Phenology, seasonality and trait relationships in a New Zealand forest

<p>The phenologies of flowers, fruits and leaves can have profound implications for plant community structure and function. Despite this only a few studies have documented fruit and flower phenologies in New Zealand while there are even fewer studies on leaf production and abscission phenologies. To address this limitation, I measured phenological patterns in leaves, flowers and fruits in 12 common forest plant species in New Zealand over two years. All three phenologies showed significant and consistent seasonality with an increase in growth and reproduction around the onset of favourable climatic conditions; flowering peaked in early spring, leaf production peaked in mid-spring and fruit production peaked in mid-summer coincident with annual peaks in temperature and photoperiodicity. Leaf abscission, however, occurred in late autumn, coincident with the onset of less productive environmental conditions. I also investigated differences in leaf longevities and assessed how seasonal cycles in the timing of leaf production and leaf abscission times might interact with leaf mass per area (LMA) in determining leaf longevity. Leaf longevity was strongly associated with LMA but also with seasonal variation in climate. All 12 species produced leaves in spring and abscised leaves in autumn. Nevertheless, leaf longevity ranged from 6 months to 30 months among species, leading to several distinct leaf longevity categories (i.e. 6-7 months, 15-18 months and 27-30 months). Finally, I examined the relationship of leaf traits with flower and fruit traits and their relation to the global leaf economic spectrum (LES) that describes multivariate correlations between a combinations of key leaf traits. The results resonated with the patterns of leaf economic spectrum for New Zealand species and provided evidence for significant correlations between leaf and fruit traits, indicating that plants with long lived leaves and higher LMA produce fruits that take more time to develop, stay on the plant longer and have larger seed size. This study contributed to bridging the gap in our understanding of the relationship between vegetative and reproductive traits, it has increased our understanding of phenological patterns in New Zealand forests, and when viewed with earlier phenological studies, provides a first step towards understanding how New Zealand forest might respond to global climate change. In addition, the research illustrates how seasonality in climate can constrain the life times of leaves. In the context of global trait research culminating into the whole plant economics spectrum, this study provides clear evidence of leaf and fruit phenological and morphological trait associations. It helps to further our understanding of phenology, seasonality and plant trait relationships for some common tree species in New Zealand and presents some novel findings that provide a basis for future research.</p>

Phenology, seasonality and trait relationships in a New Zealand forest

<p>The phenologies of flowers, fruits and leaves can have profound implications for plant community structure and function. Despite this only a few studies have documented fruit and flower phenologies in New Zealand while there are even fewer studies on leaf production and abscission phenologies. To address this limitation, I measured phenological patterns in leaves, flowers and fruits in 12 common forest plant species in New Zealand over two years. All three phenologies showed significant and consistent seasonality with an increase in growth and reproduction around the onset of favourable climatic conditions; flowering peaked in early spring, leaf production peaked in mid-spring and fruit production peaked in mid-summer coincident with annual peaks in temperature and photoperiodicity. Leaf abscission, however, occurred in late autumn, coincident with the onset of less productive environmental conditions. I also investigated differences in leaf longevities and assessed how seasonal cycles in the timing of leaf production and leaf abscission times might interact with leaf mass per area (LMA) in determining leaf longevity. Leaf longevity was strongly associated with LMA but also with seasonal variation in climate. All 12 species produced leaves in spring and abscised leaves in autumn. Nevertheless, leaf longevity ranged from 6 months to 30 months among species, leading to several distinct leaf longevity categories (i.e. 6-7 months, 15-18 months and 27-30 months). Finally, I examined the relationship of leaf traits with flower and fruit traits and their relation to the global leaf economic spectrum (LES) that describes multivariate correlations between a combinations of key leaf traits. The results resonated with the patterns of leaf economic spectrum for New Zealand species and provided evidence for significant correlations between leaf and fruit traits, indicating that plants with long lived leaves and higher LMA produce fruits that take more time to develop, stay on the plant longer and have larger seed size. This study contributed to bridging the gap in our understanding of the relationship between vegetative and reproductive traits, it has increased our understanding of phenological patterns in New Zealand forests, and when viewed with earlier phenological studies, provides a first step towards understanding how New Zealand forest might respond to global climate change. In addition, the research illustrates how seasonality in climate can constrain the life times of leaves. In the context of global trait research culminating into the whole plant economics spectrum, this study provides clear evidence of leaf and fruit phenological and morphological trait associations. It helps to further our understanding of phenology, seasonality and plant trait relationships for some common tree species in New Zealand and presents some novel findings that provide a basis for future research.</p>

Leaf water relations reflect canopy phenology rather than leaf life span in Sonoran Desert trees

Plants from arid environments display covarying traits to survive or resist drought. Plant drought resistance and ability to survive long periods of low soil water availability should involve leaf phenology coordination with leaf and stem functional traits related to water status. This study tested correlations between phenology and functional traits involved in plant water status regulation in 10 Sonoran Desert tree species with contrasting phenology. Species seasonal variation in plant water status was defined by calculating their relative positions along the iso/anisohydric regulation continuum based on their hydroscape areas (HA)—a metric derived from the relationship between predawn and midday water potentials—and stomatal and hydraulic traits. Additionally, functional traits associated with plant water status regulation, including lamina vessel hydraulic diameter (DHL), stem-specific density (SSD), and leaf mass per area (LMA) were quantified per species. To characterize leaf phenology, leaf longevity (LL) and canopy foliage duration (FD) were determined. HA was strongly correlated with FD but not with LL; HA was significantly associated with SSD and leaf hydraulic traits (DHL, LMA) but not with stem hydraulic traits (vulnerability index, relative conductivity); and FD was strongly correlated with LMA and SSD. Leaf physiological characteristics affected leaf phenology when it was described as canopy foliage duration, better than when described as leaf longevity. Stem and leaf structure and hydraulic functions were not only relevant for categorizing species along the iso/anisohydric continuum but also allowed identifying different strategies of desert trees within the ‘fast–slow’ plant economics spectrum. The results in this study pinpoint the set of evolutionary pressures that shape the Sonoran Desert Scrub physiognomy.

Phenological diversity of Maprounea guianensis (Euphorbiaceae) in humid and dry neotropical forests

Phenological diversity, seasonality and leaf longevity may affect leaf habits, reflecting plant responses to environmental conditions. Maprounea guianensis Aubl. is a widespread species in Brazil that is associated with different forest types. We investigated how phenological diversity, seasonality and leaf longevity affect leaf habits of its populations growing in humid and dry forests in the Chapada Diamantina mountains. We made monthly observations of leaf budding and fall in 62 individual trees between 2004 and 2012 (84 months), estimating leaf longevity based on phenophase evaluations. We made use of circular statistics, cross correlations and the Shannon–Wiener Index to evaluate our data. There was little variation in rainfall distribution between the study years, although water availability differed at each site. Phenophase seasonality was found to be negatively correlated with rainfall but positively correlated with photoperiod. Low phenological diversity was observed within each site, but not between sites, and leaf longevity was reduced in the dry forest. Although macroclimatic conditions were similar throughout the range of occurrence of M. guianensis in the region, we found that phenological behaviour and leaf longevity differed according to micro-site differences, demonstrating the plasticity of the species, which may favour its occupation of different environments.