Pasture succession in the Neotropics: extending the nucleation hypothesis into a matrix discontinuity hypothesis

The nucleation hypothesis appears to explain widespread patterns of succession in tropical pastures, specifically the tendency for isolated trees to promote woody species recruitment. Still, the nucleation hypothesis has usually been tested explicitly for only short durations and in some cases isolated trees fail to promote woody recruitment. Moreover, at times, nucleation occurs in other key habitat patches. Thus, we propose an extension, the matrix discontinuity hypothesis: woody colonization will occur in focal patches that function to mitigate the herbaceous vegetation effects, thus providing safe sites or regeneration niches. We tested predictions of the classical nucleation hypothesis, the matrix discontinuity hypothesis, and a distance from forest edge hypothesis, in five abandoned pastures in Costa Rica, across the first 11 years of succession. Our findings confirmed the matrix discontinuity hypothesis: specifically, rotting logs and steep slopes significantly enhanced woody colonization. Surprisingly, isolated trees did not consistently significantly enhance recruitment; only larger trees did so. Finally, woody recruitment consistently decreased with distance from forest. Our results as well as results from others suggest that the nucleation hypothesis needs to be broadened beyond its historical focus on isolated trees or patches; the matrix discontinuity hypothesis focuses attention on a suite of key patch types or microsites that promote woody species recruitment. We argue that any habitat discontinuities that ameliorate the inhibition by dense graminoid layers will be foci for recruitment. Such patches could easily be manipulated to speed the transition of pastures to closed canopy forests.     

Seed size,establishment sites and species coexistence in a Chilean rain forest

Abstract. Seedling densities on the forest floor and on elevated microsites (logs and stumps) were compared for eight woody species in a temperate rain forest in southern Chile. Degree of association with elevated microsites varied significantly between species, showed no systematic relationship with reported shade tolerance, but was significantly negatively correlated with seed mass. Large-seeded Podocarpus nubigena established preferentially on undisturbed forest floor sites, whereas seedlings of small-seeded species such as Nothofagus nitida and Laurelia philippiana were found mainly on fallen logs and stumps. The abundance of large seedlings and saplings of N. nitida on logs/stumps, and the growth forms of canopy trees, confirm that recruitment of this species occurs mainly on decaying wood. The relationship between seed size and microsite preferences may be caused by effects of seed size on (1) ability to establish in forest floor litter and (2) retention of seeds on logs. Seedling occupancy of logs and stumps varied with state of decay. Few seedlings of any species were present on logs in the early stages of decay. N. nitida established earlier than the other species, attaining maximum abundance on wood in the middle decay classes. Species richness and overall seedling abundance were highest on wood in advanced stages of decay. Seed size differences are suggested as a determinant of differential utilization of forest floor heterogeneity, and hence of plant species coexistence.     

Cattle and Weedy Shrubs as Restoration Tools of Tropical Montane Rainforest

Over the last 150 years, a large proportion of forests in Latin America have been converted to pastures. When these pastures are abandoned, grasses may slow re‐establishment of woody species and limit forest regeneration. In this study, we explored the use of cattle in facilitating the establishment of woody vegetation in Colombian montane pastures, dominated by the African grasses Pennisetum clandestinum (Kikuyo) and Melinis minutiflora (Yaraguá). First, we described woody and herbaceous vegetation in grazed and non‐grazed pastures. Second, we tested the effect of grazing and seed addition on the establishment and growth of woody species. We also determined if the effect of grazing was different in P. clandestinum and M. minutiflora pastures. We found that low stocking density of cattle greatly increased density, number of branches per individual (a measure of “shrubiness”), and basal area of woody species, but also reduced woody plant species richness and diversity. In the grazed area, the shrubs Baccharis latifolia (Chilca) and Salvia sp. (Salvia) were the most abundant. The combined effect of grazing and shading from the shrubs reduced herbaceous vegetation by 52 to 92%. In the grazing/seed addition experiment, grazing increased establishment of woody seedlings, particularly of the shrub Verbesina arborea (camargo), but the largest effect was seed addition. Where grasses are an important barrier to regeneration, grazing can facilitate the establishment of shrubs that create a microhabitat more suitable for the establishment of montane forest tree species.     

