation of model inputs and outputs over time and space can hamper this linkage. In this paper, two temporal versions of the same simple carbon dioxide (CO₂) and water exchange model, based on the concepts of water- and light-use efficiencies, were used to simulate the half-hourly and daily CO₂ and water exchange of a Douglas fir forest (Pseudotsuga menziesii (Mirb.) Franco) in the Netherlands for 2 years, before and after a thinning. We tested the performance of the models and the interpretability of changes in optimized parameter values, due to the thinning, in terms of ecosystem functioning. The performance of the half-hourly model was satisfactory, whereas the performance of the daily model was high for water exchange but clearly lower for CO₂ exchange. A comparison of the model parameters before and after the thinning showed that the coefficients of the half-hourly model could be separated into more physiologically determined and stand-determined characteristics, but this separation was not clear for the daily model. These results show that if the temporal resolution of the model is high enough, the effects of a major ecosystem manipulation, such as thinning, can be detected and interpreted using eddy flux data and a very simple biophysical model. The model parameters have an unambiguous interpretation and can be inferred from basic ecosystem observables, such as leaf area index (LAI) and aboveground biomass. A sensitivity analysis found strong correlations between parameter sets with similar model performance. For any comparison of the parameter values of different studies, ranges of parameter values and their correlations should be presented rather than one optimized value. Received 2 May 2001; accepted 15 February 2002.     

Aboveground vs. Belowground Carbon Stocks in African Tropical Lowland Rainforest: Drivers and Implications

BackgroundAfrican tropical rainforests are one of the most important hotspots to look for changes in the upcoming decades when it comes to C storage and release. The focus of studying C dynamics in these systems lies traditionally on living aboveground biomass. Belowground soil organic carbon stocks have received little attention and estimates of the size, controls and distribution of soil organic carbon stocks are highly uncertain. In our study on lowland rainforest in the central Congo basin, we combine both an assessment of the aboveground C stock with an assessment of the belowground C stock and analyze the latter in terms of functional pools and controlling factors.Conclusions/SignificanceWe suggest nutrient limitation, especially potassium, as the driver for aboveground versus belowground C allocation. However, other drivers such as C turnover, tree functional traits or demographic considerations cannot be excluded. We argue that large and unaccounted variability in C stocks is to be expected in African tropical rain-forests. Currently, these differences in aboveground and belowground C stocks are not adequately verified and implemented mechanistically into Earth System Models. This will, hence, introduce additional uncertainty to models and predictions of the response of C storage of the Congo basin forest to climate change and its contribution to the terrestrial C budget.     

The Landscape Ecology of Tropical Secondary Forest in Montane Costa Rica

Multinomial logistic models of land use/land cover in montane Costa Rica and landscape pattern analysis showed that relative to agriculture, secondary forest occurred closer to old-growth forest, further from roads, in forest reserves, and at higher elevations. Collinearity between explanatory variables yielded simple multivariate models; proportion of surrounding old growth predicted secondary forest most accurately. An old-growth matrix [mean patch size (MPS) 24.5 ha], located mainly within protected areas, dominated elevations greater than 2500 m. A matrix of agriculture (MPS 23.5 ha), with smaller patches (approximately 9 ha) of secondary forest and old growth, dominated elevations from 1500 to 2500 m. Combining secondary forest with old growth decreased forest patch number and increased MPS from 7.3 to 37.1 ha. I concluded that: (a) secondary forest pattern is nonrandom, so ancillary data will aid its mapping with satellite imagery. The variables elevation, agriculture distance, road distance, and population density distinguished secondary forest from old growth with 74% accuracy; (b) socioeconomic and biological forces probably interact to create these secondary forest patterns; and (c) the strong association between secondary forest and old growth supports the concept that tropical forest recovery depends on the landscape structure of remnant forest. Received 16 February 1999; accepted 20 August 1999.     

