# Monitoring Forest Phenology in a Changing World
## 1 Introduction
### Phenology in a Changing World  
Habitat Change--Anthropogenic pressures on the environment have caused unprecedented rates of habitat loss, fragmentation, and degradation over the last half-century [63; 64; 65; 66; 67; 68; 69; 70]. Forest loss, fragmentation, and the resulting edge effects produce fine-scale variations in light, temperature and humidity, that can in turn induce phenological changes. For example, in Southeastern Brazil there was a higher proportion of reproductive trees along forest edges (59% flowering and 73% fruiting) than inside the forest (47% flowering and 29% fruiting) [71]. Moreover, in Costa Rica, flowering and fruiting events were more common, and occurred 15 to 20 days earlier, in forest disturbed by fragmentation in comparison to undisturbed continuous forest [72], and peak flowering in trees isolated by forest fragmentation increased by double but fruit production from those flowers was halved [73]. Although individual flowers in fragmented forests were less likely to produce a mature fruit, at the scale of individual trees, the change in flowering and fruiting phenology in fragmented forest combined to increase reproductive capacity [74]. Even in agricultural landscapes, land-use intensification is the primary driver of variation in leaf flush onset dates, accounting for 66% of the variation compared to 33% caused by climate change, with an increase in leaf flush onset dates by up to 0.67 days per year caused by land-use intensification [75]. The consequences of altered phenology in human-modified forest habitats reverberate throughout ecosystems, transmitted via plant-animal interactions [76]. For example, in the tropical forests of Borneo, tree plots in logged forest were twice as likely to contain fruits or flowers as in unlogged forest [56]. The resultant increase in resource availability was considered a major factor causing correlated increases in the abundance and functional importance of small mammals within logged forests [56].  
Climate Change--Phenological events are especially sensitive indicators of global environmental change because they display strong, thresholded responses to gradual changes in abiotic conditions, such as the leaf emergence or senescence patterns defining growth seasons in temperate forests [77]. Therefore, climate change magnifies the role of phenology in the structure and function of ecological systems [5], where shifts in phenology induced through climatic change can have reverberating effects across trophic levels [78]. There are widespread reports of changes to the life cycles of plants and animals in conjunction with climate variation [35; 36; 79; 80; 81]. During the past century, the phenology of 10 bee species from Northeastern North America has advanced by a mean of 10.4 days as a result of climate change altering the phenological timings of flowering plants [35]. In Europe, climatic shifts in the Netherlands have caused an increase in the strength of asynchrony between the phenology of the Winter Moth (_Operophtera brumata_) and their host plant Oak (_Quercus robur_) [82], and drier conditions over a 17 year period in Spain resulted in higher asynchrony between pollinator butterfly species and their plants [83]. In North America, 48 passerine species showed increasing phenological asynchrony between their migratory arrival and leaf flush dates (a normal cue for migratory arrival) [84]. Even in aquatic systems such as Argentinian lakes, zooplankton have undergone significant shifts in phenological metrics following temperature increases over the last decade [85].