Stand development on reforested bottomlands in the Mississippi Alluvial Valley

Reforestation of bottomland hardwood sites in the southeastern United States has markedly increased in recent years due, in part, to financial incentives provided by conservation programs. Currently >250,000 ha of marginal farmland have been returned to hardwood forests. I observed establishment of trees and shrubs on 205 reforested bottomlands: 133 sites were planted primarily with oak species (Quercus spp.), 60 sites were planted with pulpwood producing species (Populus deltoides, Liquidambar styraciflua, or Platanus occidentalis), and 12 sites were not planted (i.e., passive regeneration). Although oak sites were planted with more species, sites planted with pulpwood species were more rapidly colonized by additional species. The density of naturally colonizing species exceeded that of planted species but density of invaders decreased rapidly with distance from forest edge. Trees were shorter in height on sites planted with oaks than on sites planted with pulpwood species but within a site, planted trees attained greater heights than did colonizing species. Thus, planted trees dominated the canopy of reforested sites as they matured. Planted species acted in concert with natural invasion to influence the current condition of woody vegetation on reforested sites. Cluster analysis of species importance values distinguished three woody vegetation conditions: (1) Populus deltoides stands (2) oak stands with little natural invasion by other tree species, and (3) stands dominated by planted or naturally invading species other than oaks. Increased diversity on reforested sites would likely result from (a) greater diversity of planted species, particularly when sites are far from existing forest edges and (b) thinning of planted trees as they attain closed canopies.     

Past and present vegetation in relation to solifluction on Ben Arkle,Sutherland

Background: Forest succession in tropical pastures usually starts from woody vegetation patches. Patches may arise within the grass matrix at microsites with favourable soil conditions or through facilitation by established nurse plants.

Aims: We report the formation of woody vegetation patches in tropical pastures after investigating whether patch formation was associated with micro-scale terrain features and whether facilitation was important for patch initiation.

Methods: The study was conducted in three pasture sites in the Atlantic forest domain of Brazil. We compared soil, terrain and species abundance patterns among pairs of woody patch and open pasture plots.

Results: The effect of variation in soil physical and chemical attributes was limited. Some species were able to establish in the grass matrix and survive disturbance from grazing and fire, while other species only established in patches, under other already established trees or shrubs. Some of these species were exotics, which are commonly eliminated in restoration efforts.

Conclusions: Allowing the establishment of species capable of withstanding pasture environments, including exotics, can accelerate succession. Furthermore, the abilities to endure competition from grasses and survive fire are key features of species suitable for the initial stages of forest restoration in tropical pastures.     

Seed Availability as a Limiting Factor in Forest Recovery Processes in Costa Rica

Abandoned pastures and secondary forests are increasingly prominent features of tropical landscapes. Forest regrowth on abandoned pastures is generally slow and virtually limited to regeneration from seeds from external sources, since agricultural activities alter site conditions. We hypothesize that seed availability is a major limiting factor in forest recovery on abandoned pastures. This hypothesis was tested by studying the seed bank, seed rain, and seed predation in a small pasture (1 ha) situated in a forest‐pasture mosaic in northwestern Costa Rica. The tree seed density in the pasture seed bank was much lower (21/m²) than the density in the seed bank of a neighboring secondary forest (402/m²). Within a period of five weeks, 23 tree seeds entered the pasture by seed rain. This number is low compared to densities found in closed forests but higher than densities reported in other studies where virtually no seeds were found beyond 20 m from the forest edge. Possibly the small size of the pasture with seed sources nearby and the small‐scale landscape mosaic enhance seed dispersal. Predation limits the seed density in pastures, with 42% of the woody species consumed by predators. The low seed density in the seed bank, and hampered recruitment combined with significant losses, pose severe restrictions to forest recovery on abandoned pastures. Moderate land use, and small sized clearings with seed sources nearby may increase the pace of recovery. Nevertheless, forest establishment may still take a considerable time. Thus, enlarging the available pool of species may be a worthwhile management strategy.     