Long-Term Impacts of Fuelwood Extraction on a Tropical Montane Cloud Forest

Fuelwood extracted from natural forests serves as a principal energy source in rural regions of many tropical countries. Although fuelwood extraction (even low intensities) might strongly impact the structure and species composition of natural forests, long-term studies remain scarce. Here, we estimate the potential long-term impacts (over several hundred years) of such repeated harvesting of single trees on tropical montane cloud forest in central Veracruz, Mexico, by applying a process-based forest growth model. We simulate a wide range of possible harvesting scenarios differing in wood volume harvested and preferred tree species and sizes, and use a set of indicators to compare their impacts on forest size structure and community composition. Results showed that the overall impact on forest structure and community composition increased linearly with the amount of harvested wood volume. Even at low levels of harvesting, forest size structure became more homogeneous in the long term because large old trees disappeared from the forest, but these changes might take decades or even centuries. Although recruitment of harvested species benefited from harvesting, species composition shifted to tree species that are not used for fuelwood. Our results demonstrate that fuelwood extraction can have marked long-term impacts on tropical montane cloud forests. The results also offer the possibility to support the design of management strategies for the natural species-rich forests that achieve a balance between economic needs and ecological goals of the stakeholders. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Photosynthesis-Nitrogen Relationships in Pioneer Plants of Disturbed Tropical Montane Forest Sites

Tropical forest disturbances lead to the establishment of secondary successional plant communities constituted by light demanding species with high relative growth rate that conduct to rapid canopy closure. Two main strategies for N nutrition are: (a) mineral N acquisition in the form of NH4 and NO3, and (b) symbiotic atmospheric N2 fixation. Given the high N requirement for maximization of leaf area and radiant energy absorption, we hypothesize that contrasting strategies of N nutrition in these environments are reflected in leaf photosynthetic characteristics. We compared the N-photosynthesis relationships and carbon balance parameters per unit leaf area as they vary with age in two species with contrasting N acquisition strategies: a N2-fixer Crotalaria anagyroides HBK (Papilionoideae), and a mineral-N user Verbesina turbacensis HBK (Asteraceae). N2 fixation capacity was associated to higher specific leaf area (SLA), higher photosynthetic capacity (Pmax) per unit leaf area and leaf mass, and higher N content per unit leaf mass. The N2-fixer species showed higher slope in the relationship Pmax-N per unit leaf mass and area when compared to the leaves of non-fixer species. Moreover, the intrinsic photosynthetic N use efficiency (Pmax/N) was higher in the N2 fixer than in leaves of the non-fixer species. Changes in N due to leaf age resulted in larger changes in CO2 flux density at the leaf level in the N2-fixer species. The higher photosynthetic capacity of the N2-fixer species was mechanistically related to higher stomatal conductance, internal CO2 concentration (ci) values closer to atmospheric CO2 concentration (ca), and lower intrinsic water use efficiency than the mineral N-user species. Despite their higher Pmax per unit leaf area, total non-structural saccharides concentration was lower in mature leaves of the N2-fixer plant as compared to the non-fixer counterpart. This might be caused by the presence of a larger root sink (symbionts) stimulating saccharides export and higher diurnal respiration rates.     

Root Morphology and Anchorage of Six Native Tree Species from a Tropical Montane Forest and an Elfin Forest in Ecuador

Root architecture of tree species was investigated at two different altitudes in tropical forests in Ecuador. Increasing altitude was accompanied by higher wind speeds and more shallow soils, while slope angles of both sites were comparable (20–50°). Three tree species typical for the montane forest at 1900 m (Graffenrieda emarginata (Ruiz & Pav.) Triana (Melastomataceae), Clethra revoluta (Ruiz & Pav.) Spreng. (Clethraceae), Vismia tomentosa Ruiz & Pav. (Clusiaceae)) and for the elfin forest at 3000 m (Weinmannia loxensis Harling (Cunoniaceae), Clusia spec. (Clusiacaea) Styrax foveolaria Perkins (Styraceae)) were examined. At 1900 m, 92% of the trees grew upright, in comparison to 52% at 3000 m. At 3000 m, 48% of the trees were inclined, lying or even partly uprooted. At this altitude, all trees with tap roots or with shoots connected by coarse rhizomes, 83% of the trees with stilt roots, and 50% of the trees in which stems or roots were supported by other trees grew upright, suggesting that these characteristics were relevant for tree stability. Root system morphology differed markedly between altitudes. In contrast to 1900 m, where 20% of structural roots originated in the deeper mineral soil, root origin at 3000 m was restricted to the forest floor. The mean ratio of root cross sectional area to tree height decreased significantly from 6.1 × 10⁻³ m² m⁻¹ at 1900 m to 3.2 × 10⁻³ m² m⁻¹ at 3000 m. The extent of root asymmetry increased significantly from 0.29 at 1900 m to 0.62 at 3000 m. This was accompanied by a significantly lower number of dominant roots at 3000 m (2.3 compared to 3.8 at 1900 m). In conclusion, native tree species growing in tropical montane and elfin forests show a variety of root traits that improve tree stability. Root system asymmetry is less important for tree stability where anchorage is provided by a deep and solid root–soil plate. When deep rooting is impeded, root traits improving the horizontal extension of the root–soil plate are more pronounced or occur more frequently. Furthermore, mutual mechanical support of roots and stems of neighboring trees seems to be an appropriate mechanism to provide anchorage in soils with low bulk density and in environments with high wind speeds.     

