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Fecundity can fluctuate dramatically from year to year due to variations in climate and

resource availability, but the advantage of studying seedlings, especially dipterocarp seedlings, is that they represent recruitment effort over a number of years and thus give an overview of the effects of fragmentation on individuals and species in fragments. The results of Chapters 2 and 3 led me to conclude that the decrease in seedling alpha diversity in plots in fragments, and increase in seedling beta diversity between fragments, could be explained by recruitment failure of some trees in some fragments, and this conclusion was supported by the findings of Chapter 4. I did not statistically explore differences between logged and unlogged continuous forest sites due to the low number of sites sampled (two per forest type), but recruitment was notably reduced in logged forest compared to undisturbed primary forest. I found that

dipterocarp seedling recruitment was significantly reduced in fragments compared to

continuous forest, with only 40% of 200 mature dipterocarp trees in fragments demonstrating any evidence of recruitment, compared to 63% in continuous logged forest sites, and 91% in continuous primary forest sites. However, the fragment sites varied considerably in this respect, with only 10% of trees showing evidence of recruitment in one fragment (site 2, Figure 4.1) but 66% in another (site 4), similar to recruitment in the logged forest sites. Similarly, amongst those trees which showed evidence of having recruited seedlings, mean seedling abundance was relatively high in primary forest (17.8 seedlings per tree within the subplot area), much lower in logged forest (5.6 seedlings per tree), and varied widely amongst fragments. For example, trees in two fragments had mean seedling abundances similar to logged forest sites ( ̴7 seedlings per tree), whereas trees in the smallest fragment (120 ha, site 1) on average recruited 71.2 seedlings, with three trees recruiting over 200 seedlings each. This variation in seedling recruitment between fragments is probably due to the fact that

fragmentation can disrupt the sequence of processes that culminate in a tree successfully recruiting a seedling in a number of individual-fragment-specific ways, via changes in fragment characteristics and pollinator, seed disperser, and herbivore populations.

On Borneo, there are no strong seasonal cues for reproduction, and many tree species rely on cues from droughts and low daytime temperatures associated with ENSO events for the initiation of general flowering events and subsequent masting (Sakai et al. 2006). I found that fragments generally had lower levels of soil moisture and a more open canopy (probably corresponding to higher ambient temperature) than continuous forest (Figure S4.2), which may affect the transmission of ENSO cues to trees in forest fragments and disrupt or promote the initiation of mass flowering, depending on the tree. If flowering is initiated there are a number of biotic interactions that may also be altered by fragmentation that are critical for seedling recruitment success. Declines in pollinator abundances are a frequently reported consequence of habitat fragmentation, often resulting in a reduction in seed set (Potts et al. 2010). If the population size of conspecific trees within a fragment is significantly reduced, they may experience increased self-pollination, or pollination by pollen from a sibling tree, resulting in increased rates of flower abscission and production of infertile fruit (Maycock et al. 2005, Ghazoul et al. 1998). Changing populations of insects, birds, and mammals can alter patterns of pre- and post-dispersal seed predation, as well as seed dispersal. Many tree species rely on birds or mammals to move seeds away from parent trees to combat the increased mortality associated with density-dependant Janzen-Connell effects (Caughlin et al. 2015). Dipterocarp recruitment in fragments is, however, unlikely to be substantially impacted by loss of seed dispersers, as they are abiotically dispersed and seeds undergo limited

secondary dispersal. Populations of both seed dispersers and predators may grow or (more often) decline as a result of fragmentation (Canale et al. 2012). Finally, germinated seeds may face competition from invasive native or non-native species, and seedling survival may be enhanced by depressed populations of herbivores in fragments (Granados et al. 2017). Consequently, loss of pollinators, seed dispersers, and herbivores can reduce or elevate seedling abundances in way that is likely to vary among fragments.

The failure of many dipterocarp trees in fragments to recruit seedlings contrasts with the fact that some dipterocarps produced seedlings in greater numbers than in continuous forest (Chapter 4). This variation among dipterocarp species may be due to the differing sensitivity of dipterocarp species to phenological cues from ENSO events (Chen et al. 2018) in combination with the factors outlined above. Hobbs and Yates (2003) reviewed and synthesised the results from 29 studies presenting data on the effects of fragmentation on the fecundity of 60 plant species, measured on 85 occasions. Only 3.5% of occasions showed a positive effect of

fragmentation on fecundity, while nearly 58% showed significant declines, and the remaining 40% showed no effect. Impacts of fragmentation are thus somewhat variable between and within studies (Hobbs & Yates 2003), and seem to be relatively unpredictable. Tree

reproduction can be inhibited at multiple stages of the seedling recruitment process, and the processes and interactions involved may be impacted in a diversity of ways depending of the characteristics of the forest fragment in question. The variation I found in dipterocarp recruitment in fragments demonstrates this point. Thus, more studies are needed in order to determine which stages of the recruitment process are most sensitive to fragmentation, how this varies amongst species with different life history characteristics, and what fragment characteristics have the most deleterious effects.