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Trees become sexually mature, depending upon species and the individual, anywhere between 1 and 50 years of age. Tree sexual classification depends upon both the flower parts present and their function. The proportion of male and female parts in flowers, and the proportion of cosexual, male and female flowers on a tree, begin to determine potential gender. The functional sexual class of a tree is based upon perfor- mance as a viable pollen provider or successful ovule parent in passing genes onto another generation. Functional estimates of gender are made by counting the number of flowers producing pollen grains and the number of flowers generating fruit and viable seeds. Individual trees which produce proportionally much more pollen within a species can be considered functionally male. Individual trees which produce proportionally much more seed within a species can be considered functionally female.  

Male and female flower parts are functional if they preform reproductive services. Appearances can be misleading. Functional flower parts in the same species can look quite different from individual to individual. Nonfunctional male and female parts can be fully developed, modified, or stunted in appear- ance, or missing altogether. Functional male and female tree parts on the same tree, may be present but may not successfully generate viable seed.

There is a strong trend in trees to be self-incapable. Many trees, through flower timing, pollen identification markers, and female part physiology, minimize self-pollination and maximize genetic advan- tages of cross-fertilization (called allogamy). Self incapability systems in trees tend to be concentrated at the point where pollen attaches to a pistil. To prevent selfing, female parts kill pollen from the same tree upon arrival, or slows pollen grain growth and the fertilization process. Trees can also undergo early seed abortion if selfed. Each selfing event can gener- ate a seed and seedling which at the start or even into middle age, can suffer from inbreeding depression and less efficient growth. For example in longleaf pine (Pinus palustris), selfing was found to cause a 60% decline in seed yields, a 53% increase in young tree mortality up to 8 years of age, and 33% less height growth through age 8.  

Citation rates are increasingly used as a currency of science, providing a basis to reward a scientist. Self-citations, an inevitable part of scholarly communication, may contribute to the inflation of citation counts and impose a considerable impact on research evaluation and academic career advancements. Self-citations are classified into two types in this study: synchronous self-citations (self-citations an author gives) and diachronous self-citations (self- citations an author receives). The main objective of this paper is to provide a comprehensive gendered analysis of synchronous and diachronous self-citations across all scientific disciplines. For this purpose, citation data of 12,725,171 articles published in 2008-2014 are extracted from Web of Science and are further scrutinized for articles of each gender. The findings reveal that men receive citations from their own papers at a higher rate than their women counterparts. They also tend to give more citations to their own publications. Gender gap in citation impact decreases when first-author’s diachronous citations are eliminated in the impact analysis. However, the gap does not vary when all-authors’ diachronous citations are excluded. The results of this research is important for effective gender-related policy-making in the science and technology arena. 

In 2015, a Canadian team found female researchers in engineering tend to publish in more influential journals, but their work is less cited.

Now, the same team is preparing to publish evidence that women across science cite their own first-authored papers less than men. This is despite their work being cited at a higher rate by their co-authors.

Gita Ghiasi, a fourth-year PhD candidate in mechanical and industrial engineering at Concordia University, Québec, presented the findings at a science indicators conference in Spain last year. She said the work contributes data to growing evidence that women's scientific contributions are played down or attributed to their male peers.

Her conference paper examined citation data of more than 12 million articles published across disciplines between 2008 and 2014, gathered from the Web of Science.

It found men cite their previous first-authored papers at a 37% higher rate than women. Furthermore, women's papers were self-cited at a higher rate by their immediate co-authors.

Gita Ghiasi and her team at Concordia University, Canada, used data drawn from Web of Science, a huge database of academic publications. Filtering for engineering journals from 2008 to 2013, the team gathered 679,338 articles with one million co-authors, assigning gender using a separate database of male and female first names. The journals selected from this database were then ranked by prestige, using Web of Science's 'Impact Factor'.

The research garnered good news and bad news... and some more bad news. Women made up only 20 percent of the authors on the papers -- significantly less than the 30 percent rate across all scientific disciplines. It also found, however, that these women were publishing in more prestigious journals on average than their male counterparts -- a 2 percent increase in Impact Factor. Despite this, however, women's papers were cited 3 percent less frequently.