Tropical Forest Fragmentation Affects Floral Visitors but Not the Structure of Individual-Based Palm-Pollinator Networks

Despite increasing knowledge about the effects of habitat loss on pollinators in natural landscapes, information is very limited regarding the underlying mechanisms of forest fragmentation affecting plant-pollinator interactions in such landscapes. Here, we used a network approach to describe the effects of forest fragmentation on the patterns of interactions involving the understory dominant palm Astrocaryum mexicanum (Arecaceae) and its floral visitors (including both effective and non-effective pollinators) at the individual level in a Mexican tropical rainforest landscape. Specifically, we asked: (i) Does fragment size affect the structure of individual-based plant-pollinator networks? (ii) Does the core of highly interacting visitor species change along the fragmentation size gradient? (iii) Does forest fragment size influence the abundance of effective pollinators of A. mexicanum? We found that fragment size did not affect the topological structure of the individual-based palm-pollinator network. Furthermore, while the composition of peripheral non-effective pollinators changed depending on fragment size, effective core generalist species of pollinators remained stable. We also observed that both abundance and variance of effective pollinators of male and female flowers of A. mexicanum increased with forest fragment size. These findings indicate that the presence of effective pollinators in the core of all forest fragments could keep the network structure stable along the gradient of forest fragmentation. In addition, pollination of A. mexicanum could be more effective in larger fragments, since the greater abundance of pollinators in these fragments may increase the amount of pollen and diversity of pollen donors between flowers of individual plants. Given the prevalence of fragmentation in tropical ecosystems, our results indicate that the current patterns of land use will have consequences on the underlying mechanisms of pollination in remnant forests.     

Carbon Stocks in an African Woodland Landscape: Spatial Distributions and Scales of Variation

Current knowledge of Africa’s carbon (C) pools is limited despite its importance in the global C budget. To increase the understanding of C stocks in African woodlands, we asked how C stocks in soil and vegetation vary across a miombo woodland landscape and to what degree and at what scales are these stocks linked? We sampled along a 5-km transect using a cyclic sampling scheme to allow geostatistical analyses. Soil C stocks in the top 5?cm (12.1?±?0.6?Mg?C?ha^?1 (±?SE)) and 30?cm depths (40.1?±?2.5?Mg?C?ha^?1) varied significantly at scales of a few meters (autocorrelation distance 14?m in 0–5-cm and 26?m in 0–30-cm interval), and aboveground (AG) woody C stocks (20.7?±?1.8?Mg?C?ha^?1) varied significantly at kilometer scales (1,426?m). Soil textural distributions were linked to topography (r ²?=?0.54) as were large-tree AG C stocks (r ²?=?0.70). AG C stocks were constrained to an upper boundary by soil texture with greater AG C being associated with coarser textured soils. Vegetation and soil C stocks were coupled in the landscape in the top 5?cm of soil (r ²?=?0.24) but not with deeper soil C stocks, which were coupled to soil clay content (r ²?=?0.38). This study is one of the most complete transect studies in an African miombo woodland, and suggests that C stock distributions are strongly linked to topography and soil texture. To optimize sampling strategies for C stock assessments in miombo, soil C should be sampled at more than 26?m apart, and AG C should be sampled at more than 1,426?m apart in plots larger than 0.5?ha.     