Influence of conspecific and heterospecific adults on riparian tree species establishment during encroachment of a humid palm savanna

Woody plant encroachment of savanna ecosystems has been related to altered disturbance regimes, mainly fire suppression and herbivore exclusion. In contrast, neighbourhood interactions among resident and colonising woody species have received little attention, despite their likely influence on the pattern and rate of tree establishment. We examined how resident palm trees (Butia yatay) and established adults of two riparian forest tree species (Allophylus edulis and Sebastiania commersoniana) influenced seed arrival and seedling performance of the latter two species in a humid savanna of east-central Argentina. Seed traps and seedlings of both riparian species were placed in herbaceous openings, and beneath palm, conspecific and heterospecific adult trees in two unburned savanna patches, and were monitored for 2 years. Only seeds of the bird-dispersed Allophylus arrived in palm microsites, yet survival of Allophylus seedlings near adult palms was limited by animal damage through trampling and burrowing, a non-trophic mechanism of apparent competition. Seeds of both riparian species dispersed into conspecific microsites, although adult trees selectively reduced growth of conspecific seedlings, a pattern consistent with the “escape hypothesis”. Further, survival of Sebastiania increased in the moister Allophylus microsites, suggesting a one-way facilitative interaction between woody colonisers. Our results indicate that dispersal facilitation by resident savanna trees may be critical to riparian species invasion after fire suppression. Distance-dependent effects of conspecific and heterospecific adult trees could contribute to shape the subsequent dynamics of woody seedling establishment. Overall, we show that indirect interactions can play a prominent role in savanna encroachment by non-resident woody species.     

Microhabitat Preference of Egernia napoleonis in Undisturbed Jarrah Forest,and Availability and Introduction of Microhabitats to Encourage Colonization of Restored Forest

An animal's microhabitat requirements can impact its ability to colonize restored areas, particularly species requiring slow developing microhabitats, such as logs and woody debris piles. Introduction of these microhabitats may be required to facilitate colonization by some species. Restored bauxite mine‐pits in the Jarrah (Eucalyptus marginata) forest of south‐western Australia contain introduced log piles at densities of 1 ha^?1. However, these have not facilitated colonization by Napoleon's skink (Egernia napoleonis), which rely on logs for habitat and are largely absent from restored sites. We radio‐tracked 12 skinks in unmined forest to determine their microhabitat preferences and examined differences in vegetation structure, and microhabitat and food availability, between restored and unmined forests to identify reasons for their absence. Restored and unmined forests differed in canopy, mid‐ and understory cover and ground substrates, which were all potential barriers to colonization. Food availability was similar between restored and unmined forest, thus not a barrier to colonization. Skinks primarily utilized long logs, large woody debris piles, and large trees; microhabitats that were scarce or absent in restored sites and, therefore, potential barriers to colonization. Using this information, we introduced small woody debris piles into restored sites in close proximity to unmined areas containing skinks to facilitate skink colonization. This showed early signs of success and suggested that the lack of logs and woody debris were barriers to colonization. However, further monitoring is required to accurately determine the long‐term value of woody debris piles in facilitating skink colonization.     

Forest regeneration in abandoned coffee plantations and pastures in the Cordillera Central of Puerto Rico

Forest structure and species composition were described in abandonedshade and sun coffee plantations and abandoned pastures in Puerto Rico. Foreststructural characteristics were similar to older forest sites afterapproximately 30 yr of recovery. The historical presence of shadecoffee plantations as the dominant agricultural activity in the region hasresulted in the homogenization of secondary forest composition. The continuousdominance of Coffea arabica and species used for shade inabandoned shade coffee contributed to a slower rate of species compositionchange in comparison to abandoned pastures. Abandoned pastures were initiallycolonized by a group of light demanding and/or wind dispersed species and thenby shade tolerant species characteristic of abandoned shade coffee plantations,suggesting that the secondary forests of abandoned shade coffee plantation arethe major source of species in this landscape. The presence of a few isolatedbig trees in sun coffee plantations appeared to facilitate colonization ofwoodyspecies similar in composition to abandoned shade coffee plantations. In amultivariate analysis, time since abandonment and elevation were the variablesthat explained the majority of variability in species composition among sites.However, a few native species (e.g. Guarea guidonia,Casearia sylvestris, Ocotealeucoxylon) were common regardless of land use history or elevation.In contrast, important old forest species (e.g. Sloaneaberteriana, Dacryodes excelsa,Manilkara bidentata) were rare or absent from most of thesecondary forest stands suggesting the need to reintroduce these species. Landmanagement and conservation efforts can be improved by incorporating theeffectsof land use history on secondary forest dynamics.     

