Assessing the strength of climate and land-use influences on montane epiphyte communities.

Epiphytes, air plants that are structurally dependent on trees, are a keystone group in tropical forests; they support the food and habitat needs of animals and influence water and nutrient cycles. They reach peak diversity in humid montane forests. Climate predictions for Central American mountains include increased temperatures, altered precipitation seasonality, and increased cloud base heights, all of which may challenge epiphytes. Although remaining montane forests are highly fragmented, many tropical agricultural systems include trees that host epiphytes, allowing epiphyte communities to persist even in landscapes with lower forest connectivity. I used structural equations models to test the relative effects of climate, land use, tree characteristics, and biotic interactions on vascular epiphyte diversity with data from 31 shade coffee farms and 2 protected forests in northern Nicaragua. I also tested substrate preferences of common species with randomization tests. Tree size, tree diversity, and climate all affected epiphyte richness, but the effect of climate was almost entirely mediated by bryophyte cover. Bryophytes showed strong sensitivity to mean annual temperature and insolation. Many ferns and some orchids were positively associated with bryophyte mats, whereas bromeliads tended to establish among lichen or on bare bark. The tight relationships between bryophytes and climate and between bryophytes and vascular epiphytes indicated that relatively small climate changes could result in rapid, cascading losses of montane epiphyte communities. Currently, shade coffee farms can support high bryophyte cover and diverse vascular epiphyte assemblages when larger, older trees are present. Agroforests serve as valuable reservoirs for epiphyte biodiversity and may be important early-warning systems as the climate changes.

Evaluación de la Fuerza de las Influencias del Clima y el Uso de Suelo sobre las Comunidades Montanas de Epífitas Resumen Las epífitas, plantas aéreas que dependen estructuralmente de los árboles, son un grupo importante en los bosques tropicales ya que mantienen las necesidades de alimento y hábitat de animales e influyen sobre el ciclo del agua y de los nutrientes. Estas plantas alcanzan su pico de diversidad en los bosques tropicales de montaña. Las predicciones climáticas para las montañas de América Central incluyen incrementos en la temperatura, alteraciones en la estacionalidad de la precipitación y un incremento en la altura de la base nubosa. Todas estas predicciones representan una amenaza para las epífitas. Aunque los bosques tropicales de montaña que aún existen se encuentran altamente fragmentados, muchos sistemas agrícolas tropicales albergan árboles que fungen como anfitriones para las epífitas, lo que permite que las comunidades de epífitas persistan incluso en paisajes con una conectividad reducida entre bosques. Usé modelos de ecuaciones estructurales para analizar los efectos relativos del clima, uso de suelo, características de los árboles e interacciones bióticas sobre la diversidad de epífitas vasculares con datos de 31 fincas de café de sombra y dos bosques protegidos en el norte de Nicaragua. También analicé las preferencias por sustrato de las especies comunes mediante pruebas de asignación aleatoria. El tamaño del árbol, la diversidad de árboles y el clima fueron factores que afectaron a la riqueza de epífitas, aunque el efecto del clima estuvo mediado casi en su totalidad por la cobertura de briofitas. Las briofitas mostraron una fuerte sensibilidad a la temperatura media anual y a la insolación. Muchos helechos y algunas orquídeas estuvieron asociadas positivamente con los tapetes de briofitas, mientras que las bromelias tendieron a establecerse entre los líquenes o sobre la corteza desnuda del árbol. La fuerte asociación entre las briofitas y el clima y entre las briofitas y las epífitas vasculares indica que los cambios climáticos relativamente pequeños podrían derivar en una pérdida rápida y en cascada de las comunidades montanas de epífitas. Actualmente, las fincas de café de sombra pueden mantener una cobertura densa de briofitas y ensambles diversos de epífitas vasculares cuando los árboles más grandes y más viejos están presentes. Los bosques agrícolas funcionan como depósitos valiosos para la diversidad de epífitas y podrían ser sistemas de alerta temprana conforme cambia el clima.