Forest Productivity and Efficiency of Resource Use Across a Chronosequence of Tropical Montane Soils

We tested the hypothesis that plants adjust to nutrient availability by altering carbon allocation patterns and nutrient-use efficiency (NUE = net primary production [NPP] per unit nutrient uptake), but are constrained by a trade-off between NUE and light-use efficiency () = NPP per unit intercepted light). NPP, NUE and ) were measured in montane Metrosideros polymorpha forest across a 4.1 x 10⁶ yr space for time substitution chronosequence in which available soil N and P pools change with site age. Although the range of N and P availability across sites was broad, there was little difference in NPP between sites, and in contrast to theories of carbon allocation relative to limiting resources, we found no consistent relationships in production allocation to leaves, fine roots or wood. However, canopy nutrient pools and fluxes were correlated with the mass of fine roots per unit soil volume and there was a weak but positive correlation of NPP with LAI. Patterns of ) and NUE across the soil developmental sequence were opposite to each other. ) increased as nutrient availability and nutrient turnover increased, while NUE decreased in response to the same influences but reached its highest values where either N or P availability and turnover of both N and P were low. A negative correlation between ) and NUE supports the hypothesis that a trade-off exists between ) and leaf characteristics affecting NUE.     

Structure of the Epiphyte Community in a Tropical Montane Forest in SW China

Vascular epiphytes are an understudied and particularly important component of tropical forest ecosystems. However, owing to the difficulties of access, little is known about the properties of epiphyte-host tree communities and the factors structuring them, especially in Asia. We investigated factors structuring the vascular epiphyte-host community and its network properties in a tropical montane forest in Xishuangbanna, SW China. Vascular epiphytes were surveyed in six plots located in mature forests. Six host and four micro-site environmental factors were investigated. Epiphyte diversity was strongly correlated with host size (DBH, diameter at breast height), while within hosts the highest epiphyte diversity was in the middle canopy and epiphyte diversity was significantly higher in sites with canopy soil or a moss mat than on bare bark. DBH, elevation and stem height explained 22% of the total variation in the epiphyte species assemblage among hosts, and DBH was the most important factor which alone explained 6% of the variation. Within hosts, 51% of the variation in epiphyte assemblage composition was explained by canopy position and substrate, and the most important single factor was substrate which accounted for 16% of the variation. Analysis of network properties indicated that the epiphyte host community was highly nested, with a low level of epiphyte specialization, and an almost even interaction strength between epiphytes and host trees. Together, these results indicate that large trees harbor a substantial proportion of the epiphyte community in this forest.     

Developing Cost-Effective Field Assessments of Carbon Stocks in Human-Modified Tropical Forests

Across the tropics, there is a growing financial investment in activities that aim to reduce emissions from deforestation and forest degradation, such as REDD+. However, most tropical countries lack on-the-ground capacity to conduct reliable and replicable assessments of forest carbon stocks, undermining their ability to secure long-term carbon finance for forest conservation programs. Clear guidance on how to reduce the monetary and time costs of field assessments of forest carbon can help tropical countries to overcome this capacity gap. Here we provide such guidance for cost-effective one-off field assessments of forest carbon stocks. We sampled a total of eight components from four different carbon pools (i.e. aboveground, dead wood, litter and soil) in 224 study plots distributed across two regions of eastern Amazon. For each component we estimated survey costs, contribution to total forest carbon stocks and sensitivity to disturbance. Sampling costs varied thirty-one-fold between the most expensive component, soil, and the least, leaf litter. Large live stems (≥10 cm DBH), which represented only 15% of the overall sampling costs, was by far the most important component to be assessed, as it stores the largest amount of carbon and is highly sensitive to disturbance. If large stems are not taxonomically identified, costs can be reduced by a further 51%, while incurring an error in aboveground carbon estimates of only 5% in primary forests, but 31% in secondary forests. For rapid assessments, necessary to help prioritize locations for carbon- conservation activities, sampling of stems ≥20cm DBH without taxonomic identification can predict with confidence (R² = 0.85) whether an area is relatively carbon-rich or carbon-poor—an approach that is 74% cheaper than sampling and identifying all the stems ≥10cm DBH. We use these results to evaluate the reliability of forest carbon stock estimates provided by the IPCC and FAO when applied to human-modified forests, and to highlight areas where cost savings in carbon stock assessments could be most easily made.     