Young restored forests increase seedling recruitment in abandoned pastures in the Southern Atlantic rainforest

Planting seedlings is a common technique for abandoned pastures restoration in the tropics, supposedly by increasing the seedling recruitment and accelerating succession. In this study we evaluated the role of a young restored forest (one year old) in enhancing seedling establishment from two sources (seed rain and seed bank), in the Atlantic Rainforest region in Southern Brazil. We compared abandoned pasture, young restored forest and old-growth forest with respect to the seedlings recruited from different sources, by monitoring 40 permanent plots (0.5 m x 0.5 m) over 20 months. From the three studied areas a total of 392 seedlings of 53 species were recruited. Species were mainly herbaceous (85%), pioneers (88%), zoochorous (51%) and small-seeded species (60%). Seedling recruitment from the seed bank (density and species richness) was higher and dominated by herbaceous species in the abandoned pasture and in the young restored forest; on the other hand, the recruitment of woody species from seed rain was more pronounced in the old-growth forest. The young restored forest increased the species richness of woody seedlings recruitment from the seed bank (two-fold) and from seed rain (three-fold) compared to the abandoned pasture. Also, the seedling density in young restored forest was still higher than abandoned pastures (seed bank: four times; seed rain: ten times). Our results show that even young restored areas enhance the establishment of woody species and should be considered an important step for pasture restoration.     

Plant–plant interactions change during succession on nurse logs in a northern temperate rainforest

Plant–plant interactions change through succession from facilitative to competitive. At early stages of succession, early‐colonizing plants can increase the survival and reproductive output of other plants by ameliorating disturbance and stressful conditions. At later stages of succession, plant interactions are more competitive as plants put more energy toward growth and reproduction. In northern temperate rainforests, gap dynamics result in tree falls that facilitate tree regeneration (nurse logs) and bryophyte succession. How bryophyte‐tree seedling interactions vary through log succession remains unclear. We examined the relationships of tree seedlings, bryophyte community composition, bryophyte depth, and percent canopy cover in 166 1.0 m² plots on nurse logs and the forest floor in the Hoh rainforest in Washington, USA, to test the hypothesis that bryophyte‐tree seedling interactions change from facilitative to competitive as the log decays. Tree seedling density was highest on young logs with early‐colonizing bryophyte species (e.g., Rhizomnium glabrescens) and lowest on decayed logs with Hylocomium splendens, a long‐lived moss that reaches depths >20 cm. As a result, bryophyte depth increased with nurse log decay and was negatively associated with tree seedling density. Tree seedling density was 4.6× higher on nurse logs than on the forest floor, which was likely due to competitive exclusion by forest floor plants, such as H. splendens. Nurse logs had 17 species of bryophytes while the forest floor had six, indicating that nurse logs contribute to maintaining bryophyte diversity. Nurse logs enable both tree seedlings and smaller bryophyte species to avoid competition with forest floor plants, including the dominant bryophyte, H. splendens. H. splendens is likely a widespread driver of plant community structure given its dominance in northern temperate forests. Our findings indicate that plant–plant interactions shift with succession on nurse logs from facilitative to competitive and, thus, influence forest community structure and dynamics.     

