Appendix1.1 Summary of sampling effort and methods of phenology observation across the five datasets1.1.1 Pakke

A long-term tree phenology monitoring study of 722 reproductive trees of 53 selected species is underway in the tropical semi-evergreen forests of the Pakke Wildlife Sanctuary and Tiger Reserve (see Datta and Rane 2013 for more details regarding the study site). The overall phenology tree sample represents 55% of the adult tree density and species composition at the study site based on prior studies (Datta 2001; Datta and Rawat 2008). Fifteen of the 20 top-ranked species are represented in the phenology sample. Other vegetation and climatic parameters are also recorded. Two to four observers carry out the monitoring every fortnight using binoculars to assess the presence of each phenophase in the tree canopies, along marked trails for each species. The phenophases recorded are the presence/absence of young leaf, mature leaf, senescent or old leaf, flower buds, open flowers, and unripe and ripe fruits. Unripe and ripe fruits are scored on a scale of 0–4, where 0 indicates no fruits and 1 denotes 25% of canopy in fruit, 2 refers to 25–50% of the canopy in fruit, 3 indicates 50–75%, and 4 denotes 100% of canopy in fruit. For this study, we used the monthly phenology data for 670 individual trees of 35 species (10–25 individuals per species) from April 2011 to September 2019. From this, data from 255 individuals of 12 species with 20–25 individuals per species were selected for representative species analyses. These representative species include Aglaia sp., Ailanthus grandis, Dalrympelea pomifera, Dysoxylum cauliflorum, Dysoxylum gotadhora, Gynocardia odorata, Horsfieldia kingii, Livistona jenkinsiana, Pterospermum acerifolium, Sterculia villosa, Stereospermum chelonoides, and Tetrameles nudiflora.

1.1.2 The Anamalais

In total, 1376 individual trees of 172 species were observed every month from March 2017 to December 2020. Phenological observations were made on 1–41 individuals per species along seven trails located in the Anamalais Plateau and Anamalai Tiger Reserve (10.3021°N, 76.8298°E – 10.4011°N, 76.9929°E) in the Anamalai Hills of the Western Ghats. All trails were located in mid-elevation tropical wet evergreen forests of the Cullenia exarillata–Mesua ferrea–Palaquium ellipticum type (Pascal 1988). From this, data from 507 individuals of 13 species, with 35–41 individuals per species were selected for representative species analyses. These representative species are Acronychia pedunculata, Antidesma menasu, Cullenia exarillata, Euodia lunu-ankenda, Gomphandra coriacea, Litsea stocksii, Mesua ferrea, Myristica dactyloides, Palaquium ellipticum, Paracroton pendulus, Persea macrantha, Vateria indica, and Villebrunea integrifolia. The trails were surveyed at the start of every month and trees were visually scored for the following phenophases: leaves (young/mature), flowers (buds, open), and fruits (unripe, ripe). Phenophase was scored on a scale of 0 to 4, 0 indicating the absence of the phenophase, and values from 1 to 4 indicating the intensity (from low to high in 25% of classes based on the extent of canopy manifesting the phenophase).

1.1.3 Rishi Valley

The study was carried out in a semi-arid tropical scrubland along the Eastern Ghats in the Deccan Plateau. The study area has distinct cool and warm, and dry and wet seasons (Ramaswami et al. 2019). Overall, 647 individual trees of 18 species (12–40 individuals per species) were observed from December 2007 to December 2016. From this, data from 600 individuals of 15 species with 40 individuals per species were selected for representative species analyses. These representative species are Acacia leucophloea, Albizia amara, Azadirachta indica, Chomelia asiatica, Delonix regia, Erythroxylum monogynum, Flacourtia sepiaria, Lantana camara, Peltophorum pterocarpum, Pongamia pinnata, Randia dumetorum, Santalum album, Strychnos nux-vomica, Tamarindus indica, and Wrightia tinctoria. The trees in Rishi Valley were monitored every fortnight. Two stages of leaf (young and mature), two stages of flower (bud and open), and two stages of fruit (unripe and ripe) were monitored. The same observer has made these observations since 2007, and phenophase quantities are recorded as ‘none’, ‘few’, and ‘many’, corresponding to the phenophase being absent, detected in 30% of the canopy, or detected in >30% of the canopy.

1.1.4 Nagarjunasagar Srisailam Tiger Reserve (NSTR)

The savanna woodland plot in NSTR is part of the long-term ecological monitoring network LEMoN India initiative (https://lemonindia.weebly.com). The site is located at an elevation of 700 a.s.l. and receives a long-term mean annual rainfall (1970–2015) of 713 mm, with eight dry months (figure 1). Most of the rainfall occurs between July and October (summer monsoon). Overall, 113 individuals (girth at breast height > 10 cm) belonging to 11 species that comprise 80% of the stem basal area in a 1-ha plot were monitored fortnightly in the year 2018. The following variables were recorded: canopy fullness (L), and the percentage of flushing (FL), mature (M), and senescing leaves (S). During each session, we assigned a visual percentage score of 0–100 for each phenophase (flushing, mature, and senescence) with a resolution of 10%. The species are Anogeissus latifolia, Bridelia retusa, Buchanania cochinchinensis, Chloroxylon swietenia, Dalbergia paniculata, Emblica officinalis, Eriolaena quinquelocularis, Grewia orbiculata, Pterocarpus marsupium, Terminalia elliptica, and Ziziphus xylopyrus.

1.1.5 SeasonWatch

This is a citizen science project collating information on tree phenology across India. In total, 120,000 individual trees of 170 species were observed either once or repeatedly every week from November 2011 to September 2023. From this, data from 47,224 individuals of 10 species with 1997–10,238 individuals per species (1 Jan 2014–30 May 2022) were selected for representative species analyses. These species are Artocarpus heterophyllus, Bauhinia purpurea, Cassia fistula, Mangifera indica, Mimusops elengi, Phyllanthus emblica, Syzygium cumini, Samanea saman., Tamarindus indica and Tectona grandis. More than 85% of these data come from the south Indian state of Kerala (data used in this study). Trees are registered with the programe by citizen scientists and are observed on a weekly basis for three stages of leaf (young, mature, and dying), two stages of flower (bud and open), and two stages of fruit (unripe, ripe, and ‘open’ in dehiscent fruit species). Observers were trained to report phenophase quantities as ‘none’, ‘few’, and ‘many’, corresponding to the phenophase being absent, detected in 30% of the canopy, or detected in >30% of the canopy.