Spatial Patterns and Predictors of Forest Carbon Stocks in Western Mediterranean

Mediterranean semi-arid forest ecosystems are especially sensitive to external forcing. An understanding of the relationship between forest carbon (C) stock, and environmental conditions and forest structure enable prediction of the impacts of climate change on C stocks and help to define management strategies that maximize the value of forests for C mitigation. Based on the national forest inventory of Spain (1997?C2008 with 70,912 plots), we estimated the forest C stock and spatial variability in Peninsular Spain and, we determined the extent to which the observed patterns of stand C stock can be explained by structural and species richness, climate and disturbances. Spain has an average stand C stock of 45.1?Mg C/ha. Total C stock in living biomass is 621 Tg C (7.8% of the C stock of European forests). The statistical models show that structural richness, which is driven by past land use and life forest history including age, development stage, management activities, and disturbance regime, is the main predictor of stand tree C stock with larger C stocks in structurally richer stands. Richness of broadleaf species has a positive effect on both conifer and broadleaf forests, whereas richness of conifer species shows no significant or even a negative effect on C stock. Climate variables have mainly an indirect effect through structural richness but a smaller direct predictive ability when all predictors are considered. To achieve a greater standing C stock, our results suggest promoting high structural richness by managing for uneven-aged stands and favoring broadleaf over conifer species.     

Carbon Quality and Stocks in Organic Horizons in Boreal Forest Soils

We investigated the mechanisms that determine the quality and quantity of organic carbon (C) stocks in boreal forest soils by analyzing both qualitative and quantitative changes in the organic fractions in the soil organic matter (OM) in a vertical gradient in the decomposition continuum of the organic horizon [litter layer (L), fermentation layer (F), and humus layer (H)] in forest soils using a sequential fractionation method at two forest types along a climatic gradient in Finland. We predicted that the concentrations of water-soluble (WSE) and non-polar (NPE) extractives should decrease and those of the acid-soluble (AS) fraction and acid-insoluble residue (AIR) should increase from the L to the F, and from the F to the H layers, but the C/N ratio of soil OM should stay constant after reaching the critical quotient. We also predicted that the AIR concentrations should be higher in the south than north boreal, and in sub-xeric than mesic forests. Consistent with our hypothesis, the concentrations of WSE and NPE fractions decreased and concentrations of AIR increased in the vertical soil gradient. The highest concentrations of the AS fraction were found in the F layer. The C/N ratio was lowest in the F layer, and the highest in the H layer, indicating that soil OM is depleted in N in relation to C along the vertical soil gradient. Concentrations of WSE and NPE were lower, and concentrations of AIR were higher in the south than in north boreal forests, which is in agreement with our hypothesis that higher soil temperatures may enhance accumulation of slowly decomposable OM in the soil. The concentrations of AIR were higher in the sub-xeric than mesic forests. Contrary to our expectations, however, the differences in the chemical quality in soil OM between the site types were amplified from the L to the H layer. The size of the C storage was significantly larger in south than north boreal sites, and larger in the mesic than in the sub-xeric sites.     

Dissolved Nitrogen, Phosphorus, and Sulfur forms in the Ecosystem Fluxes of a Montane Forest in Ecuador

The N, P, and S cycles in pristine forests are assumed to differ from those of anthropogenically impacted areas, but there are only a few studies to support this. Our objective was therefore to assess the controls of N, P, and S release, immobilization, and transport in a remote tropical montane forest. The study forest is located on steep slopes of the northern Andes in Ecuador. We determined the concentrations of NO₃-N, NH₄-N, dissolved organic N (DON), PO₄-P, dissolved organic P (DOP), SO₄-S, dissolved organic S (DOS), and dissolved organic C (DOC) in rainfall, throughfall, stemflow, lateral flow (in the organic layer), litter leachate, mineral soil solution, and stream water of three 8–13 ha catchments (1900–2200 m a.s.l.). The organic forms of N, P, and S contributed, on average, 55, 66, and 63% to the total N, P, and S concentrations in all ecosystem fluxes, respectively. The organic layer was the largest source of all N, P, and S species except for inorganic P and S. Most PO₄ was released in the canopy by leaching and most SO₄ in the mineral soil by weathering. The mineral soil was a sink for all studied compounds except for SO₄. Consequently, concentrations of dissolved inorganic and organic N and P were as low in stream water (TDN: 0.34–0.39 mg N l⁻¹, P not detectable) as in rainfall (TDN: 0.39–0.48 mg N l⁻¹, P not detectable), whereas total S concentrations were elevated (stream water: 0.04–0.15, rainfall: 0.01–0.07 mg S l⁻¹). Dissolved N, P, and S forms were positively correlated with pH at the scale of soil peda except inorganic S. Soil drying and rewetting promoted the release of dissolved inorganic N. High discharge levels following heavy rainstorms were associated with increased DOC, DON, NO₃-N and partly also NH₄-N concentrations in stream water. Nitrate-N concentrations in the stream water were positively correlated with stream discharge during the wetter period of the year. Our results demonstrate that the sources and sinks of N, P, and S were element-specific. More than half of the cycling N, P, and S was organic. Soil pH and moisture were important controls of N, P, and S solubility at the scale of individual soil peda whereas the flow regime influenced the export with stream water.     