Diversity and conservation of forest-floor arthropods on a small Seychelles island

Cousine Island, Seychelles, is of major conservation significance as it is in a biodiversity hotspot. Furthermore, it is relatively pristine, and is apparently the only tropical island over 20 ha with no alien invasive mammals. This study focuses on the island's log and litter arthropods, which were sampled by extraction methods from the dominant species, Pisonia grandis, Ficus spp. and Cocos nucifera. Stage of decomposition, and forest type in which the logs occurred, both significantly influenced the composition and structure of the arthropod assemblages. Young logs were significantly richer in species than older logs, possibly because they had the most resources and microhabitats. There were some significant changes in arthropod species richness, composition and abundance between species of young logs, but not old ones, because as logs decomposed, arthropod assemblages converged. Nevertheless, each old log species had some arthropod species not present in other log species, which has important implications for conservation. Arthropod assemblages in woody litter varied according to the forest type in which they occurred, and were different from those in logs in the same forest type. Cousine Island arthropod species richness, both in logs and litter, was comparable to figures from other tropical areas. As the logs, especially P. grandis, are home to many Seychelles endemic species, their conservation is essential. Furthermore, as the arthropods are also the main food of certain threatened Seychelles vertebrates, their conservation also underpins a food chain on this unique tropical island.     

Logs and Fern Patches as Recruitment Sites in a Tropical Pasture

Forest recovery in degraded pastures is often highly variable, possibly due to variation in the availability of adequate recruitment sites. In an actively grazed pasture in northeastern Costa Rica, this study examines how recruitment of woody species in patches of the fern Nephrolepsis sp. and near logs compares with recruitment in grassy areas. Fern patches and logs had five and eight times higher densities of woody recruits, respectively, as grassy areas. They also had more than twice the species richness and growth as grassy areas. Grass apparently presents a competitive barrier against invading woody recruits, and also attracts cattle that may trample and/or consume recruits. Both logs and patches of fern appeared to provide superior conditions for establishment and growth of woody species, and they did not attract cattle. This study suggests that fern patches and logs can be managed to accelerate forest succession.     

Effects of Postfire Logging on Soil and Vegetation Recovery in a Pinus halepensis Mill. Forest of Greece

After a wildfire in a Pinus halepensis Mill. forest, in northern Greece, the burned trees were logged and the logs were removed either by mechanical or animal traction. The effects of logging and log removal methods on soil and vegetation recovery were evaluated comparing the logged sites with a burned but unlogged site and the unburned forest. Fire and logging did not affect the soil pH and caused only a short-term reduction in organic matter content. Two years after the fire, the highest rates of soil loss were observed in the logged area where mules were used for log removal. Soil moisture showed some differences between treatments during the first year after fire but then values were similar. Logging and particularly the use of skidders for log removal caused an initial increase in the amount of exposed bare ground but later when vegetation cover increased differences were minimized. The main woody species showed a species specific response to the treatments and while seeder species were favoured in the unlogged sites the same was not true for the respouters. In general, the growth and survival of pine seedlings was not affected by treatments.     

Wetland restoration by natural succession in abandoned pastures with a degraded soil seed bank

Natural restoration of historical wetland plant communities in fallow fields with a degraded seed bank has been assumed to be possible only if source populations of the target species are present adjacent to the abandoned fields and a high density of suitable microsites is available. However, few studies have monitored both factors simultaneously and verified this assumption. We hypothesized that plant communities that are similar to historical wetlands, including back marshes, back swamps, and bogs, will reestablish in abandoned pasturelands in cases when (1) gaps for new recruitment emerge, followed by the decline of pastures; and (2) seeds with longevity are supplied from the surrounding remnant plant communities of wetlands. We conducted a survey of vegetation and microsites in pastures, abandoned pastures, and reference wetlands followed by structural equation modeling to verify our hypothesis for the natural restoration of Phragmites australis–Phalaris arundinacea and Alnus japonica–Spiraea salicifolia communities. These communities represent historical back marshes and back swamps along a river. However, our hypothesis was not verified for the natural restoration of Vaccinium oxycoccos–Sphagnum spp. communities, which represent plant communities in historical bogs grown on acidic peat that are maintained by rainfall and fog. Our findings partly support our hypothesis that decline in pastures creates gaps and that cumulative seed dispersal from nearby remnant wetlands allows the original wetland plant communities to regenerate. Further case studies are needed to determine how the natural restoration of bog plant communities occurs.     