Mistletoes and their eucalypt hosts differ in the response of leaf functional traits to climatic moisture supply.

Trade-offs between photosynthesis and the costs of resource capture inform economic strategies of plants across environmental gradients and result in predictable variation in leaf traits. However, understudied functional groups like hemiparasites that involve dramatically different strategies for resource capture may have traits that deviate from expectations. We measured leaf traits related to gas exchange in mistletoes and their eucalypt hosts along a climatic gradient in relative moisture supply, measured as the ratio of precipitation to pan evaporation (P/Ep), in Victoria, Australia. We compared traits for mistletoes vs. hosts as functions of relative moisture supply and examined trait-trait correlations in both groups. Eucalypt leaf traits responded strongly to decreasing P/Ep, consistent with economic theory. Leaf area and specific leaf area (SLA) decreased along the P/Ep gradient, while C:N ratio, leaf thickness, N per area, and δ13C all increased. Mistletoes responded overall less strongly to P/Ep based on multivariate analyses; individual traits sometimes shifted in parallel with those of hosts, but SLA, leaf thickness, and N per area showed no significant change across the gradient. For mistletoes, leaf thickness was inversely related to leaf dry matter content (LDMC), with no relationship between SLA and mass-based N. In mistletoes, reduced costs of transpiration (reflecting their lack of roots) and abundant succulent leaf tissue help account for observed differences from their eucalypt hosts. Trait-based analysis of atypical functional types such as mistletoes help refine hypotheses based on plant economics and specialized adaptations to resource limitation.

Tropical tree species differ in damage and mortality from lightning.

Lightning is an important agent of mortality for large tropical trees with implications for tree demography and forest carbon budgets. We evaluated interspecific differences in susceptibility to lightning damage using a unique dataset of systematically located lightning strikes in central Panama. We measured differences in mortality among trees damaged by lightning and related those to damage frequency and tree functional traits. Eighteen of 30 focal species had lightning mortality rates that deviated from null expectations. Several species showed little damage and three species had no mortality from lightning, whereas palms were especially likely to die from strikes. Species that were most likely to be struck also showed the highest survival. Interspecific differences in tree tolerance to lightning suggest that lightning-caused mortality shapes compositional dynamics over time and space. Shifts in lightning frequency due to climatic change are likely to alter species composition and carbon cycling in tropical forests.

Functional trait data for vascular plant species from northeastern North America.

Wisconsin's plant communities are responding to shifting disturbance regimes, habitat fragmentation, aerial nitrogen deposition, exotic species invasions, ungulate herbivory, and successional processes. To better understand how plant functional traits mediate species' responses to changing environmental conditions, we collected a large set of functional trait data for vascular plant species occupying Wisconsin forests and grasslands. We used standard protocols to make 76,213 measurements of 34 quantitative traits. These data provide rich information on genome size, physical leaf traits (length, width, circularity, thickness, dry matter content, specific leaf area, etc.), chemical leaf traits (carbon, nitrogen, phosphorus, potassium, calcium, magnesium, ash), life history traits (vegetative and flower heights, seed mass), and traits affecting plant palatability (leaf fiber, fat, and lignin). These trait values derive from replicate measurements on 12+ individuals of each species from multiple sites and 45+ individuals for a selected subset of species. Measurements typically reflect values for individuals although some chemical traits involved composite samples from several individuals at the same site. We also qualitatively characterized each species by plant family, woodiness, functional group, and Raunkiaer lifeform. These data allow us to characterize trait dimensionality, differentiation, and covariation among temperate plant species (e.g., leaf and stem economic syndromes). We can also characterize species' responses to environmental gradients and drivers of ecological change. With survey and resurvey data available from >400 sites in Wisconsin, we can analyze variation in community trait distributions and diversity over time and space. These data therefore allow us to assess how trait divergence vs. convergence affects community assembly and how traits may be related to half-century shifts in the distribution and abundance of these species. The data set can be used for non-commercial purposes. The data set is licensed as follows: CC-By Attribution 4.0 International. We request users cite both the OSF data set and this Ecology data paper publication.