西双版纳热带山地季风常绿阔叶林的群落生态学研究

依据5个25m×20m样地的调查资料, 对西双版纳热带山地的季风常绿阔叶林的群落结构、种类组成、生活型构成、多样性、种面积关系等进行了分析研究,结果显示西双版纳热带山地的季风常绿阔叶林主要由壳斗科、大戟科、茶科和樟科等树种组成; 乔木树种种类丰富,灌木、草本、藤本种类相对较少;随乔木径级的增大,个体/种的数量逐渐减小;群落中以中叶、全缘、革质、非尾尖、常绿植物占优势; 群落种-面积关系曲线在取样面积为1 500m2时开始趋于平缓,意味着该取样面积可以考虑作为群落最小表现面积.     

Species Composition,Physiognomy and Plant Diversity of the Tropical Montane Evergreen Broad-leaved Forest in Southern Yunnan

Species composition, physiognomy and plant diversity of the less known tropical montane forests in southern Yunnan were studied based on the data from 15 sampling plots in three sites. These forests are mainly dominated by the families Theaceae, Fagaceae, Lauraceae and Euphorbiaceae in floristic composition, and dominated by evergreen phanerophytes with mesophyllous leaves. These forests are similar to lower montane rain forests in equatorial southeastern Asia in floristic composition and altitudinal distributions, but differ in physiognomy by having few epiphytes, but more lianas and more plants with compound leaves. These differences could be due to strongly seasonal climate and so-called mass elevation effect in southern Yunnan. They also differ from the tropical seasonal rain forests at lower altitudes in southern Yunnan by having conspicuously lower species richness, few epiphytes, fewer mega-mesophanerophytes, more abundant micro-nanophanerophytes and hemicryptophytes and more plants with microphyllous leaves. It is suggested that these forests could be termed tropical montane evergreen broad-leaved forests, and be a vegetation type from the northern margin of mainland southeastern Asia controlled by a strongly seasonal climate.     

Comparison of Bird Communities in Primary vs. Young Secondary Tropical Montane Cloud Forest in Guatemala

Cloud forests in central Guatemala are fragmented and decreasing in area due to slash-and-burn agricultural activities. We studied bird species composition, abundance, guild composition, and site tenacity of a 102 ha plot located in a cloud forest region of the Sierra Yalijux in Guatemala, half of which was primary forest and half young secondary forest (<7-years-old). Of the 100 species present 14 were restricted to the Endemic Bird Area ‘Northern Central American highlands’ (i.e. 66% of a total of 21 endemics). Five of the 100 analysed species, including one of the restricted-range species (Troglodytes rufociliatus), had a significantly different abundance in primary and secondary forests. Theoretical analysis suggests that seven species out of a community comprised of 141 bird species are already extirpated and only three out of the 14 present restricted-range species might survive the current state of deforestation. Insectivores were the dominant guild on the plot in terms of numbers of species, followed by omnivores, frugivores and granivores. However, in terms of individuals, omnivores made up nearly half of the bird individuals in primary forest, but declined by 44% in secondary forest, whereas granivores more than doubled in this habitat type. Numbers of species per guild were not significantly different between habitats, while numbers of individuals per guild were significantly different. In general, individuals per species are significantly different in the two habitats. Results suggest that most of the species that are currently surviving in the remnant forests of the Sierra Yalijux might be fairly well adapted to a range of forest conditions, but that populations of a number of restricted-range species might be small. Even generalists species like the Common Bush Tanager (Chlorospingus ophthalmicus) are less abundant in secondary vegetation than in primary forest of the study plot.