Rainforest seed rain into abandoned tropical Australian pasture is dependent on adjacent rainforest structure and extent

It is well known that the recovery of abandoned tropical pastures to secondary rainforest benefits from the arrival of seeds from adjacent rainforest patches. Less is known, however, about how the structural attributes of adjacent rainforest (e.g. tree density, canopy cover and tree height) impact seed rain patterns into abandoned pastures. Between 2011 and 2013, we used seed traps and ground seed surveys to track the richness and abundance of rainforest seeds entering abandoned pastures in Australia's wet tropics. We also tested how seed rain diversity is related to the distance from forest, the proportion of forest cover in the landscape and several structural attributes of adjacent forest patches, specifically average tree height, canopy cover, tree species richness and density. Almost no seeds were captured in elevated pasture seed traps, even near forest remnants. Abundant forest seeds were found in ground surveys but only within 10 m of forest edges. In ground surveys, seeds from wind‐dispersed species were more abundant, but less species rich, than animal‐dispersed species. A survey of pasture seedling recruits suggested that some forest seeds must be dispersing more than 10 m into pasture at very low frequencies, but only a few species are establishing there. Recruits were predominantly animal‐dispersed not wind‐dispersed species. In addition to distance from forest and the proportion of forest within a 100‐ to 200‐m radius of sampling sites, the richness and density of adjacent forest trees were the most important factors for explaining the probability of seed occurrence in abandoned pastures. Results suggest that without some restoration assistance, the recovery of abandoned pastures into secondary rainforest in Australia's tropical rainforests will likely be limited, at least in part, by a very low rate of seed dispersal away from forest edges and by the diversity and density of trees in adjacent remnant forests.     

Microsite determinants of variability in seedling and cutting establishment in tropical forest restoration plantations

Plantations are frequently established on abandoned pasture lands to speed forest recovery. This strategy requires matching a tree species mix with the prevailing microenvironmental conditions. In four degraded pastures of the Mexican Lacandon rainforest, we planted 2,400 trees of 6 species (Guazuma ulmifolia, Inga vera, Ochroma pyramidale, Trichospermum mexicanum, Bursera simaruba, and Spondias mombin) to (1) test survival, initial growth, and establishment costs; (2) evaluate whether vegetative cuttings outperform direct seeding or transplants of nursery‐raised seedlings; (3) determine tree response to herbaceous dominance and soil compaction; and (4) scrutinize the results' consistency across sites and sampling scales of tree–microenvironment interactions (individual tree vs. averaged plot responses). After 2 years, overall survival and growth rates were high for 2 of 3 nursery‐raised species. Contrary to expectations, all seedlings outperformed the cuttings while direct seeding resulted in a cost‐effective option of intermediate efficacy. The impact of soil resistance to root penetration on tree biomass accumulation was species dependent while bulk density was not relevant. Soil‐covering, herbaceous vegetation accelerated growth in 3 of 4 tested species during the dry season. At this initial stage of forest restoration in abandoned pastures, Guazuma and Trichospermum were the most restoration‐effective species. Costs can be reduced by using direct‐seeding Inga and avoiding weeding during the dry season. Finally, our results demonstrate how species selection trials can be misleading due to site variations in tree response and to sampling scales that fail to account for small‐scale environmental heterogeneity. We recommend ways to improve the design of restoration trials.     

Influence of the larval environment on performance and adult body size of the wood-boring beetle Phoracantha semipunctata

Large body size confers a reproductive advantage to adults of the wood‐boring beetle Phoracantha semipunctata (F.) (Cerambycidae: Cerambycinae: Phoracanthini). Larvae of this species feed subcortically in stressed and dying eucalypt trees and logs. We evaluated the influence of the larval environment on larval performance and adult body size by manipulating the post‐felling age of host logs (from freshly cut to 2‐weeks‐old) and the density of colonizing neonates (low density with minimal competition for resources vs. high density with intense competition). Adult beetles emerged in greater numbers from logs that had been subjected to the aging treatment which reduced bark moisture content and favored colonization by neonates. Survival was greatest in larger logs having lower densities of neonates, but was greatly diminished in all treatments by mortality during pupation. Development time varied from 2 months to more than a year and was shortest in smaller logs having high densities of larvae. The size of adult beetles emerging from a log was not influenced by larval density, but was positively correlated with the age of logs when the neonates colonized, and log size. These findings suggest that the optimal developmental conditions for P. semipunctata larvae, in terms of larval performance and adult body size, are available in large, aged host logs having low densities of larvae. Manipulation of the larval environment in this study resulted in a considerable variation in adult body size, but large individuals were relatively more common in the wild population that was the source of neonates for the experiment. Potential body size may have been constrained by our use of only one host species and a narrow range of log dimensions.     

