Experimental and observational evidence of negative conspecific density dependence in temperate ectomycorrhizal trees
Fiona V. JevonDayna De La CruzJoseph A. LaMannaAshley K. LangDavid A. OrwigSydne RecordPaige V. KoubaMatthew P. AyresJaclyn Hatala Matthes
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Abstract Conspecific negative density dependence (CNDD) promotes tree species diversity by reducing recruitment near conspecific adults due to biotic feedbacks from herbivores, pathogens, or competitors. While this process is well‐described in tropical forests, tests of temperate tree species range from strong positive to strong negative density dependence. To explain this, several studies have suggested that tree species traits may help predict the strength and direction of density dependence: for example, ectomycorrhizal‐associated tree species typically exhibit either positive or weaker negative conspecific density dependence. More generally, the strength of density dependence may be predictably related to other species‐specific ecological attributes such as shade tolerance, or the relative local abundance of a species. To test the strength of density dependence and whether it affects seedling community diversity in a temperate forest, we tracked the survival of seedlings of three ectomycorrhizal‐associated species experimentally planted beneath conspecific and heterospecific adults on the Prospect Hill tract of the Harvard Forest, in Massachusetts, USA. Experimental seedling survival was always lower under conspecific adults, which increased seedling community diversity in one of six treatments. We compared these results to evidence of CNDD from observed sapling survival patterns of 28 species over approximately 8 years in an adjacent 35‐ha forest plot. We tested whether species‐specific estimates of CNDD were associated with mycorrhizal association, shade tolerance, and local abundance. We found evidence of significant, negative conspecific density dependence (CNDD) in 23 of 28 species, and positive conspecific density dependence in two species. Contrary to our expectations, ectomycorrhizal‐associated species generally exhibited stronger (e.g., more negative) CNDD than arbuscular mycorrhizal‐associated species. CNDD was also stronger in more shade‐tolerant species but was not associated with local abundance. Conspecific adult trees often have a negative influence on seedling survival in temperate forests, particularly for tree species with certain traits. Here we found strong experimental and observational evidence that ectomycorrhizal‐associating species consistently exhibit CNDD. Moreover, similarities in the relative strength of density dependence from experiments and observations of sapling mortality suggest a mechanistic link between negative effects of conspecific adults on seedling and sapling survival and local tree species distributions.Keywords:
Temperate rainforest
Temperate forest
Density dependence
ABSTRACT The development of scaly buds (= cataphylls) has been traditionally associated with seasonally cold climates, although only few species from the southern hemisphere were investigated in this regard. The present work focuses on apical and axillary buds of seven tree species native to the South-American Temperate Rainforests (STR). Due to differences in the lineages from which these species derived, high levels of inter-specific variation in bud structure were expected. Apical and axillary buds were dissected under stereomicroscope, and the sizes of their parent shoots were evaluated. Cataphylls and leaf primordia were counted, and the presence of colleters and/or trichomes registered. Both intra- and inter-specific variations in bud structure were found. The apical buds were scaly in two out of seven species, and naked in the other species. Axillary buds were scaly in all but one species. In general terms, larger shoots developed buds with more organs. The presence of colleters (in four species) was not restricted to those buds lacking an outer cover of cataphylls. Further studies should focus on the relevance at a broader scale of colleters and trichomes as protective structures in tree buds.
Temperate rainforest
Temperate forest
Tree (set theory)
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Temperate forest ecosystems are most extensively found throughout the Northern Hemisphere, and less extensively in the Southern Hemisphere. The specific regions containing temperate forests include Europe, North America, Asia, South America, Australia, and New Zealand. Northern temperate forests are often composed of deciduous trees that drop their leaves each year, providing a supply of rich nutrients to animals and plants as they decompose. Southern temperate forests, on the other hand, are primarily composed of broad leaved evergreen trees that keep their leaves year round. Most temperate forest ecosystems are heavily exploited and degraded. The underlying bedrock and geology of temperate forests around the world are highly variable, as are the soils, vegetation communities, disturbances, and plant adaptations found within them.
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Temperate forest ecosystems are most extensively found throughout the Northern Hemisphere, and less extensively in the Southern Hemisphere. The specific regions containing temperate forests include: Europe, North America, Asia, South America, Australia, and New Zealand. Northern temperate forests are often composed of deciduous trees that drop their leaves each year, providing a supply of rich nutrients to animals and plants as they decompose. Southern temperate forests, on the other hand, are primarily composed of broad‐leaved evergreen trees that keep their leaves year round. Most temperate forest ecosystems are heavily exploited and degraded. The underlying bedrock and geology of temperate forests around the world are highly variable, as are the soils, vegetation communities, disturbances, and plant adaptations found within them.
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Abstract The Earth's latitudinal gradient of forests encompasses boreal to temperate deciduous to temperate evergreen forests (as well as tropical forests). In addition, there are several variants of the temperate evergreen forest and there are montane forests at high elevations. Boreal and temperate forests differ in environment, structure, composition and disturbance.
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Zero-plane displacement d and roughness length z0 were compared among boreal, cool-temperate, and warm-temperate forests. The normalized zero-plane displacement d/h (where h is the tree height) increased with stand density, whereas z0/h decreased. On the other hand, d/h showed a negative correlation with plant area index (PAI), which was inconsistent with parameterization of the models. The effect of the vertical structure of the forest might be included in PAI. Seasonal variations of d/h were observed in cool-temperate and warm-temperate forests. d/h decreased from autumn to winter in these sites which corresponded to the fall of leaves. However, d/h was underestimated by the models, and the decrease in d/h for cool-temperate forest appeared to be small compared with that predicted using the models with the large decrease in PAI.
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