Difference in microhabitat-related regeneration patterns between two subalpine conifers, Tsuga diversifolia and Abies mariesii, on Mount Hayachine, northern Honshu, Japan

Seedling and tree-establishment microhabitats of Tsuga diversifolia and Abies mariesii were examined on the herb- and dwarf bamboo-dominated forest floor on Mount Hayachine, a mountain under intermediate snow conditions in northern Honshu, Japan. The four microsite types were fallen logs, buttresses, rocks and ground. The ground substratum was further divided into four subtypes by dominant undergrowth species: Lycopodium, Pteridophyllum, Carex and dwarf bamboo. The establishment of T. diversifolia seedlings on the ground was scarce, and depended mostly on non-ground microsites (i.e. fallen logs, buttresses and rocks). The seedling establishment of A. mariesii was not dependent on specific substrata, although on the ground, establishment sites were limited to the Lycopodium subtype situated on convex sites. Among the microhabitats for seedling establishment, larger trees of A. mariesii rarely occurred on higher portions of the non-ground microsites. In contrast, T. diversifolia could grow up to the height of canopy-layer trees in such microsites. Thus, non-ground microsites seem to be unsuitable for tree establishment in A. mariesii, and are probably useful microhabitats for regenerating T. diversifolia to avoid competition with A. mariesii. We also compared seedling-establishment microhabitats for the two conifers between Mount Hayachine and two other mountain regions under different undergrowth conditions (moss-dominated and dense dwarf bamboo-dominated). Our findings suggested that seedling recruitment in non-ground microsites was primarily determined by undergrowth conditions; T. diversifolia preferred such microsites where the moss-covered area was low, and A. mariesii preferred where dwarf bamboo-covered area was high.     

Woody vegetation dynamics in the tropical and subtropical Andes from 2001 to 2014: Satellite image interpretation and expert validation

The interactions between climate and land‐use change are dictating the distribution of flora and fauna and reshuffling biotic community composition around the world. Tropical mountains are particularly sensitive because they often have a high human population density, a long history of agriculture, range‐restricted species, and high‐beta diversity due to a steep elevation gradient. Here we evaluated the change in distribution of woody vegetation in the tropical Andes of South America for the period 2001–2014. For the analyses we created annual land‐cover/land‐use maps using MODIS satellite data at 250 m pixel resolution, calculated the cover of woody vegetation (trees and shrubs) in 9,274 hexagons of 115.47 km², and then determined if there was a statistically significant (p < 0.05) 14 year linear trend (positive—forest gain, negative—forest loss) within each hexagon. Of the 1,308 hexagons with significant trends, 36.6% (n = 479) lost forests and 63.4% (n = 829) gained forests. We estimated an overall net gain of ~500,000 ha in woody vegetation. Forest loss dominated the 1,000–1,499 m elevation zone and forest gain dominated above 1,500 m. The most important transitions were forest loss at lower elevations for pastures and croplands, forest gain in abandoned pastures and cropland in mid‐elevation areas, and shrub encroachment into highland grasslands. Expert validation confirmed the observed trends, but some areas of apparent forest gain were associated with new shade coffee, pine, or eucalypt plantations. In addition, after controlling for elevation and country, forest gain was associated with a decline in the rural population. Although we document an overall gain in forest cover, the recent reversal of forest gains in Colombia demonstrates that these coupled natural‐human systems are highly dynamic and there is an urgent need of a regional real‐time land‐use, biodiversity, and ecosystem services monitoring network.